Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 050453
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1153 PM CDT WED MAY 4 2016

.UPDATE...
ISSUED AT 913 PM CDT WED MAY 4 2016

DECIDED TO EXPAND THE FROST ADVISORY INTO LA CROSSE...VERNON AND
RICHLAND COUNTIES TO COVER THOSE TYPICALLY COLD VALLEYS AND
DRAINAGE SPOTS WHERE TEMPERATURES WILL LIKELY DIP INTO THE LOWER
30S BY MORNING ALLOWING FROST TO DEVELOP.

&&

.SHORT TERM...(TONIGHT THRU THURSDAY NIGHT)
ISSUED AT 318 PM CDT WED MAY 4 2016

MAIN FORECAST CONCERNS THIS PERIOD...FROST POTENTIAL
ALONG/NORTHEAST OF I-94 TONIGHT...-SHRA/SPRINKLE CHANCES THURSDAY
AFTERNOON...TEMPERATURES THRU THE PERIOD.

18Z DATA ANALYSIS HAD A BROAD BUT WEAK RIDGE OF HIGH PRESSURE FROM
NORTHWEST ONTARIO THRU SD TO CO. DEEPER BOUNDARY LAYER MIXING AND
MDT PRESSURE GRADIENT OVER THE AREA EAST OF THE RIDGE AXIS
RESULTING IN NORTH WINDS 10-20KT G20-30KTS OVER MUCH OF THE
FORECAST AREA AT MID-DAY. RA-OBS/MODEL SOUNDINGS/VIS IMAGERY
SHOWING NORTHERLY SFC- 500MB FLOW EAST OF THE RIDGE AXIS ADVECTING
A DEEP DRY AIRMASS INTO MUCH OF MN/IA/WI. SFC DEW POINTS HAD MIXED
DOWN INTO THE UPPER 20S-LOWER 30S ACROSS MUCH OF MN/NORTHERN
IA/NORTHWEST WI EARLY THIS AFTERNOON.

MODEL RUNS OF 04.12Z INITIALIZED QUITE WELL. MODELS IN GOOD AGREEMENT
TONIGHT THRU THURSDAY NIGHT AS THE PATTERN SLOWLY PROGRESSES AND
HGTS RISE/SHORTWAVE RIDGING BUILDS OVER THE UPPER MIDWEST. TREND
THRU THURSDAY NIGHT ON THE SHORTWAVE RIDGING FAVORS A COMPROMISE
OF THE EARLIER RUNS. SHORT-TERM FORECAST CONFIDENCE IS GOOD THIS
CYCLE.

