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Be More Observant – What’s Happening Now?

May 7th, 2016

Do you ever long for a clearer perspective on what is happening outdoors?  Maybe it’s a corollary of taking time to “smell the roses”, when we resolve to be more observant and fully savor the fresh breezes of spring.   This week, I write more about the types of weather observing which can be done from home – using tools such as rain gauges and home weather stations.  Next week, I’ll build upon the observing basics featured in these early May posts as we broaden our view toward getting more out of each day’s weather forecast.

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If you missed last week’s blog post, find it down the page – after this post!

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In the summer of 1974, I began recording weather observations twice a day. I took the readings from my newly installed home weather station.   For many years I used a 12-column ledger book which I adapted to this purpose.  As I have gotten older (and busier) I scaled back the observations allowing them to fit on the calendar days of a pocket planner.  This enables me to quickly look and see the temperature and rainfall trends over the past few weeks.

The key to success and enjoyment when keeping weather observations at home is consistency and organization.   One of the most satisfying aspects of keeping these records is to be able to look back at details of weather events from years ago.  If you have a natural interest for this type of detail, why not become the “weather historian” for your household?

Rain Gauge Essentials

Tube and Funnel Rain Gauge

This type of rain gauge can be purchased for about $30 and is designed to be attached to a post. Lacking an ideal location, I keep it in a five gallon bucket which is weighted to keep it upright during windy weather.

 

 

 

 

 

 

 

 

 

 

 

 

Above is a picture of my well-used rain gauge.  It is the second gauge of this type which I have owned.  I received the first one 20 years ago while touring the National Weather Service office in Duluth, MN.  After about ten years the plastic will fade and become susceptible to cracking.  Large hail will further shorten the life of this type of gauge.  The surface area of the funnel opening on top is ten times that of the graduated tube in which the rain is collected.  This makes it very easy to read rainfall to the nearest hundredth of an inch.  I think that the wider collection area at the top makes for more accurate measurements than one would get from a very small gauge.  This gauge — with the funnel and small tube removed —  even works well for measuring snowfall.

Another type of rain gauge which I used in the past is a wedge style.    With this design the gauge narrows from top to bottom, making it easy to read small amounts of rain.  This page provides pictures of various types of rain gauges, and tips on buying and mounting a rain gauge.  It even has ideas for retarding evaporation of rainfall from the gauge when you aren’t able to measure it immediately!

An ideal site for a rain gauge is away from obstructions which can hinder the rain from falling into it.  When living outside of town, I always had better success with gauges sheltered from the full force of the wind, as long as the sheltering trees or buildings were not so close as to block rain or snowfall.  It can be useful to have the gauge fairly close to the house – especially in cold weather, or when you need to take a quick measurement during a rainstorm.   For a bit more money, an electronic or digital gauge is also an option.   Based on the principle of weighing the rain to determine the amount, the electronic gauge eliminates the need to go outside to measure rain.

Home Weather Stations

The home weather station is a collection of instruments for measuring temperature, humidity, barometric pressure, wind speed and direction, and rainfall.  An online search shows that Oregon Scientific, Ambient Weather, La Crosse Technology, Honeywell, and Acurite are some of the more well-known sellers of home weather stations.  The product order page for Acurite is appealing because each weather station links to its own Youtube video which explains its features.  Some weather stations will establish a wireless connection to your home computer for downloading weather data so it can be saved or displayed.  Others will send observations via internet to websites which aggregate the observations for a portion of a state or region. Many weather stations do require some handyman skills to attach the sensors to ideal locations for measuring weather conditions.  A few inexpensive weather stations have no outdoor sensors, but instead receive signals providing data from the nearest official observing site.  I do not recommend that type of station if you want conditions from your exact location.  You may be surprised how much conditions at your house will vary from those of the nearest “official” site.

Sharing Observations

If you have a good site for a rain gauge, you can sign up for the National Weather Service’s weather observation program known as CoCoRaHS (Collaborative Community Rain, Hail and Snow Network) through which precipitation reports are sent to your local NWS office.  Looking for a less formal way to pass on your observations?  Your local NWS office also accepts and appreciates rainfall and weather reports sent via Twitter or Facebook.  Such reports are valuable to meteorologists for verification of forecasts during a storm, particularly in cases where precipitation is changing over from rain to snow.

