Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 250457
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1157 PM CDT FRI OCT 24 2014

.UPDATE...
ISSUED AT 912 PM CDT FRI OCT 24 2014

DENSE FOG HAS FORMED ACROSS PARTS OF THE AREA AGAIN THIS EVENING.
NOT EXPECTING THIS TO LAST THROUGH THE ENTIRE NIGHT AS A SURFACE
TROUGH IS SLOWLY APPROACHING THE WESTERN AREA. ONCE THIS COMES
IN...THE WINDS WILL GO AROUND TO THE WEST WITH DRIER AIR COMING IN
AS WELL. UNTIL THIS HAPPENS THOUGH...THE VISIBILITY WILL BE DOWN
TO A QUARTER MILE OR LESS AT TIMES. UNCERTAIN ON HOW FAR EAST TO
BRING THE ADVISORY AS THE 25.00Z HRRR DOES NOT SUGGEST THE LOW
VISIBILITIES WILL LAST VERY LONG FOR LOCATIONS ALONG AND EAST OF
THE MISSISSIPPI RIVER.

&&

.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 255 PM CDT FRI OCT 24 2014

MAIN FORECAST CONCERNS THIS PERIOD...LOW CLOUDS/PATCHY FOG/DZ THIS
EVENING...TEMPERATURES THRU THE PERIOD.

18Z DATA ANALYSIS HAD A SFC TROUGH/FRONT ACROSS WESTERN MN/WESTERN
IA...MAKING STEADY PROGRESS EAST. VERY MOIST LOW LEVEL AIRMASS IN
PLACE AHEAD OF THIS TROUGH/FRONT. FOG PERSISTING ACROSS MUCH OF
WI/IA HOWEVER VSBYS WERE SLOWLY IMPROVING. SOUTHWEST LOW LEVEL FLOW/
WARM ADVECTION AHEAD OF THE TROUGH SPREADING LOW CLOUDS/FOG FROM
CENTRAL IA BACK INTO THE FCST AREA. WV IMAGERY SHOWED ONE SHORTWAVE
DROPPING SOUTHEAST INTO IL AND A MORE VIGOROUS ONE MOVING EAST NEAR
LK WINNIPEG.

NO MAJOR PROBLEMS NOTED WITH 24.12Z MODEL INITIALIZATIONS. GFS A
LITTLE HIGH WITH SFC DEW POINTS ACROSS IA/SOUTHERN MN BUT NOT OFF AS
MUCH AS IT TYPICALLY IS. MODELS IN GOOD AGREEMENT AS THE SHORTWAVE
NEAR LK WINNIPEG EARLY THIS AFTERNOON TRACKS MAINLY NORTH OF LK
SUPERIOR TONIGHT THEN AS THE BULK OF THE SHORTWAVE ENERGY TRACKS
INTO QUEBEC BY LATE SAT. STRONGER HGT RISES STILL PROGGED SAT NIGHT
WITH THE MID LEVEL RIDGE AXIS TO THE MN/DAKOTAS BORDER BY 12Z SUN.
MODEL TREND TONIGHT THRU SAT NIGHT FAVORS FASTER OF EARLIER RUNS
WITH FEATURES AND MORE NORTHERLY WITH THE SHORTWAVE TRACK. SHORT-
TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

