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000
FXUS63 KARX 100349
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
949 PM CST TUE FEB 9 2010

.UPDATE...

ONLY VERY LIGHT SNOW REMAINS ACROSS THE AREA WITH MOST
VISIBILITIES NOW AT OR ABOVE 3 MILES. CALLS AROUND THE AREA THIS
EVENING INDICATE THAT ONLY A DUSTING AT MOST AS OCCURRED SINCE 6
PM AND NO PROBLEMS WITH BLOWING OR DRIFTING SNOW REPORTED. THE
REMAINING SNOW WILL END LATE THIS EVENING OR SHORTLY AFTER
MIDNIGHT SO DECIDED TO END THE ADVISORY EARLY WITH LITTLE OR NO
ADDITIONAL ACCUMULATIONS EXPECTED TO OCCUR.

04

&&

.PREV DISCUSSION... /ISSUED 604 PM CST TUE FEB 9 2010/

UPDATE...

RADAR RETURNS INDICATE NOTHING BUT LIGHT SNOW IS FALLING OVER
SOUTHEAST MINNESOTA AND NORTHEAST IOWA. NORTH WINDS ARE NOT REAL
STRONG SO ANY BLOWING SNOW THAT IS OCCURRING IS LIKELY VERY
ISOLATED IN NATURE. HAVE LET THE WINTER STORM WARNING EXPIRE AS
SCHEDULED WHILE MAINTAINING THE WINTER WEATHER ADVISORY FROM THE
MISSISSIPPI RIVER COUNTIES EAST INTO CENTRAL WISCONSIN.

04

PREV DISCUSSION... /ISSUED 302 PM CST TUE FEB 9 2010/

SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT

FORECAST CONCERNS THIS PACKAGE...SNOW/BLOWING SNOW YET THIS
EVENING...SNOW CHANCE AGAIN FRI/FRI NIGHT...TEMPERATURES THRU THE
PERIOD.

18Z DATA ANALYSIS HAD LOW PRESSURE NEAR THE OH/KY BORDER WITH A
TROUGH TO THE NORTHWEST INTO IA. PRESSURES STILL FALLING ACROSS THE
FCST AREA BUT STRONGEST FALLS OF 5+MB/3HRS OVER LK ERIE. WV IMAGERY
SHOWED THE UPPER LOW SPINNING OVER EAST CENTRAL MO...WITH MOISTURE
PLUME/TROWAL WRAPPED AROUND TO THE NORTH OF THE LOW. COLD POCKET OF
AIR AT THE SFC UNDER THE LOW...WITH TEMPS IN THE SINGLE DIGITS
ACROSS SOUTHERN IA/NORTHERN MO...WHILE TEMPS ACROSS NORTHERN IA/
SOUTHERN MN IN THE 20S. AREA RADARS SHOWED A BROAD AREA OF GENERALLY
LIGHT SNOW ACROSS WI AND NEARBY AREAS IN THE TROWAL/ MOISTURE PLUME
AND BROAD ISENTROPIC LIFT/THETA-E CONVERGENCE. SNOW TAPERING OFF
ALONG/WEST OF I-35 EARLY THIS AFTERNOON.

NO ISSUES NOTED WITH 09.12Z NAM/GFS/ECMWF/GEM INITIALIZATIONS. THESE
SOLUTIONS VERY SIMILAR FOR TONIGHT THRU THU...BEFORE DIVERGING WITH
THE TIMING/STRENGTH OF A SHORTWAVE DROPPING THRU THE NORTHWEST FLOW
ALOFT AND ACROSS THE REGION THU NIGHT INTO FRI NIGHT. DPROG/DT OF
500MB HGTS AT 09.12Z SHOWED MODEL RUNS OF 07.12Z AND 08.12Z ALL
VERIFIED QUITE WELL ACROSS NOAM/EASTERN PAC. SLIGHT EDGE ON RUN-TO-
RUN CONSISTENCY TO ECMWF...BUT ALL WERE A BIT WEAK WITH THE UPPER
LOW OFF THE NORTHERN CA COAST. THRU 36HRS MODELS CONVERGING TOWARD
COMMON SOLUTIONS WITH THE UPPER LOW MOVING OFF THE EAST COAST AND
THE ONE TO NEAR THE AZ/MEX BORDER. ECMWF WITH THE BETTER RUN-TO-RUN
CONSISTENCY. FOR 36-60HRS MODELS HAVE TRENDED TOWARD FASTER OF
THE EARLIER RUNS WITH THE SOUTHERN STREAM TROUGH INTO TX. MODEL
CONSENSUS TIGHTENING WITH THE SHORTWAVE DROPPING INTO THE DAKOTAS AT
60HRS...TRENDING TOWARD BLEND OF EARLIER MODELS ON STRENGTH/TIMING.
GFS/UKMET/GEM REMAIN ON THE FASTER SIDE WITH THIS FEATURE...ECMWF/
NAM SLOWER. MODEL CONSISTENCY IMPROVED WITH THIS LEAD WAVE IN THE
60-84HR PERIOD...BUT RUN-TO-RUN CONSISTENCY POOR WITH THE NEXT
STRONGER WAVE TO DROP INTO ND/MN AND IMPACT THE AREA JUST BEYOND THE
SHORT TERM. CHECK OF OBS VS. MODEL DATA SHOWED NAM/GFS/ECMWF/GEM
QUITE GOOD WITH THE SFC MASS FIELDS ACROSS THE CENTRAL CONUS. PER WV
IMAGERY ALL LOOKED QUITE GOOD WITH THE SHORTWAVE DETAILS OVER
CENTRAL NOAM. GFS/ECMWF/GEM BETTER WITH DETAILS IN THE UPPER LOW OFF
THE CA COAST. MODEL/ENSEMBLE CONSENSUS...INCLUDING LOCAL/REGIONAL
WRF MODELS...GOOD WITH THE 12Z-18Z PRECIP ACROSS THE CENTRAL CONUS.
NO CLEAR DETERMINISTIC MODEL FAVORITE THIS CYCLE AND AGAIN FAVORED
THE MODEL/ENSEMBLE CONSENSUS. WITH THE GOOD CONSENSUS...FORECAST
CONFIDENCE GOOD FOR TONIGHT THRU THU...THEN AVERAGE AT BEST BY
FRI/FRI NIGHT WITH THE POOR RUN-TO-RUN CONSISTENCY WITH THE NEXT
SHORTWAVE CROSSING THE REGION.

