Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200858
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
358 AM CDT WED AUG 20 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 358 AM CDT WED AUG 20 2014

LATEST WATER VAPOR IMAGERY SHOWED A BROAD UPPER LOW ANCHORED OVER
UPPER MICHIGAN WITH NORTHWEST FLOW ALOFT ACROSS THE UPPER
MISSISSIPPI RIVER VALLEY. A MOIST AIRMASS OVER THE REGION AND SOME
CLEARING HAS LEAD TO AREAS OF FOG THIS MORNING ESPECIALLY ALONG AND
EAST OF THE MISSISSIPPI RIVER. VISIBILITIES HAVE BEEN REDUCED TO
AROUND 1/4 MILE AT TIMES OVER PORTIONS OF CENTRAL AND NORTHERN
WISCONSIN. ALSO...AREAS OF DENSE FOG HAVE DEVELOPED FURTHER WEST
CLOSER TO THE I-35 CORRIDOR. SHOWERS AND THUNDERSTORMS HAVE
DEVELOPED OVER PORTIONS OF NORTHEAST NEBRASKA THROUGH SOUTHWEST
IOWA ON THE NOSE OF 850 MB MOISTURE TRANSPORT AND 900-800 MB
FRONTOGENESIS.

THE WARM FRONT IS EXPECTED TO LIFT SLIGHTLY NORTH TODAY AS WEAK LOW
PRESSURE DEVELOPS OVER EASTERN SOUTH DAKOTA. AFTER THE MORNING
FOG...WE SHOULD SEE PARTLY SUNNY SKIES TODAY WITH A GRADUALLY
INCREASE IN CLOUD COVER FROM WEST TO EAST AS A SHORTWAVE TROUGH
MOVES IN. THE WARM FRONT LOOKS TO BE SITUATED FROM CENTRAL
MINNESOTA THROUGH SOUTHEAST MINNESOTA INTO NORTHEAST IOWA THIS
EVENING AND WILL BE THE FOCUS FOR SHOWER AND THUNDERSTORM
DEVELOPMENT AS 925-850 MB MOISTURE TRANSPORT INCREASES INTO THE
FRONT. PRECIPITABLE WATER VALUES CLIMB TO AROUND 2 INCHES AND WARM
CLOUD DEPTHS INCREASE TO 4.0 TO 4.5 KM. ALSO..0-1 KM MUCAPE VALUES
CLIMB TO AROUND 1500-2000 J/KG LATE THIS AFTERNOON INTO THIS
EVENING. THE SHOWERS AND STORMS WILL BE EFFICIENT RAIN PRODUCERS
TONIGHT INTO EARLY THURSDAY MORNING AND COULD PRODUCE LOCALLY
HEAVY RAINFALL AND POSSIBLY SOME LOCALIZED FLOODING CONCERNS.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 358 AM CDT WED AUG 20 2014

SHOWERS AND STORMS SHOULD BE ONGOING EARLY THURSDAY MORNING BUT WE
SHOULD THEN SEE THIS ACTIVITY  TAPER OFF AS THE LOW LEVEL JET
WEAKENS. A WEAK COLD FRONT THEN PUSHES ACROSS THE AREA THURSDAY
AFTERNOON INTO THURSDAY EVENING WITH ANOTHER ROUND OF SHOWERS AND
STORMS POSSIBLE. 0-1KM MUCAPE VALUES CLIMB TO 1800 TO 2000 J/KG
THURSDAY AFTERNOON. ALSO...0-3 KM BULK SHEAR VALUES INCREASE TO
30 TO 35 KTS. CANNOT RULE OUT A SEVER STORM OR TWO THURSDAY
AFTERNOON DEPENDING ON HOW MUCH INSTABILITY  IS REALIZED. THE
MOST LIKELY AREA FOR THIS ACTIVITY WOULD BE ALONG AND NORTH OF
INTERSTATE 90 WITH AN EVEN BETTER CHANCE  NORTH OF INTERSTATE 94.
THE BOUNDARY THEN PUSHES SOUTH OF THE FORECAST AREA THURSDAY NIGHT
INTO FRIDAY AND AND WE SHOULD SEE A BREAK IN PRECIPITATION CHANCES
DURING THIS TIMEFRAME. THE FRONT THEN LIFTS NORTH AGAIN ON
SATURDAY THEN LOOKS TO PARK NEAR OR JUST SOUTH OF THE INTERSTATE
90 CORRIDOR ON SATURDAY. IF THIS SCENARIO PANS OUT WE SHOULD SEE
MORE SHOWERS AND STORMS DURING THE DAY ON FRIDAY ALONG THE WARM
FRONT. CAPE AND SHEAR PROFILES WOULD SUGGEST THE POTENTIAL OF
SEEING A FEW STRONG TO SEVERE STORMS OVER NORTHEAST IOWA AND FAR
SOUTHWEST WISCONSIN. FORECAST MODELS THEN DIVERGE ON WHERE TO
PLACE THE FRONT SATURDAY NIGHT INTO SUNDAY AS A TROUGH DIVES INTO
THE PACIFIC NORTHWEST AND A RIDGE BUILDS OVER THE MISSISSIPPI
RIVER VALLEY REGION. THE ECMWF CONTINUES TO BE THE MOST AGGRESSIVE
WITH THE RIDGING AND PUSHES THE WARM FRONT WELL NORTH OF THE
FORECAST AREA AND PUTS US IN A HOT AND HUMID AIRMASS. THE GFS KEEP
THE FRONT CLOSER TO HOME AND SUGGEST SEVERAL ROUNDS OF SHOWERS AND
STORMS DURING THIS TIMEFRAME. THERE REMAINS SOME DETAILS TO BE
WORKED FOR THE LATER PART OF THE WEEKEND. FORECAST CHALLENGES
CONTINUE INTO EARLY NEXT WEEK AS SOUTHWEST FLOW ALOFT ATTEMPTS TO
SET UP OVER THE UPPER MISSISSIPPI RIVER VALLEY. IF THIS PATTERN
INDEED DEVELOPS...WE WOULD BE LOOKING AT AN ACTIVE PATTERN GOING
INTO THE FIRST HAVE OF NEXT WEEK WITH SEVERAL ROUNDS OF SHOWERS
AND STORMS POSSIBLE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1151 PM CDT TUE AUG 19 2014

