HAMweather.com Area Forecast Discussion for County Warning Area FSD

Thu, 16 Feb 2012 06:57:25 GMT
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1047 PM CST WED FEB 15 2012

.DISCUSSION.../ISSUED AT 812 PM CST/
AREAS OF STRATUS/STRATOCU HANGING ON A BIT LONGER ACROSS EASTERN 
PORTIONS OF THE AREA THIS EVENING...AND THUS HOLDING TEMPS UP MORE 
THAN FORECAST WHILE CLEAR/DRIER WESTERN AREAS ARE DROPPING OFF MORE 
QUICKLY. HAVE ADJUSTED CLOUD COVER TO DELAY CLEARING IN THE EAST... 
AND ALSO ADJUSTED HOURLY TEMPS TO COVER ABOVE-MENTIONED NEEDS...BUT 
ONLY MINIMAL CHANGES TO OVERALL LOWS AS EASTERN AREAS LIKELY TO SEE 
RAPID DROP AS CLOUDS CLEAR COMPLETELY AFTER 06Z. UPDATES TO ZFP/PFM 
AND GRIDS HAVE BEEN SENT.

.AVIATION.../FOR THE 06Z TAF ISSUANCE/
VFR CONDITIONS WILL PREVAIL THROUGH 06Z FRIDAY. DIURNALLY MIXED 
WINDS WILL REACH GUSTS OF 20 TO 26 KNOTS DURING THE LATE MORNING AND 
AFTERNOON HOURS...DELAYED AN HOUR OR TWO ONSET DUE TO INVERSION WITH 
SNOWCOVER AT KSUX. /CHAPMAN

.PREV DISCUSSION.../ISSUED AT 226 PM CST/
WITH SKIES EXPECTED TO BE CLEAR TO PARTLY CLOUDY MOST OF THE 
NIGHT...THE FORECAST CHALLENGE WILL BE TEMPERATURES BOTH OVERNIGHT 
AND ON THURSDAY. FOR TONIGHT...THE QUESTION IS HOW MUCH IT WILL 
DECOUPLE. WITH A WEAK RIDGE MOVING OVER...AGREE WITH MODELS THAT 
WINDS LIKELY TO FALL BELOW 10 MPH. FOR AREAS WITH SNOW 
COVER...EXPECT THAT WILL BE ENOUGH TO ALLOW FOR RADIATIONAL COOLING 
AND LOWERED MINS INTO THE UPPER TEENS WITH AROUND 20 IN MOST OTHER 
AREAS. ON THURSDAY...AS THE RIDGE MOVES TO THE SOUTH...THE GRADIENT 
WILL INCREASE. WITH DRY GROUND AND COLD AIR ALOFT...EXPECT THAT THE 
ATMOSPHERE WILL MIX TO AT LEAST 925 MB AND ALLOW STRONGER FLOW TO 
MIX DOWN TO THE SURFACE WITH WINDS LIKELY TO GUST OVER 20 MPH AT 
TIMES IN THE AFTERNOON. THIS WILL ALSO ALLOW TEMPERATURES TO WARM 
WELL INTO THE 40S IN PLACES WITHOUT SNOW COVER. IN PORTIONS OF 
NORTHWEST IOWA...THE SNOW AND COLD START WILL CONSPIRE TO KEEP HIGHS 
IN THE 30S.

THURSDAY NIGHT INTO FRIDAY WILL SIDE CLOSEST TO THE ECMWF AND NAM 
WITH THE GFS LOOKING A LITTLE TOO DIGGY WITH THE WAVE DROPPING 
THROUGH. WHAT THIS SHOULD MEAN IS A RELATIVELY MILD NIGHT THURSDAY 
NIGHT WITH WEST WINDS GENERALLY AROUND 10 MPH MOST OF THE NIGHT. A 
FEW LOWER SPOTS COULD OCCASIONALLY DECOUPLE BUT WILL AIM FOR LOWS 
FROM THE MID TEENS TO THE LOWER 20S. CLOUDS WILL INCREASE AHEAD OF 
THE INCOMING WAVE AND WITH THE SLIGHTLY FASTER TIMING...WILL 
DECREASE LOWS ACROSS THE NORTH AND INCREASE JUST A BIT IN THE FAR 
SOUTH. THIS SHOULD RESULT IN HIGHS FROM THE MID 30S NORTH TO THE MID 
40S SOUTH. EXPECT A BAND OF CLOUDS TO SWING THROUGH AS WELL AND NOT 
OUT OF THE QUESTION TO GET A QUICK SNOW SHOWER...BUT WILL HAVE NO 
MENTION FOR NOW WITH SOME DISPARITY AMONGST THE MODELS.

WILL CONTINUE TO SIDE WITH THE ECMWF/NAM FRIDAY NIGHT INTO SATURDAY 
WHICH IS ALSO SUPPORTED BY THE GEM. THIS SUGGESTS A FAIRLY BROAD 
HIGH PRESSURE WILL SETTLE IN AND HAVE OPTED TO LOWER LOWS A FEW 
DEGREES TO ACCOUNT FOR THE EXPECTED LACK OF CLOUD COVER AND LIGHT 
WINDS...MAINLY 10 TO 15 FOR LOWS...A SMIDGE WARMER IN CENTRAL SOUTH 
DAKOTA WHERE A SOUTHEAST WIND COULD DEVELOP LATE AND KEEP 
TEMPERATURES FROM BOTTOMING OUT.  

IN THE LATTER PERIODS(SUN/WED)...UPPER LEVEL RIDGING EARLY IN THE 
PERIOD BEING REPLACED BY A TROUGH OF LOW PRESSURE ON MONDAY. MODELS 
NOT VERY AGREEABLE WITH THIS SYSTEM BUT THE OVERALL TREND HAS BEEN 
TO SWING OUT A FILLING UPPER LEVEL SYSTEM WHILE SLOWLY BRINGING AN 
UPPER LEVEL TROUGH THROUGH THE MIDDLE OF THE COUNTRY. WILL MAINTAIN 
A CHANCE FOR SNOW ON SUNDAY NIGHT INTO MONDAY NIGHT WITH SOME THREAT 
FOR RAIN AS WELL AS MODEL SOUNDINGS MARGINALLY COLD BUT...UNLESS 
SOMETHING CLOSER TO THE SLIGHTLY NEGATIVELY TILTED 0Z/12Z ECMWF 
VERIFIES...SHOULD END UP A FAIRLY MINOR SYSTEM. BROAD WEST TO 
NORTHWEST FLOW DEVELOPS BEHIND THIS WAVE AND ASSUMING NO NEW DEEPER 
SNOW COVER FROM MONDAYS SYSTEM...WE SHOULD BE LOOKING AT ABOVE 
NORMAL TEMPERATURES AGAIN...MAYBE CLOSE TO NORMAL IF ENOUGH COOLER 
AIR WRAPS SOUTH. /08

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