Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 181125

Area Forecast Discussion
National Weather Service Louisville KY
625 AM EST Wed Jan 18 2017

...Updated Aviation Discussion...

.Short Term (Now through Thursday)...
Issued at 245 AM EST Wed Jan 18 2017

A surface analysis early this morning had high pressure centered
over Missouri while yesterday`s cold front now was along the
Appalachians of NC/VA/WV. Aloft, water vapor imagery showed a tight,
quick moving shortwave dropping through Indiana and Ohio, while
satellite imagery showed plenty of stratus across the lower Ohio
Valley and back upstream toward the Upper Midwest. Locally, readings
were in the upper 30s to middle 40s.

The main forecast challenge for today is sky cover. The 00z ILX
sounding and current HRRR/RAP soundings show this moisture is
trapped within a 850-900 mb inversion. Forecast soundings through
the day show some dry air working down on this layer along with some
mixing throughout the day but with slow progress. Expect overcast
skies this morning and into the first part of the afternoon, but
some breaks and peak of sun by late afternoon are expected. Highs
mainly in the middle 40s to lower 50s.

The first in a series of southern stream impulses arrives late
tonight through Thursday as a closed upper low takes shape over the
central Plains. This will open up the Gulf with a good amount of
moisture surging northward. PWATs will climb to 1.3 inches, or
roughly 3 standard deviations above normal for Thursday,suggesting
the potential for some locally heavy rain producing showers. With
good isentropic lift and moisture transport, showers are expected to
break out early Thursday morning across southwest and south-central
KY then move north/northeast through the day. Given the high
agreement and consistency in the latest forecast models,
precipitation chances were brought up into the 70-90 percent range
for Thursday, especially in the afternoon hours. Some weak elevated
instability may bring a few rumbles of thunder as well, mainly
along/south of the Ohio River Thursday afternoon. The recent stretch
of rain and saturated soils may result in localized low-lying
flooding issues, and rises on streams and creeks.

.Long Term (Thursday night through Tuesday)...
Issued at 300 AM EST Wed Jan 18 2017

...Above normal temperatures and frequent rounds of rain during
extended period...

Thursday night - Friday night...

The latest medium range guidance continues to suggest multiple
rounds of significant rainfall in a very meridional longwave
pattern. The first event will be well underway by Thursday evening.
A closed upper low will move into the Midwest region and swing a
negatively titled trough into the Ohio Valley Thursday night. This
PVA regime will promote excellent lift across the area overnight.
With ridging centered over the Atlantic coast, deep southerly flow
will pump in copious amounts of moisture for this time of year. The
latest GFS features max precipitable water values around 1.3 inches
00-06z Friday. The NAEFS indicates PWATs running between 2-3
standard deviations above climatology. So expect another nice slug
of rain Thursday night with lows only in the upper 40s to mid 50s.
Given recent rainfall and fairly saturated soils, minor flooding
issues may become more common late this week.

Rain chances diminish from west to east Friday morning. Weak ridging
builds through the Ohio Valley on Friday. Dry weather will persist
through Friday night with central Kentucky and southern Indiana in
between weather systems. Friday looks quite warm, with highs well
into the 60s.

Saturday - Tuesday...

Saturday looks a bit warmer still with southerly flow out ahead of
yet another storm system in the Plains. Highs will likely reach the
mid to upper 60s, and 70 degrees is a possibility. Rain chances
start to increase during the latter half of Saturday as low pressure
deepens in the southern Plains. The GFS and ECMWF have actually been
pretty consistent forecasting a mid-level wave wrapping up into a
closed low across the Southeast U.S. Saturday night through Sunday
night. Multiple rounds of rain appear likely, and the rain may be
heavy at times. There is a decent chance for thunderstorms on Sunday
as the primary low moves into the region. PWAT values once again
exceed 1 inch by Sunday evening. Rain chances finally diminish
Monday night, and Tuesday looks dry.

Somewhat cooler air will work back into central Kentucky and
southern Indiana early next week with highs in the 50s.


.Aviation (12Z TAF Update)...
Issued at 625 AM EST Wed Jan 18 2017

An expansive stratus deck reaching from the Midwest to New England
and the Mid South will be the primary aviation challenge today.
Ceiling heights should be mostly just above 1000 feet, though some
occasional lowering into IFR is possible early this morning. Some
drizzle has fallen from these clouds but it has been very light and
not a hindrance to aviation.

High pressure moving in from the west today will help to scour out
the clouds as it brings in some drier air. How fast the low clouds
will break up is the big question. Right now it looks like it will
take until mid/late afternoon.




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