Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 221732
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
132 PM EDT Fri Aug 22 2014
...Updated Aviation Discussion...
Issued at 620 AM EDT Fri Aug 22 2014
Updated the forecast to delay POPs until late morning/early
afternoon. The complex of storms over north central Indiana and
northern Illinois will continue to sag south and east throughout the
day. It`s difficult to time southward progress due to the ridging
over the area, but will delay convection through most of the morning
hours with this update.
.SHORT TERM (Now through Saturday)...
Issued at 300 AM EDT Fri Aug 22 2014
...Heat and Humidity have Arrived...
Strong ridging has built in over the region keeping convection to
our north and east early this morning. The only exception will be a
few showers/storms that look to skim our northern Bluegrass counties
and possibly our southeast Indiana counties.
For the rest of the day expect isld-sct showers/storms most numerous
east of I-65. The upper level ridging will sharpen to our west
gradually pulling back the convectively active periphery tonight and
especially for Sat. As we enter the train of subtle shortwaves in
the periphery of the ridge expect westward expansion of convection
and better coverage of storms over all. Saturday we may even see a
weak back door cold front push close to the region from the NE
providing additional focus for storms. PWATs and instability will
remain high over the next few days, but wind profiles will be
marginal at best. Thus, think that scattered storms should remain
below severe limits. The strongest storms may contain heavy
rainfall...gusty winds up to 40 mph...and dangerous lightning.
Temperatures and heat indices in the short term period still look on
track with a Heat Advisory in place through Monday. Temperatures
should reach the low to mid 90s for highs today and Saturday. These
temperatures combined with dewpts in the lower 70s will result in
heat indices of 100-105 each afternoon. We won`t see much reprieve
from the heat tonight with low temps progged in the low to mid 70s
under humid conditions.
.LONG TERM (Saturday Night through Thursday)...
Issued at 300 AM EDT Fri Aug 22 2014
...Hot humid weather to continue through Wednesday...with a trend
towards cooler temperatures beginning Thursday...
500mb ridging will remain anchored over the Lower Ohio Valley, even
as the upper air pattern amplifies over North America.
An upper air trough will amplify in place this weekend off the
Mid-Atlantic Coast. Farther west, a positively tilted longwave
trough will bring cooler weather to the northern Rockies and plains
as a shortwave is forecast to move northeast early Monday north of
Ridging will build northeastwards over the weekend from the Lower
Mississippi Valley towards the western Great Lakes, but will be
prevented from moving much eastwards by the stationary trough off
the eastern coast. It will become somewhat squeezed and narrower in
amplitude early next week as the ridge axis remains just to the west
of the Commonwealth.
Unusually humid and muggy (even for August) conditions will continue
Saturday through Monday as PWATs near or above 2 inches will
accompany surface dewpoints over 70. Daytime highs Sunday and Monday
will reach the lower to mid 90s. Overnight lows will stay quite warm
and uncomfortable, falling only into the lower to mid 70s. Winds
will be quite light, with nearly calm winds overnight and variable
winds during the afternoons. Heat indices each afternoon will
probably approach or exceed 100. In what has been a coolish summer
so far, hot weather through early next week will establish our
longest stretch of hot and humid weather for the entire season.
Usually, if the Lower Ohio Valley under such a strong ridge in
August, rainfall chances are quite sparse. However, in this case,
will continue with current forecast of possible scattered afternoon
and evening thunderstorms Saturday night through Monday. With such a
moist atmosphere, and very light winds aloft. Any storm will be slow
moving and could produce localized heavy rainfall.
By Tuesday, the 500mb ridge axis will sag southeast right over the
Commonwealth. Winds will become light southwesterly by late
Wednesday as a surface trough approaches from the northwest.
Currently the GFS is faster with a potential cold front Thursday
compared with the ECMWF. Both forecast a chance of rain Thursday
along with cooler and less humid conditions by at least late
.AVIATION (18Z TAF Update)...
Issued at 126 PM EDT Fri Aug 22 2014
Categories will predominately flop between VFR and MVFR through this
evening with the lower ceilings due to a warm, moist, unstable
airmass producing this cloudiness. Could continue to see this back
and forth between the two categories through the remainder of the
TAF period. Additionally, chances for thunderstorms begin to creep
in overnight and into tomorrow as surface high pressure loses its
grip over the Ohio Valley, shifting more toward the south and
leaving the three terminals on its periphery. However, with BWG
closer to the high than LEX or SDF, the latter two locations could
have a better chance for convection within the area over the next 24
hours as compared to BWG. There is quite a bit of uncertainty at
this point as to if storms will directly impact the terminal areas
or as to the timing, given the unorganized nature of any convection
that fires up. Best timing currently looks to be this evening
through tonight across southern IN/northern KY/eastern KY, with
additional opportunities again on Saturday. Will modify/amend future
TAFs to include TS mention, if and when warranted.
Wind fields will be relatively light throughout much of the period,
with gradient winds maxing out at around 10 knots or so this
afternoon. Otherwise, winds will be lighter through tomorrow and
primarily out of the west.
KY...HEAT ADVISORY until 7 PM EDT /6 PM CDT/ Monday FOR KYZ023>031-
IN...HEAT ADVISORY until 7 PM EDT /6 PM CDT/ Monday FOR INZ076>078-