Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 120119
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
819 PM CDT FRI APR 11 2014

.UPDATE...
ISSUED AT 819 PM CDT FRI APR 11 2014

FOCUS HERE IN THE NEAR TERM IS ON MID/HIGH CLOUDS OVER THE DAKOTAS
AND THEIR ASSOCIATED WEAK REFLECTIVITY RETURNS. THESE CLOUDS ARE A
RESULT OF INCREASING ISENTROPIC LIFT / FRONTOGENESIS ABOVE A
DEVELOPING WARM FRONT OVER SOUTHERN SOUTH DAKOTA. DRY AIR SEEN ON
THE 00Z BIS SOUNDING HAS PREVENTED MUCH OF ANY LIGHT RAIN AT THE
SURFACE RIGHT NOW. NEARLY EVERY MODEL SUGGESTS THESE CLOUDS WILL
CONTINUE TO THICKEN THROUGH THE EVENING WITH SHOWER ACTIVITY
GETTING GOING OVER THE EASTERN DAKOTAS AROUND 06Z. THIS IS A
RESULT OF INCREASING PRECIPITABLE WATER FLOWING NORTHWARD ACROSS
THE PLAINS. THE SHOWER ACTIVITY BECOMES EVEN MORE WIDESPREAD AS IT
HEADS TOWARDS THE FORECAST AREA LATE TONIGHT...PARTICULARLY NORTH
OF INTERSTATE 90. GIVEN THE CONSISTENT SIGNAL AND GOOD
AGREEMENT...RAISED PRECIPITATION CHANCES EVEN MORE...ESPECIALLY
FOR SATURDAY MORNING. SOME THUNDER IS CERTAINLY POSSIBLE TOO. A
COLLECTION OF SHORTWAVES CURRENTLY OVER EASTERN MONTANA SHOULD
HELP PUSH THE SHOWERS OFF TO THE EAST THROUGH THE MORNING...SO
TRIED TO SHOW MORE OF A DIMINISHING TREND TO THE PRECIPITATION. IN
FACT...THERE ARE MANY SIGNALS THAT BY 18-19Z...MUCH OF THE
FORECAST AREA COULD BE DRY. THIS MAKES SENSE DUE TO SUBSIDENCE
TAKING PLACE.

HEADING INTO THE AFTERNOON...THERE IS A LOT OF MODEL SPREAD ON
CONVECTIVE POTENTIAL. THE 11.18Z NAM/GFS...11.12Z ECMWF/CANADIAN
ALL INITIATE NUMEROUS CONVECTION OVER NORTHEAST IOWA AND FAR
SOUTHWEST WI...ALONG A LOW PRESSURE TROUGH DROPPING SOUTHEAST
THROUGH THE AREA. NOW...ON THE OTHER HAND...HIGH RESOLUTION MODELS
SUCH AS THE 11.06Z/11.12Z HIRES ARW MODEL RUNS AND THE 11.12Z SPC
WRF-NMM ARE NEARLY DRY OR JUST HAVE SOME ISOLATED SHOWERS.
INSPECTING THE HIRES ARW MODELS...THEY HAVE A LOT LESS CAPE THAN
THOSE THAT INITIATE CONVECTION...DESPITE SHOWING SURFACE DEWPOINTS
CLIMBING INTO THE UPPER 50S. THERE ARE CERTAINLY OTHER CONCERNS
FOR CONVECTIVE POTENTIAL...

1. BOUNDARY LAYER MOISTURE POSSIBLY TOO HIGH. 925MB DEWPOINT
DEPRESSION COMPARISON BETWEEN 00Z RAOBS AND THE 11.12Z
ECMWF...11.18Z NAM/GFS SHOWED THESE MODELS WERE ANYWHERE FROM 3-7C
TOO LOW...WITH MUCH OF THIS ERROR BEING TOO HIGH ON DEWPOINT. THE
ERROR IS MOST PREVALENT AT SGF. ADDITIONALLY...MOS GUIDANCE
REMAINS 5 TO 10F COOLER ON DEWPOINTS TOMORROW AFTERNOON COMPARED
TO 2 METER GUIDANCE...SUGGESTING CAPE FROM THE MODELS MAY BE
OVERDONE.