FOR THE SHORT TERM...TROWAL NORTH OF THE UPPER LOW...ISENTROPIC LIFT
AND THETA-E CONVERGENCE WITH IT WILL PIVOT OVER THE AREA THRU THE
REST OF THE AFTERNOON...THEN SLOWLY ROTATE EAST OF THE AREA THRU
THIS EVENING. STRONG ENSEMBLE/MODEL CONSENSUS FOR SOME -SN TO LINGER
OVER THE FCST AREA THIS EVENING...ESPECIALLY ALONG/EAST OF THE MS
RIVER...WITH ADDITIONAL MINOR -SN ACCUMULATIONS. WITH SNOW ALREADY
TAPERING OFF WEST OF ROUGHLY A KRST-KOLZ LINE...WILL LET WINTER
STORM WARNING EXPIRE AT 6 PM. GIVEN ADDITIONAL SNOW ACCUMULATIONS
ALONG/EAST OF THE MS RIVER INTO THIS EVENING...WILL EXTEND WINTER
WEATHER ADVISORY THRU 03Z /9PM/. WET ROADS THIS AFTERNOON WITH SOME
SOLAR INSOLATION GETTING THRU THE CLOUD LAYER...WILL BECOME ICY THIS
EVENING WITH SUNSET AND CONTINUED -SN. LOW/LIFT PULL AWAY AFTER
MIDNIGHT WITH COLUMN ABOVE 900MB DRYING OUT BY 12Z WED. LINGERED A
SMALL -SN CHANCE AFTER MIDNIGHT THEN REMOVED -SN CHANCE AFTER 09Z.
MODEL SOUNDINGS AND 925MB RH PROGS INDICATE SOME LOWER LEVEL
MOISTURE TO BE TRAPPED UNDER AN INVERSION THRU WED. MODELS DIFFER A
BIT ON HOW QUICKLY THIS MOISTURE AND LIKELY STRATO-CU DECK ADVECTS
EAST OF THE AREA ON WED. NAM/ECMWF FASTER...GFS SLOWER. TRENDED
TOWARD MORE CLOUDS WED MORNING...THEN REMAINED OPTIMISTIC FOR
SUNSHINE/CLEARING FOR THE AFTERNOON AS THE SFC-850MB RIDGE AXIS
APPROACHES. WITH THIS RIDGE AXIS OVER THE AREA WED NIGHT...THE FRESH
SNOW COVER AND CLEAR/MOSTLY CLEAR SKIES...THU MORNING TO BE THE
COLDEST MORNING OF THE WEEK WITH SUB-ZERO LOWS MOST LOCATIONS.
MID/HIGH LEVEL MOISTURE AHEAD OF THE NEXT SHORTWAVE IN THE NORTHWEST
FLOW STARTS TO SPREAD ACROSS THE AREA THU...BUT SHOULD STILL SEE
PLENTY OF SUNSHINE. MODELS START TO DIVERGE WITH THE SPEED OF THE
NEXT SHORTWAVE THU NIGHT...GEM/GFS FASTER...NAM/ECMWF SLOWER. WITH
SREF INCREASING THE PROBABILITY OF PRECIP BY LATE THU NIGHT...DID
ADD A SMALL -SN CHANCE TO THE WEST HALF OF THE FCST AREA. EVEN WITH
DIFFERENCES AMONG THE MODELS...REASONABLE CONSENSUS AMONG THEM AND
SREF MEAN FOR THE PASSING WAVE AND WEAK SFC REFLECTION TO PRODUCE
SOME LIGHT PRECIP ACROSS THE AREA FRI INTO FRI NIGHT. RAISED -SN
CHANCES TO AROUND 30 PERCENT OVER MAINLY THE CENTRAL/WEST PARTS OF
THE FCST AREA BOTH PERIODS.

