rain changing to snow Tuesday?

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A low pressure system will move into the Tennessee valley tonight and Tuesday before moving into the mid-atlantic states. In the warm conveyor belt plenty of moisture will be drawn north in addition to a decent amount of isentropic lift. Periods of rain should develop for tonight and Tuesday morning. The region will be dry slotted for a time Tuesday before a secondary period of precipitation moves through on the backside. Temperatures overnight should be steady from the upper 30’s to low 40’s.

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 in the south with mixing ratios around 3 g/kg in the north which would indicate around an inch of rain in the south with half an inch in the north. Once again convection to our southeast which shows well on SPC WRF could keep rainfall amounts slightly lower than that from 1/4-3/4 inch, though the SPC WRF shows more rain, modeling always shows too much precipitation. Experience says go lower!

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. This region should get into Bowling green and Lexington for a time.

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 while the secondary precipitation region is moving through. I think it is questionable as if Lexington and Bowling Green see a changeover but points to the northwest should see an hour or two of snowfall with up to 1/2 inch accumulation. A few spots may even see slightly more with heavier snow rates say along I-71 or in the Elizabethtown region.  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.

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 around 13-19 mph with gusts to 25 mph.

– winds become lighter and skies clear for Wednesday as high pressure builds back in. Highs will range from the upper 30’s north to mid 40’s south. Lows will be in the mid to upper 20’s Wednesday morning.

As promised first snow map of the season!

zone 1- rain changes to snow from late Tuesday morning through the mid-afternoon. A few hours of steady snow which accumulates up to 1/2 inch on grass locally higher amounts. timing from west to east.

zone 2- 50% chance rain changes to steady snow for an hour or two early Tuesday afternoon and mid afternoon bluegrass. evening flurries. under 1/2 inch of snow on grass.

zone 3- rain then evening flurries, highest elevations may see a steadier snow with coatings up to 1/2 inch late in the afternoon or evening. concerned temps may rise in the AM into the mid 40’s southeast.

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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2 Responses to “rain changing to snow Tuesday?”

  1. Mitch Says:

    Pulling bowling green into region 3 now. Saw temp spike due to was there last hour. This concern applies further east as well.

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