FXUS63 KMPX 082213
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
413 PM CST TUE DEC 8 2009
.DISCUSSION...
THE MAJOR WINTER STORM HAS BEGUN ACROSS THE AREA AND WILL LAST
THROUGH WEDNESDAY. CHANGES WERE TO INCREASE SNOWFALL
TOTALS...EXPAND AREA OF 25-35 MPH WINDS DURING WEDNESDAY...AND
ACCORDINGLY INCREASE THE COVERAGE AREA OF WARNINGS.
SIGNIFICANT SYSTEM ENTERING THE CENTRAL PLAINS FROM COLORADO AT 4
PM THIS AFTERNOON. SUBSTANTIAL CYCLOGENESIS IS OCCURRING ACROSS THE
MID-MISSISSIPPI VALLEY. INVERTED TROUGH EXTENDS NORTHEAST FROM
THIS ACROSS KANSAS CITY TO DES MOINES TO EAU CLAIRE. DEW POINTS IN
THE MID 20S TO THE EAST OF THIS BEING UPLIFTED INTO THE AREA AS
LEAD IMPULSE LIFT NORTHEAST FROM ERN NE. WITHIN BROAD WARM AIR
ADVECTION AND ISENTROPIC UPGLIDE...THIS WAVE WILL ENHANCE EAST TO
WEST BANDS ACROSS SOUTHERN MN WITHIN THE NEXT SEVERAL HOURS. THIS
WILL EXPAND NORTH INTO THE TWIN CITIES DURING THE EVENING.
GENERALLY THESE BANDS ARE TRANSIENT...WITH LITTLE RESIDUAL TIME IN
ONE SPOT. ALSO...THE DENDRITIC SNOWFLAKE GROWTH ZONE IS NOT WITHIN
THE DEEPEST VERTICAL OMEGA AT THIS TIME. BOTH OF THESE FACTORS
CHANGE BY LATE EVENING AND OVERNIGHT INTO WED MORNING AS THE SFC
LOW DEEPENS AROUND 17 MB /SEVEN MODEL AVERAGE/ FROM 00Z WED TO 12Z
WED. THE SFC LOW SHOULD BE SRN LAKE MICHIGAN BY 12Z WED. THIS
PANHANDLE HOOKER PATH FAVORS SRN MN INTO WI. AREAL EXPANSIVENESS
OF ISENTROPIC UPGLIDE...HELPED BY A BROAD COUPLED JET STRUCTURE
SEEN ON 12Z RAOBS AND RUC ANALYSIS...WILL FAVOR SIX INCH PLUS
AMOUNTS EVEN FURTHER NORTH IN ADDITION TO THE IDEAL CORRIDOR. THE
CIPS ANALOG GUIDANCE FROM SIMILAR SYNOPTIC SCENARIOS TO THE GFS
GUIDANCE HAS FAVORED MINNEAPOLIS TO SEE SIX PLUS INCHES FROM THE
00Z AND 12Z GFS. SO THIS LENDS CREDENCE TO GREATER AMOUNTS
FURTHER NORTH...AS DO EMPIRICAL TECHNIQUES SUCH AS THE COOKE AND
GARCIA METHODS. THE GREATEST AMOUNTS AND SNOWFALL RATES IN SREF
PROBABILISTIC AND MEMBER GROUPING GUIDANCE FAVOR 9 PM TONIGHT TO 9
AM WED MORNING. THE DENDRITIC GROWTH IS ALSO MAXIMIZED IN THAT
TIME WITH F-GEN PIVOTING WITHIN THAT LAYER ACROSS MAINLY WRN WI
AND FAR ERN MN. MUCH MORE RESIDUAL TIME WILL OCCUR UNDER THE
BANDED SNOW OVERNIGHT AND WED MORNING AS THE LOW PATH IS PARALLEL
TO THE ERN CWA. RATIOS ALSO ARE FAVORED SLIGHTLY HIGHER WHICH
CONTINUES THE TREND OF THE PREVIOUS SHIFT. THIS WILL LEAD TO
SNOWFALL AMOUNTS NEAR OR IN THE DOUBLE DIGITS FROM ALBERT LEA TO
THE SE METRO TO RICE LAKE AND SOUTHEASTWARD. ONE FOOT AMOUNTS NEAR
EAU CLAIRE SEEM LIKELY.
