Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 261134
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
634 AM CDT TUE MAY 26 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 324 AM CDT TUE MAY 26 2015

MAIN CONCERN ARE SHOWERS AND THUNDERSTORM CHANCES.

LATEST MOSAIC RADAR IMAGERY SHOWS SHOWERS AND ISOLATED THUNDERSTORMS
ACROSS NORTHEAST IOWA AND SOUTHWEST WISCONSIN AND IS IN
ASSOCIATION WITH A WEAK SHORTWAVE TROUGH OVER NORTHERN IOWA PER
LATEST WATER VAPOR SATELLITE IMAGERY. A STRONGER SHORTWAVE TROUGH
OVER OKLAHOMA WAS PRODUCING SHOWERS AND SCATTERED THUNDERSTORMS
ACROSS SOUTHERN IOWA...EASTERN KANSAS AND NORTHERN MISSOURI.

THE 26.00Z GFS/NAM/ECMWF ARE IN GOOD AGREEMENT LIFTING THE SHORTWAVE
TROUGH OVER KANSAS/MISSOURI/SOUTHERN IOWA INTO THE GREAT LAKES
REGION TODAY AND TONIGHT. THE 26.00Z GFS/NAM SHOW DECENT PV
ADVECTION/QG FORCING AND DECENT MOISTURE TRANSPORT INTO THE AREA
WITH THE SHORTWAVE TROUGH. SHOWERS AND THUNDERSTORMS WILL BECOME
MORE WIDESPREAD THIS MORNING OVER THE SOUTHERN PART OF THE
FORECAST AREA AND MOVE NORTH TO NORTHEAST REST OF THE FORECAST
AREA DURING THE DAY. THE 26.00Z NAM/GFS SUGGEST 20-30 KNOTS OF
0-3KM SHEAR THROUGH EARLY AFTERNOON OVER THE SOUTHEAST AND EASTERN
PARTS OF FORECAST AREA AND QUICKLY PUSH THIS SHEAR EAST OF
FORECAST AREA BY 21Z TODAY. THE NAM/GFS TRY TO BUILD 500-1000
J/KG OF SURFACE BASE CAPE OVER THIS SAME AREA OF THE FORECAST AREA
DURING THIS TIME FRAME. DUE TO THE TIMING OF THE INSTABILITY AND
SHEAR...SEVERE RISK REMAINS LOW OVER THE SOUTHEAST PART OF THE
FORECAST AREA.

AS SURFACE LOW/SHORTWAVE TROUGH PUSHES INTO CENTRAL/NORTHERN
WISCONSIN THIS AFTERNOON...THE 26.00Z GFS/NAM DEVELOP
FRONTOGENETICAL BAND OF PRECIPITATION OVER THE NORTHWEST PERIPHERY
OF THE SURFACE LOW. SHOWERS...AND POSSIBILITY OF
THUNDERSTORMS...WILL LINGER ACROSS MUCH OF THE FORECAST AREA
THROUGH THIS EVENING.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 324 AM CDT TUE MAY 26 2015

SURFACE/SHORTWAVE RIDGE BUILDS INTO THE AREA WEDNESDAY INTO
THURSDAY MORNING AND PROVIDE DRY WEATHER ACROSS THE FORECAST AREA.
UPPER LEVEL TROUGH DIGS ACROSS THE ROCKIES AND SOUTHWESTERLY FLOW
ALOFT DEVELOPS OVER THE CENTRAL UNITED STATES THURSDAY INTO THURSDAY
NIGHT. WEAK IMPULSE/SURFACE FRONT PUSH INTO THE UPPER MIDWEST AND
NORTHERN PLAINS AFTER 18Z THURSDAY. SLIGHT DIFFERENCES IN TIMING OF
THE SURFACE FRONT/IMPULSE INTO THE FORECAST AREA ARE SEEN BETWEEN
THE 26.00Z GFS/NAM. BOTH OF THE MODELS SHOW NOSE OF 925-850MB
MOISTURE TRANSPORT INTO THE SOUTHERN PART OF THE FORECAST AREA BY
06Z FRIDAY AND SURFACE MOISTURE CONVERGENCE ALONG FRONT JUST WEST
OF FORECAST AREA. THE COMBINATION OF WEAK QG FORCING AND MOISTURE
CONVERGENCE IN ASSOCIATION WITH SURFACE FRONT/IMPULSE WILL PROVIDE
AN INCREASE OF SHOWERS AND THUNDERSTORM CHANCES AFTER 00Z FRIDAY.

MAIN FORECAST CONCERNS FRIDAY INTO MONDAY ARE PRECIPITATION
CHANCES THROUGH MUCH OF THE PERIOD. THE 26.00Z GFS/ECMWF/GEM ARE
IN GOOD AGREEMENT IN DEVELOPING WEST TO EAST ZONAL FLOW ACROSS THE
NORTHERN TIER STATES AND SLOWLY MOVE SURFACE FRONT ACROSS THE
FORECAST AREA THROUGH THE FORECAST PERIOD. THE 26.00Z EXTENDED
MODELS SHOW A SERIES OF SHORTWAVE TROUGHS MOVING ALONG THE
SURFACE FRONT THROUGH MUCH OF THE PERIOD. BIGGEST DIFFERENCES ARE TIMING
AND STRENGTH OF THE SHORTWAVE TROUGHS...AS THE 256.00Z GFS/GEM ARE
STRONGER WITH THE UPPER LEVEL TROUGH SATURDAY INTO SATURDAY NIGHT
THAN THE ECMWF. WITH DECENT MOISTURE AND LIFT ALONG THE SURFACE
FRONT...CHANCES OF SHOWERS AND THUNDERSTORMS CAN BE EXPECTED
THROUGH SATURDAY NIGHT. SURFACE RIDGE BUILDS INTO NORTHERN
WISCONSIN SUNDAY INTO MONDAY PROVIDING LESSER CHANCES OF
PRECIPITATION ACROSS THE FORECAST AREA.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 634 AM CDT TUE MAY 26 2015

AVIATION WEATHER SEEMS A BIT MORE STRAIGHT FORWARD THIS MORNING WITH
MAIN IMPACT TO VISIBILITIES AND CEILINGS BASED ON INCOMING
CONVECTION. MOST AREAS VFR THIS MORNING BUT EXPECTING RETURN TO MVFR
AS SHOWERS AND EMBEDDED THUNDERSTORMS ADVECT IN FROM THE SOUTH AS
RELATIVELY STRONG SHORT WAVE APPROACHES. COULD EVEN SEE SOME IFR
CONDITIONS IN HEAVIEST RAIN.

BASED ON TRACK OF WAVE AND RELATED SURFACE LOW...EXPECT
PRECIPITATION TO SWING IN THIS MORNING BUT LOCATION OF PIVOT WILL
MEAN WESTERN AREAS /KRST/ MAY SIT UNDER SHOWERS NEARLY ALL DAY.
COULD SEE FLUCTUATIONS IN CONDITIONS BASED ON RAIN INTENSITY.
FURTHER EAST /KLSE/ MIGHT SEE BREAK IN ACTIVITY AS EASTERN/LEADING
EDGE OF CONVECTIVE COMPLEX SWINGS THROUGH.

BEHIND THIS WAVE...EXPECT AN END TO PRECIPITATION AND RETURN TO VFR
CEILINGS. ASSUMING CLOUDS WILL HOLD IN FOR MUCH OF NIGHT...BUT IF IT
CLEARS WITH THE LIGHT WIND...COULD SEE SOME LOCAL FOG IMPACT SITES.

&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...SHEA


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