IN THE SHORT TERM...MOIST LOW LEVEL SOUTHWEST FLOW AHEAD OF THE SFC-
850MB TROUGH CONTINUES ACROSS THE FCST AREA INTO THIS EVENING...WITH
LOWER STRATUS CLOUDS/PATCHY FOG PERSISTING. BY MIDNIGHT THE
SHORTWAVE TRACKING NORTH OF LK SUPERIOR PUSHES THE SFC-850MB TROUGH/
FRONT SOUTH/EAST OF THE FCST AREA. INCREASING NORTHWEST FLOW/COLD
ADVECTION/SUBSIDENCE/DRYING IN THIS LAYER SPREADS ACROSS THE AREA
BEHIND THIS TROUGH/FRONT DURING THE LATE EVENING AND OVERNIGHT
HOURS. TRENDED CLOUDS AND ANY PATCHY FOG/DZ DOWN/OUT DURING THE
EVENING INTO EARLY OVERNIGHT HOURS. GRADIENT NORTHWEST WINDS BEHIND
THE FRONT TO KEEP THE BOUNDARY LAYER STIRRED LATE TONIGHT AND LOWS
ONCE AGAIN WELL ABOVE NORMAL. A DEEP...DRY AIRMASS AND BROAD DEEP
LAYERED SUBSIDENCE SPREAD ACROSS THE AREA FOR SAT/SAT NIGHT AS HGTS
ALOFT SLOWLY RISE AND CAN HIGH PRESSURE SLIDES SOUTHEAST ACROSS THE
REGION. 925MB TEMPS IN THE +9C TO +13C RANGE SAT AFTERNOON EVEN WITH
THE LOW LEVEL COLD ADVECTION. MODEL SOUNDINGS STILL SHOWING MIXING TO
AROUND 900MB SAT AFTERNOON...WITH 20-25KTS OF WIND IN THE TOP OF
THE MIXED LAYER. RAISED SAT AFTERNOON WIND GUSTS IN THE FCST GRIDS.
SFC RIDGE AXIS MOVES ACROSS THE AREA SAT NIGHT...FOR DECOUPLED WINDS
AND STRONG RADIATIONAL COOLING UNDER THE DEEP DRY AIRMASS/MOSTLY
CLEAR SKIES. AFTER SAT HIGHS 4F TO 8F ABOVE NORMAL...LOWS SAT NIGHT
LOOKING TO DIP TO NEAR/BELOW NORMAL. USED A BLEND OF THE NUMERICAL
GUIDANCE LOWS/HIGHS FOR TONIGHT THRU SAT NIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 255 PM CDT FRI OCT 24 2014

FORECAST CONCERNS FOR SUNDAY THRU MON NIGHT...SHRA/TSRA CHANCES SUN
NIGHT THRU MON NIGHT...TEMPERATURES.

24.12Z MODELS IN GOOD AGREEMENT SUN AS THE MID LEVEL RIDGE AXIS
MOVES ACROSS THE REGION AND TROUGHING DIGS INTO THE CENTRAL/NORTHERN
ROCKIES. RIDGE AXIS MOVES EAST OF THE AREA SUN NIGHT AS THE TROUGH
PROGRESSES THRU THE ROCKIES...WITH THE AREA UNDER INCREASING
SOUTHWEST FLOW ALOFT. TREND SUN/SUN NIGHT IS LESS DIGGING OF THE
TROUGH THRU THE CENTRAL ROCKIES. TIGHTER CONSENSUS MON AS THE TROUGH
LIFTS ACROSS THE CENTRAL/NORTHERN PLAINS. TIMING DIFFERENCES WITH
THE TROUGH MON NIGHT AS IT LIFTS INTO THE UPPER MIDWEST....BUT
THESE SMALLER THAN THE EARLIER RUNS. TREND MON/MON NIGHT IS TOWARD
A COMPROMISE ON STRENGTH/TIMING OF EARLIER RUNS. FCST CONFIDENCE
FOR SUN THRU MON NIGHT IS AVERAGE TO GOOD THIS CYCLE.

