Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 021735
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1235 PM CDT TUE SEP 2 2014

.SHORT TERM...(TODAY THROUGH TONIGHT)
ISSUED AT 339 AM CDT TUE SEP 2 2014

WATER VAPOR IMAGERY SHOWING A FAIRLY BROAD TROUGH OF LOW PRESSURE
EXTENDING ACROSS CENTRAL CANADA INTO THE U.S. NORTHERN AND CENTRAL
PLAINS. EMBEDDED WITHIN THIS TROUGH WAS A PIECE OF PVA ACROSS THE
EASTERN DAKOTAS. LIFT ASSOCIATED WITH THIS FEATURE WAS HELPING TO
FUEL A CLUSTER OF SHOWERS AND THUNDERSTORMS ACROSS SOUTHWEST
MN/NORTHWEST IA. A WEAKER TROUGH ACROSS WESTERN ONTARIO INTO EASTERN
MN WAS PRODUCING A FEW SHOWERS ACROSS NORTHWEST WI.
OTHERWISE...SKIES ACROSS THE FORECAST EARLY THIS MORNING WERE MOSTLY
CLEAR WITH TEMPERATURES HOVERING IN THE MIDDLE 50S TO THE LOWER 60S.

FOR TODAY...RAP MODEL SHOWING AFOREMENTIONED DAKOTAS TROUGH AND
WEAKENING 700-300MB PVA MOVING ACROSS THE AREA...EXITING EAST BY
NOON. ALTHOUGH MOST OF THIS FORCING WILL BE EXITING BY NOON...THERE
WILL BE A FAIRLY STEEP LAPSE RATE ASSOCIATED WITH COOLING ALOFT.
WILL KEEP LOWER-END SHOWER/THUNDER CHANCES GOING THIS MORNING...THEN
TAPER OFF FROM WEST TO EAST AFTER NOON. OTHERWISE...PLAN ON
HIGH TEMPERATURES TODAY IN THE MIDDLE AND UPPER 70S.

A WEAK RIDGE OF HIGH PRESSURE DRIFTS ACROSS THE REGION TONIGHT FOR
MOSTLY CLEAR SKIES THROUGH MOST OF THE NIGHT WITH LOWS DIPPING INTO
THE MIDDLE 50S ACROSS CENTRAL WISCONSIN TO THE UPPER 50S/NEAR 60S
ELSEWHERE. A WEAK MID-LEVEL TROUGH AND A PUSH OF 850MB WARM AIR
ADVECTION/MOISTURE TRANSPORT ACROSS THE PLAINS MAY KICK OFF
SCATTERED SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF WESTERN
IA/SOUTHERN MN TOWARD MORNING. THERE IS A SMALL CHANCE THAT SOME OF
THIS CONVECTION MAY MAKE IT INTO AREAS WEST OF THE MISSISSIPPI
RIVER. FOR NOW...HONORED THAT WITH A LOW-END 20ISH POP.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 339 AM CDT TUE SEP 2 2014

A WARM FRONT AND INCREASING 850MB MOISTURE TRANSPORT WILL PUSH
TOWARD THE AREA WEDNESDAY FOR A CHANCE OF SHOWERS AND THUNDERSTORMS.
THE BULK OF THIS TRANSPORT APPEARS TO HOLD WEST OF THE MISSISSIPPI
RIVER...BUT EASTERN PERIPHERY EXPECTED TO DRIVE SOME CONVECTION EAST
OF THE RIVER AS WELL. LOOK FOR HIGHS WEDNESDAY IN THE UPPER 70S TO
THE LOWER 80S.

