Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 061954
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
254 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 PRECIP AS THAT BOUNDARY DROPS
THROUGH THE AREA THIS EVENING AND TONIGHT. AS OF 2 PM...NOT SEEING A
WHOLE LOT OF PRECIP 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 PRECIP 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 PRECIP 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 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1155 AM CDT FRI MAY 6 2016

A COUPLE BOUNDARIES OF CONCERN TONIGHT...ALTHOUGH THE AMOUNT OF
IMPACTFUL WEATHER IS LIKELY MINIMAL.

FIRST...PRE-FRONTAL LINE OF CONVERGENCE SLATED TO MOVE TOWARD
KRST/KLSE TOWARD 00Z THIS EVENING. MESO MODELS ALL POINTING TO A MID
LEVEL DECK OF CONVECTION FIRING IN RESPONSE...10 KFT OR SO. SOME
ELEVATED INSTABILITY COULD RESULT IN ISOLATED THUNDER. VERY DRY IN
THE SUB CLOUD LAYER THOUGH...PCPN WILL HAVE A HARD TIME MAKING IT TO
THE SFC. PERHAPS MORE VIRGA. THAT SAID...THE DRY AIR WILL ENHANCE
GUSTINESS AROUND ANY SHOWER/STORM.

OVERNIGHT A COLD FRONT IS SLATED TO DROP SOUTH OF KRST/KLSE 06Z OR
SO. MORE SHOWERS ARE EXPECTED POST THE BOUNDARY...PERHAPS AN
ISOLATED THUNDERSTORM. AGAIN...SOUNDINGS SUGGESTING MID LEVEL
BASES/VFR CIGS.

WITH SOME UNCERTAINTY ON THE EXTEND OF THE SCT-BKN CONVECTION...WILL
LIKELY HOLD WITH VCSH FOR NOW. EXPECT SOME REFINEMENT TO THE
FORECAST AS THE VARIOUS LINES BECOME MORE EVIDENT.

DEEP MIXING WILL KEEP WIND GUSTS IN THE 20-25 KT RANGE THIS
AFTERNOON...WITH WINDS THEN SHIFTING NORTHERLY WITH THE PASSAGE OF
THE FRONT LATER TONIGHT.

&&

.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.......RIECK
FIRE WEATHER...LAWRENCE


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