FXUS63 KGRB 110950
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
350 AM CST FRI DEC 11 2009

.SYNOPSIS...INCREASINGLY BLOCKY FLOW AT HIGH LATITUDES WL ALLOW
MAIN WESTERLIES TO UNDERCUT CURRENT WEST COAST RIDGE. THE
WESTERLIES WL HAVE MODEST AMPLITUDE...AND INITIALLY BE
PROGRESSIVE. BY LATE IN THE FCST PERIOD THE PROGRESSION SHOULD
COME TO AN END AS UPR TROF OVER ERN NOAM GET LOCKED IN AGAINST
MASSIVE BLOCKING RIDGE CENTERED OVER THE NORTH ATL.

BLO NORMAL TEMPS AT THE START OF THE FCST PERIOD WL MODERATE BACK
CLOSER TO NORMAL. ANOTHER SWD SURGE OF COLD AIR EXPECTED DURING
THE EARLY TO MIDDLE PART OF NEXT WK...WITH TEMPS REBOUNDING AGAIN
LATE IN THE WEEK. THERE WL BE SEVERAL OPPORTUNITIES TO GET LGT
PCPN. THE ONE CHC OF SOMEWHAT MORE SUBSTANTIAL PCPN WOULD BE WITH
SYSTEM CROSSING THE AREA EARLY NEXT WK...THOUGH AT THIS POINT
AMOUNTS WITH THAT WOULD APPEAR MODEST AT BEST.
&&

.SHORT TERM...TDA/TNGT/SAT. AHH...THE JOYS OF TRYING TO FORECAST
TEMPERATURES IN AN ARCTIC AIR MASS WITH SNOW ON THE GROUND. WINDS
EARLY THIS MORNING RUNNING LIGHTER THAN WHAT YOU MIGHT EXPECT GIVEN
THE PRESSURE GRADIENT. THAT COMBINED WITH MAINLY CLEAR SKIES ALLOWED
TEMPS TO FALL BLO ZERO ACRS ALL BUT THE LAKESHORE SO FAR...AND WE/RE
NOT AT OUR MINS YET. WIND CHILL ADVISORY MARGINAL AS SITES BOUNCE
INTO AND OUT OF ADVISORY CRITERIA AS WIND SPEED FLUCTUATES. AT THIS
POINT JUST PLAN TO LET IT RUN IT/S COURSE. GUID SEEMS MUCH MORE
REASONABLE /COMPARED TO YDA/ WITH MAXES FOR TDA. EDGED MAXES
DOWN...CLOSE TO WHAT WAS OBSERVED YDA...AND FEEL PRETTY GOOD ABOUT
THOSE NUMBERS. 

THE REAL PROBLEM WITH TEMPS STARTS TNGT. WARMER AIR STARTS TO
ARRIVE ALOFT...AND GUID RESPONDING BY KEEPING MOST OF THE FCST
AREA ABV ZERO ALL NGT. IF WINDS WERE TO STAY UP ALL NGT...THAT
MIGHT BE OKAY. BUT SFC PRESSURE PATTERN IS SURPRISINGLY DIFFERENT
AMONG THE MODELS LATER TNGT. THE NAM/GFS INDICATE ENOUGH GRADIENT
TO KEEP THE WINDS UP A LITTLE. THE CANADIAN KEEPS A LITTLE MORE
RIDGING ACRS THE AREA AND WOULD PROBABLY ALLOW FOR DECOUPLING. IF
WINDS DIE OFF...THINK THE AIR MASS IS STILL COLD AND DRY ENOUGH
TO ALLOW TEMPS TO PLUNGE WAY BLO ZERO AGAIN. CONFIDENCE IN THIS
PART OF THE FCST IS VERY LOW. PREV FCST WAS ALREADY BLO GUID.
STAYED PRETTY CLOSE TO THAT...NUDGING TEMPS DOWN PERHAPS A DEG OR
TWO IN THOSE AREAS THAT TYPICALLY TANK DURING IDEAL RADIATIONAL
COOLING SITNS.

