Area Forecast Discussion
Issued by NWS La Crosse, WI

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910
FXUS63 KARX 042018
AFDARX

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

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

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

18Z DATA ANALYSIS HAD A BROAD BUT WEAK RIDGE OF HIGH PRESSURE FROM
NORTHWEST ONT 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 FCST 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 THU NIGHT AS THE PATTERN SLOWLY PROGRESSES AND HGTS
RISE/SHORTWAVE RIDGING BUILDS OVER THE UPPER MIDWEST. TREND THRU THU
NIGHT ON THE SHORTWAVE RIDGING FAVORS A COMPROMISE OF THE EARLIER
RUNS. SHORT-TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

IN THE SHORT TERM...THE SFC RIDGE AXIS TO DRIFT EAST TONIGHT AND BE
CENTERED OVER THE FCST AREA AT 12Z THU. 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 FCST AREA. PATCHY TO AREAS
OF FROST ALONG/NORTHEAST OF I-94 APPEARING QUITE LIKELY LATE TONIGHT
INTO EARLY THU 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 THU. MODELS INDICATING
AN INCREASE OF MOISTURE OVER THE AREA THU. THIS MAINLY ABOVE ABOUT
800MB BUT PW VALUES PROGGED INTO THE 0.75 INCH RANGE ACROSS THE
WEST/NORTH PARTS OF THE FCST AREA AROUND MID-DAY THU. 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 FCST AREA
AROUND MID-DAY THU. 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 FCST AREA 15-21Z THU. 925MB TEMPS BY 00Z FRI
SUPPORTING HIGHS THU IN THE MID 60S-LOW 70S. LOW LEVEL WARM
ADVECTION CONTINUES THU NIGHT...AS DO SOUTHWEST WINDS 5-10 MPH. THU
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 FCST AREA THU NIGHT. HOWEVER A LESSER SIGNAL AMONG MODELS FOR
THIS VS. THE -SHRA/SPRINKLE CHANCE THU AND LEFT THU NIGHT DRY FOR
NOW. WITH FAVORABLE DIURNAL COOLING TONIGHT...FAVORED COOLER OF
GUIDANCE LOWS. USED A BLEND OF THE GUIDANCE HIGHS/LOWS FOR THU/THU
NIGHT.

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

FOR FRIDAY THRU SATURDAY NIGHT...

MAIN FCST 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
FCST 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 FCST
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 FCST 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 FCST 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 LKS SHIFTS EAST. MODEL
REMAIN IN REASONABLE AGREEMENT MON 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. FCST 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
FCST AREA SUN NIGHT/MON. 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 FCST 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 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1218 PM CDT WED MAY 4 2016

NOTHING BUT VFR CONDITIONS THROUGH THE TAF PERIOD...WITH SOME
SCATTERED CUMULUS AND GUSTY NORTH TO NORTHWEST WINDS THROUGH LATE
AFTERNOON GIVING WAY TO CLEAR SKIES AND LIGHT WINDS OVERNIGHT.
COULD SEE SOME PATCHES OF MID CLOUDS ROLL DOWN INTO THE AREA ON
THURSDAY WITH WARMER AIR PUSHING IN ALOFT...THOUGH LIGHT WINDS UNDER
10 KNOTS WILL PERSIST THROUGH MIDDAY THURSDAY.

&&

.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 FROM 1 AM TO 7 AM CDT THURSDAY FOR WIZ017-029-033-
     034-042>044.

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

$$

SHORT TERM.....RRS
LONG TERM......RRS
AVIATION.......LAWRENCE
FIRE WEATHER...RRS



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