Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 240439
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1139 PM CDT THU OCT 23 2014

.UPDATE...
ISSUED AT 922 PM CDT THU OCT 23 2014

THE FOG CONTINUES TO EXPAND ACROSS THE AREA THIS EVENING WITH SOME
LOCATIONS ALREADY REPORTING DENSE FOG. EXPECT THIS TREND TO
CONTINUE WITH WIDESPREAD DENSE FOG POSSIBLE BEFORE MIDNIGHT.
THUS...PLAN TO MOVE THE START TIME OF THE ADVISORY UP TO THE
CURRENT TIME. SHOULD BE SLOW GOING FRIDAY MORNING COMMUTE WITH
VISIBILITIES OF A QUARTER MILE EXPECTED FOR MUCH OF THE AREA.

&&

.SHORT TERM...(TONIGHT THROUGH FRIDAY NIGHT)
ISSUED AT 245 PM CDT THU OCT 23 2014

MAIN FORECAST CONCERNS THIS PERIOD...FOG LATE TONIGHT/EARLY FRI
MORNING...TEMPERATURES/CLOUDS THRU THE PERIOD.

DATA ANALYSIS AT 18Z HAD THE BAND OF SHRA CONTINUING TO MOVE EAST
ACROSS THE AREA...WITH THE WEST EDGE NEAR A KMDZ-KVOK-KOVS LINE. WV
IMAGERY SHOWED THE RATHER VIGOROUS MID LEVEL SHORTWAVE/TROUGH MOVING
STEADILY EAST ACROSS THE REGION. VIS IMAGERY SHOWED THE CLEARING
BEHIND THE TROUGH WAS SLOWER TO MOVE EAST...WITH SHALLOW MOISTURE/
IFR CLOUD DECKS TRAPPED UNDER AN INVERSION NEAR 900MB. EARLY
AFTERNOON TEMPS IN THE LOW/MID 40S IN THE SHRA OVER CENTRAL/EASTERN
WI...TO THE UPPER 50S-MID 60S IN THE SUNSHINE OVER SOUTHWEST MN.

23.12Z MODELS INITIALIZED WELL...EVEN GFS WITH ITS SFC DEWPOINTS
ACROSS THE UPPER MIDWEST/NORTHERN PLAINS. MODELS IN GOOD AGREEMENT
AS THE MID LEVEL TROUGH QUICKLY MOVES EAST OF THE AREA TONIGHT AND
SHORTWAVE RIDGING BUILDS IN. CONSISTENT SIGNAL FOR A WEAK SHORTWAVE
FROM THE WEST TO WORK THRU THE SHORTWAVE RIDGING ACROSS REGION LATE
TONIGHT/FRI MORNING. MODELS REMAIN CONSISTENT ON A SHORTWAVE/TOUGH
TO DROP TOWARD/ACROSS LK SUPERIOR FRI NIGHT. TREND FOR TONIGHT THRU
FRI NIGHT GENERALLY FAVORS A COMPROMISE OF THE EARLIER RUNS. SHORT
TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

IN THE SHORT TERM...POST TROUGH DECREASE OF CLOUDS/CLEARING EXPECTED
TO PUSH ACROSS THE AREA TONIGHT AS THE SHORTWAVE RIDGING/RISING HGTS
BUILD IN. RAIN/CLOUDS TODAY KEEPING T/TD SPREADS ON THE LOW SIDE
OVER THE FCST AREA THIS AFTERNOON. THIS PLUS THE DECREASE OF CLOUDS
TONIGHT AND GRADIENT WINDS EXPECTED TO REMAIN LIGHT ACROSS MOST OF
THE FCST AREA SETS THE STAGE FOR AREAS TO WIDESPREAD DENSE FOG
LATER TONIGHT INTO FRI MORNING. CONTINUED STRONG SIGNAL AMONG SREF
MEMBERS FOR VSBYS BELOW 1SM OVER THE EAST 2/3 OF THE FCST AREA
CENTERED ON 12Z FRI MORNING. BASED ON WHAT HAPPENED WITH DENSE FOG
ACROSS WEST-CENTRAL MN...EASTERN SD/NEB...WESTERN IA THIS MORNING...
UPON COORD WITH NEIGHBORS WILL ISSUE A DENSE FOG ADVISORY FOR THE
ENTIRE FCST AREA FROM 06Z-15Z FRI.

