Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 122259
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
600 PM CDT FRI SEP 12 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 257 PM CDT FRI SEP 12 2014

MAIN FORECAST CONCERNS ARE FROST AND FOG POTENTIAL TONIGHT.

LATEST WATER VAPOR SATELLITE IMAGERY SHOWING VIGOROUS SHORTWAVE
TROUGH OVER THE NORTHERN PLAINS. MOSAIC RADAR INDICATING
FRONTOGENETICAL BAND OF RAIN EXTENDING FROM NORTHEAST WISCONSIN INTO
NORTHEAST IOWA PER 12.15Z RAP 700-600MB FN VECTOR CONVERGENCE.
ALSO...MOSAIC RADAR SHOWING DIURNALLY DRIVEN SCATTERED SHOWERS OVER
CENTRAL MINNESOTA UNDERNEATH MAIN SHORTWAVE TROUGH.

TONIGHT...SHORTWAVE TROUGH AND ASSOCIATED LOW LEVEL MOISTURE/RAIN
PROGGED TO PUSH QUICKLY EAST INTO MICHIGAN THIS EVENING PER THE
LATEST 12.12Z GFS/NAM AND 12.15Z RAP RELATIVE HUMIDITY FIELDS. THIS
IS EVIDENT PER LATEST VISIBLE SATELLITE IMAGERY SHOWING DIURNAL
CUMULUS FIELD WEST OF A LINE FROM FAIRMONT MINNESOTA TO NEAR DULUTH
MINNESOTA. THIS CUMULUS FIELD WILL QUICKLY EVAPORATE DUE TO LOSS OF
DAYTIME HEATING THIS EVENING AND ALLOW SKIES TO CLEAR WEST TO EAST
ACROSS THE FORECAST AREA. SURFACE RIDGE BUILDS INTO THE FORECAST
AREA BY 06Z AND PRODUCE CALM WINDS AND DRIER AIRMASS TO ADVECT IN.
TEMPERATURES WILL BE ABLE TO FALL RAPIDLY INTO THE 30S AND THE UPPER
20S IN THE COLD SPOTS OF CENTRAL WISCONSIN. FOR THIS...A FROST
ADVISORY WILL BE IN EFFECT FOR PORTIONS OF SOUTHEAST
MINNESOTA...NORTHEAST IOWA AND CENTRAL WISCONSIN TONIGHT. IN
ADDITION...THE COMBINATION OF RAIN TODAY...CALM WINDS AND INVERSION
DEVELOPING TONIGHT PER BUFKIT SOUNDINGS...AREAS OF FOG WILL DEVELOP
IN RIVER VALLEYS AND PARTS OF CENTRAL WISCONSIN AFTER 06Z.

DRY WEATHER CONDITIONS AND UNSEASONABLY COOL TEMPERATURES WILL
PREVAIL ACROSS THE AREA SATURDAY...AS SURFACE RIDGE REMAINS IN
CONTROL.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 257 PM CDT FRI SEP 12 2014

WARMER AIR ADVECTS INTO THE FORECAST AREA SUNDAY OUT AHEAD OF NEXT
SHORTWAVE TROUGH TO AFFECT THE REGION. TEMPERATURES WILL BE A FEW
DEGREES WARMER AND SLIGHTLY BELOW NORMAL.

NEXT CONCERN IS SHORTWAVE TROUGH MOVING OVER THE GREAT LAKES REGION
EMBEDDED IN THE WEST TO NORTHWEST FLOW SUNDAY NIGHT INTO MONDAY.
BOTH THE 12.12Z GFS/NAM SHOW STRONG PV ADVECTION/QG FORCING AND
FN CONVERGENCE FOCUSED OVER THE SOUTHERN HALF OF THE FORECAST
AREA. SOME SLIGHT DIFFERENCES OCCUR WITH THE PLACEMENT AND TIMING
OF SURFACE FEATURES BETWEEN THE 12.12Z GFS/NAM/ECMWF. WITH THE
MODELS CONTINUE TO SHOW DECENT DYNAMIC FORCING/LIFT IN ASSOCIATED
WITH SHORTWAVE TROUGH...WILL MAINTAIN PRECIPITATION CHANCES SUNDAY
INTO MONDAY MAINLY FOR THE SOUTHERN HALF OF THE FORECAST AREA.

