Ramblings of a Graduate Student

Not a lot is happening across most of the country tonight, at least in terms of precipitation.  The image above is a mosaic (composite) of the National Weather Service’s radars.  Areas that are shaded in blue and/or green indicate areas where a radar is detecting possible precipitation.  These areas include the eastern Great Lakes, western spine of the Appalachians,  and the eastern Rockies.  The precipitation across the eastern Great Lakes is the result of weak/light lake effect snow and the snow along the western spine of the Appalachians is the result of orographic lift.  The precipitation in the eastern Rockies is being aided by an upper-level low that will move into the plains by late week.

People throughout the eastern United States should enjoy the relatively tranquil pattern while it lasts.  Long range models continue to hint at a return to an active pattern as early as this upcoming weekend!

After spending the last three days working almost exclusively on the Snow Shot of America project (with respect to this blog anyways), today I return to regular programming on the 365 blog.  For those who aren’t familiar with the 365 blog, the purpose is to post a weather chart a day and discuss its significance to meteorologists.  I try to keep most posts at a beginning to intermediate level so a wide-range of audiences can enjoy, but the occasional technical post (to challenge my current and former undergraduate students) will make its way to the blog.  If a reader ever has a question about something posted, please feel free to post your question in the comments.  I read each and every comment and will attempt to address your questions.

Tonight, I’ll focus on yet another snow storm that has affected a large portion of the central and soon-to-be eastern portions of the United States.  The image atop this post is a water vapor image from earlier this morning. (For those who are unfamiliar with water vapor imagery, I give a brief discussion in this post.)  Below, I’ve annotated the same graphic to help facilitate understanding.  The yellow circle encompasses the atmospheric feature of interest, the “x” is the meteorological shorthand for “maX”, and the yellow line is the actual/projected path of this feature in the near term.

The shortwave trough (upper-level low) that was/is/will be responsible for the snow across the southern and eastern United States was located near Omaha, NE this morning.  On the southern and eastern side of this upper-level low center is where meteorologists would expect to find rising motion based on its current path.  If adequate moisture exists in areas where rising motion is occurring (which it did/does), precipitation would be expected.  Because the atmosphere is still relatively cold and supportive of snow, most of the precipitation that fell today, is falling tonight, and will fall tomorrow will be in the form of snow.  Now, south of the Tennessee southern border, most of the precipitation has fallen as rain, with a quick chance of mixing with or changing to snow as the precipitation ends.

Based on the current forecast track of this upper-level low, people along the east coast should prepare for yet another chance of snow.  In a normal year, this storm would have the potential to cause headaches all along the east coast from Washington D.C. to Boston.  However, based on the major winter storms that have slammed the east coast this winter, this storm will be a minor nuisance in comparison.  The only place where this might not be the case, and wider travel problems may be an issue would be from New York City north and east where winter snow has not been as great as in the Washington D.C to Philadelphia corridor.

As many of you may already know, I’m currently attempting to take “a snow shot of America” tomorrow.  For those who don’t know what that is, you may be wondering what on earth is “a snow shot of America”.  Simply put, it is a collage of pictures taken of the snow on the ground from every state.  Why tomorrow?  There is a chance that there will be snow on the ground in all 50 states at the same time.  It is unclear if this has ever happened in recorded history.

Above is this morning’s National Snow Analysis; it excludes Alaska and Hawaii, but I’ll get to those states in a minute.  As you can see by looking at the analysis, snow exists in same form or fashion in every one of the contiguous states, with the exception of Louisiana and Florida.  However, a storm moving across the southern United States is poised to change that map drastically by tomorrow.  Local National Weather Service offices in the Deep South are currently forecasting up to an 1″ of snow as far south as the beaches of far western Florida Panhandle.  2-4″ may be possible in areas just north of Pensacola, FL.

Below is the current National Watch/Warning graphic.  The hot pink color is Winter Storm Warnings.  It isn’t very often you see these extended all the way to the Gulf Coast.  Nor do you see it over such a large area this far south.  Here’s to hoping for Florida snow tomorrow!

