Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 030437
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1137 PM CDT TUE SEP 2 2014

.UPDATE...
ISSUED AT 608 PM CDT TUE SEP 2 2014

A QUICK UPDATE LOOKING AT THE SEVERE WEATHER POTENTIAL FOR
TOMORROW NIGHT. CHECKING OUT THE 02.18Z NAM/GFS AND 02.12Z
ECMWF...THEY REMAIN IN AGREEMENT IN DEVELOPING CONVECTION THAT
WILL LIKELY BE SEVERE OVER CENTRAL MN BY 00Z THURSDAY. CORFIDI
VECTORS POINT TO A SOUTHERLY MOTION...WHICH WOULD PUT SOUTHEAST MN
ALSO INTO THE THREAT AREA...AND POSSIBLY EVEN A BIT OF NORTHEAST
IA. HOWEVER...CAPPING IS ALSO BUILDING NORTHEAST INTO THE FORECAST
AREA WEDNESDAY NIGHT...WHICH COULD PUT A BLOCKADE ON HOW FAR
SOUTH CONVECTION DROPS SOUTH. SO IT LOOKS LIKE TOMORROW NIGHT WILL
BE A BATTLE BETWEEN CORFIDI VECTORS WHICH WORK WELL FOR MCS MOTION
AND CAPPING.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 228 PM CDT TUE SEP 2 2014

MAIN FORECAST CONCERNS ARE ON SEVERE THUNDERSTORM  POTENTIAL WEDNESDAY
NIGHT NORTH OF INTERSTATE 90 WITH ANOTHER ROUND OF SEVERE STORMS
POSSIBLE EAST OF THE MISSISSIPPI RIVER THURSDAY AFTERNOON AND
EVENING.

LATEST WATER VAPOR IMAGERY SHOWED A SHORTWAVE TROUGH PUSHING EAST OF
THE UPPER MISSISSIPPI RIVER VALLEY WITH  WEST/NORTHWEST FLOW SETTING
UP OVER THE REGION IN IT/S WAKE. WEAK HIGH PRESSURE WILL SETTLE OVER
THE FORECAST AREA TONIGHT PROVIDING MAINLY QUIET WEATHER. WILL HAVE
TOO KEEP A CLOSE EYE ON SOME PATCHY VALLEY FOG ALONG THE MISSISSIPPI
AND WISCONSIN RIVER VALLEYS AND OVER CENTRAL WISCONSIN CRANBERRY
COUNTRY. WITH WINDS DECOUPLING TONIGHT AND CLEAR SKIES...THIS SHOULD
SET THE STAGE FOR SOME FOG DEVELOPMENT OVER THESE AREAS.
MEANWHILE...A WARM FRONT IS EXPECTED TO LIFT NORTH OUT OF THE
CENTRAL PLAINS AND INTO THE UPPER MISSISSIPPI RIVER VALLEY. BY MID
WEDNESDAY MORNING...THE FRONT IS EXPECTED TO BE POSITIONED FROM
SOUTHWEST MINNESOTA INTO NORTH CENTRAL IOWA EXTENDING INTO CENTRAL
ILLINOIS. THE FRONT WILL LIFT NORTH THROUGH THE DAY ON WEDNESDAY
AND BY LATER AFTERNOON INTO EARLY WEDNESDAY EVENING SHOULD BE
POSITIONED ALONG THE INTERSTATE 94 CORRIDOR...FROM NEAR SAINT
CLOUD TO MINNEAPOLIS INTO CENTRAL WISCONSIN.

