Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 201124

Area Forecast Discussion
National Weather Service Louisville KY
624 AM EST Sat Jan 20 2018

.Short Term...(Today through Sunday)
Issued at 330 AM EST Sat Jan 20 2018

A narrow upper ridge axis extends northeast from Mexico toward the
Bluegrass State early this morning. Cirrus shield continues to spill
southeast from MO/IL/IN. At the surface, weak low pressure was
located near the CO/NE border, with high pressure lingering over the
Southeast. Stout SW flow below 850 mb will continue to advect higher
theta e air northward from the Gulf. Widespread stratus now blankets
areas south of the WK/BG Parkways, with these low clouds gradually
making a push toward the Ohio River. Temperatures are very steady
around 40 degrees under the stratus deck.

Went ahead and boosted blended sky cover guidance today and tonight.
The warming trend will continue today, although rate of warming will
slow compared to the past couple of days. Highs should range from
the mid 40s to around 50. By mid to late afternoon, the chance for
some drizzle or light rain increases. Kept 20-30 PoPs going this
evening into Sunday morning given weak isentropic upglide in the
saturated layer. The moisture depth also increases into the 5-10 kft
layer after 00z this evening. So a fairly murky evening/night with
lowering cloud bases and possible drizzle/light rain/mist. In
addition, added patchy fog to the forecast tonight and Sunday
morning. It`s primarily a low stratus scenario, but we`ll likely see
some fog with dewpoints surging above freezing over the lingering
snow. Lows tonight around 40 are expected. Highs should range
through the 50s on Sunday, and southern areas could make a run at 60
given dry weather during the afternoon hours.

.Long Term...(Sunday night through Friday)
Issued at 345 AM EST Sat Jan 20 2018

Sunday night looks warm and mainly dry, with central KY/southern IN
firmly in the warm sector of a strengthening low pressure system in
the Plains. The system is forecast to occlude over Iowa on Monday
and sweep a cold front through the forecast area. It looks dynamic,
with strong wind fields and very little instability. Best chance for
thunder remains south of the area. So a period of moderate rain is
expected, with winds gusting over 30 mph at times. The gusts will
continue Monday night as cold advection sets in.

Instead of bitter cold or spring-like air, we`ll actually see
temperatures near seasonal norms next Tuesday and Wednesday. Dry
weather is expected during this period, despite a shortwave trough
dropping down on Wednesday. Surface high pressure will gradually
build east toward the Ohio Valley Wednesday and Thursday. A building
mid-level ridge will also support warming temperatures late in the


.Aviation...(12Z TAF Issuance)
Issued at 620 AM EST Sat Jan 20 2018

Stratus deck brought MVFR ceilings into SDF and LEX overnight, while
BWG has remained VFR so far. HNB remains unrestricted with only
cirrus. Low-level wind shear continues to be a factor with a WSW low-
level jet over the top of light SSW winds to provide both
directional and speed shear.

By mid-morning we should mix out the LLJ, but this remains an
unusual situation where the low-level moisture is augmented by the
snow pack, allowing a stratus build-down to happen in the daylight
hours. Forecast confidence remains limited, as the short-term models
seem too pessimistic with ceilings this afternoon. Will keep
ceilings above fuel-alternate thresholds through the evening and
much of the night, but also include a scattered lower cloud deck as
a hint that fuel-alternate conditions are a possibility.

Better low-level saturation is expected toward daybreak Sunday,
mainly in HNB and SDF. Will bring in lower MVFR ceilings and VCSH to
cover patchy rain/drizzle potential at both of those sites before
daybreak. Did not see support for model improvements in ceilings
during the night, so confidence is moderate at best.




Short Term...EBW
Long Term...EBW
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