Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 302337
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
637 PM CDT WED JUL 30 2014

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 235 PM CDT WED JUL 30 2014

PRIMARY ISSUE IS DIURNAL SHOWER CHANCE AUGMENTED BY SHORT WAVE
TROUGHS ROTING AROUND THE LARGE HUDSON BAY UPPER LOW. ONE SUCH
WAVE SEEN VIA WATER VAPOR AND VISIBLE SATELLITE IMAGERY DROPPING
SOUTH ACROSS LAKE SUPERIOR EARLY THIS AFTERNOON. SOME CONVECTION
CROSSING THE LAKE ALREADY...WITH ADDITIONAL SHOWERS NOW STARTING
TO FIRE UP ACROSS NORTHWEST WI AS CUMULUS FIELD CONTINUES TO
BUILD. EARLY MORNING STRATUS HUNG ON ACROSS PARTS OF CENTRAL WI
THROUGH MID-DAY...SO THERE IS A DISCERNIBLE CLEAR SPOT IN THE CU
FIELD. DO THINK IT WILL FILL IN SOME YET THIS AFTERNOON AS HEATING
AND MIXING CONTINUES. BUT THIS AREA WILL LIKELY SEE LESS POTENTIAL
FOR SHOWERS AND ISOLATED THUNDER THROUGH EVENING. REMAINDER OF THE
AREA WILL HAVE A CHANCE FOR ISOLATED ACTIVITY WITH THE HIGHEST
LIKELIHOOD ALONG A BAND FROM THE TWIN CITIES DOWN THROUGH
SOUTHEAST MN AND NORTHEAST IA WHERE THE CAPE FIELD HAS INCREASED
TO NEARLY 1000 J/KG PER 19Z MESOANALYSIS.

ACTIVITY LOOKS TO WANE AS DIURNAL FORCING DIMINISHES. ANOTHER COOL
NIGHT IS ON TAP WITH WEAK FLOW AND CONTINUED COLD ADVECTION. WINDS
SHOULD DIMINISH AGAIN...AND WITH HIGH PRESSURE STILL BASICALLY IN
CONTROL...WOULD EXPECT TO SEE SOME VALLEY FOG AGAIN TONIGHT.

FOR THURSDAY...MODELS SUGGEST ANOTHER WEAKER SHORT WAVE TROUGH TO
MOVE INTO THE BACK SIDE OF THE TROUGH. THIS COULD PROVIDE ENOUGH
OF A FORCING MECHANISM TO ACT ON THE DIURNALLY ENHANCED ATMOSPHERE
TO GENERATE A FEW SHOWERS AGAIN. HAVE AGAIN GONE WITH THE LOW
CHANCES IN THE FORECAST GRIDS. TEMPERATURES TO REMAIN ON THE COOL
SIDE FOR LATE JULY...WITH HIGHS ONLY AROUND THE 80 DEGREE MARK.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 235 PM CDT WED JUL 30 2014

YET ANOTHER SHORT WAVE ROTATES AROUND THE UPPER LOW AND MOVES
THROUGH THE REGION ON FRIDAY. THIS ONE IS STRONGER AND LOOKS TO
BRING A COLD FRONT ALONG WITH IT. THIS ADDED CONVERGENCE SHOULD
ACT TO FOCUS DEVELOPMENT...ESPECIALLY FRIDAY AFTERNOON AND
EVENING. THIS WAVE WILL ALTER THE UPPER FLOW PATTERN JUST A
BIT...SO THAT WE TEMPORARILY GET OUT OF THE GRIP OF THE UPPER
TROUGH. WE STAY IN A WEAK NORTHWEST FLOW...PERHAPS SLIGHTLY ZONAL.
THIS SHOULD ALLOW FOR AN EVER SO SLOW WARMING TREND AS WE MOVE
INTO THE WEEKEND AND NEXT WEEK. BUT OF COURSE THERE IS SOME
UNCERTAINTY TO THIS...AS A FRONTAL BOUNDARY LOOKS TO SAG SOUTH
INTO THE REGION BY MONDAY...AND MEANDERS NORTH AND SOUTH ACROSS
THE AREA THROUGH MID WEEK. ECMWF IS FURTHEST SOUTH WITH THE FRONT
AND WITH IT IN THE VICINITY THE RAIN CHANCES WILL BE HIGHER. THUS
CLOUDS COULD BE MORE WIDESPREAD AND HOLD TEMPERATURES
DOWN...ESPECIALLY IF THE FRONT MOVES SOUTH INTO IOWA. BUT GFS AND
A FEW OTHER MODELS SUGGEST THE FRONT WILL HANG UP FURTHER TO THE
NORTH. THIS WILL KEEP THE REGION WARMER WITH A BIT LESS OF A RAIN
THREAT. PLENTY OF UNCERTAINTY REMAINS THROUGH THIS LONGER TERM
PERIOD WITH OUR REGION RIGHT ON THE EDGE.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 637 PM CDT WED JUL 30 2014

SHORT TERM FOCUS IS ON A COUPLE OF CLUSTERS OF SHOWERS AND STORMS
DROPPING SOUTH THROUGH NORTHWEST AND WEST CENTRAL WISCONSIN. ITS
POSSIBLE THESE SHOWERS IMPACT LSE...BUT HARD TO SAY WHAT STATE
THEY WILL BE IN BY THE TIME THEY GET THERE WITH TEMPERATURES TO
BEGIN COOLING SOON. THEREFORE...HAVE ONLY INCLUDED A TEMPO GROUP
BETWEEN 01-03Z FOR SHOWERS WITH NO VISIBILITY RESTRICTIONS AND VFR
CEILINGS. OTHERWISE...SKIES SHOULD CLEAR FOR THE MOST PART BY
MIDNIGHT. THIS SETS THE STAGE FOR POSSIBLE VALLEY FOG AT LSE EARLY
THURSDAY MORNING GIVEN LIGHT SURFACE WINDS EXPECTED. SOUNDINGS
DEPICT A 10-20 KT NORTHWEST WIND JUST ABOVE THE VALLEY
FLOOR...WHICH SHOULD HELP PREVENT FOG. NEIGHBORING VALLEYS BEING
MORE SHELTERED STAND A BETTER CHANCE OF SEEING FOG AND THUS HAVE
VCFG MENTIONED.

OUTSIDE OF THE ABOVE CONCERNS...VFR CONDITIONS ARE ANTICIPATED
THROUGH THURSDAY. ANY RAIN THURSDAY AFTERNOON LOOKS TOO ISOLATED
TO MENTION IN A TAF AT THIS TIME.

&&

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

$$

SHORT TERM...MW
LONG TERM...MW
AVIATION...AJ


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