Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 041135
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
635 AM CDT MON MAY 4 2015

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 305 AM CDT MON MAY 4 2015

THE COLD FRONT EXTENDED FROM NORTHEAST WISCONSIN INTO SOUTHWEST
IOWA EARLY THIS MORNING AND BY 12Z IT IS EXPECTED TO BE COMPLETELY
THROUGH THE LOCAL AREA. LOCAL AND REGIONAL RADARS ALREADY SHOWING
MOST OF THE CONVECTION HAS PUSHED OUT OF THE AREA AND WHAT IS LEFT
WILL BE OUT THE AREA BY 12Z. PLAN TO START THE DAY DRY AND KEEP
THE RAIN CHANCES SOUTH OF THE AREA FOR THE MORNING.

CONSIDERABLE UNCERTAINTY ON HOW THE AFTERNOON AND EVENING WILL
PLAY OUT. A SHORT WAVE TROUGH CURRENTLY LIFTING NORTHEAST THROUGH
COLORADO AND KANSAS IS EXPECTED TO CAUSE THE NEXT ROUND OF
CONVECTION TO FIRE OVER EASTERN NEBRASKA AND WESTERN IOWA DURING
THE AFTERNOON. THE DIFFERENCES THEN BECOME WHERE THIS SHORT WAVE
AND CONVECTION WILL TRACK. THE 04.00Z NAM AND HI-RES ARW AND NMM
WOULD INDICATE THE SHORT WAVE TROUGH WOULD CONTINUE COMING
NORTHEAST AND MOVE OVER NORTHERN IOWA TONIGHT. THIS WOULD BRING
THE CONVECTION NORTHEASTWARD AS WELL GETTING INTO SOUTHERN
MINNESOTA AND WESTERN WISCONSIN OVERNIGHT. THE 04.00Z GFS AND
ECMWF DO NOT BRING THE SHORT WAVE TROUGH QUITE AS FAR NORTH WHICH
KEEPS THE CONVECTION CONFINED MORE INTO IOWA. THESE MODELS ARE
ALSO WEAKER WITH THE MOISTURE TRANSPORT BACK INTO THE REGION AHEAD
OF THE SHORT WAVE TROUGH. WILL INCLUDE SOME RAIN CHANCES FOR
TONIGHT ACROSS THE SOUTHERN SECTIONS...BUT WILL NOT BE AS FAR
NORTH WITH THEM AS WOULD BE SUGGESTED BY THE MORE AGGRESSIVE NAM
AND HI-RES ARW AND NMM.

AFTER TONIGHT...THE CONFIDENCE ON WHERE THE FRONT WILL BE LOCATED
REALLY STARTS TO GO DOWN. THE NAM SUGGESTS THE FRONT WILL START TO
LIFT BACK NORTH TOWARD THE AREA TUESDAY WHILE THE GFS AND ECMWF
HOLD IN PLACE ACROSS SOUTHERN IOWA OR NORTHERN MISSOURI. THESE
DIFFERENCES COULD RESULT IN THE AREA BEING UNDER THE MAIN AXIS OF
OVERRUNNING RAINS NORTH OF THE FRONT PER THE NAM OR COULD END UP
BEING ALMOST TOTALLY DRY AND NEEDING ONLY SOME SMALL RAIN CHANCES
ACROSS THE SOUTH LIKE THE GFS AND ECMWF. A LITTLE BIT BETTER
CONSENSUS FOR TUESDAY NIGHT OF HAVING THE MAIN BAND OF RAIN LIFT
NORTH THROUGH THE AREA WITH SOME DRYING POSSIBLE ACROSS THE SOUTH.
THE UPPER LEVEL FLOW REALLY STARTS TO TURN TO THE SOUTHWEST
WEDNESDAY WITH A COLD FRONT EXPECTED TO BEGIN MOVING ACROSS THE
DAKOTAS AND NEBRASKA. THE NAM AND ECMWF WOULD SUGGEST THAT THE
RAIN CHANCES WEDNESDAY MIGHT BE CONFINED TO AREAS ALONG AND WEST
OF THE MISSISSIPPI RIVER WHILE THE GFS SPREADS THEM WELL EAST
ACROSS MOST OF WISCONSIN. WITH SO MUCH UNCERTAINTY ON THE POSITION
OF THE FRONT AND WHERE THE RAIN WILL BE...TRIED TO COMPROMISE
BETWEEN THE DIFFERENT SOLUTIONS AS MUCH AS POSSIBLE AND LIMITED
THE RAIN CHANCES TO THE ABOUT 50 PERCENT OR LESS.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 305 AM CDT MON MAY 4 2015