Now, about Alaska and Hawaii…Alaska has a lot of snow in the state, so I’ve never worried about them.  I was led to believe based on a The Weather Channel tweet that there was snow in the mountains of Hawaii.  This seemed perfectly logical to me, so I didn’t question it too much.  Old webcam images showed snow, and a blizzard in the past few weeks blanketed the mountains.  However, further investigation has led doubt to finding snow on the mountains.  It certainly seems possible that there is snow in a sheltered patch, however, finding the snow will be tough.  I keep reminding myself that “absence of evidence is not necessarily evidence of absence”.  In other words, just because we can’t find it, doesn’t mean it isn’t there.  Here’s to trying!

In any event, Florida snow is more rare than Hawaiian snow, so getting 49/50 and the 48 contiguous states is still an impressive feat!

Last night I mentioned in my post that it looked more and more like the winter storm for Oklahoma was going to end up being a non-story.  For most of Oklahoma, this turned out to be the case.  Whereas there were places that received several inches of a wet fluffy snow, most places didn’t see any accumulations.  Accumulations that did occur were primarily confined to grassy surfaces and travel issues were minimal.

This was not the case in far eastern and southeast Oklahoma.  Nor was it the case for a large portion of Arkansas.  The forecast when most residents went to bed called for rain, possibly mixing with snow at times, throughout the night.  No accumulations were forecast for places like Fort Smith, Little Rock, Memphis, etc.  Talk about a surprise when residents in these areas awoke to anywhere from 2-4″ of snow on the ground with more snow on the way.  So what happened?  How did snow fall in southern Kansas and eastern Oklahoma, and miss central Oklahoma?

First, as all my former synoptic students should be able to tell you, we need to diagnose why the precipitation developing where it was.  Normally, I would make them first tell me where there is precipitation, but I’ll provide that answer this time.

Above is a water vapor image valid at 0845 UTC (3:45 AM CST).  Below is the same image, annotated by me.  In the image above there are two areas in the southern plains that have brighter colors (more moisture aloft).  And as explained in previous posts, more moisture aloft is a good indicator that there is some sort of upward vertical motion transporting the moisture upward.  We’ll start our journey in these two areas (circled in the image below).

So why is their upward motion (and precipitation falling) in the area circled in red?  The answer here lies in the transport of warm, moist air about 5,000 feet (1500 meters) above the ground.  In the image below, areas that are shaded in various shades of red indicate where warm air was being advected (blown around) toward cold air.  The darker the red, the stronger the advection.

As the warm (and more moist) air begins to interact with the colder air, the warm air begins to move over the top of the cold air.  This is a common form of atmospheric lift in winter (known as isentropic lift, or, in slang, “overrunning” because the warm air is overrunning the cold air).  This atmospheric lift  was enough to produce precipitation during the night in northcentral Texas, southeast Oklahoma, and much of Arkansas.

To the northwest of this area, we have another area of atmospheric lift occurring in southern Kansas and northern New Mexico (shaded in green in the water vapor image mentioned previously).  If we look at the warm air advection map (above) we would see there is none of this occurring at that level of the atmosphere and so that isn’t the source of lift.  However, similar to how a surface cold front can sometimes provide the focus for atmospheric lift, fronts aloft can do the same.  If we look at a portion of the atmosphere typically around 10,000 feet (3000 meters) above the ground we can see that a relatively strong front was draped across southern Kansas (the brighter the colors in the image below, the stronger the front).  It turns out that convergence along the front was strong enough to induce vertical motion and, ultimately, precipitation.  As you can see, there really wasn’t much of a focusing mechanism for precipitation across much of Oklahoma, which is why we didn’t see widespread heavy snow (or rain).  Just a drizzle, mist for much of the day.

So, this explains why there was precipitation where there was, but why did the forecast rain actually fall as snow in southeast Oklahoma and western Arkansas – especially with the surface temperature above 32F?  The answer lies in what the temperature did above the ground. Normally, when temperatures are above 32F we should expect rain, right?  Well, not always.

