NO … it is NOT going to SNOW 1–4 inches in the Shenandoah valley/ western MD / eastern WVA on Wed/
HERE IS WHY
It has been brought to my attention that the folks at NWS Washington DC Baltimore office have issued Winter Weather Advisories for 1–4 inches of snow for the northern Shenandoah Valley for Wednesday. I can find no rational reason for making such a ridiculous forecast given the actual data except to say that since the GFS model is colder and NWS loves to ass kiss the GFS model. But the “soundings” show that this is a serious mistake on their part and that there is not going to be wonderful inches of snow and any portion of the Shenandoah Valley on Wednesday.
Let me show you why this forecast from the National Weather Service in Washington DC Baltimore is ridiculous. First this image represents the regional image of the winter weather advisories in northwest Virginia and Western Maryland and the Eastern third of West Virginia.
This image shows the actual weather statement from NWS centered around Harrisonburg. If you to the NWS Washington DC web site and click on the other counties you will see that the snow mounts are as high as to the 4 in the elevated terrain of the Shenandoah Valley and in West Virginia. again this is nonsense.
Sometimes weather models have those pretty colors that show snow, sleet, and freezing rain in areas which they shouldn’t. For example, if you take a look at what IS going on in the radar right now in Texas and Oklahoma you will see there is a big rain snow and rainstorm going on there. Just 36 hours ago, many of the weather models were showing anywhere from 1–4 inches of snow across the Dallas metro area with surface temperatures of 34 and 35°. That made little sense and as you can see on the radar .. Dallas and North Central Texas are seeing rain NOT snow.
In other words, this is the problem — the weather models graphics / images often show the precipitation type that is not supported by the SOUNDING.
WHAT IS THE SOUNDING.? When meteorologists use the term the sounding what we Are talking about is the projection of the atmosphere from the ground to the very top of the atmosphere. The soundings come from the high-resolution models such as 3kmNAM the HRRR the RGEM and the EURO and they are quite accurate because they only go out to about 60 to 72 hours.
Keep in mind that an order for snow to reach the ground, the atmosphere HAS to be cold from where the snow forms in the cloud all the way down to the ground and stay below 32°. Sometimes there are bubbles of warm air which appear at the lower and mid-levels of the atmosphere that cause snowflakes to melt. The melted snowflake — rain- may then fall back into a colder layer as it approaches the ground and when this happens the precipitation becomes either sleet or freezing rain.
This image shows the sounding from the high resolution 3km NAM model which is the primary short-range high-resolution model used in the United states.
At 8:00 am on Wednesday morning Harrisonburg is still DRY and the temperature is 35°, the dew point is 27°. In this image I have drawn a THICK BLACK line which represents the freezing line as you go higher up into the atmosphere. ANY precipitation to the LEFT of the Black line is frozen -either sleet or snow — and any precipitation to the RIGHT of the black line is rain. What this sounding says is that at 8:00 am Wednesday morning the atmosphere is still cold enough to support snow even though the temperature is 35° and the dew point is 27. If the precipitation were to start at 8:00 am on Wednesday the saturation or wet bulb would be around 31°, which would support snow at the surface in Harrisonburg.
This next image shows the Sounding at 10:00 am on Wednesday when the precipitation is beginning in Harrisonburg with the surface temperature is 36° with a dew point of 30. That equates to a WET BULB or Saturation temp of 33 degrees.
Notice however that there is a large bubble of warm air which I have highlighted in BLUE that at 5 to 10,000 feet above the ground temperatures are around 40°. This means the snow in the cloud is going to melt and turn to rain. The sounding goes back below 32° around 2,000 ft above the ground so the precipitation will turn into sleet or freezing rain. BUT this sounding means that it is impossible for the atmosphere to produce snow after 9:00 or 10:00 a.m. in the Shenandoah valley. This is why the NWS forecast for 1–4 inches of snow in the Shenandoah Valley, western Maryland and the eastern panhandle of West Virginia is nonsense.
By 11:00 a.m. on Wednesday morning the sounding shows the bubble of warm air highlighted in BLUE is now up to 45° and climbing!! . it has expanded significantly. There is still a slight cool spot about 1,500 ft above the ground where the temperature to the left of the Black line is 30 degrees so the liquid rain may turn into sleet or freezing rain, but it is not snow.
As long as these soundings remain valid the forecast for 1–4 inches of snow in these areas from NWS in Washington DC Baltimore is not going to verify.