 

Reports from Various Sources

Most readers probably won’t go to the effort of installing weather instruments at home.  This need not keep you from having a good source for current weather conditions.  The NWS website provides current conditions on every local forecast page, with regional and statewide summaries just a couple clicks away.   Another good source of current weather observations are the automated sensors deployed on roadsides in various states. These assist in planning for winter road maintenance.  For travelers, these sites may provide more current data than the road condition summaries on which many rely.  The roadside sensors provide not only temperature and wind conditions, but even precipitation type and pavement temperatures.  This site displays the roadside sensor data for the state of Iowa.

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What is your favorite source of current weather conditions?

How much interest do you have in conditions elsewhere in your state or region?

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In the most recent two blog posts I have covered some essentials for keeping track of what is happening in real-time outside your door.  In the coming weeks, we’ll build on this knowledge to enable the forecast to work for you every day.

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When severe weather threatens, review my suggestions for keeping ahead of the storm.

Helping the Forecast Work for You

April 30th, 2016

I don’t remember a time in my life before weather was a foremost interest.  I know that the decade of the 1960s brought some intense storms to Minnesota.  Maybe that served to trigger my curiosity at an extremely young age.  From my early days I enjoyed some simple ways of looking at the weather which I still use.  These can increase your own understanding and enjoyment of the skies and their changes.

 

Enjoying a Look Up

 

Looking out the window provides a lot of information quickly.   That’s especially true when using a cloud chart which shows photographs of various cloud formations.  There are many options for inexpensive purchase of such a chart, or use this one which is freely available online.  Many such charts also explain the type of weather which each cloud formation will bring.

 

Station plot from weather map

This is from a NWS map and provides an example of the way that surface observations were long depicted. For those familiar with the coding, this would provide temperature, dewpoint, atmospheric pressure, sky and wind conditions – and a symbol showing cloud type as indicated.

 

In previous generations of weather forecasters (prior to 1990), human observers provided cloud type observations.  The symbols for these (which appear on the cloud chart referenced above) were even plotted on surface maps.   Since weather observations became computerized twenty-five years ago, the new automated observing systems can no longer detect cloud type.  The automated systems do report the height of the cloud base – but work poorly for the higher clouds having bases above 12,000 feet.  While you may not have much time or interest in learning to identify all types of clouds, some cloud types will warn you that rain may be on the way – no matter what the forecast is saying!

 

4-30 blog1 Accas

A very useful type of which to be aware for the spring and summer months is Altocumulus Castellanus, pictured to the left.  This is one to remember — because this type of cloud often appears within one to four hours prior to developing showers or thunderstorms.  These “Accas” clouds develop when warm air is pushing into a cooler, drier air mass.  That’s the type of situation in which the forecast models most often fail to foresee warm-season rainfall.

Investigating at Ground Level

Looking outside near sunrise can help determine what happened during the night while you slept.  This insight comes from a look at the ground or at vehicles parked outside overnight.  If it is damp can you tell whether it’s from precipitation or condensation?  Condensation is water vapor that has been transformed to dew or frost because of cold temperatures. while precipitation is the falling to earth of any form of water.  One feature which helps you tell the difference is that while precipitation dampens everything outdoors, condensation usually occurs (with clear skies and) on only the coldest or dampest surfaces – such as metal automobiles or blades of grass.  That look downward will tell you whether it rained or whether it was a clear and calm night.  This may even give some idea of what weather the new morning may bring.  (A note to parents:  This look outside may also provide us with other benefits — perhaps the opportunity to look for toys which need to be put inside or chores which were unfinished from the previous day!)

Some of the thoughts in this post may seem extremely simple and obvious.  Yet by actually taking a few minutes to observe some outdoor basics you will be better prepared for evaluating the day’s weather forecast – and having that forecast work for you.

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Do you know someone who has an interest in weather and would enjoy the Wind Directions Newsletter and blog?  Please send them this link and invite them to sign up  http://winddirections.net/free-newsletter/

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Next week, I’ll write more about the types of observing which can be done with the use of home weather stations or even more simple measuring tools.

Upper Level Lows – “Blocking” Forecast Confidence?

