Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 011707
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1207 PM EST Sun Feb 1 2015

...Updated Aviation Discussion...

...Forecast Update...
Issued at 917 AM Sun Feb 01 2015

Have updated the forecast this morning to account for a slightly
quicker arrival of the precipitation into our area.  KY mesonet obs
over west-central KY and the BWG ASOS have already began to report
rainfall early this morning, meaning the column has finally
saturated after quite a bit of virga overnight into this morning.
Expect this saturation to continue to push east, thus have updated
the hourly products to account for the quicker arrival. Otherwise,
going forecast looks on track.

.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 (18Z TAF Update)...
Issued at 1205 PM EST Sun Feb 1 2015

Steady precipitation will continue to push through TAF sites this
afternoon, bringing MVFR to high-end IFR conditions at times.  Sites
out to the west have reported 2SM at times in the more moderate
rainfall, so will time these potential reduced visibilities through
the sites.  In addition, a period of high-end IFR cigs looks likely
at all sites just ahead of the cold front this evening.

Otherwise, a cold front will sweep through all sites overnight,
bringing gusty WNW winds pushing in excess of 25 knots at times.
Precipitation coverage will really wane after 02/03Z as the system
pulls east, but there could be a few lingering rain/snow showers
after this time into Monday morning.  For now, will handle this
potential shower activity with VCSH, given expected low coverage and
low confidence in exact timing.  Behind the front, gusty winds and
resultant mixing will help raise cigs back into MVFR thresholds.

&&

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

$$

Update.........KJD
Short Term.....JSD
Long Term......ZBT
Aviation.......KJD




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