Tuesday, September 28, 2010

Area Forecast Discussion - South Central/Southwest Missouri

FXUS63 KSGF 282241
AFDSGF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPRINGFIELD MO
541 PM CDT TUE SEP 28 2010

..UPDATE TO AVIATION...

DISCUSSION...

PATCHY STRATOCUMULUS CLOUDS HAS DEVELOPED OVER MUCH OF THE
FORECAST AREA THIS AFTERNOON AS DAYTIME MIXING LIFTS WHAT LITTLE
MOISTURE WE HAVE OVER THE REGION. EXPECT THESE CLOUDS TO DISSIPATE
AROUND SUNSET WITH TEMPERATURES FALLING QUICKLY THROUGH THE 60S
AND MID 50S THROUGH THE EVENING. TEMPERATURES ARE EXPECTED TO DROP
INTO THE UPPER 40S TO LOWER 50S BY SUNRISE...ABOUT 5 DEGREES LOWER
THAN MID AFTERNOON CROSS-OVER TEMPERATURES. ALSO...WIND SPEEDS
WILL DROP TO LIGHT AND VARIABLE AS THE SURFACE RIDGE AXIS OVER THE
UPPER MIDWEST SETTLES OVER THE OZARKS. SO EXPECT TO SEE SOME
PATCHY FOG DEVELOP LATE TONIGHT AND EARLY WEDNESDAY.

THE LATEST MODEL GUIDANCE CONTINUES TO BRING A DRY COLD FRONT
ACROSS THE REGION LATE WEDNESDAY NIGHT AND EARLY THURSDAY. MEAN RH
VALUES AROUND 40-50 PERCENT WILL WARRANT INCREASING CLOUD COVER
AND KEEPING MIN TEMPS SEVERAL DEGREES WARMER WEDNESDAY NIGHT.
THEREAFTER A REINFORCING SHOT OF CANADIAN AIR WILL MAKE ITS WAY
INTO THE REGION.

THE OVERALL UPPER AIR PATTERN WILL REMAIN VERY MERIDIONAL WITH
RIDGING OVER THE WESTERN CONUS AND TROUGHING OVER THE MID-ATLANTIC
REGION. THIS WILL KEEP OUR AREA IN NORTHWEST FLOW ALOFT THROUGH
EARLY NEXT WEEK. AN UPPER LEVEL DISTURBANCE PROGGED BY THE ECMWF
TO MOVE ACROSS THE REGION ON SATURDAY MAY BRING A FEW MORE CLOUDS
BUT WILL CONTINUE WITH A DRY FORECAST THROUGH THE WEEKEND.

BY SATURDAY NIGHT AND SUNDAY...A 1030 MB SURFACE HIGH OVER THE
NORTHERN PLAINS AND UPPER MIDWEST WILL BUILD SOUTHWARD TOWARD THE
OHIO VALLEY. SOME OF THE COLDEST AIR SO FAR THIS SEASON MAY CLIP
OUR EASTERN AND CENTRAL COUNTIES. FOR NOW...HAVE DROPPED MIN TEMPS
INTO THE LOWER AND MID 40S EAST OF HIGHWAY 65 ON SUNDAY NIGHT AND
MONDAY NIGHT. WOULD NOT BE SURPRISED IF THESE NEED TO BE LOWERED
MORE...ESPECIALLY IF THE TROUGH DROPS FURTHER TO THE SOUTHWEST.

TERRY

&&

AVIATION...

FOR THE 00Z TAFS...

ONLY POTENTIAL AVIATION IMPACT WILL BE FOG OVERNIGHT
TONIGHT...WITH SOME CONTINUED UNCERTAINTY AS TO THE DEGREE OF VIS
RESTRICTIONS DURING THE EARLY MORNING HOURS TOMORROW. SFC RIDGE
AXIS IS EXPECTED TO BE MOVING OVERHEAD BY 09Z-12Z...WHICH SHOULD
RESULT IN SFC WINDS DROPPING TO CALM. WITH CLEAR SKIES EXPECTED
AND CROSSOVER TEMPS IN THE LOW 50S...FOG FORMATION SEEMS LIKELY.
INTENSITY IS A MUCH MORE UNCERTAIN QUESTION...WITH GUIDANCE
SUGGESTING ANYTHING BETWEEN VFR AND LIFR.

THAT BEING SAID...HAVE OPTED TO DROP VIS AT SGF TO IFR
RANGE...THOUGH SOME GUIDANCE DOES SUGGEST POTENTIAL FOR VIS AS LOW
AS 1/2 SM. HOWEVER...WITH NO RECENT RAIN...FEEL THAT POTENTIAL FOR
SUB 1 MI VIS IS JUST TOO LOW FOR INCLUSION AT THIS TIME. AT
BBG...CLIMATOLOGICAL TENDENCY AND TERRAIN EFFECTS SUGGEST IFR IS
PROBABLE...AND POTENTIAL ALSO EXISTS FOR LIFR FOR A TIME IN THE
MORNING. JLN SHOULD REMAIN MVFR...WHERE SFC MOISTURE IS SLIGHTLY
LESS.

ANY FOG THAT FORMS SHOULD DISSIPATE WITHIN A FEW HOURS OF
SUNRISE...WITH VFR CONDITIONS EXPECTED AT ALL TERMINALS BY LATE
MORNING.

BOXELL

&&

SGF WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&

$$


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