FXUS63 KMPX 280937
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
337 AM CST SAT NOV 28 2009
.DISCUSSION...
OVERALL A TRANQUIL PERIOD INTO EARLY NEXT WEEK WITH A FEW MINOR
PRECIP CHANCES THROUGH THE MIDDLE OF NEXT WEEK. TEMPERATURES WILL
BE THE MAIN ITEM OF INTEREST WITH SOME UPS AND DOWNS INTO EARLY
NEXT WEEK BEFORE MUCH COLDER AIR ARRIVES BY MIDWEEK. GENERAL AIR
FLOW PATTERN WILL BE ACTIVE THROUGH THE PERIOD BUT THERE IS PRETTY
GOOD CONFIDENCE IN THE OVERALL EVOLUTION DURING THAT TIME. EARLY
MORNING MOISTURE CHANNEL IMAGERY SHOWS FAIRLY FLAT UPPER RIDGING
OVER THE CENTRAL U.S. WITH A ZONAL FLOW OVER THE MID SECTION OF
SOUTHERN CANADA. THE TROUGH THAT HAS BEEN SLOWLY WORKING EASTWARD
ACROSS THE GREAT LAKES AND NORTHEAST THE LAST SEVERAL DAYS IS
MAKING PROGRESS TOWARDS THE GULF OF ST. LAWRENCE. BACK TO THE
WEST...A DEEP CLOSED LOW HAS COME ON SHORE OVER CALIFORNIA WIT A
TROUGH AXIS EXTENDING TO ITS NORTH. THE FLOW ASSOCIATED WITH THIS
TROUGH IS BEGINNING TO SPLIT OVER IDAHO WITH THE CALIFORNIA LOW
BECOMING CUTOFF. TO THE NORTH OF THIS LOW IN THE NORTHERN
STREAM...A SHORTWAVE IS EVIDENT MOVING ACROSS CENTRAL SASKATCHEWAN
AND WILL BE AFFECTING THE LOCAL WEATHER TONIGHT AND SUNDAY.
TODAY THROUGH SUNDAY...WEAK SFC FRONTAL BOUNDARY WHICH APPROACHED
THE FORECAST AREA LAST NIGHT HAS SLOWED TO A CRAWL ACROSS CENTRAL MN
THIS MORNING. THE APPROACH OF THE SHORTWAVE FROM SASKATCHEWAN WILL
HELP INCREASE THE EASTWARD PROGRESS OF THE FRONT THIS AFTERNOON BUT
UNTIL THEN LIGHT SOUTH FLOW WILL BE FOUND ACROSS THE EASTERN HALF OF
THE AREA WITH LIGHT NORTH FLOW ACROSS THE WEST THIS MORNING BEFORE
INCREASING INTO THE AFTERNOON. LOW LEVEL TEMPS HAVE MODIFIED
SLIGHTLY WITH H85 TEMPS IN THE +4 TO +8 RANGE OVER THE AREA BUT THE
APPROACHING TROUGH WILL HELP THOSE TO START COOLING BY EVENING.
ABUNDANT CIRRUS CONTINUES TO STREAM NORTHEASTWARD ON THE BACK SIDE
OF THE WEAK UPPER RIDGE KEEPING THE NORTHERN CWA UNDER THE MOST
PERSISTENT COVERAGE WITH MORE VARIABLE CIRRUS COVER OVER THE SOUTH
TODAY. HIGHS SHOULD MAKE IT INTO MID 40S WITH A BIT MORE UNIFORM
DISTRIBUTION ACROSS THE CWA THAN YESTERDAY. THE SASKATCHEWAN TROUGH
WILL MOVE INTO WESTERN MN TONIGHT. RIGHT ENTRANCE REGION OF 100 KT
UPPER JET WILL MOVE ACROSS THE SOUTHERN THIRD OR SO OF MN THIS
EVENING/TONIGHT AS BAND OF Q-VECTOR CONVERGENCE SWINGS ACROSS THE
SAME AREA. THE GFS IS MOST AGGRESSIVE WITH MAGNITUDE OF
FRONTOGENESIS THAT DEVELOPS AND SWINGS ACROSS THE AREA WITH GOOD
FORCING ON THE -15C ISOTHERM SFC...WHICH IS LIKELY A BIT OVERDONE.
