Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 220436
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1236 AM EDT Fri Aug 22 2014
Issued at 1230 AM EDT Fri Aug 22 2014
Updated the forecast to tweak POPs slightly. Looks like the complex
of storms to our north will make it into southeast Indiana and
extreme northern KY as it continues to weaken.
.SHORT TERM (Now through Friday Night)...
Issued at 300 PM EDT Thu Aug 21 2014
A 500 mb ridge will continue to build across the Midwest through the
short term period. This will keep the Lower Ohio Valley in
northwesterly flow aloft, though it will become more
north-northwesterly by Friday night. At the surface the boundaries
will remain to the north keeping us in warm southerly flow.
For the remainder of the afternoon, an upper level disturbance will
continue to push east and as it does showers and storms will shift
eastward. There is still a chance for some strong storms over the
Bluegrass over the next few hours with gusty winds and possibly
small hail. This activity should move east by early evening.
Thereafter, it looks like there will be a break through much of the
evening and overnight period.
For tomorrow another shortwave will dive through the northwesterly
flow during the morning. Precipitation chances will start to
increase around daybreak, particularly across southern IN and north
central KY. A secondary weak vortmax looks to also move through
tomorrow evening. This could result in a couple of rounds of showers
and storms tomorrow. Again the best chance for storms tomorrow will
be across southern Indiana and east central Kentucky. Given the more
northwesterly flow aloft tomorrow, storms could develop a bit
further west across central KY than they did today. Still will keep
coverage scattered. The chance for strong to marginally severe
storms is a bit in question tomorrow given the ongoing early
convection and presence of clouds. Models do indicate some moderate
instability developing by afternoon, so a few strong storms with
gusty wind and small hail are not out of the question.
With the ridge building in to the west heights will build aloft.
Temperatures tomorrow will rise into the low to mid 90s. With
dewpoints in the upper 60s to lower 70s this will result in heat
indices ranging from the mid 90s in the east to the lower 100s in
the central and west part of the forecast area. Overnight lows will
remain on the warm side in the lower to mid 70s.
.LONG TERM (Saturday through Thursday)...
Issued at 332 PM EDT Thu Aug 21 2014
...Heat, Humidity, and Unsettled Weather into Early Next Week...
Once again, all eyes are on the stout upper ridge over the southeast
United States for the long term forecast. How hot and humid will it
get, and how long will it stick around?
While there was good agreement among the models on where and how the
ridge would form, there was significant disagreement on how long it
would last. The GFS has been pretty consistent over its last several
runs with its upper trof/ridge/trof pattern from the Rockies to the
western Atlantic. Also, the operational run agrees fairly closely
with the ensemble mean at 500 hPa. It does get some general support
from the CFS by the tail end of the forecast period as well.
Finally, the 12Z/21 run of the ECMWF has trended significantly
toward the current GFS solution. So, will lean heavily on the GFS
for this forecast.
Given that, the summertime southeast U.S. upper ridge is expected to
hold its ground through at least Tuesday night, providing us with
hazy, hot, and humid conditions. A trof invading from the northwest
will then flatten the ridge Wed/Thu as it cruises from the Plains to
the Great Lakes. This is a source of uncertainty in the forecast,
though, as we`ll have to see if the trof is able to eat into the
strong ridge as much as is currently advertised.
As noted in previous forecasts, storms will still be in the forecast
despite the upper ridging. The center of the ridge remains just off
to our south/west for much of the time, and mid level capping is
weak. So, isolated/scattered diurnal afternoon/evening convection
can`t be ruled out. The best chances for storms will be from
southern Indiana through the Blue Grass, and the best chances for
heat will be across western and southern portions of central
Kentucky. Mid-level lapse rates are unimpressive and wet bulb
zeroes are very high, but a few of the stronger storms could produce
some locally strong wind gusts.
Afternoon highs will be in the lower and middle 90s Saturday through
Monday, and around 90 Tuesday through Thursday. Dew points through
at least Tuesday will be very uncomfortable in the lower and middle
70s. As a result, we`ll stay warm at night with lows in the 70s.
Since one of the criteria for a Heat Advisory is heat index readings
of 100-105 for four consecutive days, we`ll go ahead and hoist the
headline for Friday through Monday. In addition to satisfying the
criteria, this will also raise awareness for weekend outdoor
activities such as the Kentucky State Fair. We`ll restrict the
advisory to about the western two-thirds of the LMK CWA where the
chances for headline-worthy heat are the greatest.
.AVIATION (0Z TAF Update)...
Issued at 643 PM EDT Thu Aug 21 2014
As high pressure aloft builds in, the main storm track should remain
just to the north and east of the terminals. A storm or two could
slip into the SDF/LOU/LEX airspace, but coverage and chances are too
slim for anything in the TAFs right now. Best shot at convection
will be at LEX Friday afternoon.
Looks like fog chances are small enough tonight to keep visibility
restrictions from the TAFs. The best chance for some MVFR HZ/BR
will be at LEX around dawn.
Winds will generally be from the southwest below 10 knots through
KY...HEAT ADVISORY from 2 PM EDT /1 PM CDT/ this afternoon to 7 PM
EDT /6 PM CDT/ Monday FOR KYZ023>031-034-038-045-053-
IN...HEAT ADVISORY from 2 PM EDT /1 PM CDT/ this afternoon to 7 PM
EDT /6 PM CDT/ Monday FOR INZ076>078-083-084-089>092.