Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 201437
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
937 AM CDT WED MAY 20 2015

.UPDATE...
ISSUED AT 937 AM CDT WED MAY 20 2015

INCREASED/MOVED PRECIPITATION CHANCES A BIT MORE NORTHWARD ACROSS
NORTHEAST IA/SOUTHWEST WI THIS MORNING INTO THIS AFTERNOON WITH
INCOMING MID-LEVEL TROUGH/CIRCULATION. LATEST RAP SHOWS
INTENSIFICATION IN MID-LEVEL/700MB FRONTOGENESIS...SO EXPECTING
DESPITE DRYER LOW LEVELS...THE F-GEN WILL BE STRONG ENOUGH TO
GENERATE SOME SHOWERS.

UPDATE ISSUED AT 802 AM CDT WED MAY 20 2015

UPDATED TO REMOVE FROST ADVISORY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 405 AM CDT WED MAY 20 2015

MAIN FCST CONCERNS THIS PERIOD...SMALL -SHRA CHANCES SOUTH TODAY...
TEMPERATURES.

DATA ANALYSIS AT 06Z HAD A BROAD AREA OF HIGH PRESSURE OVER THE
NORTHERN PLAINS AND UPPER MIDWEST. THE HIGH WAS BRINGING CLEAR
SKIES AND SUB-FREEZING TEMPS TO MUCH OF NORTHERN MN/WI INTO
CENTRAL WI EARLY THIS MORNING. WV IMAGERY SHOWED A RATHER VIGOROUS
LOOKING SHORTWAVE MOVING EAST ALONG THE NEB/SD BORDER. MID/HIGH
CLOUDS WITH THIS WAVE SPREADING ACROSS SOUTHERN MN/WI...HELPING
KEEP TEMPS ABOVE FREEZING. THE SHORTWAVE WAS BRINGING SOME LOWER
LEVEL MOISTURE TO IA...BUT EVEN THERE CLOUDS WERE MOSTLY ABOVE 5K-
6K FT. REGIONAL RADARS SHOWED REFLECTIVITY WITH THE SHORTWAVE FROM
SOUTH- CENTRAL SD TO NORTHERN MO BUT SFC OBS SHOW PRECIP REACHING
THE GROUND WAS MAINLY ALONG/SOUTH OF I-80 EARLY THIS MORNING.

20.00Z MODEL INITIALIZATIONS LOOK GOOD. MODELS OFFER A TIGHTER
CONSENSUS ON THE SD/NEB SHORTWAVE AS IT TRACKS EAST TODAY...AHEAD OF
BUT PARTLY PHASING WITH THE NORTHERN STREAM SHORTWAVE DROPPING INTO
EASTERN SD. TREND IS TO KEEP THE WAVES AS 2 SEPARATE PIECES OF
ENERGY QUICKLY FOLLOWING EACH OTHER THRU A MERGED TROUGH OVER THE
UPPER MIDWEST. TREND FAVORS STRONGER OF THE EARLIER MODELS AS THE
NORTHERN STREAM SHORTWAVE MOVES SOUTHEAST ACROSS THE REGION. WITH
THE TIGHT CONSENSUS OF SOLUTIONS...SHORT TERM FCST CONFIDENCE IS
GOOD THIS CYCLE.

