Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 140149
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
949 PM EDT Thu Mar 13 2014
Issued at 948 PM EDT Wed Mar 12 2014
The forecast is on track for tonight and only updated hourly
t/td/winds to match up with current obs.
Otherwise, main focus will be on gusty winds and fire weather
concerns for Friday. Expect southwest winds between 20 and 30 mph,
perhaps gusting up to 40 mph. Additionally, there is some concern
for an elevated fire risk as the winds, lower relative humidities,
and drying small fuels combine. Considered issuing a Fire Weather
Watch for the region around Lake Cumberland, although wanted to
mention a couple limiting factors that keep confidence too low to go
with a headline at this time. Upper level clouds will be streaming
into the area from west to east by mid to late morning and will
begin to somewhat limit insolation and mixing into a drier layer
aloft. Could see dew points in the upper 20s with temps in the low
60s for a few hours around Lake Cumberland, but this would only
yield RH values in the upper 20% range before thicker cloud cover
overspreads the area. The marginal RHs and the unknown impact of the
upper level clouds are enough to just keep the Special Weather
Statement going for now.
.SHORT TERM (Now through Friday Night)...
Issued at 311 PM EDT Thu Mar 13 2014
The synoptic pattern this afternoon features a longwave upper trough
pushing off the East Coast, with another shortwave trough moving
through the northwest flow aloft. This secondary trough will help
to induce a surface cyclone across the northern Great Lakes, which
will help drag a weak cold front towards the region Friday night.
Surface high pressure continues to slowly drift east across the
region this afternoon. In its wake, winds will become southerly
this evening into tonight. Therefore, expect temperatures to drop
off slightly this evening after sunset, before leveling off and even
rising a bit towards dawn Friday morning. Overnight lows will be in
the mid to upper 30s.
The main story on Friday will be the increasing warmth due to the
increasing winds. The aforementioned surface high will slide
southeast into the western Atlantic, while a strong area of low
pressure gets organized across the northern Great Lakes. This will
place the Ohio Valley within a strong surface pressure gradient,
making for rather windy conditions. Forecast soundings depict deep
mixing potential tomorrow, perhaps all the way up to around 850mb.
Winds at the top of this mixed layer will be around 40-45+ knots.
Highly considered issuing a Wind Advisory for tomorrow, but after
collaborating with neighboring offices, decided to hold off for
now. The main limiting factors will be the tendency for gustiness
to underachieve a bit in warm air advection regimes, along with
increasing mid/high level clouds which may hinder the expected
mixing a bit. Will pass these concerns on to the midnight shift,
but a Wind Advisory may be needed for tomorrow for 40+ mph wind
Another concern tomorrow will be an elevated fire danger. However,
there are a few things working against the issuance of any fire
weather headlines. The first is rather marginal RH values, as a
conservative dewpoint forecast only puts minimum RH values in the
30-40% range. Additionally, area fuels are still rather moist,
which overall should work to limit the potential.
Otherwise, given the deep mixing and rather dry low-level airmass,
have continued to go on the warm end of guidance for temperatures
tomorrow. This puts highs in the middle 60s for most locations.
The aforementioned surface low will drag a cold front toward the
region Friday night. Some guidance is suggesting some light showers
working into the northern Bluegrass with this front, but think the
dry air will win out. With the front beginning to stall as it heads
into the region, overnight lows will vary across the region. They
will bottom out in the upper 30s across southern IN, while southern
KY will remain in the mid 40s.
.LONG TERM (Saturday through Thursday)...
Issued at 307 PM EDT Thu Mar 13 2014
The ECMWF has been the most consistent model recently and is also
favored by WPC so we will lean toward that solution for this
forecast. having said that, a quick glance at this morning`s EC
reveals that it has trended slightly toward the latest operational
An upper trof will be approaching from the west this weekend and
move overhead Monday. Associated surface low pressure will develop
over the Plains Saturday, drop southeast, and move along the Gulf
Coast Sunday. Deep moisture will stream northward Saturday night
through Sunday night before moving off to the east Monday morning.
Precipitation type is a big question with this system. We should be
all rain Saturday night into at least Sunday afternoon. By Sunday
evening into Sunday night, however, surface temperatures fall below
freezing while warm air remains in place around 850hPa. Soundings
suggest a wintry mix may be possible. At this time it does appear
that amounts would be light...especially on the EC. The GFS paints
a bit grimmer of a picture. For now in the forecast will simply go
with a basic rain/snow mix, with future edits to be made as the time
The next upper system will dig into the Plains right behind the
departing weekend system, pushing a cold front through here
probably sometime on Wednesday. The front will be accompanied by
showers, with not much thunder indicated at this time.
Temperatures will ride the springtime roller coaster as these
systems move through. The warmest day looks to be Saturday with
highs ranging from the mid 50s to lower 60s. The coldest night will
be Sunday night with that potential wintry mix, with temperatures
dropping into the mid 20s to lower 30s north to south.
.AVIATION (00Z TAF Update)...
Updated at 725 PM EDT Thu Mar 13 2014
VFR conditions will prevail through the period, although LLWS will
be a concern tonight. Surface winds will stay up around 10 mph out
of the SSW overnight. However, a low-level jet will ramp up just
above the surface along with a sharp inversion, setting the stage
for a period of LLWS at all sites. This jet could be on the order of
40-45+ knots late tonight into Friday morning, with the highest
values expected at KLEX and KSDF. Additionally, LLWS looks to be
most likely in the lowest 1500 feet. Otherwise, skies should be
mainly clear, although some high clouds will increase later Friday
The main story during the day on Friday will be surface winds.
Southwesterly winds will increase to 20 to 25 knots, with gusts of
30 to 35 knots possible. Mid and high clouds will slowly increase
through the day.