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FXUS63 KLMK 071748

Area Forecast Discussion
National Weather Service Louisville KY
1248 PM EST Sat Dec 7 2019

.Short Term...(This evening through Sunday)
Issued at 310 AM EST Sat Dec 7 2019

Sfc high pressure centered over Illinois and Indiana early this 
morning will build eastward over Ohio and Pennsylvania later today. 
The northern edge of a stratus layer is now south of I-64, with 
clear skies across southern IN and northern KY. The clearing line 
will only slowly move south this morning, so a mostly cloudy start 
for southern KY. 

NNE winds will veer easterly during the daytime as the sfc high off 
to our north slides to the east. Consensus highs for this afternoon 
range from the mid 40s in southern IN to the lower 50s in southern 
KY. Due to high pressure off to the east and a strengthening Hudson 
Bay low, SW return flow increases early Sunday. A 30-35 kt SW LLJ 
develops by 09-12z Sun, which will keep temps steady or rising 
during that time. This could result in a tighter temp gradient for 
lows tonight. Sheltered areas in the Bluegrass could dip to 30 or 
even upper 20s, with some areas in southern KY not dipping below 40.


.Long Term...(Sunday night through Saturday)
Issued at 254 AM EST Sat Dec 7 2019

A strong, +120kt 300mb jet part of a broad upper level trough will 
begin ejecting into the southern Plains on Sunday. Models indicate 
lee cyclogenesis over the western Central Plains as the trough 
advances eastward with very cold Arctic air in Canada being drawn 
southward. In our neck of the woods, Sunday should stay dry, though 
clouds will gradually increase during the day. Showers begin 
developing after midnight Sunday as the region falls into the left 
exit region of the strong upper level jet while a strong LLJ advects 
GoM moisture northward. Overall setup looks like a classic 
isentropic lift event with light to moderate rain showers, so will 
continue advertising very high PoPs for the Monday timeframe.

The strong cold front will advance quickly from the Plains into the 
Ohio Valley by Monday night. Precipitation won't immediately end 
behind the front given the shallow nature of the cold, Arctic air 
and lift/dynamics at play, which could result in a transition to 
wintry precipitation if moisture lingers long enough. The majority 
of guidance moves precipitation out of the region before this 
becomes an issue... but it'll be something to watch closely.

After Tuesday, expect cold and dry weather to persist into the end 
of the week as an Arctic high dominates the northern US east of the 
Rockies. The high should push east of New England by Friday and 
return flow around the high becomes southerly over southern Indiana 
and central Kentucky, resulting in some moderation to temperatures. 
Another system may take aim at the region late Friday into Saturday, 
though timing and confidence remain low this far out.


.Aviation...(18Z TAF Issuance)
Issued at 1245 PM EST Sat Dec 7 2019

Satellite shows stratus deck cleared from all TAF sites now, but 
stubbornly persisting just 20 miles south of LEX. This will continue 
to slowly erode through the remainder of today.  

As the surface high currently over NE Ohio continues to drift east, 
southerly surface flow will return overnight. This will result in 
clouds returning back to the area, but ceilings should remain above 
MVFR level until the after 08/18Z, except at HNB, where CIGS AOB 020 
are expected by 08/15Z. 

Earlier indications of marginal LLWS possibilities overnight due to 
a low level jet setting up in the southerly flow have lessened per 
short term guidance updates, but still bears watching.  For now will 
not include in forecasts.




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