Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 141510
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
910 AM CST SUN DEC 14 2014

.UPDATE...
ISSUED AT 910 AM CST SUN DEC 14 2014

NOT MUCH IMPROVEMENT IN VISIBILITIES EXPECTED THROUGH MONDAY
MORNING AS MILD/MOIST AIRMASS IS LIFTED ACROSS THE REGION.
THEREFORE THE DENSE FOG ADVISORY HAS BEEN EXTENDED THROUGH NOON
MONDAY.

UPDATE ISSUED AT 528 AM CST SUN DEC 14 2014

BECOMING VERY CONCERNED THAT THE DENSE FOG ADVISORY MAY NEED TO BE
EXTENDED FOR THE ENTIRE FORECAST AREA...POSSIBLY INTO MONDAY.
WITH UPPER 40S AND LOW TO MID 50S DEWPOINTS LURKING SOUTH OF THE
AREA NEAR I-80 BEING SHOVED NORTHWARD INTO OUR RELATIVELY SPEAKING
COLDER AIRMASS...ITS POSSIBLE THIS DENSE FOG GOES NOWHERE. ON TOP
OF THAT...LIGHTER WINDS ARE PROGGED TONIGHT...FAVORING LOW
VISIBILITIES. 14.10Z LAV GUIDANCE AT MOST SITES THAT ARE CURRENTLY
EXPERIENCING 1/4 MILE OR LESS VISIBILITIES...SUCH AS RST...CCY AND
MDZ...SHOWS THOSE VISIBILITIES PERSISTING THROUGH 11Z MONDAY...THE
END OF ITS RUN. WE MAY END UP HAVING TO WAIT FOR THE RAIN ON
MONDAY TO HELP IMPROVE VISIBILITIES SOMEWHAT...THOUGH DENSE FOG
COULD EASILY REFORM AFTER THE RAIN TAILS OFF. SOMETIME AFTER
MIDNIGHT MONDAY NIGHT APPEARS WHEN WE CAN FINALLY GET RID OF THE
FOG CONCERN...ACCOMPANYING THE COLD ADVECTION REGIME DEVELOPING
THEN.

HAVE NOT DONE ANY EXTENSIONS TO THE CURRENT ADVISORY...BUT THEY
COULD HAPPEN AT ANYTIME THROUGHOUT THE MORNING. THE HIGHEST
CONFIDENCE FOR THE DENSE FOG TO PERSIST IS ACROSS TAYLOR AND
CLARK COUNTIES...WHICH COINCIDES WITH THE COLDEST FORECAST
READINGS.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 255 AM CST SUN DEC 14 2014

THE MAIN FORECAST CONCERN CONTINUES TO BE THE PRECIPITATION
CHANCES THROUGH THE PERIOD.

LOCAL OBSERVATIONS CONTINUE TO SHOW DENSE FOG WITH VISIBILITIES OF
A QUARTER MILE OR LESS COVERING A GOOD SHARE OF THE AREA. THE
14.05Z RAP BUFKIT SOUNDINGS SUGGEST THE WINDS JUST ABOVE THE
SURFACE MAY DIMINISH A LITTLE BIT THROUGH THE REST OF THE NIGHT
INTO SUNDAY MORNING WITH A SLOWLY DEEPENING SATURATED LAYER. THIS
MAY ALLOW THE DENSE FOG TO BECOME A LITTLE MORE WIDESPREAD AND FOR
THE AREAS THAT HAVE DECENT VISIBILITY TO GO DOWN SOME. PLAN TO
LEAVE THE DENSE FOG ADVISORY IN PLACE WITH NO CHANGES.

STILL DEALING WITH THE ISSUE OF HOW MUCH IF ANY DRIZZLE IS
OCCURRING WITH THE FOG. BASED ON PERSONAL OBSERVATIONS...MUCH LESS
DRIZZLE WAS OCCURRING IN THE LOCAL AREA SATURDAY EVENING THAN
PREVIOUS NIGHTS. THE RAP CONTINUES TO SUGGEST THAT WHAT OMEGA
THERE WILL BE IN THE SATURATED LAYER WILL BE VERY NEAR THE TOP OF
THIS LAYER. THE 14.00Z GFS ALSO CONTINUES TO SHOW JUST SOME VERY
WEAK ISENTROPIC UP GLIDE OF 1 UBAR/S OR LESS ON THE 290K SURFACE.
WILL MAINTAIN THE MENTION OF DRIZZLE FOR THE ENTIRE DAY...BUT WILL
LOWER THE PRECIPITATION CHANCES OF MEASURABLE DOWN TO THE 2O TO 30
PERCENT RANGE. THIS WILL ALSO GIVE AREAS INSTEAD OF WIDESPREAD
DRIZZLE WHICH MOST LIKELY WILL BETTER FIT THE SCENARIO AS WELL.

