FXUS63 KFSD 051100
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD
459 AM CST SAT DEC 5 2009

.DISCUSSION...
BUSY UPR PATTERN ACRS THE CONUS...WITH LARGE SCALE RIDGE FM DESERT 
SW INTO THE WRN PLAINS...THEN A CONFLUENT FLOW PATTERN THRU NRN 
PLAINS WITH STRONG WAVE DIGGING SWRD THRU MANITOBA...AND SET OF 
WAVES PUSHING THRU PAC NW...ASSOCIATED WITH SOME FAIRLY IMPRESSIVE 
HT FALLS FROM ERN WA INTO WRN MT. A BROADLY FRONTOGENETIC AREA IN 
PLACE FROM NRN SD INTO MN...BUT NOT A LOT OF MOISTURE TO WORK WITH 
OUTSIDE THE HELP OF THE HIGH PLAINS. WAVE PUSHING THRU NERN AREA OF 
REGION TDA WL HELP TO INCREASE JET PUSHING THRU THE PLAINS...AND 
DRIVE CDFNT SWRD THRU THE REGION.  WL LKLY SEE AN INCREASE IN CLDS 
THRU THE DAY...STARTING W AND N AND PUSHING SWRD...AND NOT SURPRISED 
TO SEE SOME MID LVL VIRGA BY LTR AFTN THRU FAR N WITHIN MID LVL 
FRONTOGENETIC ZONE AHEAD OF FIRST SHEARING WAVE FROM NWRN U.S. WITH 
CLDS PERHAPS MORE OF A FACTOR NORTH AND THE SWRD PUSH OF COOLER 
AIR...CUT BACK A BIT ON HIGHS...KEEPING FAR SOUTH AWAY FROM RECENT 
ACCUMULATING SNOW JUST ABOVE FREEZING.

AS COLD AIR PUSHES SWRD...SHUD ALSO SEE SOME LOWER CLOUDS TO N BUILD 
SWRD OVERNIGHT. WHILE DID NOT PUT IN ANY FLURRIES...WL HAVE TO WATCH
WITH TMPS IN CLOUD BEARING LEVELS AGAIN HIGHLY DENDRITIC. OTHER THAN 
TO DROP LOWS A COUPLE DEGREES SOME AREAS...DID NOT MAKE SIGNIFICANT 
CHANGES TO OVERNIGHT TMPS.

FIRST SIGNIFICANT FEATURE TO FOCUS ON IN SHORT TERM EVOLVES ON 
SUNDAY...AS SECOND PAC NW WAVE DIGS INTO THE CNTRL ROCKIES AND MOVES 
OUT INTO THE PLAINS ON SUNDAY. NICE PV WALL AND WITH MID LVL FRONT 
IN PLACE WITHIN CONFLUENCE ZONE.  EXIT OF INITIAL JET THRU MN SHOULD 
SET THE STAGE...DRIVING IN SOME DRIER LOW LVL AIR TO NRN/NERN CWA...
WHILE APPROACH OF SRN JET WITH TRAILING WAVE SHOULD BE FEATURE TO 
ENHANCE PCPN. APPEARS TO BE A NICE FRONTAL BAND EVENT...WITH LAPSE 
RATES ABOVE THE FRONT AT LEAST PASSABLE FOR SOME WKR JET/FRONT 
COMMUNICATION. FAIRLY DIVISIVE SET OF SLNS ON TRACK OF MID LVL 
LOW/FRONT...WITH GFS/CANADIAN GLOBAL AND REGIONAL/ECMWF CLOSER AND 
SOMEWHAT SWRD... AND NAM/SREF FAVORING THE MORE NWRD SLN. IN 
CONFLUENT PATTERN...WOULD TEND TO SUPPORT THE SLIGHTLY MORE SWRD 
SLN...BUT GENERALLY DID SHIFT THINGS MORE NWRD THAN COLLECTIVE OF 
SRN SETS...WITH LATEST GUIDANCE HINTING AT A SLIGHT NWRD DRIFT. DRY 
AIR WL SLOW UP INITIAL ONSET OF PCPN OVER WHAT WOULD TYPICALLY BE A 
FAIRLY RAPID MID LVL FRONTAL DEVELOPMENT TYPICALLY FASTER SATURATING 
THAN MODELS IN GOOD PV LINKUP WITH FRONTAL ZONE SETUPS...SO DID NOT 
STRAY TOO FAR FROM INDICATED SATURATION TIMING. WITH EPV FAIRLY HIGH 
ABV FRONTAL ZONE...DO NOT EXPECT STRONG NARROW BANDING...JUST A BROAD
UNFOCUSED FRONTAL BAND. RIGHT NOW...EXPECT THAT MAIN BAND AXIS WL 
SET UP FROM N OF OAX TO NEAR MCW...WHICH PUTS THE SERN CWA ON THE 
NRN EDGE OF POTENTIALLY BETTER SNOWFALL RATES.  COLLECTIVE OF TEMPS 
WOULD SUGGEST A 14-18/1 RATIO...WHICH PUTS THE SERN CWA IN THE 
THREAT FOR A LOW END ADVY EVENT SUN AFTN/EVNG. FOR NOW...SETTLED ON 
A 2-3 INCH BAND SOUTH OF A SIOUX CITY TO SIOUX RAPIDS LINE... 
DROPPING OFF PRETTY QUICKLY NWRD. PCPN SHUD TAPER OFF FAIRLY QUICKLY 
IN THE 03Z-09Z FROM W TO E.

