919
FXUS63 KFSD 282122
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
322 PM CST SAT NOV 28 2009
DISCUSSION
TRICKY FORECAST TONIGHT AS LOW LYING STRATUS HAS DEVELOPED ALONG AND
EAST OF THE BUFFALO RIDGE ACROSS SOUTHWEST MINNESOTA. STRATUS IS
ATTEMPTING TO SURGE FURTHER SOUTH...HOWEVER...IS STRUGGLING TO DO SO
WITH DRIER...DEEPER MIXED ATMOSPHERE TO THE SOUTH. VISIBILITIES ARE
GENERALLY 2-5 SM WITHIN THIS AREA OF STRATUS...EVEN IN THE MIDDLE OF
THE AFTERNOON. AS THE SUN GOES DOWN...GROWING CONCERN THAT THE
STRATUS MAY TRY TO EXPAND. NOT SURE HOW MUCH THE STRATUS WILL
EXPAND BACK TO THE WEST WITH LOW LEVEL NORTH-NORTHWEST FLOW HANGING
ON THROUGHOUT THE NIGHT...BUT HAVE ADDED MENTION OF FOG TO THE
EASTERN TWO TIERS OF COUNTIES IN CWA.
UPPER LEVEL WAVE ACROSS NORTHEAST MONTANA PRODUCING SOME STRATO
CUMULUS ACROSS EASTERN MONTANA AND LIGHT SNOW HAS EVEN BEEN REPORTED
AT KBHK. WAVE APPEARS TO BE FAIRLY MOISTURE STARVED AS IT WORKS
SOUTH AND EASTWARD...AND WITH UPPER LEVEL JET DYNAMICS MAINLY
FOCUSED TO THE NORTH...DROPPED MENTION OF FLURRIES FOR NORTHERN
COUNTIES TONIGHT. LOW TEMPERATURES WILL BE QUITE TRICKY TONIGHT...AS
THEY WILL BE DEPENDENT ON CLOUD COVER. HAVE RAISED FORECAST LOWS
ACROSS SOUTHWEST MINNESOTA WITH EXPECTATION OF LOW LYING STRATUS
MUCH OF THE NIGHT...WHILE KEPT LOWS IN THE MID 20S TOWARDS CENTRAL
SOUTH DAKOTA AS SKIES CLEAR BEHIND DEPARTING WAVE. /BT
AFTER TONIGHT...THERE IS CERTAINLY NOT A LOT GOING ON SUNDAY THRU
TUE. TONIGHTS WAVE EXITS RAPIDLY TO THE EAST ON SUNDAY LEAVING SOME
PROBLEMATIC STRATOCU IN OUR EAST...WHICH SHOULD EXIT OUR EXTREME
EAST BY EARLY TO MID AFTERNOON. THEN UPPER RIDGING THRU THE NW FLOW
ALOFT BEGINS TO TAKEOVER SUNDAY NIGHT AND MONDAY. THEREFORE WAA
BEGINS TO TAKE PLACE. SUNDAY NIGHT...WENT A SMIDGE BLO GUIDANCE
READINGS WITH DRY AIR AND LITTLE WIND IN PLACE...THEN ONCE AGAIN
WARMED UP TEMPS TO WELL ABOVE NORMAL LEVELS ON MONDAY LIKE WE HAVE
HAD GOING FOR QUITE SOME TIME NOW. MONDAY NIGHT...THE AIR MASS IS
MODIFIED SOME SO IT SHOULD BE A CATEGORY OR TWO WARMER THEN SUNDAY
NIGHT. TUESDAYS TEMPS ARE TRICKY DUE TO THE CDFNT TIMING AHEAD OF
THE ADVANCING UPPER WAVE NEAR THE CANADIAN BORDER...DETAILED BLO IN
THE EXTENDED. THE NAM IS A FEW HRS FASTER THEN THE GFS...WHICH IN
TURN IS A BIT FASTER THEN THE ECMWF/GEM IN COOLING THE H85 TEMPS.
