Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 240504
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1100 PM CST SUN NOV 23 2014

.UPDATED...
1100 PM CST SUN NOV 23 2014

DENSE FOG PERSISTING ACROSS NORTHERN WI...AND A GOOD PORTION OF
CENTRAL WI. CHECKING WITH AREA DISPATCHES...VISIBILITY REMAINS POOR
AND TRAVEL CONTINUES TO BE IMPACTED. HAVE OPTED TO EXPAND AND EXTEND
THE DENSE FOG ADVISORY THROUGH 3 AM...AND INCLUDED A CHUNK OF
CENTRAL WI. EXPECT IMPROVEMENT IN THE 2 TO 4 AM TIME FRAME AS A COLD
FRONT SWEEPS IN WITH STRONG NORTHWEST WINDS BEHIND IT.

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 247 PM CST SUN NOV 23 2014

COMPLEX SHORT TERM PERIOD WITH MANY ISSUES TO DEAL WITH.

CURRENTLY AS OF 21Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED A VERY ACTIVE PATTERN OVER THE WEST HALF OF THE COUNTRY.
UPPER LOWS WERE PRESENT OVER NORTHERN MISSISSIPPI AND NORTH
DAKOTA...WHILE POTENT SHORTWAVES WERE NOTED IN SOUTHWEST OKLAHOMA...
NORTHERN NEW MEXICO AND OVER WASHINGTON STATE. THE FORECAST AREA
LIES IN SOUTHWEST FLOW...WHERE WATER VAPOR IMAGERY SHOWS A NICE WARM
CONVEYOR BELT OVER THE EAST HALF OF THE AREA. THIS TRANSLATES TO A
BAND OF RAIN FROM EASTERN IA THROUGH SOUTHWEST WI TO THE GRB AREA.
RAP PRECIPITABLE WATER VALUES ARE AROUND 1 INCH ALONG AND SOUTH OF
THE BAND...COMPARED TO 0.75 INCHES OVER OUR NORTHWEST CWA WHERE
CONDITIONS ARE DRY. ALTHOUGH ITS DRIER IN PRECIPITABLE WATER...
DRIZZLE AND/OR LIGHT RAIN HAS BEEN PRESENT DUE TO SATURATED LOW
LEVELS AND WEAK ISENTROPIC LIFT ON THE 285-290K SURFACES. TO THE
WEST...A COLD FRONT WAS PRESENT ALONG I-35 WITH A WEAKENING BAND OF
RAIN RIGHT BEHIND IT...ASSOCIATED WITH MID LEVEL FRONTOGENESIS.
TEMPERATURES AHEAD OF THE FRONT ACROSS THE FORECAST AREA WERE MAINLY
IN THE 40S TO LOW 50S...COLDEST OVER THE DEEPER SNOWPACK IN TAYLOR
COUNTY. IN THE WAKE OF THE FRONT...READINGS WERE IN THE 30S AND
40S...UNTIL ONE GETS INTO NORTH DAKOTA BEHIND A SECONDARY COLD FRONT
WHERE READINGS ARE IN THE TEENS AND 20S. LAST ITEM OF NOTE IS THE
SEA LEVEL PRESSURE MAP WHERE A LOW EXISTS NEAR MEMPHIS ON THE NORTH
SIDE OF THE UPPER LOW THERE...ANOTHER LOW WAS OVER NORTHERN MN
AHEAD OF THE NORTH DAKOTA UPPER LOW...AND FINALLY A THIRD LOW WAS
OVER NORTHEAST OKLAHOMA AHEAD OF THE POTENT SHORTWAVES.

