Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 272329
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
629 PM CDT SAT SEP 27 2014

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 242 PM CDT SAT SEP 27 2014

MAIN FORECAST CONCERNS THIS PERIOD...ANY SMALL -SHRA CHANCES EARLY
THIS EVENING...TEMPERATURES THRU THE PERIOD.

DATA ANALYSIS AT 18Z HAD BROAD HIGH PRESSURE CENTERED OVER THE
EASTERN GREAT LAKES WITH RIDGING INTO THE MID MS VALLEY. LEE LOW
PRESSURE WAS LOCATED OVER EASTERN CO WITH TROUGHING NORTHEAST TO A
LOW OVER NORTHERN ONT. BROAD SOUTHEAST TO SOUTHWEST LOW LEVEL FLOW
CONTINUED TO BRING SEASONABLY WARM AIR NORTHWARD INTO THE UPPER
MIDWEST...WITH EARLY AFTERNOON TEMPS IN THE MID 70S TO LOWER 80S
ACROSS MUCH OF MN/IA/WI...AROUND 10F ABOVE NORMAL. WV IMAGERY SHOWED
THE MID LEVEL LOW CENTERED OVER NORTHWEST IA. SHORTWAVE ROTATING
AROUND THE EAST SIDE OF THE LOW ACROSS NORTH-CENTRAL IA/SOUTH-
CENTRAL COMBINED WITH SOME WEAK INSTABILITY PRODUCING A FEW -SHRA
LIFTING NORTH NEAR THE MN/IA BORDER.

GFS WITH ITS USUAL 5F HIGH BIAS ON SFC DEW POINTS ACROSS THE MUCH OF
THE UPPER MIDWEST...OTHERWISE 27.12Z MODELS LOOK TO HAVE INITIALIZED
QUITE WELL. SOLUTIONS FOR TONIGHT THRU SUN NIGHT TREND SIMILAR TO
EACH OTHER AND THEIR PREVIOUS RUNS. OVERALL SHORT-TERM FCST
CONFIDENCE REMAINS GOOD THIS CYCLE.

WEAK MID LEVEL LOW OVER NORTHWEST IA REMAINS NEARLY STATIONARY
TONIGHT THEN WEAKENS FURTHER SUN AS IT FINALLY SUCCUMBS TO INCREASED
BUILDING/FORCING OF THE UPPER RIDGING AHEAD OF THE MUCH STRONGER MID
LEVEL LOW COMING ACROSS THE GREAT BASIN. BY LATE SUN LITTLE REMAINS
OF THE WEAK MID LEVEL LOW AS IT IS SHOVED EAST/SOUTH OF THE REGION
BY THE WESTERN CONUS TROUGHING AND A NORTHERN STREAM SHORTWAVE
DROPPING TOWARD LK SUPERIOR.

LITTLE FORCING WITH STATIONARY MID LEVEL LOW TONIGHT. ANY CAPE AXIS
IS WEST OF THE FCST AREA LATE THIS AFTERNOON/EARLY THIS EVENING AND
CAPE DEPENDENT ON MODEL SFC DEW POINTS IN THE 60-65F RANGE BEING
CORRECT. BASED ON SFC OBS...DEW POINTS ALONG/EAST OF I-35 MOSTLY IN
THE 55-60F RANGE...WITH ANY CAPE LOOKING TO QUICKLY WANE WITH LOSS
OF DIURNAL HEATING LATE THIS AFTERNOON/EARLY THIS EVENING. LEFT
TONIGHT DRY. MODEL SOUNDINGS SHOWING LIGHTER WINDS ABOVE THE
BOUNDARY LAYER TONIGHT. BOUNDARY LAYER GRADIENT WINDS A BIT LIGHTER
THAN THOSE OF LAST NIGHT AS WELL. WITH LITTLE CHANGE OF THE LOW
LEVEL AIRMASS ADDED PATCHY LATE NIGHT/EARLY MORNING RADIATIONAL FOG
MENTION TO ALL THE RIVER VALLEYS AND THE LOW LAYING AREAS OF CENTRAL
WI. MODELS DEVELOP 500-1000 J/KG MU/SB CAPE OVER THE AREA SUN
AFTERNOON...BUT AGAIN THIS BASED ON SFC DEW POINTS IN THE 60-65F
RANGE. WITH EVAPO-TRANSPIRATION CONTINUING TO WIND DOWN WITH
MATURING/SENESCING CROPS ACROSS THE REGION...MORE REALISTIC DEW
POINTS ARE IN THE MID/UPPER 50S AS THEY HAVE BEEN THE PAST FEW
DAYS...ESPECIALLY ACROSS WI CLOSER TO THE CENTER OF THE GREAT LAKES
SFC HIGH. EVEN WITH 60-65F DEW POINTS...MODEL SOUNDINGS SHOWING 50-
75 J/KG OF CIN SUN AFTERNOON. LITTLE IN THE WAY OF  FORCING/LIFT/
CONVERGENCE SIGNALS SUN WITH A WEAK SFC RIDGE AXIS OVER THE AREA AND
ANY REMAINING ENERGY WITH THE WEAK MID LEVEL LOW/TROUGH PASSING WELL
SOUTHWEST OF THE FCST AREA AND LEFT SUNDAY DRY. WEAK SFC GRADIENTS
OVER THE AREA AGAIN SUN NIGHT AND MAY YET NEED MORE MENTION OF
PATCHY LATE NIGHT/EARLY MORNING VALLEY FOG INTO MON MORNING. WITH
THE RATHER TIGHT MODEL CONSENSUS...USED A BLEND OF THE GUIDANCE
LOWS/HIGHS FOR TONIGHT THRU SUN NIGHT.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 242 PM CDT SAT SEP 27 2014

