Area Forecast Discussion
Issued by NWS La Crosse, WI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KARX 312304
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
604 PM CDT FRI JUL 31 2015

.SHORT TERM...(TONIGHT THRU SATURDAY NIGHT)
ISSUED AT 315 PM CDT FRI JUL 31 2015

MAIN FCST CONCERNS THIS PERIOD...SMALL SHRA/ISOLATED TSRA CHANCES
LATE TONIGHT...SHRA/TSRA CHANCES/SEVERE THREAT SAT NIGHT.

18Z DATA ANALYSIS HAD STRONG LOW PRESSURE OVER HUDSONS BAY AND BROAD
HIGH PRESSURE OVER THE CENTRAL/NORTHERN PLAINS INTO THE MID MS
VALLEY. PRESSURE GRADIENT BETWEEN THE TWO REMAINED OVER WI/MN/
EASTERN IA. DIURNAL WARMING AND MIXING TO 5K FT ONCE AGAIN PRODUCING
BRISK/GUSTY NORTHWEST WINDS ACROSS MUCH OF THE REGION. MOISTURE
CLOSER TO THE LOW AND COOLER MID LEVEL TEMPS ALLOWING FOR DIURNAL
CUMULUS ALONG/NORTHEAST OF I-94. GENERALLY CLEAR SKIES ELSEWHERE.
EARLY AFTERNOON TEMPS NEAR NORMAL FOR THE LAST DAY OF JULY.

31.12Z MODEL RUNS LOOK TO HAVE INITIALIZED QUITE WELL THIS MORNING.
SOLUTIONS VERY SIMILAR AS ONE STRONGER SHORTWAVE DROPS INTO THE
EASTERN GREAT LAKES TONIGHT...WEAK SHORTWAVE RIDGING SLIDES ACROSS
THE REGION SAT THEN AS HGTS FALL SAT NIGHT AHEAD OF A STRONGER
SHORTWAVE ENERGY DROPPING SOUTH ACROSS MANITOBA AND COMING THRU THE
WESTERN NOAM RIDGING. TREND IS STRONGER WITH THE HGT FALLS/
SHORTWAVE ENERGY DROPPING TOWARD/INTO THE REGION SAT NIGHT. GIVEN
THE TIGHT MODEL CONSENSUS...SHORT-TERM FCST CONFIDENCE IS GOOD THIS
CYCLE.

WEAK SHORTWAVE OVER MT THIS AFTERNOON SLIDES QUICKLY EAST-SOUTHEAST
TONIGHT...BRINGING WITH IT A ROUND OF 850-700MB WARM ADVECTION AND
MOISTURE TRANSPORT. THIS WITH WEAK CAPE WHEN LIFTING PARCELS IN THE
850-700MB LAYER. RATHER CONSISTENT SIGNAL AMONG HIGH-RES/WRF MODELS
FOR THIS WEAK WAVE AND LOWER LEVEL THERMO-DYNAMIC FORCING TO PRODUCE
SOME ISOLATED TO SCT SHRA ACROSS THE AREA LATER TONIGHT...MAINLY
BETWEEN 06-12Z. ADDED A 20 PERCENT SHRA/ISOLATED TSRA MENTION TO
THIS PERIOD TONIGHT...MAINLY SOUTHWEST OF I-94. QUIET/DRY SAT AS
HGTS RISE A BIT AND A WEAK SFC RIDGE AXIS DRIFTS EAST ACROSS THE
UPPER MIDWEST. SFC/LOW LEVEL FLOW FINALLY SWINGS MORE WEST/SOUTHWEST
WITH LOWER LEVEL WARM ADVECTION SPREADING ACROSS THE AREA. SOME
INCREASE OF 700MB MOISTURE/CLOUDS LOOK TO OFFSET THE 925MB
WARMING...WITH HIGHS SAT SIMILAR TO THOSE OF THE PAST FEW DAYS.
MOISTURE CONTINUES TO INCREASE SAT NIGHT...AHEAD OF THE LOWER LEVEL
TROUGH AND THE FALLING HGTS ALOFT. MODEL SOUNDINGS SHOWING THE BULK
OF THE MOISTURE/SATURATION AND RESULTING MUCAPE IS ABOVE 850MB...
WITH ANYWHERE FROM 100-500 CIN/CAPPING INDICATED FOR THE SFC-925MB
LAYER SAT NIGHT. MAJORITY OF THE FORCING/LIFT WITH THE SHORTWAVE
DROPPING TOWARD THE REGION IS OVER NORTHERN MN/NORTHERN WI WHILE
HIGHER OF THE CAPE IS OVER IA/NEARBY AREAS. PER MODEL SOUNDINGS...PW
VALUES ARE IN THE 0.75 TO 1.3 INCH RANGE SAT NIGHT. LEFT SHRA/TSRA
CHANCES SAT NIGHT IN THE 20-50 PERCENT RANGE BUT DID ADD SOME
TEMPORAL RESOLUTION BRINGING THESE CHANCES SOUTHEAST ACROSS THE
AREA. CONFIDENCE NOT HIGH ON ANY SEVERE THREAT WITH TSRA SAT NIGHT.
THIS GIVEN THE ELEVATED NATURE OF THE MOISTURE/INSTABILITY...STRONG
BOUNDARY LAYER CAPPING AND BULK SHEAR WHEN LIFTING 850-700MB PARCELS
LOOKING TO BE AROUND 20 KTS. SEE SWODY2 FOR MORE DETAILS. USED A
BLEND OF THE GUIDANCE LOWS/HIGHS FOR TONIGHT THRU SAT NIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 315 PM CDT FRI JUL 31 2015

