465 
FXUS63 KFSD 110904
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
404 AM CDT SAT MAY 11 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 404 AM CDT SAT MAY 11 2013

SURFACE ANALYSIS VERY EARLY THIS MORNING SHOWING THE COLD FRONT 
EXITING OVER OUR FAR SOUTHEASTERN ZONES...WITH MID CLOUDS STRETCHING 
ALONG OUR SOUTHERN BORDER FROM THE LOWER MISSOURI RIVER VALLEY INTO 
NORTHWESTERN IOWA AT THIS TIME. EXPECT THESE CLOUDS TO CONTINUE TO 
PULL OUT OF THE AREA THROUGH THE EARLY MORNING...BUT WATCHING 
ANOTHER AREA OF MID CLOUDS SITUATED OVER EASTERN NORTH DAKOTA WHICH 
IF THEY FOLLOW THE MID LEVEL FLOW MAY GRAZE OUR FAR NORTHEASTERN
ZONES DURING THE MID MORNING. OTHERWISE...SURFACE HIGH PRESSURE
BEGINS TO BUILD SOUTHWARD INTO THE REGION TODAY...AND WITH STRONG 
SUBSIDENCE...SHOULD HAVE MAINLY CLEAR SKIES BY AFTERNOON. WITH
COLD AIR ADVECTION BEHIND THE EXITING FRONT...STEEP LAPSE
RATES...AND 850 MB WINDS OF AROUND 25 KTS...IT WILL BE A BREEZY
DAY. IN ADDITION IT WILL BE MUCH COOLER WITH TEMPERATURES A GOOD
10 TO 15 DEGREES LOWER THAN YESTERDAY...WITH HIGHS RUNNING IN THE
LOWER TO MID 50S THROUGH THE NORTHEASTERN TOW THIRDS OF THE
CWA...TO UPPER 50S AND LOWER 60S THROUGH THE JAMES RIVER AND
MISSOURI RIVER VALLEY AREAS.

THE MAIN CONCERN FOR TONIGHT AND VERY EARLY SUNDAY CONTINUES TO
BE THE STRONG POTENTIAL FOR A FROST OR FREEZE. CENTER OF THE
SURFACE RIDGE AXIS BECOMES ORIENTATED CLOSE TO I 29 THROUGH THE
NIGHT. A DECENT RETURN FLOW BEGINS IN OUR SOUTH CENTRAL SD COUNTY
ZONES BY AROUND MIDNIGHT. THIS FACT...COUPLED WITH WHAT WILL
LIKELY BE MID LEVEL CLOUDS MOVING INTO THAT AREA AFTER MIDNIGHT
AND EARLY SUNDAY...SHOULD KEEP THOSE AREAS FROST FREE THROUGH THE
NIGHT. IN FACT KEPT THOSE ZONES ABOVE MOST GUIDANCE READINGS FOR
LOW TEMPERATURES. ELSEWHERE IS A DIFFERENT STORY. STRONG
RADIATIONAL COOLING WILL BE IN PLAY WITH CLEAR SKIES AND LIGHT
WINDS. THAT SAID...ON THE EAST SIDE OF THE RIDGE AXIS...THERE MAY
BE JUST ENOUGH OF A NORTHWEST WIND TO KEEP AREAS FROM WINDOM MN TO
STORM LAKE IOWA FROM PLUMMETING TOO FAR WITH THEIR TEMPERATURES.
BUT AREAS IN EAST CENTRAL SD...ARCHING DOWN TO AROUND SIOUX
FALLS...EXTREME NORTHWEST IOWA AND MUCH OF SOUTHWEST MN WILL
LIKELY SEE FREEZE CONDITIONS. AT THIS TIME...HAVE ISSUED A FREEZE
WARNING FOR THOSE AREAS...BRACKETED BY A FROST ADVISORY. SO FAR...
IT LOOKS LIKE A HARD FREEZE IS NOT IN PLAY. BUT OF COURSE THIS
WILL BE MONITORED. 

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 404 AM CDT SAT MAY 11 2013

ON SUNDAY...THE SURFACE RIDGE AXIS REALLY DOES NOT MOVE MUCH
GIVING LIGHT WINDS. THEREFORE SUNDAY LOOKS TO BE A PLEASANT DAY
WITH HIGHS RANGING FROM ABOUT 60 EAST...TO 70 AROUND CHAMBERLAIN
SD. ON SUNDAY NIGHT...THE SURFACE RIDGE AXIS FINALLY MOVES
EASTWARD AT A RAPID CLIP. WITH TROUGHING TO THE WEST...A FAIRLY
STRONG SOUTHERLY FLOW KICKS IN. ALL GUIDANCE VALUES EXCEPT
STRAIGHT ECMWF LOOKED TOO COOL WITH THIS TYPE OF SOUTHERLY WIND
EXCEPT IN FAR EXTREME EASTERN ZONES. THEREFORE WENT WITH THE ECMWF
FOR LOWS. 

