Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 260416
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1116 PM CDT THU AUG 25 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 316 PM CDT Thu Aug 25 2016

The synoptic pattern this afternoon features a strong subtropical
ridge holding strong across the Southeast, with a trough amplifying
across the Rockies.  This has placed east-central MO and western IL
on the southern fringe of the better southwesterly flow aloft which
will persist through the short term period.

An MCV has weakened and pushed off to the northeast this morning
into early this afternoon.  In its wake, the cold front along which
it was traveling has slowly sagged into portions of west-central IL
and northern MO.  Latest visible satellite shows enhanced cu along
this frontal surface, but thus far anything has really struggled to
sustain itself.  This is likely due to some weak mid-level
subsidence behind the departing MCV/vort max which can be inferred
in some of the forecast/AMDAR soundings which suggest a weak capping
inversion still in place.  As the afternoon wears on and heating
continues, still expect isolated to scattered development along the
frontal surface, and perhaps some isolated thunderstorm development
in the more unstable airmass across east-central and southeast MO.
Given swift mid-level flow, deep-layer shear around 40-50 knots
is supportive of storm organization (mainly north of I-70), so a
conditional strong to severe thunderstorm is still on the table
through this evening. Main threats if these storms were to get
more organized would be hail to one inch and damaging winds to 60
mph.

Any convection that develops along the front this evening should
diurnally weaken. However, a low-level jet will refocus along the
boundary across the Central Plains overnight, which will cause
renewed convection. This convection will move/develop east
northeast along and north of the boundary early Friday morning as
the low-level jet veers and increases isentropic ascent across
central and eastern MO. Am not overly confident in timing/coverage
tonight into Friday morning, thus have left pops in the 40-50
percent range.

Deitsch

.LONG TERM...  (Friday through Next Thursday)
Issued at 316 PM CDT Thu Aug 25 2016

Stalled frontal boundary to begin lifting back north as a warm
front on Friday. So will see continuing chances of showers and
thunderstorms throughout the day. With decent instability and
shortwave sliding east through region, could see strong to severe
storms, especially during the afternoon and early evening hours. By
Friday night, front to shift just north of forecast area.

On Saturday, front begins to shift back to the south once again as
next in a series of upper level shortwaves lifts northeast towards
Great Lakes region, pulling surface low with it. Will see increasing
chances of storms with best chances over northeast Missouri and west
central Illinois. Then frontal boundary washes out and weak surface
ridge builds in.

This weak surface ridge to remain over region through the middle of
next week. Despite the ridging, will see diurnal chances of storms
each day. Temperatures through the period look to remain seasonably
warm with highs in the 80s and lows in the mid 60s to low 70s.

Byrd

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1052 PM CDT Thu Aug 25 2016

Convection continues late this evening between UIN and STL.
A weakening cold front extended from near COU to just north of
STL. This front will likely sag just south of the taf sites by
Friday morning. Much of the current shower and thunderstorm
activity should dissipate late tonight, but more convection may
move into the UIN area late tonight/early Friday morning on the
nose of a modest southwesterly low level jet. Scattered diurnal
convection is expected again Friday afternoon into the evening as
the weak front begins to lift back northward with moist and
unstable conditions. Surface winds will be light late tonight and
Friday morning, then east-southeasterly Friday afternoon.

SPECIFICS FOR KSTL: Convection continues late this evening between
UIN and STL. A weakening cold front extended from near COU to
just north of STL. This front will likely sag just south of STL by
Friday morning. Much of the current shower and thunderstorm
activity should dissipate late tonight. Scattered diurnal
convection is expected again Friday afternoon into the evening as
the weak front begins to lift back northward with moist and
unstable conditions. Surface winds will be light late tonight and
Friday morning, then east-southeasterly Friday afternoon.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     75  86  72  87 /  20  30  40  50
Quincy          66  81  69  85 /  40  40  50  60
Columbia        69  83  68  85 /  50  40  50  50
Jefferson City  69  84  69  87 /  50  40  50  50
Salem           73  86  71  86 /  20  20  30  50
Farmington      71  86  70  85 /  20  40  30  50

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX


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