Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 190507
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
107 AM EDT WED JUN 19 2013
...Updated Aviation Discussion...
Issued at 953 PM EDT Tue Jun 18 2013
The threat of severe weather has passed, so the Severe Thunderstorm
Watch from earlier has been dropped. Isolated thunderstorms will
still be possible tonight but shouldn`t produce much more than a few
locally heavy downpours and briefly gusty winds.
Issued at 752 PM EDT Tue Jun 18 2013
Earlier line of storms has dissipated significantly as it crosses
the Ohio River. Nevertheless, the outflow is still rushing south
and has brought northerly wind gusts of 30 to 40 mph in advance of
any rain. Widely scattered storms have developed along and ahead of
the gust front, but have only a small window to become strong/severe
early this evening.
Have updated the grid PoPs to reflect current and near future rain
Issued at 549 PM EDT Tue Jun 18 2013
Now that the thunderstorms in Indiana have gelled into a nearly
solid line of convection, have increased PoPs in our southern
Indiana and far northern Kentucky counties in the very near term
(next few hours) using propagation timing from radar data.
Mesoanalysis still suggests that the storms will begin to weaken as
they approach and cross the Ohio River, encountering a slightly less
.SHORT TERM (Now through Wednesday Night)...
Issued at 310 PM EDT Tue Jun 18 2013
...Severe Thunderstorm Watch 324 in effect until 02Z tonight...
Thin line of cumulus is developing along the front, across central
IL/IN/OH, this hour. Still expect storms to develop here, as they
get enhanced by a shortwave trough, now over northwest IL. We may
also see some development over the Bluegrass, where cumulus are
hanging around and along a differential heating boundary. Still
think the best chance for strong to severe storms will be over the
north associated with that line as it shifts southward with the
The best chance for storms over southern Indiana will range from 5-8
PM and 6-9 PM for the SDF/LEX metro. The line should accelerate
southward, getting a little ahead of the shortwave forcing. Thus
expect it to weaken as it crosses the river. Thus a severe
thunderstorm watch has been posted for a couple of tiers of counties
across my northern forecast area.
The front to our north will move across the region overnight,
shifting rain chances into the southern area. Then by daybreak all
rain chances should be down for a few days. We probably will at
least have patchy fog where the heaviest rains fall tonight and in
the usual river valleys. Have painted the best chance for fog in the
grids over the southern half of the region, where it will take
longer for drier dewpoints to get in by daybreak.
Wednesday will be a nicer day with skies clear and highs ranging
from 79-85. Lows Wednesday night will be a few degrees below normal.
.LONG TERM (Thursday through Tuesday)...
Issued at 300 PM EDT Tue Jun 18 2013
The extended forecast period will be dominated by an expanding ridge
of high pressure aloft over the southern and eastern United States,
in line with a summerlike pattern. The main belt of westerly flow
aloft will retreat a bit northward to the northern third of the U.S.
where most of the active weather will occur during this forecast
period. In between, 500 mb heights will build across the Ohio Valley
as general high pressure at the surface anchors over the eastern
CONUS. GEFS ensembles from 06z shows good member continuity and
agreement with this scenario.
This pattern will result in generally dry weather throughout a good
portion of the forecast period. However, as the air mass
destabilizes again later this week into early next week, can`t
preclude a few isolated diurnal thunderstorms. But, determining when
and if precipitation will occur is a challenge as no organized
forcing is apparent in the benign pattern. In addition, medium range
models will not be able to resolve nor time subtle shortwaves moving
into or through the ridge that might be enough to touch off isolated
or scattered thunderstorms in an unstable air mass.
On a daily basis, it does appear that Thursday will be a dry day
with relatively low humidity levels for mid-late June. Prefer the
lower GFS dewpoints Thursday (except at 00z Friday since GFS
dewpoints have a high bias at 00z) more so than the higher NAM
dewpoints. On Friday, GFS continues to indicate that some moisture
over the southern Appalachians could push west-northwestward into
southern Kentucky on the underside of the mid-level ridge axis. This
could increase moisture enough for isolated diurnal storms Friday
afternoon, but this is tenuous and perhaps overdone by GFS. Canadian
GEM tends to keep any activity over Tennessee which is possible.
Over the weekend, our forecast area looks to be basically sandwiched
between westerly flow aloft and better convective potential well to
our north, and diurnal scattered convection in a tropical air mass
across the southeastern U.S. As a result, it appears our area will
remain dry and very warm Saturday and Sunday, and possibly Monday as
well. Nevertheless, again can`t rule out a few isolated storms in
the afternoon to early evening. Then on Tuesday, the westerlies over
the Great Lakes may dip a bit farther south allowing a chance for
scattered thunderstorms to develop or propagate southeast into our
area at that time.
Temperature-wise, afternoon highs will slowly moderate into the
upper 80s and lower 90s over the weekend and early next week,
although the core of the heat will remain to our west over the
Plains states. Morning lows will moderate from the lower and mid 60s
Thursday morning to the upper 60s and lower 70s later in the
.AVIATION (06Z TAF Update)...
Issued at 105 AM EDT Wed Jun 19 2013
Line of showers and storms has continued to fade across southern
Kentucky and residual showers over southern Indiana are also
diminishing...so not expecting much in the way of additional
rainfall overnight. Latest data suggests that drier air will work
in resulting in improving ceilings overnight. VFR ceilings are
expected, but patchy fog/mist is expected to develop after 19/09Z
and MVFR vsbys will be possible at the terminals from 19/09-13Z.
Today will be pleasant as high pressure noses into the region
from the north. Diurnal afternoon cu will pop in the afternoon, and
some model data suggest that some of the cu will grow tall enough to
become small showers in southern Kentucky, but the chances are much
to small to mention in the BWG TAF at this time.