FXUS63 KMPX 291747
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1147 AM CST SUN NOV 29 2009
.UPDATE...
ADDED 18Z TAF DISCUSSION BELOW.
&&
.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.../18Z TAF ISSUANCE/
LOW LEVEL COLD ADVECTION IN THE NW FLOW KEEPING MVFR OR LOW END
VFR CIGS OVER MOST OF THE AREA INTO MID AFTERNOON..BUT DRYING
AND MORE WESTERLY FLOW WILL DEVELOP OVER WESTERN AREAS PROVIDING
CLEARING NEAR KRWF AND KAXN AFTER 22Z. CLEARING WILL PROGRESS
ACROSS THE REST OF THE AREA TOWARD BETWEEN 03Z AND 06Z. WEAK HIGH
PRES WILL PROVIDE VFR CONDITIONS THROUGH THE END OF THE
PERIOD. MID LEVEL CIGS WILL DEVELOP OVERNIGHT WEST AND MONDAY
MORNING EAST...AS A TROUGH MOVE SE OUT OF SOUTHERN CANADA. SOME
LIGHT SNOW IS POSSIBLE GENERALLY NORTH OF OUR AREA BUT COULD
AFFECT KSTC TOWARD THE END OF THE PERIOD. LOW END VFR CIGS WOULD BE
POSSIBLE WITH THIS SCENARIO.
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&
$$
MDB/JPR
