Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 211637
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1137 AM CDT THU MAY 21 2015

.UPDATE...
ISSUED AT 1056 AM CDT THU MAY 21 2015

UPDATED FORECAST TO INCLUDE A SMALL-END CHANCE FOR SHOWERS THIS
AFTERNOON ACROSS CENTRAL WI WITH PASSAGE OF MID-LEVEL/SURFACE
TROUGH. ALTHOUGH LOW LEVELS WILL BE DRY FOR NIL SURFACE-BASED
INSTABILITY...FEEL ENOUGH MID-LEVEL LAPSE RATES MAY PRODUCE A FEW
HIGHER-BASED SHOWERS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 401 AM CDT THU MAY 21 2015

MAIN SHORT-TERM FCST CONCERNS...TEMPERATURES.

06Z DATA ANALYSIS HAD HIGH PRESSURE CENTERED OVER NEB. WV IMAGERY
SHOWED A STRONGER SHORTWAVE DROPPING SOUTH ACROSS MN/SD. NO WEATHER
WITH THIS FEATURE...WITH CLOUDS ACTUALLY CLEARING ACROSS WI/IA WELL
IR IMAGERY AHEAD OF IT. A SECOND SHORTWAVE COULD BE SEEN IN WV
IMAGERY DROPPING SOUTH OF LK WINNIPEG. A SFC TROUGH WITH THIS
FEATURE WAS LOCATED NORTH OF LK SUPERIOR TO ND...SINKING SLOWLY
SOUTH. LITTLE MORE THAN SCT TO LOCALLY BKN 10K-12K CLOUDS ACROSS
ND/NORTHERN MN. CLEAR SKIES AND LIGHT WINDS ALLOWING FOR ANOTHER
COOL NIGHT ACROSS MUCH OF THE REGION.

21.00Z MODELS INITIALIZED WELL. LEAD SD/MN SHORTWAVE PASSING EARLY
THIS MORNING SETS UP MDT NORTHWEST FLOW ALOFT OVER THE UPPER MIDWEST
FOR TODAY/TONIGHT. TIGHT/IMPROVING CONSISTENCY AMONG MODELS FOR THE
SECOND SHORTWAVE SOUTH OF LK WINNIPEG TO WEAKEN AS IT DROPS SOUTH-
SOUTHEAST ACROSS THE REGION TODAY...LEAVING QUIET NORTHWEST FLOW
ALOFT TONIGHT. SHORT-TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

MODEL SOUNDING SHOWING A RATHER DEEP...DRY COLUMN OVER THE AREA
TODAY. SECOND SHORTWAVE DROPPING SOUTH ACROSS THE AREA TODAY...SO
CLOSE BEHIND THE STRONGER MN/SD WAVE...HAS TO CONTEND WITH THIS DRY
AIR. WITH LITTLE MORE THAN SCT-BKN ALTO-CU WITH THIS FEATURE EARLY
THIS MORNING...TRENDED SKY GRIDS TOWARD MORE SUNSHINE TODAY AND
REMOVED ANY SMALL -SHRA CHANCES OVER THE EAST END OF THE FCST AREA.
MODEL SOUNDINGS SHOWING MIXING TO AROUND 800MB TODAY...WITH 20-22KTS
OF NORTHWEST FLOW IN THE 850-800MB PORTION. THIS A BIT LESS WIND
THAN 20.00Z SOUNDINGS INDICATED. GIVEN PLENTY OF SUNSHINE AND THE
DEEP MIXING TODAY...NORTHWEST WINDS OF 10-20MPH WITH SOME GUSTS OF
20-25MPH STILL EXPECTED THIS AFTERNOON. THIS AS THE SFC-850MB
TROUGH GOES BY AS WELL. GRADIENT RELAXES QUICKLY THIS EVENING WITH
BROAD/WEAK HIGH PRESSURE OVER THE REGION BY 12Z FRI. 850MB TEMPS
IN THE +5C TO +8C RANGE TODAY...SUPPORTING HIGHS IN THE UPPER 60S-
LOW 70S...PERHAPS A FEW MID 70S IN FAVORED WARMER LOCATIONS.
STRONG RADIATIONAL COOLING AGAIN TONIGHT WITH LIGHT WINDS/CLEAR
SKIES AND A RELATIVELY DRY LOW LEVEL AIRMASS...WITH AS MUCH AS A
30-35F DIURNAL DROP EXPECTED ACROSS MUCH OF THE NORTHEAST 1/3 OF
THE FCST AREA. A BLEND OF THE GUIDANCE HIGHS/LOWS FOR
TODAY/TONIGHT APPEARS TO HAVE THEM WELL TRENDED.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 401 AM CDT THU MAY 21 2015

MAIN FCST CONCERNS FOR FRI THRU SAT NIGHT...SHRA/TSRA CHANCES
INCREASING SAT/SAT NIGHT...TEMPERATURES THRU THE PERIOD.

