Area Forecast Discussion
Issued by NWS La Crosse, WI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KARX 230447
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1147 PM CDT FRI AUG 22 2014

.UPDATE...
ISSUED AT 922 PM CDT FRI AUG 22 2014

THE MAIN FOCUS FOR THE OVERNIGHT PERIOD IS ON CONVECTIVE TRENDS
AND THE POTENTIAL FOR DENSE FOG.

THE MAIN BAND OF CONVECTION HAS BEEN LINGERING AROUND AN ARCHING
STATIONARY FRONT ACROSS CENTRAL IOWA. WITH A LIGHT WIND FIELD IN
PLACE FROM THE SURFACE ON UP TO AROUND 400MB...THESE STORMS HAVE
BEEN VERY SLOW MOVING BUT ALSO VERY PULSEY. THE SUITE OF MESO-
MODELS HAS HAD A HARD TIME TRYING TO FIGURE OUT WHAT WILL HAPPEN
OVERNIGHT...BUT WITH LIMITED LOW LEVEL JET FORCING AND MID LEVEL
RIDGING IN PLACE...EXPECT THAT THERE SHOULD BE A GENERAL DOWNWARD
TREND IN CONVECTIVE COVERAGE ACROSS THE EASTERN HALF OF IOWA WHERE
THE RIDGING IS IN PLACE. GOING INTO TOMORROW MORNING...THE 23.00Z
HRRR IS SHOWING THE BAND OF CONVECTION DEVELOPING TOMORROW MORNING
ACROSS CENTRAL IOWA AS THE LEAD MID LEVEL SHORT WAVE TROUGH
PROPAGATES NORTH ACROSS THE PLAINS. THIS WOULD BRING THIS BAND OF
CONVECTION IN AROUND LATE MORNING IN NORTHEAST IOWA/SOUTHEAST
MINNESOTA. WILL HAVE TO MONITOR TRENDS ACROSS NEBRASKA OVERNIGHT
TO SEE WHETHER ANY BETTER TIMING CAN BE GIVEN ON THESE
PRECIPITATION CHANCES.

THE SETUP FOR DENSE FOG IS PRETTY GOOD FOR TONIGHT WITH THIS DEEP
LAYER OF LIGHT WINDS AND HIGH SURFACE MOISTURE IN PLACE. THE MAIN
LIMITING FACTOR IS WITH CLOUD COVER BLOWING OFF OF EARLIER
CONVECTION THAT OCCURRED IN IOWA TONIGHT. WHILE IR TRENDS SHOW THE
CLOUD TOPS WARMING...THERE MAY BE ENOUGH CONVECTIVE DEBRIS AROUND
TO HOLD TEMPERATURES FROM FALLING TOO MUCH OVERNIGHT AND ALLOWING
FOR SATURATION AND THE FOG TO DEVELOP. THE POTENTIAL WILL BE
HIGHER TO THE NORTH WHERE SKIES ARE STILL CLEAR. NO PLANS TO ISSUE
A DENSE FOG ADVISORY WITH THIS CLOUD COVER AROUND NOW...BUT THE
MIDNIGHT CREW WILL HAVE TO KEEP AN EYE ON IT.

&&

.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 308 PM CDT FRI AUG 22 2014

LOW CLOUDS HANGING TOUGH ACROSS THE AREA AS LOWER LEVEL BOUNDARY
LAYER MOISTURE ON THE INCREASE. SURFACE DEW POINTS EARLY THIS
AFTERNOON WERE IN THE LOWER/MIDDLE 70S...PRETTY STICKY. SURFACE MAP
DEPICTING AN AREA OF LOW PRESSURE LOCATED OVER NORTH CENTRAL
WISCONSIN WITH A BOUNDARY LAID UP FROM THE LOW THROUGH LA CROSSE
INTO NORTHEAST IA. MEANWHILE...SURFACE CYCLOGENESIS TAKING PLACE
OVER WESTERN KS WITH A WARM FRONT EXTENDING THROUGH NORTHERN KS INTO
NORTHERN MO AND CENTRAL IL.

FOR TONIGHT...MAIN SHOWER/THUNDERSTORM ACTION WILL TAKE PLACE ALONG
THE WARM FRONT TO OUR SOUTH AS LOW LEVEL JET IMPINGES ON IT. THERE
COULD BE A FEW SHOWERS AND STORMS AS WELL ALONG THE FRONTAL BOUNDARY
IN PLACE ACROSS OUR SOUTH BUT MOISTURE TRANSPORT IS LACKING. AS
SUCH...WILL KEEP A SLIGHT SHOWER/THUNDERSTORM CHANCE IN ACROSS
PORTIONS OF NORTHEAST IA/FAR SOUTHWEST WI. WITH WEAK PRESSURE
GRADIENT TO DRIVE SURFACE WINDS TONIGHT AND ABUNDANT LOW LEVEL
MOISTURE...EXPECT AREAS OF FOG TO FORM OVERNIGHT. NOT CONFIDENT AT
THIS POINT WHETHER REDUCTION IN VISIBILITY WILL BE LOW ENOUGH FOR A
HEADLINE. WILL HAVE TO MONITOR THIS AS THE EVENING PROGRESSES.

