Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 021948
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
248 PM CDT SUN AUG 2 2015

.SHORT TERM...(TONIGHT THRU MONDAY NIGHT)
ISSUED AT 249 PM CDT SUN AUG 2 2015

MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES INTO EARLY THIS
EVENING...TEMPERATURES THRU THE PERIOD.

DATA ANALYSIS AT 18Z HAD LOW PRESSURE OVER NORTHEAST WI WITH A
TRAILING COLD FRONT SOUTHWEST INTO SOUTHERN MN. MOIST/UNSTABLE BUT
GENERALLY CAPPED AIRMASS OVER THE AREA AHEAD OF THE FRONT EARLY
THIS AFTERNOON. MAIN CONVECTION SO FAR TODAY HAS MAINLY BEEN ACROSS
THE NORTHEAST 1/3 OF WI...WHERE CONVERGENCE/LIFT WITH THE SFC-
850MB LOW/FRONT WERE STRONGER...AND AHEAD OF A SHORTWAVE DROPPING
INTO NORTHERN MN. A WARM DAY ACROSS THE AREA. DIURNAL WARMING/
MIXING AND THE WARM 925-850MB AIR RESPONSIBLE FOR THE CAPPING...HAS
ALREADY ALLOWED EARLY AFTERNOON TEMPS TO CLIMB INTO THE MID 80S TO
LOWER 90S OVER ALL BUT THE FAR NORTH END OF THE FCST AREA.

MODEL RUNS OF 02.12Z INITIALIZED WELL. MODELS IN GOOD AGREEMENT WITH
THE SHORTWAVE TROUGH/ENERGY TO PASS TONIGHT THEN FOR HGTS TO SLOWLY
RISE MON/MON NIGHT AS THE MID LEVEL LOW OVER NORTHERN ONT SLOWLY
FILLS/DRIFTS EAST. TREND FAVORS SLOWER OF THE EARLIER RUNS MON/MON
NIGHT. SHORT TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

IN THE SHORT TERM...MODEL CONSENSUS HAS THE COLD FRONT NEAR A KOLZ-
LOWER WI RIVER VALLEY LINE AT 00Z THIS EVENING. DIURNAL WARMING
STILL EXPECTED TO ERODE THE CAPPING AHEAD OF/ALONG THE FRONT BY LATE
THIS AFTERNOON AND FOR EARLY THIS EVENING. WITH REALISTIC SFC DEW
POINTS IN THE UPPER 60S/LOW 70S AHEAD OF THE FRONT /VS. MID 70S IN
THE NAM/ SB/MU CAPES OF 1500-3000 J/KG EXPECTED TO BE IN PLACE AHEAD
OF THE FRONT LATE TODAY. WILL CONTINUE WITH SOME 20-40 PERCENT
SHRA/TSRA CHANCES ACROSS MAINLY THE SOUTHEAST END OF THE FCST AREA
INTO THE EARLY EVENING HOURS UNTIL THE FRONT PUSHES SOUTH OF THE
AREA. WITH 0-6KM BULK SHEAR IN THE 35-45KT RANGE LATE TODAY...A
SEVERE STORM OR TWO WITH THE FRONTAL PASSAGE CANNOT BE RULED OUT.
SEE SWODY1 FOR MORE DETAILS. DRIER CAN HIGH PRESSURE BUILDS SOUTH
INTO THE REGION LATER THIS EVENING/OVERNIGHT. LOWER LEVEL COLD
ADVECTION/SUBSIDENCE BEHIND THE SFC-500MB TROUGH SCOURS OUT THE
MOISTURE WITH SFC DEW POINTS PROGGED TO BE IN THE MID 40S TO MID 50S
BY 12Z MON. 850MB TEMPS FALL TO THE +9C TO +14C RANGE BY 12Z
MON...AROUND 1 STANDARD DEVIATION BELOW NORMAL. AFTER LOWS SOME 5F
TO 10F ABOVE NORMAL OVER MUCH OF THE AREA THIS MORNING...MON MORNING
LOWS LOOKING TO BE A FEW DEGREES BELOW NORMAL. 850MB TEMPS REMAINS
AROUND 1 STANDARD DEVIATION BELOW NORMAL MON/MON NIGHT AS THE HIGH
CONTINUES TO NOSE INTO THE REGION...WITH LIGHT/VARIABLE WINDS
EXPECTED MON NIGHT. HIGHS MONDAY TRENDING ZERO TO 5F BELOW NORMAL.
WITH THE DRY AIRMASS/LIGHT WINDS/MOSTLY CLEAR SKIES MON NIGHT...
STRONG RADIATIONAL COOLING EXPECTED TO RESULT IN MOST LOWS DIPPING
INTO THE MID 40S TO MID 50S. USED A BLEND OF GUIDANCE LOWS/HIGHS FOR
TONIGHT/MON THEN FAVORED COOLER OF GUIDANCE LOWS MON NIGHT.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 249 PM CDT SUN AUG 2 2015