CONFIDENCE REMAINS FAIRLY HIGH THAT VALLEY FOG WILL DEVELOP
OVERNIGHT WITH THE MAIN CONCERN JUST BEING WITH SOME SCATTERED MID
LEVEL CLOUDS THAT HAVE BEEN DROPPING SOUTHEAST FROM
MINNESOTA/NORTHWEST WISCONSIN. OTHERWISE...DEW POINT SPREADS ARE
LOW...WINDS ARE CALM AT THE SURFACE AND LIGHT ON UP THROUGH THE
LOWEST 3KFT. THE MAIN QUESTION IS JUST WITH HOW FAST THE FOG WILL
FORM AND THEN DISSIPATE OVERNIGHT. ONSET STILL APPEARS TO BE
AROUND 9Z WITH DISSIPATION COMING AROUND 14-15Z BASED ON
CLIMATOLOGY. WITH THE RIDGE OVERHEAD...WINDS WILL REMAIN CALM WITH
SKIES CLEAR FOR MUCH OF THE DAY BEFORE SHOWERS AND THUNDERSTORMS
DEVELOP WEDNESDAY EVENING. THIS CONVECTION LOOKS LIKE IT WILL
DEVELOP ALONG A NORTHWEST TO SOUTHEAST BAND AND COULD BE HEAVY AT
TIMES...BRINGING VISIBILITY CONDITIONS TO IFR/MVFR.

&&

.HYDROLOGY...TONIGHT INTO THURSDAY
ISSUED AT 358 AM CDT WED AUG 20 2014

A MOIST AND UNSTABLE AIRMASS MOVES INTO THE REGION TONIGH WITH
PRECIPITABLE WATER VALUES CLIMBING TO AROUND 2 INCHES AND WARM CLOUD
DEPTHS INCREASIG TO 4 TO 4.5 KM. THIS WILL SET THE STAGE FOR
POTENTIAL HEAVY RAINFALL OUT OF ANY THUNDERSTORMS THAT DEVELOP.
NORTHEAST IOWA AND SOUTHEAST MINNESOTA LOOK TO HAVE THE HIGHEST
CHANCES OF SEEING THUNDERSTORMS TONIGHT...THEN THE STORMS ARE
EXPECTED TO PUSH INTO WESTERN AND CENTRAL WISCONSIN AFTER DAYBREAK
ON THURSDAY. THERE REMAINS CONSIDERABLE UNCERTAINTY ON HOW THE
STORMS WILL EVOLVE TONIGHT INTO THURSDAY MORNING AND WHERE THE
HEAVIEST RAINFALL WOULD OCCUR. A FLASH FLOOD WATCH MAY BE NEEDED
LATE TONIGHT INTO THURSDAY MORNING.

&&

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

&&

$$

SHORT TERM...WETENKAMP
LONG TERM...WETENKAMP
AVIATION...HALBACH
HYDROLOGY...WETENKAMP



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