GUIDANCE LOWS SIMILAR FOR TONIGHT AND APPEAR REASONABLE. WITH THE
FRESH SNOW COVER...FAVORED COLDER OF GUIDANCE HIGHS WED. WITH THE
LIGHT WINDS/CLEAR SKIES UNDER THE RIDGE AXIS WED NIGHT EVEN COLDER
OF GUIDANCE LOWS LOOK TOO WARM AND CONTINUED THE PREVIOUS FCST GRID
LOWS OF A CATEGORY OR TWO BELOW THE GUIDANCE FOR MOST LOCATIONS.
WITH THE COLD START THU MORNING...EVEN COLDER OF GUIDANCE HIGHS LOOK
ABOUT A CATEGORY TOO WARM MOST LOCATIONS. FAVORED COLDER OF GUIDANCE
LOWS THU NIGHT...WITH PERHAPS LOWS IN THE EVENING THEN SLOWLY RISING
TEMPS AFTER MIDNIGHT AS CLOUDS INCREASE. WITH DIFFERENCES AMONG THE
MODELS FOR FRI/FRI NIGHT...FAVORED A BLEND OF GFS MEX/ENSEMBLE MOS
AND HPC GUIDANCE TEMPS...WEIGHTED TOWARD THE GFS ENSEMBLE MOS.

LONG TERM...SATURDAY THROUGH TUESDAY

09.00Z MEDIUM RANGE MODELS HAVE TRENDED STRONGER THAN THEIR 08.00Z
RUNS WITH A SHORTWAVE TROUGH TO DROP INTO/ACROSS THE WESTERN GREAT
LAKES SAT/SUN. HOWEVER...CONSIDERABLE DIFFERENCES AMONG THE MODELS
WITH TIMING/TRACK/STRENGTH DETAILS OF THIS FEATURE. ECMWF ON THE
FASTER SIDE OF THE ENVELOPE...GEM ON THE SLOW/STRONG SIDE...GFS/
UKMET/GFS ENSEMBLE MEAN IN THE MIDDLE ON TIMING/STRENGTH. MEDIUM
RANGE MODELS IN BETTER AGREEMENT WITH EACH OTHER AND THEIR PREVIOUS
RUNS IN THE MON/TUE PERIOD AS LONGWAVE TROUGHING ROTATES THRU THE
EASTERN CONUS AND THE REGION REMAINS UNDER NORTHWEST FLOW ALOFT.
GIVEN THE DIFFERENCES WITH THE SAT/SUN PERIOD...LONG-TERM FCST
CONFIDENCE AVERAGE AT BEST THIS CYCLE. FAVORING A MODEL/ENSEMBLE
CONSENSUS WHICH IS SIMILAR TO GFS/UKMET...ANOTHER STRONG SHORTWAVE
POISED TO DROP ACROSS THE WESTERN GREAT LAKES SAT/SAT NIGHT AS A
CLOSED 500MB LOW AND AN INVERTED TROUGH AT THE SFC...VERY SIMILAR TO
THE SYSTEM FROM MON THRU TODAY. RAISED/ADDED A SNOW CHANCE TO
SAT/SAT NIGHT. MAY YET NEED A SMALL LINGERING SNOW CHANCE FOR SUN.
BUT GIVEN A REASONABLE MODEL CONSENSUS FOR ANOTHER CAN HIGH PRESSURE
SYSTEM TO DROP INTO THE REGION FOR THE SUN-TUE PERIOD...LEFT THESE
PERIODS DRY FOR NOW. WITH THE NORTHWEST FLOW ALOFT TEMPS LOOK TO
REMAIN BELOW NORMAL. A BLEND OF GFS MEX/HPC GUIDANCE HIGHS APPEARING
REASONABLE THRU THE DAY 4-7 PERIOD.

AVIATION...TONIGHT AND WEDNESDAY

THE LOW PRESSURE SYSTEM THAT GAVE THE AREA A LONG-DURATION/
SIGNIFICANT SNOWFALL WILL PULL INTO THE OHIO RIVER VALLEY REGION
TONIGHT. AS A RESULT...LOOK FOR THE SNOW TO CONTINUE DIMINISHING
FROM WEST TO EAST THIS EVENING. HOWEVER...NORTH WINDS AT 10 TO 20
MPH WITH GUSTS AROUND 25 MPH WILL CONTINUE TO PRODUCE SOME BLSN AT
KRST TIL MIDNIGHT. OTHERWISE...IFR VIS WILL IMPROVE TO VFR BY
MIDNIGHT WITH THE DIMINISHED SNOW AND BLSN. MVFR CIGS WILL LIKELY
CONTINUE PAST MIDNIGHT...EVENTUALLY SCATTERING OUT AFTER 10.09Z AS A
RIDGE OF HIGH PRESSURE BUILDS IN FROM THE PLAINS. QUIET/VFR
CONDITIONS WILL BE SEEN ON WEDNESDAY AS HIGH PRESSURE BUILDS OVER
THE AREA.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT/LONG TERM... RRS
AVIATION.......... DAS