Frost Advisory 4, NWS St. Louis, MO

572 
WWUS73 KLSX 270833
NPWLSX

URGENT - WEATHER MESSAGE
National Weather Service St Louis MO
333 AM CDT Wed Apr 27 2022

ILZ058>060-064-065-069-070-074-079-099>102-MOZ074-075-084-085-099-
271300-
/O.CON.KLSX.FR.Y.0004.000000T0000Z-220427T1300Z/
Greene IL-Macoupin IL-Montgomery IL-Bond IL-Fayette IL-Clinton IL-
Marion IL-Washington IL-Randolph IL-Jersey IL-Madison IL-Saint
Clair-Monroe IL-Saint Francois MO-Sainte Genevieve MO-Iron MO-
Madison MO-Reynolds MO-
Including the cities of Cahokia, Sparta, Litchfield, Farmington,
Alton, Centralia, Belleville, Salem, Edwardsville, Chester, and
Vandalia
333 AM CDT Wed Apr 27 2022

...FROST ADVISORY REMAINS IN EFFECT UNTIL 8 AM CDT THIS MORNING...

* WHAT...Temperatures as low as 35 will result in frost formation.

* WHERE...Portions of south central and southwest Illinois. Portions 
  of southeast Missouri.

* WHEN...Until 8 AM CDT this morning.

* IMPACTS...Frost could harm sensitive outdoor vegetation. Sensitive 
  outdoor plants may be killed if left uncovered.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Take steps now to protect tender plants from the cold.

&&

$$

Gosselin

861 
WWUS73 KLSX 271132
NPWLSX

URGENT - WEATHER MESSAGE
National Weather Service St Louis MO
632 AM CDT Wed Apr 27 2022

ILZ058>060-064-065-069-070-074-079-099>102-MOZ074-075-084-085-099-
271245-
/O.CAN.KLSX.FR.Y.0004.000000T0000Z-220427T1300Z/
Greene IL-Macoupin IL-Montgomery IL-Bond IL-Fayette IL-Clinton IL-
Marion IL-Washington IL-Randolph IL-Jersey IL-Madison IL-Saint
Clair-Monroe IL-Saint Francois MO-Sainte Genevieve MO-Iron MO-
Madison MO-Reynolds MO-
Including the cities of Cahokia, Sparta, Litchfield, Farmington,
Alton, Centralia, Belleville, Salem, Edwardsville, Chester, and
Vandalia
632 AM CDT Wed Apr 27 2022

...FROST ADVISORY IS CANCELLED...

Temperatures stayed just warm enough to preclude more widespread 
frost development.

$$

Gosselin

Area Forecast Discussion
National Weather Service Saint Louis MO
240 PM CDT Tue Apr 26 2022

.SHORT TERM... (Through Late Wednesday Afternoon)
Issued at 235 PM CDT Tue Apr 26 2022

Currently aloft, the CWA is under northwesterly flow on the backside
of a trough departing the Middle Mississippi Valley, leading to weak
cold air advection over the region. At the surface, an area of high
pressure is slowly making its way through the Midwest, and is
currently roughly centered over Missouri. These features have
allowed for clear skies and below normal temperatures today, and
these conditions are expected to continue into tonight. With the
clear skies and expected calm winds, radiational cooling will allow
for temperatures to drop into the mid to upper 30s for most
locations tonight. There is some concern for patchy frost tonight,
though the window for this threat will be limited and primarily
confined to portions of southeastern Missouri in low-lying areas.
Therefore, we will continue to hold off on a frost advisory.

Tomorrow, the surface high will shift eastward as subtle upper-level
ridging builds into the Midwest. In turn, low-level flow will become
increasingly southerly and advect warm air into the CWA, bumping
temperatures up to near climatological normals during the
afternoon.

Elmore

.LONG TERM... (Wednesday Night through Next Tuesday)
Issued at 235 PM CDT Tue Apr 26 2022

Guidance consensus is that the subtle upper-level ridging will
build further into the Midwest, with low-level flow advecting
deeper moisture into the region. Thanks to a warm front draped in
proximity to the CWA and subtle disturbances riding along the
ridge per deterministic guidance, the chance for showers and
isolated thunderstorms will overspread the area from west to east
Wednesday night into Thursday. This general atmospheric set up
will remain in place through Friday, keeping the chance for rain
going across the region through the day, though there will likely
be plenty of dry time.

Through the latter half of Friday and into Saturday, a shortwave
will eject out into the Central Plains and move into the Midwest. At
the surface, the corresponding low will deepen across the Central
Plains and gradually make its way into the Northern Plains and
Midwest. Ensemble guidance per WPC Cluster Analysis continues to
differ on the exact phasing of this shortwave, leading to
uncertainty in the track of the surface low, the movement of the
warm front, and timing of a cold FROPA. However, the general
thinking based on current guidance is that the warm front will
lift northeastward ahead of the advancing cold front on Saturday.
Deep-layer shear across the narrow warm sector may top out around
40 kts per ensemble and deterministic guidance, though the
limiting factor for strong to severe storm potential will be how
much we can destabilize. Ensemble-based probabilities point to as
much as 500 J/kg of SBCAPE across southeastern Missouri and
southwestern Illinois ahead of the cold front, leading to low
confidence in severe weather across the CWA at the moment.

Beyond this point in the period, ensemble guidance seems to be split
between two camps: one where the shortwave slows and remains in the
vicinity of the Middle Mississippi Valley, and one where zonal to
southwesterly flow develops over the region. The first solution
would likely lead to northwest flow being sustained over the CWA to
some degree, translating to cooler and calmer conditions. The second
solution would have Saturday's cold front stall somewhere in
proximity to the CWA, and when paired with disturbances within the
westerly/southwesterly flow aloft, may lead to continuing rain and
storm chances. This solution is reflected the current Day 6-8 CIPS
extended analog guidance, which shows a majority of GEFS-based
analogs having above normal precipitation and heightened severe
storm chances. This outcome is by no means guarantied at this lead
time, but bears watching.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1212 PM CDT Tue Apr 26 2022

Confidence is high in dry and VFR flight conditions prevailing
through the forecast period. Generally light northwesterly winds
will become lighter and variable this evening as an area of high
pressure moves across the region. Overnight into tomorrow, winds
will gradually turn to out of the south from west to east as high
pressure continues further eastward.

Elmore

&&

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

WFO LSX

Hazardous Weather Outlook
National Weather Service Saint Louis MO
245 PM CDT Tue Apr 26 2022

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-271945-
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-
245 PM CDT Tue Apr 26 2022

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

.DAY ONE...Tonight.

No hazardous weather is expected at this time.

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

There is a chance for thunderstorms across parts of the area from
Thursday through Saturday evening, and then again on Monday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated tonight.

Elmore