Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 241940
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
340 PM EDT Thu Jul 24 2014

.SHORT TERM (Now through Friday Night)...
Issued at 252 PM EDT Thu Jul 24 2014

High pressure centered near Chicago will modify as the ridge axis
migrates SE across the Ohio Valley tonight and Friday. NNE winds
will continue to advect cooler and less humid air into the region
into this evening. With winds going light/variable and skies
clearing just after sunset, we`ll have favorable radiational cooling
conditions, but enough low-level drying that any fog will be limited
mainly to the valleys. Temp forecast is on the low end of guidance,
and will run 8-10 degrees below normal.

The back side of the high will see temps gradually moderating, with
Friday night mins close to normal, and attention will turn to precip
timing as the next disturbance approaches in the NW flow aloft.
PWATs recover closer to normal, but a lot of mid-level dry air will
remain and the best forcing stays to our north through 12Z Sat.
Therefore will limit Friday night POPs to slight chance across our
southern Indiana counties, and keep Kentucky dry.

.LONG TERM (Saturday through Thursday)...
Issued at 310 PM EDT Thu Jul 24 2014

Another roller coaster temperature ride on the way in the long term
with a warmup over the weekend before another cold front arrives
late Sunday to whisk away the moisture and leave the work week
mostly dry and mild.

As the current surface High over the eastern U.S. works its way out
to sea, southerly return flow will send Gulf moisture back into the
Tennessee and Ohio Valleys by Saturday.  This will combine with a
weak short wave swinging around an upper level Low over Hudson Bay
to bring precip chances back along the Ohio River Saturday morning,
but this will be the last gasp for this system, and is not expected
to make its way south into most of Kentucky.  However, 70+ dew
points make their way across the area Saturday afternoon, setting
the stage for new convection by evening. These storms will have
plenty of moisture to work with, but with only marginal,
disorganized upper level dynamics to work with, look to be randomly
scattered in nature.  Isolated severe cannot be ruled out with
these, though, which would generally be in the form of downbursts
and hail.

On Sunday, a cold front and its attendant upper level trof will
rotate around the quasi stationary Hudson Low.  Ahead of the front,
thunderstorm chances will continue in the juicy airmass, which will
end with the frontal passage Sunday night into early Monday.  Behind
the front, cooler, drier air will follow, and remain in the forecast
area for the remainder of the extended.

Max temperatures over the weekend will be within a few degrees of
90, followed by readings dipping into mid 70s to lower 80s for the
remainder of the period. Sunday morning lows will be in the muggy
lower to mid 70s, but replaced by 60s Monday, then 50s Tuesday and
Wednesday, before rebounding back into the 60s on Thursday.

&&

.AVIATION (18Z TAF Update)...
Issued at 1255 PM EDT Thu Jul 24 2014

Low clouds clearing from north to south, but a decent cu field is
filling in behind as mixing deepens. Even so, BWG has gone VFR, but
LEX remains in fuel-alternate MVFR. Wind gusts have kicked up near
20 kt at SDF, and this has not been handled very well by the models.
Will be a press time decision whether to initialize with any wind
gusts, which would mainly be expected at SDF and LEX, but just for
the first hour or two.

Expect SCT-BKN cu for the rest of the afternoon, with LEX improving
to VFR by roughly 19-20Z. Once the sun sets, skies will clear and
winds will go light and variable for the rest of the TAF period.
Only concern would be fog potential around daybreak Friday. Enough
dry air filtering in that any fog formation will most likely be
confined to the valleys and other fog-prone locations, and not
affecting the airports. How much the dewpoints this afternoon are
able to drop will be more telling, so the 00Z TAF set should get a
better handle.

&&

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

$$

Short Term........RAS
Long Term.........JBS
Aviation..........RAS





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