FXUS63 KMPX 112131
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
331 PM CST FRI DEC 11 2009
.DISCUSSION...
THE FORECAST CHALLENGES ARE TEMPERATURES THROUGH A GOOD PART OF
THE FORECAST AS WELL AS THE NEXT APPRECIABLE SNOW CHANCE...WHICH
COMES SUNDAY NIGHT INTO MONDAY AT THE LEADING EDGE OF ANOTHER
ARCTIC SURGE INTO THE REGION.
GOES WV LOOP CONTINUES TO SHOW ACTIVE JET PATTERN REMAINING TO OUR
SOUTH WITH DEEP CYCLONIC FLOW OVER CANADA JUST STRETCHING INTO THE
NRN PART OF THE UNITED STATES. JUST SOME HIGH AND MID CLOUDS
EXPECTED OVER THE NRN PORTION OF THE FORECAST AREA TONIGHT AHEAD
OF WEAK WAVE CENTERED WELL TO OUR NORTH. WARM SECTOR WITH THIS
WAVE HAS SPREAD OVER THE FORECAST AREA AND WILL GRADUALLY CONTINUE
SO TONIGHT...MEANING A STEADY SOUTH WIND AND STEADY DEW POINTS.
TEMPS SHOULD FOLLOW SUIT...DROPPING VERY LITTLE TONIGHT. HAVE
ADAPTED THE TREND OF THE 12Z NAM BUT GONE A BIT WARMER ON THE
VALUES. TRICKY TO WEIGH THE SOUTH WINDS AND INCREASING MOISTURE VS
THE STILL FRESH DEEP SNOW PACK IN THE SOUTH AND EAST. BUT EITHER
WAY...MUCH MILDER THAN THIS MORNING.
SHEARED SHORT WAVE FORECAST BY ALL THE MODELS TO MOVE ENE INTO IA
AND SRN WI ON SAT NIGHT. PRIMARY ISENTROPIC UPGLIDE AND
CONVERGENCE FOCUSED TO THE SOUTH. AIR MASS IS COOL AND
MOISTENING...SO SHOULD NOT TAKE LONG TO SATURATE EVEN AT NRN
FRINGES. SO LITTLE CHANGES MADE TO SAT NIGHT POPS. THERMAL
PROFILES AND SIMULATED WATER VAPOR FROM THE NAM MODEL INDICATE A
POTENTIAL DISCONNECT IN THE MOISTURE FIELD. SO KEEP A MENTION OF
FZDL. BETTER CHANCE FOR LIGHT SNOW/FLURRIES. ANYTHING SHOULD BE
MINOR AND CONFINED TO THE SRN AND ERN FORECAST AREA.
NEXT SYSTEM A BIT MORE POTENT. IT HAS THE LOOKS OF A COLORADO LOW
BUT WITH SOME CLIPPER-LIKE FEATURES AS WELL. MODELS DIFFER IN
LATITUDE ON THIS BUT ALL APPEAR CONSISTENT WITH DEEPENING THE LOW
AS IT MOVES ENE TO THE NW IL AREA BY 18Z MON. TIGHT MID-LEVEL
THERMAL GRADIENT OVER THE AREA SUN NIGHT TIGHTENS MON MORNING BEFORE
SHIFTING EAST. FAVORABLE SETUP FOR SOME SNOW...BUT THE NORTH TO
SOUTH VARIABILITY IN THE MODELS HAS LED US ONLY TO INCREASE POPS
AREA WIDE FOR RIGHT NOW. COULD BE ADVISORY CRITERIA SNOWFALL
AMOUNTS SUN OVERNIGHT THROUGH THE DAYTIME HOURS ON MON SOMEWHERE
TO THE N AND NW OF THE 850 MB LOW. FORWARD SPEED IS ENOUGH THAT
CHANCES FOR ANYTHING MORE THAN THAT ARE SMALL AT THIS TIME. ON THE
HEELS OF THIS ARE A NRN STREAM CLIPPER SYSTEM NEAR 512 DM WHICH
WILL DRIVE DOWN THICKNESSES AND TEMPS ON MON NIGHT.
THE LONGER RANGE IS STARTING OUT QUITE COLD AS SURGE OF NW WINDS
PLOWS ACROSS AREA IN WAKE OF THE CLIPPER-TYPE SYSTEM. 1040 MB HIGH
BUILDS SOUTHEAST INTO THE AREA ON TUESDAY DROPPING HIGH TEMPS BACK
INTO THE SINGLE DIGITS. SOME MODERATION BEGINNING LATER ON
WEDNESDAY AS HIGH PRESSURE DROPS SE ALLOWING MILDER AIR TO RETURN
BACK NORTH. 500 MB HEIGHTS ON GFS/ECMWF ALSO SHOWING NICE RISES BY
LATE WEDNESDAY. GFS CARRIES CLIPPER ACROSS N MN THURS/THURS
NITE...WITH 12Z ECMWF MUCH WEAKER. WON'T INTRO ANY POPS WITH THIS
SYSTEM YET.
&&
.AVIATION.../18Z TAF ISSUANCE/
BASICALLY CLEAR SKIES THIS AFTERNOON WITH SOME PATCHY MID CLOUDS
ROUGHLY BETWEEN 6-10 THOUSAND FEET AGL. WEAK SHORT WAVE OVER THE
PACIFIC NORTHWEST/NORTHWEST TERRITORY OF CANADA WILL ADVANCE
SOUTHEAST OVER THE UPPER MIDWEST LATER TONIGHT AND SATURDAY.
MID/HIGH LEVEL CLOUDS INCREASING OVER THE TAF SITES OVERNIGHT AND
SATURDAY. GENERALLY VFR CONDITIONS THROUGH THE PERIOD. WEATHER
CONCERNS OVERNIGHT...LOW LEVEL WIND SHEAR...ASSOCIATED WITH WIND
SPEEDS BETWEEN 1500-2000 FEET SOUTHWEST BETWEEN 35-40 KNOTS AND
SURFACE SOUTH NEAR 10 KNOTS.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&
$$
MTF/BAP/JVM
