617 
FXUS63 KFSD 191719
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1119 AM CST MON NOV 19 2012

.DISCUSSION...
WEAK COLD FRONT MOVING ACROSS THE CWA THIS MORNING AS EXPECTED AND 
DO NOT SEE ANY CHANGES THAT NEED TO BE MADE TO THE FORECAST. /08

&&

.AVIATION.../FOR THE 18Z TAF ISSUANCE/
VFR CONDITIONS THROUGH THE PERIOD. THERE WILL BE A SMALL THREAT FOR 
LOCALIZED FOG ACROSS THE AREA TONIGHT AS HIGH PRESSURE MOVES 
OVERHEAD...BUT WITH THE DRY GROUND CONFIDENCE IN THIS IS PRETTY LOW 
SO WILL NOT INCLUDE ANYTHING BELOW MVFR IN THE TAFS. /08

&&

.PREV DISCUSSION.../ISSUED AT 253 AM CST/
NOT A LOT GOING ON IN THE SHORT AND INTERMEDIATE TERM...WITH VERY 
MILD TEMPERATURES CONTINUING. A SHORT WAVE IS EXITING OUR EASTERN 
ZONES AND POINTS TO THE SOUTH AT THIS TIME...WHICH IS HELPING TO 
GIVE SOME CLOUDINESS IN OUR FAR EASTERN ZONES IN NORTHWEST IA AND 
SOUTHWEST MN. AS THE WAVE EXITS EARLY TODAY...SO WILL THOSE CLOUDS. 
ANOTHER SHORT WAVE WILL MOVE QUICKLY EASTWARD ACROSS THE NORTHERN 
PLAINS TODAY WHICH MAY SPREAD A FEW MID AND HIGH LEVEL CLOUDS 
AROUND. BUT OVERALL...SKIES SHOULD BE CLEAR TO PARTLY CLOUDY WITH 
TEMPERATURES A BIT COOLER BEHIND A WEAK...SURFACE COLD FRONT 
PASSAGE. STILL...HIGHS SHOULD BE CLOSE TO 15 DEGREES ABOVE NORMAL
WITH READINGS IN THE 50S. 

SURFACE RIDGING WILL ENCOMPASS OUR AREA TONIGHT PRODUCING LIGHT 
WINDS. COUPLED WITH WHAT SHOULD BE CLEAR SKIES...LOWS BELOW GUIDANCE 
READINGS ARE A GOOD BET GIVEN THE ABUNDANT DRY AIR AROUND. THEREFORE 
WIDESPREAD READINGS OF MID 20S TO AROUND 30 SHOULD BE COMMON.

THEN AN UPPER RIDGE MOVES EASTWARD THROUGH THIS AREA ON TUESDAY AND 
WEDNESDAY. THIS FEATURE WILL GIVE VERY MUCH ABOVE NORMAL HIGHS AGAIN 
WITH A SOUTHERLY FLOW OF AIR DOMINATING. 925MB TO 900MB TEMPERATURES 
ARE FORECAST TO BE EXTREMELY SIMILAR ON TUESDAY AS THEY WERE FOR 
YESTERDAY. AND NOTING SIMILAR SOUTHERLY WINDS...HIGH TEMPERATURES 
SHOULD BE VERY COMPARABLE ON TUESDAY AS THEY WERE ON SUNDAY. 
WEDNESDAY WILL BE VERY WARM AHEAD OF THE NEXT COLD FRONT PASSAGE 
DETAILED BELOW. 925MB TEMPERATURES SKY ROCKET AHEAD OF THIS BOUNDARY 
AND SHOULD PUSH HIGHS CLOSE TO RECORDS. MID 60S TO LOWER 70S STILL 
LOOK WIDESPREAD SO NO NEED TO MAKE HARDLY ANY CHANGES TO THE 
PREVIOUS FORECAST AT THIS TIME. MANY GUIDANCE VALUES LOOK TOO COOL 
FOR WEDNESDAY...LIKELY A RESULT OF SOME CLIMATOLOGY BUILT IN AND NOT 
HANDLING AN AIR MASS WHICH SHOULD BE 25 TO 30 DEGREES ABOVE NORMAL 
GIVEN THE LATEST 925MB TO 900MB TEMPERATURES.  /MJF

