000
FXUS63 KFSD 201640
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1040 AM CST THU NOV 20 2008
.DISCUSSION...
QUITE A BIT DRIER AIR HAS WORKED INTO PARTS OF THE CWA THIS MORNING
BEHIND MAIN UPPER LEVEL ENERGY...ALLOWING FOR MORE SUNSHINE ACROSS
THE EASTERN HALF OF THE AREA. WITH CONTINUED COLD ADVECTION THROUGH
THE DAY...THINK THE SUNSHINE WILL EVENTUALLY BECOME SELF-DESTRUCTIVE
AND WILL CONTINUE WITH PARTLY SUNNY FORECAST MOST AREAS. WILL ALSO
KEEP MENTION OF FLURRIES IN THE FORECAST AS WEAKLY CONVECTIVE CLOUD
LAYER IS IN FAVORED TEMPERATURE RANGE TO SQUEEZE OUT SOME FLAKES
HERE AND THERE.
SPEAKING OF TEMPERATURES...LOOKS LIKE IT WILL BE DIFFICULT TO SEE
MUCH RISE WITH COLD AIR POURING SOUTHWARD INTO THE AREA. TWEAKED
HOURLY TEMPS EARLIER...BUT LITTLE CHANGE IN GOING HIGHS AT THIS
TIME. UPDATED GRIDS/PFM/ZFP HAVE BEEN SENT.
&&
.AVIATION...
PERIODS OF MVFR CIGS WILL CONTINUE INTO THE AFTERNOON...THOUGH DO
NOT EXPECT A SOLID MVFR DECK WITH SOME DRIER AIR GRADUALLY WORKING
SOUTH INTO THE AREA. SCATTERED FLURRIES WILL ACCOMPANY ANY CLOUD
COVER...AND VSBYS LARGELY EXPECTED TO REMAIN VFR. ANY DIP INTO
HIGHER END OF MVFR RANGE SHOULD BE VERY BRIEF AND WILL NOT BE
INCLUDED IN AREA TAFS. NLY SFC WINDS MAINLY 15 TO 25 KTS THROUGH
THIS AFTERNOON...THEN LIGHT WINDS TONIGHT.
&&
.PREV DISCUSSION...
IN THE NEAR TERM...COOL CANADIAN HIGH PRESSURE WL BE IN CONTROL
TODAY. CURRENT IR CONTS TO SHOW STRATOCU STREAMING DOWN FM THE
NORTH. HOWEVER THERE ARE BIG BREAKS IN IT...SUCH AS THRU WRN SD AND
ERN ND ATTM. EVEN SOME DECENT BREAKS IN SERN SD. SO AT TIMES...MAY
BE TOO PESSIMISTIC WITH CLOUD GRIDS. STILL...LLV LAPSE RATES ARE
STEEP AND WITH A VORT FILAMENT WORKING THRU THIS MORNING...ONE
CANNOT RULE OUT SOME FLURRIES. H925-H85 MOISTURE IS ABUNDANT TODAY
CWFA WIDE...ESP IN OUR WRN FA THIS MORNING. HOWEVER BOTH THE NAM AND
GFS RH TIME SECTIONS BEGIN TO RAPIDLY DRY OUT THINGS LATE THIS
AFTERNOON. SNDGS MIX TO ABOUT H875-H85 TODAY...SO OUR CURRENT TEMPS
LOOKED REAL CLOSE. NUDGED UP SOME LOCATIONS A COUPLE OF DEGS TO
ACCOUNT FOR THE MIXING.
TONIGHT SHOULD SEE RAPIDLY CLEARING SKIES IF THEY ARE NOT ALREADY
CLEAR BY 00Z. AS THE SFC HIGH PRES SYSTEM MOVES OFF TO THE EAST...
WINDS BEGIN TO TURN AROUND TO THE SE IN OUR WRN FA FAIRLY QUICKLY.
THEREFORE WENT WITH SOME NON DIURNAL THERMAL READINGS IN OUR FAR WRN
FA TONIGHT...BOTTOMING THOSE LOCATIONS OUT AROUND MIDNIGHT...THEN A
SLOW RISE. HELD THE JAMES VALLEY TEMPS RATHER STEADY AFT MIDNIGHT
DUE TO THE RETURN FLOW...BUT LIGHTER. AREAS E OF THE JAMES SHOULD
SEE TEMPS PLUMMET INTO THE SINGLE DIGITS...BRINGING THE CHILLIEST
LOWS OF THE SEASON SO FAR.
WERE STILL LOOKING AT AN UPPER LOW AND ASSOCIATED SFC WRMFNT
IMPACING OUR WX FRI AND FRI NIGHT. CONTINUED TO FOLLOW THE GFS MORE
THAN THE NAM...ALTHOUGH THE NAM HAS BECOME CLOSER IN LINE WITH THE
GFS/ECMWF/GEM PLACEMENT MOVG ITS SOLUTION FURTHER N. MOISTURE
PROFILE IS BONE DRY IN FRONT OF THIS SYSTEM...WITH RAPID SATURATION
HEADING TOWARD THE WRMFNT AND UPPER DISTURBANCE. SNOWFALL CHCS STILL
LOOK PRETTY GOOD...WITH THIS AREA FIRMLY PLACED IN A STRONG LEFT
EXIT REGION OF A JET...AND THE MODEL SNDGS SHOWING A LARGE...
EFFICIENT CLOUD LYR IN THE DENDRITIC ZONE. A GOOD PORTION OF OUR FA
MAY PICK UP A QUICK INCH OR TWO OF SNOW. IT WOULD BE MORE BUT THE
TIME FRAME OF THE BEST DYNAMICS JUXTAPOSITIONED WITH THE DEEPEST
MOISTURE PROFILE AND ISENTROPIC LIFT IS PRETTY SHORT. BOTH THE NAM
AND GFS UPPER -DIV Q IS PROGGED TO MOV SQUARELY ACROSS THIS FA...
WITH THE ISENTROPIC LIFT A BIT STRONGER THRU OUR SRN HALF THEN NRN
HALF. HOWEVER...THE MOISTURE PROFILE IS PROGGED TO BE DEEPER ACROSS
OUR NRN HALF. SO BELIEVE WE ARE LOOKING AT A HIGH POP...LOW QPF
EVENT FOR MANY SPOTS. MAX TEMPS ON FRIDAY MAY BE REALIZED IN THE
EARLY EVENING OR CLOSE TO IT. THIS IS BECAUSE OUR ERN TWO THIRDS WL
BE STARTING SO COLD. AND THE WRMFNT DOES NOT PASS THRU OUR SWRN FA
UNTIL LATE AFTERNOON. BECAUSE OF THE PROXIMITY OF THE WRMFNT...
STILL HAVE A LATE AFTERNOON MIX OF RA/SN IN OUR SWRN FA. IN ADDITION
FRIDAY EVENING...TEMPS FM H925-H9 ON THE GFS ARE STUBBORNLY WARM AT
JUST ABV 32 DEGS F NEAR THE MO RIVER VALLEY. SO IF THEY RECEIVE ANY
LIGHT PCPN...THERE COULD BE A BIT OF FZRA IN THERE FM KYKN TO SIOUX
CITY.
OTHERWISE...THE SYSTEM PULLS EWD FAIRLY RAPIDLY FRI NIGHT. LITTLE
CHANGES TO THE WEEKEND AS MODELS HAVE NOT FLIP FLOPPED WITH ANYTHING
MAJOR FOR THIS FCST.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&
$$
JH
