Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 310159
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
859 PM CDT Sat May 30 2015

.UPDATE:
Issued at 858 PM CDT Sat May 30 2015

Two things of note going on which warranted forecast updates:
upper LOW just east of STL metro has effectively frozen the
western edge of the showers/rain to just east of downtown STL and
will likely do so for the next few hours until this feature moves
further away. Have adjusted PoPs to keep likelys going for
effectively the entire evening for southwest IL. As the upper LOW
pulls away towards midnight, the remaining showers/rain should
vaporize. This is what also caused the lingering rain for downtown
STL early this evening that took longer than originally
anticipated to leave.

Giving way to...drizzle. Large swath of low clouds and a decent
low level TROF axis that snakes up the MS river has resulted in
development of areas of drizzle recently that has quickly followed
the passage of the backedge of the showers. Have used the RAP
model to take a shot at when the drizzle will come to an end with
the building in of high pressure and flow becoming anticylonic.
This will mean drizzle for areas N and W of STL metro for at least
thru midnight and for STL metro and areas to the S and E for deep
into the night. May see drizzle even linger past 12z/Sun for areas
to the S and E of STL metro but have held off for now on adding
that.

Otherwise, temps still on target for 50s tonight for most areas
with a few 40s, and with clouds lingering for much of Sunday and
N-NE low level flow, temps will recover little, with max readings
in the low-mid 60s for most locales.

TES

&&

.SHORT TERM:  (Through Late Tonight)
Issued at 338 PM CDT Sat May 30 2015

The initial short wave/vort max was located in southeast MO at 20Z with
the associated surface low/frontal boundaries between KBLV and
KMVN. Deep convection capable of high rainfall rates posing any
flood potential will remain along and east of the surface low/front
and be a potential impacts for next 2-3 hours. Thereafter the surface
low and associated fronts will move to the east of the CWA in
association with northeastward movement of the short wave. Have
trimmed the flash flood watch to this region/far eastern CWA through
700 pm. Elsewhere scattered showers will continue in the post-
frontal/low cyclonic flow and impact portions of eastern MO and
southwest IL during the evening hours as they also progress to the
east. Clouds will be locked in across the area tonight and temperatures
will be gradually falling with low level CAA.

Glass

.LONG TERM:  (Sunday through Next Saturday)
Issued at 338 PM CDT Sat May 30 2015

A broad trof is forecast to remain in the picture for the next few
days with development of a closed low within the southern portion
of the trof late tonight into Sunday. Models differ some on the
location of this low and infact several models show 2 lows, however
the main low is forecast to remain over the lower MS Valley. Will
need to monitor the possibility of a more northern low as well
moving northeast across portions of southern MO towards STL. The
GFS suggests this and thus generates some showers across the
southeast third or so of the CWA on Sunday and into Sunday evening
and Monday. It is an outlier compared to the other solutions but I
can`t totally rule it out. At this time I am keeping with a dry
forecast. Cool weather featuring below average temperatures will
be the main story Sunday into Monday with a good deal of clouds as
an expansive surface high centered in southeast Canada maintains
control.

A slowly progressive upper air pattern is forecast after Tuesday
and this will eventually lead to a ridge aloft building into the
central U.S. This change aloft, the retreat of the surface high
and return of southerly flow will lead to a big warm-up during the
later half of the week and into Saturday with highs well into the
80s. By next weekend we will need to monitor short waves trying to
top the ridge aloft and potential for an encroaching east-west
front from the north, all of which indicate an increase in
thunderstorm potential.

Glass

&&

.AVIATION:  (For the 00z TAFs through 00z Sunday Evening)
Issued at 549 PM CDT Sat May 30 2015

Showers continue to rotate through the St Louis metro area behind
the surface low over southeast IL. May need to include a tempo
group for showers or at least VCSH in the St Louis metro area tafs
til 01Z or 02Z this evening. The 1000-2500 feet cloud ceilings
will likely drop to just below 1000 feet later this evening or
overnight. The cloud ceiling should rise into the MVFR catagory by
late Sunday morning. The n-nwly surface wind will veer around to a
n-nely direction on Sunday as the surface low moves northeastward
into the OH Valley region with surface ridging extending from the
northern Plains and Great lakes region south into MO.

Specifics for KSTL: May continue to get brief showers in the STL
area until about 02Z this evening. The 2000 foot cloud ceiling
should lower to just below 1000 feet later this evening and
overnight, then rise to around 2000 feet Sunday afternoon. The
n-nwly surface wind will veer around to a nely direction Sunday
afternoon.

GKS

&&

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

$$

WFO LSX






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