FXUS63 KMPX 230552
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1152 PM CST TUE DEC 22 2009
.UPDATE...
ADDED 06Z TAF DISCUSSION BELOW.
&&
.DISCUSSION...
HAS BEEN A HECTIC DAY IN PREPARATION FOR THE COMING SIGNIFICANT
STORM... SO DETAILS WILL BE A BIT SCANT IN THIS DISCUSSION. MAIN
ISSUE IS OBVIOUSLY THE SIGNIFICANT LONG DURATION STORM WHICH WILL
IMPACT THE AREA TOMORROW NIGHT THROUGH FRIDAY NIGHT. LATEST
VISIBLE IMAGERY SHOWS THAT CLOUDS HAVE OVERSPREAD THE AREA... AND
WE SHOULD ESSENTIALLY STAY CLOUDY THROUGH THE REMAINDER OF THE
WEEK... WITH PERHAPS SOME WINDOWS OF BROKEN CLOUDS OVER THE
EASTERN PORTION OF THE AREA DURING THE TWO POTENTIAL DRY SLOT
INTRUSIONS WITH THE COMPLEX SYSTEM THAT WILL IMPACT THE AREA. THE
PLAYERS WHICH WILL BRING THINGS TOGETHER CAN ALL BE SEEN ON THE
CURRENT WATER VAPOR LOOP. THE LEAD PV ANOMALY IS MARCHING INTO
ARIZONA AT THE CURRENT TIME. THIS IS BEING CLOSELY FOLLOWED BY THE
FEATURE SEEN DIVING INTO NEVADA. FINALLY... THE THIRD FEATURE OF
INTEREST CAN BE SEEN NEAR THE BRITISH COLUMBIA ALBERTA BORDER.
WITH THE OBVIOUS COMPLEXITY OF THINGS IT IS EASY TO REALIZE THAT
MANY OF THE FORECAST DETAILS... PARTICULARLY WITH REGARD TO TIMING
AND ANY MIXED PRECIPITATION... ARE YET TO BE WORKED OUT.
HOWEVER... THE MYRIAD OF MODEL GUIDANCE BOTH DETERMINISTIC AND
ENSEMBLE SYSTEMS... ALL SUPPORT A LONG DURATION EVENT WITH PCPN
TOTALS OF BETWEEN AN INCH AND TWO AND HALF INCHES ACROSS THE
FORECAST AREA. WITH SEVERAL DIFFERENT UPPER LEVEL PV ANOMALIES
HAVING A ROLE IN THINGS... WE WILL SEE SEVERAL BOUTS OF PCPN OVER
THE ROUGHLY 60 HOUR PERIOD. MOST OF THAT PCPN LOOKS TO BE IN THE
FORM OF SNOW ACROSS THE FORECAST AREA... WITH THE SOUTHEASTERN
THIRD HAVING THE POTENTIAL TO SEE SOME SLEET AND FREEZING RAIN...
PARTICULARLY IN THE WEDNESDAY NIGHT AND THURSDAY TIME PERIOD AS
THE LEAD WAVE LIFTS NORTH TOWARD THE AREA. FOR THE FORECAST
DETAILS... STUCK WITH A BLEND OF THE GFS... ECMWF... AND
CANADIAN... WHILE USING THE SREF PROBABILITIES TO HELP PLACE SOME
OF THE CHANCES FOR MIXED PCPN.
BEFORE WE GET INTO THE MEAT OF THINGS... WE WILL HAVE SOME LIGHT
PCPN WITH WHICH TO CONTEND TONIGHT. SLOWLY INCREASE LOW LEVEL WARM
ADVECTION TOGETHER WITH ABUNDANT LOW LEVEL MOISTURE SHOULD WORK TO
PRODUCT SOME LIGHT PCPN ACROSS THE SOUTHERN PORTION OF THE AREA
TONIGHT INTO THURSDAY MORNING. WITH MID LEVEL MOISTURE LACKING...
THERE WILL BE ISSUES WITH GETTING ICE CRYSTALS TO FORM DUE TO
TEMPERATURES IN THE MOIST LAYER GENERALLY WARMER THAN -7C. SO...
WILL INCLUDE A MENTION OF FREEZING DRIZZLE TO ACCOUNT FOR THAT
POSSIBILITY. THE EVENING SHIFT WILL NEED TO KEEP AN EYE ON
THINGS... AND IF THE FZDZ BECOMES A SIGNIFICANT ISSUE AN ADVISORY
MAY BE NEEDED LATER TONIGHT.