SFC-850MB LOW/TROUGH WITH THE MID LEVEL TROUGH OVER THE ROCKIES
MOVES QUICKLY INTO CENTRAL/NORTHERN PLAINS SUN. INCREASING SOUTHEAST
TO SOUTHWEST MDT/STRONG WARM ADVECTION FLOW BETWEEN THIS TROUGH AND
THE RETREATING SFC HIGH/RIDGE AXIS SPREADS ACROSS THE REGION.
QUESTION IS HOW QUICKLY DOES THE INCREASING MOISTURE ARRIVE. 925-
700MB MOISTURE TRANSPORT SPREADS INTO THE FCST AREA SUN AFTERNOON
BUT INITIALLY A VERY DRY AIRMASS TO SATURATE AS IT DOES. 925-850MB
MOISTENS WEST OF THE MS RIVER SUN AFTERNOON WHILE MORE 850-700MB
SATURATION OCCURS EAST OF THE MS RIVER. BULK OF WARM ADVECTION
INITIALLY GOES INTO WARMING WITH SOME INCREASE OF UPWARD MOTION
INDICATED LATE SUN AFTERNOON. MAY YET NEED A SMALL -SHRA CHANCE LATE
SUN AFTERNOON BUT LEFT IT DRY FOR NOW. LIFT CONTINUES TO INCREASE
SUN NIGHT AS THE SFC-850MB TROUGH/FRONT APPROACH AND DIVERGENCE ALOFT
AHEAD OF THE MID LEVEL TROUGH SPREADS INTO THE REGION. MODELS NOW
INDICATING SOMEWHAT LESS MOISTURE TO ADVECT INTO/OVER THE AREA SUN
NIGHT...MAINLY BELOW 800MB WITH RATHER DRY SOUTHWEST FLOW IN THE
800- 500MB LAYER. STRONGEST FORCING/LIFT PROGGED OVER THE
NORTHEAST HALF OF THE FCST AREA...NORTHEAST OF A WARM FRONT
ADVANCING ACROSS THE REGION. MODELS DO STILL PROG AT LEAST 250-500
J/KG OF MUCAPE ACROSS THE AREA SUN NIGHT. 20-50 PERCENT
SHRA/ISOLATED TSRA CHANCES PER THE MODEL CONSENSUS...HIGHEST
ALONG/NORTHEAST OF I-94 STILL LOOK GOOD SUN NIGHT. MOISTURE NOW
PROGGED TO DECREASE ACROSS THE AREA AS THE 925-700MB TROUGH PASSES
AND THE FLOW BECOMES MORE WESTERLY IN THAT LAYER. GIVEN THE SFC
LOW/FRONTS IN THE AREA AND AREA AHEAD OF THE MID LEVEL
TROUGH...AND SOME WEAK MUCAPE OVER THE AREA... CONTINUED A SMALL
-SHRA/TSRA CHANCE MON. MONDAY COULD END UP MORE SUN THAN CLOUD
UNDER THE MID LEVEL DRY PUNCH...WITH 925MB TEMPS SUPPORTING HIGHS
IN THE UPPER 60S-MID 70S ACROSS THE AREA. STRONGER MID/UPPER LEVEL
FORCING/DIVERGENCE/LIFT SPREADS ACROSS THE AREA MON NIGHT AS THE
MID LEVEL TROUGH SWINGS INTO THE REGION. DEEPER SATURATION TO
700MB INDICATED ALONG WITH SOME WEAK MUCAPE. SHRA CHANCES IN THE
30-50 PERCENT RANGE WITH ISOLATED TSRA REASONABLE. MODEL/ENSEMBLE
CONSENSUS HAS HIGHS/LOWS FOR SUN THRU MON NIGHT WELL TRENDED FOR
NOW.

FOR TUESDAY THROUGH FRIDAY.../DAYS 4 TO 7/...

FORECAST CONCERNS THIS PERIOD...LINGERING -SHRA TUE...SHRA CHANCES
WITH NEXT SYSTEM WED NIGHT INTO THU NIGHT...TEMPERATURES.

24.00Z/24.12Z MEDIUM RANGE MODEL RUNS IN DECENT AGREEMENT TUE FOR
THE MAIN TROUGH/SHORTWAVE ENERGY TO LIFT NORTHEAST ACROSS THE UPPER
MIDWEST. REASONABLY GOOD AGREEMENT FOR HGTS TO FALL ACROSS THE
NORTHERN PLAINS WED WITH THE NEXT TROUGH/SHORTWAVE ENERGY...THEN FOR
THIS TROUGH/ENERGY TO MOVE ACROSS THE UPPER MIDWEST THU AND RIDGING
TO BUILD INTO THE NORTH-CENTRAL CONUS FRI. GIVEN REASONABLE BETWEEN
MODEL AND RUN-TO-RUN CONSISTENCY...CONFIDENCE IN THE DAY 4-7
PERIOD IS AVERAGE TO GOOD THIS CYCLE.

