Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 240227

Area Forecast Discussion
National Weather Service Louisville KY
927 PM EST MON NOV 23 2015

...Forecast Update...
Issued at 925 PM EST Mon Nov 22 2015

Tweaked temperatures a little, but overall just minor changes. Did
do a zone update, to bump up temperatures a category in Fayette and
to separate downtown and suburb temps in Jefferson, KY.

.SHORT TERM (Now through Tuesday Night)...
Issued at 245 PM EST Mon Nov 23 2015

The synoptic pattern late this afternoon features a trough aloft
across the eastern seaboard, placing the Ohio Valley within weak
northwest flow aloft.  This regime will transition to more of a
zonal flow pattern by the end of the short term period.

The short term period will mainly be a temperature forecast as the
upper-level flow turns more zonal.  Surface ridging will slowly side
east of the Ohio Valley, but will remain close enough to provide
mainly sunny skies and dry weather.  With the high shifting to the
east, southerly surface winds will help keep temperatures above
normal.  Have trended above guidance for highs on Tuesday which puts
them in the mid to upper 50s.  Overnight lows tonight will be 30s,
although with only a light gradient wind, valleys/sheltered
locations will likely decouple and fall into the 20s.  Lows tomorrow
night will be a bit warmer with an increased gradient wind, so
temps will be in the middle 30s.

.LONG TERM (Wednesday through Monday)...
Issued at 314 PM EST Mon Nov 23 2015

The synoptic pattern at the start of the long term period will
feature generally zonal flow aloft over the Ohio Valley.  However,
this will transition to more of a southwesterly flow regime by the
end of the week into the upcoming weekend as a trough builds into
the western CONUS.

Surface ridging will slide off the east coast Wednesday into
Thursday.  This will allow for continued southerly surface flow over
the Ohio Valley, which coupled with increasing 925-850mb
temperatures, will yield quite a pleasant late-November warmup for
the Thanksgiving holiday.  High temperatures Wednesday will top out
in the lower 60s, but will likely push into the middle 60s for
Thanksgiving!  The main caveat for temperatures on Thanksgiving will
be the potential for some increasing cloud cover as the upper-level
flow turns more southwesterly.

By Thursday night, southwesterly flow will deepen and will tap into
some GofMex moisture ahead of a strong cold front pushing into the
region.  Isentropic ascent in response to the right entrance region
of a 130-knot jet streak should help produce a band of precipitation
along and behind the surface front.  This will make for a rather wet
Black Friday into Friday night.

Guidance differs with the remainder of the long term forecast, both
with the departure of the first system and the approach of a
potential second system for Sunday.  The 23/12Z ECMWF is much slower
with the fropa on Friday night/Saturday which would linger
precipitation in the region through Saturday afternoon.  However,
the GFS is much quicker with the front.  The GEFS mean agrees more
with the ECWMF solution, so will keep chance pops going Friday night
into Saturday.

The solutions really diverge Sunday, as guidance seems to be
struggling with the ejection of the western trough into the Ohio
Valley.  The solutions seem to hinge on the amount of downstream
ridging ahead of the system, with the GFS being much more amplified
than the flatter ECMWF solution.  This amplified solution allows for
a stronger, further northwest surface low Sunday into Sunday night,
whereas the ECMWF solution would keep any activity weak and to the
south of the region.  Don`t want to buy into either solution at this
time, as ensemble data is rather erratic. Therefore, will continue
with just a general model blend with the second system which keeps
chance pops in the forecast Saturday night through Sunday night.  It
is worth noting that thermal profiles will be close to allowing for
some wintry precip on the edge of the returning precip shield Sunday
morning (if the GFS solution verified), but it would likely be short-
lived and rather non-impactful given warm grounds.  Something we
will continue to monitor.


.AVIATION (00Z TAF Update)...
Updated at 550 PM EST Mon Nov 23 2015

Sfc high pressure and weak upper level ridging will dominate the TAF
period.  VFR conditions are expected.  SW winds have relaxed and
should shift more to southerly by Tuesday morning, with lighter
speeds expected as well. We won`t see any clouds until tomorrow
morning when upper level clouds make their way into the region.


.LMK Watches/Warnings/Advisories...


Short Term.....KJD
Long Term......KJD
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