Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 250523
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1223 AM EST Wed Feb 25 2015

...Updated Aviation Discussion...

...Forecast Update...
Issued at 1003 PM EST Tue Feb 24 2015

The forecast is on track this evening and have only made tweaks to
ongoing T/Td/Wind/Sky grids to account for the latest trends. Will
continue to leave mention of flurries or light freezing drizzle in
the grids through the overnight, although not expecting any real
problems. Haven`t observed it upstream or over the area to this
point, however will continue to monitor this through the overnight.
Will watch as a cold front slides through in the pre-dawn hours,
helping lows to drop into the upper teens by dawn.

.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 (06Z TAF Update)...
Issued at 1215 AM EST Wed Feb 25 2015

Overall improved flight conditions in the TAF forecast this round.
The latest high-res model data suggests that flight conditions will
stay VFR through the overnight hours, and the previously mentioned
strato-cu deck will not develop during the pre-dawn hours.  However,
the latest 0Z GFS/MAV guidance still indicates that low cigs could
develop after 12Z, so will delay MVFR conditions further in time in
the TAF forecast.  A southern stream system may bring light snow as
far north as BWG this evening after 0Z.  Winds will be out of the SW
overnight, then turn light and variable for the morning hours and
then NE for this afternoon/evening.

&&

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

$$

Update.........BJS
Short Term.....RJS
Long Term......EER
Aviation.......AMS





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