MONDAY SHUD BE A QUIET DAY WITH LOW AND MID LVL RIDGING TAKING 
CONTROL.  GOOD SWRD DRIVE OF COLD AIR EXPECTED...AND SHUD AT LEAST 
SEE DECENT SC FIELD ALG/AHEAD OF LOW LVL RIDGE AXIS. CUT TMPS BACK 
ESPLY OVER EXPECTED NEW SNOWCOVER...WITH CAA THRU DAY NOT EXACTLY 
DOING ANY FAVORS TO MIXING POTENTIAL.

BIG QUESTION INTO MON NIGHT WL BE HOW MUCH POTENTIAL THERE WILL BE 
FOR COOLING IN THE EVENING WITH RIDGE AXIS NEARBY. RH FIELDS HAVE 
SOMEWHAT MORE A COLD AIR LOOK RATHER THAN A WIDESPREAD LOW CLOUD 
LOOK...SO EXPECT THAT SC FIELD SHUD HAVE AT LEAST SOME BREAKS 
HEADING INTO THE EVENING. RADIATIVE COOLING NEAR NEW SNOW COVER...IN 
SUCH A COOLD AIRMASS... WITH SUCH A LIGHT GRADIENT WOULD BE 
FORMIDIBLE...ESPLY THRU NW IA NEAR THE FAVORED IA GREAT LAKES AREA. 
FOR THIS REASON...SEVERELY CUT LOW TEMPS IN EXPECTATION OF AT LEAST 
A FEW BREAKS IN CLDS...BUT TMPS TREND SHUD BE QUITE NON DIURNAL WITH 
RAPID INCREASE IN CLDS FROM THE SW IN ADVANCE OF THE NEXT BIG SYSTEM.
DEVELOPING WAA MON NIGHT LKLY TO GET THINGS GOING IN TERMS OF PCPN
FAIRLY QUICKLY...THRU THE MO VLY ALREADY BEFORE MIDNIGHT...AND OVER
MUCH OF THE CWA BY DAYBREAK TUE.

CONTINUES TO BE SOME QUESTIONS REGARDING NEXT SYSTEM WHICH IS THE 
ENERGY ASSOCIATED WITH THE KICKER OF THE FIRST TWO PAC NW SYSTEMS.
EVEN IF A MORE SWRD TRACK TAKES EFFECT PER LATEST ECMWF...HARD TO
SEE MOST AREAS NOT AT LEAST RECEIVING SOME SNOWFALL...IF NOT FROM 
DYNAMICS ASSOCIATED WITH THE SRN STREAM ENERGY...THE STRONGER NRN 
STREAM SYSTEM WOULD PROVIDE THE NECESSARY PRECIP SUPPORT. GIVEN THE 
COLD...DEVELOPING GRADIENT...AND POTENTIAL FOR SIGNIFICANT SNOWFALL 
ESPLY THRU SERN CWA WITH DECENT MID LVL BNDRY IN PLACE...DID 
INCREASE POPS AND ADDED IN BLSN FOR TUE NIGHT/WED MORNING PERIOD 
WITH CONSENSUS OF SLNS INDICATING SIGNIFICANT CYCLOGENESIS TO THE 
SOUTHEAST DURING THE OVERNIGHT PERIOD. ONE THING IS THAT IT APPEARS 
TO BE MORE OF A LONGER DRAWN OUT ACCUMULATIVE EVENT...WITH WAA PCPN 
STARTING MON NIGHT INTO TUE...AND MAIN WAVE DYNAMICS AFFECTING 
MAINLY SERN CWA TUE NIGHT INTO EARLY WED MORNING. A LOT WL DEPEND ON 
THE DEGREE OF NRN/SRN STREAM PHASING...WHICH IS A BIT LESS THAN 
OPTIMAL FOR GETTING A MORE EXTREME CYCLOGENESIS.  FOR MOST 
PART...TMPS IN THE TUE/WED TIMEFRAME ALSO NUDGED DOWN...WITH 
INDICATIONS FOR SOMEWHAT RESTRICTED DIURNAL RANGE AND ENTRENCHED LOW 
LVL COLD AIR. /CHAPMAN

&&

.AVIATION...
VFR THRU 06Z SUN. CIGS BECOMING MVFR N OF INTERSTATE 90 AFTER 06Z. 

&&

.FSD WATCHES/WARNINGS/ADVISORIES...

SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.

$$