THE THANKSGIVING WEEKEND WILL BE MOST IMPACTED BY THE PASSAGE OF A 
STRONG UPPER LEVEL WAVE. ALL MODELS SHOW THIS WAVE AND ATTENDANT 
COLD FRONT MOVING THROUGH THANKSGIVING DAY. AFTER THAT DIFFERENCES 
EMERGE AS THE 00Z ECMWF AND 00Z GEM ARE BOTH AMPLIFYING THE 500 MB 
FLOW THROUGH SUNDAY. THIS SLOWS THE EASTWARD PROGRESSION OF ALL 
SURFACE FEATURES COMPARED TO THE 00Z GFS AND ALLOWS MUCH COLDER AIR 
TO DRAIN SOUTHWARD. THE GFS ENSEMBLE SHOWS A LARGE SPREAD IN 850 MB 
TEMPERATURES ON FRIDAY AND SATURDAY AND HINTS THAT THERE ARE SEVERAL 
MEMBERS MUCH COLDER THAN THE OPERATIONAL RUN. WHILE THE ECMWF AND 
GEM MAY BE TOO AMPLIFIED...THE GFS HAS A TENDENCY TO BE TOO 
PROGRESSIVE WITH THESE SYSTEMS AND PUSH THE SURFACE HIGH EAST TOO 
QUICKLY. THEREFORE HAVE TRENDED MUCH CLOSER TO THE 00Z ECMWF AND 00Z 
GEM FOR THE WEEKEND. WHILE THIS HAS A LARGE IMPACT ON 
TEMPERATURES...NO ORGANIZED PRECIPITATION IS EXPECTED DURING THE 4 
DAY WEEKEND ALTHOUGH A FEW FLURRIES MAY BE POSSIBLE ON FRIDAY IN THE 
CYCLONIC FLOW ACROSS SW MN. WITH SUCH A LOW PROBABILITY HOWEVER... 
HAVE NOT INCLUDED IN THE FORECAST AT THIS TIME.

FOR FORECAST SPECIFICS...THANKSGIVING DAY LOOKS WELL MIXED AND 
EXPECT HIGHS WELL ABOVE NORMAL IN THE 50S TO AROUND 60. THE COLDER 
AIR REALLY COMES IN THURSDAY NIGHT AND MEANS BELOW NORMAL 
TEMPERATURES BOTH FRIDAY AND SATURDAY. HAVE LOWERED HIGHS INTO THE 
30S TO AROUND 40 ON FRIDAY AND INTO THE UPPER 30S AND 40S ON 
SATURDAY. ALSO WITH THE HIGH OVER THE AREA FRIDAY NIGHT...LOWERED 
MINS TO AROUND 20. WITH COLDER AIR...STRATUS WILL SET UP ACROSS THE 
AREA AND WINDS WILL GUST FROM 20 TO 30 MPH PUTTING WIND CHILLS INTO 
THE 20S. AND IT IS POSSIBLE TEMPERATURES FRIDAY AND FRIDAY NIGHT 
COULD BE EVEN COLDER ESPECIALLY IF STRATUS IS MORE WIDESPREAD DURING 
THE DAY FRIDAY AND IT COMPLETELY CLEARS AND GOES CALM FRIDAY NIGHT. 
THERE IS ALSO A QUESTION ON HOW MUCH RECOVERY CAN BE EXPECTED ON 
SUNDAY AS SOUTHERLY FLOW RETURNS. FOR NOW...HAVE HIGHS IN THE 40S 
AND 50S. BUT IF RETURN FLOW IS SLOWER...IT COULD BE A FEW DEGREES 
COOLER./SCHUMACHER

&&

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

&&

$$