Severe Thunderstorm Warning 133, NWS La Crosse, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
230 PM CDT SAT SEP 22 2001

FORECAST CONCERNS HINGE ON THE PCPN CHANCES FOR TONIGHT INTO
MONDAY...AND THEN CLOUDS AND TEMPS AFTER THAT.

THE 17Z SURFACE ANALYSIS PLACED A LOW OVER NORTHERN ND...WITH A COLD
FRONT EXTENDING FROM THE LOW SOUTHWARD INTO THE SOUTHERN PLAINS. A
SERIES OF LOWS WERE LOCATED ON THE SOUTHERN END OF THE BOUNDARY.
ALSO...WARM FRONT RAN FROM THE MAIN LOW INTO SOUTHWEST WI. DEWPOINTS
WERE POOLING TO AROUND 60 AHEAD OF THE COLD FRONT. 88-D IMAGERY HAS
A BAND OF PRECIPITAION FROM SOUTHCENTRAL MN INTO NORTHWEST
WI...HEADED EAST.

12Z MODEL INITIALIZATION LOOK FINE...AND MODELS A BIT BETTER
COMPARISON WISE THIS GO AROUND. ETA SIDING MORE TOWARD THE
CONSISTENT AVN SOLUTIONS OF THE PAST SEVERAL RUNS. ETA/S CUTOFF 60
HR 500 MB FARTHER SOUTH THEN THE AVN...AND THINK THE AVN HAS A
BETTER HANDLE WITH IT AT THE MOMENT.

RATHER VIGOROUS SHORTWAVE WILL SPIN OVER SOUTHEAST MN BY 06Z
TONIGHT...AND THEN THE BASE OF THE 500 MB TROUGH AND SHORTWAVE
SLIDES INTO EASTERN WI BY 06Z MON. THE DYNAMICS ARE QUITE GOOD WITH
THIS WAVE...WITH DEEP QG CONVERGENCE THROUGH 12Z SUN...ALONG WITH
850 MB WARM AIR ADVECTION AND ISENTROPIC UPGLIDE. IN ADDITION...300
MB JET INTERACTIONS SHOULD AID IN LIFT TONIGHT. MOISTURE WILL NOT BE
A PROBLEM...WITH SFC PWS IN EXCESS OF AN INCH...GOOD LOW LEVEL
MOISTURE TRANSPORT...AND SFC TDS CLIMBING INTO THE UPPER 50S TO NEAR
60 SOUTH OF THE WARM FRONT. THE SHEAR ISN/T BAD...ALTHOUGH CAPES ARE
RELATIVELY LOW...UNDER 1000 J/KG. STILL...THE POTENTIAL FOR SVR
STORMS EXISTS...MAINLY ACROSS SOUTHERN SECTIONS. SIMILAR TO WHAT
OCCURRED ON THURSDAY. SO...SHOWERS AND STORMS SHOULD BE A GIVEN FOR
THE ENTIRE FORECAST AREA TONIGHT.

THE BEST DYNAMICS EXIT TO THE EAST OVERNIGHT...BUT THE FORECAST AREA
WILL STILL HAVE TO DEAL WITH CYCLONIC FLOW AND 850 MB COLD AIR
ADVECTION. THIS...ALONG WITH WRAP AROUND MOISTURE FROM THE SFC
LOW...WILL HELP SCATTER SHOWERS FOR SUNDAY. THE BEST CHANCES WILL BE
TO THE EAST...CLOSER TO THE LOW AND ANY LINGERING RAIN SHIELD FROM
TONIGHT. WINDS ARE PROBABLY THE BIGGER CONCERN FOR SUNDAY AS THE
PRESSURE GRADIENT TIGHTENS BEHIND THE DEPARTING LOW. BRISK NORTH
WINDS WILL DEFINITELY ADD SOME BIT TO THE AIR...WITH HIGH TEMPS NOT
EXPECTED TO GET OUT OF THE 50S.

BY MONDAY...A 500 MB LOW WILL CUTOFF OVER THE OH VALLEY AS A RIDGE
BUILD OFF TO THE WEST. THIS PATTERN THEN WILL HOLD FAST AS THE 300
MB JET STAYS NORTH OF CANADA. WHAT THIS MEANS FOR THIS AREA IS A
COOL NORTH TO NORTHWEST FLOW...ALTHOUGH IT DOESN/T LOOK LIKELY (AT
THIS MOMENT) THAT SHORTWAVES WILL BE ABLE TO WORK OVER THE RIDGE AND
INTO THE REGION. HOWEVER...IF THE CUTOFF LOW WOBBLES MORE TO THE
WEST...SHORTWAVE ENERGY AROUND THE LOW COULD LEAD TO SOME
PRECIPITATION CHANCES AND CLOUDS. TOUGH CALL...AND WILL LEAN TOWARD
DRY FOR THE MOMENT...WITH MOST OF THE CLOUDS TO THE EAST.

.LSE...NONE.

RIECK