IN THE SHORT TERM...SMALL -SHRA CHANCES ACROSS THE FAR SOUTH END OF
THE FCST AREA REMAIN A BATTLE OF 700-500MB FN/QG CONVERGENCE AND PV
ADVECTION WITH THE SHORTWAVE AND OVERCOMING DRIER NORTH TO NORTHEAST
FLOW/AIRMASS IN THE SFC-700MB PORTION OF THE COLUMN. PW VALUES IN
THE 0.5 TO 0.75 INCH RANGE ACROSS THE SOUTH END OF THE FCST AREA
TODAY BUT MAIN 850MB MOISTURE TRANSPORT STAYS WELL SOUTH IN MO AND
THE 700MB TRANSPORT MAINLY REACHES INTO THE SOUTHERN 2/3 OF IA.
MODELS...INCLUDING LOCAL/REGIONAL WRF MODELS ABOUT EVENLY SPLIT ON
-SHRA MAKING IT AS FAR NORTH AS THE KCCY/KOLZ AREAS. CONTINUED SOME
20-40 PERCENT -SHRA CHANCES ACROSS PARTS OF NORTHEAST IA INTO
EXTREME SOUTHWEST WI TODAY...PARTLY TO BLEND WITH NEIGHBORING GRIDS.
MAIN SHOT OF FORCING/LIFT MOVES ACROSS THE AREA THIS MORNING AND
CARRIED HIGHEST RAIN CHANCES AROUND 15Z...WITH RAIN CHANCES
DIMINISHING THRU THE AFTERNOON AS THE LEAD SHORTWAVE PASSES AND THE
COLUMN BEGINS TO DRY. MID/HIGH CLOUDS ACROSS THE AREA TODAY WILL
TEMPER HIGHS. 700-500MB TROUGH AXIS DROPS SOUTH OF THE AREA THIS
EVENING WITH AN INCREASE OF NORTHWEST TO NORTH FLOW AND DRIER AIR
SPREADING SOUTH ACROSS THE FCST AREA. CLOUDS LOOKING TO DECREASE
THIS EVENING WITH MOSTLY CLEAR TO CLEAR SKIES OVERNIGHT. ANOTHER
COOL NIGHT TONIGHT UNDER MOSTLY CLEAR SKIES...A DRY LOW LEVEL
AIRMASS AND WINDS EXPECTED TO BE LIGHT. MAY YET BE SOME PATCHY FROST
ACROSS THE NORTHEAST END OF THE FCST AREA LATE TONIGHT INTO EARLY
THU MORNING. WILL LEAVE IT TO DAY CREW TO FURTHER EVALUATE THIS
AFTER THE CURRENT ADVISORY HAS EXPIRED. FAVORED A BLEND OF THE
GUIDANCE HIGHS/LOWS FOR TODAY/TONIGHT.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 405 AM CDT WED MAY 20 2015

MAIN FCST CONCERNS FOR THU THRU FRI NIGHT...TEMPERATURES.

20.00Z MODELS IN GOOD AGREEMENT ON NORTHWEST FLOW ALOFT OVER THE
UPPER MIDWEST THU THRU FRI...AND REMAIN IN GOOD AGREEMENT FOR HGTS
TO RISE/RIDGING TO BUILD INTO THE REGION FRI NIGHT. MODELS ALSO WITH
RATHER GOOD RUN-TO-RUN CONSISTENCY THIS PERIOD. TREND BY FRI NIGHT
IS TOWARD STRONGER OF THE EARLIER RUNS WITH THE RIDGING OVER THE
REGION. FCST CONFIDENCE FOR THU THRU FRI NIGHT IS GOOD THIS CYCLE.

UNDER THE NORTHWEST FLOW ALOFT MODEL SOUNDINGS AND TIME-HGT X-
SECTIONS SHOWING A RATHER DRY AIRMASS/COLUMN OVER THE AREA FOR
THU THRU FRI. OTHER THAN PERHAPS SOME SCT AFTERNOON CUMULUS DURING
PEAK HEATING...THU THRU FRI SHAPING UP TO BE A CLEAR/SUNNY PERIOD.
DECENT CONSENSUS AMONG THE MODEL FOR A WEAK WAVE TO DROP ACROSS
THE WESTERN GREAT LAKES THU BUT ANY IMPACTS FROM THIS LOOKING TO
REMAIN WELL EAST OF THE FCST AREA. SFC PRESSURE GRADIENTS ON THE
WEAK SIDE FOR LIGHT WINDS...ESPECIALLY FRI WITH A SFC RIDGE AXIS
OVER THE REGION. MODEL SOUNDINGS INDICATING MIXING TO ABOUT 750MB
THU...WITH AROUND 25KTS OF WIND IN THE 850-750MB PORTION OF THE
MIXED LAYER. INCREASED WINDS/GUSTS A BIT THU AFTERNOON. COLUMN
MIXES TO AROUND 825MB FRI...WITH WINDS PROGGED TO BE LESS THAN
10KT THRU 800MB. 850MB TEMPS IN THE +7C TO +9C RANGE BOTH THU/FRI
AFTERNOONS... SUPPORTING HIGHS IN THE UPPER 60S TO NEAR 75. LIGHT
WINDS AND CLEAR SKIES FOR STRONGER RADIATIONAL COOLING THU
NIGHT...FOR A LARGER THAN NORMAL DIURNAL SWING OF TEMPERATURES. AS
PATTERN PROGRESSES FRI NIGHT...SFC-700MB TROUGHING STRENGTHENS IN
THE PLAINS. INCREASING SOUTH TO SOUTHWEST LOW LEVEL FLOW STARTS TO
SPREAD MOISTURE/WARMING NORTHEAST INTO THE UPPER MIDWEST...ALONG
WITH HIGHER LEVEL MOISTURE AHEAD OF THE WESTERN CONUS TROUGHING
SPILLING THRU THE RIDGING AND INTO THE REGION. TREND OF WARMER
LOWS AND SOME INCREASE OF CLOUDS FRI NIGHT LOOKS GOOD. TRENDED
TOWARD WARMER OF GUIDANCE HIGHS THU/FRI...THEN FAVORED A BLEND OF
THE GUIDANCE LOWS THU/FRI NIGHTS.