MODEL WISE...THERE ARE STILL SOME DIFFERENCES THAT HAVE SIGNIFICANT
FORECAST IMPLICATIONS. MUCH OF THE DIFFERENCES WE HAVE SEEN LATELY
THAT CONTINUE INTO TODAY REVOLVE AROUND HANDLING THOSE POTENT
SHORTWAVES IN SOUTHWEST OKLAHOMA AND NORTHERN NEW MEXICO. THE
STRONGER SURFACE LOW SCENARIOS THAT WOULD IMPACT THE FORECAST AREA
WITH MORE SNOW...LIKE OBSERVED IN THE 23.00Z NAM...BROUGHT THESE
SHORTWAVES INTO NORTHERN IL BY 12Z MONDAY. THOSE SHORTWAVE TRACKS
ALSO SHOWED IN A COUPLED UPPER JET STRUCTURE WITH ANOTHER JET STREAK
OVER ONTARIO AND LAKE SUPERIOR. HOWEVER...THE 23.12Z
NAM/GFS/CANADIAN/ECMWF SUGGEST THESE SHORTWAVES WILL TRACK THROUGH
CENTRAL IL. SO WHAT HAPPENS INSTEAD IS A DOUBLE SURFACE LOW...ONE
ASSOCIATED WITH THE NORTHERN MISSISSIPPI UPPER LOW LIFTING THROUGH
LOWER MI AND A SECOND LOW LIFTING TROUGH NORTHERN IL AT 12Z MONDAY.
WITH THE POTENT SHORTWAVES. THERE STILL ARE THE 2 JET STREAKS...BUT
THEY ARE FAR ENOUGH APART TO PREVENT COUPLING AND THUS PREVENTING A
SINGLE SURFACE LOW. THIS FORECAST LEANS TOWARDS THIS NEWER MODEL
GROUP. EVEN THIS GROUP HAS DIFFERENCES...PRIMARILY WITH THE CANADIAN
PRODUCING A LOT MORE SNOW ON MONDAY AROUND AND EAST OF THE
MISSISSIPPI RIVER.

FOR TONIGHT...THE WARM CONVEYOR BELT / FRONTOGENESIS BAND PRODUCING
THE ONGOING RAIN OVER THE SOUTHEAST HALF OF THE FORECAST AREA
REMAINS POISED TO SHIFT EASTWARD THROUGH THE EVENING. THIS EASTWARD
MOVEMENT IS DUE TO THE UPPER AND SURFACE LOWS NEAR THE MEMPHIS AREA
LIFTING INTO LOWER MICHIGAN. HOWEVER...DRIZZLE AND/OR LIGHT RAIN
SHOULD CONTINUE ELSEWHERE AS SOUNDINGS DEPICT PLENTIFUL LOW TO MID
LEVEL VERTICAL MOTION AND SATURATION...SIMILAR TO WHAT IS GOING ON
NOW. ADDITIONALLY...THAT WEAKENING BAND OF MID-LEVEL FRONTOGENESIS
SEEN ALONG I-35 IS POISED TO GRADUALLY CROSS THE FORECAST AREA WITH
THE SURFACE COLD FRONT...AIDING IN PRECIPITATION GENERATION. IT MAY
NOT BE UNTIL 09Z FOR THE FAR WESTERN FORECAST AREA TO SEE AN END TO
THE PRECIPITATION. NOTE THE TYPE SHOULD BEGIN TO CHANGE OVER TO SNOW
AS COLDER AIR IN THE DAKOTAS GETS PULLED INTO THE FORECAST AREA. ANY
ACCUMULATIONS TONIGHT SHOULD BE VERY LIGHT...DUE TO LATE CHANGE-OVER
TIME AND WARM GROUND...AND CONFINED TO MOSTLY WEST OF THE
MISSISSIPPI RIVER.

