Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 262310
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
610 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.
.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
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.
.AVIATION... (For the 00z TAFs through 00z Monday Evening)
Issued at 543 PM CDT Sun Mar 26 2017
Cloud ceilings will continue to improve this evening, although
UIN may remain in the MVFR catagory. Showers and a few storms
across eastern portions of KS and OK, ahead of an approaching
upper level and surface low will spread into the taf sites late
tonight and early Monday morning. The cloud ceiling will drop back
down into the IFR catagory as the low levels of the atmosphere
saturate. The westerly surface wind will weaken this evening,
then become easterly as the surface low approaches southwest MO,
and back around to a northwest direction Monday afternoon as the
surface low moves eastward through southern MO.
SPECIFICS FOR KSTL: Showers and a few storms across eastern
portions of KS and OK, ahead of an approaching upper level and
surface low will spread into the STL area by early Monday
morning. The cloud ceiling will drop back down into the IFR
catagory as the low levels of the atmosphere saturate. The
westerly surface wind will weaken this evening, then become
easterly as the surface low approaches southwest MO, and back
around to a northwest direction Monday afternoon as the surface
low moves eastward through southern MO. The showers and storms
will shift southeast of the STL area by early Monday evening.