Severe Thunderstorm Warning 109, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
649 PM CDT Sat Jun 25 2022

.SHORT TERM...  (Through Late Sunday Night)
Issued at 156 PM CDT Sat Jun 25 2022

Currently we find ourselves atop a broad subtropical ridge. Within
the westerlies far to our north, a trough is moving east across
south central Canada and the northern Midwest with a much weaker
related shortwave trough further south into Iowa. At the surface,
a cold front stretches south from the Canadian low and then
southwest from the secondary low in Iowa. Southwesterly low level
flow (at about 850MB) has transported much warmer and more humid
air along the frontal zone and into our region. The axis of
greatest surface moisture is across northern Missouri and into
southeast Iowa just ahead of the surface cold front which is
pushing southeast out of the Kansas City area. It is within this
moist axis that we expect thunderstorms to begin to spawn later
this afternoon as the peak in afternoon heating works on this
moist air mass to produce extreme instability just as the surface
cold front adds convergence to help overcome the cap. This is most
likely to occur across northeast Missouri into southeast Iowa
sometime between 6 and 8PM with thunderstorms potentially growing
into a line and tracking southeast from there, potentially even
into the St Louis metro by around midnight. The greatest severe
weather threat this evening will be damaging winds as strong
updrafts may produce substantial cores aloft and multicell
clusters may merge into a broader convective complex.

Further to the west along the cold front, convergence is expected
to increase overnight in Kansas and western Missouri where
additional thunderstorms are expected to form along and behind the
front extending eastward into central Missouri. This activity may
persist into the morning on Sunday as the front moves through the
southern portion of our area. We do not expect much if any severe
weather threat from this as overall instability should be
decreasing, but it will be the best chance for significant
rainfall that some areas of central and southern Missouri have had
in several weeks. Any morning showers and storms will move
southeast with the frontal zone by late Sunday morning giving way
to a partly cloudy and much cooler day. High temperatures will be
some 15 degrees cooler on Sunday compared to today.

Kimble

.LONG TERM...  (Monday through Next Saturday)
Issued at 156 PM CDT Sat Jun 25 2022

The Canadian trough digs into the Great Lakes with northwesterly
flow aloft over the Midwest early next week. This will bring
broad surface high pressure south out of the Canadian Rockies and
through the Great Plains and Midwest early next week. We expect
some pretty nice late June weather from this, as clouds will be
suppressed by the northwesterly flow and temperatures will be
several degrees below normal, in the 70s and 80s. By Midweek the
surface high moves east and we begin to see a gradual warmup that
lasts through Friday. Temperatures will again warm above 90
degrees although for the moment the humidity does not look too
bad.

The next front will drop down from the north on Friday into
Saturday and will bring our next chance for showers and
thunderstorms. There's some indication that this front will stall
in or near the area for a day or two which could lead to prolonged
chances for rainfall.

Kimble
&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 648 PM CDT Sat Jun 25 2022

Cold front will continue to move south through the forecast area
between 00z and 06z Saturday. Otherwise, VFR flight conditions
expected through the forecast period outside of the stronger
storms. All activity will taper off at TAF sites by 13z Saturday.
South to southwest winds will veer to the northwest to north on
backside of the front with some brief gusts to around 20 kts at
times.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 8 PM CDT this evening for Boone MO-Callaway
     MO-Cole MO-Moniteau MO-Osage MO.

IL...None.
&&

WFO LSX

Hazardous Weather Outlook
National Weather Service Saint Louis MO
239 PM CDT Sat Jun 25 2022

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-261945-
Greene IL-Macoupin IL-Montgomery IL-Bond IL-Fayette IL-Clinton IL-
Marion IL-Washington IL-Randolph IL-Adams IL-Brown IL-Pike IL-
Calhoun IL-Jersey IL-Madison IL-Saint Clair-Monroe IL-Knox MO-
Lewis MO-Shelby MO-Marion MO-Monroe MO-Ralls MO-Pike MO-Boone MO-
Audrain MO-Moniteau MO-Cole MO-Osage MO-Callaway MO-Montgomery MO-
Lincoln MO-Gasconade MO-Warren MO-Saint Charles MO-Franklin MO-
Saint Louis MO-Saint Louis City MO-Jefferson MO-Crawford MO-
Washington MO-Saint Francois MO-Sainte Genevieve MO-Iron MO-
Madison MO-Reynolds MO-
239 PM CDT Sat Jun 25 2022

This Hazardous Weather Outlook is for portions of eastern and
central Missouri as well as west central and southwest Illinois.

.DAY ONE...Tonight.

A heat advisory is in effect for portions of central Missouri today.

There is a chance for thunderstorms across the area this afternoon
and tonight. A few thunderstorms could become strong to severe with
damaging winds the primary threat.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

There is a chance for thunderstorms across portions of the area
Sunday morning. A chance for thunderstorms returns to the area
Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening.

Kimble

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