Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 200851
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
351 AM CDT Sun Apr 20 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 341 AM CDT Sun Apr 20 2014

Sunday will certainly feel like spring, with a warm south breeze
helping temperatures to climb into the mid 70s over southwest
Illinois, and upper 70s to around 80 degrees across the remainder
of the forecast area. While no precipitation is anticipated during
the day today, mostly sunny skies in the morning will give way
to increasing cloudcover from the west through the afternoon and
evening hours.

JP

.LONG TERM:  (Tonight through Saturday)
Issued at 341 AM CDT Sun Apr 20 2014

Sunday night looks to be dry across much of the forecast area, with
models indicating a slower yet eastward progression of showers and
thunderstorms from western Missouri associated with a southwest
shortwave progged to move into western Missouri around 00Z Monday.
Current expectation is for precipitation to gradually overspread mid
Missouri by around 09Z, and the remainder of the forecast area
during the day.  Have gone with more thunder than previous forecast
packages, especially Monday/Monday evening, given ample moisture
convergence and frontogenetical forcing associated with the cold
front moving through the forecast area during the afternoon and
evening hours. The GFS, NAM, and local WRF are also indicating
MUCAPE ahead of the front in the 1000-1200 J/kg range, and while
severe weather isn`t anticipated at this time, currently felt it
prudent to up the mention of thunder for Monday/Monday evening given
the instability present ahead of the advancing cold front.

The cold front and associated precipitation should be well southeast
of the area by Tuesday morning as the main trough axis shifts east
of the Mississippi River Valley and surface high pressure builds in
to the region in the wake of the front. Thus, temperatures Tuesday
will be cooler, though the cooldown will be short-lived as another
ridge will build over the region and amplify by Wednesday in
response to the deepening trough over the eastern CONUS and a lee
trough/developing low pressure over the plains. The GFS, GEM, and
ECMWF all continue to indicate the potential for some ridge-runner
type storms to develop Wednesday/Wednesday afternoon, though the GFS
and GEM keep any QPF just north of the forecast area Wednesday, with
the ECMWF brushing light QPF over northeast Missouri and west
central Illinois Wednesday afternoon and evening. Have maintained a
slight chance for showers and thunderstorms over the northern tier
of the forecast area on Wednesday to account for this.

Late Wednesday night through Thursday night will be the next chance
for widespread precipitation across the forecast area, as the
aforementioned low developing over the north plains begins to move
eastward toward the Great Lakes, with an accompanying cold front
progged to move through the middle Mississippi Valley.  Have not
made many changes to the going forecast at this time, given
discrepancies in timing that remain between the GFS and ECMWF, the
ECMWF continuing to be about 6 hours faster than the GFS.  Feel that
the broad-brushed chance pops, with likely pops Thursday for
portions of the area should be sufficient at this time. Model
differences aside, the cold front should be exiting the area to the
east by Friday morning. Do not expect temperatures to drop much on
Friday in the wake of the cold front, as westerly flow remains at
low levels, though as the low pressure system moves toward the
Great Lakes and another ridge begins to take shape over the plains,
Friday night and Saturday should be cooler under northwest flow, and
thus have maintained the cooler trend with temperatures at the end
of the period.

JP

&&

.AVIATION:  (For the 06z TAFs through 06z Sunday Night)
Issued at 1056 PM CDT Sat Apr 19 2014

VFR with southeast wind becoming south on Easter Sunday.

Specifics for KSTL:

VFR with southeast wind becoming south on Easter Sunday.

CVKING

&&

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

$$

WFO LSX






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