Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 130527
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
127 AM EDT THU JUN 13 2013
...Updated Aviation Discussion...
.SHORT TERM (Tonight through Thursday night)...
Issued at 315 PM EDT Wed Jun 12 2013
...Severe Weather Possible Tonight...
Main challenge tonight is the severe weather risk, which is fraught
with uncertainty as a vigorous MCS will develop over northern
Illinois. The strongest punch of this complex will push east into
Indiana and Ohio, remaining north of our area. However, with a 40-50
kt WSW jet at 850mb, the southern/western flank of the line will
dive southward into the Ohio Valley. Our severe chances will hinge
on how far south these storms can maintain their strength in the
face of very warm (20C) 850mb temps and a more stable boundary
Synoptic-scale models skew more toward Thursday morning, but we
believe they do not give enough credit to the acceleration that
happens as cold-pool processes take over. Best guess for
thunderstorms will be just either side of midnight for southern
Indiana, and midnight to 3 AM south of the Ohio River. In southern
Kentucky, south of the Parkways, chances are lower and more
dependent on the ability of the cold front to force convection over
western Kentucky. POPs will be limited to slight chance.
Main severe threat involves damaging winds, and will be greatest
along and north of I-64. Hail or even an isolated spin-up cannot be
ruled out, but just as likely is the scenario where the cold pool is
strong enough that storms will be gusting out as they dive into
Look for the actual cold frontal passage around mid-morning on
Thursday, with breezy W-NW winds developing behind it. Could see
some lingering shower activity in the morning, mainly from
south-central Kentucky up into the Bluegrass region. Temps will
start off unseasonably warm, with morning lows only in the mid 70s,
but recovery will be limited by extensive cloud cover. Max temp
forecast favors the cooler GFS MOS, mainly in the lower/mid 80s, but
with dewpoints dropping off through the day. Cooler and drier air
will continue to spill in Thursday night, with lows just below
.LONG TERM (Friday Night - Wednesday)...
Issued at 300 AM EDT Thur Jun 13 2013
A ridge...trough...ridge pattern at 500mb will be in place late
Friday as a deep trough exits New England. Out west, a potent but
small closed low will flatten ridging over the northern Rockies as
it moved east of the Canadian Rockies. By early Monday, this closed
low will elongate along an east-west axis across southern Canada as
moderate 500mb flow undercuts this trough over southern Canada. This
will produce a zonal flow over the Lower Ohio Valley for Sunday and
At the surface, Canadian high pressure over the western Great Lakes
late Friday will be responsible for a dry airmass and seasonably
cool overnight lows both Saturday and Sunday morning. After lows
near 60, highs on Saturday will warm a few degrees over Friday`s
highs, with temperatures peaking in the mid 80s. With the proximity
of this high Saturday afternoon expect mostly clear skies in the
morning with a few afternoon fair weather cumulus in the afternoon.
Winds will stay light and variable even into Saturday afternoon.
Southwesterly flow will develop by early Sunday along the backside
of this departing surface high. Gulf moisture, previous restricted
to along the Mississippi River Valley will move east and bring more
humid weather for Sunday through Tuesday.
The long term will start out with surface high pressure ridging in
from the north. Aloft we will have northwesterly flow. Dry
conditions are expected across the region Friday through Saturday.
Friday will be the coolest day of the long term with temperatures
topping out in the upper 70s to lower 80s. Dewpoints will drop into
the upper 50s to around 60. With mostly clear skies and lower
dewpoints, temperatures on Saturday morning look to drop into the
upper 50s to lower 60s as well. As the high pressure shifts east and
southerly return flow begins to set up, temperatures will rise into
the lower to mid 80s on Saturday.
The upper level flow will flatten out by Saturday night and a
shortwave will approach from the west. This will begin to spread
showers and thunderstorms into southern Indiana. Sunday the best
chance for rain looks to remain over the northern half of the
forecast area. Rain chances will then be on the increase Sunday
night and especially Monday as a weak front will cross the area.
PWAT values will increase to 1.7+ inches by Monday, so heavy rain
may accompany showers and thunderstorms. This boundary will be slow
to move through the area and precipitation chances look to linger
across the area through at least Tuesday, especially across south
Highs look to be the warmest on Sunday with temperatures topping out
in the mid to upper 80s. Temperatures through the first half of next
week will depend somewhat on how widespread precipitation is. In
general highs look to be in the mid 80s with lows in the mid 60s to
.AVIATION (06Z TAF Update)...
Issued at 127 AM EDT Thu Jun 13 2013
A strong upper shortwave trof and surface cold front remain to our
northwest, leaving a small chance for convection to still affect
SDF/LEX early this morning. However, strong capping has kept things
very quiet so far as a severe MCS moves by to our north. Will play
down thunder chances with a simple VCTS/VCSH through dawn.
The cold front should move through from northwest to southeast in
the 14Z-17Z time frame. Some showers/tstms could accompany the
front, but would be widely scattered.
Really, the main issue for aviation during this TAF period will be
the winds. Ahead of the approaching front, winds will continue
out of the southwest, occasionally gusting to around 20 knots.
The passage of the front will bring winds around to the northwest,
and gusting into the 20 to 25 knot range late this morning into this
afternoon. Winds will settle down with sunset tonight.
Post frontal cu are expected today, but will keep them low-end VFR
in the TAFs. Skies will clear tonight.