Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 261946
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
245 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 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1226 PM CDT SUN OCT 26 2014

VFR CONDITIONS WITH SOUTHEAST WINDS 7-14KTS...PLUS G18-20KTS AT
SITES LIKE KRST...TO CONTINUE THIS AFTERNOON INTO EARLY THIS
EVENING. HOWEVER 925-850MB WARM ADVECTION AHEAD OF A LOW AND TROUGH
ADVANCING ACROSS THE PLAINS WILL SPREAD INCREASING LOW LEVEL
MOISTURE ACROSS THE TAF SITES THRU THE LATE AFTERNOON AND INTO MON.
INITIAL CIGS WILL BE VFR LATE THIS AFTERNOON/EARLY THIS EVENING BUT
AS THE DEEPER LOW LEVEL MOISTURE ARRIVES CIGS ARE EXPECTED TO DROP
TO MVFR/IFR...WITH MVFR/IFR VSBY IN BR...AFTER 06Z THRU MON MORNING.
INCREASING LIFT AND INSTABILITY ALOFT ARE EXPECTED TO TRIGGER SOME
SHRA...EVEN TSRA...ACROSS THE AREA IN ROUGHLY THE 03Z-09Z TIME-
FRAME. WITH THE STRONGEST FORCING/DEEPER MOISTURE LOOKING TO COME
TOGETHER NORTHEAST OF THE TAF SITES...LEFT THIS AS A VCSH MENTION IN
THE TAFS FOR NOW. BIGGER CONCERN IS THE SATURATION OF THE SFC TO
ABOUT 800MB LATER TONIGHT/MON MORNING...WITH SOME WEAK CONVERGENCE/
LIFT IN THE 925-850MB LAYER AHEAD OF THE APPROACHING SFC TO 925MB
LOW. A RATHER CLASSIC DRIZZLE SIGNATURE AND ADDED A -DZ MENTION TO
BOTH TAFS FOR LATE TONIGHT INTO MON MORNING. &&

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

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION.....RRS



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