MAIN FCST CONCERNS FOR SUNDAY THRU MONDAY NIGHT...SHRA/TSRA CHANCES
SUN/SUN NIGHT...TEMPERATURES THRU THE PERIOD.

31.12Z MODELS IN GOOD AGREEMENT FOR THE TROUGH/SHORTWAVE ENERGY TO
DROP INTO/ACROSS THE REGION SUN/SUN NIGHT. TREND CONTINUES ON THE
STRONGER SIDE WITH THIS WAVE/ENERGY AS IT PASSES. MODELS IN DECENT
AGREEMENT FOR SLOW EASTWARD PROGRESSION OF THE LONGWAVE LOW/TROUGH
AND WESTERN NOAM RIDGING MON/MON NIGHT. IMPROVING SIGNAL FOR SOME
STRONGER SHORTWAVE ENERGY TO MOVE EAST THRU THE RIDGING...REACHING
THE CENTRAL PLAINS BY 12Z TUE BUT REMAINING WELL WEST/SOUTH OF THE
FCST AREA. FCST CONFIDENCE IN THE SUN THRU MON NIGHT PERIOD IS
GENERALLY GOOD THIS CYCLE.

FCST AREA REMAINS AHEAD OF THE SFC-925MB TROUGH/FRONT SUN.
TIGHTENING CONSENSUS FOR THIS BOUNDARY TO MOVE SOUTHEAST ACROSS THE
AREA SUN...REACHING A KGRB-KDBQ-KDSM LINE AROUND 00Z MON. FORCING
ALONG THIS TROUGH/FRONT APPEARS TO BE RATHER WEAK...WITH THE MAIN
SHORTWAVE ENERGY PASSING NORTH/EAST OF THE FCST AREA. MODEL
SOUNDINGS SHOWING CONSIDERABLE CAPPING WITH AN INVERSION BETWEEN 900-
850MB THRU MUCH OF THE DAY. FRONT MAY PASS THRU MUCH OF THE FCST
AREA BEFORE THE CAPPING ERODES ENOUGH TO ALLOW FOR CONVECTION. LEFT
SOME SMALL SHRA/TSRA CHANCES IN THE SOUTHEAST END OF THE FCST AREA
SUN MORNING...FOR POTENTIAL OF LINGERING/SLOWING SHRA/TSRA FROM SAT
NIGHT. CARRIED A 20-30 PERCENT SHRA/TSRA CHANCE FOR MUCH OF THE AREA
SUN AFTERNOON GIVEN THE UNCERTAINTIES AND THE FRONT IN THE AREA.
LEFT SOME 20-30 PERCENT SHRA/TSRA CHANCES MAINLY SUN EVENING AND
MAINLY TO BLEND WITH NEIGHBORING GRIDS. HOWEVER...PASSAGE OF THE SFC-
850MB TROUGH/FRONT NOW LOOKS TO TAKE THE SHRA/TSRA CHANCES WITH IT
WHICH WOULD LEAVE MUCH OF THE FCST AREA DRY SUN NIGHT. WEAK HIGH
PRESSURE AND DRYING SPREAD IN FOR MON/MON NIGHT. SOME WEAK LOWER
LEVEL MOISTURE TRANSPORT/ISENTROPIC LIFT ASSOCIATED WITH THE
SHORTWAVE ENERGY COMING ACROSS THE CENTRAL PLAINS GRAZES THE
SOUTHWEST END OF THE FCST AREA LATER MON NIGHT. INCLUDED A SMALL
SHRA/TSRA CHANCE ACROSS THE FAR SOUTHWEST END OF THE FCST AREA TO
BLEND WITH THE NEIGHBORING GRIDS. WARM AIRMASS OVER THE AREA SUNDAY
AHEAD OF THE FRONT WITH MDT LOW LEVEL COLD ADVECTION SPREADING OVER
THE AREA SUN NIGHT INTO MON BEHIND THE FRONT. MODEL/ENSEMBLE
CONSENSUS OF ABOVE NORMAL HIGHS IN THE LOW-MID 80S ON SUNDAY LOOKS
GOOD. STAYED WITH THE CONSENSUS BLEND OF LOWS/HIGHS FOR SUN NIGHT
THRU MON NIGHT.

