Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 061727
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1227 PM CDT MON JUL 6 2015

.UPDATE...
ISSUED AT 1041 AM CDT MON JUL 6 2015

A MESSY FORECAST FOR THE REST OF TODAY.

SHOWERS AND THUNDERSTORMS DEVELOPED IN THE 7-9 AM TIME PERIOD
FROM WESTERN WI INTO EASTERN IA...ALONG THE NOSE OF 925-850MB
MOISTURE TRANSPORT. THE STRONGEST CONVECTION WAS LOCATED IN
IOWA...CO-LOCATED WITH THE GREATER INSTABILITY. THIS AREA OF
CONVECTION WAS NOT HANDLED WELL BY ANY MODEL TO THIS POINT...AND
THE NET RESULT HAS BEEN TO STABILIZE CONDITIONS MORE THAN
EXPECTED. OTHER SHOWERS PERSIST ACROSS IOWA INTO MINNESOTA AND
NORTHWEST WI...ASSOCIATED WITH A BROAD AREA OF LOW TO MID LEVEL
FRONTOGENESIS AHEAD OF TROUGHING IN WESTERN MN...AND RIGHT
ENTRANCE REGION FORCING FROM AN UPPER JET STREAK IN NORTHERN MN.
PLENTIFUL MOISTURE IN PLACE AS WELL TO AID IN THAT SHOWER
GENERATION WITH PRECIPITABLE WATER IN THE 1.5-2 INCH RANGE.

AS THE UPPER TROUGH OVER WESTERN MN CONTINUES ITS MARCH
EAST...SO DOES THE BROAD AREA OF LOW TO MID LEVEL FRONTOGENESIS.
WITH AMPLE MOISTURE IN PLACE...WE SHOULD SEE CLOUDS AND SHOWERS
CONTINUE TO GENERATE. THUS...A WET DAY REMAINS ON TAP.
HOWEVER...THERE ARE PLENTY OF NEGATIVES FOR DEEPER CONVECTION /
SEVERE WEATHER AND HEAVY RAINFALL...

1. THE RIGHT ENTRANCE REGION HELPING TO FORCE CURRENT ACTIVITY IS
PROGGED TO LIFT TO THE NORTHEAST...SO WE LOSE THAT FORCING.

2. WITH PLENTY OF CLOUDS AND SHOWERS...INSTABILITY WILL BE HARD TO
BUILD AHEAD OF THE COLD FRONT MARCHING EASTWARD...CURRENTLY
FROM MINNEAPOLIS TO FARMINGTON MN. LESSER INSTABILITY WILL BOTH
IMPACT POTENTIAL FOR DEEPER CONVECTION AND HEAVY RAIN.

3. 700-500MB LAPSE RATES ARE MOSTLY MOIST ADIABATIC...NOT
FAVORABLE FOR DEEP CONVECTION/SEVERE WEATHER.

4. THE ONGOING CONVECTION IN EASTERN IA INTO EASTERN WI STABILIZED
CONDITIONS AHEAD OF THE FRONT...WHICH SHORTENS THE TIME WINDOW FOR
DESTABILIZATION PRIOR TO THE FRONT ARRIVAL.

THE NCEP HRRR AND GSD/BOULDER HRRR MODEL RUNS HAVE BEEN ABOUT THE
ONLY MODELS HAVING A DECENT HANDLE ON ONGOING ACTIVITY. THEY BOTH
SUGGEST MAINLY A SHOWERY DAY WITH SOME THUNDERSTORMS
POSSIBLE...PARTICULARLY IN NORTHEAST IA AND FAR SOUTHWEST WI WHERE
AN OPPORTUNITY EXISTS FOR SOME CAPE TO BUILD PRIOR TO THE FRONTAL
ARRIVAL LATE TODAY. HAVE CUT BACK THUNDERSTORM POTENTIAL OVERALL.

AFTER COORDINATION WITH SPC...THE PLAN IS FOR MOST IF NOT ALL OF
THE SLIGHT RISK TO BE REMOVED ON THE 1630Z DAY 1 UPDATE. HAVE
BEGUN TAILORING SERVICES TO DECREASE THE THREAT FOR SEVERE AND
HEAVY RAINFALL.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 255 AM CDT MON JUL 6 2015

THE FORECAST QUESTIONS FOR TODAY ARE NOT IF IT WILL RAIN /IT WILL/
BUT RATHER HOW STRONG THE STORMS COULD GET...HOW BIG IS THE SEVERE
RISK...AND WHAT IS THE HEAVY RAIN OUTLOOK.

