FXUS63 KMPX 290943
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
343 AM CST SUN NOV 29 2009
.DISCUSSION...
SEVERAL TROUGHS WILL AFFECT THE FORECAST AREA THROUGH LATE NEXT WEEK
BUT PRECIPITATION CHANCES WILL BE MINIMAL. THE MAIN IMPACT ON
SENSIBLE WEATHER WILL BE TEMPERATURE SWINGS OVER THE NEXT FEW DAYS
FOLLOWED BY A MUCH COLDER REGIME STARTING MID WEEK. MOISTURE CHANNEL
IMAGERY SHOWS A SHARP UPPER TROUGH PUSHING INTO WESTERN MINNESOTA
EARLY THIS MORNING. A TROUGH IS ALSO VISIBLE DEVELOPING AND PIVOTING
SOUTHWARD TOWARDS JAMES BAY. THESE TWO TROUGHS WILL PHASE AND EVOLVE
INTO A LARGER SCALE TROUGH OVER THE EASTERN U.S. INTO MONDAY. WATER
VAPOR ALSO SHOWS A CUTOFF UPPER LOW MEANDERING EAST-SOUTHEASTWARD
ALONG THE WESTERN U.S./MEXICO BORDER. A WELL ORGANIZED TROUGH IS
PUSHING INTO SOUTHEAST ALASKA AND HELPING TO FORCE A RIDGE OVER THE
WEST COAST WHICH EXTENDS NORTHEASTWARD INTO BRITISH COLUMBIA. THIS
RIDGING WILL QUICKLY TRANSLATE EASTWARD KEEPING NORTHWESTERLY FLOW
ALOFT OVER THE LOCAL AREA WHICH WILL PROVIDE A TRACK FOR A SERIES OF
TROUGHS TO CROSS THE AREA THROUGH THE UPCOMING WEEK.
TODAY THROUGH MONDAY...THE UPPER TROUGH AXIS WILL CROSS THE CWA
TODAY. BAND OF LIGHT SNOW/RAIN WILL BE EXITING THE EASTERN CWA BY 13
OR 14Z THIS MORNING BUT NOT BEFORE A FEW TENTHS OF SNOW ACCUMULATE
FROM BARRON AND DUNN COUNTIES EASTWARD IN WISCONSIN PRIOR TO 13Z.
COLD ADVECTION ALREADY UNDERWAY WITH H85 TEMPS COOLING TO AROUND -6
C THIS AFTERNOON. IT WILL BE A BIT BREEZY FROM THE NORTHWEST THIS
MORNING WITH WINDS SUBSIDING A BIT LATER IN THE DAY AS HIGH PRESSURE
RIDGING DROPS SOUTHEASTWARD AND WILL BE SQUARELY OVER THE AREA THIS
EVENING. CLOUDS WILL HANG IN THERE THROUGH THE MORNING WITH SOME
SCATTERING EXPECTED ACROSS THE WEST THIS AFTERNOON...WHILE EASTERN
AREAS REMAIN MOSTLY CLOUDY INTO THE EVENING. HIGHS WILL ONLY REACH
THE MID 30S. NAM AND GFS SHOW ANOTHER WEAKER AREA OF VORTICITY
LAGGING BEHIND THE TROUGH INTO THE AFTERNOON AND MAY PROVIDE ENOUGH
LIFT ALONG WITH CYCLONIC FLOW TO KEEP FLURRIES GOING ACROSS THE
EASTERN HALF OF THE AREA INTO THE AFTERNOON. NORTHWEST FLOW ALOFT
WILL BE FIRMLY IN PLACE OVER THE AREA TONIGHT WHILE THE SFC RIDGE
MOVES OFF TO THE SOUTH. A FAST MOVING SHORTWAVE WILL DIVE
SOUTHEASTWARD ACROSS SASKATCHEWAN AND MANITOBA TONIGHT AND ENTER
WESTERN MINNESOTA MONDAY MORNING. WARM ADVECTION WILL BUILD AHEAD OF
THE TROUGH BRINGING H85 TEMPS BACK UP TO AROUND 0 C BY MIDDAY
MONDAY. THE TROUGH WILL NOT HAVE MUCH MOISTURE TO WORK WITH AS IT
PASSES BY LATE MONDAY AFTERNOON. WARM ADVECTION IS QUITE STRONG WITH
HIGH ADIABATIC OMEGA VALUES SHOWING UP IN A BAND ON THE 285K AND TO
A LESSER EXTENT ON THE 290K ISENTROPIC SFCS MOVING ACROSS THE
NORTHERN CWA FROM 12Z TO ABOUT 21Z. AS EXPECTED...FRONTOGENESIS IS
QUITE STRONG BETWEEN 850 AND 700 MB IN A NARROW BAND AS WELL. ALL OF
THIS OCCURS UNDER THE LEFT EXIT REGION OF AN ADVANCING UPPER JET.
WINDOW OF BEST FORCING OVER ANY PARTICULAR LOCATION IS ONLY ABOUT 3
HRS OR SO BUT SOME LIGHT PRECIPITATION MAY BE ABLE TO BE SQUEEZED
OUT NORTH OF INTERSTATE 94...ESPECIALLY THE FURTHER NORTH ONE GOES.
