Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 062301
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
601 PM CDT FRI MAY 6 2016

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 254 PM CDT FRI MAY 6 2016

OK...WHO TURNED ON THE SWITCH FOR SUMMER? JUST A DOWNRIGHT HOT DAY
OUT THERE BY EARLY MAY STANDARDS...WITH DEEP MIXING INTO PRONOUNCED
THERMAL RIDGING IN ADVANCE OF AN APPROACHING UPPER WAVE/COLD FRONT
SENDING TEMPERATURES THIS AFTERNOON WELL INTO THE 80S AND EVEN
LOWER90. AS EXPECTED...DEW POINTS HAVE MIXED OUT VERY WELL (EVEN
MORE THAN OUR AGGRESSIVE FORECAST)...COURTESY OF DEEP MIXING TO
AROUND 700MB AND LACK OF ANY SIGNIFICANT PRE-FRONTAL MOISTURE
RETURN...WITH FIRE WEATHER CONCERNS HOLDING FIRM THROUGH THE EVENING
HOURS PRIOR TO THE FRONTAL PASSAGE. SPEAKING OF THAT FRONT...THE BIG
QUESTION REMAINS COVERAGE OF ANY PRECIPITATION AS THAT BOUNDARY
DROPS THROUGH THE AREA THIS EVENING AND TONIGHT. AS OF 2 PM...NOT
SEEING A WHOLE LOT OF PRECIPITATION ONGOING WITH THE FRONT BUT DO
SEE SOME HINTS OF BUBBLING ACCAS WITH MIXED LAYER CAPE VALUES
SPIKING TO AROUND 500 J/KG IN A VERY NARROW MOISTURE AXIS JUST IN
ADVANCE OF THE BOUNDARY.

THAT NARROW INSTABILITY AXIS SHOULD GRADUALLY SINK SOUTH INTO OUR
AREA ROUGHLY IN THE 01Z-10Z TIME FRAME PER NEAR TERM GUIDANCE/
OBSERVATIONAL TRENDS...WITH CAPE VALUES AS HIGH AS 800 TO MAYBE 1000
J/KG POSSIBLE IF (THAT`S A BIG IF) WE CAN POOL SUFFICIENT BOUNDARY
LAYER MOISTURE IN THE PRE-FRONTAL ENVIRONMENT...THOUGH INSTABILITY
WILL WANE WITH TIME AS WE PUSH DEEPER INTO THE NIGHT. NOT MUCH IN
THE WAY OF AN UPPER SUPPORT WITH ALL FORCING FROM A SHORTWAVE
PASSING NORTHEAST OF THE AREA...BUT MODEST LOW LEVEL FRONTAL
CONVERGENCE WON`T HURT. IT WILL BE INTERESTING TO SEE IF THE CURRENT
AXIS OF BETTER MOISTURE INTO EASTERN SOUTH DAKOTA AND FAR SOUTHWEST
MINNESOTA CATCHES UP TO THE BOUNDARY TO DRIVE AN AXIS OF SLIGHTLY
HIGHER INSTABILITY THE NEXT FEW HOURS. ALL IN ALL...PLAN TO KEEP
SCATTERED SHOWERS AND STORMS GOING THROUGH THE EVENING AND FIRST
PART OF THE NIGHT IN LINE WITH CURRENT NEAR TERM GUIDANCE TRENDS
WHICH SUGGEST A CONVECTIVE LINE DEVELOPING JUST ON OUR DOORSTEP...
BUT WOULDN`T BE TOTALLY SHOCKED IF NOT A LOT ENDS UP HAPPENING GIVEN
JUST HOW DRY THINGS ARE OUT THERE. STRONGLY INVERTED-V AND
ASSOCIATED DOWNDRAFT CAPE PUSHING 1000 J/KG ARGUES FOR SOME GUSTY
WIND POTENTIAL NEAR ANY CONVECTION...AND PERHAPS EVEN A DRY
LIGHTNING THREAT GIVEN CLOUD BASES AT OR ABOVE 9KFT AND EXTREME
DRYNESS BELOW THAT. A VERY MILD EVENING/FIRST HALF OF THE NIGHT IN
STORE BEFORE TEMPS SLOWLY TAKE A DIP BACK THROUGH THE MORE
COMFORTABLE 50S THROUGH SUNRISE.

LINGERING SHOWER POTENTIAL THROUGH MID MORNING SATURDAY INTO
NORTHEAST IA AND FAR SOUTHWEST WI WILL END BY 10 AM OR SO...WITH
NOTABLY COOLER AND DRIER AIR ARRIVING THROUGH THE DAY AS LOW LEVEL
RIDGING TAKES HOLD AND WINDS HOLD FROM THE NORTH. DEEPER MIXING INTO
INCREASED DRYING ALOFT SHOULD DELIVER SOME VERY COMFORTABLE HUMIDITY
LEVELS RIGHT ON THROUGH THE ENTIRE WEEKEND...AS RAIN CHANCES BECOME
RELEGATED TO CENTRAL IOWA ALONG A TIGHTER FRONTOGENETIC AXIS.
OVERALL...LOOKING LIKE AN AWESOME WEATHER WEEKEND FOR ANY OUTDOOR
ACTIVITIES.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 254 PM CDT FRI MAY 6 2016