FOR SATURDAY THRU TUESDAY...DAYS 4 TO 7...

MEDIUM RANGE MODEL RUNS OF 20.00Z IN QUITE GOOD AGREEMENT SAT/SUN
SHOWING THE MID LEVEL RIDGE AXIS TO SLOWLY MOVE EAST OF THE REGION
AND DEEP SOUTHWEST FLOW ALOFT OVER MUCH OF THE UPPER MIDWEST BY LATE
SUN. DIFFERENCES BEGIN TO APPEAR BY SUN NIGHT/MON...ON THE TIMING/
STRENGTH DETAILS OF SHORTWAVE ENERGY EJECTING OUT OF THE WESTERN
CONUS TROUGH AND TOWARD/INTO THE UPPER MIDWEST. DETAIL DIFFERENCES
CONTINUE TUE...BUT GENERAL LONGWAVE CONSENSUS FOR BROAD TROUGHING
OVER MUCH OF THE CENTRAL/WESTERN CONUS. WITH THIS TRENDING TO BE A
MORE UNSETTLED WEATHER PERIOD AND SENSIBLE WEATHER ANY ONE DAY
STRONGLY IMPACTED BY THE SHORTWAVE/MESO-SCALE DETAILS...FCST
CONFIDENCE IN THE DAY 4-7 PERIOD IS AVERAGE THIS CYCLE.

MODEL CONSENSUS HAS SOUTHERLY FLOW AND MOISTURE CONTINUING TO
INCREASE INTO THE UPPER MIDWEST SATURDAY THRU SUN. PW VALUES PROGGED
IN THE 1.5 INCH RANGE OVER MUCH OF THE FCST AREA BY 12Z SUN. THIS
WITH A BROAD INCREASE OF LOWER LEVEL THERMO-DYNAMIC FORCING/LIFT AND
INSTABILITY. MODEL CONSENSUS OF INCREASING SHRA/TSRA CHANCES FROM
WEST TO EAST ACROSS THE AREA FROM SAT THRU SUN NIGHT LOOKING WELL
TRENDED...THOUGH THE SPECIFIC DETAILS OF PERIOD HAVE YET TO BE
SORTED OUT. WITH SLOW PROGRESSION OF THE LONGWAVE PATTERN...AND
ADDITIONAL SHORTWAVES TO COME THRU LONGWAVE TROUGHING THAT IS
PROGGED TO REMAIN OVER THE WEST HALF OF THE CONUS...THE MODEL/
ENSEMBLE CONSENSUS SHRA/ TSRA CHANCES CONTINUING THRU MON/TUE ARE
REASONABLE FOR NOW. GIVEN UNCERTAINTIES WITH SHRA/TSRA CHANCES/
TIMING/COVERAGE /AND CLOUD COVER/ ANY ONE DAY...DID NOT DEVIATE
FROM THE MODEL CONSENSUS HIGHS/LOWS FOR SAT THRU TUE. IF ANY ONE
OR MORE OF DAYS 4 TO 7 END UP DRY AND SUNNIER THAN CURRENTLY
EXPECTED... HIGHS THAT DAY COULD EASILY BE 5F TO 10F WARMER THAN
THOSE IN THE FCST GRIDS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 638 AM CDT WED MAY 20 2015

MID CLOUDS...ASSOCIATED WITH A LOW PRESSURE SYSTEM MOVING THROUGH
THE SOUTHERN MISSOURI...WILL REMAIN OVER BOTH TAF SITES THROUGH
THIS EVENING...AND THEN SKIES WILL CLEAR. LIGHT WINDS WILL
GRADUALLY VEER FROM THE NORTH THIS MORNING TO SOUTH AND SOUTHWEST
BY THIS AFTERNOON AND REMAIN THAT WAY THROUGH TONIGHT.


&&

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

$$

UPDATE...DAS
SHORT TERM...RRS
LONG TERM....RRS
AVIATION...BOYNE


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