Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 250817
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
317 AM CDT MON MAY 25 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 317 AM CDT MON MAY 25 2015

MAIN FORECAST CONCERNS ARE MORNING PRECIPITATION CHANCES AND THE
POSSIBILITY OF SEVERE THREAT LATE THIS AFTERNOON AND EVENING.

LATEST WATER VAPOR SATELLITE IMAGERY SHOWS SEVERAL SHORTWAVE TROUGHS
EMBEDDED IN SOUTHWEST FLOW ALOFT EXTENDING FROM THE GREAT LAKES
REGION INTO THE ROCKY MOUNTAINS. LATEST MOSAIC RADAR INDICATING
RAIN/SHOWERS ACROSS MUCH OF THE GREAT LAKES REGION AND NORTHERN
PLAINS.

FIRST SHORTWAVE TROUGH OVER WESTERN MISSOURI WILL AFFECT THE
FORECAST AREA THROUGH 18Z. THE 25.00Z GFS/NAM SUGGEST DECENT QG
FORCING AND MOISTURE CONVERGENCE WITH THE SHORTWAVE TROUGH. WITH
LITTLE TO NO INSTABILITY OVER THE FORECAST AREA...THUNDERSTORMS ARE
NOT EXPECTED THIS MORNING. SHORTWAVE TROUGH AND ASSOCIATED SHOWERS
WILL QUICKLY LIFT NORTH OF THE FORECAST AREA AROUND 18Z TODAY.

FOCUS TURNS TO NEXT SHORTWAVE TROUGH OVER WESTERN KANSAS AND
SOUTHERN NEBRASKA MOVING NORTHEAST INTO WESTERN IOWA LATE THIS
AFTERNOON AND THIS EVENING. THE 25.00Z GFS/NAM INDICATE NOSE OF
MOISTURE TRANSPORT AND CONVERGENCE INTO THE SOUTHERN HALF OF THE
FORECAST AREA BY 00Z TUESDAY. THE 25.00Z NAM/GFS CONTINUE TO SHOW
0-6KM SHEAR OF 30 TO 40 KNOTS ACROSS THE SOUTHERN FORECAST AREA
WITH 30 KNOTS OF SHEAR IN THE 0-3KM LAYER. BIG QUESTION IS IF THE
REGION BUILDS ANY INSTABILITY OVER THE SOUTHERN FORECAST AREA THIS
AFTERNOON. THE 25.00Z GFS/NAM TRY TO BUILD 1000-1500 J/KG 0-6KM
MOST UNSTABLE CAPE BY 00Z TUESDAY. HOWEVER...WITH MORNING SHOWER
ACTIVITY AND CLOUD COVER...INSTABILITY WILL BE LIMITED. SEVERE
RISK OVER THE FORECAST AREA REMAINS LOW AT THIS TIME...DUE TO
LIMITED INSTABILITY...HOWEVER CANNOT RULE OUT THE POSSIBILITY OF AN
ISOLATED SEVERE THUNDERSTORM LATE THIS AFTERNOON INTO THIS
EVENING.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 317 AM CDT MON MAY 25 2015

TUESDAY...THE LATEST 25.00Z GFS/NAM/ECMWF HAVE TRENDED SLOWER AND
FARTHER WESTWARD WITH PLACEMENT OF SURFACE/UPPER LEVEL TROUGH THAN
PREVIOUS RUNS. THE 25.00Z GFS/NAM/ECMWF INDICATE WEAK QG FORCING
AND PV ADVECTION IN ASSOCIATION WITH THE UPPER LEVEL TROUGH SLOWLY
MOVING OVER THE UPPER MIDWEST. HAVE INCREASED PRECIPITATION
CHANCES ACROSS THE FORECAST AREA. THE 25.00Z GFS/NAM BUFKIT
SOUNDINGS SHOW SOME ELEVATED CAPE ABOVE 800MB AND 0-6KM MOST
UNSTABLE CAPE OF 500-800 J/KG ACROSS MUCH OF THE FORECAST
AREA...WITH THE NAM MORE BULLISH ON BUILDING INSTABILITY. DUE TO
SHOWER ACTIVITY AND CLOUD COVER OVER FORECAST AREA AND THE UPPER
MIDWEST...AREA WILL BE HARD PRESSED TO BUILD UP MUCH INSTABILITY
TUESDAY INTO TUESDAY NIGHT AND HAVE REDUCED THUNDERSTORM
PROBABILITIES TO ISOLATED. IF FORECAST AREA SEES ANY PEAKS OF
SUNSHINE DURING THE DAY TUESDAY. THEN...COVERAGE OF THUNDERSTORMS
WILL INCREASE.