IN THE SHORT TERM...THE SFC RIDGE AXIS TO DRIFT EAST TONIGHT AND BE
CENTERED OVER THE FORECAST AREA AT 12Z THURSDAY. LIGHT/CALM WINDS
UNDER THE RIDGE AXIS...CLEAR/MOSTLY CLEAR SKIES AND THE DRY
BOUNDARY LAYER AIRMASS /DEW POINTS IN THE UPPER 20S/LOW30S/ SETS
THE STAGE FOR STRONG RADIATIONAL COOLING TONIGHT. HIGHS TODAY ONLY
IN THE UPPER 50S/LOWS 60S AND 25-30 DEGREES OF DIURNAL COOLING
TONIGHT... ESPECIALLY IN LOW LAYING AREAS...PUTS LOWS IN THE
30-35F RANGE ACROSS AT LEAST THE NORTHEAST 1/3 OF THE FORECAST
AREA. PATCHY TO AREAS OF FROST ALONG/NORTHEAST OF I-94 APPEARING
QUITE LIKELY LATE TONIGHT INTO EARLY THURSDAY MORNING...WITH
FROST ADVISORY THOSE AREAS LOOKING GOOD. DID ADD TREMPEALEAU CO.
TO THE ADVISORY MIX. STRONGER 925- 700MB WARM ADVECTION SPREADS
ACROSS THE AREA THURSDAY. MODELS INDICATING AN INCREASE OF
MOISTURE OVER THE AREA THURSDAY. THIS MAINLY ABOVE ABOUT 800MB BUT
PW VALUES PROGGED INTO THE 0.75 INCH RANGE ACROSS THE WEST/NORTH
PARTS OF THE FORECAST AREA AROUND MID- DAY THURSDAY. THIS WITH
MODELS TRYING TO SNEAK A WEAK SHORTWAVE THRU THE SHORTWAVE RIDGING
BUILDING OVER THE REGION. SEVERAL MODELS INCLUDING HI-RES WRF
MODELS GENERATE SOME -SHRA ACROSS MAINLY THE NORTHWEST 1/2 OF THE
FORECAST AREA AROUND MID- DAY THURSDAY. GIVEN THE DRIER LOW LEVELS
AND MOST OF THE WARM ADVECTION LOOKING TO GO INTO WARMING...ANY
-SHRA/RAIN AMOUNTS SHOULD BE QUITE LIGHT. DID ADD A SPRINKLE
MENTION ACROSS THE NORTHWEST 1/3 TO 1/2 OF THE FORECAST AREA
15-21Z THURSDAY. 925MB TEMPS BY 00Z FRI SUPPORTING HIGHS THURSDAY
IN THE MID 60S-LOW 70S. LOW LEVEL WARM ADVECTION CONTINUES
THURSDAY NIGHT...AS DO SOUTHWEST WINDS 5-10 MPH. THURSDAY NIGHT
TRENDING TO BE A MUCH WARMER NIGHT THAN TONIGHT...WITH LOWS ABOVE
NORMAL. MAY YET NEED A SMALL -SHRA CHANCE ACROSS THE EAST SIDE OF
THE FORECAST AREA THURSDAY NIGHT. HOWEVER A LESSER SIGNAL AMONG
MODELS FOR THIS VS. THE -SHRA/SPRINKLE CHANCE THURSDAY AND LEFT
THURSDAY NIGHT DRY FOR NOW. WITH FAVORABLE DIURNAL COOLING
TONIGHT...FAVORED COOLER OF GUIDANCE LOWS. USED A BLEND OF THE
GUIDANCE HIGHS/LOWS FOR THURSDAY/THURSDAY NIGHT.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 318 PM CDT WED MAY 4 2016

FOR FRIDAY THRU SATURDAY NIGHT...

MAIN FORECAST CONCERNS THIS PERIOD...WARM TEMPS
FRIDAY...SHRA/TSRA CHANCES WITH FRONTAL PASSAGE FRI NIGHT/SAT
MORNING.

04.12Z MODELS REMAIN IN GOOD AGREEMENT FRI AS THE SHORTWAVE RIDGING
MOVES ACROSS THE REGION AND A STRONGER SHORTWAVE TROUGH APPROACHES
FROM THE NORTH. GOOD AGREEMENT CONTINUES FRI NIGHT AS THE SHORTWAVE
TROUGH DROPS INTO/ACROSS THE UPPER MIDWEST FRI NIGHT THRU SAT NIGHT.
TREND FAVORS STRONGER OF THE EARLIER RUNS WITH THIS TROUGH. OVERALL
FORECAST CONFIDENCE FOR FRI THRU SAT NIGHT IS GOOD THIS CYCLE.