FORECAST CONCERNS FOR MONDAY THROUGH TUE NIGHT...ANY SMALL -SHRA
CHANCES MON...SHRA/TSRA CHANCE SPREADING IN TUE NIGHT...TEMPERATURES
THRU THE PERIOD.

27.12Z MODELS REACHING A TIGHTER CONSENSUS AS THE NORTHERN STREAM
SHORTWAVE SLIDES SOUTHEAST ACROSS THE GREAT LAKES MON/MON EVENING.
TREND IS TOWARD SLOWER AND MORE OPEN WAVE OF THE EARLIER RUNS WITH
THIS FEATURE. CONSENSUS SLOWLY IMPROVING ON THE ROCKIES SHORTWAVE
ENERGY TO EJECT NORTH-NORTHEAST THRU THE CENTRAL/NORTHERN PLAINS MON
NIGHT-TUE NIGHT. TREND IS A BIT FASTER WITH THIS FEATURE LIFTING
NORTH AS MODELS TREND STRONGER ON THE SHORTWAVE ENERGY TO DIG INTO
THE NORTHERN/CENTRAL ROCKIES BEHIND IT TUE/TUE NIGHT. FCST
CONFIDENCE IN THE MON THRU TUE NIGHT PERIOD IS ON THE GOOD SIDE.

WITH THE SLOWER/WEAKER TREND OF THE SHORTWAVE TO DROP ACROSS THE
GREAT LAKES MON/MON EVENING...BULK OF THE UPPER LEVEL DYNAMICS/
FORCING PASS NORTHEAST OF THE FCST AREA. STILL SOME WEAK TO MDT 1000-
850MB FN CONVERGENCE AND WEAK MOISTURE TRANSPORT/THETA-E CONVERGENCE
TO PASS ACROSS THE NORTHEAST END OF THE FCST AREA MON WITH PW VALUES
OVER AN INCH. CONTINUED THE SMALL -SHRA CHANCES NORTHEAST OF I-94 ON
MON FOR NOW WHICH BLENDS WELL WITH NEIGHBORING GRIDS. SLOWER TREND
OF THE TROUGH/FRONT MEANS A SLOWER ARRIVAL OF THE POST FRONTAL LOW
LEVEL COLD ADVECTION AND ANOTHER WARM/ABOVE NORMAL DAY FOR MUCH OF
THE FCST AREA. RAISED MON HIGHS SOME 3 TO 5F ACROSS THE CENTRAL
PORTIONS OF THE FCST AREA...INTO THE MID/UPPER 70S. QUIET/GENERALLY
COOLER MON NIGHT/TUE AS CAN HIGH PRESSURE BEHIND THE FRONT NOSES
INTO THE AREA. COOLEST OF THE AIR OVER THE NORTHEAST END OF THE FCST
AREA MON NIGHT/TUE...WITH TEMPS CLOSER TO LATE SEPT NORMALS.
SLIGHTLY FASTER TREND OF THE ROCKIES TROUGH LIFTING NORTH THRU
PLAINS TUE/TUE NIGHT KEEPS IT AND THE LOWER LEVEL AND SURFACE
FEATURES/FORCING ON A BIT MORE WESTERLY TRACK AND SOME DELAY ON
THEIR ARRIVAL INTO THE FCST AREA TUE NIGHT. INCREASING/STRONGER
LOWER LEVEL THERMO-DYNAMIC FORCING AND MOISTURE TRANSPORT SPREADS
INTO MAINLY THE NORTHWEST HALF OF THE FCST AREA AFTER MIDNIGHT TUE
NIGHT. INSTABILITY REMAINS RATHER LIMITED TUE NIGHT BUT GIVEN
STRENGTH/DEPTH OF THE FORCING/LIFT SIGNAL...CONTINUED A SMALL TSRA
CHANCE ACROSS MAINLY THE NORTHWEST HALF OF THE FCST AREA LATER TUE
EVENING/OVERNIGHT. TRENDED TOWARD WARMER OF GUIDANCE HIGH MON
OTHERWISE USED A BLEND OF THE NUMERICAL GUIDANCE FOR LOWS/HIGHS
MON NIGHT THRU TUE NIGHT.

