Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 291732
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1232 PM CDT MON SEP 29 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 300 AM CDT MON SEP 29 2014

SCATTERED SHOWERS TRACKING ACROSS NORTHERN MN EARLY THIS
MORNING...FORMING IN A REGION OF 600-700 MB FRONTOGENETIC FORCING
AND ON THE LEADING EDGE OF A SHORTWAVE TROUGH SINKING SOUTHEAST INTO
NORTHERN MN. A FEW OTHER SHOWERS HAVE POPPED UP OVER PARTS OF SD AND
WESTERN IA...ALONG THE NOSE OF A BROAD REGION OF 850 MB MOISTURE
TRANSPORT.

WOULD EXPECT THE PCPN TO THE WEST SHOULD DIMINISH AND/OR HOLD THERE
AS THE MOISTURE TRANSPORT SHIFTS A BIT WEST DURING THE DAY.

MEANWHILE...THE SHORTWAVE TROUGH WILL CONTINUE TO DROP
SOUTHEAST...SPINNING ACROSS NORTHERN WI THIS AFTERNOON...AND EXITING
INTO MICH TONIGHT. DECENT RESPONSE IN THE LOW/MID LEVEL
FRONTOGENETIC FIELDS TIED TO THE SHORTWAVE...BUT SOME HINTS THAT
THERE COULD BE SOME 800-900 MB FRONTOGENETIC RESPONSE ON THE WESTERN
FRINGES OF THE SHORTWAVE/S ASSOCIATED FRONTAL BOUNDARY.
HOWEVER...THIS IS UNDER A SHORTWAVE RIDGE...WHICH WILL ACT AS AN
INHIBITOR TO CONVECTION. CONFIDENCE HIGH THAT THE I-94 CORRIDOR
NORTH-EAST WILL SEE A PERIOD OF SHOWERS TODAY...BUT HOW FAR THESE
RAIN CHANCES EXTEND WEST IS QUESTIONABLE. THINK AT LEAST SLIGHT
CHANCES ARE STILL WARRANTED GIVEN THE BOUNDARY/LOW LEVEL
CONVERGENCE...AND WILL HOLD WITH THESE FOR NOW.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 300 AM CDT MON SEP 29 2014

COOLER...WETTER PATTERN TAKES OVER THIS WEEK AS THE RIDGE GIVES WAY
TO A MORE ACTIVE-CYCLONICALLY FAVORED FLOW.

MODELS ALL IN GOOD AGREEMENT WITH DRIVING 3 SHORTWAVE TROUGHS ACROSS
THE UPPER MISSISSIPPI RIVER VALLEY...SWINGING THE AXIS OF THE MEAN
TROUGH ACROSS THE REGION FRI AFTERNOON.

THE FIRST WILL ORIGINATE AS A CLOSED 500 MB LOW OVER THE DESERT
SOUTHWEST...LIFTING ACROSS THE NORTHERN PLAINS TUE NIGHT. THE NEXT
WILL SLIP IN BEHIND THIS FIRST WAVE...MOVING OUT OF THE PAC NW AND
ACROSS THE REGION ON THU. THE LAST SHORTWAVE WILL DROP SOUTHEAST OUT
OF WESTERN CANADA AND ACROSS THE UPPER MISSISSIPPI RIVER VALLEY ON
FRI. IT WILL HELP CARVE OUT/DEEPEN THE UPPER LEVEL TROUGH AS IT
DOES.

WHILE THE FIRST UPPER LEVEL FEATURE WILL STAY WEST/NORTH OF THE
AREA...BUT IT WILL DRIVE A LOW LEVEL FRONTOGENETIC/WARM AIR
ADVECTIVE ARM NORTHEAST ACROSS THE REGION ON WED. BROAD MOISTURE
TRANSPORT WILL FUEL WHAT SHOULD BE A LONG NORTH-SOUTH RUNNING AREA
OF SHOWERS. SOME WEAK INSTABILITY INDICATED VIA THE NAM AND
GFS...BUT MOST OF THIS HOLDS ACROSS IA. COULD SEE A FEW
THUNDERSTORMS...BUT THE FARTHER NORTH YOU GO...THE LESSER THESE
CHANCES.

