Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 220453
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1153 PM CDT Mon Jul 21 2014

.UPDATE:
Issued at 920 PM CDT Mon Jul 21 2014

The going forecast remains on track this evening, with only minor
changes to account for near-term trends. The HRRR has continued to
indicate some showers developing over northeastern MO and west
central IL around daybreak, but recent runs have gotten more
conservative. Therefore, have maintained the dry forecast given
low confidence.

JP

&&

.SHORT TERM: (Tonight through Tuesday)
Issued at 322 PM CDT Mon Jul 21 2014

The forecast is evolving pretty much as expected today and the
trends anticipated through tomorrow still look on track. Temperatures
tonight will be milder than last night with a gradual increase in
some mid/high clouds from the northwest late tonight. Still
wondering if we might see a few high based showers with this mid
level moisture and steep lapse rates near and just after dawn
across north central/northeast Missouri, but at this point my
confidence is not high enough to add pops and later shifts will
need to keep a close eye. Otherwise the hotest day of the week is
still on tap for Tuesday with a strong low-level thermal ridge
focused across the northern half of the CWA with H85 temps above
+22 degC, favoring widespread highs in the 90s. The northwest
1/3-1/2 of the CWA should have peak heat index values above 100
degrees. If the dew points top the mid 70s across northeast
Missouri, then some locations might see heat indices hit advisory
criteria of 105+. At this point my forecast is just below that
value. Warm mid level temperatures of +12 to +14 degC should
sufficiently cap surface based convection.

Glass

.LONG TERM: (Tuesday Night through Next Monday)
Issued at 322 PM CDT Mon Jul 21 2014

A short wave will dig across the upper-mid MS valley and into the
Great Lakes Tuesday night into Wednesday, and this will send a
formidable cold front across the region. The air mass ahead of the
front will be moist and unstable and height falls/cooling aloft
associated with the upper wave should be sufficient for scattered
thunderstorms/multicell clusters with the progressing front. The
front and precipitation threat should be south of the CWA by early
Wednesday evening. Deepening of the eastern trof and and an expansive
surface high in the wake of the cold front will bring another nice
couple of days with below average temperatures for Thursday/Friday.
However by late Friday and especially Friday night into Saturday
we will be looking at increasing precipitation chances again -
first in association with several northwest flow disturbances and
the retreating front, and then with another cold front passage.

Glass

&&

.AVIATION:  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1144 PM CDT Mon Jul 21 2014

VFR with sly to swly winds aob 10kts is expected thru Tues
afternoon. SUS may see some FG a couple of hours before sunrise
Tues morning, however, confidence in this event is decreasing due
to greater dewpoint spread and ssely flow. There is some
indication that TSRA may form during the pre-dawn hours Tues
morning across the srn half of IA. If these TSRA do form, believe
they will remain N of UIN, but this remains uncertain. A cdfnt is
expected to approach the region Tues evening. This fnt may bring
isod to sct TSRA along and just ahead of the fnt with winds
becoming nly behind the fnt. Due to less and somewhat uncertain
coverage of TSRA, have only added VCTS for now.

Specifics for KSTL: VFR and dry thru the TAF period with sly to
swly winds ahead of an approaching cdfnt. This fnt is expected to
push thru the terminal late Tues night. This fnt may be
accompanied by TSRA. However, there is too much uncertainty
regarding coverage and occurrence and have kept out of TAF for now.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX





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