Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 280831
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
331 AM CDT Wed Jul 28 2021

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 315 AM CDT Wed Jul 28 2021

Strong upper level ridging continues to dominate the western two-
thirds of the CONUS and has shunted the surface and H850 high to
the to the east and south of the region, respectively. As a
result, southerly surface winds have drawn upper 60s and 70
degree dewpoints into the region beneath warm air advection on
westerly flow in the low levels. This pattern will remain in place
through at least noon tomorrow, resulting in dangerous heat
across the region.

Today, heat index readings are expected to climb to around 105 area-
wide, though some mixing cloud keep things slightly cooler,
especially over the Ozarks. Tomorrow will likely be even hotter
after another day of warm and moist advection in the low levels,
with heat index readings in the 105-110 range. Tomorrow`s heat
could be limited by an approaching cold front, but the vast
majority of guidance keeps the front to our north through peak
heating. All in all, chances remain high that we`ll meet heat
advisory criteria (105+) across much of the area today and
tomorrow, so the heat advisory remains in effect.

BSH

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 315 AM CDT Wed Jul 28 2021

Confidence is rather high that a cold front will push into the area
at some point from late Thursday afternoon through Friday morning
before stalling somewhere in the region. Much of the guidance
continues to show at least a broken line of storms along the front,
though warm temperatures atop the PBL may limit storm development
to an extent. For storms that do develop, robust instability
ahead of the front would allow for storms to become fairly strong,
but 0-6km shear in the 20-30kt range will limit storm organization
and the potential for severe weather. Precipitable water will
also be quite high ahead of the front and warm cloud depths are
expected to be as deep as 4km. This should allow for any storms to
be very efficient rainfall producers, resulting in locally heavy
rainfall. There is also a low-end risk for flash flooding, mainly
for the potential training storms along wherever the front stalls.

The pattern will remain fairly active through the weekend as an
upper level trough deepens over the eastern CONUS. This will allow
for a series of shortwaves and additional shots of cooler air to
reinforce the stalled front. This front will be the focus for
additional rounds of showers and storms, though there is still a
good deal of uncertainty as to where exactly that front will be at
any given time. This front is expected to be fairly stationary
through the weekend, which would open the door for multiple rounds
of heavy rainfall over some areas.

Things are expected to dry out early next week as the upper
trough continues to deepen and push the front out of the region.
This will allow for even cooler temperatures to build in next
week.

BSH

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 949 PM CDT Tue Jul 27 2021

Surface high pressure ridge extending from OH southwest into
southeastern MO will move slowly southeastward. Light surface
winds late tonight will become southwesterly Wednesday afternoon,
albeit still weak. Clear late tonight, then some high level clouds
on Wednesday with a few diurnal cumulus clouds possible Wednesday
afternoon. Could not rule out a brief period of light fog at SUS
and CPS late tonight/early Wednesday morning.

SPECIFICS FOR KSTL: Surface high pressure ridge extending from OH
southwest into southeastern MO will move slowly southeastward.
Light surface winds late tonight and Wednesday morning will
become south-southwesterly late Wednesday afternoon and evening,
albeit still weak. Clear late tonight, then some high level clouds
on Wednesday with a few diurnal cumulus clouds possible Wednesday
afternoon.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     97  77  99  74 /   0   0   5  30
Quincy          94  74  95  70 /   0   0  30  40
Columbia        96  74  97  74 /   0   0   5  10
Jefferson City  97  74  98  76 /   0   0   5  10
Salem           94  74  97  70 /   0   0  20  30
Farmington      96  72  99  72 /   0   0   0   5

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from noon today to 9 PM CDT Thursday for Audrain
     MO-Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
     Gasconade MO-Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln
     MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-
     Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Charles MO-
     Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Shelby MO-Warren MO-Washington MO.

IL...Heat Advisory from noon today to 9 PM CDT Thursday for Adams IL-
     Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-
     Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-
     Montgomery IL-Pike IL-Randolph IL-Saint Clair-Washington IL.

&&

$$

WFO LSX


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