Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 262040
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
340 PM CDT Sat Jul 26 2014
.SHORT TERM: (Through Late Tonight)
Issued at 324 PM CDT Sat Jul 26 2014
Primary concern continues to be convective trends for this evening.
Current trends are pointing more and more toward there being less
severe weather in our CWFA than previously expected, with the
primary threat for severe storms further north/northeast in
southeast IA and central IL. A broad area of showers and stratiform
rain associated with an MCV which is spinning its way across the
state is putting the kibosh on much of the instability which was
forecast for late this afternoon/evening. A limited ribbon of very
high CAPE (MLCAPE in excess of 3500-4000 J/Kg) remains over extreme
northeast MO into southern IA and a much larger area of high CAPE
over central and southern IL. Storms are already rumbling just
north of our CWFA in southern IA and west central IL and I would
expect these areas of storms to continue to develop and strengthen.
Still cannot rule out severe storms from Kirksville to Quincy and
southeast to Litchfield and possibly Salem...but the probability
seems to be much lower than previously expected.
After the evening severe weather threat has passed, there is still
the possibility that there could be additional development
overnight. RAP and NAM both show moderate moisture convergence at
850mb ahead of the front and generate QPF in response. Have left
chance/slight chance PoPs going for most of the area through the
night. The wind shift associated with the approaching cold front
should be sliding into the northern 1/3 of our CWFA between 09-12Z
with drier low level air trying to nose in. This should effectively
cut off the chance for additional precip in those areas in the
.LONG TERM: (Sunday through Next Saturday)
Issued at 340 PM CDT Sat Jul 26 2014
The cold front is expected to push through early Sunday morning. A
minimal rain threat will exist during the morning near it, with a
dry afternoon on tap behind it. The cooling effects will not be
felt too much early on, with another warm day expected: max temps
still look to top 90 degrees for most areas near and south of I-70.
The big difference will be lower humidity from today, however.
After Sunday, an extended dry period is forecast as a deep longwave
upper TROF sets up over eastern North America with a stout NW flow
aloft for our region. This usually means either dry, or surprise
hit-and-run systems this time of year, but almost always means below
average temps. For now, am going with dry until Thursday, with low
PoPs thereafter as a system works its way down into our region and
stays for a bit.
.AVIATION: (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1241 PM CDT Sat Jul 26 2014
Primary concern is thunderstorms this afternoon and evening.
Expecting the precipitation over west central/centra MO to
continue to move eastward. It is unclear yet how much these storms
will strengthen/expand, but some strong wind gusts and hail are
possible with this complex as it moves eastward. Another area of
concern will be in northeast MO/west central IL later this
afternoon/this evening where a complex of severe thunderstorms is
expected to develop and should move rapidly east-southeast. Wind
gusts in excess of 50kts and large hail will be possible with
this cluster. Still some uncertainty on the exact track of the
thunderstorm complex, though the most likely parts of the area to
be affected will be along and north of a line from KIRK to KSLO.
Afterthe storms move through this evening, expect VFR flight
conditions. A cold front will move through early Sunday morning
shifting the wind to the west-northwest.
Specifics for KSTL:
Primary concern at Lambert is the possibility of thunderstorms
early this evening. Current thinking is that the storms over
central/west central Missouri may not affect the terminal, but a
cluster of severe thunderstorms will develop over northern
MO/southern IA and race east-southeast. Think the best threat for
storms will be north of Lambert along and north of a line from
KIRK to KSLO. After storms clear the area this evening expect VFR
flight conditions to prevail. A cold front will pass through the
terminal early Sunday morning which will shift the wind to the
MO...HEAT ADVISORY until 7 PM CDT this evening FOR Franklin MO-
Jefferson MO-St. Charles MO-St. Louis City MO-St. Louis MO-
IL...HEAT ADVISORY until 7 PM CDT this evening FOR Clinton IL-Madison
IL-Monroe IL-St. Clair IL-Washington IL.