Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 261955
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
255 PM CDT FRI SEP 26 2014

.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 255 PM CDT FRI SEP 26 2014

MAIN FORECAST CONCERNS THIS PERIOD...TEMPERATURES.

18Z DATA ANALYSIS HAD BROAD HIGH PRESSURE CENTERED OVER THE GREAT
LAKES AND LOW PRESSURE OVER SOUTHERN SASKAT WITH TROUGHING SOUTH
INTO EASTERN CO. PRESSURE GRADIENT BETWEEN THE TWO WAS PRODUCING
LIGHT TO MDT SOUTHEAST WINDS ACROSS WI/MN/IA. ABUNDANT SUNSHINE
TODAY WAS HELPING EARLY AFTERNOON TEMPS CLIMB INTO THE 70S TO NEAR
80 ACROSS MUCH OF THE REGION...SOME 5F TO 10F ABOVE NORMAL. WV
IMAGERY WAS SHOWING A MID LEVEL LOW/CIRCULATION/SHORTWAVE CENTERED
OVER EASTERN IA. LITTLE MORE TO THIS THAN SCT ALTO-CUMULUS ACROSS
MUCH OF IA.

MODEL RUNS OF 26.12Z GENERALLY INITIALIZED QUITE WELL...BUT FOR GFS
WITH ITS ROUGHLY 5F HIGH BIAS ON SFC DEW POINTS ACROSS MUCH OF THE
UPPER MIDWEST/NORTHERN PLAINS. MODELS OFFERING A TIGHTENING
CONSENSUS FOR TONIGHT THRU SAT NIGHT AS THE WEAK MID LEVEL LOW OVER
THE MID/UPPER MS VALLEY STUCK IN THE MID LEVEL RIDGING DRIFTS
NORTHWEST AND GRADUALLY WEAKENS/ FILLS/OPENS UP. TREND FAVORS SLOWER
OF EARLIER MODELS WITH THIS FEATURE. TIGHTENING CONSENSUS AS WELL AS
THE STRONG ENERGY OFF THE CA COAST COMES ASHORE AND CARVES OUT A
DEEP/STRONG MID LEVEL LOW OVER THE GREAT BASIN BY 12Z SUN. SHORT
TERM FCST CONFIDENCE AGAIN GOOD THIS CYCLE.

TONIGHT THRU SAT NIGHT CONTINUES TO SHAPE UP AS A DRY AND SEASONABLY
MILD/WARM PERIOD. THIS AS HIGH PRESSURE HOLDS OVER THE GREAT LAKES
AND SOUTHEAST TO SOUTHWEST SFC-850MB FLOW AROUND THIS HIGH CONTINUES
TO BRING SEASONABLY WARM AIR NORTHWARD. SOUTHEAST SFC FLOW OUT OF
THE HIGH SENT DEW POINTS DOWN INTO THE UPPER 40S/LOW 50S ACROSS THE
SOUTHEAST 2/3 OF WI INTO SOUTHEAST MN/EASTERN IA ON THU. KGRB/KDVN
SOUNDINGS INDICATE THIS SHOULD HAPPEN AGAIN THIS AFTERNOON. WITH
CONTINUED SOUTHEAST SFC-925 FLOW THRU SAT NIGHT AND CROPS NORTH OF
THE OH/MO RIVERS RAPIDLY MATURING/SENESCING...SFC BASED EVAPO-
TRANSPIRATION IS QUICKLY DIMINISHING. THUS MODEL DEW POINTS IN THE
60-65F RANGE...AND SB CAPES OF 500 TO AS MUCH AS 1500 J/KG OVER THE
OVER THE FCST AREA SAT AFTERNOON APPEAR TOO HIGH. MORE REALISTIC
MIXED LAYER DEW POINTS IN THE 55-60F RANGE PRODUCE LITTLE IF ANY
CAPE SAT AFTERNOON. WILL CONTINUE TO LEAVE FCST FOR TONIGHT THRU SAT
NIGHT DRY...EVEN AS THE MID LEVEL LOW AND SOME SHORTWAVE ENERGY
ROTATES/DRIFTS NORTHWEST ACROSS IA.

MODEL SOUNDINGS/X-SECTIONS SHOW LITTLE MORE THAN SCT DIURNAL CUMULUS
FOR CLOUDS THRU SUN MORNING. MODEL SOUNDINGS SHOW 18-20KT GRADIENT
WINDS JUST ABOVE THE BOUNDARY LAYER LATE TONIGHT...NOT FAVORABLE FOR
LATE NIGHT/EARLY MORNING RADIATIONAL FOG FORMATION AND LEFT MENTION
OUT OF ALL BUT THE LOWER WI RIVER VALLEY FOR NOW. 925MB TEMPS IN THE
18C TO 20C RANGE SAT AFTERNOON SUPPORTING HIGHS IN THE MID 70S TO
AROUND 80. USED A BLEND OF THE GUIDANCE LOWS/HIGHS FOR TONIGHT THRU
SAT NIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 255 PM CDT FRI SEP 26 2014

FORECAST CONCERNS FOR SUN THRU MON NIGHT...SMALL -SHRA CHANCE WITH
BACKDOOR COLD FRONT MON/MON EVENING...TEMPERATURES THRU THE PERIOD.