LOW LEVEL WARM ADVECTION CONTINUES FRI WITH 925MB TEMPS CLIMBING
INTO THE 20C TO 22C RANGE BY 00Z SAT. SOME MODEL DETAIL DIFFERENCES
ON THESE TEMPS...BUT CONSENSUS WOULD SUPPORT HIGHS IN THE UPPER 70S-
LOW 80S FRI. WITH WARMER OF MODELS OFTEN VERIFYING BETTER IN DRY...
WARM ADVECTION SOUTHWEST FLOW...SIDED WITH WARMER OF MODELS WITH
HIGHS FRI MORE IN THE LOWER-MID 80S...SOME 10-15F ABOVE THE NORMALS.
THE WARMTH FOR THE AREA IS SHORT LIVED...AS THE SHORTWAVE TROUGH
DROPPING OUT OF CAN DRIVES A STRONG COLD FRONT SOUTH ACROSS THE
FORECAST AREA FRI NIGHT. SOME PV ADVECTION WITH THE
SHORTWAVE...ALONG WITH MUCH OF THE AREA UNDER RIGHT ENTRANCE
REGION OF A 90-100KT 250-300MB JET MAX OVER NORTHERN MN CENTERED
ON LATER FRI NIGHT. THIS WITH PW VALUES IN THE 1 INCH RANGE AHEAD
OF/WITH THE FRONT...MUCAPE AROUND 500 J/KG AND SOME SFC-700MB FN
CONVERGENCE WITH THE FRONT. CHANCE OF SHRA/TSRA MOVING SOUTH
ACROSS THE FORECAST AREA WITH THE FRONT... CENTERED ON LATE FRI
NIGHT LOOKS GOOD. STRONG LOW LEVEL COLD ADVECTION SPREAD ACROSS
THE AREA BEHIND THE FRONT LATER FRI NIGHT/ SAT MORNING WITH 925MB
TEMPS IN THE 12C-14C RANGE FOR SAT AFTERNOON. HIGHS SAT ALREADY
BACK TO NEAR NORMAL IN THE MID 60S TO NEAR 70. MDT TO BRISK NORTH
WINDS SAT WILL ALSO MAKE IT FEEL QUITE A BIT COOLER THAN FRI.
WEAK/DRIER CAN HIGH PRESSURE TO SETTLE IN BEHIND THE DEPARTING
FRONT FOR SAT NIGHT. FAVORED WARMER OF GUIDANCE HIGHS FRI THEN
SIDED WITH A BLEND OF THE GUIDANCE LOWS/HIGHS FOR FRI NIGHT THRU
SAT NIGHT.

FOR SUNDAY THRU WEDNESDAY...DAYS 4 TO 7...

MAIN FORECAST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES SUN NIGHT-
WED... TEMPERATURES THRU THE PERIOD.

MEDIUM RANGE MODEL RUNS OF 04.00Z/04.12Z IN DECENT AGREEMENT SUN FOR
RISING HGTS ALOFT AS TROUGHING OVER THE GREAT LAKES SHIFTS EAST.
MODEL REMAIN IN REASONABLE AGREEMENT MONDAY FOR SHORTWAVE RIDGING
TO MOVE ACROSS THE UPPER MIDWEST...AHEAD OF THE ROCKIES MID LEVEL
LOW AS IT EJECTS INTO THE CENTRAL PLAINS. MODEL DIFFERENCES
INCREASE FOR TUE/WED AS REMNANTS OF THIS SYSTEM WOULD EJECT INTO
THE MID/UPPER MS VALLEY. THESE DIFFERENCES BEING DRIVEN BY HOW
MUCH INTERACTION OCCURS BETWEEN IT AND NORTHERN STREAM ENERGY OVER
SOUTHWEST CAN/ NORTHWEST CONUS. FORECAST CONFIDENCE GOOD
SUNDAY...THEN ON THE LOW SIDE BY TUE/WED.