FOR TUESDAY THRU WEDNESDAY NIGHT...

MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES WED/WED
NIGHT...TEMPERATURES THRU THE PERIOD.

02.12Z MODELS REMAIN IN GOOD AGREEMENT TUE AS HGTS CONTINUE TO
SLOWLY RISE OVER THE REGION. BY TUE NIGHT MODELS BEGIN TO DIFFER ON
THE HANDLING OF SHORTWAVE ENERGY COMING THRU THE PLAINS RIDGING.
THESE DIFFERENCES CONTINUE INTO WED/WED NIGHT...WITH POTENTIAL
IMPACTS ON THE SENSIBLE WEATHER FROM LATE TUE NIGHT THRU WED NIGHT.
RUN-TO-RUN TREND IS GENERALLY STRONGER WITH THE SHORTWAVE ENERGY
CUTTING THRU THE RIDGE TUE NIGHT/WED...BUT CONSIDERABLE TIMING
DIFFERENCES BY WED/WED NIGHT. FCST CONFIDENCE IS GOOD TUE THEN
AVERAGE TUE NIGHT THRU WED NIGHT.

DRIER CAN HIGH PRESSURE FROM MON/MON NIGHT CONTINUES TO DRIFT EAST
ACROSS THE AREA TUE/TUE NIGHT...FOR A CONTINUE MORE COMFORTABLE
PERIOD OF WEATHER. 850MB TEMPS IN THE 11C TO 14C RANGE...FOR TUE
HIGHS A DEGREE OR TWO ABOVE THOSE OF MON. GFS FAST/AGGRESSIVE ON 850-
700MB MOISTURE RETURN AND A SHRA/TSRA CHANCE SPREADING INTO THE FCST
AREA LATE TUE NIGHT. WITH GFS APPEARING AS AN OUTLIER ON THIS...LEFT
TUE NIGHT DRY. FAVORING DRIER NAM/ECMWF/CAN-GEM TUE NIGHT...WITH
MOSTLY CLEAR SKIES AND LIGHT WINDS UNDER THE SFC RIDGE AXIS...TUE
NIGHT LOOKING TO BE ANOTHER NIGHT WITH LOWS IN THE UPPER 40S TO MID
50S. WITH A CONTINUED SIGNAL FOR THE APPROACH OF SOME SHORTWAVE
ENERGY WED AND LOW LEVEL MOISTURE ADVECTION WEST OF THE MS RIVER...
LEFT A 20-30 PERCENT SHRA/TSRA CHANCE THERE. NOT A LOT OF LOWER
LEVEL THERMO-DYNAMIC SUPPORT FOR CONVECTION WED NIGHT BUT WITH
APPROACH/PASSAGE OF A MID LEVEL TROUGH AXIS AND SOME INCREASE OF
MOISTURE OVER THE AREA...LEFT THE CONSENSUS 20-50 PERCENT SHRA/TSRA
CHANCE FOR WED NIGHT AS IS AS IT BLENDS WELL WITH NEIGHBORING GRIDS
FOR NOW. TRENDED TOWARD COOLER OF GUIDANCE LOWS TUE NIGHT OTHERWISE
FAVORED A BLEND OF THE GUIDANCE HIGHS/LOWS FOR TUE/WED/WED NIGHT.

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

MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES...MAINLY THU/THU
NIGHT.