NAM AND CANADIAN ARE MORE MUTED WITH THE FORCING. EVEN IF THE
STRONGER FORCING DOES PAN OUT THE MOISTURE IS THE MAIN LIMITING
FACTOR. WITH THE FORCING FOCUSED FAIRLY HIGH IN THE ATMOSPHERE AND
MEAGER MOISTURE BELOW IT...SO MEAGER THAT COLUMN SATURATION IS
UNLIKELY...IT WILL BE DIFFICULT TO GET MUCH SNOW TO THE GROUND. WILL
GO AHEAD AND ADD SLIGHT AND LOW CHANCE POPS ALONG AND NORTH OF A
LINE FROM MORRIS TO NEW RICHMOND TO LADYSMITH WITH THE HIGHEST POPS
FROM ABOUT LONG PRAIRIE TO ST. CLOUD TO AMERY. THESE AREAS HAVE THE
POTENTIAL TO SEE A BAND OF LIGHT SNOW MOVE ACROSS THIS EVENING AND
TONIGHT. IF THE BAND CAN DEVELOP THEN A DUSTING/COATING OF SNOW IS
POSSIBLE...ESPECIALLY ACROSS THE FAR NORTH. THE WEAK SFC LOW OVER
THE AREA WILL SHIFT OFF TO THE EAST THEN INTENSIFY AS THE UPPER
TROUGH ARRIVES WHICH WILL TIGHTEN THE SFC PRESSURE GRADIENT TONIGHT
INTO SUNDAY MORNING. THIS WILL RESULT IN BRISK NORTHWESTERLY WINDS
FOR AT LEAST THE FIRST PART OF SUNDAY. THE PASSAGE OF THE TROUGH
WILL BRING SHARP COLD ADVECTION AS H85 TEMPS FALL TO -6 TO -8 C BY
MIDDAY SUNDAY. HIGHS WILL RANGE FROM THE UPPER 30S TO AROUND 40.
SUNDAY NIGHT THROUGH THURSDAY...THE UPPER TROUGH WILL CONTINUE TO
INCREASE IN SCALE AS IT PHASES WITH AN UPPER LOW DEVELOPING OVER
JAMES BAY. THE CALIFORNIA CUTOFF LOW WILL DRIFT SOUTHEASTWARD INTO
NORTHERN MEXICO BY MONDAY AS RIDGING BUILDS IN TO ITS NORTH. FAST
NORTH-NORTHWEST FLOW WILL BE OVERHEAD LOCALLY MONDAY BEFORE THE
RIDGING WORKS EASTWARD TOWARDS THE AREA. A WEAK SHORTWAVE WILL ZIP
ACROSS THE AREA MONDAY BUT ONLY LOOKS TO BRING AN INCREASE IN CLOUD
COVER. A STRONGER TROUGH WILL MOVE INTO THE NORTHERN STREAM ACROSS
ALBERTA AND SASKATCHEWAN RESULTING IN A DEVELOPING SFC LOW ACROSS
THE CANADIAN PRAIRIES INTO TUESDAY. GFS/ECMWF/NAM/UKMET HAVING
TROUBLE AGREEING ON WHAT HAPPENS WITH THIS SYSTEM. RUN TO RUN
CONTINUITY HAS VARIED WITH THE GFS EXHIBITING SOME CONSISTENCY WITH
MAGNITUDE OF THE SFC LOW /SUB 995 MB/ AND SPEED WHILE THE ECMWF HAS
TRENDED WEAKER FOR SEVERAL RUNS BUT IS NOW COMING IN STRONG AND
CLOSER TO THE GFS WITH ITS 28/00Z RUN. WHILE THE DETAILS ARE
UNCERTAIN AT THE MOMENT THE BIGGER PICTURE IS A BIT MORE CLEAR. WITH
THE TROUGH APPROACHING...WARM ADVECTION WILL COMMENCE OVER THE
REGION SO FEEL PRETTY CONFIDENT THAT THERE WILL BE AT LEAST A SLIGHT
WARMUP FOR TUESDAY. THE MODELS DO AGREE THAT THE APPROACHING UPPER
TROUGH WILL PHASE WITH LOW HEIGHTS OVER JAMES/HUDSON BAY AND EVOLVE
INTO A LARGE TROUGH OVER EASTERN CANADA AND THE EASTERN U.S.