THE MAIN PRECIPITATION EVENT STILL LOOKS TO MONDAY AND MONDAY
NIGHT. THE UPPER LEVEL LOW LIFTING OUT OF THE DESERT SOUTHWEST IS
EXPECTED TO MOVE INTO THE LOWER MISSOURI RIVER VALLEY TONIGHT AS
ANOTHER UPPER LEVEL LOW DROPS SOUTH FROM CENTRAL CANADA. EVEN
THOUGH THE MAIN UPPER LEVEL RIDGE WILL BE OVER THE EASTERN
CONUS...THE GFS SUGGESTS A SECONDARY RIDGE AXIS WILL EXTEND OFF
THE MAIN RIDGE AXIS ACROSS THE UPPER MIDWEST BETWEEN THE TWO UPPER
LEVEL LOWS. THIS WOULD KEEP THE MAJORITY OF THE FORCING AWAY FROM
THE AREA WITH THE GFS SUGGESTING JUST SOME WEAK QG CONVERGENCE
OCCURRING ACROSS THE WESTERN SECTIONS OF THE AREA WITH JUST THE
VERY WEAK ISENTROPIC UP GLIDE CONTINUING ON THE 290K SURFACE. WILL
TRIM THE RAIN CHANCES BACK TO THE 20 TO 40 PERCENT RANGE FOR THE
EVENING AND THEN ALLOW AN INCREASE TO 60 PERCENT ACROSS THE WEST
FOR LATE TONIGHT.

THE UPPER LEVEL LOW FROM THE SOUTHWEST IS THEN EXPECTED TO MOVE
ACROSS THE AREA MONDAY INTO MONDAY NIGHT BRINGING MODERATE TO
STRONG PV ADVECTION IN THE 500-300 MB ACROSS THE AREA. THE QG
CONVERGENCE WILL BECOME DEEP THROUGH THE 1000-300 MB LAYER AND
SHOULD BE MODERATE IN STRENGTH. THE ISENTROPIC UP GLIDE AHEAD OF
THE LOW WILL ALSO INCREASE WITH THE GFS SHOWING UP TO 10 UBAR/S ON
THE 290K SURFACE BY MONDAY AFTERNOON. WITH THE INCREASED
FORCING...EXPECT THE PRECIPITATION TO BECOME PRETTY WIDESPREAD AND
WILL HAVE 70 TO 80 PERCENT CHANCES FOR THE ENTIRE AREA.
TEMPERATURES WILL CONTINUE TO BE WARM ENOUGH TO KEEP THIS AS ALL
RAIN. THE FORCING WILL NOT START TO DECREASE UNTIL LATE MONDAY
NIGHT...SO WILL CONTINUE WITH THE HIGH PRECIPITATION CHANCES UNTIL
DROPPING THEM DOWN TO ABOUT 60 PERCENT IN THE SOUTHWEST BY LATE
MONDAY NIGHT. BY THIS TIME...THE SURFACE WILL HAVE PASSED BY THE
REGION ALLOWING COLDER AIR TO SPREAD ACROSS THE REGION. THIS WILL
ALLOW FOR A TRANSITION OVER TO SNOW MONDAY NIGHT INTO TUESDAY
MORNING. NOT EXPECTING ANY MIXED PRECIPITATION ISSUES WITH ICE
REMAINING IN THE CLOUDS UNTIL THE PRECIPITATION COMES TO AN END.
SNOWFALL AMOUNTS NOT EXPECTED TO A WHOLE LOT WITH MAYBE UP TO A
HALF INCH OF ACCUMULATION FOR PORTIONS OF SOUTHEAST MINNESOTA
INTO NORTH CENTRAL WISCONSIN.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 255 AM CST SUN DEC 14 2014

