Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190850

Area Forecast Discussion
National Weather Service Saint Louis MO
350 AM CDT Mon Mar 19 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 320 AM CDT Mon Mar 19 2018

NZUS99 KLSX 190822

Stacked system along KS/OK border will continue to slide east
today across southern portions of Missouri. Initial activity to
diminish as it slides northeast across region.

Models still show decent low level moisture convergence and weak
CAPEs as system becomes occluded. So area of showers and storms,
currently over OK/KS as of 08z, will continue to spread east and
northeast today. The best chance for rain will be late this
morning through the afternoon hours. This will affect
temperatures across the region today, as they will be dependent
on cloud cover and precip. For now have the coolest conditions
along the I-70 corridor where highs may only reach the mid 40s.

By this evening, system will be exiting region with precipitation
tapering off from west to east. Otherwise, clouds to linger with
winds becoming northerly. So will see temps drop into the 30s.


.LONG TERM...  (Tuesday through Sunday)
Issued at 320 AM CDT Mon Mar 19 2018

Lingering rain showers across the southeastern CWA should taper
off tomorrow morning as the aforementioned low pressure system
moves away from the area. Models depict several weak PV anomalies
moving through the central CONUS during the middle of the week
within northwest flow aloft, but none of these appears to be
strong enough to support widespread pcpn. Periods of increased
cloudiness appear more likely attm, but a few sprinkles are
certainly possible.

By the end of the week and into next weekend, a lead shortwave
ahead of a much larger closed low pressure system over the PacNW
will support a chance of precipitation across MO/IL. However,
several issues are producing low confidence in the late week and
weekend forecast attm. First, the lead shortwave appears to be
too weak to break down the upper ridge as quickly as the models
suggest. Second, there are some model differences regarding the
degree of interaction between this feature and two others, and any
interaction would affect the speed and location of the upper
disturbance. Third, there is poor agreement between the ECMWF,
GFS, and GEM regarding the placement of surface features.
Fortunately, there are still several days for the models to come
into better agreement.

Temperatures will gradually warm from Tue through Sat. There may
be a sharp E-W temperature gradient across the area on Thu night
into Fri if models are correct with the placement of a warm
front. However, as noted above, poor agreement between models
regarding the placement of surface features also creates low
confidence in the temperature forecast for the end of the week and
next weekend.



.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1154 PM CDT Sun Mar 18 2018

Main changes to prev TAFs were to improve conditions at UIN and
show possible IFR cigs at COU. While IFR cigs have developed and
impacted COU, do not currently believe these will linger too long,
esp given VFR conditions so close. It is possible cigs will become
VFR at COU overnight. Otherwise, other changes were small tweaks
to precip, etc.

SPECIFICS FOR KSTL/KSUS/KCPS: Not a lot of changes from the prev
TAFs, but did add VCTS Mon afternoon. Mention of TS may need to be
added earlier, possibly to the 17z group, with future updates. VFR
conditions are not far south of the terminals and can not rule out
terminals going VFR as the sfc low moves south of the area.
Otherwise, only some minor changes.





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