2. THE 11.18Z NAM 0-2 KM CONVERGENCE IS VERY WEAK ALONG THE
TROUGH...WHICH MAY LIMIT THE CONVECTIVE EXTENT.

3. SUBSIDENCE IN THE WAKE OF THE MORNING PRECIPITATION COULD
CREATE A DECENT CAP. 11.18Z NAM SOUNDINGS ACTUALLY SHOW THIS
CAP...BUT GET RID OF IT WITHIN 1 HOUR AS A RESULT OF THE BMJ
CONVECTIVE SCHEME TAKING OFF.

IN SUMMARY...CONFIDENCE IS LOWER ABOUT BOTH SEVERE WEATHER AND
PRECIPITATION AS A WHOLE SATURDAY AFTERNOON. THEREFORE...HAVE
LOWERED PRECIPITATION CHANCES 10-20 PERCENT FOR THE AFTERNOON.

&&

.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 300 PM CDT FRI APR 11 2014

THE MAIN FORECAST CONCERNS ARE SHRA/TSRA CHANCES AND PRECIP
AMOUNTS MAINLY CENTERED ON SAT...TEMPERATURES.

DATA ANALYSIS AT 18Z HAD A WEAK LOW OVER SOUTHEAST MN...IN RESPONSE
TO A RATHER VIGOROUS SHORTWAVE MOVING ACROSS MN/WI. LIFT FROM THIS
WAVE PRODUCING SOME -RA/-SHRA AHEAD OF IT ACROSS WI...OVERCOMING THE
DRIER SFC-800MB AIRMASS. SUBSIDENCE/MID LEVEL DRYING/CLEARING
SPREADING EAST ACROSS MN INTO WESTERN WI BEHIND THE SHORTWAVE...WITH
TEMPS QUICKLY WARMING INTO THE MID 50S TO UPPER 60S ACROSS SOUTHERN
MN/NORTHERN IA. DEW POINTS WERE GENERALLY HOLDING IN THE 30S AS OF
18Z...WITH RH/S MOSTLY IN THE 35-50 PERCENT RANGE...EASING FIRE
WEATHER CONCERNS A BIT AS OF MID-DAY.

MODEL RUNS OF 11.12Z LOOK TO HAVE INITIALIZED WELL. SOLUTIONS
CONTINUE TO COME INTO TIGHTER AGREEMENT FOR TONIGHT THRU SAT NIGHT
AS TROUGHING DIGS INTO THE NORTHERN ROCKIES/NORTHERN PLAINS. TREND
FAVORS STRONGER OF EARLIER RUNS WITH THE LEAD PIECE OF ENERGY INTO
THE NORTHERN PLAINS BY 12Z SAT AND THE ENERGY DROPPING THRU THE
NORTHERN ROCKIES SAT NIGHT. ECMWF WITH SOME OF THE BETTER RUN-TO-RUN
CONSISTENCY THIS PERIOD. CHECK OF OBS VS. MODEL DATA AT 18Z SHOWED
MODELS TO BE REASONABLE WITH THE CENTRAL CONUS MASS FIELDS. PER WV
IMAGERY...ALL LOOKED GOOD WITH THE SHORTWAVE TRACKING ACROSS MN/WI
AND WITH THE UPSTREAM ENERGY OVER SOUTHWEST CAN/NORTHWEST U.S. WITH
NO ONE MODEL FAVORITE AND THE OVERALL TREND TOWARD A TIGHTER COMMON
SOLUTION...FAVORED THE MODEL/ENSEMBLE CONSENSUS. SHORT-TERM FCST
CONFIDENCE IS GOOD THIS CYCLE.

