Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 241114
Area Forecast Discussion
National Weather Service Louisville KY
614 AM EST Tue Jan 24 2017
.Short Term...(Today through Wednesday)
Issued at 323 AM EST Tue Jan 24 2017
Upper level low just off the North Carolina coast continues to spin
and lift off to the north along the east coast. In its wake, low
clouds/stratus have hung around the CWA, with a few sites reporting
drizzle and mist at this hour. AMDAR soundings from earlier this
morning show the stratus deck only up to 3-4kt AGL in depth.
Biggest forecast challenge for today will be how quickly the stratus
deck erodes. Most NWP guidance keeps the stratus in through late
morning for most of the region, with clearing occurring first in
southwestern portions of the CWA. The NAM is the most aggressive in
keeping the stratus around for the day, and keeps areas northeast of
a line from KHNB to KSME under overcast skies, while the GFS has all
but the extreme northeast portion of the CWA breaking out of the
stratus deck. For now, am leaning more toward the GFS solution and
believe the NAM is too aggressive with its boundary-layer moisture
output. Should the NAM scenario play out, forecast high temperatures
may be a bit too warm.
Overnight, drier air begins to work its way into the region, and
should see cloud cover diminish. The clearing skies will allow
temperatures to drop into the low 40s to upper 30s.
By Wednesday, a strong cold front will be approaching the Ohio River
valley. Ahead of the cold front, we`ll see very warm temperatures,
generally 15 to 20 degrees above climatological highs, and breezy
southwesterly winds. NWP guidance has shown a broad band of light
precipitation ahead of the cold front during the day Wednesday, and
have included PoPs in the forecast to account for that. The cold
front will pass through the region overnight on Wednesday.
.Long Term...(Wednesday night through Monday)
Issued at 310 AM EST Tue Jan 24 2017
...Colder Air and Light Wintry Precipitation Return...
Thursday - Saturday...
A departing cold front will usher in a much colder airmass for the
latter half of the week. Highs on Thurs will be limited to the
upper 30s/lower 40s (near normal for this time of year). A light
showery west-northwest flow will result in 20-30% chances for rain
or snow Thurs/Thurs evening. With temps still well above freezing,
little to no travel impacts are expected from any light wintry
precip that falls Thursday.
Multiple upper level shortwaves look to drop south into the Ohio
Valley for the end of the week. Most long range models indicate a
decent wave bringing more light precipitation to the region on
Friday and the latest Op GFS would suggest another subtle shortwave
for Sat as well. In coordination with surrounding offices, kept the
Fri POPs as that seems to be a common theme in the long range models
but left Sat dry for now. May need to add POPs Sat if that
secondary upper level shortwave becomes a more consistent feature in
coming model runs. As far as p-type, we`d likely see a mix of rain
and snow both days with soundings supportive of ice crystals aloft
and sfc temps varying from mid to upper 20s during the morning hours
to mid 30s to lower 40s each afternoon. While no major accumulating
snows are forecast, a light accumulation may be possible during
morning or evening hours Fri when boundary layer temps are
supportive of mainly light snow.
Sunday - Monday...
For the first part of next week, long range models are in support of
a stronger upper level trough dropping south into the Ohio Valley
bringing a light snow or light rain/snow mix to the region. This
stronger trough has the potential to bring a light accumulation of
snow to some areas.
Monday looks dry and seasonably cool before a warm-up toward mid
week next week.
.Aviation...(12Z TAF Issuance)
Issued at 612 AM EST Tue Jan 24 2017
The persistent low stratus deck looks to hang around for at least
the morning hours at all sites. Ceilings should start to raise by
mid day. Thinking for this forecast cycle is similar to the lastin
scattering out clouds at SDF and BWG by mid to late afternoon and
LEX by early evening. Skies should become mostly clear for a brief
period tonight before lower clouds move back in tomorrow morning.
Winds today will become light and variable and shift to southerly by
afternoon. Wind speeds will increase late tonight as the pressure
gradient increases ahead of a cold front moving in later tomorrow.