WITH THE SURFACE TROUGH CONTINUING TO MOVE EASTWARD INTO OUR
FORECAST AREA ON MONDAY...THERMAL RIDGING RESIDES ALONG WITH IT
GIVING QUITE A TIGHT THERMAL GRADIENT FROM WEST TO EAST. AT THIS
TIME WITH WELL MIXED WINDS GETTING A WESTERLY COMPONENT FROM THE I
29 CORRIDOR AND POINTS WESTWARD...GOING ABOVE CONSENSUS GUIDANCE
VALUES LOOKS LIKE A NO BRAINER. JUST REALLY NO EVAPOTRANSPIRATION
YET. GUIDANCE VALUES LOOKED BETTER IN OUR FAR EASTERN ZONES WHERE
UPPER 70S SHOULD PREVAIL. RIGHT NOW...NOT CONVINCED ANYWHERE IN
OUR FORECAST AREA WILL HIT RED FLAG WARNING CRITERIA MONDAY
AFTERNOON...BUT SOME LOCATIONS MAY BE CLOSE. THE PROBLEM WE HAVE
IS IT LOOKS LIKE THE STRONGEST WINDS WILL BE EAST OF I 29 WHERE WE
HAVE THE COOLEST TEMPERATURES...AND THUS THE HIGHEST HUMIDITY
VALUES. ALONG AND WEST OF I 29...THE HUMIDITY VALUES BECOME QUITE
DRY. HOWEVER THOSE AREAS ARE CLOSER TO THE TROUGH AXIS COUPLED
WITH LIGHTER WINDS ALOFT. SO WE MAY NOT HAVE ENOUGH WIND FROM I
29 WEST. THIS WILL BE REEVALUATED OF COURSE IN UPCOMING SHIFTS. 

THE SHORT WAVE RESPONSIBLE FOR THE AFOREMENTIONED SURFACE TROUGH
MORE OR LESS WEAKENS AS IT TRIES TO MOVE EAST. THEREFORE THE
SURFACE TROUGHING BECOMES DIFFUSE AND DIES MONDAY NIGHT...ONLY TO
BE REPLACED BY A PRE FRONTAL TROUGH MOVING INTO THE CENTRAL
DAKOTAS BY LATE MONDAY NIGHT. A BIT TROUBLING...THE ECMWF AND GFS
BOTH HAVE SPED UP THEIR RESPECTIVE COLD FRONTAL TIMING IN OUR
FORECAST AREA ON TUESDAY. NOW IT WILL STILL BE HOT IN OUR FORECAST
AREA FOR THIS TIME OF YEAR. BUT DID MODESTLY COOL OFF OUR
NORTHWEST ZONES...RELATIVELY SPEAKING...INTO THE UPPER 80S. OTHER
LOCATIONS WE KEPT IN THE LOWER 90S. WITH THE FRONTAL TIMING TAKEN
LITERALLY...WOULD NOT BE SURPRISED AT ALL IF SOME AREAS IN
NORTHWEST IOWA HIT THE MID 90S. AS ON MONDAY...WE WILL HAVE TO
WATCH TUESDAY FOR FIRE WEATHER CONCERNS. HOWEVER AT THIS
TIME...THE DEW POINT VALUES AND THUS HUMIDITY READINGS LOOK TOO
HIGH FOR RED FLAG CONCERNS. 

THE REST OF THE WEEK WILL BE COOLER AFTER THE COLD FRONTAL PASSAGE
ON TUESDAY. UPPER PATTERN LOOKS TO BE QUASI ZONAL WITH RAINFALL
CHANCES REALLY HIT AND MISS. WILL LIKELY BE A LOT MORE MISS THAN
HIT. HOWEVER NEXT WEEKEND AFTER THE EXTENDED PERIOD STILL LOOKS
ACTIVE WITH RAIN AND EMBEDDED THUNDERSTORMS. 

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1028 PM CDT FRI MAY 10 2013

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. A NARROW BAND OF
LIGHT SHOWERS ACCOMPANYING THE COLD FRONTAL PASSAGE WILL TRACK
SOUTHEAST THROUGH THE EASTERN FORECAST AREA THROUGH THE NEXT FEW
HOURS. DRY AIR A THE LOSS OF DAYTIME HEATING WILL KEEP SHOWER IMPACT
MINIMAL AS THIS ACTIVITY CONTINUES TO DISSIPATE INTO THE EARLY
MORNING HOURS. WINDS WILL TURN NORTH RIGHT BEHIND THE FRONT BECOME QUITE
BREEZY...ESPECIALLY ACROSS SOUTHWEST MINNESOTA AND ADJACENT COUNTIES
WHERE GUSTS TO 30 KT WILL BE POSSIBLE FOR A FEW HOURS. WINDS WILL
REMAIN RATHER BREEZY OVERNIGHT FROM THE NORTH NORTHWEST...BUT ARE
EXPECTED TO INCREASE ONCE AGAIN TO 15 TO 30 KT LATE SATURDAY MORNING
THROUGH MID EVENING.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...FROST ADVISORY FROM 3 AM TO 9 AM CDT SUNDAY FOR SDZ052-058-059-
     064-065-068>071.

     FREEZE WARNING FROM 3 AM TO 9 AM CDT SUNDAY FOR SDZ038>040-
     053>056-060>062-066-067.

MN...FROST ADVISORY FROM 3 AM TO 9 AM CDT SUNDAY FOR MNZ081-090.

     FREEZE WARNING FROM 3 AM TO 9 AM CDT SUNDAY FOR MNZ071-072-080-
     089-097-098.

IA...FROST ADVISORY FROM 3 AM TO 9 AM CDT SUNDAY FOR IAZ003-013-014-
     020>022-031-032.

     FREEZE WARNING FROM 3 AM TO 9 AM CDT SUNDAY FOR IAZ001-002-012.

NE...FROST ADVISORY FROM 3 AM TO 9 AM CDT SUNDAY FOR NEZ013-014.

&&

$$

SHORT TERM...JM/MJF
LONG TERM...MJF
AVIATION...