THE NEW WORK WEEK LOOKS TO BRING A MORE ACTIVE WEATHER REGIME BACK
TO THE AREA...AS CLOSED LOW PRESSURE OVER THE SOUTHWEST CONUS
GRADUALLY OPENS UP WHILE LIFTING TOWARD THE UPPER MISSISSIPPI VALLEY
BY TUESDAY. THAT SETUP WILL LIFT BROAD SURFACE LOW PRESSURE AND A
WARM FRONT BACK NORTH TOWARD OUR AREA WITH TIME...WITH AN UPTICK IN
DEEPER MOISTURE AND VARIOUS BOUTS OF BETTER FORCING LIKELY
DELIVERING ROUNDS OF RAINFALL INTO MIDWEEK. STILL SOME QUESTION
ABOUT JUST WHEN PRECIPITATION MIGHT ARRIVE...WITH INITIAL
MOISTURE ADVECTION/LIFT GOING INTO SATURATION OF A QUITE DRY
AIRMASS SUNDAY NIGHT THROUGH MIDDAY MONDAY. PER RECENT TRENDS...IT
WOULD APPEAR THE MORE WIDESPREAD PRECIPITATION COVERAGE WILL HOLD
OFF UNTIL MONDAY AFTERNOON AND BEYOND...WITH SOME CHANCE FOR
THUNDER AT TIMES PENDING DEGREE OF AVAILABLE INSTABILITY. CAN
ENVISION THE BETTER THUNDER THREAT BISECTING THE CWA SOUTH TO
NORTH WITH NORTHERN AREAS WELL REMOVED FROM THE WARM
FRONT...THOUGH CONFIDENCE IN SPECIFICS THIS FAR OUT REMAINS ON THE
LOWER SIDE. SPEAKING OF LOWER CONFIDENCE...TEMPS IN THIS SETUP FOR
EARLY/MID WEEK ARE TRICKY AS ANY WIDESPREAD RAIN AND CLOUDS COULD
EASILY HOLD READINGS DOWN QUITE A BIT. FOR NOW...A CONSENSUS BLEND
ARGUES FOR SEASONABLE READINGS INTO THE 60S EACH DAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 601 PM CDT FRI MAY 6 2016

THE COLD FRONT EXTENDED FROM NEAR KDLH INTO SOUTHERN SOUTH DAKOTA
LATE THIS AFTERNOON. THIS FRONT WILL CONTINUE TO MOVE SOUTH AND
PASS THROUGH BOTH SITES LATE THIS EVENING OR EARLY IN THE
OVERNIGHT HOURS. THE CONCERN AHEAD OF THE FRONT IS WHETHER ANY
CONVECTIVE ACTIVITY WILL OCCUR. THE MAJORITY OF THE HI-RES MODELS
WOULD SUGGEST THE FRONT WILL PASS THROUGH WITHOUT ANYTHING
OCCURRING ALONG IT...BUT MOST OF THEM ARE ALSO NOT HANDLING THE
CURRENT ACTIVITY ALONG THE FRONT VERY WELL EITHER. THE 06.21Z HRRR
ACTUALLY HAS A GOOD DEPICTION OF THE CURRENT ACTIVITY AND DOES
BRING THROUGH A LINE OF SHOWERS AHEAD OF THE FRONT THIS EVENING.
BASED ON THIS WILL CONTINUE TO MENTION A VCSH FOR BOTH SITES. THE
06.18Z NAM INDICATES THERE WILL BE SOME WEAK FRONTOGENESIS OVER
THE AREA THIS EVENING IN THE 850-700 MB LAYER WHICH COULD PRODUCE
A SECONDARY ROUND OF SHOWERS UNTIL THE FRONT MOVES THROUGH. WILL
COVER THIS BY KEEPING THE VCSH GOING UNTIL THE FRONT MOVES
THROUGH. VFR CONDITIONS EXPECTED BEHIND THE FRONT WITH JUST SOME
MID TO HIGH LEVEL CLOUDS AND NORTH WINDS OF 10 TO 15 KNOTS.

&&

.FIRE WEATHER...
ISSUED AT 254 PM CDT FRI MAY 6 2016

VERY HIGH FIRE DANGER CONTINUES ACROSS THE AREA THROUGH THE
EVENING WITH DEEP MIXING SENDING RH VALUES DOWN THROUGH THE 15-20
PERCENT RANGE AND TEMPERATURES SOARING THROUGH THE UPPER 80S AND
LOWER 90S. HUMIDITY LEVELS WILL BE SLOW TO RECOVER THROUGH THE
EVENING BUT HUMIDITY RECOVERY WILL ACCELERATE IN THE WAKE OF A
PASSING COLD FRONT AFTER MIDNIGHT. STILL EXPECT WE MAY SEE
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS AS THAT FRONT
PASSES...BUT WITH VERY HIGH CLOUD BASES AND LOTS OF DRY AIR
BELOW...DO HAVE SOME CONCERN BOTH WITH THE THREAT FOR SOME DRY
LIGHTNING AS WELL AS INCREASED GUSTY WINDS NEAR ANY SHOWERS AS
PRECIPITATION FALLS OUT OF A 10KFT CLOUD BASE. COOLER CONDITIONS
BUT CONTINUED LOWER HUMIDITY LEVELS ARE EXPECTED FOR THE
WEEKEND...BUT WITH WINDS MUCH LIGHTER THAN THOSE NOTED TODAY.

&&

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

$$

SHORT TERM...LAWRENCE
LONG TERM...LAWRENCE
AVIATION...04
FIRE WEATHER...LAWRENCE


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