FXUS63 KMPX 120001
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
601 PM CST FRI DEC 11 2009
.UPDATE...
ADDED AVIATION DISCUSSION FOR 00Z TAFS BELOW...
&&
.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.../00Z TAF ISSUANCE/
SFC HIGH PRESSURE RIDGING CONTINUES TO MOVE OFF TO THE EAST THIS
EVENING. SOUTH TO SOUTH-SOUTHEAST WINDS WILL CONTINUE THROUGH
SATURDAY MORNING BEFORE STARTING TO TURN MORE SOUTHEASTERLY THEN
EASTERLY THROUGH THE AFTERNOON AS A WEAK LOW PRESSURE AREA MOVES
IN. ONLY CLOUDS THROUGH SATURDAY AFTERNOON WILL BE SCATTERED MID
AND HIGH CLOUDS. LOW MVFR/IFR STRATUS WILL BE APPROACHING FROM THE SOUTH
LATER SATURDAY AFTERNOON AND SATURDAY EVENING. EXACT TIMING WILL
NEED TO BE REFINED AND COULD POSSIBLY ARRIVE MORE QUICKLY THAN
CURRENTLY EXPECTED. AM ALSO WATCHING THE POTENTIAL FOR FREEZING DRIZZLE
SATURDAY NIGHT ACROSS EAST CENT MN AND WEST CENT WI.
KAXN...SOUTH WINDS WILL BECOME MORE SOUTHEASTERLY DURING THE DAY
SATURDAY. VFR EXPECTED THRU THE PERIOD BEFORE LOW MVFR/IFR STRATUS
APPROACHES SATURDAY EVENING.
KSTC...SOUTH WINDS WILL BECOME SOUTHEASTERLY SATURDAY. VFR CONDS
EXPECTED THROUGH THE PERIOD BUT TIMING OF ARRIVAL OF STRATUS WILL
HAVE TO BE WATCHED AS IT MAY QUICKLY ARRIVE JUST AFTER 00Z
SATURDAY EVENING.
KRWF...MAIN CONCERN WILL BE APPROACH OF LOW MVFR/IFR STRATUS.
HAVE LEFT IT OUT OF THE TAF FOR NOW WITH THE EXPECTATION IT WILL
HOLD OFF UNTIL AFTER 00Z SATURDAY EVENING BUT A LATE AFTERNOON
ARRIVAL IS POSSIBLE.
KMSP...SOUTH TO SOUTH-SOUTHEAST WINDS OF AROUND 6 KTS WILL
CONTINUE THIS EVENING BUT MAY SLACKEN TO A FEW KNOTS TOWARDS
DAYBREAK BEFORE INCREASING TO 6 TO 9 KTS FOR SATURDAY AFTERNOON.
EXPECT LOW MVFR/IFR TO ARRIVE SATURDAY EVENING BUT EXACT ARRIVAL
TIME IS NOT CERTAIN YET.
KEAU...VFR EXPECTED THROUGH THE PERIOD WITH LIGHT WINDS TONIGHT
THANKS TO THE PROXIMITY OF THE RIDGE. ATMOSPHERE IS VERY DRY SO AM
NOT EXPECTING ANY FOG DEVELOPMENT.
KRNH...VFR EXPECTED THROUGH THE PERIOD BUT WILL NEED TO WATCH
ARRIVAL TIME OF LOW MVFR/IFR STRATUS SATURDAY EVENING. ..MDB..
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&
$$
MTF/BAP/MDB