THE POTENTIAL FOR THE WET WEATHER PATTERN WILL CONTINUE RIGHT
THROUGH THE UPCOMING WEEKEND. THE SOUTHWEST FLOW WILL REMAIN IN
PLACE BUT MIGHT SHOW SOME SIGNS OF BREAKING DOWN LATE IN THE
PERIOD. THE REMAINS OF THE UPPER LEVEL LOW CURRENTLY OFF THE
SOUTHERN CALIFORNIA COAST WILL GET LIFTED NORTH PAST THE AREA
EARLY IN THE PERIOD AS THE LARGER UPPER LEVEL LOW OFF THE PACIFIC
NORTHWEST COAST SINKS SOUTH. THIS SYSTEM SHOULD THEN LIFT
NORTHEAST AND START TO GET INTO THE UPPER MIDWEST FOR THE WEEKEND.
THE COLD FRONT THAT STARTS TO APPROACH WEDNESDAY LOOKS TO GET
PUSHED THROUGH THE REGION THURSDAY NIGHT AND FRIDAY...BUT THE
SOUTHERN END OF THE FRONT WILL BECOME STATIONARY SOUTH OF THE AREA
AS THE NEXT UPPER LEVEL LOW STARTS TO LIFT OUT OF THE DESERT
SOUTHWEST. THIS PART OF THE FRONT SHOULD THEN GET LIFTED BACK
NORTH INTO THE AREA FOR THE WEEKEND AS AN AREA OF LOW PRESSURE
MOVES NORTHEAST THROUGH THE MISSOURI RIVER VALLEY. THIS WILL
RESULT IN ABOUT A 30 TO 50 PERCENT FOR RAIN EACH DAY THROUGH THE
PERIOD.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 635 AM CDT MON MAY 4 2015

MAIN AVIATION CONCERNS ARE THUNDERSTORMS AT BOTH LSE/RST TAF
SITES AFTER 03Z TUESDAY. HIGH PRESSURE WILL BUILD INTO NORTHERN
MINNESOTA AND OVER LAKE SUPERIOR TODAY. THIS WILL PROVIDE VFR
CONDITIONS AT BOTH RST/LSE TAF SITES TODAY. THEN FOCUS TURNS TO
FRONT LIFTING NORTH INTO SOUTHERN IOWA AND NORTHERN MISSOURI
TONIGHT. A COUPLE OF DISTURBANCES MOVING ALONG THE FRONT WILL
ALLOW FOR THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS ACROSS
IOWA. THE BIG QUESTION WILL BE HOW FAR NORTH THE DISTURBANCE AND
ASSOCIATED CONVECTION MOVES TONIGHT. THE LATEST 04.06Z GFS/NAM AND
HIGHER RESOLUTION MODELS ARE IN BETTER AGREEMENT THAN PREVIOUS
RUNS...AND SUGGEST DISTURBANCE/CONVECTION REMAINS ALONG AND SOUTH
OF THE MINNESOTA/IOWA BORDER THROUGH 12Z TUESDAY/TAF PERIOD. WILL
LEAVE OUT ANY MENTION OF SHOWERS OR THUNDERSTORMS THROUGH THE TAF
PERIOD.

NEXT CONCERN AT TAF SITES IS THE POSSIBILITY OF MVFR/IFR CONDITIONS
AFTER 06Z TUESDAY. THE 04.06Z GFS/NAM SHOW LOW LEVEL MOISTURE
ADVECTING NORTHWARD INTO SOUTHERN MINNESOTA AND NORTHERN IOWA. THE
04.06Z NAM FARTHER NORTH WITH LOW LEVEL MOISTURE THAN THE GFS AND
INDICATES TAF SITES WOULD BE MVFR CEILING CONDITION AFTER 06Z
TUESDAY. FOR NOW...HAVE INTRODUCED SCATTERED DECK/CLOUDS OF
4000-4500 FEET AT BOTH TAF SITES.

&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION...DTJ


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