National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KLMK 190004
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
804 PM EDT Sun Apr 18 2021

...Updated Aviation Discussion...

.Short Term...(This evening through Monday)
Issued at 245 PM EDT Sun Apr 18 2021

Afternoon satellite imagery reveals partly cloudy skies across the
region.  Cu field has a bit more coverage than expected which has
kept temperatures down slightly.  KY Mesonet readings show current
temps around 60 degrees in most places.  Area radars show a few
scattered showers, mainly north of the Ohio River.  In the near
term, expect temperatures to top out in the 59-64 degree range with a
few scattered showers mainly north of the Ohio River and west of I-
65.

Main weather feature of note is a mid level vorticity maximum over
western MO.  This feature is forecast to move eastward this
afternoon and evening.  Rain showers continue to develop over
central and SE MO this afternoon.  This activity should continue to
expand in coverage as the vorticity max moves closer to our area.
As this feature rolls eastward, a cluster of mainly rain showers
will move through western KY this evening and then through mainly
south-central Kentucky late this evening and into the overnight
hours.  Best chances for rainfall look to be south of a line from
roughly Jasper, IN to around Richmond Kentucky.  The Bluegrass
region may escape this system and remain dry, but cloudy overnight,
however, a few showers may get as far north as the Lexington area.

Overall threat of thunderstorms looks to be fairly low this evening
and into the overnight period.  This is mainly due to weak
environmental wind fields, meager moisture profiles, and lack of
surface based instability.  While model soundings do show some
elevated instability, still can`t rule out a rumble or two of
thunder or a couple of lightning strikes from any stronger cores
that develop.  The best chances of any thunderstorms would be west
of the I-65 corridor.

Temps this evening will be in the upper 50s to the lower 60s before
falling off into lower 40s overnight.  Clouds should start to mix
out late tonight across the west.  Should this occur, combination of
clear skies, light winds, and some wet ground may result in an area
of fog formation.  As of this writing, I think the best chances of
fog would be along and west of the I-65 corridor.

For Monday, the mid-level vorticity maximum will continue off to the
east and some mid-level ridging will build into the area.  Partly to
mostly sunny skies are expected.  Highs on the day should top out in
the 63 to 68 degree range.  A few of the typically warmer urban
spots could hit 69 or 70.

.Long Term...(Monday night through Sunday)
Issued at 256 PM EDT Sun Apr 18 2021

Tuesday afternoon, a southwest to northeast oriented cold front will
begin to push cloud cover into the CWA from the northwest, and by
Tuesday night, precipitation will begin to work its way across the
CWA. It`s this precipitation that is going to be the main focus over
the next couple of days because it will likely bring snowfall to the
region.

This front is strong and will bring a significant temperature drop
with it. Highs on Tuesday that range from the mid 60s to low 70s
will drop into the 30s by Wednesday morning. This system also
carries a decent amount of moisture that will converge Gulf moisture
from the south and Pacific moisture from the northwest.
Precipitation will remain behind the front. This is the cool side of
the front, and it will help precipitation remain frozen before
hitting the ground. Any precipitation that begins as rain will
quickly change to snow without a warm nose giving the chance for
sleet. The question still remains how much will fall as rain, and
how much as snow.

Looking across model guidance, the GFS is bullish on total
precipitation amounts (0.50 to 0.75"). the NAM has streaks of these
higher amounts across the region, but I used blended amounts in the
forecast with slightly over 0.25" in southwest Indiana, and tapered
amounts off to the southeast with less than 0.10" in the Lake
Cumberland region of Kentucky. Believe most of this will fall as
rain, but have around 0.25" of snow in parts of Crawford and
Harrison Counties (IN) and areas to their north. Snow amounts will
fall off quickly, leaving only trace amounts southeast of the Ohio
River in Kentucky. Warm ground temperatures will limit impacts
across the area.

Behind the front, surface high pressure and a more zonal pattern
move into the Lower Ohio Valley. This brings more sunshine but cool
temperatures remain. Highs on Thursday range from the mid 50s in the
Bluegrass to near 60 in Bowling Green. Then, highs in the 60s stick
around from Friday through Sunday. That`s around 10 degrees below
normal. Low temperatures near freezing will likely bring frost to
many areas Thursday and Friday mornings. These cold temperatures are
around 20 degrees cooler than normal.

Friday night into Saturday, another cold front is expected to bring
the next round of rainfall to the region.

&&

.Aviation...(00Z TAF Issuance)
Issued at 803 PM EDT Sun Apr 18 2021

A fairly potent upper disturbance will rotate through our region
this evening and tonight, bringing some light showers most notably
at HNB/BWG. Will only mention VCSH at SDF/LEX. Bkn-Ovc ceilings
around 5-8 K feet should remain VFR, but some brief lower ceilings
down near 4 K feet also can`t be ruled out overnight.

Toward dawn, some patchy fog could briefly develop if we clear out
quick enough, however most indications that cloud cover will hang on
long enough to mitigate larger fog concerns. Did hint at some 6sm BR
at HNB/LEX/BWG for a few hours around sunrise.

Otherwise, Monday will be nice with mostly sunny skies and a steady
WSW surface wind.

CONFIDENCE: Medium-high confidence on shower activity for this
afternoon and evening.  Low confidence on fog development overnight.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Short Term...MJ
Long Term....KDW
Aviation...BJS