Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 240905
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
405 AM CDT TUE MAR 24 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 405 AM CDT TUE MAR 24 2015

MAIN FCST CONCERNS THIS PERIOD...PRECIP TYPES/AMOUNTS LATE
THIS AFTERNOON THRU TONIGHT...TEMPERATURES.

06Z DATA ANALYSIS HAD HIGH PRESSURE CENTERED OVER THE GREAT LAKES
WITH RIDGING WESTWARD ACROSS SOUTHERN WI. LOW PRESSURE WAS LOCATED
OVER SOUTHWEST MT AND OK PANHANDLE. HIGH PRESSURE WAS BRINGING CLEAR
SKIES TO MUCH OF WI...WHILE INCREASING SOUTHWEST FLOW AND FALLING
PRESSURES AHEAD OF THE LOWS WERE ALLOWING LOW CLOUDS TO PERSIST AND
INCREASE THE HIGH CLOUDS OVER MN/IA. EARLY MORNING TEMPS ON THE COLD
SIDE ACROSS WI UNDER THE CLEAR SKIES/LIGHT WINDS...WHILE CLOUDS AND
MORE SOUTHEAST WIND AROUND THE HIGH HOLDING TEMPS IN THE UPPER 20S
TO MID 30S ACROSS MUCH OF MN/IA.

NO ISSUES NOTED WITH 24.00Z MODEL INITIALIZATIONS. SOLUTIONS
CONVERGING ON A TIGHTER CONSENSUS AS SHORTWAVE ENERGY OVER WY/CO
EARLY THIS MORNING COMES ACROSS THE CENTRAL PLAINS TODAY THEN AS IT
AND THE SOUTHERN PORTION OF THE TROUGH AXIS QUICKLY MOVES ACROSS THE
REGION TONIGHT. TREND THRU TODAY AND TONIGHT FAVORS MORE PROGRESSIVE
AND OPEN WAVE SOLUTIONS OF THE EARLIER MODEL RUNS. FCST CONFIDENCE
FOR TODAY/TONIGHT IS GENERALLY GOOD  GIVEN THE TIGHTER OVERALL
CONSENSUS...BUT SOME DETAIL DIFFERENCES REMAIN CONCERNING PRECIP
TYPES TONIGHT.

IN THE SHORT TERM...GENERALLY QUIET THIS MORNING AS DRIER/COOL HIGH
PRESSURE HOLDS OVER THE AREA...WITH MAINLY AN INCREASE OF HIGH
CLOUDS. SHORTWAVE/TROUGH AXIS IS APPROACHING/CROSSING THE MO RIVER
AT 00Z WED BUT THE FASTER MORE OPEN WAVE TREND SPREADS INCREASING
MOISTURE/LIFT ACROSS THE SOUTHWEST HALF OF THE FCST AREA THRU THE
MID/LATE AFTERNOON HOURS. THE FASTER MORE OPEN TREND RESULTS IN
SOMEWHAT LESS WARMING ALOFT AROUND 850MB...WITH MAX TEMPS ALOFT
AROUND 00Z WED NOW MORE IN THE -1C TO +2C RANGE. WITH THE 900-
700MB PORTION OF THE COLUMN STARTING OUT DRY...APPEARS EVAPORATIVE
AND DYNAMIC COOLING WILL BE MORE ABLE TO OVERCOME THE WARM LAYER
ALOFT NOW...WITH PRECIP COMING IS AS -RA AND QUICKLY CHANGING TO
SNOW ALONG/NORTHWEST OF ROUGHLY A KCCY-VIROQUA-ADAMS/FRIENDSHIP
LINE AS THE BAND LIFTS NORTHEAST ACROSS THE FCST AREA. POTENTIAL
FOR SOME SLEET AS WELL ALONG WITH SNOWFALL RATES OF 1 INCH OR MORE
PER HOUR. COLUMN LOSES ICE IN THE CLOUDS AS MID LEVEL DRYING
SPREADS IN BEHIND THE MAIN PRECIP BAND. SIGNAL FOR A PERIOD OF
-DZ/-FZDZ AS SOME LINGERING FORCING/LIFT REMAINS BEHIND THE MAIN
PRECIP BAND. WHERE THE PRECIP WOULD FALL MAINLY AS SNOW...2 TO 4
INCHES COULD FALL IN AS LITTLE AS A 2-3HR PERIOD. GIVEN THIS...THE
POTENTIAL FOR THE WINTRY MIX AND TRAILING -DZ/-FZDZ...WILL ISSUE A
WINTER WEATHER ADVISORY FOR ROUGHLY THE NORTHWEST 2/3 OF THE FCST
AREA CENTERED ON TONIGHT. ADVISORY BROKEN UP FOR EXPECTED TIMING
OF THE BAND OF HEAVIER SNOW/WINTRY MIX AS IT TRANSLATES NORTHEAST
ACROSS THE FCST AREA.