THIS PERIOD STARTS OUT WITH A WEAK RIDGE OF CAN HIGH PRESSURE
SLIDING ACROSS THE REGION...AND THE RISING HGTS ALOFT. MOTHERS
DAY CONTINUES TO TREND TOWARD A DRY AND MOSTLY SUNNY DAY. SOME
DETAIL DIFFERENCES AMONG MODELS ON 925-850MB TEMPS SUN...BUT HIGHS
SUN LOOKING TO BE IN THE 60F-70F RANGE...CLOSE TO NORMAL. BY SUN
NIGHT ECMWF...WITH A FASTER/MORE NORTHERLY EJECTION OF THE MID
LEVEL LOW INTO THE PLAINS...IS ALREADY SPREADING INCREASING
MOISTURE/INSTABILITY...AND SHRA/TSRA CHANCES NORTHEAST INTO THE
FORECAST AREA SUN NIGHT/MONDAY. ECMWF WITH A MORE NORTHERLY TRACK
OF THE MID LEVEL LOW REMNANTS AND MORE DIGGING OF THE NEXT
NORTHERN STREAM SHORTWAVE INTO THE NORTHERN ROCKIES BEHIND
IT...CONTINUES WITH SHRA/TSRA CHANCES ACROSS MUCH OF THE UPPER
MIDWEST TUE/WED. GFS WITH LESS INTERACTION BETWEEN THE 2 SYSTEMS
TRACKS THE MID LEVEL LOW MORE ACROSS THE MID MS VALLEY
TUE/WED...AND WOULD LEAVE MAINLY THE SOUTH END OF THE FORECAST
AREA WITH ANY SHRA/TSRA CHANCES TUE/WED. 04.12Z CAN-GEM SPLITS THE
GFS/ECMWF DIFFERENCES SUN NIGHT INTO TUE. UNTIL THE NORTH-SOUTH
STREAM INTERACTION DETAILS SORT THEMSELVES OUT AND DAY 5-7
CONFIDENCE IMPROVES...WITH STAY WILL THE MODEL/ENSEMBLE CONSENSUS
OF MOSTLY 20-40 PERCENT SHRA/TSRA CHANCES SUN NIGHT INTO WED.
925-850MB TEMPS PROGGED TO CHANGE LITTLE FOR SUN-WED.
MODEL/ENSEMBLE CONSENSUS OF HIGHS/LOWS NEAR THE EARLY MAY NORMALS
INTO THE MIDDLE OF NEXT WEEK LOOKS WELL TRENDED AT THIS TIME.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1153 PM CDT WED MAY 4 2016

HIGH PRESSURE AT THE SURFACE WAS CENTERED FROM NEBRASKA INTO
CENTRAL ONTARIO LATE THIS EVENING. THIS HIGH WILL CONTINUE TO SINK
SOUTHEAST AND MOVE ACROSS THE AREA OVERNIGHT. THE HIGH IS EXPECTED
TO CONTINUE PROVIDING VFR CONDITIONS THROUGH THE
PERIOD...ALTHOUGH THERE MAY BE SOME MID LEVEL CLOUDS THURSDAY
AFTERNOON AS A WEAK SHORT WAVE TROUGH SLIDES ACROSS THE GREAT
LAKES REGION. WINDS WILL BE LIGHT THROUGH THE PERIOD WITH THE
DIRECTION GOING AROUND TO THE SOUTHWEST ON THE BACK SIDE OF THE
HIGH.

&&

.FIRE WEATHER...FRIDAY
ISSUED AT 318 PM CDT WED MAY 4 2016

ON FRIDAY...TEMPERATURES WILL CLIMB INTO THE LOWER AND MID 80S.
MINIMUM AFTERNOON HUMIDITIES ARE EXPECTED TO FALL INTO THE 25 TO 35
PERCENT RANGE...WHILE WEST WINDS GUST INTO THE 20 TO 25 MPH RANGE.
THE STRONGER OF THE WINDS WILL BE ACROSS THE OPEN COUNTRY AREAS OF
NORTHEAST IA/SOUTHEAST MN. MODEL SOUNDINGS SHOWING MIXED SFC DEW
POINTS AROUND 50F SAT AFTERNOON. IF THESE MIX TO LOWER VALUES...
AFTERNOON HUMIDITIES ON FRI COULD BE MORE IN THE 20-30 PERCENT
RANGE. THESE CONDITIONS MAY CAUSE ELEVATED FIRE DANGERS AND COULD
CREATE ISSUES FOR THOSE PLANNING ON DOING ANY OUTDOOR BURNING ON
FRI.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...FROST ADVISORY UNTIL 7 AM CDT THURSDAY FOR WIZ017-029-033-034-
     041>044-053-055.

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

$$

UPDATE...04
SHORT TERM.....RRS
LONG TERM......RRS
AVIATION...04
FIRE WEATHER...RRS



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