SO FOR NOW...COMPROMISED WITH THE MIDDLE OF THE ROAD GFS SOLUTION.
IT SHOULD BE NOTED THAT NONE OF THESE SOLUTIONS HAVE MUCH OF AN
IMPACT ON THE SFC WIND...AS THEY ARE ACTUALLY ALL PRETTY CLOSE
WITH THE WIND SHIFT. BUT THERE ARE THESE DIFFERENCES IN TERMS OF HOW
FAR BACK THE CHILLY AIR IS SITTING. SO FAR NOW...KEPT MID 40S GOING
IN OUR NORTH...WARMING TO THE LOWER 50S IN OUR SOUTH. /MJF
THE EXTENDED TUE NIGHT THROUGH SATURDAY IS STILL HIGHLIGHTED BY A
FAIR AMOUNT OF VARIANCE BETWEEN THE VARIOUS MEDR MODELS. IN
GENERAL...THE GFS CONTS TO BE A QUICKER AND MORE DEEP OUTLIER WITH
THE COLD UPPER LOW MOVG ACROSS THE NRN PLAINS AND S CENTRAL CANADA
TUE NIGHT THRU WED NIGHT. THE OPERATIONAL GFS FROM 00Z WAS INDEED A
DEEP AND QUICK OUTLIER COMPARED TO NEARLY EVERY OTHER ENSEMBLE
MEMBER. THE 06Z GFS DID SLOW DOWN THE COOL AIR SURGE A BIT ON WED
AND NOT DIG IT SWD SO MUCH...BUT THE 12Z GFS WENT RIGHT BACK TO A
MORE COLD SOLUTION. FOR NOW...SINCE THE GFS ENSEMBLE MEAN WAS SLOWER
AND LESS DIGGY WITH THE CHILLY AIR...CHOSE TO FOLLOW MORE OF A ECWMF
AND GEM GLOBAL SOLUTION. THESE LATTER TWO SOLUTIONS DO BRING COOL
AIR DOWN INTO THIS AREA DURING THE MIDDLE OF THE WEEK...BUT NOT
QUITE AS COLD AS THE GFS. THEN BY LATE IN THE WEEK ON FRI AND
SAT...SOME MODIFICATION OF THE AIR MASS BEGINS AS THE COLD UPPER LOW
EJECTS EWD ACROSS THE GRTLKS. AT THE SFC...WE SHOULD EXPERIENCE A
LOT OF NW WIND...SOME OF WHICH WL BE RATHER BREEZY OR WINDY ON WED
AND THUR WITH PERSISTENT CAA. IN ADDITION...STRATOCU MAY BE ABUNDANT
AS THE COOL AIR POURS DOWN ON WED...LASTING INTO THURSDAY AT LEAST
IN OUR EAST. FOR NOW...KEPT PCPN CHCS NIL THRU THE EXTENDED. THERE
COULD BE A FEW FLURRIES IN OUR ERN HALF WED AND WED NIGHT...BUT
CERTAINLY NOT ENUF TO MENTION RIGHT NOW. /MJF
AVIATION
PREDOMINANTLY VFR CONDITIONS THROUGH 18Z SUNDAY. IFR STRATUS HAS
MAINTAINED ITSELF THROUGHOUT THE DAY ALONG AND EAST OF BUFFALO RIDGE
AND EXPECT SOME EXPANSION TO THE SOUTH AND SLIGHTLY WEST THROUGH THE
OVERNIGHT. UPPER LEVEL WAVE EXPECTED TO MOVE ACROSS THE AREA WILL
RESULT IN SOME STRATOCUMULUS. EXPECTING CEILINGS TO GENERALLY
REMAIN VFR...BUT MAY BRIEFLY FALL INTO THE 2000-3000 FT RANGE
OVERNIGHT. NORTHWEST WINDS ARE EXPECTED TO INCREASE TO 10-20 KNOTS
BEHIND THE DEPARTING WAVE ON SUNDAY. /BT
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
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