Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 312349
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
649 PM CDT MON AUG 31 2015

.SHORT TERM...(TONIGHT AND TUESDAY)
ISSUED AT 224 PM CDT MON AUG 31 2015

BROAD SOUTH TO SOUTHWEST FLOW ACROSS AREA HAS BEEN MOISTENING LOWER
LAYER UP SO BESIDES 70 PLUS SURFACE DEW POINTS MAKING ANOTHER
APPEARANCE...ALSO BATTLING AREAS OF STRATUS FROM OVERNIGHT INVERSION
THAT IS SLOW TO BREAK. EVEN DIURNAL CUMULUS IS OBSCURED BY
ATMOSPHERIC SMOKE MAKING FOR OVERALL POOR DEFINITION TO SKY COVER TO
START THE WEEK.

PASSING SHORT WAVE TROUGH ACROSS MANITOBA IS DRAGGING FRONT OR
TROUGH INTO NORTHERN MINNESOTA...BUT OUR AREA WILL REMAIN IN
SOUTHWEST FLOW INTO TUESDAY. SOME MODEL GUIDANCE TRYING TO GENERATE
SMALL AREAS OF RAIN AHEAD OF THIS BOUNDARY BUT PLAN ON KEEPING DRY
FORECAST GOING.

MAIN ISSUE TONIGHT IS WHETHER ADDITIONAL STRATUS WILL FORM. SEEMS TO
BE CONSISTENT SIGNAL IN SHORT TERM MODEL OF INVERSION STRENGTHENING
AGAIN TONIGHT ALONG WITH ANOTHER SURGE OF LOWER LEVEL MOISTURE.
STRATUS COULD BE TRANSIENT THOUGH...MAINLY IMPACTING NORTHWEST
HALF OF AREA BEFORE EXITING TUESDAY MORNING. CONFIDENCE IS MEDIUM
SO WHILE SKY COVER BUMPED UP...DID NOT COMPLETELY CARRY OVERCAST
ALL NIGHT. GRADIENT TONIGHT SHOULD LIMIT FOG SOMEWHAT SO DO NOT
EXPECT A FULL RECURRENCE OF THIS MORNING.

A FEW DEGREES WARMER ON TUESDAY AS WELL FOR WARM AND MUGGY START OF
SCHOOL FOR MANY.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 224 PM CDT MON AUG 31 2015

AMPLIFICATION OF FLOW WILL HIGHLIGHT MEDIUM/LONG RANGE AS MEAN
TROUGH DIGS INTO WESTERN U.S. AND LARGE RIDGE DOMINATES SOUTHERN
PLAINS INTO GREAT LAKES. MAIN PROBLEM IS WHEN TO START RAIN THREAT
AS WEAK IMPULSES CROSS RIDGE INTO NORTHERN MIDWEST.

SOME TIMING DIFFERENCES BUT SEVERAL MODELS HINT AT FIRST SHORT WAVE
EJECTING INTO CORNBELT LATE TUESDAY NIGHT...WITH SUBTLE RAIN RISKS
BY WEDNESDAY ALREADY. THIS IS ON NOSE OF LOW LEVEL MOISTURE
TRANSPORT. EVEN SOME HINTS THAT LEFT OVER BOUNDARIES COULD GENERATE
MORE CONVECTION INTO THURSDAY BUT CONFIDENCE REMAINS RELATIVELY LOW
SO WILL KEEP RAIN CHANCES LOW AT THIS POINT.

THIS ONLY SETS UP FOR SEVERAL MORE WAVES POSSIBLE AS UPPER
TROUGH/LOW BUILDS INTO WESTERN U.S. BY LATE WEEK. COULD SEE RAIN
THREATS ON AND OFF FRIDAY NIGHT INTO THE WEEKEND...ESPECIALLY NORTH
AND WESTERN AREAS AS RIDGE BUILDS STRONG TO THE SOUTHEAST. TOO EARLY
FOR A LOT OF DETAIL YET BUT OVERALL RAIN CHANCES SEEM HIGHER THIS
WEEKEND THAN THIS WEEK LEADING UP TO IT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 649 PM CDT MON AUG 31 2015

CHALLENGING AVIATION FORECAST OVERNIGHT FOR THE 06-15Z PERIOD AS
MOISTURE IS IN PLACE AGAIN TONIGHT OVER THE AIRFIELDS WITH CLEAR
SKIES. AGAIN...WINDS WOULD SUGGEST THAT MORE OF A LOW-STRATUS
LAYER WOULD BE PREFERRED. HAVING SOME CHALLENGES COMPARING IT TO
SUNDAY NIGHT AND THIS MORNING...AS TODAY WAS A BETTER MIXING DAY
AND TEMPERATURES WARMED A BIT. HOWEVER...THE DEWPOINTS FOLLOWED
THE TEMPERATURES AND ROSE AS WELL.

BOTTOM LINE IS THAT CURRENT OBSERVATIONS AND CLEAR SKIES SUGGEST
THAT A STEP TOWARD A MORE PESSIMISTIC FORECAST IS WARRANTED. A
MAJORITY OF THE MODEL GUIDANCE SUGGESTS EITHER IFR FOG OR STRATUS
WILL FORM...ESPECIALLY WEST AND NORTH OF KLSE IN THE LOW-LEVEL
MOISTURE AXIS. AND THE TREND IN THE LATEST MODELS GUIDANCE IS MORE
PESSIMISTIC. SOME GUIDANCE SUGGESTS AN MVFR CIG WOULD
FORM...WHICH WOULD THEN LIMIT THE FOG FROM BECOMING LIFR /POSSIBLY
MORE OF A 2SM BR/.

WILL CONTINUE TO MONITOR CONDITIONS AND UPDATE AS NEEDED.

&&

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

$$

SHORT TERM...SHEA
LONG TERM...SHEA
AVIATION...BAUMGARDT


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