Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 182301
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
600 PM CDT SAT OCT 18 2014

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 305 PM CDT SAT OCT 18 2014

MAIN FORECAST CONCERNS FOR TONIGHT THRU SUN NIGHT...CLOUD AND
TEMPERATURE TRENDS.

18Z DATA ANALYSIS HAD A BROAD RIDGE OF HIGH PRESSURE CENTERED FROM
WESTERN ONT TO KS. WV IMAGERY SHOWED A RATHER VIGOROUS SHORTWAVE
EXITING THE REGION AND DROPPING INTO THE OH VALLEY. SUBSIDENCE
BEHIND THIS WAVE AND ANTI-CYCLONIC FLOW WITH THE SFC-850MB RIDGE
AXIS BUILD EAST WERE CLEARING OUT THE STRATO-CU CLOUDS OVER MUCH OF
WI/EASTERN MN/NORTHEAST IA. WEST OF THE LOWER LEVEL RIDGE AXIS LOW
CLOUDS SLOWER TO MIX/ERODE...APPEARING MORE TRAPPED UNDER A STRONGER
SUBSIDENCE INVERSION. WITH A RATHER CHILLY 925MB AIRMASS OVER THE
REGION...TEMPS SLOW TO WARM TODAY EVEN WITH THE SUNSHINE.

NO PROBLEMS NOTED WITH 18.12Z MODEL INITIALIZATIONS. SOLUTIONS VERY
SIMILAR FOR TONIGHT THRU SUN NIGHT AS SHORTWAVE RIDGING BUILDS OVER
THE AREA THIS AFTERNOON/EVENING...THEN AS HGTS FALL WITH APPROACH/
PASSAGE OF THE NEXT STRONGER SHORTWAVE TOPPING THE WESTERN NOAM
LONGWAVE RIDGE AND DROPPING INTO THE WESTERN GREAT LAKES. SOLUTIONS
FAVOR A COMPROMISE OF THE EARLIER RUNS WITH ECMWF OFFERING THE
BETTER RUN-TO-RUN CONSISTENCY. SHORT-TERM FCST CONFIDENCE IS GOOD
THIS CYCLE.

MODELS STRUGGLING A BIT AS THEY USUALLY DO WITH THE LOWER LEVEL
MOISTURE/CLOUDS TRAPPED IN/UNDER INVERSIONS THIS TIME OF YEAR. GFS/
ECMWF LOOKING BETTER WITH THE POST-SHORTWAVE SUBSIDENCE/CLEARING
WORKING SOUTH ACROSS WI/EASTERN MN THIS AFTERNOON...WITH THE LOWER
CLOUDS MORE PERSISTENT OVER WESTERN MN/IA. AS THE 925MB FLOW BECOMES
MORE SOUTHWEST/WEST AHEAD OF THE LOW/TROUGH MOVING ACROSS CENTRAL
CAN TO THE DAKOTAS...THIS RESIDUAL 925MB MOISTURE/ANY CLOUDS OVER
WESTERN MN/IA WOULD BE ADVECTED INTO/ACROSS THE FCST AREA AFTER
MIDNIGHT. MODEL SOUNDINGS AND TIME-HGT X-SECTIONS ALSO SHOWING
PLENTIFUL 400-200MB MOISTURE AND WEAK UPWARD MOTION TO SPREAD ACROSS
THE AREA LATER TONIGHT AHEAD OF THE APPROACHING MID LEVEL TROUGH.
SFC PRESSURE GRADIENT STARTS TO TIGHTEN OVER THE AREA LATER TONIGHT
AHEAD OF THE APPROACHING SFC-850MB TROUGH...ALONG WITH MDT/STRONG
925-850MB WARM ADVECTION. RAISED LOWS A BIT TONIGHT...ESPECIALLY
WEST OF THE MS RIVER.

STRONGEST OF THE LOWER LEVEL WARM ADVECTION/THERMO-DYNAMIC FORCING
MOVES ACROSS THE FCST AREA SUN MORNING. MODEL SOUNDINGS/X-SECTIONS
SHOWS THIS LIFT GOING INTO TRYING TO SATURATE THE 850-500MB PORTION
OF THE COLUMN. BETTER SATURATION OF THIS PORTION OF THE COLUMN
OCCURS OVER THE NORTHEAST END OF THE FCST AREA SUN AFTER...WHERE IT
IS THE COOLEST. EVEN THERE SATURATION APPEARS MARGINAL AT BEST FOR
-SHRA...AND REMOVED THE SMALL CHANCES ACROSS CLARK/TAYLOR COUNTIES
WHICH BLENDS WELL WITH NEIGHBORING GRIDS. STRONG DRYING AT/ABOVE
700MB SPREADS ACROSS THE AREA SUN NIGHT IN THE WAKE OF THE MID LEVEL
TROUGH...WITH SOME POST TROUGH CYCLONIC LOW LEVEL FLOW AND 925-850MB
MOISTURE TO CLIP THE NORTHEAST END OF THE FCST AREA. MDT LOW LEVEL
COLD ADVECTION TO SPREAD ACROSS THE AREA LATER SUN NIGHT...ALONG
WITH A MODEST SFC PRESSURE GRADIENT FOR SOME WINDS/BOUNDARY LAYER
MIXING AND WARMER LOWS. GENERALLY FAVORED WARMER OF GUIDANCE LOWS
TONIGHT THEN A BLEND OF HIGHS/LOWS SUN/SUN NIGHT.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 305 PM CDT SAT OCT 18 2014

