Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 291120
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
620 AM CDT MON JUN 29 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 312 AM CDT MON JUN 29 2015

LATEST WATER VAPOR SATELLITE IMAGERY SHOWS UPPER LEVEL TROUGH OVER
THE EASTERN UNITED STATES AND UPPER LEVEL RIDGE OVER THE WESTERN
UNITED STATES INTO THE CANADIAN ROCKIES. SEVERAL PIECES OF ENERGY
EMBEDDED IN THE NORTHWESTERLY FLOW ALOFT PER WATER VAPOR SATELLITE
IMAGERY. ONE IMPULSE WAS PRODUCING SHOWERS OVER CENTRAL AND
SOUTHWEST WISCONSIN PER KARX RADAR. DUE TO MOIST BOUNDARY LAYER
AND MOSTLY CLEAR SKIES PATCHY FOG HAS DEVELOPED OVER PARTS OF
THE FORECAST AREA.

MAIN FORECAST CONCERNS TODAY INTO THIS EVENING ARE PRECIPITATION
CHANCES.

THE 29.00Z GFS/NAM INDICATE NEXT SHORTWAVE TROUGH NEAR LAKE WINNIPEG
TO IMPACT THE FORECAST AREA THIS AFTERNOON INTO THIS EVENING. THE
29.00Z GFS/NAM SHOW PV ADVECTION IN THE 500-300MB LAYER/STEEP LOW
LEVEL LAPSE RATES/INSTABILITY WITH SHORTWAVE TROUGH. THE LATEST
HIGH RESOLUTION MODELS...ARW/NMM/HRRR...SHOW DIFFERENCES IN TIMING
OF THE CONVECTION INTO THE FORECAST AREA TODAY INTO THIS EVENING.
THE 29.00Z DETERMINISTIC AND HIGH RESOLUTION MODELS SUGGEST
CONVECTION WILL DEVELOP MID TO LATE THIS AFTERNOON AND CONTINUE
INTO THE EVENING HOURS ACROSS MUCH OF THE FORECAST AREA. HAVE
TRENDED THE HIGHER PRECIPITATION CHANCES AFTER 21Z TODAY TO 03Z
TUESDAY.

THE NEXT CONCERN ARE SEVERE POSSIBILITIES. THE 29.00Z GFS/NAM/RAP
SHOW UP TO 20 KNOTS OF 0-3KM SHEAR AND BUFKIT SOUNDINGS INDICATE
MANLY STRAIGHT HODOGRAPHS THROUGH THIS LAYER LATE THIS
AFTERNOON/THIS EVENING MAINLY WEST OF THE MISSISSIPPI RIVER. THE
29.00Z GFS/NAM AND 29.03Z RAP BUILD UP TO 2000 J/KG OF SURFACE
BASE CAPE ACROSS THE FORECAST AREA. WITH WEAK SHEAR IN THE 0-3KM
LAYER...LARGE HAIL WILL BE A POSSIBILITY WITH SOME OF THE
STRONGER THUNDERSTORMS LATE THIS AFTERNOON INTO THIS EVENING.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 312 AM CDT MON JUN 29 2015

WEAK SURFACE RIDGE BUILDS INTO NORTHERN MINNESOTA AND SHORTWAVE
ENERGY PUSHES INTO SOUTHERN/EASTERN WISCONSIN TUESDAY. WITH THE
29.00Z GFS/NAM SUGGEST STEEP LOW LEVEL LAPSE RATE AND THE BETTER
INSTABILITY OVER THE EASTERN FORECAST AREA...SMALL PRECIPITATION
CHANCES CONTINUE TO BE WARRANTED OVER THIS AREA.

THE 29.00Z GFS/NAM/ECMWF ARE TRENDING A FARTHER WESTWARD SOLUTION
WITH THE PIECES OF ENERGY EMBEDDED IN THE NORTHWESTERLY FLOW ALOFT
WEDNESDAY INTO WEDNESDAY NIGHT. PLUS...SURFACE RIDGE BUILDS INTO
NORTHERN MINNESOTA AND NORTHERN WISCONSIN AND DEVELOP A DRIER
NORTHEASTERLY FLOW INTO THE FORECAST AREA. HAVE REDUCE
PRECIPITATION CHANCES ACROSS THE WESTERN PORTIONS OF THE FORECAST
AREA...BASED ON THE DRIER NORTHEASTERLY FLOW AND WESTERN SHIFT OF
THE SHORTWAVE ENERGY.

MAIN FORECAST CONCERNS THURSDAY INTO SUNDAY ARE PRECIPITATION
CHANCES THROUGH THE PERIOD. THE 29.00Z GFS/ECMWF/GEM ARE IN
AGREEMENT IN WEAKENING UPPER LEVEL TROUGH OVER THE GREAT LAKES
REGION/EASTERN UNITED STATES AND DEVELOP WEST TO EAST ZONAL FLOW
ALOFT BY 12Z SUNDAY ACROSS THE NORTHERN TIER STATES. THE BIGGEST
DIFFERENCE BETWEEN THE 29.00Z GFS/ECMWF/GEM IS TIMING OF THE
INDIVIDUAL IMPULSES INTO THE GREAT LAKES REGION THROUGH THE FORECAST
PERIOD. THE 29.00Z MODELS SUGGEST ENOUGH LIFT/FORCING/MOISTURE
CONVERGENCE WITH THE IMPULSES. WILL CONTINUE TREND OF PERIODIC SMALL
PRECIPITATION CHANCES THROUGH MUCH OF THE FORECAST PERIOD.
TEMPERATURES WILL REMAIN SLIGHTLY BELOW OR NEAR NORMAL DURING THE
FORECAST PERIOD.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 620 AM CDT MON JUN 29 2015

LIGHT WINDS...MOSTLY CLEAR SKIES AND RECENT RAINS HAVE ONCE AGAIN
ALLOWED AREAS OF MVFR/IFR BR/FG/CIGS TO DEVELOP ACROSS THE AREA.
THIS WILL IMPACT THE TAF SITES THRU 13Z TO 14Z THIS MORNING...BEFORE
LATE JUNE SUNSHINE AND NORTHWEST WINDS WORK TO DISSIPATE THE BR/FG.

MIDDLE OF THE DAY FROM 14-22Z APPEARS QUIET WITH SCT VFR CUMULUS AND
LIGHT NORTHWEST WINDS. THIS AHEAD OF THE NEXT SHORTWAVE AND ROUND OF
SCT SHRA/TSRA TO MOVE ACROSS THE AREA. PRESENT TIMING CONSENSUS
AMONG THE GUIDANCE WOULD SPREAD THE SHRA/TSRA ACROSS THE TAF SITES
IN THE 22Z-01Z TIME-FRAME...THOUGH A FEW SHRA/TSRA COULD BE IN THE
AREA AS EARLY AS 20Z. WILL LEAVE A VCTS/CB MENTION AT BOTH KRST/KLSE
IN THE 22Z-01Z PERIOD. SUBSIDENCE/DRYING SPREAD SOUTH ACROSS THE AREA
FOR THE LATER EVENING/OVERNIGHT HOURS INTO TUE MORNING...FOR
GENERALLY GOOD VFR CONDITIONS AFTER THE SHRA/TSRA EXIT. MAY YET NEED
A BR MENTION AT KLSE AFTER 09Z TONIGHT BUT LEFT THAT OUT FOR NOW AS
RADIATIONAL FOG SIGNAL FOR TONIGHT NOT AS STRONG AS THE PAST COUPLE
NIGHTS.

&&

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

$$

SHORT TERM...DTJ
LONG TERM....DTJ
AVIATION.....RRS



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