Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KLSX 150504
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1204 AM CDT Mon Sep 15 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 322 PM CDT Sun Sep 14 2014

Low level ridge extending from the Ohio Valley into the lower and
middle MS Valley will drift eastward tonight, but maintain an
influence on southeast MO and southern IL promoting overnight lows
in the upper 40s. Meanwhile the main concern will be the threat of
showers and thunderstorms tonight. Westerly flow aloft will advect a
region of relatively steep mid level lapse rates presently across
the Plains across Missouri and into IL tonight. Beneath this, a
rather broad low level jet will ramp up this evening across the
central Plains and veer to more westerly overnight.  The
differential advections will result in elevated instability with the
LLJ providing good moisture transport/warm advection and lift.
Current thoughts are elevated showers and thunderstorms will develop
near the terminus of LLJ with showers and thunderstorms spreading
across northern MO and into west central IL during the late night
hours. Given the progressive nature of the flow aloft, I have
favored the more agressive eastward and southern extent of the NAM
and local WRF.

Glass

.LONG TERM:  (Monday through Next Sunday)
Issued at 322 PM CDT Sun Sep 14 2014

(Monday through Wednesday)

Main concern deals with precipitation chances through Monday night.

The GFS and NAM are in decent agreement with the speed and depth of
the shortwave trough currently that is dropping south into Montana
that is expected to deepen and move southeast across Missouri and
Illinois late on Monday.   Expect the greatest concentration of
showers and thunderstorms to be across central and northeast
Missouri and west central Illinois on Monday morning where the GFS
and NAM is showing the strongest low level moisture convergence
ahead of the approaching trough.  This morning`s 12Z NSSL WRF
depicts this idea, showing showers and thunderstorms over northern
Missouri on Monday morning.  Will keep categorical PoPs going during
morning, and then keep likely PoPs going into the afternoon over
central parts of the CWA as the cold pushes south through the CWA.
There will be some lingering showers over southeast Missouri into
southern Illinois into Monday night as the cold front exits the area.

Tuesday and Tuesday night then will be dry as heights rise behind
the trough.  I did add some slight chances of thunderstorms across
central Missouri on Wednesday and Wednesday night as the GFS has
been consistent in showing some light QPF with a weak shortwave
moving southeast across the area in northwesterly flow aloft.

For temperatures, I used a blend of MOS guidance tomorrow, favoring
the cooler NAM values where I expect there to be precipitation and
earlier frontal passage in the north earlier in the day.   Used a
blend of MOS guidance for highs on Tuesday which works well in
mixing down 900mb temperatures.  Lows are the the agreeable MOS
guidance.

(Thursday through next Sunday)

Still looks like the end of the work week should stay dry as surface
high moves across the area.  The chance of rain will increase next
weekend as both the ECMWF and GFS show a trough approaching from the
west on Saturday with the attendant cold front crossing the area
Saturday night and Sunday.  Temperatures will climb back to near
normal by late in the week as 850mb temperature climbs into the mid
teens Celsius.

Britt

&&

.AVIATION:  (For the 06z TAFs through 06z Monday Night)
Issued at 1152 PM CDT Sun Sep 14 2014

Some isolated showers/thunderstorms have begun to develop over
northwest MO on nose of low level jet. Still expect activity to
slide east across northern MO, so have showers/isolated
thunderstorms moving into KUIN by 08z. Then as jet veers to the
east, activity to slide southeast and diminish a bit as it
approaches tafs along I-70. So kept vcnty shower mention for now.
In the meantime, cold front to make progress to the south across
forecast area moving thru KUIN by 18z, KCOU by 19z and metro area
between 20z-21z. As for winds, to persist from the south, before
veering to the west then north behind the boundary. Cigs to remain
vfr til frontal passage, then lower to mvfr behind the front.

Specifics for KSTL:
Some isolated showers/thunderstorms have begun to develop over
northwest MO on nose of low level jet. Still expect activity to
slide east across northern MO. Then as jet veers to the east,
activity to slide southeast and diminish a bit as it approaches
the metro area. So kept vcnty shower mention for now. In the meantime,
cold front to make progress to the south across forecast area
moving thru metro area between 20z- 21z. As for winds, to persist
from the south, before veering to the west then north behind the
boundary. Cigs to remain vfr til frontal passage, then lower to
mvfr behind the front.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.