NO CHANGE IN THE MODELS...WHICH HAVE BEEN CONSISTENT/INSISTENT IN
TAKING AN UPPER LEVEL TROUGH WEST-EAST ACROSS THE CANADIAN/US BORDER
TODAY...DRIVING ITS ASSOCIATED COLD FRONT ACROSS THE UPPER
MISSISSIPPI RIVER AS IT DOES. STRONG FRONTOGENETIC RESPONSE WITH THE
BOUNDARY - SHOWN IN TIME/HEIGHT X-SECTIONS. BULK OF THE SHORTWAVE
ENERGY HOLDS NORTH...BUT 300 MB JET RIGHT ENTRANCE REGION LIKELY TO
AID IN THE UPWARD MOTIONS. PLENTY OF LIFT FOR A LINE/AREA OF SHOWERS
AND STORMS - EVIDENCED BY THE ONGOING CONVECTION TO THE WEST.
MORNING LINE WITH CONTINUE ITS TREK EAST...WITH MESO MODELS POINTING
TO A LULL IN THE CHANCES BEFORE REFIRING OF SHOWERS/STORMS ALONG THE
FRONT MOVE IN FOR THE AFTERNOON. WILL TRY AND PAINT THE RAIN CHANCES
THIS WAY.

THERE CONTINUES TO BE A DISCONNECT BETWEEN THE BEST WIND SHEAR AND
THE CAPE AXIS - A LIMITING FACTOR TO SEVERE POTENTIAL. AN AXIS OF
UPWARDS OF 2500 J/KG OF MUCAPE DEVELOPS OVER WESTERN WI BY
18Z...SHIFTING SOUTHEAST BY 00Z. AGAIN - THE NAM REMAINS MORE ROBUST
THAN THE GFS. THE DEEPER...STRONGER SHEAR LIES BEHIND THE
FRONT...BUT THERE IS SOME OVERLAP AROUND THE BOUNDARY...ESPECIALLY
IN THE 0-3 KM LAYER WHERE THE NAM AND GFS SUGGEST 30-40 KTS ARE
POSSIBLE. BUT...CLOUDS AND ANY LINGERING SHOWERS/STORMS THIS MORNING
INTO THE AFTERNOON WILL CUT INTO THAT POTENTIAL INSTABILITY. STRONG
STORMS SEEM LIKE A CERTAINTY - BUT THE SEVERE POSSIBILITIES WILL
DEPEND GREATLY ON WHETHER INSTABILITY CAN BUILD. AS THIS
MOMENT...THE HIGHER THREAT WOULD BE FROM LATE AFTERNOON INTO EARLY
EVENING - ROUGHLY 21-01Z. LOCATIONS WOULD BE FROM NORTHEAST IA INTO
CENTRAL WI.

FOR THREATS...THE HIGH 0-3 KM SHEAR SUPPORTS DAMAGING WIND POTENTIAL
IF A STORM CAN ORIENTATE ITSELF NORMAL TO THE VECTOR -
EAST/NORTHEAST MOVERS. NOT MUCH OF A DRY SUB CLOUD LAYER PER BUFKIT
SOUNDINGS...SO NO HELP FOR WINDS THERE. THINK LARGE HAIL IS GOING TO
HAVE A HARD TIME DEVELOPING. WARM CLOUD DEPTH IS VERY HIGH. BUFKIT
SOUNDINGS HAVE RATHER SKINNY / LONG CAPE. BELIEVE A LOT OF SMALL
HAIL WILL BE POSSIBLE...BUT IN EXCESS OF 1 INCH COULD HAVE A
DIFFICULT TIME. SIGNIFICANT RAINFALL REMAINS HIGH...AND MORE ON THAT
IN THE HYDROLOGY SECTION BELOW.

ONE LAST THING...SEE SOME ISOLATED TORNADO POTENTIAL...MORESO FOR
SOUTHWEST WI PER LATEST MODELS. NAM/GFS PEG 20+ KTS OF 0-1 SHEAR BY
LATE AFTERNOON OVER NORTHEAST IA/SOUTHWEST WI...WITH 0-1KM CAPE
UPWARDS OF 200 J/KG. MESO MODELS PLACE A SFC LOW OVER CENTRAL IA BY
00Z THIS EVENING...WITH THE COLD FRONT AND POTENTIALLY OTHER SFC
BOUNDARIES IN THE AREA. DOESN/T APPEAR TO BE ENOUGH SHEAR TO SUPPORT
SUPERCELLS...BUT IF A STORM CAN ATTACH ITSELF TO A BOUNDARY...THE
POTENTIAL TO INGEST ENOUGH HELICITY TO SPIN SOMETHING UP IS
THERE. IT NOT A GREAT THREAT...BUT IT BEARS WATCHING.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 255 AM CDT MON JUL 6 2015

