REVIEW OF THE SNOW FORECASTS 20 FEB 2020 FOR SOUTHSIDE HAMPTON ROADS VA
STARDATE 202002.23 1300 EST
*** CLICK ON SOME IMAGES TO SEE FULL SIZE ***
In this essay in review the I am going to take a look at the meteorological conditions and the forecast regarding the events of February 20 and specifically the lack of snow accumulations in portions of Hampton roads. Not only will I discuss the actual of atmospheric conditions but the various types of forecasts that were issued regarding the overall event and the potential for the event to a bit more significant that was.
This is not a case of the various short range forecast models busting per se. While some of the short range models did show is somewhat lower snow amounts over the coastal areas of southside Hampton roads... the main problem with the forecast was the temperatures and the dew points. While snow lovers in Hampton Roads were somewhat frustrated by this event... it is a mistake to proclaim that getting the forecast correct for the wrong reasons still counts as a good forecast.
If the initial forecast by Mr. Smith is for no significant snow then it is changed for several inches of snow but the end result saw no accumulating snow ...Mr. Smith does not get credit for the correct overall forecast.
And if Mr. Smith's forecasts no snow then changes the forecasts to one of several inches and then some sort of unexpected development happens... the forecast of no accumulating snow
is still wrong.
The initial event showed up on the European model back on February 14 as a potential major snowstorm for the southeast US into the lower Middle Atlantic from the European model. The European model have developed a large closed Upper Low in the southern portion the jet stream stretching from Kentucky to Arkansas and northeastern Texas. The model forecasted that the 500mb Upper Low would developing NEUTRAL tilt as it moved to the Carolina Coast. The rotation of the Upper Low from a positive Tilt - a southwest to northeast alignment to one where the 500mb Low is aligned ina north to south direction would cause a significant coastal LOW to form along the Carolina Coast and track over or very close to Cape Hatteras. This would bring about a significant snowstorm for much of the Carolinas and the eastern third of Virginia into the lower Delmarva.
While the various global models over the next several days would play hide and seek with this coastal LOW for the most part they showed a weaker system then what the European model was showing back on February 14. One of the driving factors of this winter has been stronger than normal or enhanced jet stream in the northern Pacific and North American. It is the enhanced jet stream which is one the reasons why the European model solution on February 14 for a major storm on February 22-23 third will fall apart. The enhanced jet stream was going to restrict or prohibit the development of a large closed upper low so that the big snowstorm scenario was not going to occur.
Many the initial forecasts from NWS as well as local TV stations in the Richmond metro and Hampton roads area were downplaying the snow potential significantly. The coast Low looked pretty weak on all of the models. Even the most aggressive model with this snow consistently forecasted a very sharp northern edge to the potential snow shield which replaced areas such as Richmond and the Middle Peninsula on the far northern edge of the accumulating snow line. For the most part... this appeared to be a North Carolina Southeast Virginia snowfall which is more less how things ended up working out
However as the event drew closer the snow amounts started to inch up on many of the short range models and this was reflected in the Wednesday forecasts
It has been suggested by some that the northeast winds from off the ocean and Chesapeake Bay into the areas of Portsmouth Ocean view, Norfolk and the coastal areas of Virginia Beach kept low level or surface temperatures 1 or 2° warmer than forecasted which played a critical difference in keeping temperatures above 32° during the afternoon/evening hours of February 20. While the ocean and lower portions of the Chesapeake Bay may have had some impact.. in my view is that the ocean and they influence was only an indirect cause of the snow not sticking in the south side coastal portions of Hampton Roads.
This initial map shows the actual surface conditions from cough most of North Carolina Virginia Maryland Delaware as of 7:00 AM in the morning of January 20. Although it may be difficult to read what is important here are the temperatures and the dew points across eastern and southeastern Virginia. Wakefield was reporting a temperature of 41° for the dew point of 28 which results in a wet bald (saturation point ) 35 degrees. Norfolk Temp was 44 dew point of 28 which is wet bulb of 39. However... the north and northeast winds continue to bring in somewhat colder air with significantly lower dew points from central and Northern Virginia.
