Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 300806
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
306 AM CDT THU APR 30 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 306 AM CDT THU APR 30 2015

LATEST WATER VAPOR SATELLITE IMAGERY SHOWS UPPER LEVEL RIDGE OVER
NORTHERN PLAINS AND UPPER LEVEL TROUGH OVER THE GREAT LAKES
REGION. LATEST 08Z SURFACE ANALYSIS INDICATES HIGH PRESSURE OVER
NORTHERN MINNESOTA INTO SOUTHERN ONTARIO.

THE 30.00Z GFS/NAM ARE IN GOOD AGREEMENT IN BUILDING
SHORTWAVE/SURFACE RIDGE OVER THE FORECAST AREA TODAY INTO TONIGHT.
SUBSIDENCE UNDER SHORTWAVE/SURFACE RIDGE WILL ALLOW FOR DRY WEATHER
AND MOSTLY SUNNY/MOSTLY CLEAR SKIES ACROSS THE FORECAST AREA TODAY
INTO TONIGHT.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 306 AM CDT THU APR 30 2015

THE 30.00Z GFS/NAM/ECMWF ARE IN DECENT AGREEMENT TRACKING SHORTWAVE
TROUGH OVER THE NORTHERN ROCKIES ACROSS THE FORECAST AREA FRIDAY.
THIS WILL FLATTEN UPPER LEVEL RIDGE OVER THE GREAT LAKES REGION.
THE 30.00Z GFS/NAM/ECMWF WEAKEN SHORTWAVE TROUGH...AS IT FLATTENS
THE RIDGE. THIS WILL WEAKEN THE LIFT/MOISTURE CONVERGENCE IN
ASSOCIATION WITH SHORTWAVE TROUGH. WITH THE COMBINATION OF DRY
AIRMASS OVER THE FORECAST AREA AND WEAKER LIFT/MOISTURE
CONVERGENCE WITH SHORTWAVE TROUGH. HAVE TRENDED DRIER AND LOWERED
PRECIPITATION CHANCES ACROSS THE FORECAST AREA FRIDAY.

FRIDAY NIGHT INTO SATURDAY...WEST TO EAST ZONAL FLOW DEVELOPS ACROSS
THE NORTHERN TIER STATES. A COUPLE OF WEAK SHORTWAVE TROUGHS
EMBEDDED IN THE ZONAL FLOW MOVE ACROSS THE UPPER MIDWEST AND GREAT
LAKES REGION. WEAK SOUTHERLY MOISTURE RETURN/CONVERGENCE AND LIFT IN
ASSOCIATION WITH THE SHORTWAVES WILL ALLOW FOR SMALL PRECIPITATION
CHANCES MAINLY ACROSS PARTS OF NORTHEAST IOWA DURING THE DAY
SATURDAY...WHERE THE BETTER MOISTURE CONVERGENCE AND LIFT IS
LOCATED.

AN ACTIVE WEATHER PATTERN DEVELOPS SATURDAY NIGHT INTO WEDNESDAY.
THE 30.00Z GFS/ECMWF/GEM ARE IN AGREEMENT WITH WEST TO EAST ZONAL
FLOW ACROSS THE NORTHERN TIER STATES THROUGH 00Z TUESDAY.
THEN...THE MODELS DIG UPPER LEVEL TROUGH OVER THE WESTERN UNITED
STATES AND WEAK SOUTHWESTERLY FLOW ALOFT DEVELOPS. A SERIES OF
SHORTWAVE TROUGHS WILL MOVE ALONG THE SURFACE BOUNDARY SATURDAY
NIGHT INTO MONDAY. THE 30.00Z GFS/ECMWF/GEM SHOW DECENT MOISTURE
TRANSPORT/CONVERGENCE AND LIFT WITH THE SHORTWAVE TROUGHS. THIS
WILL PRODUCE PERIODS OF SHOWERS AND THUNDERSTORM CHANCES SATURDAY
NIGHT INTO MONDAY. THE 30.00Z GFS/ECMWF/GEM INDICATE DIFFERENCES
IN PLACEMENT OF SURFACE BOUNDARIES AND TIMING OF SHORTWAVE TROUGHS
INTO THE UPPER MIDWEST AND GREAT LAKES REGION DURING THIS TIME
FRAME. CONFIDENCE IS INCREASING THE FORECAST AREA WILL SEE A
PERIOD OF SHOWERS AND THUNDERSTORMS.

UPPER LEVEL TROUGH DIGS OVER THE WESTERN UNITED STATES TUESDAY INTO
WEDNESDAY. PIECES OF ENERGY EJECT OUT OF THE UPPER LEVEL
LOW/TROUGH OVER THE SOUTHWEST UNITED STATES INTO THE CENTRAL
UNITED STATES. THE 30.00Z GFS/ECMWF SHOW SIGNIFICANT DIFFERENCES
WITH PHASING OF THE UPPER LEVEL LOW/TROUGH OVER THE SOUTHWEST
UNITED STATES AND THE UPPER LEVEL TROUGH OVER THE PACIFIC
NORTHWEST. THIS WILL HAVE IMPACTS ON TIMING OF IMPULSES MOVING INTO
THE CENTRAL UNITED STATES TUESDAY INTO WEDNESDAY.
FOR NOW...WILL CONTINUE WITH CHANCES OF SHOWERS AND THUNDERSTORMS
ACROSS THE FORECAST AREA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1105 PM CDT WED APR 29 2015

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. SCATTERED
ALTOCUMULUS WILL SLIDE ACROSS THE TAF SITES OVERNIGHT WITH CLOUD
BASES OF 8 TO 10 KFT. HIGH PRESSURE WILL PROVIDE DRY AND QUIET
WEATHER AT THE TAF SITES DURING THE DAY ON THURSDAY PERSISTING
INTO THURSDAY EVENING.


&&

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

$$

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


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