In places like Fort Smith, AR and Little Rock, AR, the warm air (above 32F) at the surface was very shallow – no more than about 1000 feet deep.  As the initial precipitation fell across the area, it fell in the form of light rain – at the surface.  It was actually snow aloft, but it melted back to rain as it fell through the warm layer just above the surface.  Most forecasters thought that the precipitation would be light enough that the snowflakes would have time to melt as the fell through the warm layer and thus little to no snow would fall throughout most of the night.

However, as heavier precipitation began to develop around midnight, the precipitation began falling so fast that it did not have time to completely melt as it fell through the warm layer near the ground.  Normally, this would continue while the heavy precipitation fell and then transition back to rain as the heavier precipitation moved away.  Unfortunately for meteorologists, the precipitation remained heavy for a longer time than expected.  This allowed more and more big, wet snowflakes to make it to the ground before completely melting.  This had two effects: 1) it allowed snow to begin to stick to the ground as it was falling – there wasn’t enough time for a snowflake to melt before the next snowflake landed and 2) as the snow fell into the warm layer, the warm layer began to cool – similar to how a drink cools as you put ice into it.  The cooling of the warm layer allowed for less melting of the snow which meant more snow reached the ground.  As more reached the ground, the surface temperatures began to cool, allowing more snow to stick, and we’re off to the races.  This heavy precipitation induced snowfall is why when the precipitation was less intense, there was a tendency for it to mix with or switch back to rain across southeast Oklahoma and much of Arkansas.

Now, in southern Kansas, the temperature was below 32F throughout the entire atmosphere and melting of the snowflake was not an issue.  Thus, the snow wasn’t as much of a surprise (in fact it was well forecast) as it was for places to the south and east.

Tonight is/was the 2nd Annual NWC Benefit Bash.  It was an event I started last year to help raise money and awareness for victims of weather related disasters.  Last year the event raised money for a young girl who lost both her parents in the 10 February 2009 Lone Grove, OK EF-4 tornado.  This year the event raised money for the Central Oklahoma Chapter of the American Red Cross to help restore their depleted funds after the Christmas Eve Blizzard in 2009.

In keeping with the theme, the image below is a water vapor satellite image from approximately noon central standard time on Christmas Eve.  It shows a very strong upper-low poised just south of Oklahoma.  As Oklahomans quickly learned, the track the upper-low took is very favorable for heavy snow in the Oklahoma City metro.  Ultimate, when all was said and done, Oklahoma City broke the all-time record for most snow in 24 hours and the most snow from a single storm with an official total of 13.5″ of snow at Will Rogers World Airport.

With this said, another snow storm is poised to affect the southern plains late tomorrow into early Tuesday.  I’ll have more on this tomorrow.

Today weatherpersons all across the United States are celebrating National Weatherperson’s Day.  I know a lot of people consider Groundhog Day (2 February) to be National Weatherperson’s Day because, after all, what screams weatherperson more than a furry rodent looking for its shadow?  However, they would be wrong.  It is celebrated on 5 February because today is the anniversary of American John Jeffries’ birth, who began recording daily weather observations in Boston, MA in 1774.  Jeffries is considered to be one of the first weather observers in what became the United States.  This day celebrates meteorologists’ continuous efforts to produce the best forecasts and warnings.

With this said, there is a lot of high-impact weather to observe across the United States today.  The strong shortwave trough over eastern Colorado last night has continued to dive east-southeast into central Kansas and is aiding in the development of widespread snow across eastern Kansas and much of Missouri.  Also, the conglomeration of weak shortwave troughs over the Gulf of Mexico last night continue to track off to the northeast aiding the development of extremely widespread precipitation across much of the eastern United States.

The areas shaded in blue are places where a computer model believes the precipitation is falling as snow; orange is a mixture of rain, freezing rain, sleet, or snow; and green is rain (or thunderstorms).  As you can see, snow is evident from the far western edge of the map (in reality it extends all the way into Missouri) all the way to the east coast.  All of this precipitation will slowly move east over the next 24-36 hours yielding a near historic snowfall for the Washington D.C. area.  In fact, Washington D.C. is under a Blizzard Warning!  16-22″ of snow is expected to fall overnight!

Below is the text of a Special Weather Statement issued by the National Weather Service Forecast Office in Sterling, VA (which covered the Washington D.C. metro).  Notice the strong wording and the 20-30″ totals that are expected.  Earlier today I saw some model guidance that predicted almost 40″ of snow!  Sheesh!