WILL GO AHEAD AND ADD SLIGHT POPS TO THESE AREAS STARTING AT 12Z
MONDAY. PRECIP TYPE WILL BE A BIT TRICKY WITH THE PUSH OF WARM AIR
BUT THE FORCING APPEARS TO BE CENTERED IN THE SUB FREEZING LOW AND
MID LEVEL AIR SO WILL KEEP ALL SNOW IN THE FORECAST FOR NOW. THERE
IS AN OFF CHANCE THAT IF THE WARM AIR ALOFT ARRIVES MORE QUICKLY AND
PRECIP DOES FALL...THERE COULD BE SOME LIGHT FREEZING RAIN IN THE
FAR NORTHWEST AROUND 12Z. HAVE INDICATED RISING TEMPS TOWARDS
DAYBREAK IN THE WEST AS WELL. THE TROUGH AND WAA WILL EXIT TO THE
EAST LATE MONDAY AFTERNOON. WITH THE WARMER AIR ALOFT TEMPS MONDAY
ARE EXPECTED TO BE IN THE LOWER 40S SOUTHWEST BUT REMAIN CHILLY IN
THE NORTHEAST AND EAST WHERE CLOUDS WILL REMAIN AND THE WARMER AIR
ALOFT WILL NOT BE REALIZED AT THE SFC.
TUESDAY THROUGH THURSDAY NIGHT...A STRONG SHORTWAVE MOVING ACROSS
ALBERTA AND SASKATCHEWAN INTO TUESDAY MORNING WILL WORK TO DEEPEN A
SFC LOW THAT WILL CROSS LAKES WINNIPEG AND MANITOBA ON TUESDAY. THE
UPPER RIDGE AHEAD OF THIS SYSTEM WILL BE PUSHED OVERHEAD TUESDAY
MORNING ALONG WITH A WEAK SFC RIDGE. ANOTHER BUT LESS INTENSE PUSH OF WARM
ADVECTION WILL MOVE ACROSS THE AREA LATE MONDAY NIGHT AND TUESDAY
MORNING AHEAD OF THE LOW AND PUSH H85 TEMPS UP TO BETWEEN 0 AND +4 C
OR EVEN A BIT HIGHER. THIS WILL QUICKLY BE REPLACED BY SHARP COLD
ADVECTION FOLLOWING THE PASSAGE OF THE ASSOCIATED COLD FRONT
STARTING IN THE NORTHWEST TUESDAY AFTERNOON. WITH THE LOW REMAINING
TO THE NORTH OF THE INTERNATIONAL BORDER FORCING FOR ASCENT WILL
REMAIN TO THE NORTH AS WELL SO AM NOT EXPECTING ANY PRECIPITATION
TUESDAY OR TUESDAY NIGHT. HIGH TEMPS TUESDAY WILL BE TOUGH AND WILL
NEED TO DIURNAL TRENDS AND TIMING OF FRONTAL PASSAGE. NORTHWEST MAY
SEE EARLY HIGHS WITH TEMPS FALLING DURING THE AFTERNOON IF SPEED OF
THE SYSTEM STAYS ON TRACK WHILE THE EAST SHOULD SEE A MORE TYPICAL
DIURNAL TREND. SOME MODEL DISAGREEMENT EXISTS IN TERMS OF THE
MAGNITUDE OF THE COLD AIR WITH THE GFS BEING THE COLDEST BRINGING
H85 TEMPS AS COLD AS -10 C OR SO BY WEDNESDAY MORNING WITH THE NAM
AND ECMWF 2 TO 4 DEGREES WARMER. EITHER WAY IT WILL BE MUCH COLDER
FOR WEDNESDAY WITH HIGHS LIKELY ONLY AROUND 30 DEGREES NORTH TO THE
LOWER 30S SOUTH. THE COLD AIR AND CYCLONIC FLOW MAY BRING SOME
FLURRIES OR LIGHT SNOW TUESDAY NIGHT AND WEDNESDAY...ESPECIALLY
EAST. MODEL DISAGREEMENT GROWS SLIGHTLY INTO THURSDAY ON WHAT THE
UPPER FLOW PATTERN DOES BUT ECMWF AND GFS BOTH BRING A REINFORCING
SHOT OF COLD AIR IN LATER WEDNESDAY WITH BOTH INDICATING FURTHER
COOLING TO AROUND -14 C AT H85. THIS WOULD MAKE THURSDAY EVEN COLDER
WITH A MORNING START IN THE TEENS WITH RECOVERY ONLY INTO THE UPPER
20S THURSDAY AFTERNOON. SMALL SNOW SHOWER CHANCES WILL EXIST WITH
ANY TROUGH PASSAGE OR BURST OF COLD ADVECTION BUT NOTHING
SIGNIFICANT IS EXPECTED. ..MDB..
&&
.AVIATION.../06Z TAF ISSUANCE/
AMS LAST COUPLE HRS FINALLY BECOMING MORE SATURATED AS CIGS HV BEEN
STEADILY LOWERING ACROSS CENTRAL MN. EVE RAOBS SHOWED FREEZING
LEVELS ABOVE 3500 FEET SO PCPN HAS GENERALLY BEGUN AS A RPD OF -RA
BFR CHGG TO -SN. MOST PCPN WL HV SAGGED S OF AXN BY 06Z. TREND OF
MPX RADAR HAS SHOWN A SE MVMT ARND 15 KTS ON LEADING EDGE OF PCPN
WHICH WOULD BRING IT TO MSP BTWN 06Z AND 07Z. WINDOW FOR PCPN AT
STC/MSP/RNH AND EAU LASTING ARND 3 HOURS. VSBYS COULD LOWER TO
2-4SM DRNG -SN. RATHER WDSPRD AREA OF MVFR CIGS EXTENDING ACRS E
1/2 NODAK. THESE CONDS SHUD RMN AT AXN/RWF TIL AFT 18Z AND UNTIL 00Z
OR LATER MSP AS WELL AS RNH AND EAU.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&
$$
MDB/BAP
