Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 061141

Area Forecast Discussion
National Weather Service Louisville KY
641 AM EST SAT FEB 6 2016

...Updated Aviation Discussion...

.SHORT TERM (Now through Sunday)...
Issued at 245 AM EST Sat Feb 6 2016

Sfc high pressure and an upper level trough passing well to our
south this weekend will leave the Ohio Valley free of any major
weather concerns.  Expect partly cloudy skies through Sunday with
slightly above normal temps.  Highs today should reach the upper 40s
to lower 50s.  Tonight return flow will increase especially across
our southern Indiana and west central KY counties keeping these
areas a bit more mild in the lower 30s for lows.  East of I-65
expect lows to drop into the mid 20s to around 30.  Sunday southwest
winds may turn a bit breezy with highs creeping up into the 50-55
degree range.

.LONG TERM (Sunday night through Friday)...
Issued at 325 AM EST Sat Feb 6 2016

Sunday Night - Wednesday...

An anomalously deep trough will get carved out over the eastern U.S.
for the first half of the work week in response to a strong ridge
along the west coast.  A strong northern stream low pressure system
will dive south into the Midwest leading the charge.  This low
pressure will push a cold front through the Ohio Valley Sun night.
There is some model variance as to how quickly precipitation along
the front will commence Sun night.  The GFS is most aggressive with
precipitation starting Sun evening before midnight while the
ECMWF/NAM are less optimistic and lower on precipitation amounts
especially before midnight.  The current forecast reflects a blend
of the mid range models in regards to precip timing and precip
amounts Sun night. With this mind, precipitation should begin as a
light rain late Sun evening and then transition to snow from NW to
SE after midnight.

By sunrise Mon morning, most locations will see light snow.  As the
upper low dives deep into the Midwest, colder air will rush into the
area on Monday.  Temperatures and precip type will be a challenge
for Monday.  The pattern and soundings would support mainly on and
off light snow showers throughout the day on Monday.  However, sfc
temps may rise just enough especially east of I-65 to result in a
change over back to rain/snow mix.  Or perhaps p-type may remain
mostly snow but melting on contact with the sfc as most locations
still look to see highs on Monday above freezing for at least part
of the day.  Will need to fine tune the temp curve and p-types for
Mon as this weather system is better captured by the short range
models.  For now, trended Mon colder and snowier.  Also of note,
soundings Mon afternoon/evening indicate a thin ribbon of
instability well into the dendritic growth zone which could result
in moderate to at times heavy bursts of snow.

We`ll remain in a cold, snow showery pattern Mon night-Wed as the
the upper trough slowly progresses eastward.  P-type looks to be all
light snow Mon night-Wed with snow ratios increasing to 15:1 to 20:1
as a much colder airmass settles in.  Bursts of moderate snow will
again be possible Tues during the day as lapse rates steepen a bit.

Preliminarily, light snow accumulations Mon-Wed look to range around
1 inch to possibly up to around 3 inches total for the 3 day period.
Stay tuned as we tweak the snowfall forecast in coming days.

Tues/Wed look to be the coldest days in the 7 day forecast with
highs only reaching the mid to upper 20s.  Lows look to drop into
the teens.  As previously mentioned, however, these numbers may need
to be adjusted if a decent snow cover can be established.

Thursday - Friday...

Temps look to moderate by the end of the work week back into the 30s
and maybe even lower 40s for highs as the upper trough begins to
move east of the area. Both the 0Z GFS/ECMWF hint at one last
shortwave diving down into the region some time Thu or Fri providing
another round of light snow to the region.  However, big differences
in the progression of the trough/colder air moving east and
shortwave timing exist amongst long range models.  Therefore will
keep Thu/Fri dry for now and side temps toward the model blend.


.AVIATION (12Z TAF Update)...
Updated at 635 AM EST Sat Feb 6 2016

Scattered high-level cirrus clouds prevail across the area this
morning. Scattered mid clouds also could affect SDF at times today.
Otherwise, conditions will be VFR through the forecast period.
Surface winds will be southwest at 4-8 kts today and then south-
southwest at 5 kts or less tonight.


.LMK Watches/Warnings/Advisories...


Short Term........AMS
Long Term.........AMS
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