FINALLY STARTING TO SEE A CONSENSUS BETWEEN THE MODELS WITH HOW
THE CANADIAN UPPER LEVEL LOW IS HANDLED. THE GFS LOOKS TO HAVE
COME AROUND TO SHOWING THE SAME EVOLUTION THAT THE ECMWF HAS BEEN
SHOWING FOR SEVERAL RUNS. THE UPPER LEVEL LOW IS EXPECTED TO COME
DOWN OVER THE NORTHERN GREAT LAKES TUESDAY NIGHT AND CONTINUE TO
BE PROGRESSIVE AND MOVE OFF THE NORTHEAST COAST THURSDAY NIGHT.
THIS WILL ALLOW HIGH PRESSURE TO BUILD IN AT THE SURFACE BEHIND
THE EARLY WEEK SYSTEM AND THEN REMAIN OVER THE UPPER MIDWEST FOR
THE REMAINDER OF THE PERIOD.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 528 AM CST SUN DEC 14 2014

THE PERSISTENT FLOW OF GULF OF MEXICO MOISTURE INTO COOLER AIR
OVER THE TAF SITES CONTINUES TO PRODUCE FOG AND STRATUS. CEILINGS
ARE STUCK AT LIFR WHILE VISIBILITIES ARE HOLDING AT VLIFR AT RST
AND IFR AT LSE. ANTICIPATING LITTLE CHANGE IN THESE CONDITIONS
DURING THE MORNING. DAYTIME HEATING MAY...UNDERSCORE MAY...IMPROVE
CONDITIONS A LITTLE FOR THE AFTERNOON. BROUGHT RST UP TO LIFR IN
VISIBILITY...AND AT LSE MVFR IN VISIBILITY AND IFR IN CEILING...
BASED ON WHAT HAPPENED YESTERDAY. HOWEVER...RST COULD EASILY STAY
STUCK AT VLIFR IN VISIBILITY THE WHOLE AFTERNOON. CONDITIONS WILL
GO DOWNHILL AGAIN TONIGHT WITH SLIGHTLY LIGHTER WINDS PROGGED AND
THE FLOW OF MOISTURE CONTINUING.

LOOKING AHEAD...A BRIEF REPRIEVE FROM THE POOR VISIBILITIES IS
POSSIBLE DURING THE LATE MORNING AND AFTERNOON ON MONDAY AS RAIN
MOVES THROUGH THE TAF SITES. STILL...ONCE THE RAIN TAILS OFF...IT
LOOKS TO BE BACK IN THE THICK FOG. SOMETIME BETWEEN 05-10Z TUESDAY
APPEARS TO BE WHEN THE FOG WILL FINALLY BEGIN TO EXIT THE TAF
SITES.


&&

.CLIMATE...
ISSUED AT 255 AM CST SUN DEC 14 2014

UNSEASONABLY MILD AIR REMAINS OVER THE AREA TODAY. THE RECORD HIGH
AT ROCHESTER IS 52 AND 56 FOR LA CROSSE. WHILE IT DOES NOT LOOK
LIKE LA CROSSE WILL COME CLOSE TO SETTING A RECORD...IT WILL BE
VERY CLOSE FOR ROCHESTER WITH A CURRENT FORECAST OF 51. THE
CLOUDY SKIES AND FOG MAY END UP BEING THE LIMITING FACTOR IF
TEMPERATURES DO NOT WARM AS MUCH AS EXPECTED.

ON THE OTHER HAND...RECORD WARM LOWS ARE ALL BUT CERTAIN FOR
TODAY. THE CURRENT RECORD WARM LOW AT ROCHESTER IS 37 SET IN 1928
WHILE LA CROSSE IS 41 SET IN 1891. THE CURRENT EXPECTATION IS THAT
TEMPERATURES WILL REMAIN IN THE 40S THROUGH MIDNIGHT TONIGHT.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL NOON CST MONDAY FOR WIZ017-029-032>034-
     041>044-053>055-061.

MN...DENSE FOG ADVISORY UNTIL NOON CST MONDAY FOR MNZ079-086>088-
     094>096.

IA...DENSE FOG ADVISORY UNTIL NOON CST MONDAY FOR IAZ008>011-018-019-
     029-030.

&&

$$

UPDATE...DAS
SHORT TERM...04
LONG TERM...04
AVIATION...AJ
CLIMATE...04


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