Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 271504
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1004 AM CDT WED APR 27 2016

.UPDATE...
ISSUED AT 1004 AM CDT WED APR 27 2016

HAVE UPDATED THE FORECAST TO BETTER REPRESENT INCOMING RAIN BAND
FROM THE SOUTH TODAY...AND HOW IT ROTATES NORTHWARD. THIS BAND IS
WELL REPRESENTED BY LOW-LEVEL WARM ADVECTION AND FRONTOGENESIS ON
MANY LEVELS /PER 27.14Z RAP/ AND IS EXPECTED TO CONTINUE TO ROTATE
NORTHEAST TOWARD WI THROUGH THE DAY. LIGHTNING DATA IS ACTIVE IN
THE LINE CURRENTLY AND DID ADD A MENTION OF THIS TO NERN IA AND
EXTREME SWRN WI.

WITH VERY DRY EASTERLY FLOW BELOW ABOUT 800MB ACROSS WI...THE
CHALLENGE IS HOW FAR NORTH WILL THE BAND PRECIPITATE AND WILL IT
SLOW. WOULD THINK THE LATER IDEA OF SLOWING OR DISSIPATING BANDS
IS THE MOST VALID. EXPECT THERE TO BE ADDITIONAL DEVELOPMENT OF
BANDS OR A BROADENING BAND WITHIN THE BROADER FRONTOGENESIS REGION
AS IT ROTATES NORTH...WITH LEADING EDGE DISSIPATION. CONFIDENCE
IS HIGHEST IN NERN IA FOR RAINFALL BUT DRY AIR IN PLACE QUICKLY
REDUCES CONFIDENCE MOVING NORTHEAST.

THE FORCING WILL SHIFT NORTH TODAY AND BY 00Z/7 PM BE LOCATED
ROUGHLY ALONG A KMSP-KMSN ROUGH LINE...ALONG WITH A LIGHT RAIN
BAND. AREAS SOUTH SHOULD MOVE TOWARD A DRIER EVENING /NERN IA/ AND
HAVE LOWERED THE RAIN CHANCES TO BEGIN THE DRYING TREND THERE.
WILL ASSESS THE POST MIDNIGHT TIME FRAME A BIT LATER AS TRENDS IN
OBSERVATIONS DEVELOP.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 324 AM CDT WED APR 27 2016

MAIN CONCERN TODAY IS THE ONSET OF RAIN AS THE LARGE COMPLEX
APPROACHES FROM THE SOUTHWEST. DRY EASTERLY FLOW AHEAD OF IT IS
SLOWING THE EASTWARD PROGRESS...AND MODEL TRENDS HAVE ALSO SLOWED
THE PROGRESSION. MOST OF THE FORECAST TWEAKS THIS MORNING HAVE
RELATED TO SLOWING DOWN WHEN THE RAIN WILL START...AND HOW FAR
NORTH IT EVENTUALLY GETS BEFORE STALLING OUT. LOOKING AT A PLETHORA
OF SHORT RANGE MESO MODELS...THE EARLIEST THE RAIN REACHES THE FAR
SOUTHWEST COUNTIES OF OUR SERVICE AREA IS BETWEEN 16-18Z. IT WILL BE
AFTERNOON BEFORE THE RAIN BEGINS TO IMPACT THE MAJORITY OF THE LOCAL
AREA...AND CLOSER TO SUNSET BEFORE IT REACHES OUR FAR NORTHERN
EXTENT. THE STRONGEST FORCING AND INSTABILITY REMAINS CONFINED WELL
TO OUR SOUTH...SO THE RISK FOR ANY THUNDER IS TOO LOW TO WARRANT A
MENTION. BUT THE FRONTOGENETIC AND ISENTROPIC FOCUS IS RATHER
GOOD...AND ANTICIPATE THAT BANDS OF RAIN WILL DEVELOP AND REMAIN
QUASI-STATIONARY IN THE VICINITY OF THE I-90 CORRIDOR LATER TODAY.
CONVECTION TO THE SOUTH WILL LIKELY STEAL MUCH OF THE MOST
SIGNIFICANT MOISTURE SUPPLY...BUT AMOUNTS BETWEEN 0.50 AND 1.00
INCHES LOOK LIKE A GOOD BET FROM NORTHEAST IOWA AND SOUTHWEST
WISCONSIN...INTO ADJACENT PORTIONS OF SOUTHEAST MINNESOTA. RAIN
WILL CONTINUE THROUGH TONIGHT AND INTO THURSDAY BEFORE TAPERING OFF
BY EVENING.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 324 AM CDT WED APR 27 2016