THE PRIMARY LOW LEVEL HEIGHT FALL/RISE COUPLET PASSES TO OUR SOUTH
WITH THIS SYSTEM...BUT MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT
OF STRONG WINDS THROUGHOUT THE ENTIRE GRADIENT AREA OF THIS
CYCLONE. FACTORS WHICH ARE FAVORABLE FOR STRONG GUSTY WINDS OF 30
KTS IN SOUTH CTRL MN TO 25 KTS IN WEST CTRL WI ARE THE INCOMING
COLD AIR ADVECTION STEEPENING LOW LEVEL LAPSE RATES...A
UNIDIRECTIONAL COLUMN IN THAT AREA...AND AN ASTOUNDING
ISALLOBARIC EFFECT WITH DEEP SFC PRESSURES AS A BASELINE. HAVE
EXPANDED BLIZZARD WARNING NORTH AND EASTWARD. BLOWING AND DRIFTING
SHOULD CONTINUE MANY HOURS AFTER THE SNOWFALL CEASES DUE TO THE
HIGH SNOW TO LIQUID RATIO NATURE OF THE SNOW ON THE GROUND.
HAVE ADDED WIND CHILL MENTION INTO WSW AND HWO DUE TO THE
PLUMMETING TEMPS ON WEDS. -25 WIND CHILLS WILL BE NEARED ON WED IN
WRN MN AND LIKELY ACROSS CTRL MN WED NIGHT WHEN A WIND CHILL
ADVISORY MAY BE NEEDED.
A COLD PATTERN IS FAVORED IN THE LONG RANGE AS REGION IS MIRED IN
DEEP NORTHWEST FLOW EARLY IN PERIOD AS COLD ARCTIC VORTEX
PROGRESSES SOUTHWARD OUT OF NORTHWEST CANADA THEN ACROSS S MB AND
ONTARIO OVER THE WEEKEND. 850 TEMPS REMAIN B15 TO B20 RANGE THRU
MUCH OF PERIOD WITH BRIEF SLIGHT MODERATION AS WEAK SHORTWAVES
RIDE SE THRU THE AREA....ONE ON SATURDAY AND ANOTHER ABOUT SUNDAY
NIGHT/MONDAY. WILL ADD SOME -SN AS THESE FEATURES MOVE THRU. WITH
SNOW COVER EXPECTED ACROSS THE AREA DURING THIS PERIOD...MINIMUM
TEMPERATURES ESPECIALLY WILL LIKELY BE QUITE COLD. ADJUSTED TEMPS
DOWNWARD TO ACCOUNT FOR THIS.
&&
.AVIATION.../18Z TAF ISSUANCE/
DETERIORATING CONDITIONS UNDERWAY...
UPPER LEVEL LOW PRESSURE MOVING ACROSS THE ROCKIES IS HELPING TO
STRENGTHEN A SFC LOW ACROSS COLORADO WHICH WILL WORK EAST-
NORTHEAST ACROSS KANSAS...IOWA...AND NORTHERN ILLINOIS INTO EARLY
WEDNESDAY. LIGHT SNOW ACROSS MUCH OF SOUTHERN MN AND WESTERN WI AT
18Z WILL EXPAND NORTHWARD AND INTENSIFY THROUGH THE AFTERNOON FROM
SOUTH TO NORTH. THE BRUNT OF THE SNOWFALL WILL OCCUR THIS EVENING
AND TONIGHT WITH NORTHEAST WINDS INCREASING THIS EVENING THEN
TURNING NORTHWEST OVERNIGHT AND BECOMING VERY STRONG. STRONGEST
WINDS LOOKING HIGHER THAN EARLIER FORECAST AND EXPECTED FROM AROUND
DAYBREAK THROUGH MIDDAY. SUSTAINED SPEEDS OF 20 TO 25 KTS WITH
GUSTS OF 30 TO 35 KTS ARE EXPECTED WITH THE STRONGEST SPEEDS
ACROSS EAST/SOUTH CENT MN AND WEST CENT WI. SLIGHTLY HIGHER
SUSTAINED SPEEDS AND GUSTS ARE POSSIBLE. CHALLENGES WILL BE
DETERMINING PERIOD OF HEAVIEST SNOW/LOWEST VSBY AND ALSO VSBY
LEVELS IN BLOWING SNOW LATE TONIGHT THROUGH THE DAY WEDNESDAY.
DETAILS FOLLOW...
KAXN...SNOW WILL BE MOVING IN OVER THE NEXT HOUR OR TWO AND STEADILY
INCREASE INTO THE EVENING BRINGING VSBY DOWN TO AROUND 3/4SM THIS
EVENING AND TONIGHT. SNOW WILL WILL TAPER OFF LATE WEDNESDAY
MORNING BUT BLSN WILL CONTINUE. SNOW ACCUMULATION OF 3 TO 5
INCHES IS EXPECTED.
KSTC...SNOW INTENSITY WILL VARY THROUGH 21Z OR SO THEN INTENSIFY
INTO EARLY EVENING. HEAVIEST SNOWFALL RATES ARE EXPECTED TO RANGE
FROM 1/2 TO 3/4 IN/HR FROM MID EVENING THROUGH THE OVERNIGHT. SNOW
INTENSITY WILL DECREASE AFTER DAYBREAK BUT ADDITIONAL
ACCUMULATIONS LOOK TO OCCUR THROUGH LATE MORNING. TOTAL
ACCUMULATIONS AROUND 6 INCHES EXPECTED.
