Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 210841
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
341 AM CDT TUE APR 21 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 341 AM CDT TUE APR 21 2015

MAIN FCST CONCERNS THIS PERIOD...STRONG WINDS THIS AFTERNOON...
-SHRA/-SHSN CHANCES TODAY INTO THIS EVENING...TEMPERATURES.

06Z DATA ANALYSIS HAD A 984 MB LOW SOUTHWEST OF JAMES BAY CANADA
WITH BROAD TROUGHING TO THE SOUTHWEST INTO NORTHERN MN. TIGHT
PRESSURE GRADIENT AND STEEPER LOW LEVEL LAPSE RATES REMAINED ACROSS
THE REGION...ESPECIALLY MN/WI WHERE WEST TO NORTHWEST WINDS OF 15 TO
20MPH GUSTING 25-35 MPH WERE QUITE COMMON. ONE SHORTWAVE OVER
NORTHERN MN INTO NORTHWEST WI WITH THE MID LEVEL LOW COMBINED WITH
SOME DEEPER MOISTURE AND TIGHTER 925-700MB CYCLONIC FLOW/
CONVERGENCE WERE PRODUCING SOME -SN/-SHSN OVER NORTHEAST MN INTO THE
NORTHWEST 1/4 OF WI. FURTHER SOUTH...WIDELY SCT -SHRA/-SHSN NOTED
OVER EAST CENTRAL MN INTO WESTERN WI.

21.00Z MODELS LOOK TO HAVE INITIALIZED WELL. SOLUTIONS QUITE SIMILAR
AS THE MID LEVEL LOW OVER NORTHERN MN DROPS ACROSS THE U.P. OF MI
TODAY THIS MORNING/EARLY THIS AFTERNOON...THEN LIFTS INTO EAST
CENTRAL ONTARIO LATE TODAY/TONIGHT. SOLUTIONS GENERALLY FAVOR
COMPROMISE OF THE EARLIER RUNS WITH DEEP...COLD CYCLONIC FLOW OVER
THE UPPER MIDWEST THIS PERIOD. SOME DIFFERENCES ON LIGHT QPF
PRODUCTION UNDER/SOUTH OF THE MID LEVEL LOW TODAY BUT THIS NOT
UNEXPECTED. OVERALL SHORT-TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

IN THE SHORT TERM...TIGHT PRESSURE GRADIENT REMAINS OVER THE AREA
AGAIN TODAY...WITH STEEP LOW LEVEL LAPSE RATES/MIXING TO 850MB THIS
AFTERNOON. BIT MORE WIND IN THE MIXED PORTION OF COLUMN THAN
SUNDAY...25-30KTS AT 925MB AND AROUND 35KTS AT 850MB. 700MB TEMPS
AROUND -16C AS WELL THIS AFTERNOON WITH POTENTIAL OF MIXING TO
800MB. WILL MATCH UP WITH THE NEIGHBORS AND ISSUE A WIND ADVISORY
FOR ROUGHLY THE SOUTHWEST 1/3 OF THE FCST AREA FROM 16Z-23Z TODAY.
MODEL SOUNDINGS/X-SECTIONS SHOWING CONSIDERABLE MOISTURE/SATURATION
IN THE 900-500MB LAYER TO ROTATE ACROSS ROUGHLY THE NORTHEAST 2/3 OF
THE FCST AREA TODAY. THIS WITH THE -16C 700MB COLD POOL...A LOBE OF
VORTICITY ROTATING AROUND THE UPPER LOW AND THE TIGHTER 925-700MB
CYCLONIC CONVERGENCE...SETS THE STAGE FOR AT LEAST SCT -SHRA/-SHSN
ACROSS THE NORTHEAST HALF OF THE FCST AREA TODAY. RAISED PRECIP
CHANCES A BIT TODAY ACROSS THE NORTHEAST HALF OF THE FCST AREA...
WITH 60+ PERCENT ACROSS THE FAR NORTH END. COLUMN COLD ENOUGH FOR -
SHSN AS FAR SOUTH AS I-90 THRU MID MORNING. DIURNAL WARMING/ MIXING
OF LOWER PORTION OF THE COLUMN LOOKS TO CHANGE BULK OF PRECIP TO -
SHRA BY LATE MORNING...BUT STRONGER SHOWER CORES AND DRIER AIR BELOW
900MB FOR EVAPORATIVE COOLING MAY ALLOW SOME -SN/SLEET/SNOW PELLET
SHOWERS TO OCCUR WELL INTO THE AFTERNOON. DAY CREW WILL HAVE TO
MONITOR WARMING...AND OBS...AND MAY NEED TO INCLUDE THAT IN GRIDS AS
THE DAY WEARS ON. SECONDARY SHORTWAVE ROTATES IN AND ACROSS THE
AREA THIS EVENING...WITH A BETTER PV ADVECTION SIGNAL. RAISED
-SHRA/ -SHSN CHANCES/LINGERED THEM LONGER OVER THE EAST SIDE OF
THE FCST AREA THIS EVENING. 925-500MB SUBSIDENCE AND DRYING OF THE
COLUMN SPREADS ACROSS THE FCST AREA LATE THIS EVENING/OVERNIGHT...
WITH AND END TO THE -SHRA/-SHSN. SOME CLEARING LATER TONIGHT AS
WELL. PRESSURE GRADIENT CONTINUES TO RELAX TONIGHT BUT SFC WINDS
LOOKING TO REMAIN IN THE 7-14KT RANGE FOR BOUNDARY LAYER MIXING.
EVEN WITH THE WINDS...LOWS LOOKING TO FALL TO NEAR/BELOW FREEZING.
A BIT EARLY FOR FROST/FREEZE HEADLINES AT THIS POINT...BUT ANOTHER
WEEK OF THE WARMER TEMPS OF LAST WEEK WOULD HAVE LIKELY MADE THEM
NEEDED. USED A BLEND OF THE GUIDANCE HIGHS/LOWS FOR TODAY/TONIGHT.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 341 AM CDT TUE APR 21 2015

