Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 060223
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
923 PM EST Thu Mar 5 2015

...Updated Aviation Discussion...

...Forecast Update...
Issued at 915 PM EST Thu Mar 5 2015

Broken strato-cu has been slow to erode. They extend from near
Louisville southwards through Barren County, and will drift southwards
over the next several hours. Skies should clear before midnight at
Louisville and Lexington. Light winds, snow cover and clearing
skies will promote very cold temperatures overnight with subzero
temperatures possible at most locations.

.SHORT TERM (Now through Sunday)...
Issued at 318 PM EST Thu Mar 5 2015

...Bitter Cold Tonight...

Once the high clouds in the east move out, and scattered flat
diurnal cu dissipate, arctic high pressure advancing from the mid
Mississippi Valley to the Tennessee Valley will provide us with
mostly clear/partly cloudy skies, light winds, and COLD temperatures
through the short term.

The main question is how cold to go tonight.  We have up to 25
inches of fresh snow pack.  The high moving in is of arctic origin
and will be located directly overhead right at the climatologically
coldest time of day early Friday morning.  Winds will be nearly
calm.  Skies should be mostly clear.  This high is progged to be
slightly stronger than the high that took some locations into the
-20s on February 20.  Low temperatures upstream this morning under
the high in the northern Plains were in the teens below zero, with
only a few inches of snow on the ground there.

Sky cover is the biggest source for bust potential tonight.  Model
data are showing low level moisture hanging around through the
night, but given the strength of the high and the lack of clouds
associated with it upstream, will lean towards less cloudiness in
the forecast.

Given all that, will go for negative teens tonight along the stripe
of deepest snow cover, which also happens to be located with where
the northeast-southwest elongated high is expected to line up at
dawn.  Can`t rule out a few -20s in the very coldest spots, such as
the Kentucky Mesonet stations in the counties of Ohio, Hardin,
Franklin, and Harrison.

Outside of the band of deepest snow, will still go with single digit
subzero readings.

We`ve never seen temperatures this cold in March before, so there is
no small amount of trepidation with this forecast.  It`s never easy
to forecast all-time monthly record lows.  If we get more clouds
than currently predicted, then lows have the potential of being much
warmer...possibly "just" around zero.

The high will be a slow mover on Friday, so we really won`t get into
any return flow during the day.  As a result, and given the very
cold start to the day (even if not as cold as currently forecast),
we went well below guidance for highs, especially in the snowiest
areas.  Will go for low to mid 20s.  We`ll have plenty of March sun,
which has done a good job of warming temperatures a few degrees this
afternoon even with the snow.

Friday night lows will probably be in the evening, then steadying
out overnight and possibly rising a bit in southern Indiana.  For
now will go with single digits over the deepest snow pack and teens
elsewhere.

.LONG TERM (Sunday night through Friday)...
Issued at 300 PM EST Thu Mar 5 2015...

...Warmer weather on the way!...

In contrast to weather conditions the past couple of days, the
extended forecast looks quite benign, with a significant warm up by
the middle of next week. Snow will melt, and spring will seem
closer.

This weekend, northwest flow aloft will prevail which will keep
temperatures below normal (normal highs for this time of year are in
the lower to mid 50s), especially given the ambient deep snow cover.
Nevertheless, there will be some moderation with afternoon readings
topping out mostly in the 30s Saturday (except lower 40s near the
Tennessee border), and in the 40s Sunday afternoon. This is a few
degrees below model statistical guidance.

A southern stream system over TX and the Gulf Coast states Sunday
and Sunday night could bring limited moisture northward into the
Tennessee Valley. Models generally keep precip just south of
Kentucky Sunday night and Monday so will go with a dry forecast in
most areas. Based on thermal trends, if any precip does fall, it
should be scattered light rain showers.

During the first half of next week, flow aloft relaxes and becomes
more westerly. This will create some downsloping flow and warmer air
across the Plains states. Some of that air should begin to work
eastward toward the Ohio Valley by mid next week. As a result, dry
weather is expected Monday thru Thursday in central Kentucky and
southern Indiana with a continued warming trend. High temps should
be in the 40s Monday (perhaps 50 near the Tennessee line), in the
50s Tuesday, mid 50s to lower 60s Wednesday, and probably in the 60s
Thursday if the forecast pattern holds.

The GFS and ECMWF show the next good chance for precip, in the form
of rain, to be Friday into next weekend (faster ECMWF) or next
weekend (slower GFS).

&&

.AVIATION (00Z TAF Update)...
Issued at 610 PM EST Thu Mar 5 2015

Arctic high pressure moving in from the northwest bring clear skies
and light winds overnight. Some scattered flat cu will erode just
after sunset. Mostly clear skies will develop tonight and continue
Friday.
North winds will diminish to around 5 mph by midnight and become
calm by dawn.

&&

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

$$

Update.........JSD
Short Term.....13
Long Term......TWF
Aviation.......JSD





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