21.00Z MODELS IN GOOD AND TIGHTENING AGREEMENT AS NORTHWEST FLOW
ALOFT PERSIST OVER THE UPPER MIDWEST FRI/FRI NIGHT. FLOW THEN
TRANSITIONS TO SHORTWAVE RIDGING AND SOUTHWEST FLOW ALOFT OVER THE
REGION BY 12Z SUN...AHEAD OF THE NEXT STRONG TROUGH MOVING INTO THE
PLAINS. CAN-GEM WITH THE BETTER RUN-TO-RUN CONSISTENCY ON THE
RIDGING/HGTS OVER THE REGION SAT NIGHT. TREND BY SAT NIGHT GENERALLY
FAVORS STRONGER OF THE EARLIER RUNS WITH THE RIDGING ALOFT AND
STRONGER OF EARLIER RUNS WITH THE TROUGHING COMING THRU THE ROCKIES.
FRI THRU SAT NIGHT FCST CONFIDENCE IS GOOD FRI/FRI NIGHT THEN
AVERAGE TO GOOD SAT/SAT NIGHT.

MODIFIED CANADIAN HIGH PRESSURE DRIFTS ACROSS THE REGION FRI THEN
INTO THE OH VALLEY FRI NIGHT. DRY...SUNNY DAY WITH LIGHT WINDS
EXPECTED SAT. MODEL SOUNDINGS SHOWING MIXING TO 825MB ON FRI...WITH
WINDS IN THE TOP OF THE MIXED LAYER ON FRI ONLY AROUND 5KTS. 850MB
TEMPS ON FRI PROGGED ABOUT 1C WARMER THAN THOSE OF THU...WITH FRI
HIGHS LOOKING TO BE MORE IN THE LOW-MID 70S. GRADIENT STARTS TO
TIGHTEN FRI NIGHT WITH THE HIGH MOVING OFF AND LOW PRESSURE
DEVELOPING IN THE PLAINS. AT LEAST LIGHT SOUTH TO SOUTHEAST WINDS
EXPECTED LATER FRI NIGHT...ALONG WITH SOME 500-300MB MOISTURE
STREAMING OUT OF THE WESTERN TROUGH AND INTO THE RIDGING OVER THE
REGION. ANOTHER COOL NIGHT ACROSS THE NORTHEAST 1/3 OF THE FCST
AREA BUT LOWS ALONG/WEST OF THE MS RIVER TRENDING CLOSER TO NORMAL
FRI NIGHT.

WITH MODEL CONSENSUS TRENDING TOWARD MORE RIDGING OVER THE AREA SAT
INTO SAT NIGHT...MAIN MOISTURE AXIS REMAINS WEST OF THE FCST AREA AT
LEAST EARLY SAT. THIS MOISTURE AXIS/INCREASE OF MOISTURE INTO THE
FCST AREA IS DELAYED AS WELL...WITH THE DEEPER OF THE MOISTURE/
SATURATION NOT ARRIVING UNTIL SAT EVENING OR EVEN LATER SAT NIGHT.
CAPE REMAINS LIMITED WITH LESSER MOISTURE INCREASE SAT AND LIFT
REMAINS WEAKER UNDER THE RIDGING AND AS WELL. REDUCED SHRA/TSRA
CHANCES ON SAT AND IF PRESENT TRENDS CONTINUE...SAT LIKELY TO END UP
WITH A DRY FCST ESPECIALLY EAST OF THE MS RIVER. RAIN CHANCES
INCREASE SAT NIGHT AND CONTINUED WITH 30-50 PERCENT SHRA/TSRA
CHANCES SAT NIGHT...HIGHEST AFTER MIDNIGHT WHEN DEEPER OF THE
MOISTURE...THE MID LEVEL RIDGE AXIS START TO MOVE EAST OF THE FCST
AREA AND SOME STRONGER LOW LEVEL THERMO-DYNAMIC FORCING STARTS TO
ARRIVE. TRENDED TOWARD WARMER OF GUIDANCE HIGHS FRI THEN USED A
BLEND OF THE GUIDANCE LOWS/HIGHS FOR FRI NIGHT THRU SAT NIGHT.