Even though the temperatures were well above freezing across all of central and southern Virginia when the precipitation began... the mid levels and the low levels of the atmosphere were cold. This image shows the 850mb temperatures at 9:00 AM on the morning of the 20th. (850 mb level is about 1 mile above the ground and during the cold season it is where most the precipitation forms as snow if the atmosphere is cold enough to support it).
We can see the readings were well below zero across northeastern North Carolina and all of eastern and southeastern. Virginia. However just because the atmosphere is cold enough for the precipitation to form as snow up during the cold season months doesn't mean that the precip is going to stay snow. The precipitation that forms snow has to make it all the way to the surface. Looking at the 925mb which is about 2000 feet above the ground if we can see that the temperatures over Southeast Virginia and Northeast North Carolina or at zero to +1° C while Richmond was -3. This shows that the low levels the atmosphere still had too cool off a couple more degrees to support snow in Southeast Virginia.
By late afternoon and early evening, the 925mb temperatures had in fact drop significantly over Southeast Virginia and interior portions of north-central and Northeast North Carolina. Here we can seem readings around -32 -4° C at the 925mb level about 7:00 PM on the evening of February 20.
At this point the atmosphere was now cold enough to support snow from 850mb all the way down to the ground. in southeast Virginia and northeast North Carolina.
The 12:00 PM observations show the influence of the colder dry air over portions of Central Virginia but not necessarily into southeastern Virginia. The Richmond had a temperature 40° the dew point of 25 which resulted in a wet bulb of 33° cold enough to support snow. This was also the case locations such as Petersburg and Chesterfield. Norfolk with a temperature of 45 and a dew point of 28 resulted in a wet bulb of 37°. Newport News and Williamsburg had a wet bulb of around 35°which again is still too warm to allow of snow to cumulate on the ground.
At 2:00 PM Wakefield and Franklin were reporting temperatures of 39° with the dew 27 and the precipitation type was still rain. This is also the case for Rocky Mount or Roanoke Rapids near the Virginia North Carolina border. Notice however that temperatures in Southeast Virginia in and around Norfolk which still 42° for the dew point of 26 and Elizabeth City was reporting a temperature 46° and dew point of 31. Both of these had wet bulb temperatures that were simply too warm to support snow at this time.
By 3:00 PM however the interior portions of Southeast Virginia are cold enough to support snow. Notice that Hampton roads Executive Airport which is located on the border of Chesapeake/ Suffolk was reporting a temperature of 32° with a dew point of 30 and moderate snow. This is also the case of Franklin and Wakefield with both locations showing temperatures and dew points around 32° and all snow. The rain had changed over to snow at the Norfolk Navel with a temperature of 37° and dew point of 32. That kind of temperature/dew point readings support a wet-bulb well above 33°which meant that it would be difficult if not impossible for the snow to accumulate.
Note that over the interior portions of South Central Virginia along the North Carolina border locations such as South Hill...l Emporia Franklin ... Chases city and Lawrenceville were all reporting snow and a temperature around 32 or 33°
Because of the developing moderate snow along the North Carolina Virginia border SPC NWS issued a mesoscale HEAVY SNOWFALL discussion around 3:00 PM February 20 which called for moderate snow up to 1 inch per hour snowfall rates over northeastern interior portions of North Carolina into southside of Hampton Roads. This clearly was a mistake. Even the areas which saw the best snow along the Virginia North Carolina border -from Suffolk to Franklin over to South Hill and places such as Murfreesboro Rocky Mount and Roanoke Rapids... the maximum snowfall amounts report in these areas was around 5 inches. The snow continued from 3:00 PM to about 11:00 PM in these areas which ....according to SPC should have results in snowfall amounts of 6-8" . Clearly the 1 inch/ hour snowfall amounts did not actually occur.