BY TUE...MODELS HAVE THE SFC LOW WITH THE TROUGH OVER LK SUPERIOR...
THE SFC-850MB TROUGH/COLD FRONT WELL EAST OF THE AREA AND LOW LEVEL
COLD ADVECTION SPREADING ACROSS MN/IA/WI. APPEARS ANY LINGERING
-SHRA CHANCES TUE ARE NOW IN THE MORNING AND OVER THE NORTHEAST END
OF THE FCST AREA. MORE SEASONABLE AIRMASS SPREADS IN TUE WITH 925MB
TEMPS BY 00Z WED IN THE +3C TO +7C RANGE. SOME LOW LEVEL WARM
ADVECTION RETURNS WED AS THE NEXT LOW ADVANCES INTO THE NORTHERN
PLAINS. LOWER LEVEL MOISTURE RETURN AHEAD OF THIS NEXT LOW/TROUGH
APPEARS LIMITED BUT WITH THE MID LEVEL TROUGH/SHORTWAVE ENERGY TO
DROP ACROSS THE REGION...SMALL -SHRA CHANCE WED NIGHT/THU PER THE
MODEL/ENSEMBLE CONSENSUS OKAY FOR NOW. SMALL LINGERING PRECIP
CHANCE ACROSS THE NORTHEAST END OF THE FCST AREA THU NIGHT...WHEN
COLUMN WOULD BE COLD ENOUGH TO SUPPORT PRECIP TYPE AS -RA/-SN OR
-SN. COLD CANADIAN HIGH PRESSURE EAST OF THE MID LEVEL RIDGE AXIS
ON TRACK TO BUILD IN TO END THE WEEK. FOR NOW...A CHILLY BUT DRY
EVENING IS IN STORE FOR THE TRICK-OR-TREATERS. MODEL/ENSEMBLE
CONSENSUS OF THE HIGHS/LOWS FOR TUE THRU FRI APPEARS WELL TRENDED
AT THIS TIME.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1157 PM CDT FRI OCT 24 2014

THE DRIER AIR FROM THE WEST HAS FINALLY BEGUN TO WORK INTO THE
AREA AS THE DEW POINT HAS DROPPED DOWN INTO THE UPPER 40S AT BOTH
KTOB AND KAUM. IN RESPONSE TO THIS...THE VISIBILITY HAS COME UP TO
MVFR AT KTOB BUT HAS BEEN SLOW TO BEGIN IMPROVING ELSEWHERE. THE
25.03Z RAP AND 25.00Z NAM CONTINUE TO SUGGEST THE WIND SHIFT AND
DRIER AIR WILL WORK INTO KRST BY 06Z...BUT THIS SEEMS OPTIMISTIC
AND WILL HOLD ONTO THE DENSE FOG A LITTLE LONGER BEFORE FINALLY
ALLOWING THE WIND SHIFT WITH THE DEVELOPMENT OF VFR CONDITIONS TO
OCCUR AROUND 08Z. KLSE MAY NOT SEE MUCH OF A VISIBILITY
RESTRICTION DUE TO THE LACK OF ANY CLEARING SO EXPECT THE MVFR TO
IFR CEILINGS TO REMAIN IN PLACE UNTIL ABOUT 10Z OR SO...FOLLOWED
BY VFR CONDITIONS. HIGH PRESSURE THEN BUILDS IN FOR THE REMAINDER
OF SATURDAY WITH LITTLE OR NO CLOUD COVER. THE NAM STILL INDICATES
THE POTENTIAL FOR SOME WIND GUSTS TO AROUND 20 KNOTS SATURDAY
AFTERNOON IN THE MIXED LAYER.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL 4 AM CDT SATURDAY FOR WIZ032.

MN...DENSE FOG ADVISORY UNTIL 4 AM CDT SATURDAY FOR MNZ079-086>088-
     094>096.

IA...DENSE FOG ADVISORY UNTIL 4 AM CDT SATURDAY FOR IAZ008>011-018-
     019-029-030.

&&

$$

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



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