26.12Z MODELS IN IMPROVING AGREEMENT SUN/SUN NIGHT AS THE WEAK MID
LEVEL LOW/TROUGH OVER IA CONTINUES TO OPEN UP AND MOVE WELL EAST OF
THE AREA BY 12Z MON. CONSENSUS IMPROVING ON THE NORTHERN STREAM
SHORTWAVE TO DROP SOUTHEAST ACROSS THE GREAT LAKES MON...FAVORING A
COMPROMISE ON THE STRENGTH AND FASTER OF EARLIER MODELS ON THE
TIMING. MODELS REMAIN CONSISTENT WITH MID LEVEL LOW LIFTING
NORTHEAST THRU THE GREAT BASIN/ROCKIES SUN/SUN NIGHT...THEN OPENING
THE SYSTEM AND LIFTING IT INTO THE CENTRAL PLAINS AS A STRONG/
NEGATIVE TILT TROUGH BY 12Z TUE. SOME SHORTWAVE STRENGTH/LOCATION
DIFFERENCES WITH THIS TROUGH BY 12Z TUE BUT THIS NOT UNEXPECTED.
FCST CONFIDENCE FOR SUN THRU MON NIGHT IS GOOD THIS CYCLE.

QUIET/DRY/WARM WEATHER CONTINUES SUN/SUN NIGHT THE WEAK MID LEVEL
SYSTEM WEAKENS AND MOVES EAST OF THE AREA. SUNDAY TO BE ANOTHER WARM
DAY WITH 925MB TEMPS AGAIN IN THE +18C TO +20C RANGE FOR HIGHS AGAIN
IN THE MID 70S TO AROUND 80. MODEL COMPROMISE ON THE SHORTWAVE
DROPPING SOUTHEAST ACROSS THE GREAT LAKES MONDAY NOW SENDS A COLD
FRONT SOUTH ACROSS THE AREA MON/MON EVENING. DYNAMICS WITH THE
SHORTWAVE TO JUST CLIP THE NORTHEAST SIDE OF THE FCST AREA MON...
ALONG WITH THE STRONGER OF THE LOW LEVEL MOISTURE TRANSPORT/
THETA-E CONVERGENCE PASSING NORTHEAST OF THE FCST AREA. HOWEVER
MDT 1000-850MB FN CONVERGENCE AND PW VALUES OF 1 TO 1.25 INCH
ACCOMPANY THE SFC-850MB FRONT/TROUGH AS IT PUSHES THRU THE AREA.
POTENTIAL FOR SOME WEAK CAPE AS WELL. CONTINUED WITH A SMALL -SHRA
MENTION MONDAY MAINLY NORTHEAST OF I-94 AND TRENDED MON NIGHT DRY
WITH THE FASTER MOVEMENT OF THE FRONT/FORCING THRU THE AREA. FRONT
REACHES THE SOUTH END OF THE FCST AREA LATE MON...WITH 925MB SILL
IN THE 18C TO 20C RANGE LATE IN THE AFTERNOON. MON HIGHS TO BE
COOLER ACROSS THE NORTH END OF THE FCST AREA WHILE THE SOUTH END
WILL AGAIN SEE HIGHS IN THE 75-80 DEGREE RANGE. PUSH OF LOW LEVEL
COLD ADVECTION SPREADS ACROSS THE AREA MON NIGHT FOR SOME COOLER
LOWS...ESPECIALLY ACROSS THE NORTHEAST 1/2 OF THE FCST AREA. BLEND
OF THE NUMERICAL GUIDANCE HIGHS/LOWS FOR SUN THRU MON NIGHT LOOKS
GOOD AT THIS TIME.

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

FORECAST CONCERNS FOR TUE THRU FRI...SHRA/TSRA CHANCES TUE NIGHT
THRU THU NIGHT...TEMPERATURES THRU THE PERIOD.