IN THE SHORT TERM...QUIET THIS EVENING AS WEAK SFC-500MB RIDGING
SLIDES QUICKLY EAST ACROSS THE REGION. FLOW TRANSITIONING TO
WESTERLY OVERNIGHT ALLOWS FOR A QUICK RETURN/INCREASE OF 925-700MB
WARM ADVECTION/ISENTROPIC LIFT AND A RAPID NORTHWARD SPREAD OF
INCREASING 925-700MB MOISTURE AHEAD OF LOW PRESSURE MOVING EAST
ACROSS THE NORTHERN PLAINS. THIS UNDER SOME WEAK PV ADVECTION AHEAD
OF THE SHORTWAVE AND UNDER THE RIGHT ENTRANCE REGION OF 100-120KT
300MB JET NORTH OF THE AREA. MDT/STRONG SFC-700MB FN CONVERGENCE
INDICATED AHEAD OF THE SFC-700MB LOW/TROUGH AS WELL. STRONGEST/
DEEPEST OF THE FORCING/LIFT SIGNAL AND MOISTURE TRANSLATE EAST
ACROSS THE AREA LATE TONIGHT THRU MID AFTERNOON SAT. CARRIED A DRY
FCST THRU THE EVENING THEN SPREAD INCREASING PRECIP CHANCES WEST TO
EAST ACROSS THE AREA LATE TONIGHT/SAT MORNING. PRECIP CHANCES IN THE
60-90 PERCENT RANGE FOR MUCH OF THE AREA MUCH OF SAT. MUCAPE PROGGED
TO REMAIN QUITE LIMITED OVER THE AREA THRU 12Z SAT. BUT GIVEN THE
STRENGTH OF THE LIFT SIGNAL...WILL MAINTAIN A SCT TSRA MENTION LATE
TONIGHT. MUCAPE IN THE INFLOW AIRMASS PROGGED TO BE IN THE 250-1K
J/KG RANGE BY MID-DAY SAT WITH SHRA AND SCT TSRA MUCH OF SAT.
HEAVIEST PRECIP LOOKS TO FALL ACROSS NORTHERN WI...NORTH OF THE SFC
LOW AND SFC-850MB FRONTAL BOUNDARY. MAIN FORCING/LIFT MOVES EAST/
SOUTH OF THE FCST AREA BY LATER SAT NIGHT...WITH -SHRA/TSRA CHANCES
MAINLY ACROSS THE SOUTHEAST END OF THE FCST AREA AFTER MIDNIGHT SAT
NIGHT. PRECIP LATE TONIGHT INTO SAT EVENING TRENDING TO BE 1/4 TO
1/2 INCH...LOCALLY 3/4 INCH IN ANY STRONGER TSRA. GIVEN 40-50KTS OF
0-6KM SHEAR AND PROXIMITY TO CAPE POOL...STILL CANNOT RULE OUT A FEW
STRONG TO SVR TSRA ACROSS THE SOUTH END OF THE FCST AREA SAT
AFTERNOON/EARLY SAT EVENING. SEE SWODY2 FOR DETAILS. FAVORING THE
MODEL/ENSEMBLE CONSENSUS USED A BLEND OF THE GUIDANCE LOWS/HIGHS FOR
TONIGHT THRU SAT NIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 300 PM CDT FRI APR 11 2014

MAIN FORECAST CONCERNS FOR SUNDAY THRU MONDAY NIGHT...MAINLY RAIN
CHANCES SUN/SUN NIGHT...COLD TEMPERATURES MON/MON NIGHT.