DRY WEATHER IS EXPECTED WEDNESDAY INTO WEDNESDAY NIGHT...AS
SURFACE/SHORTWAVE RIDGE BUILDS INTO THE UPPER MIDWEST AND GREAT
LAKES REGION.

MAIN FORECAST CONCERNS THURSDAY INTO SUNDAY ARE PRECIPITATION
CHANCES THROUGH MUCH OF THE PERIOD. THE 25.00Z GFS/ECMWF/GEM DEVELOP
WEST TO EAST ZONAL FLOW ALOFT ACROSS THE NORTHERN TIER STATES
THROUGH THE FORECAST PERIOD. THE MODELS SHOW SEVERAL PIECES OF
ENERGY EMBEDDED IN THE WEST TO EAST ZONAL FLOW ALOFT TO TRACK ACROSS
THE GREAT LAKES REGION THURSDAY NIGHT INTO SUNDAY. THE BIGGEST
DIFFERENCES BETWEEN THE MODELS IS TIMING OF THE IMPULSES AND
PLACEMENT/MOVEMENT OF SURFACE FEATURES THROUGH THE PERIOD...AS THE
25.00Z ECMWF IS QUICKER IN PUSHING SURFACE FRONT EAST AND
BUILDING SURFACE RIDGE INTO THE FORECAST AREA SATURDAY NIGHT AND
SUNDAY. THE 25.00Z GFS/ECMWF/GEM INDICATE MOISTURE
CONVERGENCE/LIFT IN ASSOCIATION WITH EACH IMPULSE AND ALLOW FOR
CHANCES OF PRECIPITATION THURSDAY NIGHT INTO SUNDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY MORNING)
ISSUED AT 1149 PM CDT SUN MAY 24 2015

SCT -SHRA CONTINUE TO LIFT NORTH ACROSS THE AREA...IN BROAD
SOUTHERLY AND MOISTURE RICH FLOW AHEAD OF A SHORTWAVE LIFTING INTO
WESTERN MO. THE WARM FRONT SOUTH OF THE AREA CONTINUES TO MAKE SLOW
PROGRESS NORTHWARD...WITH WIDESPREAD MVFR/IFR CIGS/VSBYS IN BR
ACROSS SOUTHERN MN/NORTHERN IA/WESTERN WI AHEAD OF IT. THE FRONT AND
SHORTWAVE WILL CONTINUE TO LIFT NORTH OVERNIGHT...WITH SCT TO
NUMEROUS -SHRA EXPECTED TO CONTINUE. ONCE THE WAVE PASSES AND THE
FRONT LIFTS NORTH OF THE TAF SITES...CIGS/VSBYS EXPECTED TO IMPROVE
AS BRISK/GUSTY SOUTH TO SOUTHWEST WINDS SPREAD DEEPER MIXING AND
SOME DRYING INTO THE AREA. TREND IS FOR CIGS TO RISE INTO THE 2000-
3500 FT RANGE FOR THE AFTERNOON WITH VSBYS BECOMING VFR. ANOTHER
SHORTWAVE LOOKS TO APPROACH MONDAY EVENING...WITH AN INCREASE OF
MOISTURE/LIFT SPREADING BACK INTO THE AREA. SOME INSTABILITY WILL
BUILD ACROSS THE AREA AS WELL. INCLUDED A VCSH MENTION IN THE 00-06Z
PERIOD FOR NOW AS DETAILS MON EVENING ARE FAR FROM CERTAIN. MAY NEED
A TSRA/CB MENTION AFTER 26.00Z DEPENDING ON HOW THE DETAILS SORT
THEMSELVES OUT IN LATER FCST CYCLES.

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

$$

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


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