Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 202026
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
326 PM CDT Fri Apr 20 2018

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 243 PM CDT Fri Apr 20 2018

After an unseasonably cold and frosty early morning, temperatures
have quickly warmed into the lower 60s across much of the region.
This rapid warming was due to plenty of solar insolation along
with a very dry atmosphere with very low relative humidity. Lows
tonight will be warmer than the previous night, albeit still a
little below normal. The cloud cover will increase on Saturday
well ahead of an upper level low and associated surface low over
the central Plains, but it appears that any precipitation will
remain west of the forecast area with the lower levels of the
atmosphere still relatively dry. Even though there will be more
cloud cover on Saturday, high temperatures should be similar to
Friday.

GKS

.LONG TERM...  (Saturday Night through Next Friday)
Issued at 243 PM CDT Fri Apr 20 2018

The upper level low and associated surface low will drop
southeastward through the southern Plains and pass well south of
the forecast area on Sunday, moving through AR with showers moving
into southeast MO Saturday night and into southwest IL on Sunday.
The northern fringes of the precipitation shield will move
through the Interstate 70 corridor, although the better QPF will
still be confined to southeast MO and southwest IL. There is still
some uncertainty as to how quickly the upper level low will
depart our region, but with the typical slow nature of these
weather systems showers will likely linger across southeast MO and
southwest IL Sunday night and Monday. There should be a break in
the threat for rain Monday night and Tuesday, but then a northern
stream upper level trough and associated cold front will drop
southeastward through the forecast area with showers Tuesday night
and Wednesday. The operational GFS model is a little stronger and
quicker with the progression of the upper level trough and cold
front compared to the slower and weaker solution of the ECMWF. The
models then bring a deepening upper level trough and another cold
front through our area with showers Thursday night into Friday.
This upper level troughing and successive cold fronts will keep
the temperatures from getting too warm with the tendency to
remain at or at least slightly below normal for late April.

GKS

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1146 AM CDT Fri Apr 20 2018

Ridge of high pressure centered over northwest IL will continue
moving slowly eastward. An east-southeast surface wind can be
expected through the period. VFR conditions will continue with
just an increase in mid-high level cloudiness expected tonight and
Saturday, well ahead of a low pressure system moving into the
southern Plains.

SPECIFICS FOR KSTL: Ridge of high pressure centered over northwest
IL will continue moving slowly eastward. An east-southeast
surface wind can be expected through the period. VFR conditions
will continue with just an increase in mid-high level cloudiness
expected tonight and Saturday, well ahead of a low pressure system
moving into the southern Plains.

GKS

&&

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

$$

WFO LSX



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