Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 242313
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
613 PM EST Tue Feb 24 2015
...Updated Aviation Discussion...
.SHORT TERM (Now through Wednesday Night)...
Issued at 300 PM EST Tue Feb 24 2015
Have a weak cold front approaching the region at this time. 88D
returns upstream are negligible, but visible satellite does show
some clouds with local obs reporting ceilings in the 2500-4000 foot
range. IR satellite indicates the clouds are mostly too warm to
support snow, save for some colder tops near Chicago. Forecast
soundings for the overnight indicate the top of the cloud layer
likely will continue too warm for good snow crystal development, so
have backed off on the snow wording and gone instead with isolated
flurries this evening with some patchy freezing drizzle possible as
humidities rise after midnight.
Given that we may see some breaks in the clouds early on, dropped
forecast lows a degree or two across the area, now mostly in the
upper teens. Forecast soundings indicate we could end up with more
cloud cover through the day Wednesday, thanks to a thin moist layer
in the low levels. These clouds will make a difference in just how
warm it gets tomorrow. GFS-based MAV guidance calls for readings
much warmer than what I have in this package, whereas the NAM-based
MET guidance is lower.
Next up will be a storm system crossing well south of the region.
Models have trended north with this low. Add into the mix a northern
stream system that will approach the region from the northwest.
Given the northern trend, put light snow accumulations into the
forecast for our southeast area Wednesday night. Also expanded the
slight chance for snow through the entire area because of potential
snow from that northern stream system, but do not have any
significant accumulations over the northeast half of the area.
Bumped forecast low temperatures up quite a bit from the previous
forecast, given the added cloud cover from that system. Now have
lows ranging from the mid teens in my far northern counties to the
mid 20s along the TN border.
.LONG TERM (Thursday through Tuesday)...
Issued at 302 PM EST Tue Feb 24 2015
The lower Ohio Valley will see one more shot of Arctic air at the
end of this week before temperatures return to closer to normal for
the beginning of next week. We will also transition from mainly snow
chances to multiple rounds of rain with a few brief shots of wintry
precipitation mixed in.
Thursday - Saturday
A weakening shortwave will move through the upper level flow
Thursday into Thursday night. The better chance for snow with this
system looks to be to the north and west of the area. Soundings
across the region show some dry air aloft that never completely
saturates. However, there will be a chance for some snow showers
during this time frame.
Very cold high pressure will then build in once again behind this
system Friday through Saturday. This high will shift off to the east
through Saturday night. Friday and Saturday mornings will once again
feature very cold temperatures with lows in the teens to the south
and the low single digits in the north. Highs Friday will only reach
into the 20s. Saturday should see some moderation in temps with
highs in the 30s.
Sunday - Tuesday
This time frame will see a transition to a much wetter and warmer
pattern, though some wintry precipitation cannot be ruled out. The
first wave will move up out of the southwest and into the forecast
area during the day on Sunday. Southerly winds will bring much
warmer and moister air on Sunday. Though this precipitation could
start out as a mix, it will transition to all rain by mid day as
temperatures rise into the 40s to lower 50s. Currently the models
have high pressure and cold temperatures building in from the north
Sunday night with temps falling below freezing across portions of
the area. Will continue a mix of rain and snow, but there is some
concern of possibly freezing rain if a warm layer stays in place
aloft. This far out, model solutions are certain to change, so have
kept this out of the forecast for now.
There could be a short break in precipitation before a deepening
surface low moves out of Texas Tuesday and up across the forecast
area. Very abundant moisture will be available with this system and
we could see a good surge of warm air. Some elevated thunderstorms
certainly seem possible Tuesday with potentially very heavy
rainfall. All in all some areas could see upwards of 2-3 inches
Sunday through Tuesday, so flooding could become an issue once again.
.AVIATION (00Z TAF Update)...
Issued at 613 PM EST Tue Feb 24 2015
TAF sites will be VFR for a few more hours, however will have to
monitor progress of a stratocu deck later this evening as it moves
into the area from the NW ahead of a cold front. Do think this deck
will initially be VFR based on upstream obs and the pre-frontal
regime. However, as the front passes just after midnight MVFR
ceilings are possible through the pre-dawn hours. Around sunrise,
through the late morning the lowest ceilings could drop below
fuel-alternate or worse. Tops of the saturated layer are marginal
for ice crystal development, so we could see some patches of
freezing drizzle and/or flurries Wednesday morning.
Expect some improvement in ceilings by midday through the afternoon,
with a light NE wind taking hold.