Area Forecast Discussion
Issued by NWS La Crosse, WI

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111
FXUS63 KARX 180403
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1100 PM CDT SUN MAY 17 2015

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 303 PM CDT SUN MAY 17 2015

MAIN CONCERN IS SEVERE THREAT LATE THIS AFTERNOON INTO THIS
EVENING.

LATEST WATER VAPOR SATELLITE IMAGERY SHOWS UPPER LEVEL LOW/TROUGH
OVER EASTERN SOUTH DAKOTA AND WESTERN MINNESOTA...IN ADDITION A
SHORTWAVE TROUGH OVER SOUTHEAST NEBRASKA AND SOUTHWEST IOWA.
LATEST 19Z SURFACE ANALYSIS INDICATES SURFACE LOW OVER SOUTHEAST
NORTH DAKOTA AND WEST CENTRAL MINNESOTA...WITH A COLD FRONT
EXTENDING SOUTH INTO WESTERN IOWA. LATEST SATELLITE IMAGERY SHOWS
STRATUS OVER FORECAST AREA BECOMING MORE CELLUAR AND SCATTERED
SHOWERS DEVELOPED OVER NORTH CENTRAL WISCONSIN AND PARTS OF
SOUTHEAST MINNESOTA PER LATEST ARX RADAR.

WITH THE STRATUS DECK OVER MUCH OF THE REGION THROUGH EARLY
AFTERNOON HOURS...THIS HAS LIMITED INSTABILITY OVER FORECAST AREA
THIS AFTERNOON...WITH THE 17.19Z LAPS SHOWING 200-800 J/KG OVER
FORECAST AREA AND AROUND 1000-1200 J/KG ALONG AND JUST AHEAD OF
THE COLD FRONT. THE LATEST SPC MESOSCALE ANALYSIS INDICATES 40
KNOTS OF 0-6KM SHEAR OVER FORECAST AREA...WITH THE BEST SHEAR IN
THE 0-3KM SHEAR PER 17.18Z RAP OF 30 TO 40 KNOTS ALONG AND AHEAD
OF SURFACE FRONT. SPC MESOSCALE 0-1KM SHEAR INDICATES ABOUT 10 TO
20 KNOTS ALONG AND AHEAD OF COLD FRONT. WITH MINIMAL INSTABILITY
AND SHEAR DECREASING OVER FORECAST AREA...SEVERE THREAT OVER
FORECAST AREA HAS DECREASED. HOWEVER CANNOT RULE OUT AN ISOLATED
SEVERE THUNDERSTORM WITH DAMAGING WINDS...LARGE HAIL OR POSSIBLY
AN ISOLATED TORNADO LATE THIS AFTERNOON INTO THIS EVENING.

MONDAY...FORECAST AREA REMAINS UNDER THE INFLUENCE OF THE UPPER
LEVEL LOW/TROUGH OVER SOUTHERN ONTARIO AND LAKE SUPERIOR. THE
17.12Z GFS/NAM INDICATE COLD AIR ADVECTING INTO THE FORECAST
AREA...WITH 925MB TEMPERATURES FALLING TO 0 TO MINUS 2 DEGREES
CELSIUS OVER THE FORECAST AREA. HIGH TEMPERATURES ARE EXPECTED TO
BE WELL BELOW NORMAL...WITH READINGS IN THE UPPER 40S TO LOWER 60S
ACROSS THE FORECAST AREA. TIGHT PRESSURE GRADIENT WILL ALLOW FOR
WINDS TO BE SUSTAINED AT 15 TO 20 KNOTS AND GUSTS OF 20 TO 30
KNOTS.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 303 PM CDT SUN MAY 17 2015

TUESDAY INTO WEDNESDAY...SURFACE RIDGE BUILDS INTO MUCH OF MINNESOTA
AND NORTHERN WISCONSIN. SUBSIDENCE UNDERNEATH THE RIDGE SHOULD ALLOW
FOR DRY WEATHER AND SLIGHTLY BELOW NORMAL TEMPERATURES TUESDAY AND
TUESDAY NIGHT. PATCHY TO AREAS OF FROST IS POSSIBLE ACROSS PARTS OF
CENTRAL WISCONSIN TUESDAY NIGHT INTO WEDNESDAY MORNING. MID TO HIGH
CLOUDS STREAMING AHEAD OF SHORTWAVE TROUGH SOUTHWEST OF FORECAST
AREA MAY NOT ALLOW TEMPERATURES TO FALL INTO THE LOWER TO MIDDLE
30S. TIMING OF MOISTURE ABOVE 700MB WILL BE THE BIGGEST FACTOR AND
THIS IS EVIDENT BY THE 17.12Z GFS/NAM.