02.00Z/02.12Z MEDIUM RANGE MODEL RUNS IN AGREEMENT FOR FALLING HGTS
OVER THE NORTH-CENTRAL CONUS THU AS SHORTWAVES MOVE THRU THE CENTRAL
NOAM RIDGING. MODEST AGREEMENT FOR TROUGHING TO MOVE ACROSS THE
UPPER MIDWEST FRI WITH SOME REBUILDING OF THE NORTH-CENTRAL CONUS
RIDGING...THEN FOR THIS RIDGING TO BUILD EAST FRI NIGHT/SAT. BETTER
AGREEMENT AMONG 02.12Z GFS/ECMWF FOR SHORTWAVE TROUGHING TO BE
MOVING ACROSS THE NORTHERN PLAINS SUN. PLENTY OF SHORTWAVE DETAIL
DIFFERENCES FOR THU-SUN...WITH RUN-TO-RUN CONSISTENCY LESS THAN
DESIRABLE ALREADY ON THU. DAY 4-7 CONFIDENCE IS BELOW AVERAGE THIS
CYCLE.

WITH A SIGNAL FOR A COUPLE OF SHORTWAVES TO FLATTEN THE NORTH-
CENTRAL CONUS RIDGING AND MOVE INTO/ACROSS THE UPPER MIDWEST
THU...WITH A SFC WAVE AND MOISTURE TRANSPORT INTO THE AREA...
CONSENSUS 20-40 PERCENT SHRA/TSRA CHANCES FOR THU REASONABLE. THIS
EVEN WITH ALL THE BETWEEN MODEL AND RUN-TO-RUN VARIABILITY. GIVEN
ALL THE TIMING/STRENGTH DIFFERENCES ON SHORTWAVES AND ALL THE RUN-TO-
RUN VARIABILITY...WILL LIKELY NEED TO MOVE THE LATE-WEEK SHRA/TSRA
CHANCES AROUND BEFORE THE DETAILS SETTLE DOWN. 02.12Z ECMWF WOULD
ALREADY MOVE THE BULK OF THE LATE WEEK SHRA/TSRA CHANCES INTO THU
NIGHT INTO FRI NIGHT. PRESENT TIMING WOULD BRING HIGH PRESSURE AND
SHORTWAVE RIDGING ACROSS THE AREA SAT. TIMING DIFFERENCES ON HOW
QUICKLY THE NEXT TROUGH ACROSS THE NORTHERN PLAINS SPREADS MOISTURE
AND SHRA/TSRA CHANCES BACK INTO THE AREA SUN. GIVEN THE LESSER
CONFIDENCE BY FRI...WILL STAY THE COURSE WITH THE SMALL CONSENSUS
SHRA/TSRA CHANCES OR DRY PERIODS FOR FRI THRU SUN. TEMPERATURES FOR
THU-FRI TREND TO BELOW NORMAL WITH MORE CLOUDS/POTENTIAL SHRA/
TSRA...THEN NEAR NORMAL FOR SAT/SUN WITH SOME SHORTWAVE RIDGING/
RISING HGTS AHEAD OF THE NEXT NORTHERN PLAINS TROUGH. MODEL/ENSEMBLE
CONSENSUS WITH HIGHS MOSTLY IN THE 70S AND LOWS MOSTLY IN THE 50S
FOR THU-SUN LOOKS WELL TRENDED AT THIS TIME.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1135 AM CDT SUN AUG 2 2015

COLD FRONT WILL SWEEP SOUTHEAST ACROSS THE AREA THIS AFTERNOON...
SPARKING SHRA/TS MOSTLY ALONG ITS EASTERN FLANKS. MESO MODELS
FAVORING BRINGING IT THROUGH DRY FOR KRST...AND COULD MISS KLSE
ALSO. A LOT OF UNCERTAINTY AS ONGOING CONVECTION IS ELEVATED POST
THE FRONT...WHILE MORE WIDESPREAD SHRA/TS ARE EXPECT TO FIRE ALONG/
AHEAD OF THE FRONT LATER THIS AFTERNOON. THE FRONT WILL LIKELY BE
SOUTH OF THE TAF SITES BY THAT TIME...LIMITING THE THREAT. WILL KEEP
TAFS DRY FOR THE TIME BEING...BUT WILL MONITOR RADAR TRENDS CLOSELY
AND MAKE UPDATES AS NEEDED.

GUSTY/STRONG WINDS AHEAD AND POST THE FRONT...SETTLING DOWN A BIT
THIS EVENING.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION.....RIECK



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