 April 24th, 2016

Forecast confidence can really drop when certain types of weather patterns are present.  In this post, I discuss one such weather pattern which can be common during the spring.  It’s important to remember that our weather is driven by what takes place in the upper levels of the atmosphere.  Analogous to the way that good form for a baseball player begins with proper footwork, an accurate forecast requires computer models to correctly represent how the upper level systems will move and develop.  The spring months can be a particularly frustrating time with respect to upper level low pressure systems.  We are eager for — maybe even counting on — sun and warmth during late April and May.  If an upper level low pressure system is nearby and cut off from the main jet stream, what we end up with can be days of cloud cover, rain, and cooler than normal temps.  This pattern occasionally occurs in winter, but seems more common in spring when the northern branch of the jet stream has lifted north of the Canadian border while the subtropical jet stream has yet to shift northward into the northern US.

Upper Level Low Pressure - Satellite Picture

This Satellite picture from NOAA is characteristic of spring weather in the vicinity of strong upper-level low pressure.

This image from the late afternoon of Thursday, April 21st shows a satellite picture of the Great Lakes region upon which I have drawn the surface features – low pressure and frontal boundaries.  See the swirl of cloudiness near the Iowa – Illinois border?  This is the center of an upper level low.  Forecast models often depict a lot of cloud cover near such features, but notice how many areas in Iowa, southeast Minnesota, and parts of Wisconsin had clear skies (reflected as dark color from the perspective of the weather satellite looking down upon the earth).  There are also many patches or bands of cloudiness seen near this upper level system and some of these clouds were producing heavy showers and even some thunderstorms at the time of this picture.    This “all or nothing” type of pattern can be fairly common near upper level low pressure systems during the spring months, and can result in a “30% chance of showers” turning out very wet indeed for some.

NWS Hourly Forecast Graphic Sample

This sample image shows part of the display for the NWS Hourly Forecast graphic available for a 6-day period for all locations in the US. It’s easy to see when the rain chances are highest and also to get an idea of how much rain could fall in each 6-hour time frame (click to view full size).

Many are indignant when a half inch of rain falls when the probability of rain is so low.   How could that 30% chance have been the most correct forecast in this situation?  It’s important to remember that the percentage chance of rain (as used by many forecasters) has to do with the expected coverage, and gives no information at all about the intensity or amounts of rain which are possible.  This is one reason that I appreciate the hourly forecast graphics (see sample above) available from the NWS website.

Hour by Hour Variability

When an upper level low is lurking overhead, the weather may change quite a bit during the course of a day — and the time of day may not determine the best rain chance.   While it is true that the heating of the day can really fire up instability during the afternoon hours near such a feature, smaller disturbances circulating around the main upper-level low can touch off showers even during the nighttime and early morning.   There may be cloud cover and rain during one hour of the day, then sunshine dominating the next.  Several reports of rainbows came in from the central and eastern Midwest last Thursday evening as skies quickly cleared behind departing showers.  (In the Cincinnati area, a rainbow was also observed Friday evening – for a second consecutive day).  This is truly the type of weather pattern when those who don’t like the weather may need just wait a few minutes!

When upper level low pressure is nearby there is higher than usual forecast uncertainty.  Space and time may limit forecasters’ ability to convey the decreased confidence, but forecast users can be sure that uncertainty grows when an upper-level low is nearby.  Keeping this in mind, one is wise not become too jubilant if the day starts sunny when rain was forecast!

Severe Weather Connection

Another reason I think this topic is timely is that strong upper level low pressure becomes more hazardous as temperature and dewpoint values more often climb toward summertime levels from late April into May and June.  The cold air aloft which is typical of upper level low pressure creates explosive instability as the low-level air mass becomes more energetic.  That cold air aloft can allow significant hail to form during the spring even with relatively low-topped thunderstorms, and also contributes to the potential for damaging winds and strong tornadoes.  Those who closely observe weather patterns will note that by mid-summer, hailstorms typically will occur only with very tall cumulonimbus clouds, because in July and August significant upper-level low pressure systems are most often confined to northern Canada.  After July 4th in most of the US it’s only cold enough much higher in the atmosphere for large hail to form.  That’s a big reason why the severe weather season in the western Corn Belt peaks about six weeks earlier than the average date of our hottest summer temperatures.

