Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 282318
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
618 PM CDT Sun Sep 28 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 257 PM CDT Sun Sep 28 2014

The few short-lived spotty showers this afternoon in central MO
are associated with a vort max over western MO and are strongly
tied to diurnal instability. This vort max will move southeastward
tonight but instability should vanish after sunset, so see little
threat of sprinkles or isolated showers past 00z. Diurnal cu
should generally diminish with expansive high pressure continuing
to dominate the region and overnight lows quite comparable to last
night/early this morning. Some river valley fog will also be
possible from the pre-dawn hours to just after sunrise Monday.

Glass

.LONG TERM:  (Monday through Next Sunday)
Issued at 257 PM CDT Sun Sep 28 2014

A signficant pattern change will take place this week featuring
progression and amplification. Little impact expected on Monday with
high pressure in the lower troposphere continuing to dominate,
resulting in above normal temperatures and tranquil weather. A
deepening trof from southeast Canada into the Great Lakes and
northeast U.S. will send a backdoor cold front into northern
sections of the CWA on Tuesday, but it appears to be rather ill-
defined and should have no sensible weather other than knocking
a few degrees off the high temperatures. Things begin to change on
Wednesday as the western U.S. longwave trof begins to progress
into the central U.S.. More pronounced southerly low level flow is
forecast to develop and this will result in gradually deepening
moisture across the area as high pressure retreats eastward. The
models are exhibiting some timing differences with the eastward
spread of precipitation on Wednesday. The GFS is the most
agressive with a greater southwesterly component to the low-mid
tropospheric flow, and the NAM/local WRF the slowest with a
decidely more south-southeasterly low-level component. At this
time I have gone with a blend which brings chance pops into
central MO. The most active period appears to unfold from Wednesday
night into Thursday night with showers and thunderstorms likely.
First on Wednesday night a series of lead weak impulses in the
southwest flow aloft will traverse the region and combine with a
strengthening/veering LLJ and pronounced WAA regime. Then
Thursday/Thursday night the main shortwave trof and associated
cold front will move across the region accompanied by deep large
scale ascent. Much cooler weather expected in the wake of the cold
front Friday along with gusty northwest winds. I kept some slight
chance pops in the forecast Friday within the cyclonic flow across
the northeast half of the CWA, but this is more for a sake of
continuity as the digging secondary shortwave is further north
than indicated previously. Seasonably cool weather will persist on
Saturday with near normal temperatures for Sunday.

Glass

&&

.AVIATION:  (For the 00z TAFs through 00z Monday Evening)
Issued at 613 PM CDT Sun Sep 28 2014

VFR flight conditions and light variable winds will continue to
prevail under the influence of weak high pressure. Once again
expecting localized areas of MVFR and IFR fog in river valleys
overnight and before sunrise Monday. Fog should dissipate quickly
after sunrise and VFR conditions are expected thereafter.

Specifics for KSTL:

VFR flight conditions and light variable winds will continue to
prevail under the influence of weak high pressure.

Carney

&&

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

$$

WFO LSX






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