WARMEST HIGHS IN THE FCST AREA TODAY ALONG/NORTHEAST OF I-94 WITH
MORE SUNSHINE AND LITTLE/NO SNOW COVER. USED A BLEND OF GUIDANCE
HIGHS/LOWS FOR TODAY/TONIGHT.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 405 AM CDT TUE MAR 24 2015

MAIN FCST CONCERNS FOR WED THRU THU NIGHT...LINGERING PRECIP WED
MORNING...SMALL PRECIP CHANCES ACROSS MAINLY THE NORTH PARTS OF THE
FCST AREA WED AFTERNOON THRU THU...TEMPERATURES.

24.00Z MODELS SHOW TIGHTENING AGREEMENT WED...BUT ARE ALSO MORE
PROGRESSIVE/LESS DIGGING WITH THE SECONDARY NORTHWEST FLOW SHORTWAVE
INTO THE UPPER MIDWEST. CONSENSUS IS GOOD WED NIGHT/THU FOR COLD/
STRONG MID LEVEL TROUGHING TO SWING ACROSS THE UPPER MIDWEST...WITH
THE TROUGH AXIS PASSING AROUND 12Z THU. GOOD SIGNAL FOR HGTS TO
START TO RISE THU NIGHT...BUT THE REGION IS UNDER BRISK NORTHWEST TO
NORTH FLOW ALOFT ON THE BACK SIDE OF THE TROUGH. GIVEN THE TIGHTER
CONSENSUS...FCST CONFIDENCE FOR WED THRU THU NIGHT IS ON THE GOOD
SIDE.

LEAD/SOUTHERN SHORTWAVE WILL BE QUICKLY EXITING EAST OF THE REGION
WED MORNING...WITH 850-500MB WESTERLY FLOW AND DRYING SPREADING
ACROSS THE FCST AREA BEHIND IT. LAST TO SEE THE DEEPER DRYING WILL
BE THE NORTH END OF THE FCST AREA. WITH THE NORTHWEST FLOW WAVE
ROTATING ACROSS NORTHERN MN/WI ON WED...LINGERED SOME 25-50 PERCENT
PRECIP CHANCES ACROSS MAINLY CLARK/TAYLOR COUNTIES WED/WED EVENING
WHILE REDUCING PRECIP CHANCES ELSEWHERE ACROSS THE FCST AREA. AREA
REMAINS STUCK UNDER CYCLONIC SFC-700MB FLOW WED/WED NIGHT...SO
APPEARS LOWER CLOUDS WILL LINGER ACROSS MUCH OF THE FCST AREA AND
TEMPER HIGHS/LOWS THESE PERIODS. A WEAK SFC-850MB TROUGH SLIDES
ACROSS THE FCST AREA THU...AS LARGER SCALE ANTI-CYCLONIC FLOW/CAN
HIGH PRESSURE/LOW LEVEL COLD ADVECTION BUILD INTO THE UPPER
MIDWEST THU/THU NIGHT. SMALL CONSENSUS -RA/-SN CHANCE MAINLY
ALONG/NORTHEAST OF I-94 ON THU OKAY FOR NOW. THE LOW LEVEL COLD
ADVECTION SENDS 925MB TEMPS INTO THE -13C TO -18C RANGE BY 12Z
FRI. WITH CLEARING SKIES...LIGHT WINDS AND SOME SNOW COVER...THU
NIGHT/FRI MORNING SHAPING UP TO BE ONE OF THE COLDER MORNINGS IN
THE PAST 2 TO 3 WEEKS. GENERALLY USED A BLEND OF THE GUIDANCE
HIGHS/LOWS FOR WED THRU THU NIGHT.

FOR FRIDAY THRU MONDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...-RA/-SN CHANCES WITH PASSING
TROUGH/FRONT SAT/SAT NIGHT...TEMPERATURES THRU THE PERIOD.

