Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 122040
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
340 PM CDT Sat Apr 12 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 338 PM CDT Sat Apr 12 2014

Warn front has surged northward with tenmperatures rising to around
80 across the area. Gusty southerly winds will continue overnight as
the approaching cold front and low pressure area get better
organized. Thunderstand development expected closer to the front
overnight from Kansas into Iowa...with most of the activity expected
in Iowa. Further south model soundings...especially GFS which seemed
to initialize the best this morning...show a cap maintaining
overnight. Storms may move into Northeast MO and West Central IL by
12z...but development futher will likely be tough. Pops have
generally be decreased overnight. Overnight min temperatures also
kept a bit above guidance given the wind staying up overnight.


JPK


.LONG TERM:  (Sunday through Next Saturday)
Issued at 338 PM CDT Sat Apr 12 2014

(Sunday through Tuesday night)

Main concern continues to be the potential for a few severe
thunderstorms and locally heavy rainfall on Sunday afternoon and
Sunday night as the cold front moves southeast across the the area.
Not much change to the overall thinking of the forecast as
atmosphere will be fairly well capped most of the morning and
propagation vectors keep the expected MCS over IA, so showers and
storms chances should be stay confined to the the northern part of
the CWA during the morning hours.  By afternoon, a combination of
strong surface-850mb moisture convergence in conjuction with
increasing ascent with the mid level trough should be enough to
justify the categorical pops we already have going across central
and northeast Missouri/west central Illinois.  Kept near 100 percent
pops tomorrow night as low level convergence is strong underneath
the strong ascent of the trough.

Severe weather potential will mainly be during the late afternoon
and early hours along and ahead of the cold front over central, east
central and southeast Missouri as well as adjacent sections of
Illinois when convective inhibition erodes enough for a few if the
storms to become surface based.  Deep layer shear around 40kts will
be sufficient for a organized storms to produce damaging winds and
large hail.  Precipitable water values are around 1.4 inches, so the
storms will be capable of producing of heavy rainfall.

Did keep the likely pops for light rain a bit longer on Monday
morning as ascent from the upper trough does linger over CWA most of
the day per the GFS/ECMWF.  Also added a chance of light rain over
the eastern counties into Monday evening.   Upper trough will move
east of the area by 06Z Monday night, so kept Tuesday and Tuesday
night dry.

Kept the same temperature trends behind the front Sunday night into
Monday.  It still looks like temperatures by Tuesday morning will be
near or below freezing over much of the area after a weekend of well
above normal temperatures.

(Wednesday through next Saturday)

While both the GFS and ECMWF show a 500mb trough moving across the
central CONUS late mid-late next week, the GFS is much more
amplified with it than the ECMWF.  Consequently, it brings the
attendant cold front through the area slightly quicker on Friday,
and draws less moisture northward from the Gulf than the GFS would.
While the ECMWF does show some run-to-run continuity problems, the
GFS issues are slightly worse, so will favor the ECMWF with this
forecast.


Britt

&&

.AVIATION:  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1206 PM CDT Sat Apr 12 2014

GUSTY SOUTHERLY SURFACE WINDS WILL PREVAIL TODAY INTO TONIGHT IN
ADVANCE OF STRENGTHENING COLD FRONT OVER THE PLAINS. THUNDERSTORM
DEVELOPMENT EXPECTED OVENIGHT PRIMARILY IN THE VICINITY OF THE
FRONT FROM KANSAS ACROSS NEBRASKA INTO IOWA. SOUTHERN DEVELOPMENT
INTO NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS POSSIBLE AS THE
LOW LEVEL JET VEERS OVENIGHT. DEVELOPMENT FUTHER SOUTH IN QUESTION
GIVEN STRONG CAPPING THAT MAINTAINS...ESPECIALLY PER THE GFS. NAM
HAS MORE INSTABILITY BUT GFS VERIFIED BETTER THIS AM SO WILL GO
WITH IT FOR NOW. CONDITIONS GO DONWHILL SUNDAY AFTERNOON AS THE
FRONT MOVES CLOSER AND INSTABILITY INCREASES.

Specifics for KSTL: AM INCLINED TO GO WITH A DRY AND VFR FORECAST
FOR NOW. PRETTY STRONG CAPPING OVERNIGHT SO AM LEANING AGAINST ANY
THUNDERSTORM DEVELOPMENT MAKING IT THIS FAR SOUTH. NAM HAS BEEN
HAMMERING AWAY AT MVFR-IFR CONDITIONS ACROSS THE AREA BY 12Z.
GIVEN THAT IT WAS SIMILAR FOR THIS AM AND NONE DEVELOPED...AM
INCLINED TO GO WITH THE GFS. EVEN THOUGH THE GFS BRINGS IN MVFR
CEILINGS BY 12Z AS WELL...CONFIDENCE NOT REAL HIGH ON THIS RIGHT
NOW. BREEZY AND LOW VR LOOKS BETTER. A CHANCE POP WOULD NOT BE OUT
OF THE QUESTION FOR THE 18 - 00Z PERIOD, BUT THINK IT WILL BE
BETTER FOR THE LATTER HALF OF THE TIME SO WILL LEAVE IT OUT.
PLENTY OF TIME YET TO NAIL THIS DOWS.

JPK

&&

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

$$

WFO LSX






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