11.12Z MODELS CONTINUE TO COME INTO BETTER AGREEMENT AS PART 2 OF
THE WEEKEND SYSTEM SLIDES ACROSS THE AREA SUN/SUN NIGHT...WITH GFS/
ECMWF OFFERING DECENT RUN-TO-RUN CONSISTENCY IN THIS TIME FRAME. NAM
APPEARING AS A SLOWER/STRONGER OUTLIER WITH THE TROUGH AXIS/SHORT-
WAVE ENERGY BY 00Z MON. GIVEN GOOD AGREEMENT AMONG THE CAN-GEM/GFS/
ECMWF SUN/SUN NIGHT...SIDED WITH THE CONSENSUS OF THESE MODELS FOR
THE SUN-MON NIGHT PERIOD. FCST CONFIDENCE IS AVERAGE TO GOOD FOR
SUN THRU MON NIGHT.

SFC-850MB TROUGH/FRONT FROM SAT SETTLES NEAR A KANSAS CITY MO TO
CHICAGO LINE FOR SUN/SUN EVENING...WITH THE TIGHT BAROCLINIC ZONE
NORTH OF IT OVER MUCH OF IA/WI/SOUTHERN MN. AS PART 2 OF THE
TROUGH/SHORTWAVE ENERGY DIGS INTO THE NORTHERN PLAINS THE 700-500MB
FLOW BACKS AHEAD OF IT...PUSHING A RATHER MOIST 700-500MB AIRMASS UP
AND OVER THE SFC-850MB TROUGH/FRONTAL BOUNDARY AND BAROCLINIC ZONE.
THIS PRODUCES RATHER IMPRESSIVE 295-310K ISENTROPIC LIFT IN THE 700-
500MB LAYER OVER THE AREA CENTERED ON SUN AFTERNOON. THIS UNDER
FALLING HGTS ALOFT AHEAD OF THE TROUGH AND UNDER THE FAVORABLE RIGHT
ENTRANCE REGION OF A 110-130KT 300MB JET MAX OVER ONT. MDT 700-500
FN CONVERGENCE INDICATED AS WELL. STRONGEST/DEEPEST OF THE
ISENTROPIC LIFT AND MOISTURE...PW VALUES OF 3/4 TO 1 INCH...ARE OVER
THE SOUTHEAST HALF OF THE FCST AREA FROM LATER SUN MORNING INTO SUN
EVENING. CARRIED HIGHEST RAIN CHANCES AND AMOUNTS OVER THE SOUTHEAST
HALF OF THE FCST AREA FROM LATE SUN MORNING INTO SUN EVENING.
FURTHER NORTH...THE HIGHER UP FORCING/LIFT AND MOISTURE MAY STRUGGLE
TO PRECIP THRU THE DRYING NORTHERLY FLOW IN THE DEEPER SFC TO 850-
750MB LAYER. CONTINUED SOME 50-70 PERCENT RAIN CHANCES ACROSS THE
NORTHWEST HALF OF THE FCST AREA SUN AFTERNOON WHERE FORCING/LIFT
APPEARS STRONG ENOUGH TO OVERCOME THE DRIER LOW LEVEL AIR.

CAPE POOL IS JUST SOUTH OF THE FCST AREA SUN. GIVEN THE STRENGTH/
DEPTH OF THE FORCING/LIFT AND PROXIMITY OF SOME CAPE...CONTINUED A
TSRA CHANCE ACROSS THE FAR SOUTHEAST END OF THE FCST AREA SUNDAY.
FORCING/LIFT TRANSLATE EAST/SOUTH OF THE FCST AREA THRU SUN
NIGHT...AND CONTINUED TO TREND PRECIP CHANCES DOWNWARD/OUT LATER
SUN NIGHT/MON MORNING. DEEPENING COLD ADVECTION SPREADS SOUTH
ACROSS THE AREA SUN NIGHT WITH THE COLUMN COOLING ENOUGH FOR
PRECIP TO FALL AS SNOW DURING THE LATE EVENING/OVERNIGHT HOURS.
HOWEVER...BY LATE EVENING THE FORCING/LIFT IS WANING AND ANY
PRECIP AFTER 03Z- 06Z MON LOOKS QUITE LIGHT WITH ANY SNOW
ACCUMULATIONS MINOR AND MAINLY ON GRASSY AREAS.