MEDIUM RANGE MODEL RUNS OF 24.00Z IN GOOD AGREEMENT FOR HGTS TO
SLOWLY RISE FRI/FRI NIGHT AS THE COLD MID LEVEL TROUGH MOVES INTO
EASTERN NOAM. GOOD CONSENSUS CONTINUES SAT AS SHORTWAVE RIDGING
AHEAD OF A SHORTWAVE TROUGH DIVING OUT OF CAN BUILDS OVER THE UPPER
MIDWEST. OVERALL TREND APPEARS STRONGER WITH THIS SHORTWAVE TROUGH
AS IT APPROACHES/PASSES SAT NIGHT/SUN. SOME TIMING DIFFERENCES BY
SAT NIGHT/SUN BUT THIS MORE OR LESS EXPECTED IN THE DAY 6 TIME-
FRAME. HGTS START TO RISE AGAIN ALREADY SUN NIGHT/MON. DAY 4-7 FCST
CONFIDENCE IS AVERAGE THIS CYCLE.

DAY 4-7 PERIOD STARTS OUT COLD AND DRY WITH CAN HIGH PRESSURE AND
THE COLD 925MB AIRMASS OVER THE UPPER MIDWEST. THE SFC HIGH SLATED
TO REMAIN NEARLY STATIONARY THRU SAT MORNING WITH 925MB TEMPS ONLY
SLOWLY MODERATING INTO THE -9C TO -13C RANGE BY 12Z SAT. FRI/FRI
NIGHT TO BE SEASONABLY COLD...WITH HIGHS/LOWS TRENDING TO BE 10-15F
BELOW NORMAL AT THIS TIME. LOW LEVEL WARM ADVECTION TO RETURN
SAT...WITH THE STRONGER OF THIS TO SPREAD ACROSS THE REGION SAT
NIGHT AHEAD OF THE SFC-500MB TROUGH/FRONT. QUESTION REMAINS HOW MUCH
MOISTURE WILL RETURN AHEAD OF THIS TROUGH/FRONT. GFS/CAN-GEM MORE
ROBUST WITH THE MOISTURE RETURN THAN ECMWF...AND GENERATE SOME
PRECIP WITH/AHEAD OF THE TROUGH/FRONT SAT NIGHT INTO SUN. 25-40
PERCENT -RA/-SN CHANCES SAT NIGHT INTO SUN MORNING GIVEN TIMING
DIFFERENCES LOOK GOOD FOR NOW. ACTUAL PRECIP CHANCES LIKELY TO BE
MORE OF A 6 HR PERIOD WITH THE TROUGH PASSAGE ONCE TIMING DETAILS
SETTLE DOWN. COLD ADVECTION BEHIND THE TROUGH IS SHORT LIVED WITH
WARM ADVECTION LOOKING TO QUICKLY RETURN MON. FOLLOWED THE MODEL/
ENSEMBLE CONSENSUS FOR HIGHS/LOWS IN THE FRI THRU MON PERIOD.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1135 PM CDT MON MAR 23 2015

AN MVFR STRATUS DECK WILL BE CLEAR OF RST BY 7Z AS DRIER LOW LEVEL
AIR CONTINUES TO PUSH INTO THE REGION. THE MAIN FOCUS WILL THEN
SHIFT TO TUESDAY EVENING AS PRECIPITATION MOVES IN FROM THE
SOUTHWEST. A SLIGHT WARM LAYER ABOVE FREEZING COULD CAUSE THE
PRECIPITATION TO START OUT AS SLEET/SNOW PELLETS...MORE SO AT LSE
THAN RST...BEFORE CHANGING OVER TO ALL SNOW. VISIBILITY WILL LIKELY
DROP TO IFR AS THE SNOW MOVES IN WITH THE HEAVIEST PERIOD COMING IN
THE EVENING.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM CDT
     WEDNESDAY FOR WIZ032>034-041-042-053.

     WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM CDT
     WEDNESDAY FOR WIZ017-029-043-044.

MN...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 4 AM CDT
     WEDNESDAY FOR MNZ086-087-094-095.

     WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM CDT
     WEDNESDAY FOR MNZ079-088-096.

IA...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 4 AM CDT
     WEDNESDAY FOR IAZ008>010-018-019.

     WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM CDT
     WEDNESDAY FOR IAZ011.

&&

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION.....HALBACH


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