Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 252348
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
648 PM CDT WED MAR 25 2015

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 338 PM CDT WED MAR 25 2015

AT 3 PM...TWO SYSTEMS WERE KEEPING SKIES MAINLY CLOUDY ACROSS THE
UPPER MISSISSIPPI RIVER VALLEY. THE FIRST OF THE LOW PRESSURE
SYSTEMS WAS LOCATED NORTH OF THE MINNESOTA ARROWHEAD. THE SECOND
LOW PRESSURE SYSTEM WAS LOCATED OVER OKLAHOMA. THERE WERE A FEW
HOLES IN THESE CLOUDS FROM THE MINNESOTA/IOWA BORDER EAST INTO
WISCONSIN. THE MAIN FORECAST CONCERN FOR TONIGHT AND THURSDAY IS
WHETHER WE WILL SEE ANY CLEARING. THE 25.12Z MODELS SUGGEST THAT
THE LOW LEVEL MOISTURE SOUTH OF INTERSTATE 94 WILL SLOWLY DRY
OUT THIS EVENING. AS THIS OCCURS...THE LOW CLOUDS SHOULD ERODE
EXPOSING THE HIGHER CEILING ALOFT /AT OR ABOVE 20K FEET/. THERE
ARE HINTS IN THE SOUNDINGS THAT THESE HIGHER CLOUDS WILL ERODE
DURING THE LATE EVENING ALONG INTERSTATE 90. THE CONCERN THEN
HINGES ON HOW MUCH CLOUDS WILL BE ASSOCIATED WITH A SHORT WAVE
TROUGH DROPPING SOUTH OUT OF SOUTHERN CANADA. THE NSSL WRF
SYNTHETIC VISIBLE SATELLITE PRODUCT INDICATES THAT THERE MAY BE A
BRIEF PERIOD OF CLEAR SKIES SOUTH OF INTERSTATE 94 BETWEEN 26.03Z
AND 26.06Z BEFORE THE CLOUDS ASSOCIATED WITH THE SHORT WAVE TROUGH
MOVES SOUTH INTO THESE AREAS.

ON THURSDAY...THE 25.12Z MODELS ARE IN GOOD AGREEMENT THAT THE
CLOUDS WILL GRADUALLY ERODE FROM THE WEST AND NORTH AS SUBSIDENCE
DEVELOPS IN THE WAKE OF THE SHORT WAVE TROUGH DURING THE MORNING.
STEEP 900 TO 850 MB LAPSE RATES MAY PROVIDE A SCATTERED TO
OCCASIONAL BROKEN DECK OF CLOUDS DURING THE AFTERNOON.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 338 PM CDT WED MAR 25 2015

ON THURSDAY NIGHT AND FRIDAY MORNING...THE GFS CONTINUES TO BE
MUCH COLDER WITH ITS BOUNDARY LAYER TEMPERATURES THAN THE ECMWF.
THE GFS WOULD SUGGEST THAT TEMPERATURES COULD FALL INTO THE SINGLE
DIGITS ACROSS SOUTHEAST MINNESOTA AND NORTHEAST IOWA. MEANWHILE
THE ECMWF HAS ITS BOUNDARY LAYER TEMPERATURES IN THE 10 TO 15
DEGREE RANGE. WITH THE MODEL CONSENSUS MORE IN AGREEMENT WITH
ECMWF...TRENDED THE LOW TEMPERATURES TOWARD IT.

ON FRIDAY NIGHT...THE 25.12Z MODELS CONTINUE TO SHOW THAT THE LONG
WAVE RIDGE WILL SLOWLY NUDGE EASTWARD TOWARD THE UPPER MISSISSIPPI
RIVER VALLEY. JUST AHEAD OF THIS RIDGE...A SHORT WAVE TROUGH WILL
DIVE TO OUR SOUTHWEST ALONG THE BAROCLININC ZONE BETWEEN THE
DEPARTING EASTERN TROUGH AND THE WESTERN RIDGE. AT THIS TIME...IT
LOOKS LIKE THE BEST FORCING WILL REMAIN TO OUR WEST AND
SOUTHWEST...AND SOUNDINGS SHOWS A VERY DRY AIR MASS BELOW 650 MB.
DUE TO THIS...KEPT THE FORECAST DRY.

FROM SATURDAY NIGHT INTO SUNDAY MORNING...THE LONG WAVE RIDGE
WILL BUILD EAST INTO THE UPPER MISSISSIPPI RIVER VALLEY. ON THE
EASTERN PERIPHERY OF THIS RIDGE...ANOTHER SHORT WAVE TROUGH WILL
MOVE SOUTHEAST THROUGH THE REGION. STRONG WARM AIR ADVECTION AHEAD
OF THIS SYSTEM LEADS TO A QUICK SATURATION ABOVE 600 MB LATE
SATURDAY NIGHT. IN ADDITION...THERE ARE VERY STEEP LAPSE RATES.
HOWEVER BELOW THIS LAYER...THE AIR MASS REMAINS VERY DRY AND WARM.
PRECIPITATION TYPE WITH THIS SYSTEM WILL BE HIGHLY DEPENDENT UPON
ON HOW STRONG AND FAST THAT THE EVAPORATIVE COOLING CAN OCCUR. AT
THIS TIME...THE GFS AND ECMWF SUGGEST THAT AREAS SOUTH OF
INTERSTATE 94 WILL BE MAINLY RAIN WITH A WINTRY MIX OF THIS
INTERSTATE.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 648 PM CDT WED MAR 25 2015

LATEST SATELLITE TRENDS AND FORECAST GUIDANCE SUGGEST STRATUS DECK
UNLIKELY TO BREAK-UP THIS EVENING...SO REMOVED BRIEF SCATTERED
CONDITIONS AT BOTH KRST/KLSE FROM PREVIOUS FORECAST. EXPECT LOW
VFR/HIGH MVFR CEILINGS THROUGH THE PERIOD. GUSTY WESTERLY WINDS
THIS EVENING TO SUBSIDE AFTER SUNSET...BUT REMAIN IN THE 8 TO 12
KT RANGE OVERNIGHT. SOME GUSTINESS TO RETURN FOR THURSDAY AS WINDS
SHIFT SLIGHTLY TO THE NORTHWEST.

&&

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

$$

SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION...ROGERS



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