000
FXUS63 KFSD 032148
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
348 PM CST WED DEC 3 2008
.DISCUSSION...
WEAK LITTLE WAVE WILL MOVE FROM NORTHERN PARTS OF THE WESTERN HIGH
PLAINS INTO THE EASTERN DAKOTAS TONIGHT. VERY COLD THERMAL PROFILE
SO OBVIOUSLY ALL SNOW...BUT WITH VERY LIMITED MOISTURE...AMOUNTS
SHOULD BE FAIRLY LIGHT. CURRENT FORECAST GOING WITH ABOUT A TRACE TO
AN INCH FROM ABOUT BROOKINGS TO PIPESTONE TO JACKSON AND SPENCER AND
WILL MAINTAIN THOSE AMOUNTS. WILL DECREASE THE HIGHER POPS OVER
SOUTHERN PARTS OF NW IA SOME...AND INCREASE A LITTLE OVER THE
NORTH...BUT OVERALL PRETTY GOOD PLACEMENT. TEMPERATURES NOT EASY
TONIGHT AS A WEAKENING IN THE WIND FIELD THIS EVENING WILL LIKELY
LEAD TOWARDS A PRETTY QUICK FALL IN THE EASTERN TWO THIRDS OF THE
CWA...THEN DEW POINTS AND TEMPERATURES WILL RISE A LITTLE AS THE
NORTHWEST WINDS KICK IN AGAIN. AFTER THIS...LATE TONIGHT INTO EARLY
TOMORROW MORNING...COLDER AIR WILL WORK IN FROM THE NORTH AND
TEMPERATURES WILL LIKELY FALL WELL INTO THE MORNING OVER THE NORTH.
FRONTOGENETICALLY FORCED SNOW BAND MAY BE LINGERING IN NERN CWA
EARLY ON...BUT OVERALL COVERAGE WL ON THE DOWNTREND EARLY IN THE
DAY. REINFORCING CDFNT EXITS VERY EARLY...WITH DAY DOMINATED BY CAA.
AIRMASS IS A COUPLE DEGREES C COLDER THRU THE LOWER ATMOSPHERE THAN
TDA...SO REALLY EXPECT TMPS TDA TO BE UPPER BOUND TO POSSIBILITIES.
THE COLD AIR ALFT AND RESULTANT LOWER STABILITY AND SLIGHTLY
CYCLONIC ENVIRONMENT WL LKLY RESULT IN MORE IMPRESSIVE CLOUD STREET
DEVELOPMENT ON THURSDAY...AS WELL AS BETTER ORGANIZATION OF SCT SNOW
SHOWERS. OTHER THAN A FEW LINGERING FLURRIES EARLY IN THE EVENING
AS CLOUDS DISSIPATE...WL BE DRY THU NIGHT AS MASSIVE SFC RIDGE SINKS
INTO THE CNTRL PLAINS. CLASSIC DECOUPLING FOR LOWER ELEVATIONS WITH
NEW SNOWCOVER...STRONG DIRECTIONAL VARIATION IN WNDS.
ON FRIDAY...ANOTHER WAVE IN NW FLOW CRASHES SEWRD INTO THE NRN
PLAINS ON FRIDAY...DRIVING CLIPPER WAVE INTO MN LATE DAY. NAM IS A
VERY SLOW OUTLIER COMPARED TO ALL OTHER GUIDANCE. SHUD BRING A RAPID
INCREASE IN HIGH CLOUDS EARLY FRIDAY...WHICH WL TAKE THE EDGE OFF
ANY WARMING WHICH THE SW LOW LVL FLOW MIGHT THREATEN. ATM IS QUITE
DRY DOWN LOW...WHICH WL LKLY KEEP ANY PCPN THREAT OUT OF AREA THRU
THE DAY...BUT LOOK FOR A GOOD DEAL OF VIRGA THRU THE LATER AFTN AS
MAIN ENERGY DROPS TOWARD WRN/CNTRL MN.
DEEPER LIFT FORCING WITH MN WAVE SHUD ALLOW FOR A SMALL THREAT FOR
LIGHT SNOWS DURING THE EVENING ACRS SWRN MN AND NEIGHBORING IA GREAT
LAKES AREA AS WAVE SINKS SWRD...BUT MORE IMPORTANTLY THE NEXT IN
LINE OF COLD PUSHES WILL CRASH SWRD. COULD BE SOME SHALLOW
FRONTALLY FORCED SNOW SHOWERS MOVING SWRD NEAR AND POST FRONTAL.
HIGH PRESSURE WL BUILD SWRD ON SAT WITH ANOTHER COLD AND BLUSTERY
DAY. TMPS VERY REMINISCIENT OF RECENT COLD PUSHES...IF ONLY A BIT
MORE MODERATED. WINDOW STILL OPEN FOR VERY CHILLY SUNDAY MORNING...
WITH SOME QUESTION ON HOW QUICKLY HIGH CLOUDS MAY INTERFERE WITH
THE COOLING NEAR RIDGE AXIS THRU ERN MN AND IA CWAS. OTHERWISE...
MIGHT HAVE GONE A FEW MORE DEGREES DOWN ARND MWM/SPW AREAS.
IN THE EXTENDED RANGE /SUN THRU WED/ LOOKS TO BE THE BATTLE OF
ENSEMBLES AGAINST OPERATIONAL...WITH MOST OF THE OPERATIONAL RUNS OF
LATE AT ODDS WITH THE BULK OF ENSEMBLE SLNS. ENS MEANS AND LARGER
CLUSTER BY FAR SUGGEST THAT THERE WL BE MORE SPLITTING TO FLOW...
DIGGING MORE TOWARD SWRN U.S. AND MORE NRN STREAM DOMINANCE.
OVERALL...THESE SUGGEST A SLN CLOSER TO ECMWF...WHICH 12Z GFS HAS
SLIDE STEPPED TOWARD. SUNDAY LKLY TO FEATURE WAA ZONE INTENSIFYING
THRU SUN NIGHT HEADING E/NE. TEMP DO WARM ALOFT ENOUGH TO THREATEN
SOME OTHER TYPE OF PCPN THAN JUST SNOW...AND MAY EASILY END UP SOME
LIGHTER FREEZING RAIN OR SLEET ON WARMER SIDE OF BAND SUN NIGHT INTO
MON. MAIN DYNAMICS WITH NEXT WAVE AGAIN LOOK TO AFFECT AREAS MOST
STRONGLY WELL TO N AND E. MORE COLD AIR BEHIND SYSTEM WITH ANOTHER
TUESDAY INTO WED SFC RIDGE. SEVERAL INDICATIONS THAT MAY BE A SNOW
EVENT FOR WED AS WAVES CLIP ALG IN NW FLOW...BUT WITH LARGER SCALE
VARIATIONS IN TROUGH/RIDGE LOCATION...WL KEEP CLEAR FOR NOW.
&&
.AVIATION...
EXPECT VFR THROUGH EARLY EVENING WITH SCATTERED TO OCCASIONALLY
BROKEN MVFR CLOUDS. AFTER ABOUT 2Z...CLOUDS AND SNOWFALL CHANCES
WILL INCREASE FROM THE NORTH AND MVFR CEILINGS AND VISIBILITIES WILL
BE SPORADICALLY POSSIBLE THROUGH ABOUT 12-15Z.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
MN...NONE.
SD...NONE.
NE...NONE.
&&
$$
08/CHAPMAN