MODEST ROUND OF LOWER LEVEL WARM ADVECTION/MOISTURE TRANSPORT AHEAD
OF A SFC-700MB TROUGH SLIDES ACROSS THE AREA FRI. THE MID LEVEL
SHORTWAVE MOVES ACROSS THE AREA FRI MORNING WHILE THE MAIN 925-
850MB MOISTURE INCREASE SPREADS ACROSS THE AREA FRI AFTERNOON/
EVENING. NAM INSISTS ON PRODUCING SOME LIGHT QPF ACROSS THE
SOUTH/WEST PORTIONS OF THE FCST AREA FRI AFTERNOON/EVENING BUT
THIS LOOKS OVERDONE DUE TO 1/ THE SHALLOWNESS OF THE MOISTURE 2/
MOISTURE IS UNDER AN INVERSION NEAR 850MB AND 3/ THE SHORTWAVE IS
WELL SOUTH/EAST OF THE AREA BY 00Z SAT. CANNOT RULE OUT SOME
PATCHY -DZ BUT MOISTURE LOOKS EVEN TOO SHALLOW FOR THIS AND LEFT
FRI AFTERNOON/EVENING DRY. SOME INCREASE OF LOWER STRATO-CU CLOUDS
EXPECTED FOR FRI AFTERNOON/EVENING...IMPACTING TEMPERATURES. MIXED
925MB TEMPS FRI AFTERNOON WOULD SUPPORT HIGHS IN THE MID 60S-LOW
70S...BUT WITH POTENTIAL FOR THE LOWER AFTERNOON CLOUDS WILL LEAVE
FRI HIGHS IN THE LOW-MID 60S. LOW LEVEL WARM ADVECTION CONTINUES
FRI EVENING...AHEAD OF THE APPROACHING TROUGH/COLD FRONT WITH THE
LK SUPERIOR SHORTWAVE. 925MB TEMPS PEAK IN THE +13C TO +18C RANGE
AROUND 06Z SAT WITH THE STRONGER LOW LEVEL COLD ADVECTION ARRIVING
AROUND 12Z SAT. FRONT COMES THRU DRY FRI NIGHT AS 925-700MB LAYER
IS DRY. GIVEN BOUNDARY LAYER WINDS FOR MIXING FRI NIGHT BOTH AHEAD
OF AND BEHIND THE FRONT...FRI NIGHT LOWS CONTINUE TO LOOK QUITE
MILD FOR LATE OCT. USED A BLEND OF THE GUIDANCE LOWS/HIGHS FOR
TONIGHT THRU SAT NIGHT.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 245 PM CDT THU OCT 23 2014

MAIN FORECAST CONCERNS FOR SATURDAY THRU SUNDAY NIGHT...SHRA/TSRA
CHANCES SUN NIGHT...TEMPERATURES THRU THE PERIOD.

23.12Z MODELS IN GOOD AGREEMENT SAT THRU SUN AS A SHORTWAVE TROUGH
PASSES SOUTHEAST ACROSS THE GREAT LAKES EARLY SAT THEN HGTS OVER THE
REGION SLOWLY RISE LATER SAT THRU SUN. GOOD MODEL CONSISTENCY FOR
THE LONGWAVE RIDGE AXIS TO BE NEAR THE MS RIVER AT 00Z MON AND
LONGWAVE TROUGHING TO BE OVER THE ROCKIES. TREND AT 00Z MON FAVORS
SLOWER OF THE EARLIER MODEL RUNS. RIDGE AXIS QUICKLY MOVES EAST
SUN NIGHT WITH INCREASING SOUTHWEST FLOW ALOFT BY 12Z MON AS THE
ROCKIES TROUGH BEGINS TO EJECT INTO THE PLAINS. FCST CONFIDENCE
FOR SAT THRU SUN NIGHT IS ON THE GOOD SIDE.