KRWF...SNOW WILL STEADILY INCREASE IN INTENSITY THROUGH THE
AFTERNOON WITH VSBY DROPPING TO AROUND 3/4SM. FURTHER
INTENSIFICATION WILL OCCUR THIS EVENING WITH 1/4 TO 1/2SM VSBY
EXPECTED BY LATE EVENING AND CONTINUING TOWARDS DAYBREAK...WITH
1/2 TO 1 IN/HR RATES. SNOW WILL TAPER OFF TOWARDS MID MORNING BUT BLSN
WILL CONTINUE TO REDUCE VSBY. TOTAL SNOWFALL OF 6 TO 8 IN.
KMSP...SNOW INTENSITY WILL VARY THROUGH 20 OR 21Z WITH VSBY
REDUCTIONS TO JUST UNDER 2SM AT TIMES BUT PREDOMINANTLY IN THE 3
TO 5SM RANGE. SNOW INTENSITY IS EXPECTED TO INCREASE MARKEDLY
AROUND 23Z WITH 3/4 TO 1 1/2 VSBY PREVAILING WITH SNOWFALL RATES
OF AROUND A 1/2 IN/HR POSSIBLE. HEAVIEST SNOW EXPECTED FROM 02 OR
03Z THROUGH 09Z WITH 1/2 TO 1 IN/HR RATES AND VSBY DROPPING TO
1/2SM WITH REDUCTIONS TO 1/4SM POSSIBLE IN SNOW AIDED BY BLOWING
SNOW WHICH WILL BECOME MORE PREVALENT AFTER 05Z OR SO. ACCUMULATING
SNOW LOOKS TO CONTINUE AFTER 09Z THROUGH THE MORNING BUT AT A
LIGHTER RATE WITH CONTINUED VSBY REDUCTIONS. TOTAL SNOWFALL OF 7
TO 9 IN.
KEAU...DURATION OF INTENSE SNOWFALL WILL BE LONGEST HERE. SNOW
WILL VARY IN INTENSITY THROUGH LATE AFTERNOON BEFORE INCREASING
THIS EVENING. VSBY THIS EVENING EXPECTED TO FALL TO 1/2 TO 3/4SM
WITH PERIODS OF 1/4SM LATE THIS EVENING AND TONIGHT...WITH HELP
FROM BLSN. SNOWFALL RATES OF 1/2 TO 1 IN/HR EXPECTED THIS EVENING
AND TONIGHT. SNOW WILL LIKELY REMAIN INTENSE THROUGH 15Z OR SO WEDNESDAY
BEFORE STARTING TO WANE. SNOW ACCUMULATION AROUND A FOOT IS
EXPECTED AND VSBY WILL LIKELY REMAIN REDUCED TO 1SM OR LESS
THROUGH THE MORNING.
KRNH...MUCH THE SAME SITUATION AS KMSP BUT AMOUNTS OF 8 TO 10
INCHES EXPECTED. SNOW INTENSITY WILL VARY THROUGH 20Z OR SO WITH A
RANGE OF VISIBILITIES. INTENSIFICATION WILL OCCUR LATE THIS
AFTERNOON AFTER ABOUT 20Z WITH A FURTHER INCREASE AROUND AND AFTER
00Z. INTENSITY WILL BE GREATEST THIS EVENING AND TONIGHT AND LAST
LATER INTO LATE MORNING...WITH RATES OF 1/2 TO 1 IN/HR. ..MDB..
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...BLIZZARD WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR BLUE
EARTH-BROWN-FARIBAULT-FREEBORN-GOODHUE-LE SUEUR-MARTIN-
NICOLLET-RICE-STEELE-WASECA-WATONWAN.
WINTER WEATHER ADVISORY UNTIL 6 PM CST WEDNESDAY FOR BENTON-
CHIPPEWA-DOUGLAS-KANABEC-KANDIYOHI-LAC QUI PARLE-MEEKER-
MILLE LACS-MORRISON-POPE-REDWOOD-RENVILLE-STEARNS-STEVENS-
SWIFT-TODD-YELLOW MEDICINE.
WINTER STORM WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR
ANOKA-CARVER-CHISAGO-DAKOTA-HENNEPIN-ISANTI-MCLEOD-RAMSEY-
SCOTT-SHERBURNE-SIBLEY-WASHINGTON-WRIGHT.
WI...BLIZZARD WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR CHIPPEWA-
DUNN-EAU CLAIRE-PEPIN-PIERCE.
WINTER STORM WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR
BARRON-POLK-RUSK-ST. CROIX.
&&
$$
MTF/MDB
