area forecast discussion
National Weather Service Louisville Kentucky
926 PM EDT Friday may 24 2013
Forecast update...
issued at 925 PM EDT Fri may 24 2013
Current forecast looks to be in good shape. Only made very minor
tweaks this evening. Patchy fog over south central Kentucky and river
valleys as well as isolated patches of frost over the coolest
Bluegrass valleys still look possible, but not probable. The
airmass seems a little dry for either. Also, dewpts have remained
in the upper 30s over the Bluegrass which will probably prohibit low
temps from reaching frost formation levels.
&&
Short term (now - Saturday night)...
issued at 327 PM EDT Fri may 24 2013
..very patchy frost possible in eastern valleys tonight...
Surface high pressure centered over Lake Michigan has established
control across the Ohio Valley. Meanwhile, northwest flow aloft will
hold between eastern Continental U.S. Trough and central Continental U.S. Ridge. The main
concern for tonight will be how low temperatures get under good
radiational cooling conditions. Current dewpoints are generally in
the low to mid 40s, however upper 30s dew points lurk just to the
north. Expect dew points to drop some more over the next few hours
as a light advective component from the north and mixing contribute
to overall drier air. This will set the stage for tonight as clear
skies and calm winds allow temperatures to drop. Most locations
should stay in the low to mid 40s, however a few of the coolest
eastern valleys may drop into the upper 30s. There is some concern
for a few patches of frost in the most sheltered valleys and cool
spots. Most spots will not see frost, so will not continue the
Special Weather Statement. Also may see some patchy fog in river
valleys toward dawn.
Will keep the forecast dry on Saturday, however will see an increase
in upper level clouds. Will see temperatures recover to the mid 70s
across southwestern portions of the County Warning Area under warmer 850 mb temps and
less cloud cover, however eastern and central portions of the County Warning Area
will stay in the 65 to 70 degree range. There will be deep enough
moisture aloft for some virga to fall out, however think it will be
too dry in the lowest levels for any precipitation to hit the
ground.
Will continue to mention small chances for a measurable rain shower
as we get into Saturday night as deeper moisture from upstream
continues to move into the area. There is some model support for
upstream mesoscale convective system to dive across our area, which is fitting in this
northwest flow pattern. However, not confident enough in this
scenario at this time. Will continue to monitor trends. Lows on
Saturday night will be milder, generally in the upper 40s and lower
50s.
Long term (sunday through friday)...
issued at 250 PM EDT Fri may 24 2013
We will begin this period with a warm front oriented northwest to
southeast across the region, flow aloft also from the northwest, and
some weak hard to time vortmaxes coming down in that flow. Despite
the timing, several models are bringing in qpf, with the 4km NAM the
most robust having an mesoscale convective system come through the region during the day. We
look to have continued chances for showers/storms through at least
Monday, when that warm front will lift north and pull the best
chances away from the region. The temperature forecast through
Monday will depend on timing of these waves, but in general went
with 70s for Sunday and around 80 Monday.
From Tuesday on, a ridge will build aloft, with it becoming centered
over US by Thursday. The result will mean below normal rain chances
and above normal temps. Readings will bump up to the mid 80s Tuesday
but could approach 90 Wednesday through Friday.
&&
Aviation (00z taf issuance)...
issued at 700 PM EDT Fri may 24 2013
VFR conditions will prevail through the taf period. After a clear
and calm night, mid and high level clouds will begin to move in by
the late morning hours on Saturday into Saturday afternoon. These
clouds look as if they'll be expansive enough to create a broken to overcast
deck near fl120 across klex and ksdf. Some guidance continues to
hint at even some light rain reaching the surface with this cloud
cover, but with very dry air beneath the cloud-bearing layer, think
much of the precipitation will fall as virga. Thus, will continue
to leave any precipitation out of the forecast at this time. Winds
through the day on Saturday will be generally light out of the
east.
&&
Lmk watches/warnings/advisories...
in...none.
Kentucky...none.
$$
Update...........ams
short term.......bjs
long term........rjs
aviation.........Kd
