Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

FXUS63 KLSX 240355

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1055 PM CDT Mon May 23 2022

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 215 PM CDT Mon May 23 2022

A surface high is sliding across the Great Lakes region, it`s
peripheral influence felt by easterly winds and periods of mostly
clear sky. In areas that have seen a couple hours of sunshine
have warmed into the mid to upper 60s, and are on track to be a
couple degrees warmer than yesterday.

In the mid-levels, a longwave trough has deepened into the
western half of the CONUS and moved eastward, amplifying the
southwesterly mid-level flow across the region. Overnight a low-
level trough will develop across the Oklahoma and Texas panhandles
in response to the advancing mid-level trough. The subsequent
southerly low-level flow across the mid-Mississippi Valley will
continue to advect warm, moist air into the region overnight and
into the day tomorrow. Precipitation will blossom across areas to
our west Tuesday associated with the warm air advection and the
warm front of the approaching low. While these showers and
isolated thunderstorms are expected to stay to the west of our
forecast area, I cannot rule out a stray showers forming across
portions of central and northeast Missouri Tuesday. The better
chance of showers and isolated thunderstorms continues to be tied
to the advance of a mid-level shortwave into the forecast area
Tuesday evening into Wednesday. This more robust ascent will be
able to tap into the plentiful moisture that built across the
region over preceding days. Instability appears to be at a
premium, though with cooling heights aloft associated with the
approaching mid-level trough and warming in the low-levels, an
isolated thunderstorm or two is possible.

Temperatures on Tuesday will be a few degrees warmer than today,
highs will push the low to mid 70s across most of the forecast area
under the warm air advection regime.


.LONG TERM...  (Wednesday through Next Monday)
Issued at 215 PM CDT Mon May 23 2022

Key messages in the extended forecast:

1. Best chance for showers and thunderstorms this period will be
Tuesday night into Wednesday.

2. Thunderstorm chances are starting to improve as the surface low
is expected to track northwest of the forecast area.

3. Memorial Day weekend is shaping up to be seasonally warm and dry.

Showers and thunderstorms will continue into a portion the day
Wednesday as the mid-level longwave trough continues its march
eastward into the mid-Mississippi Valley and the surface low moves
north-northeast into the region. The cold front will march through
the forecast area Wednesday night into the overnight hours, bringing
another round of showers and thunderstorms to the area. A
northwesterly trend in the location of the surface low as it passes
through the mid-Mississippi Valley is opening the region up to
increased instability ahead of surface low and attendant cold
front. Some guidance is starting to indicate sufficient
instability for thunderstorm development across portions of the
CWA, but this instability is dependent on surface warming ahead of
the cold front and could be limited by ongoing precipitation or
lingering cloud cover. Regardless, this mid-week system continues
to be one to watch. 25-30 kts of southerly 0-6 km and effective
bulk shear will help to organize any thunderstorms that develop
along the cold front. How much, if any, dry time will occur
between these two rounds is uncertain at this time.

While sufficient moisture will be available for numerous showers and
thunderstorms during the mid-week, the threat for heavy rainfall and
flooding impacts is diminishing across the area. The EFI and Shift-
Of-Tails is no longer highlighting the forecast area for
climatologically high QPF amounts, and the WPC QPF Cluster Analysis
shows that the axis of heaviest rainfall will stay to our south.

A majority of the WPC Cluster Analysis members indicate that by
Friday the mid-level trough will be exiting the area, and the rising
heights associated with the advancing ridge will help shunt
precipitation to the east. However, about 30% favor a slower
progression of the mid-level trough, which could keep light
precipitation lingering across the forecast area into Friday. The
mid-level ridge will build into the region by the weekend as the mid-
level jet scoots north of the forecast area. While I cannot rule out
a stray shower or thunderstorm, rising heights aloft will result
in a mostly dry forecast.

Temperatures will increase over the weekend in response to the
advance of the mid-level ridge. The NAEFS ensemble guidance is
indicating 850mb temperatures will be near the 90th climatological
percentile for the time of year. While surface temperatures do not
currently look like record-breakers, we will warm up above normal
for the holiday weekend.



.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1043 PM CDT Mon May 23 2022

Little to no impact is expected tonight through at least mid-
morning Tuesday with VFR persisting in this timeframe. Between
mid-morning and early afternoon, gusty east-southeasterly winds
are expected to return with gusts approaching 20 knots through the

The main concern will be in the late afternoon and evening as a
warm front lifts northward through the region. KCOU/KJEF will see
the potential for shra/vcts as as soon as 21z-00z period, but it
is likely to remain scattered/isolated. Latest hi-res products
are a little quicker with the east/northeast progress, introducing
shra/vcts to metro terminal between 02z-04z, overspreading much
of the area with shra/vcts by 06z. With the quicker solutions,
moisture depth and resulting cigs are more likely to drop from VFR
to MVFR. There are indications that localized pockets of marginal
vsby reductions and IFR cigs will accompany pockets of heavier
rainfall potential late in the period.





WFO LSX is the U.S. government's official web portal to all federal, state and local government web resources and services.