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Area Forecast Discussion (AFD)

Issued by Louisville, KY (LMK)

FXUS63 KLMK 180602

Area Forecast Discussion
National Weather Service Louisville KY
102 AM EST Fri Jan 18 2019

.Forecast Update...
Issued at 1046 PM EST Thu Jan 17 2019

Forecast is in pretty good shape tonight. Radar is showing some 
drizzle and we received a report of drizzle along Interstate 65 in 
the Elizabethtown area, so went ahead and added some patchy drizzle 
to the forecast for the next few hours, primarily east of I-65. 
Drizzle chances should diminish overnight as the depth of the 
available moisture decreases and a cold front over central Kentucky 
pushes eastward.

Looking ahead...low pressure coming out of the Ozarks tomorrow 
night, with a warm front arcing along the length of Kentucky, will 
bring widespread rain to the region after midnight. Precipitable 
water amounts of 1.1" will be near record levels for the date, 
though QPF during the overnight hours should remain well below 6-
hour FFG values. Isolated elevated rumbles of thunder will be 
possible with 850mb theta-e ridge/60kt jet, primarily west of I-65 
and south of the Ohio River.


.Short Term...(This evening through Friday)
Issued at 300 PM EST Thu Jan 17 2019

A weak surface low is passing just to the north of the Ohio River 
with a cold front set to move W to E across the area later this 
evening. Isentropic lift aided by a 20-30 knot low level jet is 
causing light rain over much of the area, especially along and north 
of I-64. This rain is expected to end later this evening as the LLJ 
pushes east and the frontal boundary pushes through. Temps have 
pretty much peaked in the low to mid 40s across the area, and will 
fall back into the 30s tonight mainly on a light cold advection 
component. The cold air is not expected to catch up to the moisture 
in time to create any p-type issues, so will continue with rain 
ending messaging for early tonight. Cloudy skies will continue to 
prevail as 1000-850 mb moisture is trapped beneath an inversion.

We'll see a continued cloudy, but dry day on Friday as surface high 
pressure and dry zonal flow aloft briefly control the pattern. Highs 
look to struggle again to the low and mid 40s with some of the 
southern Indiana counties likely staying in the upper 30s.

.Long Term...(Friday night through Thursday)
Issued at 250 PM EST Thu Jan 17 2019

...Plenty of Changing Weather Saturday and Saturday Night...

Saturday a potent low pressure system will cross the southern 
Commonwealth, bringing a variety of weather. Rain should be moving 
into the region in the morning. With a warm front somewhere across 
the state in the morning, we cannot rule out a wintry mix in our 
southern IN and northern Bluegrass counties, especially should that 
front end up a little farther south than in the current forecast. 
This package will keep the forecast as all rain. Rainfall totals 
have come down just a tad with this suite of models. Still think 
areawide we will see 1-2 inches of rain through Sunday morning. 
Higher amounts go over our southern and eastern counties, which do 
have some lower flash flood guidance. Ensemble river forecast 
guidance gives a chance for the Green River and possibly the other 
quick risers in Boston and Peaks Mill. Given we are not expecting 
widespread flooding, will continue to hold off on any kind of a 
flood watch.

Winds will become more light and variable as the low moves through, 
but then the back side we will see some strong cold air advection. 
We should see light rain switch over to snow in the evening hours. 
Models continue to depict an area of enhanced snow in a region with 
a coupled jet structure somewhere over Indiana. Should this band 
make it into our southern Indiana counties, we would see more snow 
than what this forecast depicts. Didn't stray too far from the 
previous package, with most of the area seeing at least a half inch 
and our northern counties up in the 1-3 inch range.

Precip should come to an end during the nighttime hours, from west 
to east across the region. Temperatures will be crashing hard 
though. Strong winds will help dry our roads some, but would not be 
surprised to see slick spots develop as temperatures by daybreak 
Sunday drop to the upper teens to mid 20s, likely close to the highs 
for the day. 

After a very cold start to the work week, lows in the single digits 
likely in most of southern Indiana and parts of north central 
Kentucky, we should start warming up a little. High pressure will 
move east of the region Monday afternoon. By Tuesday morning, we'll 
see some warm air advection bring in more precipitation. We could 
see some wintry precip at onset, depending on starting temperatures. 
Then with gusty southerly winds, we'll get back to plain rain 
Tuesday. Precip should continue until another cold front crosses the 
region sometime Tuesday night or Wednesday. Once again, we could see 
some back side switch over to snow. High pressure should move in for 
Thursday, but CMC is an outlier showing another low crossing the 
Appalachians. Will discount for now and lean more for the 
ensemble/GFS/Euro solutions.


.Aviation...(06Z TAF Issuance)
Updated at 1259 AM EST Fri Jan 18 2019

Dry weather will dominate through the next 24 hours, but IFR/Fuel 
Alternate stratus will linger throughout the period. RH overviews 
and forecast soundings show some ceiling improvement during the 
afternoon, perhaps enough for SDF at least to rise above 2 kft. 
Slightly reduced vsbys due to light fog/mist between 06-12z. 5-7 kt 
NW wind early this morning will become light and variable after 
sunrise with sfc ridging building across the region today. 

Tonight, winds will turn easterly and increase as a strong storm 
system ejects out of the southern Plains. Widespread rain will 
spread into HNB/SDF/BWG between 06-12z Saturday. The bulk of the 
rain looks to hold off until after 12z at LEX. Expect heavy rain and 
poor flying conditions on Saturday. 




Short Term...BJS
Long Term...RJS