Tracking the Forecast – Late Freeze vs. Apples

April 10th, 2016

I find people who grow apples and other tree fruits most admirable for their hard work and patience.  Tree crops aren’t harvested for the first time until years after planting, then the yield on the investment of time and resources accrues for a lifetime.  My friend Maury (founder of Wills Family Orchard near Adel, Iowa) introduced me to a variety of apple known as William’s Pride – one of my all-time favorites for its sweetness and early maturity.  This tasty variety enhanced my interest in the health of the orchard during the years I lived in Central Iowa.  In years past, I tracked growing degree days to assist Maury with plans for pest management, gave my opinion on late freeze threats and prognosticated rainfall patterns for late spring development of the apple crop.  In return I have listened with delight to many stories of successes and challenges from the orchard.

Upper Air Pattern Causing Late Freeze

Several days ahead of the April 9th freeze, weather maps showed cold high pressure would bring unseasonable chill to Iowa and Minnesota. (Forecast image from unisys.com.  Click to view full size image)

 

Late this past Monday afternoon (April 4th), I received a call from Maury expressing concern that this year’s apple blossoms might be subject to a late freeze at the end of the week (Saturday morning).  After a brief look at weather maps (such as the one shown here) and local forecasts I confirmed that Maury’s concerns were well-founded. Not only did conditions look very threatening but probably had the potential to be even colder than many forecasts were saying.  For the next five days, the Friday night outlook became the subject of my watchful care.  I began to chart the Saturday morning forecast conditions from the NWS website for the orchard location west of Des Moines – adding to the chart twice a day as forecasts were updated.  During the first 24 hours, the temperature forecast changed little, but forecast dewpoints and cloud cover fell significantly.  I know from past experience that the slope on which Maury’s orchard sits often receives temperatures colder than the surrounding reporting stations on clear, calm nights.  Thus dewpoints in the 10s (standing as a benchmark for the potential nighttime lows) represent a significant threat to blooming fruit trees.

On Tuesday, I pulled up the record temperatures for the Des Moines airport.  Record lows for every day of April prior to the 19th had fallen to 21 degrees or colder.  Surely, the 24 degrees for four hours which would produce 90% loss of the now-opening apple blossoms would not be unprecedented.  This situation seems sadly similar to the April, 2012 freeze which decimated not only that year’s apple crops but also large quantities of grapes from Iowa to Michigan after the warmest March on record had enticed millions of fruit trees into an unusually early bloom.

By Wednesday morning (the 6th), I was seeing evidence that a layer of clouds depicted by one of the forecast models was expected to be just west of the central Iowa area late Friday night.    Surprisingly, the NWS forecasts for western Iowa gave little credence to this area of clouds.  Maybe it would turn out to be just a fluke in the forecast models, but often these models – which have improved greatly in the past 30 years – will pick up on something which human forecasters miss.  If a bit of warmer air could begin returning aloft into western Iowa before sunrise on Saturday, clouds would form – even directly over the chilly high pressure at the surface.   During a similar freeze threat in April of 2015 Maury’s orchard was spared due to an unforeseen area of clouds which moved across western Iowa three to four hours before sunrise.

Thursday morning weather data was awaited with anticipation.  Once we are within 48 hours of an important event there is a lot more forecast data to provide clues.   In this case, the forecast models were divided into two camps.  One holding onto potential cloud cover (with even more clouds just after sunrise), and the other having a forecast of clear skies.  Reason for hope, but

Late Freeze Forecast Tracker

Late freeze forecast for southwestern Dallas County, Iowa (numbers in black transcribed from NWS website). Note the lower trend in temperatures and dewpoints in days leading up to the freeze (click to view full size image)

very much reason for concern as all other factors suggested near record lows possible Saturday morning.  My tracking spreadsheet shows the downward trend of temperatures and dewpoints from the NWS hourly forecast which I recorded twice daily during the week.

As a weather forecaster with a heart for helping people, it’s easy to want to grasp at anything to give hope of a better outcome.  Sometimes the outlook is so consistent that it’s necessary to find different ways of saying that there isn’t much change from the previous outlook.  I like to draw upon historical comparisons or current conditions “upstream” which illustrate how the forecast may play out.  This helps to add perspective and consistency to the forecast message, Even though I no longer make the forecasts, I enjoy commenting (kindly) on others’ forecasts based on my experience.