MAIN FCST CONCERNS FOR WED THRU THU NIGHT...COLD TEMPERATURES.

20.12Z MODELS IN GOOD AGREEMENT WED/WED NIGHT FOR THE MID LEVEL LOW/
TROUGH AXIS TO DRIFT SLOWLY EAST...WITH THE UPPER MIDWEST UNDER A
COLD NORTHWEST FLOW ALOFT. HGTS SLOWLY RISE THU/THU NIGHT AS THE LOW
PULLS INTO MAINE/QUEBEC AND TROUGHING MOVES INTO THE ROCKIES BUT
FLOW REMAINS OUT OF THE NORTHWEST. WITH THE TIGHTER/IMPROVING
CONSENSUS...FCST CONFIDENCE IN THE WED THRU THU NIGHT PERIOD IS GOOD
THIS CYCLE.

THE WED THRU THU NIGHT PERIOD IS DOMINATED BY SEASONABLY COLD AND
DRY CAN HIGH PRESSURE. SOME MOISTURE FROM LK SUPERIOR...STEEP LOW
LEVEL LAPSE RATES AND THE COLD AIR ALOFT LOOK TO SPREAD A SMALL -
SHRA/-SHSN CHANCE INTO THE FAR NORTH END OF THE FCST AREA WED...
OTHERWISE WED-THU NIGHT TREND DRY AS THE SFC RIDGE AXIS SLOWLY
DRIFTS EAST TOWARD/OVER THE AREA. 925MB TEMPS IN THE 0C TO -6C RANGE
AT 12Z THU AND IN THE +4C TO -2C RANGE AT 12Z FRI. NAEFS SHOWING
850MB TEMPS 1 TO 2 STANDARD DEVIATIONS BELOW NORMAL ACROSS MUCH OF
THE UPPER MIDWEST THRU 12Z FRI. SFC RIDGE AXIS MAY BE CLOSE ENOUGH
FOR WINDS TO DECOUPLE WED NIGHT BUT THIS LOOKS MORE CERTAIN THU
NIGHT WITH THE RIDGE AXIS SOMEWHERE OVER WI. BOTH NIGHT TRENDING
COLD WITH LOWS NEAR OR BELOW 32F. AGAIN...A WEEK OR SO LATER IN THE
SEASON/MORE ADVANCED GROWTH/DEVELOPMENT OF VEGETATION AND FROST/
FREEZE HEADLINES WOULD BE NEEDED. APPROACH OF THE HIGH PRESSURE AND
SLOWLY RISING HGTS ALOFT TO BRING MORE SUNSHINE TO THE AREA
WED/THU. DEEP MIXING TO 750MB INDICATED FOR WED...WITH WINDS IN THE
900-750MB PORTION OF THE COLUMN STILL IN THE 20-30KT RANGE. BREEZY
AGAIN WED AFTERNOON...BUT LESS SO THAN SUNDAY AND TODAY. MORE
SUNSHINE WED/THU WILL HELP HIGH TEMPS RECOVER INTO THE 50S. 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...MAINLY RAIN CHANCES FRI/FRI NIGHT
AND AGAIN LATE SUN INTO MON...TEMPERATURES.

