FXUS63 KMPX 082348
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
548 PM CST TUE DEC 8 2009
.UPDATE...FOR 00Z AVIATION DISCUSSION BELOW
&&
.DISCUSSION.../ISSUED 413 PM CST TUE DEC 8 2009/
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.../00Z TAF ISSUANCE/
MODERATE INTENSITY SNOW WILL PLAGUE THE TAF SITES THIS
EVENING...AND BECOME HEAVY AT TIMES DURING THE OVERNIGHT HOURS. WIDESPREAD
IFR CONDITIONS WILL PREVAIL...WITH DIPS INTO THE LIFR CATEGORY
COMMON BETWEEN 02Z AND DAYBREAK WEDNESDAY. NORTH-NORTHEAST WINDS
WILL BACK TO THE NORTHWEST AND STRENGTHEN TONIGHT AS THE PRESSURE
GRADIENT ASSOCIATED WITH THE DEEPENING LOW PRESSURE SYSTEM
TIGHTENS...WITH GUSTS AROUND 30 KTS EXPECTED TO DEVELOP BY 09Z.
GUSTS TO BETWEEN 30 AND 35 KTS WILL BE POSSIBLE ON WEDNESDAY
MORNING. RESULTANT BLOWING SNOW WILL WORSEN THE VSBYS ON
WEDNESDAY...AND PROLONG IFR CONDITIONS ON WEDNESDAY AFTERNOON EVEN
AFTER THE SNOW TAPERS.
KAXN...VSBY DECLINING TO AROUND 3/4SM THIS EVENING AS SNOW
INTENSITY AND WINDS INCREASE. SNOW TAPERS OFF LATE WEDNESDAY
MORNING BUT BLSN YIELDS IFR VSBYS THROUGH THE AFTERNOON.
KSTC...VSBY DECLINING TO AROUND 3/4SM THIS EVENING...WITH PERIODS
OF 1/2SM IN SNOW/BLSN BETWEEN 04Z AND 10Z. SNOW TAPERS OFF LATE MORNING
BUT BLSN WILL CONTINUE TO REDUCE VSBY THROUGH THE AFTERNOON.
KRWF...SNOW INTENSIFICATION WILL OCCUR THIS EVENING WITH 1/4 TO
1/2SM VSBY BETWEEN 03Z AND 09Z. SNOW TAPERS OFF MID MORNING BUT
BLSN WILL CONTINUE TO REDUCE VSBY THROUGH THE AFTERNOON.
KMSP...SNOW INTENSITY EXPECTED TO INCREASE BETWEEN 00Z AND
03Z. PREVALENT VSBYS OF 1/2SM BETWEEN 04Z AND 12Z...WITH PERIODS OF
1/4SM EXPECTED DUE TO THE COMBINATION OF SNOW/BLSN BETWEEN 04Z
AND 08Z. ACCUMULATING SNOW LOOKS TO CONTINUE THROUGH THE MORNING
BUT AT A LIGHTER RATE WITH CONTINUED VSBY REDUCTIONS AROUND 1SM.
SNOW TAPERS OFF DURING THE AFTERNOON...BUT BLSN WILL YIELD VSBY
REDUCTIONS TO AROUND 2SM DURING THE EVENING.
KEAU...VSBY THIS EVENING EXPECTED TO FALL TO 1/2 TO 3/4SM WITH
PERIODS OF 1/4SM AFTER MIDNIGHT...WITH HELP FROM BLSN. SNOW WILL
LIKELY REMAIN INTENSE THROUGH 15Z OR SO WEDNESDAY...ALTHOUGH IFR
CONDITIONS WILL PERSIST THROUGH THE AFTERNOON.
KRNH...SNOW INTENSITY EXPECTED TO INCREASE BETWEEN 01Z AND
03Z. PREVALENT VSBYS OF 1/2SM BETWEEN 03Z AND 12Z...WITH PERIODS OF
1/4SM EXPECTED DUE TO THE COMBINATION OF SNOW/BLSN BETWEEN 04Z
AND 08Z. ACCUMULATING SNOW LOOKS TO CONTINUE THROUGH THE MORNING
BUT AT A LIGHTER RATE WITH CONTINUED VSBY REDUCTIONS TO BETWEEN
3/4SM AND 1SM.
&&
.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.
&&
$$
LS/MTF