I like to follow one particular forecast, such as the NWS hourly graphics, and see how the trend varies over time.  I also read the forecaster’s discussion (example for Sioux Falls forecast office) to see their focus points and opinions about conflicting forecast models.  I compare forecasts in my area of interest to those in surrounding counties to see any patterns which are observable across a small area.  For example, if there is a cloudier forecast the farther west I look (change with location) or a cloudier forecast as the event draws closer (change over time) that would diminish my confidence in the forecast of a hard freeze.  As of Thursday evening, I was seeing none of these hopeful trends, but a couple forecast models were still calling for late night clouds.

In my morning comments on Friday, I anticipated a 50% chance that enough clouds would form to keep the temperature a bit warmer, but that even with some clouds, readings could still drop into the lower 20s.  At noontime, Maury informed me that his Friday was spent putting frost-protective fabric over many of the trees, to thus gain 4 to 6 degrees of protection.  I was happy there was something that could be done since the meteorological developments were not encouraging.  In my location 200 miles to the north of Maury, the air mass was demonstrating the intensity of its chill, as the early afternoon temperature in Marshall, MN was struggling to climb above 32 degrees even with full sunshine, a roaring north wind and bare ground.   It was also extremely dry, with afternoon dewpoints plunging to 10 degrees and even lower.

I was somewhat hopeful, upon waking in the wee hours of Saturday morning to learn that cloudy skies were covering much of the Dakotas, and that even Des Moines was reporting some cloud cover.  Unfortunately this cloud cover remained rather scattered and thin especially prior to sunrise.  Even with these high clouds, Des Moines airport dropped to 25, very much in line with the forecasts and as cold as anticipated.  In the rural areas west of Des Moines, upper teens were common.  At the orchard, with Maury noting that the Spectrum Technologies weather station recorded a low of 17.5 degrees I estimate that it was below 24 degrees for four to six hours.  Such temperatures would ordinarily have caused a nearly complete loss of the crop, though the full extent of any damage will not be known for another day or two.

The Weather Radio – Cause for Alarm?

April 3rd, 2016

Almost twenty years ago during a particularly stormy spring in the area where we lived, my wife informed me that our young daughters were growing increasingly terrified of storms – not due to anything which had happened outside, but due to the frequent alert tones coming from the weather radio. Over time, I learned to receive severe weather information in a manner less jarring to innocent bystanders. As I shared in my post of mid-March, I really enjoy the efficiency (and peacefulness) of following weather updates online. Yet there are times when the weather radio needs to stand vigil as a domestic sentry while all members of the household get their rest.

NOAA Weather Radio – Selective Programming

For many years after the nationwide launch of NOAA Weather radio in the 1970s, everyone within the listening area of a broadcast would receive an alert tone whenever a warning was issued for any portion of the area.  In other words, one could not elect to receive warnings for only a single county.  Except for people like me who enjoyed getting all the updates, it was too much interruption.  Many probably chose not to use the alarm feature.  This changed in the 1990s with the advent of the Specific Area Message Encoding (SAME) feature.  This technology allows users of SAME-enabled weather radios to program the alarm to sound only for their individual county, or for a selected combination of counties.  When you program your SAME county code(s) into the weather radio, you eliminate any alerts that are not within those counties. (North of the border, SAME-enabled technology was integrated into Weatherradio Canada’s network in 2004.)  The programming can be fairly straightforward with the help of the weather radio user’s manual.  It will be necessary to find the SAME code for your county in order to program the radio to sound alerts for the correct location, and the National Weather Service has provided a web page with these codes.   The early spring is a very good time of year to make sure your radio is programmed to sound the alerts for your county – particularly if you have moved or obtained a new weather radio since last summer.   This page has links to online owner’s manuals for a

NOAA Weather Radio Receiver

This is the weather radio model which I have used for many years (Image from Midland Company)

number of the more common weather radio models.  These manuals provide directions for programming the SAME-enabled alert functions.   Another option for those who lack the skill or interest for such a chore:  NWS Meteorologists appearing at public events during the early spring months often will program weather radios that people bring to them.

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What model of weather radio do you use at your home or business?

 

What are your favorite features in a weather radio?

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Weather Radio Receivers – Unique Features

Some newer receivers allow for disabling of alarms for certain events which might not be important to you (for example flood warnings if you live on land situated well above the flood plain).  This feature may be called “Event Blocking” or “Defeat Siren“.

