FXUS63 KFSD 291658
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1055 AM CST SUN NOV 29 2009
.DISCUSSION...
UPDATED THE FORECAST THIS MORNING TO LOWER TEMPERATURES WEST OF
INTERSTATE 29. LOW CLOUDS AND STRATUS LINGERING SLIGHTLY LONGER
THAN ANTICIPATED...AND EXPECT STRATOCUMULUS TO DEVELOP ALONG THE
BACKSIDE OF THE STRATUS TO MAKE IT A STRUGGLE TO FULLY MIX TO 925
HPA. UPDATED PRODUCTS POSTED. /BT
&&
.AVIATION...
AREA OF STRATUS...GENERALLY FROM 2000 TO 3000 FT AGL...WILL
GRADUALLY SHIFT TO THE SOUTH AND EAST. EXPECT THAT THE OVC SKIES
WILL MOVE EAST OF KFSD AND KSUX BY 20Z. HOWEVER...WITH COLD TEMPS
ALOFT AND DAYTIME HEATING...EXPECT STRATOCU TO REFORM THIS
AFTERNOON. THIS WILL LIKELY AFFECT AREAS EAST OF THE JAMES RIVER
VALLEY. ONCE THE SUNSETS BY 22Z EXPECT MAIN STRATUS TO BE EAST OF
THE AREA WITH STRATOCU RAPIDLY DISSIPATING LEAVING VFR CONDITIONS.
EXPECT W TO NW FLOW TO CONTINUE THROUGH THE NIGHT.
&&
.PREV DISCUSSION...
TEMPERATURES REMAIN THE PRIMARY FOCUS OF THE FORECAST THROUGH THE
NEXT FEW DAYS...WITH THE STREAK OF ABOVE NORMAL READINGS CONTINUING
INTO TUESDAY BEFORE STRONG COLD FRONT PLUNGES SOUTHWARD TUESDAY AND
TUESDAY NIGHT.
FOR TODAY...FAIRLY WIDESPREAD AREA OF STRATUS TO OUR NORTH POISED TO
SLIDE INTO CENTRAL/EASTERN PORTIONS OF THE CWA THIS MORNING. STRATUS
WILL LINGER LONGEST INTO THE EARLY-MID AFTERNOON ACROSS PORTIONS OF
SOUTHWEST MINNESOTA/NORTHWEST IOWA...AND WILL KEEP HIGH TEMPERATURES
THERE CLOSER TO COOLEST GUIDANCE IN THE MID TO UPPER 30S. MORE SUN
AND MODEST MIXING WITH WEST-NORTHWEST FLOW SHOULD YIELD MID 40S FOR
AREAS WEST OF THE JAMES RIVER.
VERY MILD AIR AGAIN TAKING OVER FOR MONDAY WITH 925MB TEMPS OF +5C
IN THE NORTHEAST CWA TO +10C IN THE SOUTHWEST. COULD HAVE SOME MID
LEVEL WARM ADVECTION CLOUDS DEVELOP OVER THE CWA TONIGHT AND LINGER
OVER THE NORTHEAST CWA EARLY IN THE DAY...BUT SHOULD MOVE OUT OF THE
AREA BY EARLY AFTERNOON AND WOULD NOT EXPECT THEM TO HAMPER WARMING
TOO MUCH AS STRONGER WESTERLY FLOW SHOULD ALLOW FOR STRONG MIXING.
MOST AREAS SHOULD SEE HIGHS ABOUT 10 DEGREES WARMER ON MONDAY THAN
TODAY.
NEXT COUPLE OF NIGHTS WOULD EXPECT TO SEE SOME ELEVATION DEPENDENT
TEMPS ACROSS THE AREA WITH RELATIVELY LIGHT THOUGH NOT COMPLETELY
CALM WINDS. WARMEST READINGS WILL LIKELY BE ACROSS GREGORY COUNTY
AND ALSO EAST OF THE BUFFALO RIDGE IN SOUTHWEST MINNESOTA...WHERE
LOW LEVEL FLOW FROM THE SOUTHWEST FAVORS GOOD DOWNSLOPE. THIS COULD
BE MORE DRAMATIC MONDAY NIGHT THAN CURRENTLY FORECAST...AND LATER
SHIFTS MAY HAVE TO WARM THE FAR NORTHEAST FURTHER AS 925MB TEMPS
CLIMB TO +6C BY 12Z TUESDAY.
COLD FRONT PUSHES THROUGH THE CWA TUESDAY...AND ASIDE FROM THE
OPERATIONAL GFS STILL BEING ON THE FAST SIDE WITH THE SURFACE
BOUNDARY...MODELS SEEM TO BE SETTLING ON TIMING SIMILAR TO PREVIOUS
FORECAST...PUTTING THE FRONT IN THE SOUTHEAST CORNER OF OUR CWA BY
00Z WEDNESDAY. TIMING OF LOW LEVEL COOLING BEHIND THE FRONT SEEMS TO
BE MORE IN QUESTION...WITH NAM SHOWING MUCH MORE AGGRESSIVE 850MB
COLD PUSH THAN EITHER ECMWF OR GEM. NAM ACTUALLY AMONG THE WARMEST
MODELS AT 18Z AHEAD OF THE BOUNDARY...BECOMING ONE OF THE COLDEST
BY 00Z BEHIND THE FRONT. IF NAM TAKEN AT FACE VALUE...COULD SEE
STRONGER NON-DIURNAL TREND TO TEMPS WITH READINGS WARMING QUICKLY BY
MIDDAY...THEN FALLING OFF IN THE NORTHWEST THROUGH THE AFTERNOON...
THOUGH INITIAL COOLING ALOFT MAY LEAD TO WARMER TEMPS BRIEFLY AS
DEEPER MIXING RESULTS. HAVE NOT GOTTEN TOO AGGRESSIVE WITH AFTERNOON
COOLING DUE TO THIS...BUT DO HAVE TEMPS IN OUR NORTHWEST BECOMING
FAIRLY STEADY AFTER 18Z AND TAILING OFF AFTER 21Z.
THIS COLD FRONT WILL SIGNAL TRANSITION BACK TO MUCH MORE SEASONAL
AIR ACROSS THE REGION...WITH SUBZERO 850MB TEMPS BECOMING ENTRENCHED
OVER THE AREA THROUGH THE END OF THE WEEK. WHILE THE MID-LATTER PART
OF THE WEEK WILL FEEL MUCH COOLER...READINGS WILL GENERALLY BE CLOSE
TO OR JUST A FEW DEGREES BELOW EARLY DECEMBER NORMALS. /JH
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
$$
JH/SCHUMACHER
