Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 202318
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
618 PM CDT MON APR 20 2015

.SHORT TERM...(TONIGHT THROUGH TUESDAY)
ISSUED AT 235 PM CDT MON APR 20 2015

500 MB LOW/UPPER LEVEL TROUGH MEANDERS SLOWLY EASTWARD ACROSS THE
UPPER MISSISSIPPI RIVER TONIGHT-TUE...THEN WOBBLES OVER SOUTHEAST
CANADA FOR A FEW DAYS. BITS OF UPPER LEVEL ENERGY WILL ROTATE AROUND
THE UPPER LEVEL FEATURE BUT THE DEEPER SATURATION HOLDS ACROSS
NORTHERN PARTS OF MN/WI. STRONG SWATH OF 925-700 MB COLD AIR
ADVECTION DRIVES SOUTHEAST TONIGHT-TUE...GREATER ACROSS IA. BUFKIT
SOUNDINGS STILL SHOWING AS MUCH AS A 100 MB LAYER OF WEAK
INSTABILITY TUE AFTERNOON...ASSOCIATED WITH A SATURATED LAYER. ALL
IN ALL...THE MIX OF CYCLONIC UPPER LEVEL FLOW...LOW LEVEL COLD AIR
ADVECTION...WEAK INSTABILITY...FAVORABLY LOW/MID LEVEL LAPSE
RATES...AND SOME SATURATION FAVORS AREAS/SCATTERED SHOWERS.
LOCATIONS TO THE NORTH WILL HAVE THE BEST CHANCES...SPREADING
SOUTHWARD TUESDAY AFTERNOON. SOME SNOW COULD MIX IN TO THE NORTH
EARLY/LATE.

BUFKIT SOUNDINGS POINT TO DEEP MIXING ON TUESDAY...ESPECIALLY SOUTH
OF I-90 INTO IOWA. MIXING UPWARDS OF 800 MB WITH MOMENTUM TRANSFER
OF 30 TO 35 KTS. SFC PRESSURE GRADIENT TUE FAIRLY SIMILAR TO THIS
AFTERNOON. EXPECTING CLOUDY/MOSTLY CLOUDY CONDITIONS FOR THE I-90
CORRIDOR NORTHWARD...LIMITING THE MIXING. WITH MORE SUN SOUTH...FULL
MIXING COULD BE REALIZED. SEE SOME POTENTIAL FOR WIND ADV TUE
AFTERNOON - ESPECIALLY PARTS OF NORTHEAST IA. SOMETHING TO WATCH.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 235 PM CDT MON APR 20 2015

GOOD AGREEMENT IN THE MODELS WITH PERSISTENT COOL NORTHWEST FLOW
THROUGH THE REST OF THE WORK WEEK. DIFFERENCES CROP UP FOR THE
WEEKEND AS THE ECMWF/GEM POINT TO SOME WEAK UPPER LEVEL RIDGE
BUILDING WHILE THE GFS MAINTAINS THE TROUGH - EVEN DEEPENING
IT/CARVING IT OUT MORE. WHILE ALL SOLUTIONS FAVOR KEEPING THE LOCAL
AREA DRY...THERE WOULD BE IMPACTS ON TEMPS. THE GFS WOULD KEEP HIGHS
IN THE LOW/MID 50S WHILE THE EC POINTS TO A RETURN TO NORMAL -
AROUND 60. MODELS HAVE BEEN FAIRLY CONSISTENT WITHIN
THEMSELVES...BUT STILL NOT SOLD ON THE RIDGING. WILL STICK WITH
CONSENSUS SOLUTIONS FOR THE WEEKEND FOR NOW.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 618 PM CDT MON APR 20 2015

THE LARGE UPPER LEVEL LOW OVER SOUTHWEST ONTARIO WILL MOVE SLOWLY
TO THE EAST THROUGH THE PERIOD. THIS WILL KEEP THE SURFACE LOW
PARKED OVER SOUTHERN ONTARIO JUST NORTH OF LAKE SUPERIOR. WITH
THIS SLOW MOVING PATTERN...THE UPPER MIDWEST WILL REMAIN UNDER A
CYCLONIC FLOW. WITH PLENTY OF MOISTURE IN THIS CYCLONIC
FLOW...EXPECT THE CLOUDS TO REMAIN IN PLACE THROUGH TUESDAY WITH
THE CEILINGS COMING DOWN TO MVFR THIS EVENING AND THEN LIFTING
BACK UP TO VFR TUESDAY MORNING. THERE COULD ALSO BE SOME PASSING
SHOWERS FROM TIME TO TIME IN THIS FLOW...AS INDICATED BY THE
20.22Z HRRR...BUT THE CONFIDENCE ON WHETHER ANY OF THIS WILL
IMPACT THE TAF SITES IS TOO LOW TO EVEN INCLUDE A VCSH. THE 20.18Z
NAM BUFKIT SOUNDINGS SHOW THE GOOD LOW LEVEL LAPSE RATES REMAINING
IN PLACE THROUGH THE PERIOD AS WELL. THIS WILL MAINTAIN THE WEST
TO NORTHWEST WINDS WITH SUSTAINED SPEEDS IN THE 15 TO 20 KNOT
RANGE. THE GUSTS WILL ALSO CONTINUE THROUGH THE PERIOD WITH THESE
INCREASING TO AROUND 30 KNOTS BY MID TO LATE MORNING TUESDAY
MORNING.

&&

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

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION...04



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