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FXUS63 KLMK 251727

Area Forecast Discussion
National Weather Service Louisville KY
1227 PM EST Sat Feb 25 2017

...Updated Aviation Discussion...

...Forecast Update...
Issued at 922 AM EST Sat Feb 25 2017

Some light returns are showing up on radar this morning and we have 
had a recent report of flurries in Louisville. Have kept in the 20% 
chance for rain/snow showers mainly along and north of I-64, but 
also added in scattered flurries in this area and areas a bit to 
the south. Otherwise, no major changes made.

.Short Term (Now through Sunday)...
Issued at 300 AM EST Sat Feb 25 2017

Water Vapor analysis reveals an occluded ULL over Wisconsin with our 
CWA presently in a dry slot, with a line of convection across the 
Appalachian Mountains just ahead of the dry slot. At the surface, a 
995mb low was located over Lake Huron and had a strong cold front 
stretched down to the Gulf Coast region. The cold front has cleared 
our CWA, and pressure rises and CAA behind the cold front have led 
to breezy westerly to northwesterly winds at this hour. 

The backside of the ULL currently over Wisconsin will pass through 
northern parts of the CWA after sunrise and advect in some low level 
moisture. Most NWP guidance keeps the CWA dry during the morning and 
early afternoon hours, but a couple of models suggest some very 
light precipitation would be possible. Forecast soundings reveal 
very limited moisture depth, on the order of a few thousand feet, 
but low-level lapse rates are steep and even have a little 
instability. For now, will keep low PoPs in the forecast mainly 
across northern portions of the CWA. Temperature profiles will be 
supportive of snow in some areas of the CWA, but not expecting much 
in the way of accumulations as ground temperatures are quite warm 
and air temperatures should be near or above freezing at the 
surface.  Speaking of temperatures, does not appear we will warm up 
much during the day today, as strong CAA will only allow 
temperatures to rise into the low 40s for many spots.

Clouds will clear out this evening and winds will lighten as a 
surface high moves just south of the CWA and the nocturnal inversion 
sets in. Temperatures overnight will drop to some of the coldest 
values we've had in a while, with some areas getting down into the 
low 20s.

By Sunday, surface high moves east toward the Carolina coastline, 
and anticyclonic flow around the high will begin to advect in some 
warmer air from the south. Daytime highs will still be a bit cooler 
than we're used to, but near climatological normals, with most spots 
in the upper 40s to lower 50s. Clouds will increase late in the day 
ahead of the next system that will bring precipitation to the region.

.Long Term (Sunday night through Friday)...
Issued at 300 AM EST Sat Feb 25 2017

Long term period looks to be fairly active with multiple rounds of 
precipitation, especially in the Monday through Wednesday timeframe. 

Upper level flow starts off near zonal late Sunday across the CONUS, 
but begins to become more southwesterly across the eastern half of 
the country by mid-week. Multiple shortwaves within the flow will 
impact the CWA, but NWP guidance is not very consistent with the 
timing and strength of the systems during this timeframe. Despite 
model inconsistencies, it does appear that we will be wet during 
this time, and could see 1 to 2 inches of rainfall for the Monday 
through Wednesday period, with the "wettest" day being Wednesday at 
this point as a strong trough pushes through the region.

Additionally, some models are showing weak instability, generally 
500-1000J/Kg, during the Tuesday and Wednesday period. Deep layer 
shear would be supportive of organized convection, so will continue 
to monitor model output and trends in the coming days for severe 
weather potential.

Trough clears the region by Wednesday evening, and things will dry 
off and cool down briefly Thursday. The GFS/ECMWF bring a northern 
stream shortwave into northern portions of the CWA late Thursday and 
early Friday. Temperature profiles could support a rain/snow mix, 
but any accumulations look to be very limited given the quick moving 
nature of the system.


.Aviation (18Z TAF Update)...
Issued at 1227 PM EST Sat Feb 25 2017

A deck of stratocu about three thousand feet thick according to 
(much appreciated) PIREPs is pivoting across the region beneath an 
upper trof. The clouds have managed to drop some flurries but no 
more than that is expected this afternoon. As a matter of fact, even 
the flurries should cease, though at least sct-bkn clouds will hang 
on through much of the daylight hours. Ceilings will be low-end VFR.

Winds will remain gusty from the WNW this afternoon.

Clouds will clear out from west to east this evening as high 
pressure advances from the Ozarks to the Tennessee Valley. Winds 
will become light and variable.

On Sunday we'll get into return flow with S-SSW breezes and 
increasing high clouds.




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