A VERY MOIST AIRMASS PUSHES INTO THE FORECAST AREA IN THE WAKE OF
THE WARM FRONT WITH DEWPOINTS CLIMBING INTO THE LOWER 70S. A MID
LEVEL TROUGH PUSHES INTO THE REGION LATE IN THE AFTERNOON INTO THE
EARLY EVENING HOURS AND WILL PROVIDE THE SUPPORT FOR THE DEVELOPMENT
OF THUNDERSTORMS. SBCAPE VALUES AND SHEAR WOULD SUPPORT SUPERCELL
STORMS ALONG THE WARM FRONT WITH THE POTENTIAL FOR LARGE
HAIL...DAMAGING WINDS...A TORNADO OR TWO..AND POSSIBLY THE THREAT
FOR HEAVY RAINFALL. SBCAPE VALUES CLIMB INTO THE 2500-3500 J/KG
RANGE ALONG THE FRONT...WHILE 0-6 KM BULK SHEAR VALUES OF 45 TO 55
KTS. IN ADDITION...0-1 KM BULK SHEAR VALUES INCREASE INTO THE 20 TO
25 KT RANGE LATE IN THE AFTERNOON THEN CONTINUE TO INCREASE INTO THE
EVENING HOURS AS THE LOW LEVEL JET RAMPS UP.  ANOTHER IMPRESSIVE
FEATURE IS THE STRONG 850 MB MOISTURE TRANSPORT INTO THE WARM FRONT
WEDNESDAY  NIGHT. PRECIPITABLE  WATER VALUES ARE FAIRLY HEALTHY AS WELL
WITH VALUES RANGING FROM 1.5 TO 1.8 INCHES. WARM CLOUD DEPTHS WOULD
FAVOR HEAVY RAINFALL OUT OF THE STORMS AS WELL WITH VALUES CLIMBING
TO AROUND 4.2 KM DURING THE OVERNIGHT HOURS.

LATEST THINKING IS THAT STORMS WILL INITIATE OVER CENTRAL
MINNESOTA...MOST LIKELY SUPERCELLS THEN WILL RACE EAST AND FORM
BOWING STRUCTURES AS THEY MOVE INTO PORTIONS OF WEST CENTRAL
WISCONSIN. GIVEN THE RAMP UP IN 0-1 KM SHEAR...A TORNADO THREAT WILL
CONTINUE INTO THE EVENING HOURS ALONG THE BOWING STRUCTURES. THE NAM
IS SUGGESTING CONVECTION COULD REFIRE BEHIND THE INITIAL SURGE OF
CONVECTION WHICH WOULD INCREASE THE CONCERN FOR HEAVY RAIN AND
POSSIBLY FLASH FLOODING IF STORMS WOULD REPEAT OVER THE SAME AREAS.
HIGHEST CONFIDENCE FOR SEVERE STORMS AT THIS TIME WOULD BE ALONG AND
NORTH OF THE WISCONSIN HIGHWAY 10 CORRIDOR. THE STORMS MAY TURN
MORE SOUTHEASTERLY AS THEY MOVE INTO WEST CENTRAL WISCONSIN AND
THEN THEY WOULD HAVE THE POTENTIAL TO MAKE IT INTO PORTIONS OF
SOUTHWEST AND CENTRAL WISCONSIN.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 228 PM CDT TUE SEP 2 2014