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

MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES FOR TUE NIGHT AND
BEYOND...TEMPERATURES.

MEDIUM RANGE MODELS OF 31.00Z/31.12Z IN REASONABLY GOOD AGREEMENT
FOR THE UPPER MIDWEST TO REMAIN UNDER NORTHWEST FLOW ALOFT THRU NEXT
WEEK. THIS AS A MID LEVEL LOW OVER JAMES BAY ON TUE DRIFTS VERY
SLOWLY EAST INTO QUEBEC BY FRI AND RIDGING OVER THE ROCKIES ON TUE
ONLY MOVES TO CENTRAL NOAM BY FRI. OVERALL TREND FAVORS A TIGHTENING
CONSENSUS OF THE EARLIER RUNS. FCST CONFIDENCE FOR TUE THRU FRI IS
AVERAGE THIS CYCLE.

EVEN WITH A RATHER GOOD CONSENSUS AMONG THE MODELS WITH THE LONGWAVE
PATTERN OVER NOAM TUE-FRI...PLENTY OF DETAIL DIFFERENCES WITH
SHORTWAVE DETAILS IN THE FLOW. SHORTWAVE ENERGY CROSSING THE PLAINS
STAYS WEST OF THE AREA TUE...WITH SOME CONSENSUS FOR SOME PORTION OF
THIS ENERGY TO PUSH ACROSS THE REGION WED. SOME SIGNAL FOR ANOTHER
WAVE TO COME THRU THE RIDGING AND MOVE ACROSS THE REGION THU...THEN
A MORE NORTHERN STREAM WAVE TO DROP SOUTH OUT OF CAN INTO THE UPPER
MIDWEST FRI. WILL LEAVE TUE DRY WITH HIGH PRESSURE...A DRIER AIRMASS
AND LACK OF SHORTWAVE ENERGY MOVING ACROSS THE AREA. MOISTURE STARTS
TO INCREASE TUE NIGHT/WED...WITH A WAVE OF LOW PRESSURE AND THE
SHORTWAVE ENERGY WORKING EAST ACROSS THE CENTRAL/NORTHERN PLAINS.
MORE/DEEPER MOISTURE THEN PROGGED OVER THE AREA FOR WED NIGHT INTO
FRI...AS OTHER SHORTWAVES WOULD RIPPLES ACROSS THE REGION. CONSENSUS
SHRA/TSRA CHANCES IN THE 20-40 PERCENT RANGE FOR WED THRU FRI OKAY
FOR NOW UNTIL THE DETAILS SORT THEMSELVES OUT. WITH THE CONTINUED
NORTHWEST FLOW ALOFT...MODEL CONSENSUS TEMPERATURES A CATEGORY OR
TWO BELOW NORMAL FOR TUE-FRI APPEAR REASONABLE.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 604 PM CDT FRI JUL 31 2015

LARGE AREA OF HIGH PRESSURE EXTENDS FROM NORTH DAKOTA INTO
MISSOURI LATE THIS AFTERNOON. NORTHWEST FLOW ALOFT OVER THIS HIGH
HAS BROUGHT SOME SHORT WAVE TROUGHS OVER THE GREAT LAKES REGION
WITH SOME SCATTERED STORMS THERE. SOME SUGGESTIONS BY THE 31.18Z
NAM THAT ANOTHER ONE OF THESE WAVES MAY SLIDE ACROSS MINNESOTA AND
WISCONSIN LATE THIS EVENING INTO THE OVERNIGHT. SOME OF THE HI-RES
MODELS PICK UP ON THIS AND PRODUCE SOME WIDELY SCATTERED SHOWERS
WITH THIS WAVE. LOOKING AT THE FORECAST SOUNDINGS FROM THE
NAM...IF THESE SHOWERS DEVELOP...THEY WOULD BE HIGH BASED AND WITH
LOTS OF DRY AIR IN THE LOWER LEVELS...WOULD PROBABLY ONLY BE ABLE
TO PRODUCE SOME SPRINKLES OR A VERY SHORT LIVED SHOWER. PREVIOUS
FORECAST HAD ALREADY PUT IN VCSH FOR THIS AND WILL CONTINUE
THIS...BUT CONFIDENCE IS VERY LOW THAT THESE WILL DEVELOP.
OTHERWISE...LOOKING AT THE CONTINUANCE OF VFR CONDITIONS THROUGH
THE PERIOD WITH WEST TO NORTHWEST WINDS OF 10 KNOTS OR LESS.

&&

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

$$

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


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.