Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 030712
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
312 AM EDT Fri Jul 3 2015
.SHORT TERM (Now through Saturday)...
Issued at 300 AM EDT Fri Jul 3 2015
...Flash Flood Potential Continues Through This Evening...
Main weather features are a nearly stationary front draped across
Kentucky, and yet another upper-level impulse swinging into the
mid-Mississippi Valley. Better instability has been suppressed
mainly into Tennessee, but expect that to change later today.
Expect shower and T-storm development again in the heat of the day,
with the greatest coverage and strongest storms south of the front
where instability is greater. Plenty of cloud cover to limit
heating, but with convective temps in the mid/upper 70s it won`t
take much at all. Tall/skinny CAPE, deep warm cloud layers, high
precipitable water, and slow storm motion on the order of 10 kt at
best, all support heavy rain as the main threat. And with 1-hr Flash
Flood Guidance running less than an inch in a few spots, even brief
heavy rainfall could create serious flash flood concerns. Thus the
Flood Watch will continue to fly into this evening, and while that
may or may not be long enough, confidence is too low to extend it at
By Saturday there should be enough NW flow and ridging to push the
moisture axis and forcing farther south and east. Still carrying
chance POPs mainly south of the Western Kentucky and Bluegrass
Parkways, tapering to a dry forecast over southern Indiana. Heavy
rainfall could again be a threat in south central Kentucky, but
we`ll refine that before we consider extending any headlines.
.LONG TERM (Saturday Night through Thursday)...
Issued at 303 AM EDT Fri Jul 3 2015
Saturday Night - Monday...
The main eastern CONUS troughing will be lifting out of New England
on Saturday night while surface high pressure builds in, however a
weak upper low will be left meanderaing around the central
Appalachian spine through Monday. This feature looks to kick just
enough moisture back toward our SE CWA to keep some Iso to widely
Sct (20-30%) mention Saturday/Sunday afternoon/evening. For the most
part, think that we`ll be able to keep the nights dry once evening
convection dies off. As a result, have mostly dry conditions for the
NW two-thirds of the CWA during this time. Can`t rule out a spotty
shower or storm back this far NW, but certainly won`t be to the
degree that we`ve seen over recent days. Will go with highs in the
mid 80s under the drier pattern, but wouldn`t be surprised to see a
few spots hit the upper 80s. Lows should be in the low and mid 60s
Monday Night - Thursday...
Upper ridging and meandering upper low will be shunted off to the
east through mid week as a shortwave moves from the northern Plains
through the Great Lakes. This will bring more zonal flow over the
Ohio River Valley, with a trailing cold front approaching and then
stalling out nearly parallel to the upper flow. As a result,
sensible weather will transition back to what looks like a wetter
pattern with temperatures dependent on where the boundary sets up
and each afternoon`s convection.
Scattered warm advection showers should arrive by dawn on Tuesday
mainly across our west, with better chances arriving later in the
day as the front approaches. Will then go with at least scattered
coverage (30-50%) through Thursday as the lingering boundary acts as
a trigger. Generally going with highs in the low and mid 80s, and
lows in the upper 60s and low 70s.
Overall, not too concerned about severe weather with the storms as
better deep layer shear values will be furthern north within the
stronger belt of westerlies. A few stronger storms may be able to
develop on instability, however would be more pulse in nature. Heavy
rain may become a concern as precipitable water values will be up
around 2 inches through the column.
.AVIATION (06Z TAF Update)...
Issued at 105 AM EDT Fri Jul 3 2015
Should remain convectively quiet overnight, with the only
uncertainty stemming from weakening storms near the KY/TN border.
Given the weakening trend, will keep that out of BWG overnight. Main
issue in the overnight will be fog. BWG is likely to be most
problematic given heavy rainfall earlier in the day, and proximity
to the nearly stationary boundary. Primary limiting factor is cloud
cover, and we expect it to be more of a stratus than fog event. Will
go IFR ceiling, with vis right on the IFR/MVFR borderline. Similar
philosophy in LEX due to less antecedent cloud cover, but will keep
SDF as a fuel-alternate MVFR for now.
After that, convective timing becomes the main challenge. Will jump
on board with the hi-res models, which all seem to fire convection
around mid-afternoon. However, confidence is not high enough in a
direct impact, so at this time will carry VCTS/CB mentions.
Extensive and persistent cloud cover will keep MVFR ceilings in
place, with only SDF remaining above fuel-alternate thresholds.
T-storm chances taper down late enough in the evening that we`ll not
add the extra line in BWG and LEX for just the final hour or two.
Will show the SDF planning period dry from midnight onward, but with
ceilings back down to fuel alternate.
KY...FLASH FLOOD WATCH through this evening FOR KYZ023>043-045>049-
IN...FLASH FLOOD WATCH through this evening FOR INZ076>079-083-084-