MAIN FORECAST CONCERNS FOR MON THRU TUE NIGHT...TEMPERATURES AND
CLOUDS.

18.12Z MODELS IN GOOD AND IMPROVING AGREEMENT FOR RIDGING TO BUILD
EAST ACROSS THE NORTHERN PLAINS AND INTO THE UPPER MIDWEST DURING
THE MON THRU TUE NIGHT PERIOD. TREND FAVORS A COMPROMISE OF THE
EARLIER RUNS. FCST CONFIDENCE IN THIS PERIOD IS GOOD THIS CYCLE.

MON THRU TUE NIGHT CONTINUES TO SHAPE UP AS A DRY/QUIET PERIOD AS
THE RISING HGTS/RIDGING ALOFT BUILDS INTO THE UPPER MIDWEST AND SFC
HIGH PRESSURE HOLDS NEAR/OVER THE REGION. SOME LOW LEVEL MOISTURE/
CLOUDS BEHIND THE LOW DROPPING SOUTHEAST ACROSS THE GREAT LAKES
LINGER OVER THE NORTHEAST END OF THE FCST AREA MON. BIT OF A BACK-
DOOR COLD FRONT AND NORTHEAST FLOW AROUND THE SFC-850MB RIDGING
NORTH OF LK SUPERIOR TRIES TO PUSH SOME LOWER LEVEL MOISTURE/CLOUDS
WEST/SOUTH INTO THE FCST AREA LATE MON NIGHT INTO TUE NIGHT. PER THE
MODEL ENSEMBLE CONSENSUS...LEFT MON NIGHT THRU TUE NIGHT MOSTLY
CLEAR FOR NOW. AREA UNDER WEAK LOW LEVEL COLD ADVECTION MON THRU TUE
NIGHT IN THE EAST-NORTHEAST FLOW AROUND THE RIDGING NORTH OF LK
SUPERIOR. 925MB TEMPS IN THE 5C TO 12C RANGE MON AFTERNOON AND 4C TO
7C RANGE TUE AFTERNOON. CLEAR/MOSTLY CLEAR SKIES AND LIGHT WINDS
UNDER THE DRIER CAN HIGH PRESSURE SHOULD ALLOW FOR LARGER DIURNAL
TEMP SWINGS EARLY NEXT WEEK. HIGHS MON/TUE LOOKING TO BE NEAR/ABOVE
NORMAL WHILE LOWS MON/TUE NIGHTS APPEAR NEAR TO BELOW NORMAL. BLEND
OF THE NUMERICAL GUIDANCE HIGHS/LOWS FOR MON THRU TUE NIGHT LOOK TO
HAVE THIS WELL TRENDED.

FOR WED THROUGH SAT.../DAYS 4 TO 7/...

MAIN FORECAST CONCERNS THIS PERIOD...SMALL -SHRA CHANCE CENTERED ON
THU...ABOVE NORMAL TEMPERATURES THRU THE PERIOD.

MEDIUM RANGE MODEL RUNS OF 18.00Z/18.12Z SHOW IMPROVING AGREEMENT
FOR RIDGING OVER THE UPPER MIDWEST WED WITH A WEAKENING SHORTWAVE
TROUGH TO BE LIFTING INTO THE CENTRAL/NORTHERN PLAINS. PLENTY OF
DETAIL DIFFERENCES WITH THIS TROUGH BY THU AS IT MOVES INTO/ACROSS
THE MID/UPPER MS VALLEY BUT TREND REMAINS WEAKENING OF THIS FEATURE
AS IT MOVES THRU THE RIDGE AXIS. STRONG CONSENSUS FOR RISING HGTS/
RIDGING OVER THE NORTH-CENTRAL CONUS FRI. 18.12Z GFS/ECMWF IN BETTER
AGREEMENT ON SAT VS. 18.00Z RUNS...ON AMOUNT OF RIDGING ALOFT OVER
THE REGION. 18.00Z ECMWF WAS A STRONGER/FASTER OUTLIER WITH A
SHORTWAVE TROUGH TO DROP ACROSS THE GREAT LAKES. ITS LATEST RUN HAS
TRENDED MORE TOWARD THE GFS...HOLDING MORE RIDGING ALOFT/HIGHER HGTS
OVER THE UPPER MIDWEST ON DAY 7. FAVORED A MODEL/ENSEMBLE CONSENSUS
WITH AVERAGE CONFIDENCE IN THE DAY 4-7 PERIOD.