MAIN FORECAST CONCERN ARE PRECIPITATION CHANCES FRIDAY...OTHERWISE
TEMPERATURES TUESDAY THROUGH FRIDAY. THE 12.12Z GFS/GEM/ECMWF
CONTINUE TO HAVE GOOD RUN TO RUN CONSISTENCY IN DIGGING UPPER LEVEL
TROUGH OVER THE NORTHEAST UNITED STATES AND GREAT LAKES REGION AND
SURFACE RIDGE DOMINATING THE UPPER MIDWEST TUESDAY THROUGH THURSDAY.
WITH SUBSIDENCE OVER THE FORECAST AREA...DUE TO SURFACE RIDGE...DRY
WEATHER CONDITIONS CAN BE EXPECTED ACROSS THE FORECAST AREA DURING
THIS TIME FRAME. TEMPERATURES SHOULD BE NEAR OR SLIGHTLY BELOW
NORMAL TUESDAY THROUGH THURSDAY...AS THE 12.00Z GFS/GEM/ECMWF
INDICATE 850MB TEMPERATURES RANGING FROM PLUS 5 TO PLUS 10 DEGREES
CELSIUS AND 12.12Z GEFS SHOW STANDARD ANOMALIES OF MINUS 0.5 TO
MINUS 1 DEGREE CELSIUS. SIGNIFICANT DIFFERENCES SHOW UP BETWEEN THE
12.12Z GFS/ECMWF FRIDAY...AS THE 12.12Z GFS MORE AMPLIFIED WITH
UPPER LEVEL RIDGE OVER THE UPPER MIDWEST THAN THE ECMWF AND THE
12.12Z ECMWF IS SLOWER IN PROGRESSING THE UPPER LEVEL RIDGE INTO THE
UPPER MIDWEST AND GREAT LAKES REGION. THIS HAS IMPACTS ON HOW FAST
WARMER AIR ADVECTS INTO THE REGION AND TIMING OF SURFACE WARM FRONT
INTO THE FORECAST AREA. THIS SURFACE WARM FRONT WILL BE THE FOCUS
OF PRECIPITATION CHANCES FRIDAY...WITH BOTH THE 12.12Z GFS/ECMWF
INDICATE DECENT 850MB MOISTURE TRANSPORT AND CONVERGENCE IN
ASSOCIATION WITH IMPULSE OVER THE NORTHERN PLAINS AND NORTHERN
ROCKIES. CONFIDENCE IN FORECAST ON FRIDAY IS LOW DUE TO TIMING AND
STRENGTH OF UPPER LEVEL RIDGE.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 600 PM CDT FRI SEP 12 2014

LOTS OF DIURNAL ELEMENTS TO THE CLOUDS WEST OF THE MISSISSIPPI RIVER
EARLY THIS EVENING...AND EXPECT THESE TO QUICKLY DISSIPATE WITH
SUNDOWN. IN THE EAST...THE CLOUD MASS IS ASSOCIATED WITH A DEPARTING
UPPER LEVEL SHORTWAVE...AND THESE WILL TAKE A BIT LONGER TO CLEAR.
KRST SHOULD SCATTER OUT EARLY THIS EVENING...WHILE IT MIGHT HOLD OFF
UNTIL AFTER 03Z FOR THE CLEARING LINE TO REACH KLSE.

WITH CLOUDS HOLDING T/TD SPREADS CLOSE THROUGH THE DAY...AND
CLEARING SKIES JUST IN TIME FOR NIGHTTIME...ITS A FAVORABLE SETUP
FOR DIURNAL COOLING INDUCED RIVER VALLEY FOG. NOT AS MUCH T/TD
SPREAD TO MAKEUP. SFC WINDS ARE ALSO EXPECTED TO BE LIGHT THROUGH
THE NIGHT. HOWEVER...A SIGNIFICANT DRAWBACK WILL BE THE DEPTH OF THE
LIGHT WIND LAYER. RAP/NAM BUFKIT SOUNDINGS SUGGEST AT 10+ KTS OF
WIND BY 300 FT FOR MOST OF THE NIGHT. GENERALLY...THIS IT NOT
FAVORABLE FOR DENSE FOG. CERTAINLY...SOME VSBY RESTRICTIONS ARE
POSSIBLE...AND COULD SEE THICKER FOG/STRATUS BANK SITTING ON THE
MISSISSIPPI RIVER...BUT UNSURE IF IT WILL SPREAD ACROSS KLSE.
SOMETHING TO WATCH CLOSELY TONIGHT.

HIGH PRESSURE BUILDS IN SATURDAY...AND WILL RESULT IN VFR CONDITIONS
OUTSIDE OF THE EARLY MORNING FOG POTENTIAL. WINDS WILL GRADUALLY
SWING FROM WEST TO SOUTHWEST. LATER SAT NIGHT...SOME CIGS NEAR 4KFT
COULD RETURN AS LOW LEVEL WARM AIR ADVECTION AND WEAK MOISTURE
TRANSPORT LEAD A SHORTWAVE MOVING EAST ACROSS THE NORTHERN PLAINS.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...FROST ADVISORY FROM 3 AM TO 8 AM CDT SATURDAY FOR WIZ017-029-033-
     034-042>044.

MN...FROST ADVISORY FROM 3 AM TO 8 AM CDT SATURDAY FOR MNZ086-087-094-
     095.

IA...FROST ADVISORY FROM 3 AM TO 8 AM CDT SATURDAY FOR IAZ008>010-018-
     019-029.

&&

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...RIECK


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