Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 311924
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
224 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 SURGENCE 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 REOCCURRENCE 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 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1225 PM CDT MON AUG 31 2015

INCREASING SOUTH-SOUTHWEST LOWER LEVEL FLOW WAS ALLOWING FOR MORE
MIXING TODAY...WITH THE MVFR/IFR STRATO-CU DECK ERODING/LIFTING
NORTH OF THE TAF SITES BY 17Z TODAY. MORE DIURNAL WARMING/DEEPER
MIXING THIS AFTERNOON SHOULD RAISE SCT CUMULUS HGTS INTO THE 2500 FT
RANGE FOR THE AFTERNOON. SOUNDINGS/X-SECTIONS THEN SHOW DRYING BELOW
900MB IN THE SOUTHWEST FLOW FOR TONIGHT INTO TUE...WITH A MOISTURE
INCREASE TONIGHT AROUND 850MB OR ABOUT 4000 FT AGL. CARRIED THIS AS
A SCT035/SCT040 DECK AT KRST/KLSE RESPECTIVELY FOR TONIGHT-TUE
MORNING. WITH A MOIST BOUNDARY LAYER AIRMASS AND NOCTURNAL
COOLING...CONTINUED A MENTION OF SOME MVFR BR DURING THE LATE NIGHT
AND EARLY MORNING HOURS...MAINLY 08Z-14Z.

&&

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

$$

SHORT TERM...SHEA
LONG TERM...SHEA
AVIATION...RRS


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