Flood Watch 3, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1207 PM CST Sun Mar 6 2022

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 302 AM CST Sun Mar 6 2022

Convection has exited the area along with the cold front this
morning, and as of 3 AM the cold front is draped near
Springfield, IL through the St. Louis metro to near West Plains,
MO. This front will continue to sink southward today until it
stretches along the Arkansas-Missouri border by this afternoon.

Southwesterly flow aloft continues over the region and another
shortwave is exiting the Mountain West into the Kansas-Oklahoma
region. At the surface a low has formed across Oklahoma, connected
to the southern end of last night's cold front. Through the course
of the day the shortwave and surface low will move northeastward in
tandem into the mid-Mississippi Valley. Last night's front will
remain stalled near the Arkansas-Missouri border, with warm, moist
conditions to the south of the front and cooler conditions to the
north. Ensemble and deterministic guidance is indicating that
near 1000 J/kg of MUCAPE, 500 J/kg of SBCAPE, and a healthy cap
will develop along and south of the boundary during the afternoon.
These values could be underdone given how instability over
performed yesterday, and will be something to watch as the day
progresses.

WAA along southerly flow south of the boundary will generate
scattered showers and elevated thunderstorms across the southeast
Missouri and southern Illinois during the late afternoon and
evening. The elevated instability along the boundary will help
thunderstorms bloom, but the lack of significant instability north
of the boundary will keep these thunderstorms from becoming strong
to severe. Thunderstorms that form within the warm sector south of
the boundary during the late afternoon and early evening will have
access to deep layer instability and 30-40 kts of effective bulk
shear. These storms have the potential to form into discrete
tornadic supercells. The location of the frontal boundary this
afternoon will determine which areas are at risk for afternoon
severe thunderstorms.

The center of the surface low is expected to track northeast along I-
44 in Missouri during the evening hours, increasing coverage of the
showers and thunderstorms and lifting last night's front northward
as a warm front. As the low moves northeastward through the forecast
area during the evening hours it will drag an attendant cold
front through southern Missouri and southern Illinois. A second
round of thunderstorms is expected along this front as it moves
through near midnight. These thunderstorms will be able to access
the largely untapped instability through southern Missouri and
Illinois. 40 kts of effective bulk shear and 50-60 kts of 0-6 km
shear will be available across this area to organized the
thunderstorms that form along the cold front. Storms that become
severe will be capable of producing damaging winds and tornadoes.
The day 1 SPC slight and enhanced risk outlooks highlights the
area of concern for severe thunderstorm development tonight.

Showers and thunderstorms will persist across the remainder of the
forecast area as the surface low continues to push northeastward. A
corridor of heavy rainfall is expected along I-44 in Missouri and I-
70 in Illinois close to the center of the surface low, near 1.5
inches of rainfall through the entire system. This is a little lower
than previous forecasts, and the corridor of heaviest precipitation
has moved north. Soil moisture is less than 70% across the region,
and this precipitation is expected to fall over at least 6 hours.
Therefore, widespread flooding is not expected, though ponding or
localized nuisance flooding cannot be ruled out underneath strong
thunderstorms.

By early Monday morning the cold front and associated
severe thunderstorms will be east of the forecast area, and by mid-
morning Monday the region is expected to be largely precipitation
free. Behind this system northwesterly flow, an overcast sky, and
CAA will cool temperatures significantly Monday.MRM

.LONG TERM...  (Monday Night through Saturday)
Issued at 302 AM CST Sun Mar 6 2022

A surface high and westerly flow aloft will help keep the region dry
during the mid-week period. A slow warming trend will kick off after
Monday's cool temperatures. By mid-week a long wave trough will
begin to dig into the western CONUS, the axis of which will swing
into the central CONUS by the end of the work week. The next chance
of precipitation will come in association with this trough and a
surface low moving through the region. Temperatures will cool once
more below normal for the weekend behind this end of work week
system.

MRM

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1151 AM CST Sun Mar 6 2022

A broad area of MVFR ceilings with bases below 2000ft will linger
across southeast Missouri this afternoon, and will spread
northward as well as lower to IFR this evening. Additionally,
showers and thunderstorms will develop late this afternoon across
southern Missouri and spread north and northeast to affect the
entire area before 03Z this evening. Some of the storms could be
very strong to severe with 50kt+ wind gusts and a few tornadoes
across parts of southeast Missouri and southern Illinois this
evening. The system causing this inclement weather will move
northeast overnight, and precipitation should end for most of the
area before 12Z. Some lingering light snow is possible across
parts of northeast Missouri and west central/south central
Illinois.

SPECIFICS FOR KSTL:

VFR flight conditions are expected to prevail at Lambert until
this evening when showers and thunderstorms will affect the
terminal. CIGS/VSBYS will likely deteriorate rapidly to IFR range after
01Z when the precipitation begins to impact the terminal. Once the
ceilings drop to IFR, it seems likely that IFR conditions will
prevail at least through most of Monday morning. There may be some
occasional light snow on Monday morning, but temperatures should
be too warm for any accumulation, and any visibility impacts from
the snow should be brief.

Carney

&&

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

WFO LSX

Hazardous Weather Outlook
National Weather Service Saint Louis MO
334 AM CST Sun Mar 6 2022

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-070945-
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-Saint Francois MO-Saint Louis City MO-Saint Louis MO-
Sainte Genevieve MO-Shelby MO-Warren MO-Washington IL-Washington MO-
334 AM CST Sun Mar 6 2022

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 for parts of the area through the
evening. A few storms could become strong to severe, primarily
across southeastern Missouri and southern Illinois. Damaging wind
gusts in excess of 60 mph and a tornado or two are the primary
threats.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening.

MRM

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