Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 262309
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
609 PM CDT SUN OCT 26 2014

.SHORT TERM...(TONIGHT THROUGH TUE NIGHT)
ISSUED AT 245 PM CDT SUN OCT 26 2014

FORECAST FOCUS IS ON THE RAIN CHANCES FROM LATE TONIGHT INTO
TUE...WITH A VARIETY OF WEATHER ELEMENTS PLAYING A ROLL IN WHERE AND
WHEN.

TONIGHT...LOW LEVEL MOISTURE TRANSPORT RAMPS UP...WITH A 40 KT 850
MB JET NOSING INTO WESTERN WI BY 06Z...TRANSITIONING NORTHEAST BY
12Z. LOW LEVEL WARM AIR ADVECTION LEADS ITS PARENT SHORTWAVE TROUGH
INTO THE UPPER MISSISSIPPI RIVER VALLEY...925-850 MB MAX AROUND 06Z.
SOME NORTHWEST-SOUTHEAST RUNNING FRONTOGENETIC RESPONSE ALONG 900
MB...IN THE VICINITY OF THE NOSE OF THE JET AND LOW LEVEL WARM PUSH.
THIS TOO IS MAXED AT 06Z. GFS/NAM MUCAPES SUGGEST 500+ J/KG OF
MUCAPE POSSIBLE OVERNIGHT FOR THE LOCAL AREA. THERE WOULD SEEM TO BE
PLENTY OF LIFT AND INSTABILITY TO WARRANT AREAS OF SHOWERS AND
THUNDERSTORMS. HOWEVER...DEPTH OF MOISTURE MIGHT PAINT A DIFFERENT
PICTURE.

LOOKING AT A SOUTHWEST-NORTHEAST RUNNING X-SECTION DEPICTS A
SHALLOW INCREASE IN SATURATION TONIGHT...HOLDING UNDER 700 MB UNTIL
YOU WORK INTO NORTHERN/NORTHEAST WI. BUFKIT SOUNDINGS HAVE THIS
SATURATION UNDER AN APPRECIABLE INVERSION...WITH OMEGA CO-LOCATED IN
THE MOISTURE. HOWEVER...THE INSTABILITY IS ABOVE THE INVERSION...AND
THE CLOUD LAYER MIGHT NOT BE ABLE TO TAP THIS SOURCE OF LIFT AS A
RESULT - AT LEAST FOR PARTS OF THE AREA. IN FACT...MOST OF THE
SOUNDINGS ACROSS THE AREA SUGGEST DRIZZLE WOULD BE THE PCPN TYPE.
DEEPER CLOUD LAYER AND GREATER POTENTIAL TO RESOURCE THE ELEVATED
INSTABILITY LIES TO THE NORTHEAST...GENERALLY I-94 AND EAST/NORTH.
THINK THE SCENARIO WILL PLAY OUT WITH A 2-4 HOUR WIND OF A
SHOWER/STORM THREAT...ON THE NOSE OF THE LOW LEVEL JET...WITH
GREATER PROBABILITIES OF DRIZZLE POST THE CONVECTIVE BAND. WILL
STICK WITH SHOWER MENTION FOR ALL PCPN CHANCES FOR SIMPLICITY.

THE SYSTEM/S SFC COLD FRONT MOVES IN FROM THE WEST ON MONDAY...WITH
THE LEADING EDGE OF THE UPPER LEVEL SHORTWAVE TROUGH BUSTING INTO
WESTERN MN BY 00Z. RIBBON OF LOW LEVEL MOISTURE TRANSPORT RUNS ALONG
AND SOUTH OF THE FRONT...PARALLEL TO ITS ORIENTATION...WITH UP TO
500 J/KG OF MUCAPE DEVELOPING JUST SOUTH OF THE BOUNDARY. ANTICIPATE
CONVECTION DEVELOPING ALONG AND SOUTH OF THE FRONT...WITH
THE BEST CHANCES JUST SOUTH/EAST OF THE LOCAL AREA.

TO THE NORTH...SFC LOW CONGEALS INTO ONE MAIN CENTER AS IT LIFTS
INTO SOUTHEAST CANADA. WESTWARD HANGING SFC TROUGH OFF THE LOW LOOKS
TO HOLD ACROSS NORTHERN MN/SOUTHERN CANADA. BITS OF UPPER LEVEL
ENERGY WILL SPIN AROUND THE UPPER LEVEL/TROUGH. EXPECT SOME PCPN
RESPONSE FROM THESE PIECES OF ENERGY AND THE SFC TROUGH. RH FIELDS
HOLD THE DEEPER SATURATION TO THE NORTH...WITH THE DEEPER LIFT.
WHILE THE MOST FAVORABLE CONDITIONS FOR PCPN WILL LIE NORTH AND THEN
SOUTH WITH THE FRONT...ENOUGH UNCERTAINTY AND WHERE VARIOUS BITS OF
UPPER LEVEL ENERGY AND WHERE THE SFC FRONT WILL BY AT XX TIME THAT
SMALL CHANCES ARE WARRANTED FOR MOST OF THE AREA MONDAY/MONDAY NIGHT
/GREATER SOUTH-NORTH/.

