Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 241141
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
640 AM CDT SUN APR 24 2016

.SHORT TERM...(TODAY THROUGH MONDAY NIGHT)
ISSUED AT 329 AM CDT SUN APR 24 2016

A BIT OF A TRICKY PRECIP AND CONVECTIVE FORECAST OVER THE NEXT 36
HOURS AS A RATHER POTENT UPPER LOW SPINNING OVER NORTHERN COLORADO
EARLY THIS MORNING WORKS SLOWLY EASTWARD IN OUR DIRECTION...ARRIVING
HERE LATE TONIGHT INTO MONDAY. LITTLE CHANGE TO THE OVERALL PATTERN
AS DISCUSSED IN THIS SPACE YESTERDAY...WITH A SURFACE/ELEVATED WARM
FRONT EXPECTED TO WAVER SLOWLY BACK AND FORTH FROM THE NORTHERN
PLAINS INTO CENTRAL MINNESOTA AND NORTHERN WISCONSIN...WITH THAT
FEATURE THE BIGGEST FOCUS FOR WIDESPREAD RAINFALL THROUGH THE DAY ON
MONDAY. FARTHER SOUTH PRECIP CHANCES WILL HAVE TO RELY ON PERIODS OF
BETTER FORCING...AND TIMING OF THOSE STILL REMAINS SOMEWHAT IN
QUESTION...WITH QUITE A FEW QUESTIONS REGARDING TEMPERATURES AND
RESULTANT INSTABILITY BOTH TODAY AND AGAIN MONDAY. ALL TOLD...STILL
DO EXPECT SOME NEEDED RAINFALL ACROSS THE AREA THROUGH MONDAY OR
MONDAY NIGHT...BUT CONFIDENCE IN WIDESPREAD HEAVIER AMOUNTS STILL
HANGS ON THE LOWER SIDE.

FIRST THINGS FIRST...THE FORECAST AT THE MOMENT IS PLAYING OUT ABOUT
AS EXPECTED YESTERDAY...WITH THE MOST WIDESPREAD PRECIP HOLDING JUST
NORTH OF THE CWA...TIED TO THE BEST LOW LEVEL JET FORCING AND
MOISTURE TRANSPORT INTO THE ELEVATED WARM FRONT. AS OF 06Z ONE BAND
HAS DEPARTED TO THE EAST WHILE ADDITIONAL PRECIP CONTINUES TO
DEVELOP OVER CENTRAL MINNESOTA. FARTHER SOUTH...JUST A SMATTERING OF
VERY HIGH-BASED SHOWERS/SPRINKLES WITHIN AN AGITATED ACCAS FIELD
(MODEST LAPSE RATES ALOFT) CROSSING MUCH OF THE AREA...WHILE MORE
ENHANCED CONVECTION IS ROLLING EAST OUT OF THE CENTRAL HIGH
PLAINS...TIED TO A LEAD SHORTWAVE EJECTING OUT OF THE ROCKIES CLOSED
LOW. THAT PARTICULAR FEATURE SHOULD ROCKET NORTHEASTWARD...ARRIVING
HERE BY LATE MORNING INTO EARLY AFTERNOON. ASSOCIATED QUICK UPTICK
IN LOWER LEVEL MOISTURE ADVECTION SHOULD BE ENOUGH TO ALLOW FOR A
NARROW CORRIDOR OF CONVECTIVE DEVELOPMENT/MAINTENANCE AHEAD OF THAT
WAVE...IMPACTING AREAS ESPECIALLY WEST OF THE MISSISSIPPI.
DRYING/SUBSIDENCE AND SHORTWAVE RIDGING BEHIND THAT LEAD WAVE LOOKS
TO POTENTIALLY SHUT OUT MUCH OF THE AREA FROM PRECIP INTO LATE
AFTERNOON.

DURING THAT SAME STRETCH...WILL BE WATCHING LIKELY CONVECTIVE
DEVELOPMENT BACK OUT OVER EASTERN NEBRASKA INTO WESTERN IOWA WITHIN
AN AXIS OF PRETTY GOOD MID LEVEL DIFLUENCE AND INCREASING
INSTABILITY AHEAD OF THE INCOMING UPPER WAVE. SUFFICIENT DEEP SHEAR
SHOULD FAVOR STORM ORGANIZATION INTO MID EVENING AS THAT ACTIVITY
MARCHES EAST (LIKELY AS A PSUEDO-LINEAR FEATURE PER SHEAR
VECTORS). HOWEVER...DECREASING INSTABILITY WITH EASTWARD EXTENT
WILL LIKELY TEND TO DIMINISH CONVECTIVE INTENSITY WITH TIME AS
ACTIVITY WORKS INTO OUR AREA. PER FORECAST RAOBS...MOST UNSTABLE
CAPE PROFILES FOR A PARCEL LIFTED FROM 900-850 MB SHOW AROUND
500-900 J/KG WITH EFFECTIVE SHEAR AROUND 30-40 KNOTS...MAYBE
ENOUGH FOR A ROGUE STRONGER STORM OR TWO IF WE CAN MANAGE A BIT
MORE INSTABILITY... THOUGH INCREASINGLY NOCTURNAL NATURE OF
CONVECTION WON`T HELP MATTERS. IN FACT...WOULDN`T BE SHOCKED TO
SEE LITTLE LIGHTNING EAST OF THE MISSISSIPPI WITH JUST SOME
REMNANT SHOWERS BENEATH THE BROAD MID LEVEL DIFLUENCE AXIS.

