Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 201935
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
235 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 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1229 PM CDT MON APR 20 2015

MAIN AVIATION CONCERNS ARE MVFR CONDITIONS AND WINDS AT BOTH RST AND
LSE TAF SITES. THE REGION WILL REMAIN UNDER THE INFLUENCE OF LOW
PRESSURE OVER THE GREAT LAKES REGION AND SOUTHERN ONTARIO THROUGH
THE TAF PERIOD. LATEST VISIBLE SATELLITE IMAGERY SHOWS STRATUS DECK
COVERING THE ENTIRE GREAT LAKES REGION WITH THE LATEST METARS
REPORTING CEILING HEIGHTS IN THE MVFR RANGE. THE 20.12Z GFS/NAM
SUGGEST LOW LEVEL MOISTURE/STRATUS DECK TO WRAP AROUND THE LOW
PRESSURE AND INTO THE TAF SITES THROUGH THE PERIOD. WITH FILTERING
OF SUN THROUGH THE STRATUS DECK THIS AFTERNOON...CEILING HEIGHTS MAY
RISE INTO THE VFR RANGE. AS THE SUN SETS THIS EVENING...CEILINGS MAY
LOWER BACK INTO THE MVFR RANGE. PREVIOUS TAFS HAVE GOOD TREND ON
THIS AND WILL FOLLOW WITH MINOR ADJUSTMENTS TO TIMING.

WITH A TIGHT PRESSURE GRADIENT ACROSS THE AREA. NORTHWEST WINDS WILL
CONTINUE TO BE SUSTAINED AT 20 TO 25 KNOTS WITH GUSTS TO NEAR 25 TO
30 KNOTS THIS AFTERNOON INTO TUESDAY AT BOTH RST/LSE TAF SITES.

&&

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

$$

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


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