000
WWUS81 KLWX 051734
SPSLWX

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1234 PM EST FRI FEB 5 2010

DCZ001-MDZ004>007-009>011-013-014-016>018-VAZ042-050>057-501-502-
060145-
DISTRICT OF COLUMBIA-FREDERICK MD-CARROLL-NORTHERN BALTIMORE-
HARFORD-MONTGOMERY-HOWARD-SOUTHERN BALTIMORE-PRINCE GEORGES-
ANNE ARUNDEL-CHARLES-ST. MARYS-CALVERT-LOUDOUN-ORANGE-CULPEPER-
PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX-
ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA-
KING GEORGE-NORTHERN FAUQUIER-SOUTHERN FAUQUIER-
INCLUDING THE CITIES OF...WASHINGTON...FREDERICK...WESTMINSTER...
GAITHERSBURG...COLUMBIA...BALTIMORE...ANNAPOLIS...WALDORF...
ST MARYS CITY...LEESBURG...CULPEPER...MANASSAS...MANASSAS PARK...
FAIRFAX...ALEXANDRIA...FALLS CHURCH...FREDERICKSBURG...WARRENTON
1234 PM EST FRI FEB 5 2010

...RECORD SNOWFALL FORECAST IN THE BALTIMORE-WASHINGTON DC REGION...

...EXTREMELY DANGEROUS WINTER WEATHER CONDITIONS DEVELOPING TONIGHT...

GUSTY NORTHEAST WINDS 20 TO 30 MPH WITH VISIBILITIES FREQUENTLY
FALLING BELOW ONE-QUARTER MILE DUE TO HEAVY SNOW WILL DEVELOP
TONIGHT TO PRODUCE NEAR-BLIZZARD AND EXTREMELY HAZARDOUS WINTER WEATHER
CONDITIONS TONIGHT THROUGH SATURDAY MORNING.  TRAVEL IS HIGHLY
DISCOURAGED TONIGHT AND WILL BE VERY DANGEROUS.

LOOKING BACK AT THE BIGGEST STORM OF RECORD FOR WASHINGTON DC... THE
JANUARY 1922 KNICKERBOCKER STORM...28.0 INCHES OF SNOW WAS
PRODUCED FROM 3.02 INCHES OF LIQUID WATER.  CURRENT FORECASTS FOR
THIS EVENT HAVE TOTAL LIQUID FALLING FROM THIS STORM APPROACHING 3
INCHES...WHICH ACCORDINGLY WOULD CREATE A SNOWFALL THAT WILL RIVAL
THE KNICKERBOCKER STORM TOTAL.  GENERALLY ACROSS THE REGION...20 TO
30 INCHES OF SNOW WILL FALL BY SATURDAY EVENING.

BALTIMORES RECORD OF 26.8 INCHES FROM THE PRESIDENTS DAY FEBRUARY 2003
STORM WILL ALSO BE THREATENED.

A FEW PRECAUTIONARY AND PREPAREDNESS ITEMS TO NOTE:

1.  FOLLOW MANUFACTURERS INSTRUCTIONS WHEN OPERATING A GENERATOR OR
AXILLARY HEATER.  ENSURE PORTABLE GENERATORS ARE ADEQUATELY VENTILATED.

2.  TRAVEL CONDITIONS TONIGHT ACROSS THE REGION WILL BE EXTREMELY
DANGEROUS AND LIFE THREATENING.  HELP YOUR LOCAL AND STATE
GOVERNMENT FIRST RESPONDERS AND TRANSPORTATION AGENCIES BY STAYING
OFF ROADS LATER THIS EVENING AND TONIGHT.

3.  FOLLOW LOCAL AND STATE GOVERNMENT EMERGENCY DECLARATION ORDERS.
IF YOU ABSOLUTELY NEED TO TRAVEL IN AN EMERGENCY...DO NOT TRAVEL
ALONE.  LET SOMEONE KNOW YOUR TIMETABLE AND YOUR PRIMARY AND
ALTERNATE ROUTES.  CARRY WITH YOU A WINTER STORM SURVIVAL KIT WHICH
INCLUDES A MOBILE PHONE...BLANKETS...FLASHLIGHT WITH EXTRA
BATTERIES...HIGH CALORIE NON-PERISHABLE FOOD AND WATER...AND A
SHOVEL.