21.00Z MEDIUM RANGE MODELS IN GENERAL AGREEMENT FOR THE PATTERN TO
BE PROGRESSIVE FRI/SAT WITH RISING HGTS OVER THE EASTERN CONUS AND
TROUGHING MOVING THRU THE ROCKIES INTO THE PLAINS. HOWEVER PLENTY OF
SHORTWAVE DETAIL DIFFERENCES ALREADY BY FRI...WHICH WOULD IMPACT THE
SENSIBLE WEATHER ACROSS THE UPPER MIDWEST. AGREEMENT FOR WEAK SHORT-
WAVE RIDGING OT BUILD INTO THE REGION SAT. NEXT STRONGER TROUGHING
IS INTO THE PLAINS SUNDAY...THEN APPROACHING/CROSSING THE REGION SUN
NIGHT/MON. RUN-TO-RUN CONSISTENCY LEAVES QUITE A BIT TO BE DESIRED
BY SUN/MON WITH TROUGHS OFF BOTH COASTS AND UNCERTAIN FLOW ACROSS
THE CONUS BETWEEN THEM. FCST CONFIDENCE FOR FRI THRU MON...AS FAR AS
PRECIP CHANCES IS BELOW AVERAGE. AVERAGE CONFIDENCE FOR TEMPERATURES
TO RETURN TO NEAR NORMAL BY SUN/MON.

TROUGHING MOVING INTO THE PLAINS FRI DEVELOPS LOW PRESSURE OVER THE
CENTRAL/SOUTHERN PLAINS...BUT QUESTION IS NOW FAR NORTH INTO THE
MID/UPPER MS VALLEY THE INFLUENCE OF THIS LOW GETS. ECMWF/GEM WITH
MORE SHORTWAVE RIDGING AHEAD OF THIS FEATURE...AND WOULD SPREAD
MOISTURE/PRECIP CHANCES INTO MN/IA/WI FRI/FRI NIGHT. GFS WITH LESS
SHORTWAVE RIDGING HOLDS NORTHWEST FLOW ALOFT OVER THE REGION THRU
FRI NIGHT...AND KEEPS MN/IA/WI DRY. WITH LESSER CONFIDENCE STAY WITH
THE SMALL CONSENSUS MAINLY -SHRA CHANCES FRI/FRI NIGHT. RISING HGTS/
SHORTWAVE RIDGING WOULD BRING DRY HIGH PRESSURE TO THE REGION FOR
SAT/SAT NIGHT. NEXT TROUGH THRU THE ROCKIES DEVELOPS LEE TROUGHING
FROM MT TO TX ON SUN...WITH SOME FORM OF THIS TROUGH/LOW PUSHING
INTO THE MID/UPPER MS VALLEY SUN NIGHT/MON. DEEPER SOUTHERLY FLOW
AHEAD OF THIS SYSTEM WOULD BRING WARMER LOW LEVEL AIR/INCREASING
MOISTURE NORTHWARD FOR SUN INTO MON. RAIN CHANCES OF 20-30 PERCENT
SUN NIGHT/MON PER THE MODEL/ENSEMBLE CONSENSUS APPEAR REASONABLE.
MODEL/ENSEMBLE CONSENSUS OF THE HIGHS/LOWS FOR FRI THRU MON ALSO
APPEAR WELL TRENDED FOR NOW.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1140 PM CDT MON APR 20 2015

THE WESTERN EDGE OF THE CLOUD DECK HAS BEEN ERODING SOME THIS
EVENING. HOWEVER...LOOKING UPSTREAM INTO MINNESOTA...IT LOOKS LIKE
THE WESTERN EDGE HAS BEEN HOLDING FIRM AND AS THIS ROTATES DOWN
ACROSS THE AREA...EXPECT THAT SKIES WILL BE REMAIN BROKEN TO
OVERCAST THROUGH TUESDAY. FOR THE MOST PART THE CEILINGS HAVE
REMAINED VFR...BUT STILL EXPECTING THESE TO COME DOWN TO MVFR.
CURRENT MVFR CEILINGS ARE UPSTREAM OVER CENTRAL MINNESOTA AND
THESE SHOULD ROTATE ACROSS THE AREA OVERNIGHT. STILL SOME RETURNS
ON THE RADAR WITH THE 21.02Z HRRR CONTINUING TO SHOW SOME
SCATTERED ACTIVITY THROUGH THE NIGHT...BUT CONFIDENCE THAT ANY OF
THESE WILL HIT THE TAF SITES REMAIN LOW. THE 21.00Z NAM BUFKIT
SOUNDINGS CONTINUE TO SHOW THE GOOD LOW LEVEL LAPSE RATES
REMAINING THROUGH THE ENTIRE PERIOD TO MAINTAIN THE GUSTY WEST TO
NORTHWEST WINDS. THE STRONGEST WINDS WILL COME LATE TUESDAY
MORNING THROUGH THE AFTERNOON WHEN THE MIXING BECOMES THE DEEPEST
ALLOWING THE GUSTS TO BE AROUND 30 KNOTS.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...WIND ADVISORY FROM NOON TODAY TO 6 PM CDT THIS EVENING FOR
     MNZ086-087-094-095.

IA...WIND ADVISORY FROM NOON TODAY TO 6 PM CDT THIS EVENING FOR
     IAZ008>010-018-019-029-030.

&&

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION.....04



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