ATTENTION THEN TURNS TO THE WARM FRONT WHICH WILL START MAKING A
NORTHWARD PUSH INTO THE AREA SATURDAY/SATURDAY NIGHT. MODELS IN GOOD
AGREEMENT IN KEEPING BEST AXIS OF MOISTURE TRANSPORT WEST OF THE
AREA INTO WESTERN IA/MN AND EASTERN DAKOTAS AS THE SURFACE LOW LIFTS
NORTHWARD FROM THE CENTRAL INTO THE NORTHERN PLAINS. WILL STILL BE
WATCHING FOR A SLIGHT SEVERE THREAT SATURDAY AFTERNOON INTO SATURDAY
EVENING AS THE NAM IS PRODUCING SOME ELEVATED MUCAPE IN THE 2500-
4000J/KG RANGE. 0-3KM BULK SHEAR RATHER WEAK IN THE 10-20 KT
RANGE...SO EXPECTING PULSE-TYPE NATURE TO THUNDERSTORM ACTIVITY.
HEAVIER RAINFALL POTENTIAL WILL ALSO HAVE TO BE WATCHED WITH
PRECIPITABLE WATER VALUES IN THE 1.5-2 INCH RANGE. AFTER 06Z
SUNDAY...LOOKING FOR CONVECTION TO GET PULLED NORTH/WESTWARD OUT OF
THE AREA AS THE WARM FRONT PROGRESSES OUT OF THE AREA.

OTHERWISE...GETTING INCREASINGLY STEAMY GOING INTO SATURDAY MAINLY
SOUTH OF I-94 WITH HIGHS TOPPING OFF IN THE LOWER/MIDDLE 80S AND DEW
POINTS IN THE 70S. PLAN ON HEAT INDICES BY LATER IN THE AFTERNOON IN
THE 90-95 DEGREE RANGE.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 308 PM CDT FRI AUG 22 2014

HOT AND HUMID DAY ON TAP FOR SUNDAY WITH THE AREA ENTRENCHED IN
STRONGLY CAPPED WARM SECTOR. NAM VERY CONSISTENT INDICATING 26-30C
925MB AIR GETTING PULLED NORTHWARD INTO THE AREA...WITH THE HOTTEST
AXIS OF THIS AIR ALONG/WEST OF THE MISSISSIPPI RIVER. PLAN ON HIGHS
RANGING FROM THE 85-90 DEGREE RANGE ACROSS CENTRAL WISCONSIN...TO
THE LOWER 90S ALONG AND WEST OF THE MISSISSIPPI RIVER. THESE
TEMPERATURES COMBINED WITH DEW POINTS IN THE 70S EXPECTED TO PRODUCE
HEAT INDICES IN THE 90S TO AROUND 100 DEGREES. A HEAT ADVISORY MAY
BE NEEDED FOR PORTIONS OF THE AREA SUNDAY AND WILL CONTINUE TO BE
ASSESSED.

A COLD FRONT WILL THEN PUSH INTO THE AREA SUNDAY NIGHT FOR A GOOD
CHANCE OF SHOWERS AND THUNDERSTORMS. MODELS IN GOOD AGREEMENT IN
THIS BOUNDARY WILL LAY UP ACROSS THE AREA THROUGH THURSDAY FOR
CONTINUED SHOWERS AND THUNDERSTORM CHANCES...WITH HIGHEST LIKELIHOOD
TUESDAY INTO WEDNESDAY. WILL HAVE TO KEEP A CLOSE EYE ON HEAVY RAIN
POTENTIAL IN THIS SCENARIO GIVEN PRECIPITABLE WATERS IN THE 1.5-2 INCH
RANGE ALONG WITH UPPER JET DYNAMICS. OTHERWISE...LOOKING LIKE
TEMPERATURES WILL BE DEPENDENT ON CLOUD COVER AND RAIN COVERAGE. SO
FAR...LOOKING LIKE HIGHS IN THE MIDDLE 70S TO MIDDLE 80S ON
MONDAY...COOLING INTO THE 70S TUESDAY THROUGH THURSDAY.

LOOKS LIKE SOME DRYING THURSDAY NIGHT/FRIDAY AS HIGH PRESSURE BUILDS
IN FROM CANADA. HIGHS FRIDAY EXPECTED TO REMAIN IN THE 70S.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1147 PM CDT FRI AUG 22 2014

THE MAIN FOCUS IS ON THE POTENTIAL FOR FOG TONIGHT AND HOW MUCH
THE EXPANSIVE HIGH LEVEL CLOUD COVER WILL HOLD THE FOG BACK FROM
FORMING. THIS WIDESPREAD CLOUD COVER HAS KEPT TEMPERATURES FROM
FALLING MUCH THIS EVENING...BUT DEW POINT DEPRESSIONS REMAIN
FAIRLY LOW...SO AM EXPECTING THAT THE FOG WILL STILL FORM...JUST
LATER THAN PREVIOUSLY THOUGHT. SHOULD THE CLOUD COVER REMAIN AS
THICK AS IT CURRENTLY IS...THEN THERE MAY BE MORE CONCERNS THAT
THE FOG DOES NOT DEVELOP. DUE TO THIS UNCERTAINTY...BACKED OFF ON
THE 1/4SM FOG AND UPPED CONDITIONS A BIT. BEYOND THE
FOG...QUESTIONS REMAIN ABOUT THE NEXT ROUND OF CONVECTION THAT
COULD COME THROUGH IN THE AFTERNOON AS A LEAD IMPULSE MOVES INTO
THE REGION. A BRIEF PERIOD OF SHOWERS/STORMS WILL BE POSSIBLE
WHICH COULD CAUSE CONDITIONS TO DROP BACK DOWN TO MVFR/IFR.

&&

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

$$

UPDATE...HALBACH
SHORT TERM...DAS
LONG TERM....DAS
AVIATION...HALBACH


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.