MODERATION WL BE UNDERWAY BY SAT. BUT DON/T REALLY SEE A TOTAL
EXCHANGE OF AIR MASSES...AND WE/VE GOT A FOOT OF SNOW ON THE GROUND.
WENT A FAIR AMNT BLO GUID...AND A COUPLE DEG COLDER THAN WHAT WE
HAD GOING. 

GUID CONTINUES TO WAY OVERDO THE CLOUDS IN THE COLD AIR MASS. BUT
WITH ISENT LIFT STARTING UP...SHOULD EVENTUALLY SEE SOME HIGH CLDS
AND PATCHES OF MID CLDS ACRS THE RGN.

.LONG TERM...SATURDAY NIGHT THROUGH NEXT FRIDAY. THREE MAIN
FEATURES (AT LEAST) FOR THIS FORECAST PERIOD. THE FIRST IS THE
PROSPECT FOR CLOUDS AND LIGHT PRECIPITATION IN THE BROAD WARM
ADVECTION SATURDAY NIGHT AND SUNDAY. THERE USUALLY SEEMS TO BE
EXTENSIVE LOW CLOUDS AND LIGHT PRECIPITATION AS ARCTIC AIR RETREATS
AND SUSTAINED WARM ADVECTION OVERRUNS THE SHALLOW COLD AIR. WENT
WITH A CHANCE OF LIGHT SNOW FOR NOW THOUGH THERE IS SOME POTENTIAL
FOR FREEZING DRIZZLE AS THE MOISTURE IS FORECAST TO BE WHERE
TEMPERATURES ARE ABOVE -10C. 

NEXT FEATURE IS LOW PRESSURE MOVING FROM THE CENTRAL OR SOUTHERN
PLAINS TO THE GREAT LAKES MONDAY. THE GFS AND GEM ARE IN
REASONABLE AGREEMENT ABOUT A LOW MOVING FROM NORTHERN KANSAS TO
NEAR GREEN BAY WHILE THE ECMWF IS WEAKER AND FURTHER SOUTH. LOOKS
LIKE THERE WOULD BE SOME PRECIPITATION REGARDLESS OF WHICH
SOLUTION MIGHT BE CORRECT. MOST OF PRECIPITATION WOULD BE IN
NORTHERN WISCONSIN NORTHWEST OF TRACK OF SURFACE LOW. THERE IS
ALSO SOME POTENTIAL FOR PRECIPITATION TYPE ISSUES IN THE EAST
CENTRAL COUNTIES AS BOUNDARY LAYER TEMPERATURES ARE CLOSE TO
FREEZING. INCREASED CHANCES OF SNOW TO LIKELY IN THE NORTH. DIDN'T.T
MENTION ANY MIXED PRECIPITATION BUT IT IS A POSSIBILITY. SEVERAL
INCHES OF SNOW COULD FALL IN THE NORTH AND MIGHT MERIT AN ADVISORY
DEPENDING ON WHAT LATER MODELS RUNS DO WITH THIS SYSTEM.

THE THIRD FEATURE IS THE NEXT ROUND OF ARCTIC AIR POISED TO DROP
INTO THE PLAINS STATES AND GREAT LAKES TUESDAY AND WEDNESDAY.
WELL BELOW ZERO TEMPERATURES EXPECTED TUESDAY AND WEDNESDAY MORNINGS.
MOS GUIDANCE FROM THE GFS (MEX) IS LIKELY SKEWED BY CLIMATOLOGY
AND WOULD EXPECT COLDER TEMPERATURES.
&&

.AVIATION...EXPECT MAINLY VFR CONDITIONS DURING THE PERIOD AS SFC
HIGH PASSES TO THE SOUTH.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...

WIND CHILL ADVISORY UNTIL 9 AM CST THIS MORNING
WIZ005-010>013-018>021-030-031-035>039-045-048-049-073-074-

&&

$$
SKOWRONSKI/RDM