River Flood Warning 102, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
529 AM CDT Tue Jul 2 2024

.KEY MESSAGES...

- Several rounds of thunderstorms are expected through Thursday
  with a risk for severe weather and locally heavy rainfall with
  possible flash flooding.

- The first round of strong to severe thunderstorms will be this
  evening over parts of central and northeast Missouri into west
  central Illinois.

- Hot and humid weather is expected over parts of the area through Thursday.
  Heat index values over central and northeast Missouri will
  climb above 100 degrees this afternoon.

&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 330 AM CDT Tue Jul 2 2024

Dry weather is expected today before a upper trough currently over
the Rockies moves into the Missouri Valley by this evening. The
ascent caused by trough will cause thunderstorms to develop along a
front across northwest Missouri and southwest Iowa this afternoon.
These storms are expected to eventually move east into the northern
CWA by this evening. MLCAPES of 1000-2000+ J/kg and deep layer shear
of 30-40 knots suggests that these storms should be able to continue
to be severe as they move into northeast Missouri before decreasing
in strength as they move east during the late evening and early
overnight hours as the instability diminishes to the south and east.
Available CAMS are showing the most likely mode will be linear by
the time the storms move into the CWA, so damaging winds remains the
primary threat along with a brief QLCS tornado. Large hail is also
possible.  I also expect locally heavy rainfall as PWATS will be
over 2-2.5" and there will be deep warm cloud depths. Have held off
on issuing a Flood Watch as CAMS are showing progressive storm
motions and little potential for training at this time.

The coverage of showers and thunderstorms will decrease they move to
the southeast overnight as ascent from the upper trough moves off to
the northeast and the instability will decrease farther to the south
and east.  There will be the potential for mainly scattered shower
and thunderstorm development on Wednesday as the cold front/outflow
boundary moves southeast through the CWA.  Given the CAPE/shear
parameters over southeast Missouri into southwest Illinois tomorrow
afternoon, a few severe thunderstorms will be capable of producing
damaging winds.

Winds have shifted to the south-southeast over the area as the
surface high has now moved into the northeast CONUS.  Higher
humidity will stream back into the western CWA with 70 dewpoints
expected over central and northeast Missouri by this afternoon. With
highs climbing back into the lower to middle 90s today, heat index
values will be in the 100-105 degree range over central Missouri
today. Highs tomorrow will be in the upper 80s to lower 90s as the
front/outflow boundary moves across the area.  Still with dewpoints
in the lower-mid 70s, some locations over southeast Missouri will
have heat index readings near 105.

Britt

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 330 AM CDT Tue Jul 2 2024

The best chance for thunderstorms (70-90%) during the entire
forecast period areawide will continue to be late Wednesday night
into Thursday morning when there will be the another upper trough
moving along the front and a 35 knot low level jet setting up strong
moisture convergence over the area.  Both the ECMWF and the GEFS are
showing PWATS that are at the max climatology for the date pointing
to the potential for locally heavy rainfall. Then there will be the
potential for another round for severe weather on Thursday afternoon
and evening when yet another shortwave trough will interact with a
front over central and southeast Missouri. The LREF is showing
MLCAPES of 2000-2500 J/kg and deep layer shear around 30-40 knots
which suggests that a few severe storms will be capable of producing
large hail and damaging winds.

The LREF is showing that a cold front should move through the area
on Thursday night which will keep high chance/likely POPs (40-60%)
for showers and thunderstorms.  Here again the the atmosphere will
remain conducive the locally heavy rainfall until this fronts moves
through the area.  Then high pressure will move across Missouri and
Illinois and most of the LREF members are showing the area dry
Friday night through Saturday night before next trough approaches
the area late in the weekend and early next week.

Britt

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 524 AM CDT Tue Jul 2 2024

Mainly dry and VFR conditions are expected through 00Z. Then
showers and thunderstorms over western Missouri will move into the
area this evening, affecting UIN between 03-07Z, and COU and JEF
after 06Z.  Any of the heavier showers or thunderstorms will have
the potential to reduce ceilings and visibilities to MVFR or
possible IFR conditions in heavy rain. The stronger storms will
have the potential to produce wind gusts over 35 knots at UIN
tonight. Winds will be out of the south today with gusts to 20
knots at UIN.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

WFO LSX

Hazardous Weather Outlook
National Weather Service St Louis MO
427 AM CDT Tue Jul 2 2024

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-030930-
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 IL-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-
427 AM CDT Tue Jul 2 2024

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

.DAY ONE...Today and tonight.

There is a chance of thunderstorms late this afternoon into tonight.
A few of these storms could be severe over northeast and central
Missouri as well as west central Illinois. The primary threat will be
damaging winds, with brief tornado and large hail also possible.
Locally heavy rainfall is also possible.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

There is a chance of thunderstorms Wednesday through Friday. A few
thunderstorms could be severe Wednesday afternoon and evening as
well as Thursday. Locally heavy rainfall will continue to be
possible.

There is a chance of thunderstorms again on Sunday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening.

Britt