Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 242009
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
309 PM CDT WED AUG 24 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 159 PM CDT Wed Aug 24 2016

A s/w ejecting out ahead of the main trof over the srn Plains will
continue to lift newd this evening. This s/w is progd to take on
more of an MCV structure as it lifts into MO/IA region late
tonight. Sct TSRA remain possible across much of the region this
evening. Storms have not developed as prev anticipated. However,
storms may still develop this afternoon across central portions of
the CWA where sfc convergence is greater.

Focus shud quickly become area of moisture convergence
across wrn portions of the CWA ahead of the approaching wave. This
wud suggest a longer duration of TSRA across nrn portions of the
CWA this evening. There is some uncertainty regarding duration of
precip tonight across the nrn portions of the CWA. Still, there is
still enuf threat for heavy rainfall/flash flooding tonight across
the current watch area to keep the watch as-is.

With ample CAPE across the region and deep layer shear around 40
kts, any storms that do develop will be capable of becoming severe
with large hail and damaging winds as the primary threat. However,
can not rule out some organized storms with a tornado threat.

Tilly

.LONG TERM...  (Thursday through Tuesday)
Issued at 348 AM CDT Wed Aug 24 2016

The cold front will continue moving slowly south Thursday and
Thursday night.  Current indications are that it won`t be as
unstable Thursday afternoon and evening with MLCAPE mainly in the
1500-2000 J/Kg range.  Additionally, it guidance is showing a decent
amount of CINH along and south of the I-44 corridor in Missouri and
the I-70 corridor in Illinois south of the front.  This should limit
areal coverage and intensity of the storms Thursday afternoon and
Thursday night.  Think greatest chance will continue to be along the
front during the afternoon and early evening.  The focus for
convection will likely shift westward into Kansas during the late
evening where the low level jet will be strongest.  However, 10-15kt
south-southwest flow at 850mb persists over the southern 1/2 of our
CWFA through much of the night, so chance PoPs are warranted.

Looks like good model agreement that the front will drift down over
the Ozarks by 12-15Z Friday morning.  NAM is much faster bringing it
back to the north Friday afternoon, but the GFS and ECMWF keep it
down south of I-70 all day.  Have therefore kept PoPs out of the
northeastern 1/3 of the area.  Warm front moves back to the north by
Saturday morning which will bring warm and humid air back to the
region.  Low level ridge over the Ohio Valley and the central
Appalachians will keep southerly low level flow locked in over our
area through Tuesday.  ECMWF tries to push a weak cold front as far
south as the I-70 corridor Monday night into Tuesday morning, but
the GFS has no front at all...so I didn`t vary temperatures from
Sunday/Monday to Tuesday very much.  There will be a persistent
chance of diurnal convection Saturday through Tuesday in the warm
humid airmass.  Not much to focus convection so blanket
chance/slight chance PoPs are in order.  Temperatures will continue
to be seasonable...primarily in the low to mid 60s for lows and mid
80s for highs.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1240 PM CDT Wed Aug 24 2016

Swly winds will continue and eventually become nwly to nly on
Thurs behind an approaching cdfnt. A number of questions regarding
precip chances thru the period. A line of congested CU has
developed stretching from K1H2, swwd to just south of KCPS to near
KUUV. An outflow bndy, or perhaps a bore wave, is evident in the
latest sat data. Believe this will help initiate TSRA along the
congested CU somewhere east and south of KSTL, but may impact
KCPS, hence the tempo group. Otherwise, best chances for precip
will be at UIN this evening into the overnight hours. This area of
precip shud lift NE of the region Thurs morning.

Tilly

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     93  77  91  71 /  40  40  40  30
Quincy          89  70  84  65 /  50  90  40  20
Columbia        91  69  86  67 /  30  50  40  50
Jefferson City  92  70  87  68 /  30  50  40  50
Salem           90  73  90  70 /  40  40  20  20
Farmington      91  72  90  70 /  30  20  20  30

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flash Flood Watch from 7 PM CDT this evening through Thursday
     morning for Knox MO-Lewis MO-Marion MO-Monroe MO-Ralls MO-
     Shelby MO.

IL...Flash Flood Watch from 7 PM CDT this evening through Thursday
     morning for Adams IL.

&&

$$

WFO LSX


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