Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 192138
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
338 PM CST Wed Nov 19 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 337 PM CST Wed Nov 19 2014

Cold front extending from a surface low over northwestern MI
southwest through southern IL and southeastern MO will shift
southeast of our forecast area this evening.  Post frontal
cloudiness may move through portions of northeast MO and west
central IL this evening, but it appears that most of the cloud cover
will be north and east of the forecast area tonight.  The strong and
gusty northwest wind will diminish this evening as the surface ridge
across the northern Plains behind this cold front builds
southeastward into western MO.  This reinforcing shot of cold air
will lead to below normal low temperatures tonight.

GKS

.LONG TERM:  (Thursday through Next Wednesday)
Issued at 337 PM CST Wed Nov 19 2014

Dry and unseasonably cold weather can be expected for Thursday and
Thursday night with northwesterly mid-upper level flow, and as the
surface ridge moves slowly eastward through the region.
Precipitation should spread northeastward into our forecast area
Friday afternoon and night as a south-southwesterly low level jet
brings low level warm air advection along with increasing low level
moisture to our area ahead of an approaching shortwave moving
eastward through the central Plains.  Dry air in the boundary and
surface layer on the western periphery of the surface ridge should
slow the onset of precipitation on Friday until the surface
temperature rises above the freezing mark for at least most of the
forecast area.  This dry air layer will likely lead to evaporative
cooling possibly cooling the atmosphere low enough that the
precipitation may begin as a mixture of rain and sleet.  The NAM
looks a little too cool for surface temperatures Friday afternoon
and followed closer to the warmer GFS MOS guidance.  Low-mid level
warm air advection with strong southwesterly winds at 850 mb and
surface winds becoming southerly will lead to slowly rising
temperatures Friday night.  Much warmer, near normal temperatures
can be expected for the weekend.  The best chance of rain along
with the highest precipitation amounts should occur late Saturday
night and Sunday as a strong negatively tilted upper level trough
and associated surface low move northeastward from the southern
Plains through our area.  The GFS model moves the surface low
through southeast MO and southern IL on Sunday, while the ECMWF has
a more northwest track through central MO just north and west of
STL.  The ECMWF solution would likely lead to more thunderstorms
with much of the forecast area in the warm sector of the storm
system.  Colder air will filter into our area Sunday night on the
backside of the surface low.  The GFS model ends the precipitation
Sunday night, but the ECMWF model keeps the chance of precipitation
going through Monday as shortwaves move through our area south of
the upper level low centered over the Great Lakes region.  This
latter model solution would lead to the potential for light snow
late Sunday night and Monday.

GKS

&&

.AVIATION:  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1131 AM CST Wed Nov 19 2014

The wind has shifted to the northwest and become gusty in the wake
of the latest cold front. Expect a broken deck of VFR stratus to
sweep across the area this afternoon and scatter this evening.
Wind to relax but remain west/northwest heading into Thursday.

Specifics for KSTL:

The wind has shifted to the northwest and become gusty in the wake
of the latest cold front. Expect a broken deck of VFR stratus to
sweep across the area this afternoon and scatter this evening.
Wind to relax but remain west/northwest heading into Thursday.

CVKING

&&

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

$$

WFO LSX






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