FXUS63 KFSD 111626
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1020 AM CST FRI DEC 11 2009

.DISCUSSION...

QUIET MORNING ACROSS THE AREA WITH VIRTUALLY CLEAR SKIES AND LIGHT 
WINDS OVER THE ENTIRE CWA. PRESENT FORECAST IS IN GOOD SHAPE...WITH 
ONLY MINOR EDITS MADE FOR REAL TIME TRENDS. NEW PFM OUT.  /JM

&&

.AVIATION...

VFR THROUGH SATURDAY MORNING. A PRETTY GOOD CHANCE FOR MVFR OR IFR 
CONDITIONS...MAINLY CEILINGS...DURING THE DAY ON SATURDAY.

&&

.PREV DISCUSSION...

MAIN CHALLENGES IN THIS FORECAST PACKAGE WERE TEMPERATURES AND 
PRECIP CHANCES/TYPE SUNDAY NIGHT. 

FOR TODAY...WINDS WILL BEGIN TO TURN SOUTHERLY THIS MORNING AS 
SURFACE RIDGE OVER THE SOUTHEASTERN US BEGINS TO SHIFT OFF TO THE 
EAST.  EXTREMELY POOR MIXING CONDITIONS EXPECTED TODAY WITH STOUT 
INVERSION ALOFT AND SNOW COVER IN PLACE.  SIDED WITH HIGH 
TEMPERATURES NEAR ISOTHERMAL FROM 925 HPA WHICH WAS A DEGREE OR TWO 
WARMER THAN WHAT WAS IN THE PREVIOUS FORECAST. 

FORECAST BECOMES SOMEWHAT MORE COMPLICATED TONIGHT AS LOW LYING 
STRATUS IS EXPECTED TO DEVELOP ACROSS THE SOUTHERN 
PLAINS...ADVECTING NORTH ON LOW LEVEL JET AHEAD OF A WEAK TROUGH 
APPROACHING FROM THE WEST.  COULD SEE SOME HIGH CLOUDS NORTH OF 
INTERSTATE 90...BUT OTHERWISE EXPECT MOSTLY CLEAR SKIES THROUGH 
SATURDAY MORNING.  AS THE DAY PROGRESSES ON SATURDAY...APPEARS AS 
THOUGH LOW CLOUDS AND STRATUS WILL SURGE NORTH ACROSS AT LEAST THE 
EASTERN HALF OF FORECAST AREA.  BACK EDGE OF THE STRATUS IS ILL 
DEFINED...BUT THINK IT WILL LIE CLOSE TO WEAKENING BOUNDARY TRYING 
TO WORK EAST ACROSS FORECAST AREA.  AS SYSTEM WEAKENS...THINK THE 
BOUNDARY WILL WASH OUT AND THE FOCUS WILL SHIFT TO THE WEST AS A 
RELATIVELY STRONG SHORTWAVE CRASHES INTO THE NORTHERN CALIFORNIA 
COAST. AHEAD OF THIS WAVE...LOW LEVEL FLOW TURNS SOUTH EAST LOCKING 
IN LOW LYING STRATUS.  TEMPERATURES ON SATURDAY ARE PROBLEMATIC AS 
THEY WILL BE HIGHLY DEPENDENT ON CLOUD COVER. FOR NOW...SIDED WITH 
ISOTHERMAL FROM 925 HPA WHICH IS FOR THE MOST PART COOLER THAN 
GUIDANCE.  

WITH PLENTY OF LOW LEVEL MOISTURE HANGING AROUND SATURDAY 
NIGHT...COULD SEE SOME AREAS OF FOG WITH SOME EMBEDDED DRIZZLE 
DEVELOP.  CONFIDENCE IN DRIZZLE IS NOT THAT HIGH....BUT KEPT MENTION 
IN ESPECIALLY ACROSS SOUTHWEST MINNESOTA WHERE MOISTURE APPEARED TO 
BE DEEPER.  

PREVIOUSLY MENTIONED SHORTWAVE APPEARS TO BE SHREDDED AS IT MAKES 
ITS WAY ACROSS THE ROCKIES...BUT ATTEMPTS TO RE ORGANIZE TO A 
DEGREE SUNDAY AFTERNOON INTO SUNDAY NIGHT. AS PREVIOUS FORECASTER 
MENTIONED...THERE IS SOME ISENTROPIC LIFT WITH THIS FEATURE...BUT 
STRONGER LIFT APPEARS TO BE FOCUSED ACROSS SOUTHERN PORTIONS OF 
FORECAST AREA ALONG THE SOUTH DAKOTA NEBRASKA BORDER.  DEEPER 
MOISTURE APPEARS TO BE CONCENTRATED FURTHER TO THE NORTH...BUT 
CONCERNED ABOUT WHETHER THE DENDRITIC LAYER WILL BECOME SATURATED 
WITH RESPECT TO ICE INTRODUCING ICE INTO THE LAYER. THIS SEEMS TO BE 
MORE CERTAIN NORTH OF INTERSTATE 90. SOUTH OF INTERSTATE 90...MAY 
SEE SOME FREEZING DRIZZLE IF ANY PRECIPITATION DEVELOPS AT ALL. 

COLD FRONT ASSOCIATED WITH THIS WAVE WORKS THROUGH SUNDAY NIGHT INTO 
MONDAY OPENING UP THE DOOR FOR MUCH COOLER ARCTIC AIR TO SPILL BACK 
DOWN INTO THE PLAINS. WITH STRONG COLD AIR ADVECTION ON 
MONDAY...WILL LIKELY SEE VERY LITTLE RECOVERY IN TEMPERATURES WITH 
THE POTENTIAL FOR FALLING TEMPERATURES IN THE EAST. TUESDAY LOOKS TO 
REMAIN FAIRLY COOL BEFORE TEMPERATURES BEGIN TO MODERATE TOWARDS MID 
WEEK. 

&&

.FSD WATCHES/WARNINGS/ADVISORIES...

SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.

&&

$$
BT/08