000
FXUS63 KARX 232257
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
557 PM CDT THU MAY 23 2013

.SHORT TERM...(TONIGHT THROUGH SUNDAY)
ISSUED AT 315 PM CDT THU MAY 23 2013

MAIN FORECAST CONCERN ARE FROST TONIGHT...THEN PRECIPITATION
CHANCES FRIDAY NIGHT INTO SUNDAY.

LATEST WATER VAPOR SATELLITE IMAGERY INDICATING UPPER LEVEL TROUGH
OVER THE GREAT LAKES REGION AND CUT-OFF UPPER LEVEL LOW OVER
THE NORTHWEST UNITED STATES. LATEST 19Z SURFACE ANALYSIS SHOWING
SURFACE RIDGE BUILDING INTO NORTHERN MINNESOTA AND PRODUCING GOOD
SUBSIDENCE OVER THE REGION...WITH MOSTLY SUNNY SKIES PER LATEST
VISIBLE IMAGERY.

THE 23.12Z GFS/NAM/ECMWF CONTINUE TO SHOW DISCREPANCIES ON HOW FAR
EAST SHORTWAVE TROUGH OVER-TOPS UPPER LEVEL RIDGE AND PUSHES INTO
FORECAST AREA FRIDAY NIGHT INTO SUNDAY. THE 23.12Z GFS/NAM ARE MUCH
MORE PROGRESSIVE WITH SHORTWAVE TROUGH THAN THE ECMWF. THUS...THE
23.12Z GFS/NAM BOTH ARE FARTHER EAST THAN THE ECMWF. THIS WILL HAVE
IMPACTS ON PRECIPITATION CHANCES ACROSS FORECAST AREA FRIDAY NIGHT
INTO SUNDAY. CONFIDENCE IN FORECAST FRIDAY NIGHT INTO SUNDAY IS
LOW...BASED ON THESE DIFFERENCES.

TONIGHT INTO FRIDAY...SURFACE RIDGE BUILDS INTO EASTERN WISCONSIN
AND PROVIDES LIGHT WINDS AND MOSTLY CLEAR/MOSTLY SUNNY SKIES.
DEW POINTS HAVE FALLEN INTO THE UPPER 20S TO LOWER 30S ACROSS
PORTIONS OF CENTRAL AND WESTERN WISCONSIN THIS AFTERNOON. THIS
SHOULD ALLOW TEMPERATURES TO PLUMMET OVER THESE AREAS AND FALL
INTO THE LOWER TO MIDDLE 30S AND FROST DEVELOPMENT. HAVE EXPANDED
FROST ADVISORY INTO WESTERN WISCONSIN FOR TONIGHT.

NEXT CONCERN IS PRECIPITATION CHANCES FRIDAY NIGHT INTO THE
MEMORIAL DAY WEEKEND. SURFACE RIDGE BUILDS EAST OF AREA AND RETURN
SOUTHERLY FLOW ADVECTS MOISTURE NORTHWARD INTO THE UPPER MIDWEST
FRIDAY NIGHT. WITH THE LATEST DETERMINISTIC MODELS CONTINUE TO BE AT
ODDS AS TOO HOW FAR EAST SURFACE FRONT/BAROCLINIC ZONE ALOFT MOVES...
WILL DETERMINE DEVELOPMENT OF COMPLEXES OF SHOWERS/THUNDERSTORMS
UPSTREAM OF FORECAST AREA TO TRACK INTO FORECAST AREA FRIDAY NIGHT
INTO SATURDAY.

THE 23.12Z GFS/NAM INDICATE DECENT MOISTURE TRANSPORT AT 925-850MB
LAYER AND DECENT ISENTROPIC LIFT AT 300K SURFACE IN ASSOCIATION WITH
THE SERIES OF SHORTWAVE TROUGHS TO MOVE ALONG AND NORTH OF SURFACE
FRONT/BAROCLINIC ZONE FRIDAY NIGHT INTO SUNDAY. THE BEST LIFT AND
MOISTURE TRANSPORT WILL BE FOCUSED WEST OF THE MISSISSIPPI RIVER
THROUGH MUCH OF THE WEEKEND AND THIS AREA WILL HAVE THE BETTER
PRECIPITATION CHANCES. EAST OF THE MISSISSIPPI RIVER LESS CHANCES OF
PRECIPITATION CAN BE EXPECTED...WITH FAR EASTERN AREAS POSSIBLY
REMAINING DRY.

THE 23.12Z GFS/NAM CONTINUE TO SHOW ELEVATED INSTABILITY OF 200-500
J/KG MAINLY WEST OF MISSISSIPPI RIVER OVER PORTIONS SOUTHEAST
MINNESOTA AND NORTHEAST IOWA. WITH BETTER INSTABILITY WEST OF
FORECAST AREA AND NO SURFACE BASE CAPE OVER FORECAST AREA. DO NOT
EXPECT THUNDERSTORMS TO BECOME SEVERE OVER THE WESTERN FORECAST
AREA.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 315 PM CDT THU MAY 23 2013

MAIN FORECAST CONCERNS ARE PRECIPITATION CHANCES THROUGH THE PERIOD.
THE 23.12Z GFS/ECMWF CONTINUE TO BE IN DISAGREEMENT ON
AMPLIFICATION OF UPPER LEVEL RIDGE AND PLACEMENT OF SURFACE FRONT
ACROSS THE UPPER MIDWEST. THE 23.12Z GFS IS MORE PROGRESSIVE IN
FLATTENING RIDGE AND PUSHING SHORTWAVE TROUGHS INTO THE AREA...
WHEREAS THE 23.12Z ECMWF IS MORE AMPLIFIED WITH THE UPPER LEVEL RIDGE
AND PLACES SURFACE FRONT SOUTH OF THE FORECAST AREA. CONFIDENCE
CONTINUES TO BE LOW THROUGH THE FORECAST PERIOD...BASED ON THESE
MAJOR DIFFERENCES BETWEEN THE DETERMINISTIC 23.12Z MODELS. FOR
NOW... WILL CONTINUE WITH SMALL CHANCES OF PRECIPITATION THROUGH THE
FORECAST PERIOD. THIS ALSO WILL HAVE IMPACTS ON TEMPERATURES...AS
THE 23.12Z GFS IS MORE PROGRESSIVE IN ADVECTING WARMER AIR INTO THE
UPPER MIDWEST THAN THE ECMWF.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 557 PM CDT THU MAY 23 2013

VFR CLEAR CONDITIONS EXPECTED THROUGH THE TAF PERIOD AS A RIDGE OF
HIGH PRESSURE LINGERS ACROSS THE REGION. WINDS WILL GO LIGHT
OVERNIGHT AND THEN PICK UP AGAIN TOMORROW MORNING AS THE RIDGE
AXIS SHIFTS TO THE EAST. SOME GUSTS IN THE 15-20KT RANGE WILL BE
POSSIBLE IN THE AFTERNOON...PARTICULARLY AT RST.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 7 AM CDT FRIDAY FOR
     WIZ017-029-032>034-041>044.

MN...NONE.
IA...NONE.
&&

$$

SHORT TERM.....DTJ
LONG TERM......DTJ
AVIATION...HALBACH