FOR MONDAY...ATTENTION FOCUSES ON THE LOW AND POTENT SHORTWAVES
LIFTING THROUGH ILLINOIS AT 12Z MONDAY. THERE IS A STRONG CONSENSUS
FOR PRECIPITATION IN THE WAKE OF THE LOW...CORRELATED WITH A LEFT
EXIT REGION OF A JET STREAK COMING INTO THE OHIO VALLEY.
ADDITIONALLY...A STRONG POCKET OF MID LEVEL FRONTOGENESIS WITH
NEGATIVE EPV ABOVE FOLLOWS IN THE WAKE OF THE LOW. THAT
FRONTOGENESIS STRENGTHENS AS THE COLD AIR FROM THE DAKOTAS MEETS UP
WITH THE POTENT SHORTWAVES LIFTING NORTHEASTWARD...ALSO CAUSING A
SWITCHOVER TO SNOW. CONSENSUS...OUTSIDE OF THE CANADIAN...SUGGESTS
THE HEAVIER SNOW TRACKING THROUGH NORTHERN IL AND SOUTHERN
WI...CLIPPING GRANT AND RICHLAND COUNTIES...POSSIBLY JUNEAU AND
ADAMS TOO. BOTH SNOWFALL AMOUNTS AND BLOWING POTENTIAL ARE GOING TO
BE KEPT DOWN QUITE A BIT WITH SOUNDINGS DEPICTING A DEEP AGGREGATION
LAYER AND ONLY 50 MB OR SO OF DENDRITIC GROWTH ZONE. ADDITIONALLY...
WARM GROUND AND LACK OF SNOW WILL HELP LIMIT BLOWING. IN
COLLABORATION WITH MKX AND DVN...HAVE ISSUED A WINTER WEATHER
ADVISORY FOR GRANT AND RICHLAND. ELSEWHERE...THERE SHOULD STILL BE
SOME LIGHTER SNOW WITH A WEAKER MID LEVEL FRONTOGENESIS ZONE
MARCHING WEST TO EAST...AND DEEP SATURATION. AMOUNTS DO NOT WARRANT
AN ADVISORY ELSEWHERE AT THIS TIME.

IN THE FOG DEPARTMENT...CONDITIONS HAVE YET TO IMPROVE ACROSS
TAYLOR/CLARK COUNTIES. HI RES MODEL VISIBILITY PROGS...WHICH
ARE HANDLING THE FOG THERE WELL...DO NOT SHOW ANY CLEARING UP UNTIL
THE 06-09Z PERIOD WHEN WINDS START TO INCREASE. THEREFORE...HAVE
EXTENDED THE ADVISORY UNTIL 06Z. VISIBILITIES HAVE ALSO BEEN LOW
OVER THE FAR WESTERN FORECAST AREA...THOUGH THESE SHOULD IMPROVE
SOON AS THE WINDS PICK UP. WILL NEED TO KEEP AN EYE ON VISIBILITIES
THROUGH NORTHEAST IOWA AND SOUTHWEST/CENTRAL WI AS THE HEAVIER RAIN
MOVES OUT...WITH SOME SIGNAL THEY COULD DROP TO WARRANT AN ADVISORY.

LASTLY...REGARDING WINDS...SHOULD SEE SUSTAINED SPEEDS OF 15-30 MPH
WITH GUSTS MAYBE UP TO 40 MPH ON MONDAY. DO NOT SEE ANY WIND
ADVISORY NEED AT THIS TIME...THOUGH. THESE NORTHWEST WINDS WILL
RESULT IN A FALLING TEMPERATURE TREND FROM NOW THROUGH MONDAY.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 247 PM CST SUN NOV 23 2014

NO MATTER WHAT SOLUTION PANS OUT FOR MONDAY...THE TREND CONTINUES TO
BE FOR SNOW TO DIMINISH MONDAY NIGHT AS THE ENTIRE STORM SYSTEM
EXITS EASTWARD INTO QUEBEC. THERE IS SOME UNCERTAINTY ON HOW QUICK
THE SNOW EXITS...MAINLY DUE TO ONE MORE WEAK SHORTWAVE PASSING. WITH
STRATUS LINGERING IN THE DENDRITIC GROWTH ZONE...IT MAKES SENSE TO
CONTINUE TO CARRY PRECIPITATION CHANCES LONGER TOO THAN WHAT MODEL
QPF WOULD SAY FOR ENDING SNOW. BETTER CHANCE FOR CLEARING COMES IN
TUESDAY AS A SURGE OF DRIER...SUBSIDENT AIR COMES IN AHEAD OF A
SURFACE LOW AND SHORTWAVE DROPPING THROUGH THE DAKOTAS. IN FACT...WE
SHOULD GET INTO A WARM ADVECTION REGIME LATER IN THE DAY TO ALLOW
TEMPERATURES TO CLIMB INTO THE MID TO UPPER 20S.