MODIFYING CAN HIGH PRESSURE HOLDS OVER THE AREA WED. AREA ON THE
WEST SIDE OF THE HIGH FOR SOME INCREASE OF SOUTH TO SOUTHWEST LOW
LEVEL FLOW AHEAD OF THE PLAINS LOW/SHORTWAVE. SOME LOW LEVEL WARM
ADVECTION SPREADS ACROSS THE AREA HOWEVER 925MB TEMPS ONLY IN THE
+7C TO +10C RANGE BY 00Z THU...FOR HIGHS MOSTLY IN THE MID-UPPER
50S. WEAKENING MID LEVEL TROUGH SLIDES INTO/ACROSS THE REGION LATE
WED NIGHT THRU THU EVENING. NOT MUCH FOR A SFC-850MB REFLECTION OF
THIS TROUGH. DISJOINTED LOWER LEVEL THERMO-DYNAMIC FORCING SIGNAL A
BEST BUT PW VALUES PROGGED INTO THE 0.75 TO 1 INCH RANGE WITH THE
TROUGH. SMALL -SHRA CHANCE FOR MUCH OF THE FCST AREA WED NIGHT/THU
FINE FOR NOW UNTIL THE DETAILS SORT THEMSELVES OUT. WITH REBUILDING
HGTS/RIDGING FRI...LOW LEVEL WARM ADVECTION QUICKLY SPREADS ACROSS
THE AREA FROM THE WEST. 925MB TEMPS IN THE 10C TO 15C RANGE FOR FRI
AFTERNOON AND SAT. DEPENDING ON HOW MUCH WESTERLY GRADIENT FLOW
THERE IS FOR MIXING...CONSENSUS HIGHS IN THE LOW-MID 60S FRI AND
UPPER 50S-LOW 60S SAT MAY BE 5F TO 10F TOO COOL. STAYED WITH THE
MODEL/ENSEMBLE CONSENSUS HIGHS/LOWS IN DAY 4-7 GOOD FOR NOW.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1134 AM CDT SAT OCT 18 2014

BAND OF APPROX 2 KFT MVFR CIGS HAVE PERSISTED ACROSS WESTERN MN
THROUGH THE AFTERNOON...BUT HAS BEEN SHOWING DIMINISHING TRENDS. SOME
INITIAL CONCERN THAT SOME OF THESE CLOUDS COULD ADVECT EAST TOWARD
KRST/KLSE AS WINDS VEER TONIGHT. RAP RH FIELDS AND SATELLITE TRENDS
SUGGEST ANY LINGERING LOW CLOUD SHOULD STAY NORTH - AND WILL STICK
WITH THIS FOR THE FORECAST.

LIGHT SFC/NEAR SFC WIND FIELD WITH HIGH PRESSURE OVERHEAD SUGGESTS
SOME POTENTIAL FOR RIVER VALLEY FOG. T/TD SPREAD WAS XX F AT
23Z...BUT THIS CAN BE OVERCOME. HOWEVER...THERE ARE A COUPLE
DRAWBACKS. FIRST IS THE HIGH PRESSURE SLIPS SOUTHEAST
OVERNIGHT...ALLOWING FOR THE WINDS RIGHT ABOVE THE NOCTURNAL
INVERSION TO INCREASE. THE SECOND IS HIGH/MID LEVEL CLOUDS MOVING IN
FROM THE WEST...AHEAD OF AN UPPER LEVEL SHORTWAVE TROUGH TRACKING
INTO THE NORTHERN PLAINS. AT THIS TIME...THINK THE CLOUDS WILL BE A
BIT TARDY TO IMPACT FOG POTENTIAL AT KLSE...LEAVING THE INCREASING
WINDS AS THE MAIN DETERRENT. THINK SOME THIN BR/STRATUS WILL DEVELOP
ALONG THE RIVER...BUT MAY NOT SPREAD OUTSIDE OF ITS BANKS. WILL KEEP
KLSE FOG FREE FOR NOW...BUT IT WILL NEED MONITORING.

HIGH/MID LEVEL CIGS FOR A PORTION OR THE DAY SUNDAY...WITH
INCREASING SOUTHERLY WINDS BY MID MORNING. EXPECT A FEW HIGHER
GUSTS...WITH SUSTAINED AROUND 15KTS OR SO. WINDS WILL BECOME
WESTERLY SUNDAY NIGHT AS THE SHORTWAVE/S SURFACE FRONT MOVES
THROUGH. NOT EXPECTING ANY PCPN.

&&

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

$$

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



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