Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 262037
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
337 PM CDT Sun Mar 26 2017

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 334 PM CDT Sun Mar 26 2017

Weak surface ridge to continue building into region this evening,
as next closed low lifts northeastward out of southern plains
towards forecast area. Developing warm front associated with this
system to lift northward on nose of LLJ, so will see increasing
chances of showers and some thunderstorms by midnight over central
MO. Then the activity will spread east and northeast through rest of
forecast area by daybreak.

During the day on Monday as surface low tracks along I-44 corridor
in MO, will see strong to severe storms possible, mainly over
southeast MO and southern IL where MU CAPES between 1000 and 2000
J/kg, decent effective shear and plenty of low level moisture. This
system to move out a bit quicker than yesterday`s, so will see
showers and storms taper off through the mid to late afternoon hours
from west to east.

As for temps, will see lows tonight in the mid 40s to mid 50s and
highs on Monday will be in the mid 50s to near 70.

Byrd

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 334 PM CDT Sun Mar 26 2017

All the guidance continues to support an active pattern through the
weekend with an especially wet period from Wednesday through early
Friday.

Present indications are that any precipitation on Monday night
should be confined to the early evening and mainly be located from
southeast MO into south central IL. The upper trof moving through
the region on Monday will be centered through the far eastern CWA at
00Z Tuesday and exiting quickly eastward into the OH Valley. The new
forecast trims back the western extent of the POPs and even this may
be a bit overdone, with the greatest threat of lingering showers in
south central IL.

Tuesday looks like a tranquil day with height rises aloft in the
wake of the departing system and in advance of the next deep upper
trof/low. High pressure will dominate the low-levels and low-level
moisture trapped within the ridge should make for a mostly cloudy
day with near average temps.

The ECMWF and GFS have come into better agreement with the large
scale mass fields Wed/Thurs with the GFS now trending towards the
more persistent ECMWF solution. The largest differences evolve
Friday into the weekend.

The gradual progression of the next southwest upper trof/low through
the south/central Rockies on Tuesday night will result in backing
flow aloft as well as height falls as a lead impulse moves into
western MO. The mass changes attendant with this system will also
lead to the development of a southerly LLJ which will remain focused
into eastern KS/western MO through 12Z Wednesday, and this is where
the majority of the precipitation should remain through daybreak.

Slow progession of the upper trof into the southern/central Plains
on Wednesday will result in continued height falls aloft/backing
upper flow and a slow eastward shift of the southerly LLJ. Thus the
greatest precipitation threat will be centered through western MO
and into parts of central MO through Wednesday afternoon. The
threat/coverage of precipitation should ramp-up Wednesday night into
Thursday as the upper trof and nearly vertically stacked system
continues to progress east and deep southerly flow and moisture
transport evolves, including a pronounced southerly LLJ. Attendant
with this would be a chance of thunderstorms.

As alluded to above, the GFS and ECWMF diverge Friday into the
weekend. The ECWMF is more progressive overall with this mid-late
week system departing early Friday and then the next upper trof/low
into the Plains on Sunday, and into the MS Valley on Monday. At
this point there is no clearly preferred solution and the forecast
is an ensemblistic approach with another threat of showers late
Saturday night into Sunday.

Glass

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 114 PM CDT Sun Mar 26 2017

First in a series of closed lows has lifted northeast away from
forecast area, so MVFR/IFR cigs will continue to lift through the
evening hours. However, as next system moves in from the
southwest, cigs will lower back down to MVFR/IFR. Otherwise,
southwest to west winds to become light and variable this evening,
then pick back up from the east to southeast as warm front lifts
northward through region on Monday.

SPECIFICS FOR KSTL:
First in a series of closed lows has lifted northeast away from
metro area, so MVFR cigs will scatter out by 22z Sunday. However,
as next system moves in from the southwest, cigs will lower back
down to MVFR by 12z Monday. Otherwise, southwest to west winds to
become light and variable this evening, then pick back up from
the southeast as warm front lifts northward through region on
Monday. Eventually winds will be from the southwest after 20z
Monday.

Byrd

&&

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

$$

WFO LSX



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