Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 061131
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
631 AM CDT MON JUL 6 2015

.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 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 631 AM CDT MON JUL 6 2015

A COLD FRONT WILL PUSH SHOWERS AND THUNDERSTORMS THROUGH THE AREA
TODAY. LOOK FOR PREVALENT SHRA/TS AT KLSE AND KRST THROUGH THIS
MORNING WITH PERHAPS A BIT OF A LULL LATER THIS MORNING INTO EARLY
THIS AFTERNOON. LOOKING FOR REDEVELOPMENT OF STORMS ALONG THE COLD
FRONT IN THE 20-21Z TIME FRAME...THEN CLEARING THE AREA AFTER 00Z.
OTHERWISE...PREVALENT MVFR CONDITIONS EXPECTED TODAY WITH BOUTS OF
IFR. LOOK FOR VFR CONDITIONS AFTER 23Z AT KRST AND 04Z AT KLSE AS
DRIER CANADIAN AIR FILTERS INTO THE REGION BEHIND THE COLD FRONT.

&&

.HYDROLOGY...
ISSUED AT 255 AM CDT MON JUL 6 2015

MODELS STAY THE COURSE WITH PAINTING EXCELLENT CONDITIONS FOR
EFFICIENT RAIN PRODUCERS AND A HEAVY RAIN POTENTIAL TODAY. PWS
EXCEED 2 INCHES...WARM CLOUD DEPTH OF 4000+ M...AND A STEADY INFLUX
OF WARM SOUTHERLY AIR RICH IN MOISTURE. AMPLE LIFT ALONG AND POST
THE COLD FRONT TO PUT THIS MOISTURE TO GOOD USE. NAEFS ANOMALIES
STILL RIGHT AROUND +3 TOO. RAINFALL RATES WILL BE HIGH IN THE
STRONGER STORMS - KEY FOR URBANIZED FLOODING. THANKFULLY...THE
NORTHEAST-SOUTHWEST ORIENTATION AND GENERAL PROGRESSIVE TREND OF THE
SHOWERS/STORMS WITH THE SYSTEM SHOULD LIMIT THE POTENTIAL FOR
TRAINING STORMS. BUT IF THEY WOULD OCCUR...FLOODING QUICKLY BECOMES
A CONCERN. THE HIGHER THREAT SHOULD BE THIS AFTERNOON/EVENING.
DOWNWARD TREND IN STORM INTENSITY AS THE CURRENT STORMS TO THE WEST
MOVE IN WILL GET A BUMP UP FOR THE AFTERNOON AS INSTABILITY BUILDS
AHEAD OF THE LINE. OVERALL...LOCALIZED 2-3 INCH AMOUNTS ARE EASILY
WITHIN REACH.

&&

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

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION...DAS
HYDROLOGY....RIECK


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