AREA WILL BE BETWEEN SYSTEMS ON FRIDAY WITH BRIEF RIDGING PROVIDING
FOR A DRY DAY. WE SHOULD SEE SOME SUN AS WELL...SO DESPITE COOL
NORTH TO NORTHEAST FLOW...HIGHS SHOULD APPROACH 60 DEGREES. BUT THE
NEXT IN A PARADE OF CLOSED SYSTEMS IS ALREADY PLOWING THROUGH THE
DESERT SOUTHWEST BY THIS TIME...AND IT WILL MOVE TOWARD OUR AREA FOR
THE WEEKEND. THE OVERALL SETUP IS NEARLY IDENTICAL...WITH A LARGE
RAIN SHIELD SPREADING OUT AHEAD OF IT. AND ONCE AGAIN THE ONSET WILL
BE PROBLEMATIC WITH DRY EASTERLY FLOW AHEAD OF THE APPROACHING RAIN.
BUT THE MODELS HAVE BEEN SHOWING MORE DIVERGING SIGNALS IN THE MOST
RECENT RUNS. PREVIOUSLY...A WEAKENING CLOSED LOW WAS EXPECTED TO
MOVE ACROSS THE REGION THROUGH THE WEEKEND PROVIDING RAINY AND COOL
WEATHER. BUT THERE ARE SOME INDICATIONS NOW THAT THE MAIN
CIRCULATION MAY RETROGRADE BACK INTO THE TROUGH AS A LARGER PIECE
OF ENERGY DIGS INTO THE BACK SIDE. IF THIS OCCURS...WE MAY NOT SEE
MUCH RAIN AT ALL...SO WE WILL HAVE TO MONITOR THIS. FOR NOW DID
LOWER THE RAIN CHANCES...BUT DID NOT REMOVE THEM YET WITH THE
UNCERTAINTY. IT IS LOOKING LIKE A PATTERN SHIFT WILL TAKE PLACE BY
THE MIDDLE OF NEXT WEEK...WITH A MORE HIGHLY AMPLIFIED FLOW REGIME.
THIS LEADS TO THE POSSIBILITY OF A LARGE HUDSON BAY LOW TO DROP INTO
THE GREAT LAKES REGION...LEADING TO A COOL PERIOD. TIME WILL TELL...

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 634 AM CDT WED APR 27 2016

RATHER BENIGN WEATHER EXPECTED INTO EARLY AFTERNOON WITH JUST SOME
THICKENING MID OR HIGH CLOUDS AND INCREASINGLY GUSTY EASTERLY
WINDS...WITH SOME GUSTS TO 30 KNOTS OR BETTER EXPECTED FOR KRST.
PERIODS OF SHOWERS WILL MAKE A VALIANT ATTEMPT TO WORK NORTHWARD
INTO LATE AFTERNOON AND THROUGH TONIGHT...BUT THERE REMAINS SOME
QUESTION ABOUT JUST HOW WIDESPREAD PRECIPITATION WILL BECOME GIVEN
JUST HOW MUCH DRY AIR IS IN PLACE ACROSS THE AREA. SHOULD SHOWERS
BECOME MORE WIDESPREAD FASTER THAN EXPECTED (OR LIFT FARTHER
NORTH)...CEILINGS MAY DIP TOWARD MVFR LEVELS BY LATE EVENING.
HOWEVER...BASED ON CURRENT TRENDS IT APPEARS ANY MVFR CONDITIONS
WILL HOLD OFF UNTIL AFTER MIDNIGHT.


&&

.HYDROLOGY...
ISSUED AT 324 AM CDT WED APR 27 2016

SIGNIFICANT RAINFALL OVER THE PAST SEVERAL DAYS UPSTREAM OF THE
REGION WILL PRODUCE RISES ON THE MISSISSIPPI RIVER OVER THE NEXT FEW
WEEKS. CURRENT PROJECTIONS SUGGEST THE RIVER WILL BE RISING TO
WITHIN 2-4 FEET OF FLOOD STAGE BY EARLY MAY. THOSE WITH INTERESTS
ALONG THE RIVER SHOULD MAKE PREPARATIONS FOR HIGHER WATER LEVELS
IN EARLY MAY.

&&

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

$$

UPDATE...BAUMGARDT
SHORT TERM...MW
LONG TERM...MW
AVIATION...LAWRENCE
HYDROLOGY...MW



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