ON THURSDAY...THE WARM FRONT SHOULD BE WELL NORTH OF THE FORECAST
AREA WITH ANY EARLY MORNING CONVECTION ENDING AND PUSHING EAST OF
THE AREA. A HUMID AND WARM AIRMASS WILL BE IN PLACE WITH
TEMPERATURES CLIMBING INTO THE MID TO UPPER 80S. THESE TEMPERATURES
COMBINED WITH DEWPOINTS IN THE LOWER 70S WILL MAKE IT FEEL
UNCOMFORTABLE WITH HEAT INDEX VALUES CLIMBING INTO THE LOWER TO MID
90S. A COLD FRONT IS EXPECTED TO SWEEP THROUGH THE REGION THURSDAY
AFTERNOON INTO THURSDAY EVENING BRINGING CHANCES FOR MORE SHOWERS
AND STORMS. THERE IS A VERY STRONG CAP TO OVERCOME ON THURSDAY WITH
800 MB TEMPERATURES HOVERING RIGHT AROUND 23 C. LOCATIONS ACROSS
WESTERN INTO CENTRAL WISCONSIN LOOK TO HAVE A BETTER CHANCE AT
BREAKING THIS CAP WITH THE FRONT ARRIVING LATER IN THE AFTERNOON
UNDER MAXIMUM DAYTIME HEATING. SHOWERS AND STORMS SHOULD ERUPT ALONG
THE FRONT...MAINLY WISCONSIN THEN PUSH EAST OF THE FORECAST AREA
BY THURSDAY EVENING. THE MAIN THREAT FROM THESE STORMS LOOKS TO BE
DAMAGING WINDS AND POSSIBLY LARGE HAIL. A MUCH MORE COMFORTABLE
AIRMASS MOVES INTO THE FORECAST AREA IN THE WAKE OF THE COLD FRONT
LATE THURSDAY NIGHT INTO FRIDAY AS HIGH PRESSURE BUILDS IN AND
WEST/NORTHWEST FLOW ALOFT SETS UP. PLAN ON HIGH TEMPERATURES
FALLING BACK INTO THE 70S. THE HIGH LOOKS TO REMAIN IN
CONTROL...PROVIDING DRY AND QUIET WEATHER INTO THE WEEKEND.
HOWEVER...WE WILL HAVE TO KEEP AN EYE ON VALLEY FOG POTENTIAL. THE
NEXT CHANCE FOR SHOWERS AND STORMS ARRIVES LATE MONDAY INTO
TUESDAY AS SOUTHWEST FLOW ALOFT ATTEMPTS TO BECOME ESTABLISHED
OVER THE REGION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1137 PM CDT TUE SEP 2 2014

A RIDGE OF HIGH PRESSURE NOSING NORTHWARD INTO THE REGION EARLY
THIS MORNING BRINGS CONCERN FOR VALLEY FOG AT LSE. HOWEVER...
PASSING CIRRUS CLOUDS COMBINED WITH WINDS INCREASING RIGHT ABOVE
THE GROUND THROUGH THE NIGHT SHOULD HELP PREVENT FOG FROM FORMING
AT LSE. HAVE CONTINUED THE VCFG SINCE FOG SHOULD BE IN NEARBY
VALLEYS...ALONG WITH A SCT LIFR DECK SINCE THE POTENTIAL EXISTS
FOR SOME STRATUS TO FORM OVER THE VALLEY.

A WARM FRONT ABOVE THE GROUND REMAINS ON TRACK TO LIFT THROUGH
THE TAF SITES LATE THIS MORNING...WHICH COULD CLIP RST AND MAYBE
EVEN LSE WITH SOME SHOWERS COMING FROM A VFR CLOUD BASE. THE MAIN
WARM FRONT APPROACHES THE TAF SITES LATE THIS AFTERNOON WHICH TOO
COULD PRODUCE SOME SHOWER ACTIVITY...AIDED BY DAYTIME HEATING.
THIS SAME HEATING SHOULD CAUSE SOUTHERLY WINDS TO GUST 20-25 KT.
A BREAK IN PRECIPITATION IS POSSIBLE EARLY IN THE EVENING...THEN
THE POTENTIAL EXISTS FOR A COMPLEX OF STRONG TO SEVERE
THUNDERSTORMS TO IMPACT THE TAF SITES LATE IN THE EVENING. A LOW
LEVEL JET NOTED BY LOW LEVEL WIND SHEAR IN THE TAFS WILL SUPPORT
THESE STORMS. UNCERTAINTY EXISTS ON THE COMPLEX
TRACK...THEREFORE...HAVE ONLY INTRODUCED A VCTS WITH VFR
CONDITIONS AT THIS TIME. SHOULD THIS COMPLEX HIT THE TAF
SITES...IFR OR LOWER CONDITIONS ARE LIKELY...ALONG WITH NORTHWEST
WIND GUSTS OVER 30 KT.

&&

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

$$

UPDATE...AJ
SHORT TERM...WETENKAMP
LONG TERM...WETENKAMP
AVIATION...AJ


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