ON WEDNESDAY WE WILL SEE MOISTURE INCREASE AHEAD OF THE SHORTWAVE
THAT WILL BE LIFTING NORTH TOWARD THE AREA. WARM ADVECTION WILL
INCREASE IN EARNEST BY EVENING... WITH SUFFICIENT FORCING AND
MOISTURE HELPING TO KICK OFF PCPN ACROSS THE SOUTH DURING THE
AFTERNOON... THEN NORTH THROUGH THE REMAINDER OF THE AREA DURING
THE EVENING AND OVERNIGHT HOURS. BEGAN THE WINTER STORM WARNING
FROM SOUTH TO NORTH WITH THE GENERAL ARRIVAL OF THE STEADIER PCPN.
THINGS SHOULD GENERALLY BE IN THE FORM OF SNOW... BUT THE STRONG
WARM ADVECTION LOOKS TO RESULT IN AN ELEVATED WARM LAYER AROUND
800-850MB WITH TEMPERATURES PERHAPS GETTING ABOVE 0C IN THAT LAYER
ACROSS THE SOUTH AND SOUTHEAST PORTION OF THE FORECAST AREA BY
THURSDAY MORNING. SO... MENTIONED SOME POSSIBILITY OF SLEET AND
FREEZING RAIN IN THAT AREA WITH SNOW ELSEWHERE. THIS LEAD PV
ANOMALY TENDS TO SHEAR OUT ACROSS THE AREA ON THURSDAY... AND WE
WILL LIKELY SEE SOME WEAKENING AND A POTENTIAL LULL IN THE PCPN AS
THAT OCCURS.
BY THURSDAY NIGHT THE NEXT SHORTWAVE/PV ANOMALY WILL BE WORKING TO
REDEVELOP THE SURFACE LOW FARTHER SOUTH NEAR ARKANSAS. THIS
FEATURE WILL THEN SWING NORTH AS THE 500MB FLOW BECOMES NEGATIVELY
TILTED. IT SHOULD EVENTUALLY WORK TO DRIVE THE SURFACE LOW NORTH
INTO IOWA BY FRIDAY MORNING. AS ALL OF THIS OCCURS WE SHOULD SEE A
SECOND AREA OF SIGNIFICANT PCPN DEVELOP AND LIFT NORTH TOWARD THE
AREA. AS THIS IS OCCURRING THE WAVE CURRENTLY NEAR BC/ALBERTA WILL
BE WORKING ITS WAY AROUND THE BASE OF THE UPPER TROUGH... HELPING
TO INTENSIFY THE LOW AS IT LIFTS NORTH INTO IOWA. SOME MIXTURE OF
SLEET AND FREEZING RAIN WILL STILL BE POSSIBLE ACROSS THE
SOUTHEASTERN PORTION OF THE AREA DURING THE THURSDAY NIGHT INTO
FRIDAY TIME FRAME... ALTHOUGH IT APPEARS THE SECOND SURGE OF WARM
ADVECTION MAY KEEP THE ELEVATED WARM LAYER JUST TO OUR SOUTHEAST.
THESE ARE THE SORTS OF DETAILS THAT SHOULD COME INTO CLEARER FOCUS
OVER THE NEXT 24 HOURS OR SO.
ON FRIDAY IT APPEARS WE WILL BE CONTENDING WITH AN OCCLUDING
SYSTEM TO OUR SOUTH AND SOUTHEAST WHICH WILL THEN SLOWLY LIFT
NORTHEAST TOWARD WISCONSIN. HOWEVER... WITH A SIGNIFICANT PV
ANOMALY STILL PROGGED TO LIFT NORTHEAST TOWARD WISCONSIN. THIS
WOULD HELP KEEP THE SNOW GOING IN THE DEFORMATION/TROWAL AREA THAT
LOOKS TO BE LOCATED ACROSS THE FORECAST AREA ON FRIDAY AND INTO
FRIDAY NIGHT. THINGS SHOULD START WINDING DOWN FRIDAY NIGHT AND
SATURDAY... ALTHOUGH SOME LIGHT SNOW AND FLURRIES WILL LIKELY
PERSIST ACROSS THE EASTERN PORTION OF THE AREA FOR MUCH OF SATURDAY.
