Flooding in Wisconsin, May 1 to 18, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
309 PM CDT MON APR 30 2001

FORECAST CONCERNS THIS PACKAGE...SHRA/TSRA CHANCES THROUGH THE
PERIOD.

19Z DATA ANALYSIS SHOWED THE COLD FRONT NEAR A KINL-KSTC-KFSD LINE...
WEAKENING AS SHORT-RANGE MODELS INDICATED. FAIRLY BROAD BAND OF
SHRA...POSSIBLE -TSRA PRECEDED THE FRONT FROM NORTHEAST MN INTO
CENTRAL IA IN AN AREA OF MID/UPPER LEVEL FORCING. BAND WAS MAKING
STEADY PROGRESS EAST...BUT WAS HAVING TO OVERCOME SOME DRIER LOW
LEVEL AIR. TIGHTEST PRESSURE GRADIENT HAS SHIFTED INTO EASTERN WI
WHERE WIND GUSTS OF 30 TO 40 MPH WERE COMMON. GRADIENT RELAXED
CONSIDERABLY BEHIND THE FRONT. WV IMAGERY SHOWED MODELS TO HAVE GOOD
HANDLE ON UPPER FEATURES AT 18Z...ALONG WITH A DECENT SUB-TROPICAL
MOISTURE CONNECTION OVER THE REGION AHEAD OF THE TROUGHING IN THE
CENTRAL/NORTHERN PLAINS. NEXT MORE SIGNIFICANT SHORTWAVE WAS TAKING
AIM AT THE WA COAST.

12Z MODELS ALL LOOK TO HAVE INITIALIZED WELL THIS MORNING...THOUGH
HAVE TO GIVE THE NOD TO AVN WITH BOTH SURFACE FEATURES AND UPPER
JETS. EVEN WITH SUBTLE INITIALIZATION DIFFERENCES...ALL MODELS OFFER
SIMILAR SOLUTIONS THRU 48-60HRS...AND ARE QUITE CONSISTENT WITH
THEIR PREVIOUS RUNS. FAVORED ETA/AVN SOLUTIONS...THOUGH DIFFERENCES
IN MODELS TO HAVE LITTLE IMPACT ON SENSIBLE WEATHER THRU TUE NIGHT.

IN THE SHORT TERM...MN COLD FRONT PUSHES SLOWLY EAST AND CONTINUES
TO WEAKEN TONIGHT. DECENT VORTICITY LOBE PUSHES ACROSS THIS EVENING
WITH THE FRONT. THIS MAINTAINS THE MID LEVEL TROUGH AND MID/UPPER
LEVEL FORCING FOR SHRA/ISOLATED -TSRA ACROSS THE AREA THRU THE
EVENING HOURS. SINKING/DRYING SPREAD ACROSS THE AREA LATER TONIGHT
BEHIND THE MID LEVEL TROUGH...ALREADY EVIDENT OVER PARTS OF THE
NORTHERN PLAINS. QUESTION IS HOW FAR SOUTH WILL THE SURFACE
BOUNDARY GET BEFORE BEING RETURNED NORTHWARD AHEAD OF THE NEXT LEE
LOW ALREADY STARTING TO DEVELOP IN MT/ALB/SASKAT. BELIEVE IT WILL NOT
GET FAR. AREA GETS WARM SECTORED ON TUE AHEAD OF THE NEXT SYSTEM. ETA
SURFACE DEWPOINTS AGAIN LOOK IN ERROR FOR TUE. EVEN WITH MORE REAL
AVN DEWPOINTS...PLENTY OF INSTABILITY OVER THE AREA BY LATER TUE.

SHORTWAVE MOVING ONTO WA COAST THIS AFTERNOON MOVES TO SOUTHERN
SASKAT BY 12Z TUE...THEN TO SOUTHERN MANITOBA BY 00Z WED...DEVELOPING
A 5H LOW. STRONG COLD FRONT WITH THE SURFACE LOW/SHORTWAVE APPROACHES
THE AREA BY LATE AFTERNOON TUE. MODERATE TO STRONG SHOT OF LOW LEVEL
FRONTOGENESIS AND 850-700MB Q-G CONVERGENCE...PLUS 850MB MOISTURE AND
WARM ADVECTION WITH/AHEAD OF THE FRONT. MODEL SOUNDINGS INDICATE GOOD
SPEED/DIRECTION SHEAR BY 00Z WED...AHEAD OF THE APPROACHING FRONT.
ALL THIS...ALONG WITH THE EXPECTED TIMING...SPC SWODY2 LOOKS GOOD.

FRONT PUSHES QUICKLY THROUGH THE AREA TUE NIGHT...THEN QUESTION AGAIN
IS HOW FAR SOUTH WILL IT GET BEFORE IT STALLS. MODELS PROG MODERATE/
STRONG SOUTHWEST FLOW IN THE MID/UPPER LEVELS ACROSS THE CENTRAL
U.S...WHICH BACKS WITH TIME AS THE NEXT SHORTWAVE DIGS INTO THE
CENTRAL/SOUTHERN ROCKIES. DOUBT FRONT WILL GET TOO FAR SOUTH OF THE
FORECAST AREA BEFORE STALLING. FRONT TO THEN REMAIN THE FOCUS FOR
PRECIP DEVELOPMENT AS INEVITABLE BITS AND PIECES OF SHORTWAVE ENERGY
EJECT OUT OF THE WESTERN TROUGH/LOW AND TOWARD THE REGION IN THE
SOUTHWEST FLOW ALOFT.

PRESENT EXTENDED FORECAST HAD CHANCE SHRA/TSRA FOR WED-FRI AND LOOKS
GOOD. AS WESTERN UPPER LOW DEEPENS AND BECOMES CUT-OFF...RIDGING
DEVELOPS OVER THE CENTRAL U.S. INTO SOUTHERN CANADA. AS RIDGING
STRENGTHENS...CANADIAN HIGH PRESSURE SLIDES IN FOR THE WEEKEND.
MEDIUM/LONG RANGE MODELS INDICATING WESTERN LOW TO OPEN UP AND LIFT
OUT ACROSS THE AREA IN THE MON/TUE TIMEFRAME NEXT WEEK.

NUMERICAL TEMP GUIDANCE SIMILAR FOR TONIGHT AND LOOKS GOOD WITH
PRESENT DEWPOINTS AND EXPECTED SHRA/TSRA. AFTER THAT...USED BLEND OF
NGM-FWC/AVN-MAV FOR TUE/TUE NIGHT...FOLLOWED WARMER MAV NUMBERS FOR
WED. FWC/MAV POPS SIMILAR. FAVORED MAV POPS:...AND RAISED ALL OF THEM
TO LIKELY CATEGORY FOR TUE NIGHT.

.LSE...NONE.

RRS