THE SHORTWAVE TROUGH AND SURFACE LOW DROPPING THROUGH THE DAKOTAS
FOR TUESDAY NIGHT AND WEDNESDAY HAS BEEN TRENDING SOUTHWARD IN THE
23.12Z ECMWF...FOLLOWING THE 23.06Z/12Z GFS/NAM. THE 23.12Z CANADIAN
IS ABOUT THE ONLY MODEL NOW WITH THE MORE NORTHERN TRACK. HAVE
ADJUSTED THE FORECAST FOR A MORE SOUTHERN TRACK. DPVA PLUS A SURGE
OF WARM AIR ADVECTION LOOKS TO RESULTS IN A BRIEF BUT HEAVY SNOW
BAND AHEAD OF THE SURFACE LOW. WITH THE SOUTHERN TREND BUT OVERALL
GOOD CONSENSUS TO HAVE THE SNOW BAND...RAISED CHANCES ON WEDNESDAY
TO 60 ACROSS THE SOUTHERN PORTION OF THE FORECAST AREA. MAY GET A
QUICK 1-2 INCHES OUT OF THE BAND...ENOUGH TO IMPACT TRAVEL.

A DRIER BUT COLDER FORECAST IS ON TAP FOR WEDNESDAY NIGHT AND
THANKSGIVING AS ARCTIC HIGH PRESSURE BUILDS INTO THE REGION. 925MB
TEMPS DOWN TO -12 TO -16C SHOULD RESULT IN HIGHS IN THE TEENS TO
MAYBE 20 AT BEST.

THE FORECAST AFTER THANKSGIVING BECAME MUCH MORE UNCERTAIN
TODAY. THERE ARE NOW INDICATIONS OF MORE TROUGHING DIGGING DOWN
THROUGH BRITISH COLUMBIA...WHICH HELPS TO TURN THE UPPER FLOW MORE
ZONAL...AND THUS SEND A WARMER PACIFIC AIRMASS TOWARDS US.
ADDITIONALLY...A WARM FRONT LOOKS TO MOVE THROUGH THE AREA ON
FRIDAY...WHICH COULD PRODUCE A LITTLE SNOW. NOW...THE 23.12Z
GFS/CANADIAN DRIVE A SHORTWAVE THROUGH THE REGION FRIDAY NIGHT AND
ALLOWS ARCTIC AIR TO RETURN FOR THE WEEKEND. THE 23.12Z ECMWF ALLOWS
THIS SHORTWAVE TO STAY FARTHER NORTH...KEEPING THE AREA IN THE WARM
SECTOR. FOR NOW...HAVE STAYED WITH THE CONSENSUS PRIOR TO THE NEW
ECMWF ARRIVAL...BUT THE WEEKEND TEMPS ARE DEFINITELY SUBJECT TO
CHANGE GREATLY. GENERALLY THE WEEKEND LOOKS DRY...THOUGH.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1100 PM CST SUN NOV 23 2014

EXPECTING RAIN TO CHANGE OVER TO SNOW BEFORE 08Z FOR KRST...AND
CLOSE TO 12Z FOR KLSE. CIGS WILL REMAIN SUB 1 KFT THROUGH THE
MORNING...WITH A GRADUAL...SMALL BUMP UP FOR THE AFTERNOON/EVENING.
MODELS SUGGESTING A POSSIBLE BRIEF BREAK IN PCPN/INTENSITY/COVERAGE
COULD OCCUR EARLY MORNING...WITH ANOTHER PIECE OF UPPER LEVEL
ENERGY/SFC TROUGH BRINGING ANOTHER ROUND OF LOW VSBY -SN FOR LATE
MORNING/AFTERNOON. IMPACTS WOULD BE FELT MORE AT KLSE. SHOULD SEE
VSBY IMPROVEMENT BY THE EVENING. ACCUMULATIONS UP TO 3 INCHES
POSSIBLE AT KLSE...LESSER AMOUNTS AT KRST.

STRONG AND GUSTY NORTHWEST WINDS WILL PERSIST THROUGH THE DAY AND
INTO THE EVENING HOURS OF MONDAY.

&&


.ARX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL 3 AM CST MONDAY FOR WIZ017-029-034-
     042>044.

     WINTER WEATHER ADVISORY FROM 6 AM MONDAY TO MIDNIGHT CST MONDAY
     NIGHT FOR WIZ055-061.

MN...NONE.
IA...NONE.

&&

$$

UPDATED......RIECK
SHORT TERM...AJ
LONG TERM....AJ
AVIATION.....RIECK



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