FOR WEDNESDAY THROUGH SATURDAY.../DAYS 4 TO 7/...

FORECAST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES WED THRU THU...
LINGERING SHRA CHANCES FRI...COOLING TEMPERATURES.

GOOD CONSENSUS AMONG 27.00Z/27.12Z MODELS WED AS THE LEAD SHORTWAVE
ENERGY LIFTS FROM NEAR THE ND/MN/MAN BORDER NORTHWARD THRU MAN AND
THE NEXT ENERGY DIGS ACROSS WY. BETTER AGREEMENT WITH THE WY ENERGY
AS IT THEN HEADS TOWARD THE REGION WED NIGHT/THU...FAVORING A
COMPROMISE OF THE EARLIER RUNS ON STRENGTH/TIMING. IMPROVING
COMPROMISE CONSENSUS THU NIGHT/FRI FOR YET A THIRD STRONGER PIECE OF
ENERGY TO DROP INTO THE LONGWAVE TROUGH...DEEPENING IT OVER THE
UPPER MIDWEST FOR FRI/SAT. UPPER MIDWEST IS UNDER COOLER NORTHWEST
FLOW OR THE COOL TROUGH ALOFT FRI/SAT. FCST CONFIDENCE IS AVERAGE
TO GOOD WED THRU SAT.

SHORTWAVE TROUGH LIFTING INTO MAN WED PUSHES A ROUND OF LOWER LEVEL
THERMO-DYNAMIC FORCING/LIFT INTO MAINLY THE NORTHWEST 2/3 TO 3/4 OF
THE FCST AREA WED...BIT SLOWER THAN EARLIER MODEL RUNS. MOISTURE
AXIS WITH PW VALUES OF 1 TO 1.5 INCHES PUSHES INTO THE AREA BUT THE
CAPE AXIS GENERALLY REMAINS WEST OF THE FCST AREA WED. HIGHER
SHRA/TSRA CHANCES WED MAINLY OVER THE NORTHWEST 2/3 OF THE FCST
AREA. THE DEEPER/STRONGER LOWER LEVEL THERMO-DYNAMIC FORCING
TRANSLATES EAST ACROSS THE FCST AREA WED NIGHT/THU. THIS WITH
FALLING HGTS ALOFT AND SOME PV ADVECTION AHEAD OF THE SECONDARY
SHORTWAVE/MAIN TROUGH AXIS. CONSENSUS RAIN CHANCES IN THE 60-70
PERCENT RANGE FOR MUCH OF THE AREA WED NIGHT/THU WELL TRENDED FOR
NOW AND WILL LIKELY TREND TOWARD 80-100 PERCENT ONE OR BOTH OF
THESE PERIODS AS THEY APPROACH. CAPE PROGGED TO BE ON THE WEAK
SIDE WED NIGHT/THU BUT GIVEN THE STRENGTH/DEPTH OF THE FORCING/
LIFT SIGNAL WILL CONTINUE WITH SCT TSRA IN THE FCST GRIDS THESE
PERIODS. SFC-850MB FRONT/TROUGH SLIDES EAST OF THE AREA THU NIGHT
TAKING THE BULK OF THE LOWER LEVEL FORCING/MOISTURE WITH IT. DEEP
MID LEVEL TROUGHING/CYCLONIC FLOW WITH COOLER 850-500MB TEMPS
PROGGED OVER THE AREA FRI. COOLER TEMPS ALOFT COMBINED WITH
RESIDUAL 925-850MB MOISTURE PRODUCE WEAK CAPE FRI AFTERNOON. -SHRA
CHANCES FRI APPEAR REASONABLE. DRIER HIGH PRESSURE BUILDS IN SAT.
MODEL/ENSEMBLE CONSENSUS HIGHS/LOWS TRENDING COOLER AND BELOW
NORMAL BY FRI/SAT LOOK GOOD.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 629 PM CDT SAT SEP 27 2014

THE ONLY FORECAST CONCERN IS WITH THE POTENTIAL FOR VALLEY FOG
TONIGHT AS WINDS WILL STAY LIGHT AND SKIES WILL REMAIN CLEAR
THROUGH TOMORROW AFTERNOON. WITH DEEP LIGHT WINDS AND CLEAR SKIES
TONIGHT...IT LOOKS LIKE AN IDEAL RADIATIONAL COOLING NIGHT SO
THERE SHOULD BE SOME FOG THAT FORMS IN SOME OF THE RIVER VALLEYS.
THE QUESTION IS WITH HOW WIDESPREAD IT WILL BE AFTER A DRY DAY
TODAY. WILL MONITOR CONDITIONS INTO THIS EVENING TO SEE WHETHER
ANY LOWER VISIBILITIES WILL OCCUR.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...HALBACH



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