THE NEXT SHORTWAVE SWEEPS IN RIGHT BEHIND THIS FIRST...AND IS
PROGGED TO BE MUCH WEAKER. IT WILL GRADUALLY CATCH UP TO THE
FRONTOGENETIC/WARM AIR ADVECTIVE BAND...BUT WELL EAST OF THE LOCAL
FORECAST AREA. COULD HAVE SOME SATURATION ISSUES HERE TOO...AS
MODELS SUGGEST DECENT MID LEVEL DRYING BEHIND THE RAIN BAND.
SO...IMPACTS FROM THIS SHORTWAVE COULD BE MINIMAL.

THE CANADA SHORTWAVE IS NEXT...AND LOOKS TO PACK A BIT MORE OF A
PUNCH. STRONG 300-500 MB QG CONVERGENCE WITH THIS FEATURE...WHICH
EXTENDS DOWN IN THE ATMOSPHERE...BUT BECOMES CONSIDERABLY WEAKER AS
IT DOES. DOESN/T LOOK LIKE THIS SHORTWAVE WILL HAVE A LOT OF LOW
LEVEL SUPPORT. IT WILL BRING ITS OWN SATURATION THOUGH...AND SHOULD
PROVIDE ENOUGH LIFT FOR AN AREA OF SHOWERS. CURRENT MODELS TRENDS
WOULD KEEP MOST OF THIS ACTIVITY ACROSS NORTHERN PARTS OF MN/WI.

ON THE WHOLE...THE BEST RAIN CHANCES ACROSS THE FORECAST AREA WILL
COME TUE NIGHT THROUGH WED NIGHT.

WITH THIS SHIFT AWAY FROM THE STRONG UPPER LEVEL RIDGE OF RECENT
DAYS...COOLER...MORE SEASONABLE AIR WILL RETURN. FRI AND SAT LOOK TO
BE THE COLDEST OF THE WEEK.

NEXT WEEKEND IS GOING TO LOOK A LOT DIFFERENT THAN THE WARM AND
SUNNY ONE THAT JUST WRAPPED UP. CYCLONIC FLOW A LOFT WILL CONTINUE
WITH WEAK HIGH PRESSURE AT THE SURFACE. SOME HINTS THAT A RIPPLE IN
THE UPPER LEVEL FLOW COULD SPIN ACROSS THE REGION...WHICH COULD
BRING SOME LIGHT RAIN CHANCES TO THE NORTH. TEMPERATURES WILL HOLD
AT OR BELOW THE EARLY OCTOBER NORMALS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1232 PM CDT MON SEP 29 2014

A COLD FRONT CONTINUED TO PUSH SOUTH ACROSS THE AREA EARLY THIS
AFTERNOON. A BROAD AREA OF MVFR CLOUDS COVERED MUCH OF MN/WI
BEHIND THE FRONT...WITH SOME LCL IFR CIGS/VSBYS IN BR RIGHT BEHIND
THE FRONT. THE IFR CIGS/VSBYS ABOUT TO CLEAR THE KRST AREA AS SOME
DRIER SFC-925MB AIR AND STRONGER SUBSIDENCE BEHIND THE FRONT
ARRIVES. BAND OF POST-FRONTAL -SHRA WAS SPREADING SOUTHEAST ACROSS
MAINLY WI...AND MAY CLIP THE KLSE AREA. INCLUDED A 19-22Z VCSH
MENTION AT KLSE FOR NOW.

THE LOWER CLOUDS/MOISTURE STUCK IN/UNDER A STRONG AND STRENGTHENING
INVERSION NEAR 900MB TONIGHT INTO TUE. ONCE THE MID LEVEL SHORTWAVE
AND STRONGEST LOW LEVEL COLD ADVECTION PASS...SUBSIDENCE WEAKENS.
APPEAR THE MOISTURE/MVFR CLOUDS WILL PERSIST THRU THE NIGHT INTO TUE
MORNING. THESE CLOUDS AND NORTHEAST GRADIENT WINDS OF 5-7KTS WILL
LIMIT THE RADIATIONAL VALLEY FOG POTENTIAL TONIGHT AND LEFT ANY LATE
NIGHT/EARLY MORNING BR OUT OF BOTH THE TAFS. WILL REMAIN OPTIMISTIC
THAT SOME DIURNAL WARMING/MIXING TUE MORNING AND ANTI-CYCLONIC FLOW
WITH THE SFC-925MB RIDGE AXIS WILL HELP BREAK UP THE LOWER CLOUD
DECK.

&&

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

$$

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



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