Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 021928
AFDARX

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

.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 ERRUPT
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 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1235 PM CDT TUE SEP 2 2014

IN WAKE OF MOST RECENT SHORT WAVE TROUGH SKIES CLEARED OUT THIS
MORNING WITH WIDESPREAD VFR CONDITIONS PREVAILING. AND WITH HIGH
PRESSURE BUILDING IN TONIGHT...THAT SHOULD CONTINUE INTO TONIGHT.
GRADIENT WITH RETURN FLOW WILL KEEP THINGS A BIT MORE MIXED WEST OF
MISSISSIPPI RIVER TONIGHT BUT EAST OF RIVER...LIGHTER WINDS AND
DECOUPLING WILL ALLOW FOR FAVORED VALLEY FOG FORMATION LEADING TO
SPOTTY IFR CONDITIONS. KLSE MAY ESCAPE FOG SCENARIO WITH LOW LEVEL
WINDS REMAINING A BIT TOO STRONG BUT WILL INCLUDE IN VICINITY WITH
MORE FAVORABLE FOG SET UP EAST AND SOUTH OF SITE.

RETURN FLOW IN RESPONSE OF UPSTREAM WAVE WILL KICK INTO HIGH GEAR ON
WEDNESDAY AND WITH THAT EXPECT RAPID LOW LEVEL MOISTURE RETURN. THIS
COULD CREATE A STRATUS DECK THAT ADVECTS NORTHWARD IMPACTING SITES
MAINLY WEST. STILL COULD BE VFR BUT TREND TOWARD MVFR CEILINGS WILL
NEED TO BE MONITORED.

&&

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

$$

SHORT TERM...WETENKAMP
LONG TERM...WETENKAMP
AVIATION...SHEA



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