SAT THRU SUN DOMINATED BY CAN SFC HIGH PRESSURE. DRY NORTHWEST
FLOW ALOFT OVER THE AREA SAT/SAT NIGHT. LOW LEVEL COLD ADVECTION
CONTINUES SAT BUT 925MB TEMPS IN +9C TO +13C AT 00Z SUN. UNDER
SUNNY SKIES...SAT HIGHS STILL LOOK TO BE IN THE UPPER 50S-MID 60S
EVEN WITH THE COLD ADVECTION. 925MB WINDS IN THE 25KT RANGE SAT
WITH SOUNDINGS SHOWING MIXING TO 900MB SAT AFTERNOON...FOR
BRISK/BREEZY/GUSTY NORTHWEST WINDS. SFC RIDGE AXIS SLIDES ACROSS
THE AREA SAT NIGHT. WINDS DECOUPLE AND UNDER CLEAR SKIES STRONG
RADIATIONAL COOLING/LARGE DIURNAL SWING EXPECTED SAT NIGHT. SFC-
850MB RIDGE AXIS QUICKLY MOVES EAST OF THE AREA SUN WITH A RETURN
OF SOUTHEAST TO SOUTH LOW LEVEL FLOW/WARM ADVECTION. LOW LEVEL
MOISTURE RETURN BEGINS TO SPREAD ACROSS THE SOUTHWEST END OF THE
FCST AREA LATE SUN. INITIALLY A VERY DRY SFC-500MB AIRMASS TO
MOISTEN UP. THE MOISTURE/THETA-E AXIS AND STRONGER LOW LEVEL WARM
ADVECTION REMAIN WEST/SOUTH OF THE FCST AREA THRU 00Z MON. LEFT
SUNDAY DRY FOR NOW BUT MAY YET NEED A SMALL -SHRA CHANCE ACROSS
THE SOUTHWEST END OF THE FCST AREA LATE IN THE AFTERNOON. LEAD
ROUND OF STRONGER/DEEPER LOW LEVEL MOISTURE TRANSPORT/THETA-E
CONVERGENCE AND WARM ADVECTION AHEAD OF THE PLAINS TROUGH/LOW
SPREADS ACROSS THE AREA SUN NIGHT. IMPROVING CONSENSUS FOR A WARM
FRONT AHEAD OF THE LOW IN THE PLAINS TO BE LIFTING ACROSS IA SUN
NIGHT...PROVIDING AN ADDED FOCUS/ISENTROPIC LIFTING MECHANISM
NORTH OF THIS BOUNDARY. 250-500+ J/KG OF MUCAPE PROGGED IN THE
AIRMASS BEING LIFTED OVER THE WARM FRONT SUN NIGHT. CONSENSUS RAIN
CHANCES IN THE 20-50 PERCENT RANGE LOOK GOOD SUN NIGHT...AND
CONTINUED THE MENTION OF TSRA. GENERALLY STAYED WITH A BLEND OF
THE NUMERICAL GUIDANCE HIGHS/LOWS FOR SAT THRU SUN NIGHT.

FOR MONDAY THROUGH THURSDAY.../DAYS 4 TO 7/...

MAIN FORECAST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES MON/MON
NIGHT...SHRA CHANCES TUE/TUE NIGHT...TEMPERATURES THRU THE PERIOD.

MEDIUM RANGE MODEL RUNS OF 23.00Z/23.12Z IN GOOD AGREEMENT MON AS
THE LONGWAVE TROUGH MOVES INTO THE PLAINS. REASONABLE AGREEMENT
AMONG MODELS TUE AS THE TROUGH/MAIN ENERGY LIFTS INTO THE MID/UPPER
MS VALLEY. TREND MON/TUE FAVORS A COMPROMISE OF THE EARLIER RUNS ON
TIMING/STRENGTH OF THIS TROUGH. RATHER GOOD AGREEMENT BETWEEN
ECMWF/GFS ON WED WITH BROAD TROUGHING OVER MUCH OF CENTRAL/EASTERN
NOAM AND SOME FORM OF RIDGING OVER THE US/CAN ROCKIES. DIFFERENCES
BY THU...MAINLY WITH PROGRESSIVENESS OF A NORTHWEST FLOW SHORTWAVE
INTO THE REGION...WHICH IS NOT UNUSUAL AT DAY 7. 23.12Z ECMWF/GFS IN
BETTER AGREEMENT THU THAN THEIR 23.00Z RUNS WERE. ECMWF OFFERS THE
BETTER RUN-TO-RUN CONSISTENCY WED/THU. FCST CONFIDENCE IS AVERAGE TO
GOOD MON-WED THEN AVERAGE ON THU.

