Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 271127
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
627 AM CDT WED MAY 27 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 342 AM CDT WED MAY 27 2015

LATEST 08Z SURFACE ANALYSIS INDICATES LOW PRESSURE OVER NORTHEAST
IOWA. LATEST MOSAIC RADAR SHOWS FRONTOGENETICAL BAND OF LIGHT RAIN
EXTENDING FROM NORTH CENTRAL WISCONSIN INTO SOUTHEAST MINNESOTA.

MAIN FORECAST CONCERNS TODAY IS HOW LONG FRONTOGENETICAL BAND OF
LIGHT RAIN OVER THE EASTERN PARTS OF THE FORECAST AREA AND
DIURNALLY DRIVEN SCATTERED SHOWERS/ISOLATED THIS AFTERNOON ACROSS
WESTERN WISCONSIN. LATEST 27.05Z HRRR/27.00Z NAM/27.03Z RAP SHOWS
FRONTOGENETICAL BAND OF LIGHT RAIN TO LINGER OVER THE EASTERN
PORTION OF THE FORECAST AREA AROUND 18Z TODAY. GIVEN THE SLOW
MOVEMENT OF THE PRECIPITATION...WILL DELAY EXIT OF LIGHT RAIN
OVER THE EASTERN PARTS OF THE FORECAST AREA. THIS WILL ALSO IMPACT
CLOUD TRENDS AND POSSIBLY HIGH TEMPERATURES OVER THE EASTERN
FORECAST AREA.

WEAK SHORTWAVE TROUGH ON THE BACKSIDE OF THE SURFACE LOW
IS PROGGED TO TRACK OVER WESTERN WISCONSIN AFTER 18Z TODAY. THE
LATEST 27.06Z HRRR/27.00Z GFS/NAM INDICATE DIURNALLY DRIVEN
SCATTERED SHOWERS AND POSSIBLY A THUNDERSTORM OR TWO TO DEVELOP
OVER WESTERN AND CENTRAL WISCONSIN. HAVE CONTINUE TREND FROM
PREVIOUS FORECAST TO KEEP MENTION OF SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS OVER WESTERN AND CENTRAL WISCONSIN.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 342 AM CDT WED MAY 27 2015

FOCUS THEN TURNS TO NEXT SYSTEM TRACKING ACROSS THE FORECAST AREA
THURSDAY NIGHT INTO FRIDAY NIGHT. THE 27.00Z GFS/NAM/ECMWF ARE IN
GOOD AGREEMENT IN DIGGING UPPER LEVEL TROUGH OVER THE
NORTHERN/HIGH PLAINS THURSDAY AND SLOWLY PUSHING SURFACE COLD
FRONT ACROSS THE FORECAST AREA THURSDAY NIGHT INTO FRIDAY NIGHT.
THE 27.00Z GFS/NAM/ECMWF EJECT PIECES OF ENERGY EMBEDDED IN
SOUTHWESTERLY FLOW ALOFT ALONG THE SURFACE FRONT AND INTO THE
FORECAST AREA. DIFFERENCES OCCUR WITH TIMING OF THE FIRST IMPULSE
IMPACTING THE FORECAST AREA THURSDAY NIGHT...AS THE NAM IS MORE
PROGRESSIVE THAN THE GFS/ECMWF. WILL FOLLOW THE SLOWER PROGRESSION
OF THE IMPULSE INTO THE SOUTHERN MINNESOTA/NORTHERN IOWA DURING
THIS TIME FRAME. THEN...MORE DIFFERENCES OCCUR BETWEEN THE 27.00Z
GFS/NAM/ECMWF FRIDAY INTO FRIDAY NIGHT...AS THE 27.00Z GFS IS
FASTER IN MOVEMENT OF THE SURFACE FRONT ACROSS THE FORECAST AREA
AND THE 27.00Z NAM/ECMWF DEVELOP SURFACE LOW ALONG FRONT. THIS
WILL HAVE AN IMPACT ON HOW FAST THE FRONTOGENETICAL BAND OF
PRECIPITATION MOVES ACROSS THE FORECAST AREA FRIDAY NIGHT. AT THIS
TIME...HAVE TRENDED WITH THE SLOWER NAM/ECMWF FRIDAY INTO FRIDAY
NIGHT.

THE 27.00Z GFS/NAM SUGGEST 20-30 KNOTS OF 0-3KM SHEAR AND TRY TO
BUILD 0-6KM MOST UNSTABLE CAPE OF 1500 TO 2500 J/KG OUT AHEAD OF
THE FRONT FRIDAY. HOWEVER...DEPENDING ON SHOWER
ACTIVITY/CONVECTION AND CLOUD COVER OVER THE FORECAST AREA
THURSDAY NIGHT AND FRIDAY...INSTABILITY COULD BE OVERDONE IN THE
MODELS THIS FAR OUT. FOR RIGHT NOW...SEVERE THREAT ACROSS THE AREA
REMAINS LOW FRIDAY.

MAIN FORECAST CONCERNS SATURDAY INTO TUESDAY ARE TEMPERATURES
THROUGH FORECAST PERIOD. THE 27.00Z GFS/ECMWF/GEM ARE IN AGREEMENT
IN DEVELOPING WEST TO EAST ZONAL FLOW ACROSS THE NORTHERN TIER
STATES THROUGH 12Z MONDAY...THEN DIFFERENCES OCCUR ON AMPLIFICATION
OF RIDGE OVER THE NORTHERN PLAINS. THE 27.00Z GEM MORE AMPLIFIED
THAN THE ECMWF/GFS...WITH THE 27.00Z GFS KEEPING WEST TO EAST ZONAL
FLOW OVER THE NORTHERN PLAINS AND GREAT LAKES REGION.
SURFACE/SHORTWAVE RIDGE DOMINATES THE FORECAST AREA THROUGH MUCH OF
THE FORECAST PERIOD. TEMPERATURES ARE EXPECTED TO BELOW NORMAL
SATURDAY INTO SUNDAY...AS SURFACE RIDGE BUILDING IN FROM CANADA
FILTERS COOLER AIRMASS INTO FORECAST AREA. THE 27.00Z GFS/ECMWF
INDICATE 850MB TEMPERATURES COOL TO PLUS 1 TO PLUS 5 DEGREES CELSIUS
SATURDAY INTO SUNDAY. TEMPERATURES MODERATE TO NEAR NORMAL BY
TUESDAY...WITH SOUTHERLY WINDS ON BACKSIDE OF SURFACE RIDGE ADVECT
IN WARMER TEMPERATURES.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 627 AM CDT WED MAY 27 2015

IFR/MVFR CONDITIONS WILL GRADUALLY BECOME VFR BY MID TO LATE
MORNING TODAY AS DRIER AIR STARTS TO WORK INTO THE REGION NEAR THE
SURFACE. A WEAK FRONT EDGES SOUTH TODAY ACROSS EASTERN MINNESOTA
AND WESTERN WISCONSIN AND MAY GENERATE ISOLATED SHOWERS OR
THUNDERSTORMS THIS AFTERNOON NEAR THE TAF SITES BUT CONFIDENCE WAS
NOT HIGH ENOUGH TO INCLUDE THEM IN THE TAF AT THIS TIME. RIDGING
BUILDS IN OVERNIGHT PROVIDING MOSTLY CLEAR SKIES AND VFR
CONDITIONS.

&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...WETENKAMP



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