Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 251710
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1210 PM CDT SAT APR 25 2015

.UPDATE...
ISSUED AT 927 AM CDT SAT APR 25 2015

LOOKING AT THE TRENDS IN THE 25.12Z RAP AND 25.13Z HRRR IT APPEARS
ANY CHANCES FOR RAIN TODAY WILL BE LIMITED TO THE VERY SOUTHERN
PARTS OF THE AREA. THE RAP INDICATES THERE IS A WEAK SHORT WAVE
TROUGH ON THE NORTHEAST SIDE OF THE UPPER LEVEL LOW THAT COULD
PRODUCE SOME WEAK FORCING OVER THE AREA BEFORE SHIFTING OFF TO THE
EAST DURING THE MID AND LATE AFTERNOON HOURS. SOME WEAK
FRONTOGENESIS IN THE 850-700 MB LAYER COULD ALSO ROTATE BACK NORTH
INTO THE AREA AROUND 18Z. TRIMMED THE NORTHERN EXTENT OF THE RAIN
CHANCES FOR THE REST OF THE DAY TO CONFINE THEM TO THE FAR
SOUTHERN AREAS. ALSO LOWERED THEM DOWN FROM THE 60 TO 70 PERCENTS
TO ABOUT 30 OR 40 PERCENT. THE RAP SHOWS ALL THE CAPE REMAINING
WELL TO THE SOUTH WITH NO ELEVATED CAPE IN EITHER THE KDBQ OR KBLR
FORECAST SOUNDINGS SO HAVE DROPPED THE THUNDER MENTION.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 255 AM CDT SAT APR 25 2015

FORECAST FOCUS IN THE SHORT TERM IS THE RAIN THREAT TODAY. CLOSED
CIRCULATION SPINNING THROUGH KS EARLY THIS MORNING...HEADING EAST
AND WEAKENING THROUGH THE DAY TODAY. DEFORMATION AND FRONTOGENETIC
FOCUS ON THE NORTHERN EDGE OF THIS SYSTEM WILL SPREAD RAIN AND
EMBEDDED THUNDERSTORMS ACROSS IA AND NORTHERN IL. MAIN DILEMMA IS
HOW FAR NORTH RAIN WILL GET. VARIOUS MODEL SOLUTIONS OVER THE PAST
SEVERAL DAYS HAD BEEN SUGGESTING RAIN WOULD SPREAD NORTH AS FAR
AS THE I-90 CORRIDOR. BUT THE LAST FEW RUNS HAVE NOW SHIFTED THAT
FOCUS FURTHER SOUTH. LOOKING AT THE FORCING AND THE INFLUX OF MORE
DRY LOW LEVEL AIR ON EAST/NORTHEAST WINDS SUPPORT A TIGHTER
RAIN/NO-RAIN GRADIENT AND THE SOUTHWARD SHIFT. THIS TREND IS
ALREADY BORNE OUT LOOKING AT OVERNIGHT RADAR LOOPS SHOWING THE
DIMINISHING TREND. SO MOVED THE FORECAST IN THIS DIRECTION FOR
TODAY. RAIN THREAT WILL END BY SUNSET AS HIGH PRESSURE OVER MB/ONT
BUILDS SOUTHWARD INTO THE REGION. AIRMASS DRIES AND BOUNDARY LAYER
TEMPERATURES TUMBLE. A CHILLY NIGHT IS ON TAP...ESPECIALLY OVER
OUR TYPICAL COOL AREAS OF CENTRAL WI.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 255 AM CDT SAT APR 25 2015

LOOKING INTO THE LONGER TERM...UPPER FLOW PATTERN REMAINS BLOCKED
THANKS TO THE EAST COAST CLOSED LOW WHICH PERSISTS INTO AT LEAST
TUESDAY. THIS KEEPS SURFACE HIGH PRESSURE AND DRY EASTERLY FLOW
POURING INTO THE AREA. A WEAK SHORT WAVE TROUGH DROPS INTO THE
BACK SIDE OF THE UPPER LOW LATE ON TUESDAY. THIS COULD BRING A FEW
LIGHT SHOWERS TO PARTS OF THE AREA...BUT WITH A VERY DRY
ATMOSPHERE THE CHANCES WILL BE QUITE LOW. THE PATTERN TRANSITIONS
TO MORE OF AN OMEGA LOOK BY LATE IN THE WEEK...PUTTING THE AREA
MORE IN THE UPPER RIDGE. THUS...A WARMING TREND IS ON TAP WITH
TEMPERATURES BACK ABOVE NORMAL. THE NEXT SIGNIFICANT CHANCE FOR
ANY RAINFALL LOOKS TO BE NEXT WEEKEND AS THE PERSISTENT SOUTHERLY
FLOW FINALLY GETS ENOUGH MOISTURE INTO THE REGION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1210 PM CDT SAT APR 25 2015

VFR CONDITIONS EXPECTED THROUGH THE PERIOD. HIGH PRESSURE OVER
ONTARIO WILL REMAIN NEARLY STATIONARY INTO SUNDAY AFTERNOON BUT
BECOME STRONGER ENABLING THE RIDGE AXIS TO EXTEND OVER THE AREA.
THE HIGH WILL CONTINUE TO BRING IN DRIER AIR WHICH WILL ALLOW THE
CLOUDS TO SCATTER OUT THROUGH THE AFTERNOON AND BECOME CLEAR EARLY
THIS EVENING. THE EAST WINDS WILL DROP TO LESS THAN 10 KNOTS AS
THE RIDGE AXIS STRENGTHENS AND REMAIN LIGHT THROUGH SUNDAY
MORNING.

&&

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

$$

UPDATE...04
SHORT TERM...MW
LONG TERM...MW
AVIATION...04


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