FXUS63 KMPX 120546
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1146 PM CST FRI DEC 11 2009

.AVIATION... /06Z TAF ISSUANCE/ 

TWO FEATURES OF INTEREST DURING THE TAF PERIOD. FIRST IS SC
PUSHING NORTH ACROSS KS AND MO. MODELS ARE HANDLING THE MOISTURE
POORLY. SATURATION SIGNATURE ON THE NAM 290K THETA SURFACE
SUGGESTS CEILINGS IN THE 3500 FOOT RANGE SPREADING ACROSS SOUTHERN
MN AND WEST CENTRAL WI DURING THE LATE AFTERNOON. PURE
EXTRAPOLATION OF THE CEILINGS OVER KS ATTM WOULD BRING THEM TO
NORTHERN IA BY 17Z. HENCE...A CEILING LIKELY AT KMSP...KRNH AND
KEAU IN THE 21Z TO 23Z TIME FRAME. OTHER CONCERN IS AN ARCTIC COLD
FRONT THAT WILL BE NEARING KAXN AROUND 13/00Z. THE FRONT WILL
PUSH SE ACROSS ALL OF THE TAF SITES BY 13/12Z. MOS GUIDANCE REALLY
PUSHING CEILINGS DOWN IN THE KAXN AND KSTC AREA BY EARLY SATURDAY
AFTERNOON. THINK THIS IS TOO EARLY AND INDICATED LOW MVFR CEILINGS
DEVELOPING WITH FROPA IN THE EVENING.  

KAXN...BKN-OVC090-110 OVERNIGHT AS WAA PUSHES THROUGH. SCT-BKN CI
ON SATURDAY. CEILINGS AROUND 015 FORECAST BY 13/03Z WITH ARCTIC
FROPA. 

KSTC...BKN-OVC090-110 OVERNIGHT AND EARLY SATURDAY MORNING AS WAA
PUSHES THROUGH WITH SCT-BKN CI FOR THE BALANCE OF THE DAY. CEILINGS
AROUND 020 FORECAST BY 13/05Z WITH ARCTIC FROPA.

KRWF...MAINLY JUST SCT-BKN CI OVERNIGHT AND MUCH OF SATURDAY. SITE
WILL BE ON THE WESTERN EDGE OF THE SC LIFTING NORTHEAST THROUGH
THE PLAINS. HOWEVER...CEILINGS AROUND 020 FORECAST BY 13/03Z WITH
ARCTIC FROPA. 

KMSP...SCT-BKN CI OVERNIGHT AND SATURDAY MORNING. CONFIDENCE NOT
HIGH ON WHEN CEILINGS IN THE 030-040 FOOT RANGE WILL REACH KMSP
SATURDAY AFTERNOON. FOR NOW HAVE INDICATED BKN035 BY 12/22Z.
CEILINGS TO DETERIORATE DURING THE EVENING WITH 010-015 EXPECTED
BY 13/06Z.

KRNH...SCT-BKN CI OVERNIGHT AND SATURDAY MORNING. CONFIDENCE NOT
HIGH ON WHEN CEILINGS IN THE 030-040 FOOT RANGE WILL REACH KRNH
SATURDAY AFTERNOON. FOR NOW HAVE INDICATED BKN035 BY 12/23Z.
MVFR CEILINGS BETWEEN 020-030 SHOULD DEVELOP DURING THE EVENING AS
LOW LEVEL MOISTENING INCREASES.

KEAU...SCT-BKN CI OVERNIGHT AND SATURDAY MORNING. CONFIDENCE NOT
HIGH ON WHEN CEILINGS IN THE 030-040 FOOT RANGE WILL REACH KEAU
SATURDAY AFTERNOON. FOR NOW HAVE INDICATED BKN035 BY 12/23Z.
MVFR CEILINGS BETWEEN 020-030 SHOULD DEVELOP DURING THE EVENING AS
LOW LEVEL MOISTURE CONTINUES TO INCREASE. 

&&

.DISCUSSION... /ISSUED 331 PM CST FRI DEC 11 2009/

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.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

$$

RAH/MTF/BAP