FXUS63 KMPX 260446 AAA
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1050 PM CST WED NOV 25 2009
.UPDATED FOR AVIATION DISCUSSION BELOW...
.DISCUSSION...
SINCE NOON...RADAR RETURNS NORTH OF THE TWIN CITIES HAVE
INDICATED A GENERAL INCREASE IN AREAL COVERAGE OF THE -RA/-DZ.
HOWEVER...SEVERAL FACTORS HAS LIMITED -SN ACROSS MOST OF
CENTRAL/EAST- CENTRAL/PORTIONS OF SOUTH-CENTRAL MN...AS WELL AS
WEST-CENTRAL WISCONSIN.
THESE FACTORS ARE...
FIRST...PERSISTENT WARM BOUNDARY LAYER ACROSS THE EASTERN 1/2 OF
CWA. THIS CONTINUES TO BE NOTED ON THE 13KM RUC WHICH HAS THE MAX
WET-BULB LAYER (0-500M) OVER +1.5C BISECTING THE CWA FROM THE
WEST TO EAST. THIS IS USUALLY IS A GOOD INDICATOR OF WHERE THE
TRANSITION OF SN TO RA IS. SECONDLY...SATELLITE TRENDS AND IMAGERY
NOTED THAT NOT ALL OF THE CLOUDS ACROSS THE CWA HAD CLOUD ICE
NUCLEI...WHICH IS NEEDED FOR -SN. THERE HAS BEEN A FEW REPORTING
STATIONS IN WESTERN MN WHICH HAD -SN BECOME -RA BUT CRITICAL
TEMPERATURES REMAINED THE SAME (BASICALLY CLOUDS TEMPERATURES WERE
ABOVE -10C). NOW...USING THE RUC 13KM MAX WET-BULB LAYER...IT
REMAINS TOO WARM FOR MOST OF THE EASTERN 1/4 OF CWA TO SWITCH OVER
TO -SN UNTIL THIS EVENING. THE TWIN CITIES METRO AREA WILL BE
TRANSITIONING BETWEEN THE -SN IN THE WESTERN SUBURBS BY 5 PM...BUT
IT MAY BE UNTIL 7 OR 8 PM UNTIL THE EASTERN SUBURBS TURN OVER TO
ALL SNOW. THEREFORE...WITH MOST OF THE DEEP LAYER MOISTURE QUICKLY
EXITING THE STATE FROM NW TO SE...SNOWFALL AMTS WILL BE LIMITED
AND MAINLY FOR THE FAR SE CWA WHERE THE MOISTURE/TEMPERATURES AND
LIFT WILL BE MAXIMIZED LATER TODAY/THIS EVENING. A QUICK ONE TO
TWO INCHES WILL BE POSSIBLE AROUND OWATONNA...CANNON FALLS AND
NORTHFIELD.
BY 06Z...NEARLY ALL OF THE DEEP MOISTURE AND SYNOPTIC SCALE LIFT
WILL BE ACROSS SOUTHERN WISCONSIN. SO HAVE TRENDED TO JUST
FLURRIES IN THE FAR SE AFTER MIDNIGHT.
NOT MUCH CHANGE IN THE EXTENDED PERIOD AS MOST OF THE ENERGY WILL
BE ACROSS CANADA AND THE SOUTHERN U.S. FOR THE BULK OF THE 7 DAY
PERIOD AFTER TONIGHT. SOME MODIFICATION ARE NOTED IN TEMPERATURES
FOR FRI/SAT...AS THICKNESS VALUES INDICATE MID TO UPPER 40S
POSSIBLE ACROSS SOUTHERN MN.
AS WITH PREVIOUS DISCUSSION...THE MEDIUM RANGE FORECAST PERIOD IS
HIGHLY DEPENDENT ON HOW THE SOUTHERN/NORTHERN JET STREAMS PHASES
OR DO NOT. TYPICALLY...DURING THE EL NINO YEARS...THE SOUTHERN JET
IS MORE LIKELY TO INFLUENCE THE MAIN WEATHER ELEMENTS ACROSS THE
LOWER 48 STATES. THESE TRENDS IN THE CURRENT MODELS SEEM TO BE
TRUE...AT LEAST THRU NEXT WEDNESDAY. ONE ITEM TO NOTE...PAST
WEDNESDAY OF NEXT WEEK...LONGER RANGE MODELS ARE INDICATING A
SIGNIFICANT CHANCE IN THE UPPER LEVEL FLOW. WITH THE FLOW
CURRENTLY MORE MODIFIED AND PACIFIC AIRMASS ORIENTED...BY THE END
OF NEXT WEEK...THERE COULD BE MORE OF AN ARCTIC TYPE OF AIRMASS
MOVING INTO THE UPPER MIDWEST. TIME WILL TELL! ..JLT..
&&
.AVIATION.../06Z TAF ISSUANCE/
MVFR CIGS REMAIN IN THE WAKE OF THE LOW PRESSURE SYSTEM EXITING TO
THE SOUTHEAST. SOME CYCLONIC FLOW ON THE BACKSIDE OF THE LOW WILL
KEEP LOWER CIGS AROUND THROUGH MUCH OF THE NIGHT OUT OVER THE WESTERN
FA. SOME CLEARING POSSIBLE TOWARD 12Z AS DRYING/SUBSIDENCE
CONTINUES. TIMING OF CLEARING INTO THE EAST MORE OF A
PROBLEM...WITH 00Z GFS SLOWING THE DRYING QUITE A BIT. WILL FOLLOW
LAMP GUIDANCE FOR NOW...AND IS CLOSE TO WHAT PREVIOUS FORECAST
WAS...WITH VFR DEVELOPING OVER MN FA THROUGH 15Z AND COMING TO KEAU
ABOUT 18Z THU. REST OF FCST SHOULD BE QUIET WITH VFR CONDS THRU 12Z
FRI. SOME CIRRUS AROUND AND WINDS BECOMING MORE SOUTHERLY WITH THE
PASSAGE OF THE SFC RIDGE.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&
$$
JLT/DWE
