Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 212317
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
617 PM CDT TUE OCT 21 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 255 PM CDT TUE OCT 21 2014

QUIET WEATHER CONDITIONS ARE EXPECTED THROUGH TOMORROW AFTERNOON
AS A RIDGE OF HIGH PRESSURE TRACKS EAST THROUGH THE GREAT LAKES.
THE LAST CHUNK OF STRATUS IN CENTRAL WISCONSIN HAS QUICKLY BEEN
DISSIPATING THIS AFTERNOON AND WILL COMPLETELY CLEAR OUT BY LATE
THIS AFTERNOON. WINDS ARE COMING AROUND TO THE SOUTHEAST AND
INCREASING IN THE LOW LEVELS...WHICH SHOULD MITIGATE HOW
WIDESPREAD ANY RIVER VALLEY FOG CAN GET TONIGHT.

THE MAIN FOCUS INTO TOMORROW AFTERNOON IS WITH WHETHER ANY
SPRINKLES OR LIGHT RAIN SHOWERS WILL FALL IN A BAND OF LOW LEVEL
WARM AIR ADVECTION AHEAD OF THE NEXT TROUGH. 21.12Z NAM/GFS
FORECAST SOUNDINGS SHOW SOME SATURATION OCCURRING BETWEEN
850-750MB THOUGH ANY LIFT IS VERY WEAK AND MAY NOT BE ENOUGH TO
PRODUCE THE SHOWERS. WITH CONFIDENCE NOT VERY HIGH IN WHETHER
ANYTHING WILL FORM...HAVE KEPT THE FORECAST DRY THROUGH THE LATE
AFTERNOON TOMORROW.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 255 PM CDT TUE OCT 21 2014

THE TWO MAIN STORIES GOING INTO THE EXTENDED PERIOD IS WITH THE
RAIN CHANCES WEDNESDAY NIGHT INTO THURSDAY AFTERNOON FOLLOWED BY
THE WARMUP COMING THIS WEEKEND.

AS FOR THE RAIN CHANCES...CONFIDENCE IS FAIRLY HIGH THAT THERE
WILL BE SOME RAIN THAT MOVES THROUGH WEDNESDAY NIGHT INTO
THURSDAY...BUT THE QUESTION IS WITH HOW LONG IT WILL
LAST/ACCUMULATE. BEYOND THE INITIAL 850-750MB WARM AIR
ADVECTION...THE LIFT COMES IN A FAIRLY NARROW BAND ALONG A
700-500MB TROUGH. THERE IS SOME FRONTOGENESIS THERE AS WELL IN THE
MID LEVELS...BUT THE BETTER PV ADVECTION APPEARS TO TRACK TO THE
NORTH AND EAST OF THE REGION AS THE MAIN TROUGH DIGS SOUTHEASTWARD
ACROSS THE WESTERN GREAT LAKES. THE 21.12Z ECMWF APPEARS TO BE THE
STRONGEST WITH ITS LIFT SINCE IT BREAKS OFF A PIECE OF THE 500MB
TROUGH AND PROPAGATES IT FURTHER SOUTHEAST COMPARED TO THE OTHER
GUIDANCE. HAVE GENERALLY GONE WITH A TENTH OF AN INCH TO UNDER A
HALF INCH OF QPF FOR THIS SYSTEM SINCE THE MOISTURE FEED IS IN
THIS NARROW CHANNEL. THE MAIN TRENDS WITH THE 21.12Z GUIDANCE IS
TO SPEED UP THE CLEARING OF THE RAIN THURSDAY AFTERNOON WITH THE
21.12Z ECMWF THE SLOWEST AND THE MAIN REASON THAT THERE EVEN ARE
ANY PRECIPITATION CHANCES LEFT IN THE FORECAST AFTER 18Z THURSDAY.

ALL SIGNS CONTINUE TO POINT TO A WARM WEEKEND AHEAD...PARTICULARLY
ON SUNDAY WHEN STRONG SOUTHERLY LOW LEVEL ADVECTION KICK IN AHEAD
OF THE NEXT SYSTEM. STANDARDIZED ANOMALIES FOR TEMPERATURES AT
925/850MB ARE NOT T00 HIGH AT +1 TO +2...BUT STILL HELP TO SIGNAL
THAT CONDITIONS WILL BE ABOVE NORMAL. HAVE CONTINUED THE TREND OF
KEEPING FORECAST HIGHS ABOVE GUIDANCE WITH HIGHS IN THE 60S TO LOW
70S.

THE NEXT SYSTEM MOVES IN ON MONDAY/TUESDAY AND SHOULD BE THE NEXT
CHANCE FOR SOME WIDESPREAD HEAVIER RAINS AS A SURFACE LOW RUNS UP
FROM THE SOUTHERN PLAINS INTO THE UPPER MISSISSIPPI RIVER VALLEY.
SOME TIMING/INTENSITY DIFFERENCES BETWEEN THE 21.12Z GFS/ECMWF BUT
THE OVERALL MESSAGE IS SIMILAR.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 617 PM CDT TUE OCT 21 2014

VFR CONDITIONS EXPECTED THROUGH THE PERIOD. HIGH PRESSURE OVER THE
NORTHERN GREAT LAKES WILL MOVE VERY SLOWLY SOUTHEAST THROUGH
WEDNESDAY AFTERNOON. AT THE SAME TIME...A COLD FRONT WILL ADVANCE
OUT OF THE NORTHERN ROCKIES AND ACROSS MUCH OF THE DAKOTAS
WEDNESDAY. THIS WILL PRODUCE A TIGHTENING PRESSURE GRADIENT ACROSS
THE AREA WITH SUSTAINED SOUTH WINDS AT OR ABOVE 10 KNOTS FOR BOTH
SITES BY MID TO LATE MORNING. ALSO EXPECTING ENOUGH MIXING TO
CREATE SOME GUSTS TO AROUND 20 KNOTS AT KRST FOR THE LATE MORNING
AND AFTERNOON. AT THIS TIME...IT APPEARS THAT ANY RAIN AND
CEILINGS ASSOCIATED WITH THE FRONT WILL HOLD OFF UNTIL WEDNESDAY
EVENING OR NIGHT.

&&

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

$$

SHORT TERM...HALBACH
LONG TERM...HALBACH
AVIATION...04



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