FOR SUNDAY THROUGH WEDNESDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES AND TEMPERATURES
THRU THE PERIOD.

MEDIUM RANGE MODEL RUNS OF 21.00Z IN GOOD AGREEMENT AS THE ROCKIES
TROUGHING PUSHES INTO THE PLAINS SUN AND THE MID LEVEL RIDGE AXIS
MOVES TO NEAR LK MI/SUPERIOR. MODELS SHOWING IMPROVING AGREEMENT FOR
A STRONG PIECE OF ENERGY/MAJOR PORTION OF THE TROUGH TO LIFT TOWARD/
ACROSS THE WESTERN SUN NIGHT/MON. TREND IS SLOWER/STRONGER WITH THE
FEATURES SUN NIGHT/MON. GOOD CONSENSUS FOR HGTS TO RISE ACROSS
THE CENTRAL CONUS TUE AS MORE TROUGHING/ENERGY APPROACHES THE WEST
COAST. HOWEVER...ALL MODELS HAVE A STRONGER SHORTWAVE MOVING
ACROSS THE CENTRAL PLAINS TOWARD THE REGION ON TUE WITH THIS
ENERGY/ TROUGH TO MOVE ACROSS THE UPPER MIDWEST TUE NIGHT. MIXED
SIGNALS WITH THE FLOW OVER THE REGION WED...HOWEVER A STRONGER
SIGNAL FOR MORE ENERGY/TROUGHING TO BE MOVING INTO THE WESTERN
CONUS ON DAY 7. GIVEN DEPENDENCY OF SHRA/TSRA CHANCES/SENSIBLE
WEATHER MUCH OF THE DAY 4-7 PERIOD ON THE NUANCES OF SMALLER SCALE
DETAILS AND TIMING...FCST CONFIDENCE IN THIS UNSETTLED TRENDING
PERIOD REMAINS AVERAGE.

STRONGER FORCING/DEEPER MOISTURE WOULD SPREAD INTO/ACROSS THE
AREA SUN/SUN NIGHT AS THE SFC LOW AND SIZABLE PORTION OF THE MID
LEVEL TROUGH/ENERGY MOVES INTO THE REGION. PLENTY OF DETAIL
DIFFERENCES WITH WHERE THE LOW AND ITS FRONTS END UP BY MON NIGHT
AND WHERE THE STRONGER/DEEPER OF THE FORCING/LIFT WOULD PASS.
MODELS CONTINUE TO INDICATE CAPE REMAINING ON THE LOW SIDE THRU
SUN/SUN NIGHT. EVEN SO...CONSENSUS SHRA/TSRA CHANCES INCREASING
INTO THE 60- 70 PERCENT RANGE BY SUN NIGHT LOOK REASONABLE. 21.00Z
CONSENSUS WOULD HAVE THE LOW PASS WITH SOME DRYING AND LOWER
SHRA/TSRA CHANCES MON INTO MON NIGHT...HOWEVER TIMING BY DAY 5 HAS
LIMITED CONFIDENCE. REMNANTS OF THE TROUGH LIFTING ACROSS THE
CENTRAL PLAINS TUE AND ACROSS THE REGION TUE NIGHT WOULD SPREAD
INCREASING MOISTURE/LIFT BACK INTO THE AREA FOR DAYS 6 TO 7. 30-50
PERCENT SHRA/TSRA CHANCES FOR TUE THRU WED OKAY FOR NOW. NOT ALL
THE PERIODS FROM SUN THRU WED WILL END UP WET...BUT GIVEN
POTENTIAL MODEL TRENDS AND DEPENDENCE ON TIMING AND MESO-SCALE
DETAILS...DETERMINING WHICH OF THE SUN-WED DAYS WOULD END UP DRY
IS DIFFICULT AT BEST IN THE DAY 4-7 TIMEFRAME. CONSENSUS
HIGHS/LOWS FOR SUN-WED GOOD FOR NOW...BUT MAY WELL BE SOME 5F-10F
TOO COOL ANY ONE DAY IF MORE SUNSHINE WOULD PREVAIL AND THE DAY
ENDS UP DRY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1137 AM CDT THU MAY 21 2015

LOOK FOR WINDS TO SUBSIDE THIS EVENING AS HIGH PRESSURE BUILDS
INTO THE REGION. CLEAR SKIES AND GENERALLY LIGHT/VARIABLE WINDS ARE
EXPECTED TONIGHT INTO FRIDAY AS THE HIGH DRIFTS ACROSS THE AREA.

&&

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

$$

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



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