DEEPENING SURFACE LOW PRESSURE OVER THE DAKOTAS WILL PUSH A WARM
FRONT THROUGH THE AREA WEDNESDAY NIGHT AND INCREASE 850MB MOISTURE
TRANSPORT. MODEL CONSENSUS SHOWS THIS FORCING FUELING A COMPLEX OF
THUNDERSTORMS MAINLY ALONG AND NORTH OF I-94. WENT WITH LIKELY POPS
ACROSS THIS AREA BASED ON THIS SIGNAL. WILL HAVE TO WATCH FOR A
SEVERE POTENTIAL AS WELL WITH MODEL CONSENSUS INDICATING MUCAPE
INCREASING INTO THE 1500-3000J/KG RANGE WITH 0-6KM BULK SHEAR 30-
35KT. MAIN SEVERE THREAT APPEARS TO BE DAMAGING WINDS...SOME HAIL...
AND WITH PRECIPITABLE WATER APPROACHING 1.9 INCHES...HEAVY RAINFALL.

LOOK FOR THE WARM FRONT AND BULK OF THUNDERSTORMS TO LIFT NORTHEAST
OUT OF THE AREA AFTER SUNRISE THURSDAY MORNING. THIS PUTS THE AREA
IN THE WARM SECTOR ON THURSDAY WITH NAM INDICATING A FAIRLY STRONG
CAP SETTING UP. SOUTHERLY FLOW EXPECTED TO PUSH TEMPERATURES WELL
INTO THE 80S. WITH DEW POINTS INCREASING INTO THE LOWER 70S...PLAN
ON HEAT INDICES IN THE 90S.

THE CAP IS EXPECTED TO HOLD CONVECTION AT BAY THROUGH MOST OF
THURSDAY AFTERNOON...BUT WITH APPROACH OF MID-LEVEL TROUGH AND
SURFACE COLD FRONT SINKING SOUTHEASTWARD INTO THE AREA BY EARLY
EVENING... CONVECTION IS EXPECTED TO FIRE. MODEL CONSENSUS PRODUCES
MUCAPE IN THE 3500-5000J/KG RANGE WITH 0-6KM BULK SHEAR OF 30-45KT.
WILL HAVE TO KEEP A CLOSE WATCH ON THIS FOR SEVERE POTENTIAL. LOOK
FOR THE FRONT AND ASSOCIATED THUNDERSTORMS TO SINK SOUTHWARD ACROSS
THE AREA OVERNIGHT.

THERE WILL BE A LINGERING CHANCE OF SHOWERS AND THUNDERSTORMS ACROSS
THE FAR SOUTH ON FRIDAY...SOUTH OF I-90...BUT BULK OF THE AREA WILL
SEE DRIER/COOLER AIR FILTERING IN AS CANADIAN HIGH PRESSURE MAKES IT
WAY ACROSS THE NORTHERN PLAINS. HIGH TEMPERATURES ON FRIDAY ARE
EXPECTED TO BE IN THE UPPER 60S TO THE MIDDLE 70S.

HIGH PRESSURE LOOKS TO TAKE HOLD OF THE REGION THROUGH THE WEEKEND
FOR DRIER/COOLER EARLY FALL-LIKE CONDITIONS. PLAN ON HIGHS SATURDAY
AND SUNDAY REMAINING IN THE UPPER 60S/LOWER 70S WITH OVERNIGHT LOWS
IN THE UPPER 40S TO THE LOWER 50S.

GFS/ECMWF AT ODDS ON MONDAY WITH THE ECMWF HOLDING HIGH PRESSURE AND
DRIER CONDITIONS ACROSS THE REGION. THE GFS SHOWS A MORE PROGRESSIVE
PATTERN...BRINGING IN A MID-LEVEL TROUGH AND A CHANCE OF
SHOWERS/THUNDERSTORMS. MODEL TRENDS LOOK TO BE ON A DRYING TREND
OVERALL...SO MAY END UP BEING DRY EVENTUALLY. TOOK A MODEL CONSENSUS
AT THIS POINT WHICH PRODUCES A LOW-END 20-30 POP.

&&

.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...DAS
LONG TERM...DAS
AVIATION...SHEA


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