LOW LEVEL COLD ADVECTION CONTINUES MON/MON NIGHT AS A CHUNK OF
CANADIAN/POLAR AIR SPREADS SOUTH ACROSS THE UPPER MIDWEST. 850MB
TEMPS IN THE -8C TO -12C RANGE BY 00Z TUE...SOME 1 TO 2 STANDARD
DEVIATIONS BELOW NORMAL WITH WHAT IS SHAPING UP TO BE A PERIOD OF
MUCH BELOW NORMAL TEMPERATURES EARLY NEXT WEEK. LATEST MODEL HAS
TRENDED MORE CHANNELED AND FURTHER NORTH/EAST WITH A NORTHERN
STREAM SHORTWAVE TO DROP ACROSS THE AREA MON NIGHT AND HAVE
REMOVED SMALL -SN CHANCES FROM MON NIGHT. USED A BLEND OF THE
GUIDANCE HIGHS/LOWS FOR SUN THRU MON NIGHT.

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

MAIN FORECAST CONCERNS THIS PERIOD REMAIN THE BELOW/MUCH BELOW
NORMAL TEMPS TUE/WED...THEN PRECIP CHANCES WED INTO FRI.

MEDIUM RANGE MODEL RUNS OF 11.00Z AND 11.12Z CONTINUE TO COME INTO
TIGHTER AGREEMENT WITH COLD LONGWAVE TROUGHING TO SWING ACROSS THE
UPPER MIDWEST TUE. TREND FAVORS SLOWER OF THE EARLIER MODEL RUNS
WITH THIS TROUGHING. LESSER MODEL AGREEMENT ALREADY WED AS THE FLOW
TRANSITIONS TO QUASI-ZONAL ACROSS THE NORTHERN CONUS AND SHORTWAVE
ENERGY BEGINS TO EJECT ACROSS THE NORTHERN ROCKIES/PLAINS. BY THU
MORE TROUGHING/ENERGY EJECTS INTO THE PLAINS...WITH SOME FORM OF
THIS TROUGHING MOVING INTO THE MID/UPPER MS VALLEY BY LATE NEXT
WEEK. PLENTY OF MODEL TIMING/STRENGTH DETAIL DIFFERENCES AND RATHER
POOR RUN-TO-RUN CONSISTENCY ALREADY BY WED. FCST CONFIDENCE IS GOOD
TUE THEN BELOW AVERAGE FOR WED-FRI.

COLD...DRY CAN HIGH PRESSURE CONTINUES TO SETTLE ACROSS THE REGION
TUE WITH 850MB TEMPS AROUND 2 STANDARD DEVIATIONS BELOW NORMAL.
DEPENDING ON EXTENT OF ANY CLOUD COVER UNDER THE COLD POOL...HIGHS
TUE MAY STRUGGLE TO REACH 40F AT MANY LOCATIONS. TRANSITION TO QUASI-
ZONAL FLOW AND TROUGHING/ENERGY CROSSING THE ROCKIES DEVELOPS A LEE
LOW N THE CENTRAL/NORTHERN PLAINS. PLENTY OF DIFFERENCES BY WED AS
TO WHERE THE WARM FRONT EAST OF THIS LOW SETS UP AND HOW MUCH/HOW
QUICKLY THE LOWER LEVEL WARM ADVECTION/MOISTURE RETURNS NORTHWARD
INTO MN/IA/WI. GFS WOULD QUICKLY SPREAD A HIGHER CHANCE OF PRECIP
AND ACCUMULATING SNOW ACROSS THE NORTH HALF OF THE FCST AREA
WED/WED NIGHT. DETAIL DIFFERENCES CONTINUE FOR THU/FRI AS PIECES
OF ENERGY EJECT INTO THE PLAINS AND EVENTUALLY INTO THE UPPER
MIDWEST. GIVEN THE LOWER CONFIDENCE IN ANY ONE DETERMINISTIC
SOLUTION BY THU/FRI... STAYED WITH THE MODEL/ENSEMBLE CONSENSUS
PRECIP CHANCES IN THE 20-40 PERCENT RANGE FOR MUCH OF THE WED THRU
FRI PERIOD. WITH THE SWITCH TO MORE WESTERLY FLOW FOR WED-FRI...
TEMPS TO RECOVER FROM THE MUCH BELOW NORMAL VALUES OF MON/TUE.
WITH MODELS IMPLYING WHAT WOULD BE MORE CLOUDS ACROSS THE REGION
WED THRU FRI...TEMPS FOR WED-FRI WOULD GENERALLY REMAIN BELOW
NORMAL. MODEL/ENSEMBLE CONSENSUS HIGHS/LOWS FOR TUE-FRI APPEAR
WELL TRENDED AT THIS TIME.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 638 PM CDT FRI APR 11 2014

