Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 162330
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
630 PM CDT SAT AUG 16 2014

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 341 PM CDT SAT AUG 16 2014

AT 3 PM...A LINE OF SHOWERS AND THUNDERSTORMS WERE LOCATED ALONG A
BACKDOOR CANADIAN COLD FRONT EXTENDED FROM LAKE ITASCA MINNESOTA
TO TWO RIVERS WISCONSIN. SURFACE BASED CAPES ALONG AND AHEAD OF
THIS FRONT ARE RUNNING IN THE 1000 TO 1500 J/KG RANGE. WHILE THERE
IS DECENT INSTABILITY...THE 0-6 KM EFFECTIVE SHEAR IS ONLY 25 TO
30 KNOTS AND THE DOWNDRAFT CAPE ARE LESS THAN 500 J/KG. THE MODELS
ARE IN GOOD AGREEMENT THAT THERE WILL BE LITTLE CHANGE IN THESE
PARAMETERS THIS EVENING...AS A RESULT NOT EXPECTING ANY SEVERE
WEATHER ALONG THIS FRONT THROUGH THIS EVENING. WITH PRECIPITABLE
WATER VALUES AROUND 1.8 INCHES AND WARM CLOUD DEPTHS RUNNING
BETWEEN 4 AND 4.5 KM...THESE SHOWERS AND THUNDERSTORMS WILL BE
VERY EFFICIENT RAIN PRODUCERS.

FOR LATE TONIGHT AND SUNDAY...THE 16.12Z AND 16.18Z MODELS ARE
SHOWING THAT THE 900 TO 800 MB FRONTOGENESIS WILL REMAIN MODERATE
TO STRONG THROUGH TONIGHT AND WEAK TO MODERATE ON SUNDAY. THESE
MODELS ARE IN VERY GOOD AGREEMENT THAT THIS FRONT WILL STRUGGLE
TO GET ANY FURTHER SOUTH THAN THE INTERSTATE 90 CORRIDOR. THIS
VERY MUCH DIFFERENT THAN YESTERDAY WHERE THE MODELS WERE WEAKENING
THE FRONT RAPIDLY DURING THE NIGHT AND IT WAS SOUTH OF THE AREA BY
SUNDAY. DUE TO THESE CHANGES...ADDED PRECIPITATION INTO THE
OVERNIGHT AND SUNDAY. LIKE THIS AFTERNOON...THE 0-3 AND 0-6 KM
SHEAR REMAINS LESS THAN 25 KNOTS...THUS NOT EXPECTING ANY SEVERE
WEATHER HOWEVER WITH PRECIPITABLE WATER VALUES AROUND 1.8 INCHES
AND WARM CLOUD DEPTHS RUNNING BETWEEN 4 AND 4.5 KM...THESE SHOWERS
AND THUNDERSTORMS WILL BE VERY EFFICIENT RAIN PRODUCERS.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 341 PM CDT SAT AUG 16 2014

ON SUNDAY NIGHT...A SHORT WAVE TROUGH...CURRENTLY OVER NORTH
DAKOTA...WILL MOVE EAST THROUGH THE FORECAST AREA. THIS FASTER
TREND SHOWED UP IN THE 16.00Z AND 16.06Z MODELS AND CONTINUED WITH
TODAY/S RUNS TOO. DUE TO THIS INCREASED AND SPEED UP THE RAIN
CHANCES ACROSS THE AREA. WHILE THE 0-3 KM AND 0-6 KM SHEAR ARE NOT
FAVORABLE FOR SEVERE WEATHER...THE PRECIPITABLE WATER /1.6 TO 1.8
INCHES/ AND WARM CLOUD DEPTHS /4 TO 4.5 KM/ WILL BE FAVORABLE FOR
HEAVY RAIN.

FROM MONDAY INTO TUESDAY...ANOTHER SHORT WAVE TROUGH CURRENTLY
LOCATED OVER THE CANADIAN ROCKIES WILL MOVE SLOWLY EAST THROUGH
THE FORECAST AREA. THIS SYSTEM WILL PRODUCE VERY LITTLE 0-3 KM OR
0-6 KM SHEAR ACROSS THE AREA...SO NO SEVERE WEATHER IS
ANTICIPATED. THE HEAVY RAIN THREAT IS A BIT LOWER DUE TO LOWER
PRECIPITABLE WATER VALUES AROUND 1.5 INCHES AND WARM CLOUD LAYER
DEPTHS BETWEEN 3.5 AND 4 KM.

LOOKING TOWARD THE END OF THE WEEK...BOTH THE OPERATIONAL GFS AND
ECMWF ARE HINTING AT MUCH WARMER TEMPERATURES POTENTIALLY REACHING
90 DEGREES IN SOME LOCATIONS FROM FRIDAY INTO THE UPCOMING
WEEKEND. THE GFS IS A BIT FASTER WITH ITS COLD FRONT MOVING
THROUGH THE AREA THAN THE ECMWF. AS A RESULT...THE GFS ONLY HAS
ITS VERY WARM TEMPERATURES /FOR AT LEAST THIS SUMMER/ FOR ONE
DAY...AND THE ECMWF KEEPS THEM AROUND FOR AT 3 DAYS. HOWEVER AS
STATED YESTERDAY...ONE HAS TO BE CAREFUL WITH THIS BECAUSE
THE POSITIVE PACIFIC DECADAL OSCILLATION IS NOT THAT FAVORABLE FOR
A WESTERN LONG WAVE TROUGH LIKE THE DETERMINISTIC MODELS ARE
SHOWING. LOOKING AT THE 12 GFS ENSEMBLE MEMBERS...ONLY 2 ARE EVEN
CLOSE TO THE GFS DETERMINISTIC RUN.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 629 PM CDT SAT AUG 16 2014

COLD FRONT SLATED TO PASS THROUGH KRST/KLSE TONIGHT...LIKELY AFTER
MIDNIGHT. SLIGHT CHANCE THAT CURRENT SHOWERS/STORMS WILL BE STILL
ONGOING DURING ITS PASSAGE...BUT LIKELY TO BE JUST AN EASTERLY
WIND SHIFT. FORECAST SOUNDINGS SHOW SURGE OF 950-900 MB MOISTURE
BEHIND FRONT WHICH SATURATES TO FORM AN IFR/LIFR STRATUS DECK
LASTING THROUGH SUNDAY MORNING. THERE IS RELATIVELY HIGH
CONFIDENCE IN THIS HAPPENING...SO HAVE CONTINUED TRENDS IN TAFS.
VISIBILITY SIGNALS ARE LESS CERTAIN...BUT MORE LIKELY TO SEE IFR
AT KRST THAN KLSE. SHOWERS AND STORMS ARE POSSIBLE SUNDAY...BUT
CONFIDENCE IS TOO LOW AT THIS POINT TO INCLUDE. MORNING STRATUS
WILL SLOWLY BURN OFF AND LIFT TO VFR.

&&

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

$$

SHORT TERM...BOYNE
LONG TERM....BOYNE
AVIATION.....ZT



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