For the hearing-impaired it’s possible to obtain specialized weather radios which alert with flashing lights or even by vibrating like cell phones.  In locations with poor reception, it’s good to be aware that some weather radio receivers come with external antenna jacks (normally in the back of the unit).  These will allow you to connect to a larger antenna which can be either indoors or outdoors.

As you learn more about how the forecast can work for you every day (and night), it will become more apparent what type of weather radio features can best work for you.

 

 

March 19th, 2016

Keeping Ahead of Severe Storms

This post shows you how to obtain weather information in a timely way which minimizes stress and disruption when severe storms threaten.

Thunderstorm Outlooks

Information available online allows me to obtain severe weather outlooks up to five days in advance — and any watches or warnings — very efficiently.   Did you know that convective (thunderstorm) outlooks from the Storm Prediction Center are available several days ahead of time?   The two images below provide an example of how this type of forecast often will be made more specific during the day of a severe weather event.  (Clicking on any of these images will allow you to view at a larger size.)

Thunderstorm Outlooks

Thunderstorm Outlooks

These forecasts are usually quite accurate.  Hail reports from Tuesday March 14th coincided very well with the enhanced risk area from the Day 1 outlook shown above.

Storm Warnings

Any needed warnings are issued by local National Weather Service forecast offices — of which there are 122 across the United States.  I really like this national map which shows any watches, warnings, and advisories with color coding (note the color key at the bottom).  Even more useful is the local map with county outlines which appears when I click on the national map at any location for which I need more details.

Storm Warnings

In this situation, a warning covered portions of four counties. This image clearly represented the portions of those counties most at risk. (Image from NWS website.)

This example of such a local map came from North Carolina on March 14th   Notice that the portion of each county included in a severe thunderstorm warning (orange) is shown — an example of a great online advantage, as this depiction clarifies the exact locations covered by the warning!

My weather radio will sound an alarm for warnings (sent by my nearby station in the NOAA Weather Radio network), and many local television stations now have excellent on-air meteorologists with excellent severe weather coverage.   While I consider the weather radio alarm an important safety feature like a smoke alarm (more on this in coming weeks), and televised information can be essential in certain situations, most of the time I prefer obtaining  warning details online.  A second reason this is so?  When storms become widespread I avoid a long list of warnings, advisories, and other repetitious programming.  Instead, the specific information for my own county is viewed directly.  I can also see at a glance what is happening in nearby counties which allows me to track the worst weather as it approaches my location.

Storm Reports

Because Storm Reports are collected by the Storm Prediction Center, I can look at this map to see where severe hail and wind, and any tornadoes, have occurred so far today.

Severe Storm Risk Categories

In General, the higher risk categories indicate increased potential of more numerous and/or more intense thunderstorms.

The chart to the left explains the risk categories now used in the Storm Prediction Center outlooks.  In future spring blog posts, I will revisit these categories in greater detail.

As this post finishes, I would like to ask for your opinion.  What information do you find most helpful before and during severe storms?  Please email your replies to the address below.  Your comments will help me toward my goal of providing information which is the most useful for you.  

Other questions…

  • What is your preferred source of severe weather information?
  • What is the biggest difficulty you find when seeking or using severe weather information?
  • What is the aspect of severe weather forecasts or warnings about which you most would like to learn more?

winddirections1@gmail.com

Early Signals of Changing Forecasts

Sometimes, the forecaster’s discussion will indicate greater confidence in an event several days away than is shown in the official forecast.  I found the following comment in a forecast discussion during the summer of 2015…

  • RAISED POPS (Probabilities of Precipitation) TO NEAR 30 PERCENT…BUT THESE WILL INCREASE AS THE EVENT DRAWS NEAR.

On other occasions, the forecaster will tell you the reason that the forecast will probably need to change as an event draws closer.  For example,

  • SOME UNCERTAINTY ON SUNDAY… BUT IF IT STAYS SUNNY WILL LIKELY END UP WARMER THAN CURRENT FORECAST.

 

A Myriad of Models

Professional meteorologists have many, many forecast models to use when making forecasts.  This abundance, however, creates a problem.  Which of the two dozen model versions of future weather is the best representation?  The image below shows a “plume” from a SREF (short range ensemble forecast) which depicts how the various models — each represented by a colored line — depict the snowfall accumulation for Sioux Falls, SD from the December 28th to 30th winter storm.  Forecast models have varying strengths and weaknesses, and these will often vary by season.  When forecasts need to be changed, it may be a case in which a typically less-trusted forecast model turns out to have the best handle on a particular storm!

