Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 182054
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
354 PM CDT Sat Apr 18 2015

.SHORT TERM:  (Through Tonight)
Issued at 353 PM CDT Sat Apr 18 2015

A vigorous upper LOW was over eastern CO this afternoon as a weak
upper RIDGE was moving off to our east.  This is resulting in
increasing southerly upper flow and moisture thru the column over
our region.  A strong upper level disturbance was grazing the TX
Gulf of Mexico coast.  A weak southeast flow at the surface
prevailed with abundant mostly high level cloud cover over our
region, resulting in mostly cloudy skies.  Temps were once again
seasonably warm with readings in the 75-80 range.  A broken band of
SHRA/TSRA was over western-central MO moving to the north-
northeast.

The broken band of SHRA/TSRA is anticipated to continue moving NNE
and just edge the western CWA thru portions of central and northeast
MO thru this evening.  Isolated SHRA/TSRA is possible further east
towards STL metro as some upper level support moves in and given
moisture rich column.

That strong upper level disturbance from the TX Gulf coast will race
N-NE into our region late tonight and result in a surface LOW
reflection over the lower OH valley.  Look for an area of rain to
develop with some imbedded TSRA possible initially thru southeast MO
and far southern IL towards midnight and then expand northward
towards STL metro and southwest IL late.  Elsewhere, rain chances
will be pretty meager overnight with token low chance PoPs.

Min temps should be in the range of persistence or a bit warmer,
dropping to around 60 degrees, which is on the high-end of MOS.

TES

.LONG TERM:  (Sunday through Next Saturday)
Issued at 353 PM CDT Sat Apr 18 2015

(Sunday through Tuesday)

Focus thru this period will be PoPs on Sun into Mon.

Have continued a slow trend based on latest mdl, RADAR and sat
trends. Still, am concerned going forecast is too fast on Sun.
Believe the mdl solns are opening the upper low too quickly and
generating/lifting the sfc low nwd thru the region too fast.
However, it is difficult to say if this is true, how fast it is.
There is some question about strong to possibly severe storms on
Sun. Latest mdl guidance suggests the first batch of RA moving out
of the ern CWA during the early afternoon hours, while a second area
of precip will be headed twd the wrn portions of the CWA associated
with the main trof. This may provide a very brief window where
pockets of insolation could develop and support a few strong
updrafts. With CAPE around 1000 J/kg or less and deep layer shear at
20 kts or less, do not currently anticipate anything organized
across the CWA. However, with a s/w progd just S of the CWA, main
question will be the nrn extent of the svr threat.

Have also added some slight chance PoPs for Tues as the home grown
mdl solns track the s/w rounding the base of the trof across the srn
portions of the CWA. If these mdls trend twd the ECMWF/GEM solns,
these PoPs can be removed. In the meantime, felt a low PoP was
needed.

As for temps, trended cooler for Sun, but warmer Sun night with
ample cloud cover. However, there may be enuf breaks in the clouds
on Sun that updated forecasts may need to trend warmer. Thru Tues,
have trended warmer only due to the fact that mdls seem to struggle
to go warm enuf lately.

(Wednesday through Saturday)

Focus continues to be RA thru the extd. Kept low PoPs thru Thurs
night with a backdoor fnt across the region. Is some question to the
placement of this fnt as well as available moisture and forcing.
Kept PoPs in low chance category beyond to keep some flavor of the
prev forecast as well as trending twd the latest guidance and noting
uncertainty.

With questions in precip mentioned above, have trended slightly
warmer than guidance thru the period.

Tilly

&&

.AVIATION:  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1255 PM CDT Sat Apr 18 2015

Two areas of concern with regard to rain. The first is a broken
band of SHRA/TSRA that has been edging east very slowly. The
thinking with this is that it will edge into central and northeast
MO this afternoon before it then pulls away to the north. This
will result in rain in the vicinity for COU for much of the
afternoon and then edging UIN during the evening. Some isolated
TSRA possible for STL metro this afternoon but looks too small to
mention at this time until we actually see something develop. The
other area of concern is larger area of rain that will develop
late tonight and into Sunday morning as a new area of low pressure
develops to our south and tracks to our east on Sunday. This area
of rain should impact STL metro by late tonight and then UIN by
late Sunday morning. COU appears to be more on the edge but enough
guidance is showing that some of this will fill-in to include rain
mention for them as well. Otherwise, easterly flow will back
northerly on Sunday as the LOW pulls away.

Specifics for KSTL: Isolated TSRA possible late this afternoon but
probs too small to mention. Otherwise, larger area of rain to
impact the airport late tonight and should include lower non-VFR
CIGs on Sunday morning--but questionable how low to go. For now
have MVFR levels. Increasing evidence of some re-development of
scattered TSRA late Sunday afternoon and into the evening and have
transferred the thunder mention to this period which looks more
favorable for thunder, if any happens.

TES

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     60  71  54  64 /  70  80  70  10
Quincy          59  67  49  61 /  40  80  70  10
Columbia        59  69  48  63 /  60  80  70   5
Jefferson City  58  70  49  63 /  50  80  70   5
Salem           59  68  53  63 /  80  90  70  20
Farmington      58  71  51  63 /  80  70  70  10

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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