Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 011115
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
615 AM EST Sun Feb 1 2015

...Updated Aviation Discussion...

.SHORT TERM (Now through Monday)...
Issued at 300 AM EST Sun Feb 1 2015

...A few slick spots possible Monday morning...

Phasing northern and southern jet stream energy will create a
significant winter storm that will spread heavy snow from Iowa
through New England. Low pressure now developing near Kansas City
will deepen and move east, crossing southern Indiana during the late
afternoon hours today.

Initial light snow associated with isentropic lift over an elevated
warm front will retreat farther north across central Indiana and
southern Ohio. Kentucky and southern Indiana will stay dry through
mid-morning. Strengthening southerly winds above 2k feet will mix
just a bit with the boundary layer and help keep our overnight lows
in the mid 30s, even across southern Indiana.

Winds will increase later today and reach 10 to 20 mph with some
higher gusts by early afternoon, especially over our southern and
eastern counties, which will remain farther away from the track of
the surface low. Temperatures will warm into the mid to upper 40s
across southern Indiana, and probably into the lower 50s across our
eastern and southern counties.

Widespread rain will move east with the leading edge along I - 65
around noon, overspreading the entire forecast area by late
afternoon. Rain will continue through mid to late evening
diminishing from west to east. Widespread precipitation amounts of
one half inch are anticipated. Drizzle is likely this evening
through the early morning hours.

Much colder air will rush in near or shortly after midnight
accompanied by blustery northwest winds. Flurries, or even some
scattered light snow showers will develop towards dawn Monday. Any
snow accumulations early Monday will be very light. Some patchy slick
roads may develop due to this and a pretty rapid freezing of wet
roads.

Expect mostly cloudy skies and blustery winds along with snow
flurries Monday. Highs will stay near or below freezing.

.LONG TERM (Monday Night through Saturday)...
Issued at 300 AM EST Sun Feb 1 2015

The synoptic pattern Monday night through Tuesday is expected to
feature broad northwest flow aloft from the Northern Plains through
Mid-Atlantic region. At the surface, Canadian high pressure builds
in from the west and centers itself Tuesday morning over eastern
Kentucky. Plan on a seasonably cold night with lows ranging from the
upper teens to middle 20s. We`ll have mid/high clouds passing during
the night which will limit the radiational cooling effects. Highs
Tuesday should climb into the 40s with partly to mostly sunny skies.
Wednesday will be a warmer, near normal day as southerly flow picks
up in response to the departing high and an approaching front from
the northwest.

The main challenge for the long term period is the precipitation
chances associated with the aforementioned front late Wednesday
evening into Thursday morning. 01.00z guidance points to a frontal
passage through southern Indiana after sunset Wednesday and past
southern Kentucky between midnight and 6 am Thursday. Aloft, there
are a couple shortwave troughs that swing overhead, enhancing lift
across the region. In addition, the forecast area is favorably
located within the right entrance of the upper level jet. The 31.00z
trended stronger with its frontogenetical forcing through the mid
levels and would result in banded precipitation across much of the
forecast area late Wednesday evening through Thursday morning. The
GFS/GEM/ECMWF came in with reasonable agreement this cycle, albeit
the ECMWF was slower by about 6 hours. Overall, still being 4-5 days
out, confidence is average at best but felt that there is enough of
a signal to increase precipitation chances to the 30-40 percent
range. Thermal profiles show precipitation would begin as rain or
rain/snow mix Wednesday evening but transition over to snow
overnight as colder air continues to surge southward. Overall, this
system bears watching as the current setup would drop some
accumulating snow across the area, negatively impacting the Thursday
morning commute.

After this system passes, another round of Canadian high pressure
arrives from the northwest and looks to provide the Ohio Valley with
a few seasonably cold and dry days to end the work week. Models are
then in reasonable agreement showing a slow moderating trend in
temperatures for next weekend.

&&

.AVIATION (12Z TAF Update)...
Issued at 610 AM EST Sun Feb 1 2015

Rain will arrive at SDF and BWG close to 17z this afternoon, and at
LEX around 19z. Steady rain will then last for 4 to 6 hours, with
ceilings lowering to MVFR. Prior to this however, even though
ceilings will lower, they will stay VFR.

Light southerly winds will increase by late morning and reach 10 to
20 mph, with some higher gusts by early afternoon, especially at LEX
and BWG.

Although ceilings will continue as fuel-alternate MVFR, rain will
end by mid-evening with winds becoming westerly at around 10 mph. A
cold front will move southeast of the Ohio River around 06z. Winds
will increase from the northwest at all TAF sites to around 12 to 16
mph by 09z with some gusts in excess of 25 mph. Some scattered light
snow showers or flurries may develop after 06z, but coverage is
expected to preclude inclusion in the TAFs.

&&

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

$$

Short Term........JSD
Long Term.........ZBT
Aviation..........JSD





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