Range of forecast snowfall accumulations from early morning forecast models on December 27th, 2015 (click on image to view at full size)

Range of forecast snowfall accumulations from early morning forecast models on December 27th, 2015 (click on image to view at full size)

How can this uncertainty be used to the advantage of a forecast user?  You probably have noticed  that snow events which are slow to get going almost always underperform expectations in terms of snow amounts.  In this instance, the models which represented the high end of possible snow accumulations produced most of that snow around sundown on the 28th — and very few of the models were forecasting more than an additional inch or two of snow after 12Z (or 6AM CST) on December 29th.  Though advisories for winter weather were slow to be removed from the official forecast, some areas around Marshall had not received more than a half inch of snow — so it was already clear (based on this forecast plume) that the event would not be a big snow maker for Marshall and areas to the northwest!

 

Keeping Ahead of Changing Forecasts

The Twin Cities forecast for the snowstorm which began Christmas night was a difficult one because snow amounts were expected to vary from northwest to southeast across the metro area.  This was due both to the location of heavier precipitation and to the potential for mixed precipitation which would limit snowfall accumulations.

NWS forecasters expected 3.9 inches of snow from this event, of which 2.4 inches was expected to fall after 7am on Saturday, December 26th.

NWS forecasters expected just under 4 inches of snow from this event, of which 2.5 inches was expected to fall after 7AM on Saturday, December 26th.

 

 

 

 

 

 

 

 

By Saturday morning, it was clear that snowfall amounts would be less than those in the forecast 24 hours prior.  The revised outlook called for just an additional 1.3 inches of snowfall during the day Saturday the 26th.

Lower snowfall totals which were anticipated based on earlier forecast models were by this time incorporated into the forecast.

Lower snowfall totals which were anticipated based on earlier forecast models were by this time incorporated into the forecast.

 

This was an example of a change to the forecast which was not a surprise based on the following portion of the forecasters’ discussion from Christmas morning!

FORECAST SNOW AMOUNTS RANGE FROM 5 INCHES IN THE NORTHWEST METRO TO 3 INCHES IN THE SOUTHEAST METRO. THIS IS DEFINITELY ON THE HIGH SIDE OF THE SREF PLUMES* WHERE AROUND 2 TO 3 INCHES IS FORECAST.

*SREF (Short Range Ensemble Forecast) Plumes depict the results of more than two dozen forecast models — along with the average result –on a single chart.  Viewing in this way gives a good perspective on the range of possible outcomes.  

In other words, this very highly regarded forecast tool had indicated the lower amounts (eventual snow accumulation for Twin Cities airport from this December 26th event ended up at 2.3″ – which by the way was the Twin Cities’ first snowfall greater than 1 inch during the month).

Forecasters are very careful not to under-forecast snow events because of the very disruptive effect on travelers, and the “average” of all forecast models is not necessarily chosen as the forecast amount.  The final forecast depends on many factors including the strengths and weaknesses, recent performance, and accuracy of depicting present conditions by the various models.

 

 

 

Soil Moisture Restored During May

The driest portions of the Midwest at the start of May were favored by above to much above normal rainfall during the month, along with slightly below normal temperatures.   This made generally good conditions for early-planted fields to germinate and emerge ahead of the normal pace, though late-May cloud cover was persistent and some fields were nipped by late frosts.   This MonthPNormMidwest to 5-30-15map from the High Plains Regional Climate Center shows that most areas west of the Mississippi River exceeded their normal rainfall for the month and parts of west-central into northern Minnesota and adjoining sections of North Dakota (where blowing dust had been a problem during April) had more than twice their normal rainfall for May.  This continues a trend for southwest Minnesota in which all but one of the past five years enjoyed above normal May precipitation.   We

In the five years since 2010, only 2014 has had a drier than normal May across southwest Minnesota.

In the five years since 2010, only 2014 has had a drier than normal May across southwest Minnesota.

remember last year being exceptionally wet during the early part of the growing season but May of 2014 was actually drier than normal — and dry enough to avoid a complete disaster in what was a very slow planting season.

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