Special Weather Statement, NWS St. Louis, MO

Area Forecast Discussion
National Weather Service Saint Louis MO
350 AM CDT Sat Aug 17 2019

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 350 AM CDT Sat Aug 17 2019

Main concern in the short term is the potential for severe weather
and flooding this morning.   Will leave the flash flood watch in
effect through this morning.

Showers and thunderstorms continue to develop across western
Missouri and Kansas early this morning in an area of strong 925-
850mb moisture convergence just north of a surface warm front. These
clusters of storms will move east over the next few hours as the
nose of the 40kt low level jets veers to the east.  This will bring
the storms through the CWA between 4-10 am. There is still some
potential for a few severe thunderstorms given the latest
objective analysis depicting MUCAPES over the area between
1000-2000 J/kg and deep layer shear of 40-50kts suggesting that a
few cells could produce large hail and damaging winds. In
addition, will leave the flash flood watch in place given forecast
PWATs near 2.0" and deep layer cloud layers of 13.0K ft. This
indicates that the storms will be very efficient rain producers.
In addition, there will be the potential for training, hence the
concern for flash flooding.  Thunderstorms will move east and
diminish by mid morning as the low level jet weakens and continues
to veer to the east.

The front will move north during the day, but the atmosphere will
become capped, so will only carry a slight chance of thunderstorms
over northeast Missouri and west central Illinois. The chance for
thunderstorms will increase tonight as the GFS/NAM are in decent
agreement that another shortwave trough will move across the
Midwest late tonight into early Sunday. There will be sufficient
instability/ moisture transport ahead of the attendant cold front
to go with likely PoPs over central and northeast Missouri as well
as west central Illinois with chance PoPs elsewhere. The chance
of thunderstorms will continue along the front in a very unstable
atmosphere into Sunday afternoon.

Britt

.LONG TERM...  (Sunday Night through Friday)
Issued at 350 AM CDT Sat Aug 17 2019

Main concern for next week is the potential for heat on Monday and
Tuesday. The deterministic global models as well as the GEFS mean
continue to show an upper high building across the central CONUS.
While this will cause heights to rise which will suppress
convective development development, the GFS and Canadian is
showing a low level front stalling over the area which will act
for the focus for some thunderstorm development which lends to
forecast uncertainty. The ECMWF and GFS are depicting 850mb
temperatures in the lower 20s C which support surface temperatures
in the 90s, and a surface boundary could cause pooling of
dewpoints in the 70s. This would result in heat index values
reaching 105 in some areas both Monday and Tuesday assuming that
enough thunderstorms do not develop either day.

By Tuesday night and Wednesday, a shortwave trough will move
through the Midwest in the northwesterly flow aloft bringing a
chance of showers and thunderstorms. Cooler air will move in
behind the attendant cold front causing temperatures to fall
closer to normal. Another system late in the week will bring
another chance of showers and thunderstorms.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1130 PM CDT Fri Aug 16 2019

Forecast confidence has increased since the last TAF issuance.
Guidance has come into better agreement, matching well with how I
anticipate the morning to play out.

Storms have finally begun to develop in eastern KS. Initial
storms have develop a bit farther south than anticipated, but I'm
expecting the focus for additional storm development to shift NE
through the morning hours. Forecast guidance in good agreement
showing these storms impacting UIN just prior to sunrise. Model
consensus is worse further south, with confidence in storm chances
decreasing toward I-70. However, given the southward extent of
the storms currently over eastern KS, confidence in storms
impacting COU and the STL terminals is high enough to include a
tempo group in those TAFs.

Storms are expected to diminish after sunrise and generally remain
out of the forecast through the remainder of the TAF period. The
exception is toward the MO/IA border, where more storms are expected
to develop tomorrow evening. Not confident they will actually
impact UIN, so sticking with VCTS for the time being.

BSH

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flash Flood Watch until 1 PM CDT this afternoon for Audrain MO-
     Boone MO-Callaway MO-Knox MO-Lewis MO-Marion MO-Monroe MO-
     Montgomery MO-Pike MO-Ralls MO-Shelby MO.

IL...Flash Flood Watch until 1 PM CDT this afternoon for Adams IL-
     Brown IL-Pike IL.

&&

WFO LSX

Hazardous Weather Outlook
National Weather Service Saint Louis MO
445 PM CDT Fri Aug 16 2019

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-171200-
Adams IL-Audrain MO-Bond IL-Boone MO-Brown IL-Calhoun IL-Callaway MO-
Clinton IL-Cole MO-Crawford MO-Fayette IL-Franklin MO-Gasconade MO-
Greene IL-Iron MO-Jefferson MO-Jersey IL-Knox MO-Lewis MO-Lincoln MO-
Macoupin IL-Madison IL-Madison MO-Marion IL-Marion MO-Moniteau MO-
Monroe IL-Monroe MO-Montgomery IL-Montgomery MO-Osage MO-Pike IL-
Pike MO-Ralls MO-Randolph IL-Reynolds MO-Saint Charles MO-
Saint Clair IL-Saint Francois MO-Saint Louis City MO-Saint Louis MO-
Sainte Genevieve MO-Shelby MO-Warren MO-Washington IL-Washington MO-
445 PM CDT Fri Aug 16 2019

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

.DAY ONE...Tonight.

Thunderstorms are likely tonight. Some of these storms may be severe
with damaging winds, hail, and isolated tornadoes possible. Heavy
rainfall is also possible, and a Flash Flood Watch has been issued
for areas where the heaviest rainfall is expected.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

There is a chance of thunderstorms across the area through Sunday. A
few of these storms could be strong to severe on Saturday, Saturday
night, and Sunday.

There is also a chance of thunderstorms from Tuesday through
Thursday.

Heat index readings will climb to around 100 to 105 degrees across
parts of the area on Monday and Tuesday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed tonight and overnight.

Kanofsky

Special Weather Statement
National Weather Service St Louis MO
409 AM CDT Sat Aug 17 2019

MOZ026-027-034-171000-
Marion MO-Monroe MO-Shelby MO-
409 AM CDT Sat Aug 17 2019

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN MARION...SOUTHERN
SHELBY AND NORTHEASTERN MONROE COUNTIES UNTIL 500 AM CDT...

At 408 AM CDT, Doppler radar was tracking a strong thunderstorm over
Clarence, moving east at 30 mph.

Penny size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Monroe City, Shelbina, Warren, Clarence, Shelbyville, Maud, Emden,
Philadelphia and Hunnewell.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3969 9171 3962 9172 3961 9230 3979 9229
      3989 9174
TIME...MOT...LOC 0908Z 262DEG 24KT 3971 9223

Carney