MOIST AIRMASS WITH UP TO 250-500 J/KG MUCAPE PROGGED OVER THE AREA
MON/MON NIGHT. THIS AHEAD THE SFC-MID LEVEL TROUGH MOVING INTO THE
PLAINS AND LIFTING TOWARD THE REGION. PLENTY OF DETAIL DIFFERENCES
WITH THE STRENGTH/LOCATION OF THE SFC LOW/STRONGER FORCING LIFTING
TOWARD/ACROSS THE UPPER MIDWEST AT THE DAY 4 TIME-FRAME BUT THE 20-
50 PERCENT SHRA/TSRA CHANCES PER THE MODEL/ENSEMBLE CONSENSUS QUITE
REASONABLE FOR NOW. BY TUE THE MODEL CONSENSUS HAS THE SFC-700MB LOW
AND MID LEVEL SHORTWAVE ENERGY LIFTING ACROSS THE REGION...WITH A
DEFORMATION BAND OF MOISTURE/FORCING TO ROTATE ACROSS THE AREA.
AGAIN PLENTY OF DETAIL DIFFERENCES OUT IN DAY 5 BUT 25-50 PERCENT
SHRA CHANCES PER THE CONSENSUS GOOD AT THIS TIME. SFC THRU MID LEVEL
SYSTEM TO LIFT OUT TUE NIGHT...WITH DIMINISHING -SHRA CHANCES.
COOLER AIRMASS/WEAK SHORTWAVE RIDGING AND SFC HIGH PRESSURE IN ITS
WAKE FOR WHAT SHOULD BE A DRY DAY WED. TIMING DIFFERENCES BY THU
IMPACT POTENTIAL -SHRA CHANCES SPREADING BACK INTO THE FCST AREA.
GIVEN LESSER CONFIDENCE OUT ON DAY 7...STAYED WITH THE  MODEL/
ENSEMBLE CONSENSUS. GIVEN ALL THE LOWER LEVEL DETAIL DIFFERENCES IN
DAYS 4-7...THE BLEND OF THE MODEL/ENSEMBLE GUIDANCE HIGHS/LOWS
FOR MON-THU LOOK WELL TRENDED AT THIS TIME.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1139 PM CDT THU OCT 23 2014

THE FOG HAS SETTLED IN AT BOTH TAF SITES WITH IFR CONDITIONS. THE
VISIBILITY HAS YET TO COME DOWN TO IFR AT KLSE AS THE VALLEY SEEMS
TO BE PROTECTING IT SOME...AS IT IS AT OTHER MISSISSIPPI RIVER
VALLEY AIRPORTS. HOWEVER...BELIEVE THIS IS ONLY TEMPORARY AND WILL
CONTINUE THE TREND OF BRINGING THE VISIBILITY DOWN TO 1/4SM FOR
THE OVERNIGHT INTO FRIDAY MORNING. THE TREND IN THE RAP THIS
EVENING HAS NOT BEEN AS QUICK TO DISSIPATE THE FOG AS THE
AFTERNOON RUNS SO HAVE HELD ON TO THE LOW VISIBILITIES THROUGH THE
MIDDLE OF THE MORNING WITH THE LOW CEILINGS DISSIPATING DURING THE
LAST HALF OF THE MORNING. THE MODELS CONTINUE TO SHOW A MID LEVEL
SHORT WAVE TROUGH COMING ACROSS THE AREA FRIDAY AFTERNOON WITH
MIXED SIGNALS WHETHER THIS WILL PRODUCE A MVFR CEILING OR NOT. THE
24.00Z NAM CONTINUES TO BE THE MOST AGGRESSIVE AND HAS MVFR
CEILINGS DEVELOPING EARLY IN THE AFTERNOON. THE 24.02Z RAP AND
24.00Z GFS HAVE ALSO TRENDED THIS WAY WHILE THE 23.21Z SREF MEAN
REMAINS DRIER. MIXED SIGNALS IN THE NUMERICAL GUIDANCE AS WELL
WITH THE GFS BASED MOS AND LAMP GUIDANCE NOT SHOWING ANYTHING FOR
THE AFTERNOON WHILE THE NAM BASED MOS HAS THE MVFR CEILINGS. FOR
NOW...WILL CONTINUE WITH JUST SHOWING SOME SCATTERED CLOUDS AS
CONFIDENCE IN THE AMOUNT OF MOISTURE WITH THIS SYSTEM REMAINS LOW.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL 10 AM CDT FRIDAY FOR WIZ017-029-032>034-
     041>044-053>055-061.

MN...DENSE FOG ADVISORY UNTIL 10 AM CDT FRIDAY FOR MNZ079-086>088-
     094>096.

IA...DENSE FOG ADVISORY UNTIL 10 AM CDT FRIDAY FOR IAZ008>011-018-019-
     029-030.

&&

$$

UPDATE...04
SHORT TERM...RRS
LONG TERM....RRS
AVIATION...04



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