26.00Z/26.12Z MEDIUM RANGE MODEL RUNS OFFER IMPROVING AGREEMENT TUE
AS THE MAIN ENERGY WITH THE WESTERN CONUS TROUGH LIFTS NORTHEAST
ACROSS THE NORTHERN PLAINS. TREND FAVORS A COMPROMISE OF STRENGTH/
TIMING OF THE EARLIER MODEL RUNS. MODELS REMAIN SIMILAR WITH THE
LONGWAVE FEATURES WED/THU. HOWEVER SHORTWAVE DETAIL DIFFERENCES
EMERGE AS THE LEAD SHORTWAVE LIFTS INTO CANADA AND ADDITIONAL
SHORTWAVE ENERGY DIGS DOWN THE WEST SIDE OF THE LONGWAVE TROUGH WED
THEN AS THIS ENERGY MOVES ACROSS THE PLAINS AND TOWARD THE REGION
WED NIGHT/THU. OVERALL TREND IS MORE PROGRESSIVE WITH THE SHORTWAVE
FEATURES WED/THU. PLENTY OF LONG/SHORT WAVE DETAIL DIFFERENCES AMONG
THE MODELS BY THU NIGHT/FRI WITH POOR RUN-TO-RUN CONSISTENCY. SOME
CONSENSUS THU NIGHT/FRI FOR RISING HGTS OVER WESTERN NOAM AND
DOWNSTREAM TROUGHING OVER CENTRAL NOAM. DAY 4-7 FCST CONFIDENCE IS
GOOD TUE TRENDING TO BELOW AVERAGE BY THU/FRI.

GOOD CONSENSUS FOR THE FRONT FROM MON/MON EVENING TO BE WELL
SOUTH OF THE FCST AREA TUE WITH HIGH PRESSURE RIDGING FROM ONT
OVER WI AND NEARBY AREAS. WEAK LOW LEVEL WARM ADVECTION ALREADY
RETURNS ON TUE WITH 925MB TEMPS IN THE 10C TO 16C RANGE /COOLEST
NORTHEAST OF I-94/ BY 00Z WED. SOME COOLER HIGHS TUE...BUT STILL
LOOKING TO BE IN THE MID 60S TO LOWER 70S UNDER PARTLY CLOUDY/
MOSTLY SUNNY SKIES. STRONGER LOW LEVEL THERMODYNAMIC FORCING AHEAD
OF THE TROUGH/LOW LIFTING ACROSS THE PLAINS SPREADS INTO/ACROSS
THE AREA TUE NIGHT/ WED... ALONG WITH THE FALLING HGTS ALOFT...PW
VALUES AROUND 1.5 INCHES...WEAK CAPE TUE NIGHT AND 250-750 J/KG
CAPE WED. INCREASING SHRA/TSRA CHANCES TUE NIGHT...TRENDING TOWARD
LIKELY WED PER THE MODEL/ ENSEMBLE CONSENSUS LOOK GOOD. 925MB
TEMPS BACK IN THE +16C TO +20C RANGE WED. HOWEVER MORE CLOUDS AND
THE SCT SHRA/TSRA TO HOLD TEMPS DOWN...BUT STILL ABOVE LATE SEPT
NORMALS. THE SECONDARY PIECE OF SHORTWAVE ENERGY ALONG WITH THE
SFC FRONT/LOW LEVEL TROUGH PROGGED TO COME ACROSS THE AREA WED
NIGHT/THU WITH ANOTHER ROUND OF STRONGER/DEEPER FORCING/LIFT AND
WEAK TO MDT CAPE. SHRA/TSRA CHANCES IN THE 40-60 PERCENT RANGE
THESE PERIODS GOOD FOR NOW BUT AS THE CONSENSUS/DETAILS CONTINUE
TO TIGHTEN...WILL LIKELY NEED 80-100 PERCENT SHRA/TSRA CHANCES
SOMETIME IN THE WED THRU THU PERIOD. DECREASING RAIN CHANCES THU
NIGHT AS THE SFC-MID LEVEL TROUGH AXIS MOVES EAST OF THE AREA...
CONSIDERABLE TIMING DIFFERENCES BETWEEN GFS/ECMWF FOR THU NIGHT.
DRY CONDITIONS FRI AS COOLER/DRIER CAN HIGH PRESSURE SETTLES INTO
THE REGION. TEMPS BY FRI TREND BELOW NORMAL AS THIS HIGH SETTLES
IN...WITH THE MODEL/ENSEMBLE CONSENSUS HIGHS/LOWS FOR TUE THRU FRI
LOOKING GOOD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1235 PM CDT FRI SEP 26 2014

VFR WEATHER WILL CONTINUE THROUGH THE PERIOD. HIGH PRESSURE AT THE
SURFACE WILL REMAIN OVER THE EASTERN GREAT LAKES MAINTAINING A SOUTH
FLOW OVER THE REGION. ENOUGH OF A GRADIENT TO HAVE SUSTAINED SPEEDS
OVER 10 KNOTS THIS AFTERNOON AT KRST AND THEN DROPPING BELOW 10
KNOTS ONCE THE LOW LEVEL INVERSION STARTS TO DEVELOP. NOT EXPECTING
ANY FOG TO FORM OVERNIGHT AT KLSE. WINDS JUST ABOVE THE SURFACE ARE
FORECAST TO BE IN THE 15 TO 20 KNOT RANGE WHICH SHOULD BE TOO MUCH
MIXING TO ALLOW THE FOG TO FORM. IN ADDITION...THE 26.12Z NAM
SUGGESTS SATURATION MAY NOT OCCUR AT THE SURFACE FURTHER LIMITING
THE POTENTIAL FOR FOG.

&&

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

$$

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


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