WIll rain change to snow Tuesday?

Here is a forecast overview

– rainy morning perhaps ending as snow around lunchtime
– no hazards expected from snow chance
– high pressure and sunny skies return Wednesday

Forecast: A storm system which has been slowly moving across the
southern United States will lift northward into the Tennessee valley
before moving east into the mid-Atlantic states. An abundant amount of
lift and moisture will be drawn ahead of this system to provide
periods of rain from Monday night into Tuesday this will also keep
temperatures rather steady in the lower 40’s Tuesday morning. However
colder air will move into the region behind the main period of rain. A
secondary area of lift will move into the region around lunchtime
leading to another period of precipitation. As precipitation falls
with the second region of lift cooler air will be transported from the
upper levels leading to falling temperatures to mid 30’s for a time
early Tuesday afternoon. There is a good chance this secondary area of
precipitation ends as snow for a few hours early Tuesday afternoon.
The good news for most is that ground temperatures are very warm, even
if snow occurs hazardous roadways should not develop as temperatures
will stay above freezing the entire day and even rise back to around
40 after the precipitation ends by mid-afternoon Tuesday. Any snow
accumulation will be confined to grass and be under 1/2 inch where and
if snow does occur. Winds will also be gusty on the order of 13-19 mph
with higher gusts to 25 mph due to this system. It will feel more like
winter Tuesday. Skies will clear Tuesday nigh as high pressure
allowing temperatures to fall into the mid and upper 20’s with highs
Wednesday in the 40’s with mostly sunny skies. Winds will be lighter Wednesday from 5-10 mph. Updates will be
provided if the snow chance for Tomorrow looks to provide a more
substantial threat than indicated in this forecast.


I’ll go into more detail about it here.

– I talk about lift several times in this discussion. One source of lift with the main period of rainfall overnight and early Tuesday once again is isentropic. With the last system you recall the rainfall forecast was slightly overdone. This was due to thunderstorms over the south robbing the region of moisture coming our way. Once again mixing ratios are around 5 g/kg which would indicate around an inch of rain though once again convection to our southeast which shows well on SPC WRF could keep rainfall amounts around the 3/4 inch range, though the SPC WRF shows more rain, modeling always shows to much precipitation. Experience says go lower!

– low pressure is classic with a warm conveyor belt passing over the region Tonight and Tuesday morning with the region dry slotted for a few hours late Tuesday Morning then in the cold conveyor belt Tuesday afternoon

– Around 12z Wednesday modeling is indicating a secondary region of 700 mb  enhanced Omega over Western Kentucky coupled with forcing/lift due to the temperature contrast known as frontogensis. This should get banded or a band of precipitation on the backside of the system. This area of precipitation should track northeast into northern Kentucky through the afternoon. However the BG region should get some of the action.

– The cooling processes mentioned for the banded backside precipitation is known as dynamical cooling where precipitation falls to cool the atmosphere. Right now I think this should occur allowing the temperatures to fall into the mid 30’s during the time when the secondary precipitation region is moving through. Thus the chance Bowling Green does have snow for a time around noon Tuesday.

– After the precipitation ends however temperatures should rise a degree or two closer to 40 thus even if does snow during the small window any accumulation on a very warm ground will melt and roads will remain well above freezing and wet. Any accumulation stays under 1/2 inch.

– In terms of guidance agreed with elements of the SPC-WRF though a few hrs slow, the 12z NAM/ECMWF runs as well looked good. GFS had a poor time capturing the mesoscale features as was not used. Overall went with raw NAM/ECMWF guidance on temperatures and went a little higher than all guidance for winds Tuesday.


Long range: Euro weekly model appears to be wrong for next week. Modeling operational ECMWF, CMC and JMA  show a deep trough over the region for the middle part of next week this would not equal warmer than normal weather and in fact could bring more chill  and snow chances.  If you follow the 4th most accurate model the GFS it will come around to that hopefully sooner than later.

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