WEDNESDAY...SHORTWAVE TROUGH FLATTENS UPPER LEVEL SHORTWAVE RIDGE
WEDNESDAY OVER NEBRASKA AND IOWA. WITH DRY AIRMASS IN PLACE OVER
FORECAST AREA AND THE DEEPER FORCING/LIFT ASSOCIATED WITH SHORTWAVE
TROUGH SOUTH OF FORECAST AREA...HIGHER PRECIPITATION/SHOWER
CHANCES WILL REMAIN MAINLY SOUTH OF FORECAST AREA WEDNESDAY.
HOWEVER...THE 17.12Z GFS/NAM SUGGEST 500-300MB PV ADVECTION ALONG
THE MINNESOTA AND IOWA BORDER DURING THE DAY WEDNESDAY. WILL
INTRODUCE A SMALL PRECIPITATION CHANCE OVER THE EXTREME SOUTH PART
OF THE FORECAST AREA...AS THE 17.12 GFS/NAM DEVELOP LIGHT QPF...A
HUNDREDTH OR TWO...OVER THE EXTREME SOUTHERN PART OF THE FORECAST
AREA.

MAIN FORECAST CONCERNS FROM WEDNESDAY NIGHT INTO MEMORIAL DAY
WEEKEND ARE PRECIPITATION CHANCES FOR MEMORIAL DAY WEEKEND. THE
17.12Z GFS/ECMWF/GEM ARE IN GOOD AGREEMENT IN BUILDING IN
SHORTWAVE/SURFACE RIDGE INTO THE UPPER MIDWEST AND GREAT LAKES
REGION WEDNESDAY NIGHT INTO FRIDAY PROVIDING DRY WEATHER AND
SLIGHTLY TO NEAR NORMAL TEMPERATURES BOTH DAYS. FOCUS TURNS TO
MEMORIAL DAY WEEKEND...WHERE THE 17.12Z GFS/ECMWF ARE IN GOOD
AGREEMENT IN EJECTING PIECES OF ENERGY OUT OF UPPER LEVEL LOW/TROUGH
OVER THE SOUTHWEST UNITED STATES INTO THE CENTRAL UNITED STATES.
BOTH THE 17.12Z GFS/ECMWF SHOW INCREASING LOW LEVEL JET/MOISTURE
TRANSPORT/CONVERGENCE AND LIFT/FORCING SATURDAY INTO SUNDAY INTO THE
FORECAST AREA. WILL CONTINUE TO TREND OF SHOWERS AND THUNDERSTORMS
SATURDAY INTO SUNDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1100 PM CDT SUN MAY 17 2015

LOW CLOUDS ADVANCING QUICKER EAST THAN ORIGINALLY ANTICIPATED...AND
WILL BE ACROSS KRST/KLSE AROUND 06Z. ONCE IN...EXPECT THE MVFR
CLOUDS TO HOLD INTO THE MORNING HOURS...WITH SOME DIURNAL BUMP UP
INTO VFR BY MID/LATE MORNING MON. LIKELY SEE A RETURN TO MVFR CIGS
MONDAY EVENING.

STRONG WINDS AT KRST FOR THE FIRST PART OF THE OVERNIGHT...SUSTAINED
20 TO 25 WITH GUSTS UPWARDS OF 35 KTS. MODELS SUGGEST IMPROVEMENT BY
09Z OR SO...BUT WINDS SHOULD CONTINUE NEAR 20 KTS WITH HIGHER GUSTS
INTO EARLY MON EVENING AT KRST. SLIGHTLY LESS AT KLSE. THERE WILL BE
IMPROVEMENT LATER MONDAY NIGHT AS HIGH PRESSURE STARTS TO APPROACH
FROM THE NORTHERN PLAINS.

&&

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

$$

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



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