4.  IF YOU GET STRANDED IN YOUR VEHICLE...DO NOT LEAVE YOUR CAR TO
TRY TO WALK FOR ASSISTANCE...YOU CAN QUICKLY BECOME DISORIENTED IN
WIND DRIVEN SNOW AND COLD.  THIS STORM WILL SUBSIDE SATURDAY
AFTERNOON...SO WAIT IN YOUR CAR FOR EMERGENCY HELP TO ARRIVE.
PERIODICALLY RUN YOUR ENGINE FOR ABOUT 10 MINUTES EACH HOUR FOR
HEAT. ENSURE YOUR EXHAUST PIPE IS CLEARED OF SNOW AND ICE.  CRACK
YOUR WINDOWS TO AVOID CARBON MONOXIDE POISONING. TIE A COLORED CLOTH
TO YOUR CARS ANTENNA TO BE VISIBLE TO RESCUERS. FROM
TIME-TO-TIME...MOVE YOUR ARMS...LEGS...FINGERS...AND TOES TO KEEP
BLOOD CIRCULATING.

5.  AVOID OVEREXERTION WHEN SHOVELING SNOW.  BREAK THE SHOVELING
DOWN INTO SMALLER JOBS AND TAKE FREQUENT BREAKS.

6.  IN CASE OF POWER SUPPLY DISRUPTIONS...HAVE AVAILABLE FLASH
LIGHTS WITH EXTRA BATTERIES...EXTRA FOOD AND WATER...EXTRA MEDICINES.

7.  ENSURE ANY PETS AND FARM ANIMALS HAVE PLENTY OF WATER...FOOD...
AND SHELTER.

FINALLY...THE KEY TO GETTING THROUGH THIS AND OTHER PERIODS OF
HAZARDOUS WINTER WEATHER IS WITH ADVANCE PLANNING AND BEING AWARE OF
CURRENT CONDITIONS.  THIS STORM WILL BE WINDING DOWN EARLY SATURDAY
EVENING...SO DO YOUR PART AND LET YOUR LOCAL AND STATE GOVERNMENTS
RESTORE ROADWAYS TO NORMAL CONDITIONS BY STAYING AT HOME.

$$

LEE/CS

A very active weather pattern is shaping up for the next 10 days or so beginning with a shortwave tough (upper-low) moving through the southern United States.  I debated whether to talk about this upper-low as it currently is moving through the south central US or discuss what will happen (partly as a result of this upper-low) along the east coast starting tomorrow into the weekend (another major snow storm for the mid-Atlantic states!).  I figured there would be a lot to talk about tomorrow with respect to the mid-Atlantic snow so I decided to talk about the southern plains tonight.

Below is a radar image taken tonight from the National Weather Service radar in southwest Oklahoma.  At the time this image was taken, southwest Oklahoma was experiencing light to occasionally moderate intensity rain – at the surface.  Why do I make this distinction?  Because above 6000 feet above the ground it was actually snowing!

The radar image above has what is known to meteorologists as a “bright band” signature.  The bright band is the dark green and yellow pixels that appear to make a circle around the radar (the cyan dot with KFDR label).   What is happening is that high in the cloud, the precipitation starts out as snowflakes in the cold air aloft.  As the snow falls and gets closer to the surface it encounters air that is above 0C (32F) that causes the snowflake to begin to melt.  This partially melted snowflake shows up on a radar image much more easily than a snowflake or a raindrop itself would show up.  This causes the level with the most partially melted snowflakes to show up as a bright band or bright circle around the radar site.  (Without getting in the math and physics of it all, everywhere along the the dark green and yellow circle is essentially at the same height.   It has to due with the curvature of the earth’s surface.)

Because the image below has a fairly easily identifiable bright band, I can say with a lot of confidence that it is snowing higher up in the clouds.  Now, the million dollar question, will any of those snowflakes make it to the ground?