In addition... the issuance of this discussion by SPC/ NWS probably colored a lot of meteorologists' perceptions about what was happening over the coastal areas of southside Hampton roads. It certainly impacted my perceptions. It was believed that if you saw the snowfall rates of 1" / hour move into Southside Hampton roads... it would force the low-level temperatures down a couple of degrees which in turn will allow the snow to begin to accumulate in the coastal areas to Portsmouth Norfolk and Virginia Beach. Again that did not happen because the snowfall rates did not achieve an intensity of 1 inch per hour.
At 7:00 PM observations show the continued problems over the southside coastal area of Hampton Roads. Norfolk's temperature was 36° with a dew point of 33 which gives you a wet bulb near 35°which is too warm to support snow accumulation at the surface. Virginia Beach had fallen down from 37° but the dew point will still 32. Again this results in a wet bulb of 35°. Norfolk naval station showed a surface of 35 with the dew point of 33 or wet bulb of 34° which again is 1 or 2° too warm.
Over in the Peninsula and interior portions of Southeast Virginia however that difference of 1 or 2° was having a significant impact. There were areas of light to moderate snow over the Hampton Roads Executive Airport ( on the border of Suffolk / Chesapeake) and in Franklin and Wakefield. Newport News was reporting 3/4 mile e visibility with a temperature of 34° a dew point of 30 and a wet bulb of 32.
Meanwhile over the interior portions of Southeast Virginia including the North Carolina Virginia border location such as for Ft Pickett Chase city Clarksville South Hill Emporia were all reporting temperatures of 32° and moderate snow.
By 11:00 PM light snow over the southern portions of the Richmond metro area had come to an end and it was ending across the North Carolina Virginia border towns and locations. But in Hampton Roads the problem of no snow accumulations remained along the coastal areas of Portsmouth Norfolk and Virginia Beach were surface he temperatures were still running around 34 and 35° with a dew point around 32°. In all these locations the wet-bulb temps were too warm to support snow accumulation at the surface. Notice that at this point the Norfolk Naval station.... as well as Virginia Beach and the city of Norfolk... were now reporting due North -- not NE - winds but surface temperatures were still not dropping nor were the dew points.
The initial burst of temperatures during the morning and midday hours into the middle 40s over the coastal areas of southside Hampton roads and northeast and North Carolina was a factor which I missed --as well as almost all other forecasters whether it was in the private sector TV or NWS. The 5° temperature difference between Max temperatures in Richmond vs. Norfolk proved to be significant and was enough to keep wet bulb temperatures above 32° which is what prevented the snow from accumulating. Most of the short-range models the day before did not have temperatures reaching the middle 40s over the south side of Hampton roads which one the reasons why it was not giving enough attention by different forecasters including myself.
If this event had occurred day 8 or 12 hours later the large arctic HIGH in the middle portions of the country would have advanced further to the east and this in turn would of driven colder / drier air deeper located in central and northern Virginia deeper into Hampton roads and North Carolina. This in turn would have ensured a much more significant snow event for Hampton roads without having to worry about wet bulb temperatures and or the dew point.
Interestingly even though there was some argument in the meteorological community as to how much actual precipitation would get into Hampton roads... final figures show that the precipitation amounts were close to 0.5 inches. IF that this is been all snow it would clearly have supported at least a 2 to 4 inch snowfall and possibly either 3 -6' or a 4-8" snowfall depending on the temperature profiles and the snow ratios. As usual... the snowfall maps from the short-range models as shown on weather pages such a Weathebell, Weather models.com and to lessor degree ...Tropicaltidbits.com were incorrect .. extreme... and amplified.
On the other hand, there are some weather models side on the Internet which use a variable snow ratio output depending on actual conditions and forecasting conditions at the surface and at the mid-levels the atmosphere. Those models showed a much more reasonable snowfall prediction for Southeast Virginia and northeast North Carolina and they should be getting a lot more attention than the overdone ridiculous over amplified snowfall maps showing up on weather bell and weathermodels.com web sites.
Finally SOME have asked about the TIP jar link. Given the partially busted forecast for portions of Hampton Roads I think its " wrong" to post it on the FB page.
But I will post it here .... TIP JAR LINK