MEANWHILE...ISENTROPIC UPGLIDE INDICATED ON THE 295 F SFC FOR THE
BETTER PART OF MON MORNING/EARLY AFTERNOON...CO-LOCATED WITH THE LOW
SATURATION. SIGNAL STILL FAVORS DRIZZLE. HAVE INCREASED RAIN CHANCES
IN THE I-94 CORRIDOR AS A RESULT. AGAIN...KEEPING PTYPE AS SHOWERS
FOR SIMPLICITY. THAT SAID...THIS COULD UNFOLD INTO AN AREAS OF
DRIZZLE - LITTLE IF ANY ACCUMULATION - TYPE SCENARIO.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 245 PM CDT SUN OCT 26 2014

GFS/ECMWF/GEM ALL IN GOOD AGREEMENT WITH SLIDING AN UPPER LEVEL
SHORTWAVE TROUGH ACROSS THE NORTHERN GREAT LAKES AFTER 06Z FRI.
WHILE TIMING WITH THE VARIOUS MODELS ARE COMPARABLE...THERE ARE
DIFFERENCES WITH HOW FAR WEST THE MAIN PIECE OF ENERGY WILL BE. THE
GEM AND GFS CURRENTLY FAVOR TRACKING THE SHORTWAVE INTO MICH...WHICH
WOULD KEEP THE BULK OF ANY RESULTING PRECIPITATION EAST OF THE
FORECAST AREA. THE 00Z EC WAS A BIT FARTHER WEST...AND THUS BRINGS A
SWATH OF PCPN INTO THE REGION. HOWEVER...12Z CAME IN WITH A SOLUTION
MORE LIKE THE GEM/GFS. MODELS HAVE BOUNCED AROUND A BIT WITHIN
THEMSELVES...NOT LENDING A LOT OF CONFIDENCE IN WHETHER THE WEST OR
EASTERN SOLUTION IS BETTER. WILL STICK WITH CONSENSUS SOLUTION FOR
NOW.

COLDER AIR RETURNS MID WEEK AND WILL STICK AROUND INTO THE WEEKEND
AS THE REGION COMES UNDER THE INFLUENCE OF AN UPPER LEVEL TROUGH.
EXPECTING AT OR BELOW NORMALS TEMPS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 609 PM CDT SUN OCT 26 2014

LEADING EDGE OF THE ISENTROPIC UP GLIDE HAS RESULTED IN SOME VFR
CEILINGS DEVELOPING WITH SOME SHOWERS/STORMS OVER WESTERN
WISCONSIN. EXPECT THAT THESE SHOWERS/STORMS WILL CONTINUE TO
REMAIN EAST OF THE TAF SITES THIS EVENING AS THE ISENTROPIC UP
GLIDE CONTINUES TO ADVANCE NORTHEAST. THE FORCING WILL INCREASE
OVERNIGHT AS A SHORT WAVE TROUGH APPROACHES FROM THE SOUTHWEST.
ADDITIONAL SHOWERS ARE EXPECTED TO DEVELOP AHEAD OF THIS SHORT
WAVE TROUGH...BUT AGAIN EXPECT THAT MOST OF THIS ACTIVITY WILL BE
OVER WISCONSIN WHERE THE BETTER ISENTROPIC UP GLIDE WILL RESIDE.
THE 26.20Z HRRR SUGGESTS SOME OF THESE SHOWERS COULD BE CLOSE TO
KLSE SO WILL INCLUDE A VCSH STARTING AROUND 06Z. THE BEST CHANCE
FOR SOME PRECIPITATION MAY COME LATE TONIGHT INTO MONDAY MORNING
AS A SURFACE LOW APPROACHES FROM THE SOUTHWEST WITH THE SHORT WAVE
TROUGH. IN THE SOUTHWEST FLOW...THERE SHOULD BE 1 TO 2 UBAR/S OF
UP GLIDE ON THE 300K SURFACE. WITH INCREASING LOW LEVEL MOISTURE
AHEAD OF THE SURFACE LOW...EXPECT TO SEE THE CEILINGS RAPIDLY COME
DOWN TO MVFR AND THEN IFR WITH SOME DRIZZLE AS WELL. THE VERTICAL
MOTION LOOKS TO BE A LITTLE STRONGER AND LAST LONGER AT KLSE SO
HAVE GONE WITH CATEGORICAL DRIZZLE. KRST MAY SEE SOME DRIZZLE AS
WELL...BUT A LITTLE MORE UNCERTAINTY THERE DUE TO WEAKER LIFT
SIGNAL. THE WINDS SHOULD COME AROUND TO THE NORTHWEST IN THE
AFTERNOON ONCE THE SURFACE LOW GOES BY AND THIS WILL SHUT OFF THE
LIFT TO END THE DRIZZLE AND ALLOW THE CEILINGS TO GO BACK UP TO
MVFR OR VFR.

&&

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

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION...04



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