826 
FXUS63 KFSD 232035
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD
235 PM CST FRI NOV 23 2012

.DISCUSSION.../ISSUED AT 235 PM CST/
DENSE CIRRUS SHIELD EXPANDING OUT OF THE WESTERN HIGH PLAINS INTO 
THE FORECAST AREA.  AT THE SURFACE...HIGH PRESSURE ACROSS THE 
CENTRAL DAKOTAS IS EXPECTED TO SHIFT EAST.  THIS WILL LEAD TO 
RAPIDLY DECREASING WINDS TOWARDS SUNSET...AND WITH COOL DRY AIRMASS 
SHOULD SEE TEMPERATURES FALL QUICKLY THIS EVENING.  RAISED LOW 
TEMPERATURES JUST A DEGREE OR TWO IN MOST LOCATIONS WITH IMPACT OF 
CIRRUS ON RADIATIONAL COOLING. 

SURFACE RIDGE QUICKLY SHIFTS SOUTH AND EAST OF THE AREA TOMORROW 
MORNING LEADING TO INCREASING SOUTHERLY FLOW ACROSS THE AREA.  
INVERSION IS RELATIVELY WEAK...SO SHOULD SEE WINDS INCREASE FAIRLY 
QUICKLY AFTER SUNRISE. 925 HPA TEMPS RETURN TO LEVELS ABOVE 
0C...RESULTING IN TEMPERATURES CLIMBING BACK TO ABOVE NORMAL LEVELS. 

COOL FRONT THEN MOVES THROUGH THE AREA SATURDAY NIGHT/SUNDAY AS 
UPPER WAVE MOVES ACROSS SOUTHERN CANADA/NORTHERN MINNESOTA. TRAILING 
WESTWARD EXTENSION OF THIS WAVE WILL BRING INCREASE IN MID-HIGH 
LEVEL CLOUDS SOUTHWARD THROUGH THE FORECAST AREA SATURDAY NIGHT... 
BUT NOT EXPECTING ANY PRECIPITATION AS BULK OF ENERGY SLIDES WELL 
NORTHEAST OF OUR AREA. COOLER BEHIND THE FRONT SUNDAY WITH HIGHS IN 
THE MID 30S NORTH TO AROUND 40 FAR SOUTH.

ANOTHER WAVE SLIDES FARTHER SOUTH ACROSS THE NORTHERN/CENTRAL PLAINS 
SUNDAY NIGHT/MONDAY...RIDING ALONG MID LEVEL FRONT WHICH LOOKS TO BE 
NEAR OR JUST SOUTH OF MISSOURI RIVER VALLEY. MID LEVEL FRONT SHOULD 
HELP FOCUS PRECIP IN OUR SOUTHERN CWA...WITH NORTHERN AREAS FIGHTING 
DRIER NORTH-NORTHEAST LOW LEVEL FLOW. BULK OF PRECIPITATION SHOULD 
BE OFF-AND-ON LIGHT SNOW SUNDAY AFTERNOON THROUGH MONDAY...WITH 
POTENTIAL FOR AN INCH OR TWO SPREAD OVER THIS PERIOD ACROSS THE FAR 
SOUTHWEST CORNER OF THE CWA...ESPECIALLY WITH HIGHER ELEVATION IN 
GREGORY COUNTY. SECONDARY SHOT OF COLDER AIR WILL SETTLE INTO THE 
AREA WITH THIS SYSTEM FOR MONDAY...WITH HIGHS SIMILAR TO OR JUST 
SLIGHTLY WARMER THAN TODAY.

STILL QUITE A BIT OF DISPARITY AND UNCERTAINTY IN TEMPERATURES THE
THROUGH REMAINDER OF THE LONGER RANGE...TUESDAY THROUGH FRIDAY... 
THOUGH GFS/ECMWF SEEM TO BE IN LITTLE BETTER AGREEMENT IN GENERAL 
PATTERN...SHOWING WEAK WAVE SLIDING THROUGH TUESDAY...FOLLOWED BY 
BROAD RIDGING/QUASI-ZONAL FLOW WEDNESDAY...WITH ANOTHER WAVE MOVING 
INTO THE AREA THURSDAY/FRIDAY TIME FRAME. GFS A LITTLE FASTER WITH 
THIS LATE WEEK WAVE...RESULTING IN SOMEWHAT COOLER HIGH TEMPERATURES 
THURSDAY THAN INDICATED BY GEM/ECMWF WHICH ARE SLOWER TO BRING THE 
WAVE INTO THIS AREA. ECMWF HAS TENDED TO PERFORM BETTER AT THESE 
LONGER RANGES...AND THUS WILL LEAN WARMER THURSDAY WITH HIGHS MAINLY 
IN THE 40S...THOUGH GEM/ECMWF SHOWING POTENTIAL FOR SOME 50S ACROSS 
AT LEAST SOUTHERN PARTS OF THE FORECAST AREA. MILD AIR LINGERS INTO 
FRIDAY WITH HIGHS AGAIN IN THE 40S. MORE CONFIDENCE IN GENERAL LACK 
OF PRECIPITATION THROUGH THE LONGER RANGE THAN IN TEMPERATURES... 
WITH BOTH MODELS HOLDING ANY UPPER LEVEL ENERGY WELL NORTH OF THE 
AREA. 

&&

.AVIATION.../FOR THE 18Z TAF ISSUANCE/
MVFR STRATUS ACROSS NORTHWEST IOWA AND SOUTHWEST MINNESOTA WILL 
GRADUALLY SHIFT EAST TODAY LEADING TO VFR CONDITIONS. BREEZY 
NORTHWEST WINDS WILL GRADUALLY DECREASE TODAY...WITH LIGHT WINDS 
OVERNIGHT AS SURFACE HIGH PRESSURE MOVES ACROSS THE AREA.  SOUTHERLY 
FLOW WILL INCREASE QUITE RAPIDLY ON SATURDAY SHORTLY AFTER SUNRISE 
AS GRADIENT QUICKLY INCREASES FROM WEST TO EAST ACROSS THE AREA. 

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
MN...NONE.
NE...NONE.
SD...NONE.

&&

$$