MODELS CONTINUE TO SUGGEST THE ZONAL UPPER LEVEL FLOW SHIFTS TO
BROAD RIDGING ACROSS THE CENTRAL U.S. BY THE UPCOMING WEEKEND.
TRENDS FAVOR KEEPING MOST RIPPLES IN THE FLOW NORTH OR SOUTH OF THE
LOCAL AREA...WITH PERHAPS A SHORTWAVE TOPPING THE RIDGE FRI
NIGHT/SAT. NOT A LOT OF CONSISTENCY IN THIS STEAD THOUGH...WITH THE
GFS/GEM/EC ALL SHOWING VARYING DEGREES OF FLIP FLOPPING WITH PLACING
SMALL CHANCE HERE AND THERE. THE LIKELIHOOD OF A DRY WORK WEEK AFTER
MONDAY GETS AN UPTICK AS A RESULT. CONSENSUS SOLUTION THROWING IN
SOME POPS FOR FRI-SUN WITH GFS/EC SUGGESTING RIDGE RUNNERS BRINGING
A SHOWER/STORM THREAT. CONFIDENCE NOT HIGH...BUT WILL STAY WITH
CONSENSUS FOR NOW.

WITH THE ANTICIPATED SHIFT TO RIDGING A LOFT BY THE WEEKEND...LOOK
FOR TEMPS TO RETURN OR RISE ABOVE THE SEASONABLE NORMALS. IT COULD
GET RATHER STEAMY TOO AS THE GFS AND EC SUGGEST MID 60S DEWPOINTS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1227 PM CDT MON JUL 6 2015

PRECIPITATION HAS ENDED AT THE TAF SITES...BUT MORE PRECIPITATION
IS ON ITS WAY FROM CENTRAL MN...ASSOCIATED WITH A COLD FRONT
MARCHING SOUTHEASTWARD. MOST OF THE PRECIPITATION IS SHOWERS DUE
TO NOT ENOUGH INSTABILITY TO GROW THE SHOWERS INTO STORMS. AS
SUCH...ALL THUNDER HAS BEEN PULLED FROM THE TAFS. LOOK FOR THE
SHOWERS TO CROSS RST BETWEEN 19-21Z AND AT LSE FROM 20-23Z.
VISIBILITY REDUCTIONS SHOULD BE MAINLY VFR...THOUGH A BRIEF DROP
TO MVFR IS POSSIBLE. CEILINGS ARE THE BIGGER ISSUE WITH AN MVFR
CLOUD DECK IN PLACE AT LSE AND MORE ON THE WAY JUST WEST OF RST.
BOTH TAF SITES SHOULD SETTLE INTO MVFR CONDITIONS FOR THE REST OF
THE AFTERNOON...LINGERING INTO A GOOD PORTION OF THE EVENING AS
THE COLD FRONT PASSES AND TRAPS LOW LEVEL MOISTURE. DRYING
EVIDENCED BY CLEARING ACROSS NORTHWEST MINNESOTA WILL MAKE INTO
THE TAF SITES LATE IN THE EVENING...ACCOMPANIED BY A 7-15 KT
NORTHWEST WIND...TO HELP SCATTER OUT THE MVFR CLOUDS. THE VFR
CONDITIONS LOOK TO PERSIST INTO TUESDAY AS HIGH PRESSURE OVER THE
WESTERN DAKOTAS BUILDS IN.

&&

.HYDROLOGY...
ISSUED AT 1227 PM CDT MON JUL 6 2015

ALTHOUGH THE ENVIRONMENT IS GENERALLY FAVORABLE FOR HEAVY
RAIN...THE CONCERN FOR HEAVY RAIN HAS DIMINISHED DUE TO THE
LOWERED CONFIDENCE OF THUNDERSTORMS OCCURRING. MUCH OF THE AREA IS
ENCOMPASSED BY CLOUDS...WITH SHOWERS NOW BEGINNING TO MARCH IN
FROM CENTRAL MN. THE COMBINATION OF BOTH ARE HOLDING BACK
INSTABILITY...THUS LIMITING THUNDERSTORM DEVELOPMENT. SHOULD ANY
THUNDERSTORMS DEVELOP LATER THIS AFTERNOON...MOST LIKELY IN
NORTHEAST IA INTO FAR SOUTHWEST WI...SOME BRIEF HEAVY RAINS ARE
POSSIBLE BUT FLOODING DOES NOT APPEAR TO BE A CONCERN.

&&

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

$$

UPDATE...AJ
SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION...AJ
HYDROLOGY...AJ



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