Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 191748

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1248 PM CDT Mon Mar 19 2018

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

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 18z TAFs through 18z Tuesday Afternoon)
Issued at 1228 PM CDT Mon Mar 19 2018

Strong low pressure over southwest Missouri is driving a broad
area of showers and a few thunderstorms up into central and
eastern Missouri as well as southwest Illinois this afternoon. The
heaviest rain will fall along and south of the I-70 corridor today
and into the evening, with widespread low MVFR and IFR cigs/vsbys
associated with the rain. VFR flight conditions are expected to
prevail north of the precipitation across northeast Missouri and
west central Illinois. Rain will taper to sprinkles or drizzle
overnight and flight conditions should improve to higher end MVFR
between 2000-3000ft across most areas except probably the eastern
Ozarks which will likely stay in the lower clouds into Tuesday


Expect low MVFR conditions with intermittent IFR through much of
the afternoon at Lambert. An occasional rumble of thunder is also
possible. The heaviest rain should move north and east of the
terminal by 00Z, but think sprinkles or a little drizzle with cigs
below 2000 feet will continue to prevail for several more hours.
Latest guidance suggests that the last of the precip could move
out of the Metro Area by 06Z or shortly thereafter. Expect
ceilings to lift after this occurs, but am not sure how much.
However, most guidance agrees that flight conditions will improve
to VFR at some point Tuesday morning.





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