Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 221716
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1216 PM CDT MON SEP 22 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 339 AM CDT MON SEP 22 2014

AT 3 AM...A 1026 MB SURFACE HIGH WAS CENTERED OVER EASTERN
NEBRASKA. WHILE THE AREA IS UNDER CLEAR SKIES...WE SAW A RAPID
INCREASE IN OUR RADAR RETURNS FROM NEAR LA CROSSE TO BETWEEN
22.02Z AND 22.04Z....AND THEY HAVE REMAINED OVER THOSE AREAS
THROUGHOUT THE NIGHT. WHILE SOME OF THIS WAS OUR NORMAL ANOMALOUS
PROPAGATION OF THE RADAR BEAM THAT WE SEE AS THE NOCTURNAL
INVERSION DEVELOPS...THE 30 TO 40 DBZ RETURNS ARE MIGRATORY BIRDS
THROUGH THE AREA. WE KNOW THIS BECAUSE THE CORRELATION
COEFFICIENTS ARE RUNNING BETWEEN 0.65 AND 0.9. WITH NO
PRECIPITATION IN THESE AREAS...THIS MEANS THAT THESE RADAR TARGETS
ARE BIOLOGICAL IN NATURE. WE KNOW IT IS MIGRATORY BIRDS BECAUSE OF
THE TIME OF YEAR AND THAT THE VAD WIND PROFILE IS SHOWING 30 TO
45 KNOT WINDS BETWEEN 2 AND 15K FEET. TYPICALLY IN THESE SYNOPTIC
SITUATIONS WE DO NOT GET THIS MANY WIND LEVELS ALOFT WITHOUT
CLOUDS. IN ADDITION THESE WIND SPEEDS ARE RUNNING ABOUT 15 TO 25
KNOTS HIGHER THAN WHAT SHOW UP IN THE SOUNDINGS. THIS ADDITIONAL
SPEED IS FROM THE MIGRATORY BIRDS. THE HIGHEST CONCENTRATION OF
BIRDS ARE RUNNING BETWEEN 2 AND 8K FEET.

BESIDES THE BIRDS TONIGHT...BEEN WATCHING THE SLOW DEVELOPMENT OF
FOG. DENSE FOG IS ALREADY REPORTED AT BOSCOBEL AND BLACK RIVER
FALLS. WITH LIGHT WINDS /LESS THAN 10 KNOTS/ UP TO 2500 FEET AND
OUR WEB CAM ALREADY SHOWING A LAYER OF STRATUS IN THE VALLEYS...WE
EXPECT TO SEE A CONTINUAL DEVELOPMENT OF AREAS TO WIDESPREAD FOG.
FOLLOWED THE 930 TO 10 AM CLIMATOLOGY WITH THE DISSIPATION OF
THIS FOG.

TONIGHT...LOOKS TO BE EVEN MORE FAVORABLE FOR THE DEVELOPMENT OF
FOG IN THE RIVER VALLEYS AND CENTRAL WISCONSIN WITH LIGHT WINDS
UP TO 25K FEET AND CLEAR SKIES. AS A RESULT...WENT WITH WIDESPREAD
DENSE FOG FROM 2-3 AM THROUGH 930-10 AM.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 339 AM CDT MON SEP 22 2014

TUESDAY NIGHT...THE 22.00Z MODELS ARE IN GOOD AGREEMENT THAT WEAK
850 MB MOISTURE TRANSPORT WILL DEVELOP ACROSS SOUTHEAST MINNESOTA
AND NORTHEAST IOWA AHEAD OF A TROUGH MOVING OUT OF THE PLAINS.
BUFKIT SOUNDINGS BETWEEN 06Z AND 12Z ARE SATURATED BETWEEN 5 AND
20K FEET AND THERE IS OMEGA BETWEEN 5 AND 10K FEET. THIS RESULTS
IN THE MODELS GENERATING SOME LIGHT RAIN ACROSS THIS AREA. SINCE
ALL OF DETERMINISTIC MODELS WERE IN AGREEMENT...ADDED A 15 TO
24 PERCENT CHANCE OF RAIN TO THE FORECAST.

FROM WEDNESDAY INTO WEDNESDAY NIGHT...SHOW THAT THE 500 MB SHORT
WAVE TROUGH SHEARS APART ACROSS THE AREA. ONE PART MOVES NORTH AND
IS ABSORBED BY THE POLAR JET STREAM. MEANWHILE THE SOUTHERN PIECE
MOVES SOUTHWEST AND FORMS A CLOSED 500 MB LOW. WHILE THERE IS
AGREEMENT THAT THIS WILL OCCUR. THERE ARE DIFFERENCES IN
PRECIPITATION. BOTH THE ECMWF AND CANADIAN PRODUCE PRECIPITATION
ACROSS THE FORECAST AREA. MEANWHILE THE GFS AND NAM KEEP THIS
PRECIPITATION ACROSS SOUTH CENTRAL MINNESOTA AND WESTERN IOWA.
SINCE ECMWF SOUNDINGS ARE NOT SHOWING MUCH LIFT CO-LOCATED WITH
THE MOISTURE...KEPT THE FORECAST AREA.

FOR THE REMAINDER OF THE FORECAST PERIOD /THURSDAY THROUGH
SUNDAY/...IT LOOKS DRY AS HIGH PRESSURE REMAINS LOCATED ACROSS
THE AREA. 850 MB TEMPERATURES ARE RUNNING 10 TO 14C WHICH IS ABOUT
2 STANDARD DEVIATIONS ABOVE NORMAL. THIS RESULT IN TEMPERATURES
ABOUT 10 DEGREES WARMER THAN NORMAL.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1216 PM CDT MON SEP 22 2014

HIGH PRESSURE WILL REMAIN OVERHEAD THROUGH TONIGHT. THIS WILL
PROVIDE FOR CLEAR SKIES AND LIGHT WINDS WITH IDEAL RADIATIONAL
COOLING CONDITIONS. THIS IS EXPECTED TO LEAD TO FAIRLY EXTENSIVE
EARLY MORNING FOG AND STRATUS IN THE RIVER VALLEYS WHICH WILL IMPACT
KLSE AIRPORT. EXPECTING LIFR CONDITIONS AT KLSE TO DEVELOP BETWEEN
09-10Z...THEN LASTING THROUGH 14Z. SOUTH-SOUTHWEST WINDS OVERNIGHT
AT KRST AIRPORT  ARE EXPECTED TO KEEP THE NEAR SURFACE/LOWER
BOUNDARY LAYER MIXED TO PREVENT WIDESPREAD FOG FORMATION. WILL
INCLUDE A 6SM BR MENTION IN THE 09-13Z TIME FRAME. OTHERWISE...
AFTER THE FOG/STRATUS LIFTS IN THE MORNING...PLAN ON VFR
CONDITIONS THROUGH THE REST OF THE DAY.

&&

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

$$

SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION...DAS



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