WEDNESDAY AND THURSDAY WITH A LONGWAVE RIDGE TO ITS WEST. THIS
PATTERN WILL SUPPORT THE ADVECTION OF SOME OF THE COLDEST AIR YET
THIS SEASON WITH H85 TEMPS STILL LOOKING TO FALL TO COLDER THAN -12
C OR SO WEDNESDAY AND THURSDAY. IN TERMS OF PRECIPITATION...THIS
CLIPPER TYPE SYSTEM WILL HAVE ITS FORCING FOCUSED MOSTLY TO THE
NORTH OF THE AREA AND BE MOISTURE STARVED SO RIGHT NOW MINIMAL
SNOWFALL LOOKS TO OCCUR TO THE SOUTH OF THE LOW TRACK. THAT COMBINED WITH
THE UNCERTAINTY OF THE MAGNITUDE AND TRACK RESULTS IN CONTINUATION
OF MINIMAL POPS ACROSS THE NORTHERN CWA INTO WEDNESDAY WITH THE
CYCLONIC FLOW AND COLD ADVECTION ON THE BACK SIDE OF THE LOW.
..MDB..
&&
.AVIATION.../06Z TAF ISSUANCE/
WEAK LOW PRESSURE TROUGH OVER EASTERN SOUTH DAKOTA AND WESTERN MN IS
WASHING OUT THIS EVENING. FLOW VERY WEAK NOW ACROSS SOUTHWEST MN
AND WITH LIMITED CLOUD COVER SOME MVFR FOG DEVELOPED. HIGHER SFC
DEWPTS RESIDE OVER THIS PORTION OVER THE FA. WITH THE PATTERN
PRETTY MUCH SET...WILL MENTION MVFR FOG DEVELOPING 06Z-09Z IN MN FA
AND A BIT LATER INTO WC WI WHERE DEWPOINTS ARE LOWER AND FROST MAY
BE MORE OF AN ISSUE OVERNIGHT. CIRRUS WILL MOVE ACROSS THE AREA
OVERNIGHT ITNO THE DAY SATURDAY AS SECONDARY COLD FRONT SAGS SOUTH
INTO THE AREA. 00Z MODEL RUN DEVELOPING MORE LOW LEVEL MOISTURE
SATURDAY AFTERNOON OVER THE NORTHWEST FA AS COLDER AIR MOVES IN AND
TROUGH MOVES EAST. WILL MENTION SOME 4K FT STRATOCUMULUS AT KAXN
AND KSTC IN THE AFTERNOON ALONG WITH LOWERING AC/MID CLOUD DECK.
WILL LIKLEY SEE SOME MVFR CIGS DEVELOP AROUND THE 00Z SUN TIME FRAME
THIS LOCATION...GRADUALLY SAGGING INTO THE KMSP AREA BY 08Z SUN.
SFC WINDS WILL REMAIN LIGHT AND EVENTUALLY BECOME N-NWLY AND
INCREASE A BIT WITH COLD FRONTAL PASSAGE. COULD SEE SOME FLURRIES
OVER CENTRAL MN LATE BUT WILL LEAVE OUT OF TAFS FOR NOW.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&
$$
MDB/DWE