A LOW PRESSURE SYSTEM OVER THE DAKOTAS WILL TRACK TOWARDS THE TAF
SITES DURING THE NEXT 24 HOURS...WITH ITS WARM FRONT PASSING
THROUGH SATURDAY MORNING AND COLD FRONT LATE SATURDAY AFTERNOON.
PLENTIFUL DRY AIR AROUND...EVEN DURING ALL OF THE FRONTAL
PASSAGES...SHOULD HELP TO KEEP CONDITIONS MOSTLY VFR FOR THE TAFS.
HOWEVER...THERE COULD BE A BRIEF PERIOD OF MVFR VISIBILITIES AS
SHOWERS MOVE THROUGH DURING THE 12-16Z PERIOD. THESE SHOWERS COULD
ALSO CONTAIN SOME THUNDER...BUT THE PROBABILITY IS TOO LOW TO
MENTION IN THE TAF AT THIS TIME. A LOT OF CHANGES ARE EXPECTED
WITH WIND DIRECTION AS THIS SYSTEM TRACKS THROUGH...GOING FROM THE
CURRENT NORTHWEST TO SOUTHEAST QUICKLY THIS EVENING...TO SOUTH
WITH THE WARM FRONTAL PASSAGE LATE IN THE MORNING...AND FINALLY
WEST TO NORTHWEST LATE IN THE DAY AS THE COLD FRONT TRACKS
THROUGH. SPEEDS INCREASE TOO...ESPECIALLY WITH THE WARM FRONT
WHERE MAYBE SOME GUSTS COULD OCCUR. THERE IS ALSO THE CONCERN FOR
LOW LEVEL WIND SHEAR LATE TONIGHT INTO SATURDAY MORNING BUT RIGHT
NOW ITS TOO MARGINAL TO MENTION.


&&

.FIRE WEATHER...
ISSUED AT 300 PM CDT FRI APR 11 2014

BRIEF PERIOD OF CRITICAL FIRE WEATHER CONDITIONS STILL POSSIBLE LATE
THIS AFTERNOON. HOWEVER SFC DEW POINTS GENERALLY REMAINING IN THE
MID 30S WITH 19Z RH/S MOSTLY IN THE 30-40 PERCENT RANGE. STILL
POTENTIAL FOR DEW POINTS TO MIX INTO THE UPPER 20S WHICH WOULD DROP
RH/S INTO THE 25-30 PERCENT RANGE WITH WEST WINDS OF 10-15 MPH AND
GUSTY FOR A PERIOD LATE THIS AFTERNOON/VERY EARLY THIS EVENING.
BEYOND THAT...WIDESPREAD RAINS EXPECTED CENTERED ON SAT MORNING
AND AGAIN ON SUNDAY AFTERNOON...WITH WEEKEND TOTALS OF 3/4 TO 1.5
INCHES ACROSS MUCH OF THE FCST AREA.

&&

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

$$

UPDATE...AJ
SHORT TERM.....RRS
LONG TERM......RRS
AVIATION...AJ
FIRE WEATHER...RRS



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