STILL LOOKING LIKE THE UPPER WAVE WILL OPEN UP AS IT DRIFTS OVERHEAD
ON MONDAY...WITH A SURFACE WAVE SKIRTING JUST SOUTH OF THE I-90
CORRIDOR. THAT PLACES MUCH OF THE SOUTHERN/EASTERN CWA POTENTIALLY
IN THE WARM SECTOR ONCE AGAIN FOR MONDAY AFTERNOON...THOUGH THERE
ARE STILL SOME QUESTIONS ABOUT CLOUDS AND AVAILABLE INSTABILITY.
ENOUGH SHEAR REMAINS PRESENT INTO THE AFTERNOON TO WARRANT WATCHING
CLOSELY SOUTH/EAST OF LA CROSSE...THOUGH THE OPENING NATURE TO THE
WAVE AND DECREASING FORCING DOESN`T EXACTLY BOLSTER CONFIDENCE. ON
THE OTHER HAND...WITH GOOD POOLED LOW LEVEL MOISTURE AND BACKED FLOW
JUST IN ADVANCE OF THE SURFACE LOW...A SNEAKY TORNADO THREAT MAY NOT
BE TOTALLY OUT OF THE QUESTION. AS THAT WAVE PASSES...LOOKING LIKE
SHALLOW BUT MUCH CHILLIER AIR WILL ARRIVE INTO MONDAY NIGHT WITH LOW
STRATUS AND MAYBE EVEN SOME DRIZZLE POTENTIAL.

.LONG TERM...(THURSDAY THROUGH SATURDAY)
ISSUED AT 329 AM CDT SUN APR 24 2016

ANOTHER ACTIVE STRETCH OF WEATHER INTO MID/LATE WEEK AND PERHAPS
AGAIN INTO NEXT WEEKEND...THOUGH WITH PLENTY OF QUESTIONS ABOUT
PRECIP TIMING AND EVENTUAL COVERAGE THIS FAR NORTH. TUESDAY STILL
LOOKING FAIRLY QUIET WITH MAYBE SOME STRATUS ISSUES FOR A TIME AS
HUDSON BAY RIDGING ROLLS THROUGH THE AREA. AFTER THAT...THE NEXT
WESTERN TROUGH SHOULD MAKE ITS APPROACH...BUT RUN-TO-RUN
CONSISTENCY AMONG GUIDANCE LOOKS TO BE GETTING POORER WITH
TIME...WITH SOME HINTS NOW THAT THE BEST FORCING AND MOISTURE WILL
REMAIN SOUTH OF THE AREA AND PRECIP MAY HAVE SOME DIFFICULTY
LIFTING NORTH AS STRONGER LOW LEVEL RIDGING AND MUCH DRIER AIR
RESIDE JUST TO THE NORTH. LOOKING DRY BY LATE WEEK WITH HIGH
PRESSURE AGAIN IN CONTROL BEFORE WE HAVE TO WATCH THE NEXT WESTERN
TROUGH PERHAPS MAKING A MOVE IN OUR DIRECTION TOWARD LATER
SATURDAY OR SUNDAY. TEMPS THROUGH THE PERIOD SHOULD TREND BELOW
NORMAL...WITH PERHAPS A CHILLY NIGHT OR TWO DOWN NEAR FREEZING IN
SOME AREAS DURING THOSE PERIODS WHERE CANADIAN HIGH PRESSURE HOLDS
FIRM (MOST LIKELY TOWARD FRIDAY NIGHT).

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 640 AM CDT SUN APR 24 2016

TIMING OF CONVECTION WILL LIKELY BE MAIN CONCERN FOR AVIATION
INTERESTS WITH MAINLY VFR CONDITIONS EXPECTED THROUGH FORECAST.

WARM AIR ADVECTION AND MOISTURE TRANSPORT ON LOW LEVEL JET INTO
REGION GENERATING RELATIVELY HIGH BASED SHOWERS THIS MORNING. EXPECT
THIS ACTIVITY TO WAIN AS LOW LEVEL CONVERGENCE BACKS AND FOCUS FOR
LATER DEVELOPMENT SHIFTS WEST.

ALSO BEEN WATCHING NEXT BATCH OF CONVECTION ACROSS IOWA...BUT THIS
TOO SHOULD GRADUALLY WEAKEN AS IT MIGRATES NORTH-NORTHEAST. WILL
HONOR IT WITH SOME SHOWERS LATER THIS MORNING WITH LOW CONFIDENCE IN
EXTENT OF COVERAGE AT THIS POINT.

HOW REST OF DAY AND TONIGHT PAN OUT ARE ALSO IN QUESTION. COULD BE
QUITE A BIT OF DRY TIME WITH VFR CEILINGS UNTIL MORE ORGANIZED
CONVECTION MOVES IN FROM THE SOUTHWEST THIS EVENING...AHEAD OF
CLOSED UPPER LOW. WILL HAVE TO WAIT UNTIL CLOSER TIME FRAME TO WORK
IN DETAILS.

&&

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

$$

SHORT TERM...LAWRENCE
LONG TERM...LAWRENCE
AVIATION...SHEA



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