SUBSEQUENT FORECASTS SHOULD BE ABLE TO GET A BETTER HANDLE ON THE
TIMING OF THE HEAVIER BURSTS OF SNOW... AS WELL AS THE POTENTIAL
FOR SLEET/FREEZING RAIN AND ANY POSSIBLE ACCUMULATIONS OF THAT
MIXED PCPN. AT THIS POINT... IT APPEARS THE MIXED PCPN SHOULD
GENERALLY REMAIN JUST SOUTH AND EAST OF THE TWIN CITIES METRO
AREA... ALTHOUGH THERE COULD BE WINDOWS OF TIME DURING WHICH SOME
FREEZING DRIZZLE WILL BE POSSIBLE DURING ANY PSEUDO DRY-SLOTS AND
LULLS IN THE PCPN. WITH THE GUIDANCE LIKELY COMING INTO BETTER
AGREEMENT ON THE DETAILS AS WE HEAD INTO TOMORROW... WILL LIKELY
BE ABLE TO FOCUS MORE CLOSELY ON THE ISENTROPIC ASCENT PROGS FOR
THE INITIAL SURGE OF PCPN... AND SPECIFIC FRONTOGENESIS AND UPPER
JET FORCING FOR THE LATER STAGES.
AS FOR THE LATER PERIODS... SATURDAY NIGHT THROUGH TUESDAY...
PRIMARILY WENT WITH THE HPC GUIDANCE FOR THE DETAILS GIVEN OUR
GREATER FOCUS ON THE SHORT RANGE SIGNIFICANT WEATHER.
&&
.AVIATION.../06Z TAF ISSUANCE/
FIRST PARTS OF THE FORECAST PERIOD SOMEWHAT QUIET FOR NORTHEAST
PARTS OF THE AREA WITH VFR CIGS AND SCT020-025...FROM KSTC TO
KMSP TO KRNH AND KEAU. AN EASTERLY FETCH OF DRIER AIR WAS KEEPING
MVFR CIGS OFF TO THE SOUTHWEST AND THIS PATTERN WILL PERSIST FOR
THE MOST PART...THROUGH THE MORNING OR EARLY AFTERNOON. MVFR CIGS
WILL LIKELY PERSIST AT KAXN AND KRWF. SOME WEAK LIFT WELL AHEAD OF
THE MAIN STORM MAY CAUSE SOME LIGHT SNOW OR FREEZING DRIZZLE VCNTY
KRWF WITH IFR CIGS AND VSBYS NEAR 3SM. THE FIRST WAVE OF WARM
ADVECTION AND LIFT WILL MOVE INTO FAR SOUTHERN MN IN THE AFTERNOON
WITH LIGHT SNOW DEVELOPING. MVFR CIGS WILL SPREAD BACK OVER ALL
SITES...FOLLOWED BY LIGHT SNOW BEFORE THE END OF THE FORECAST
PERIOD FOR ALL SITES. THE GREATEST RISK OF IFR CIGS AND VSBYS WILL
BE SOUTHWEST OF A LINE FROM KAXN TO KMSP. LOWERS VSBYS CLOSER TO
3/4SM POSSIBLE AT KMSP AFTER 06Z.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING FROM 6 PM WEDNESDAY TO 6 AM CST SATURDAY
FOR BLUE EARTH-BROWN-FARIBAULT-FREEBORN-LAC QUI PARLE-LE
SUEUR-MARTIN-NICOLLET-REDWOOD-RENVILLE-RICE-SIBLEY-STEELE-
WASECA-WATONWAN-YELLOW MEDICINE.
WINTER STORM WARNING FROM 6 AM THURSDAY TO 6 AM CST SATURDAY FOR
BENTON-DOUGLAS-KANABEC-MILLE LACS-MORRISON-POPE-STEVENS-
TODD.
WINTER STORM WARNING FROM MIDNIGHT WEDNESDAY NIGHT TO 6 AM CST
SATURDAY FOR ANOKA-CARVER-CHIPPEWA-CHISAGO-DAKOTA-GOODHUE-
HENNEPIN-ISANTI-KANDIYOHI-MCLEOD-MEEKER-RAMSEY-SCOTT-
SHERBURNE-STEARNS-SWIFT-WASHINGTON-WRIGHT.
WI...WINTER STORM WARNING FROM MIDNIGHT WEDNESDAY NIGHT TO 6 AM CST
SATURDAY FOR BARRON-CHIPPEWA-DUNN-EAU CLAIRE-PEPIN-PIERCE-
POLK-RUSK-ST. CROIX.
&&
$$
TRH/JPR
