Severe Thunderstorm Warning 9, NWS Duluth, MN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DULUTH MN
1008 PM CDT SAT APR 21 2007

.UPDATE...

NARROW LINE OF THUNDERSTORMS FORMED ALONG BOUNDARY FROM NORTHEAST
AITKIN COUNTY THROUGH CENTRAL SAINT LOUIS INTO WESTERN LAKE COUNTY
LATE THIS EVENING. SMALL HAIL AND BRIEF HEAVY RAIN EXPECTED WITH
THESE STORMS...BUT RADAR SIGNITURES HAVE INDICATED SEVERE
ACTIVITY NOT LIKELY.

OF GREATER CONCERN LATE THIS EVENING IS THE MCS THAT FORMED OVER
EASTERN SOUTH DAKOTA...AND NOW MOVING TOWARDS CWA. FORECAST
UPDATE FOR TONIGHT CENTERED AROUND IMPACT OF THIS FEATURE UPON
AREA. LEADING EDGE OF THUNDERSTORM AND RAIN COMPLEX WAS BEGINNING
TO IMPACT EXTREME SOUTHWESTERN CWA (CASS AND CROW WING COUNTIES)
AROUND 10 PM AND EXPECTING QUICK INVASION OF HEAVY RAIN AND STORMS
INTO NORTHWESTERN HALF OF CWA THIS EVENING. WILL BE MONITORING
CLOSELY THIS EVENING FOR SEVERE WEATHER POTENTIAL...ESPECIALLY FOR
WESTERN HALF OF CWA...MOSTLY FOR LARGE HAIL.

&&

.DISCUSSION...

&&

.PREV DISCUSSION... /ISSUED 304 PM CDT SAT APR 21 2007/

DISCUSSION...

SHOWERS AND THUNDERSTORMS PERSISTED TODAY ALONG A THERMAL AXIS
FROM THE ARROWHEAD...TO THE TWIN PORTS...AND SOUTH ALONG THE I-35
CORRIDOR. ALTHOUGH THE TSTMS BECAME LESS WIDESPREAD IN THE
AFTERNOON HOURS. A STRONG SW LL FLOW ALLOWED FOR THE STORMS TO
MOVE VERY QUICKLY TO THE NNE AT 40 TO 45 KT. ALTHOUGH NO WIND
DAMAGE WAS REPORTED WITH THE FAST MOVING STORMS...PLENTY OF HALF
INCH HAIL ACCOMPANIED THESE CELLS. THE THERMAL RIDGE HAS DRIFTED
ABOUT 30 MILES EAST FROM THIS MORNING AND IS NOW ALONG A LINE
FROM BAYFIELD TO RICE LAKE...AND INTO THE ERN TWIN CITIES METRO.
THE RUC ALSO SHOWS THIS REGION IS CO-LOCATED WITH A NARROW AREA
OF MAX ISENTROPIC LIFT AS WELL AS BOUNDARY LAYER MASS CONVERGENCE.
THESE FAST MOVING SHOWERS AND THUNDERSTORMS WITH SMALL HAIL WILL
CONTINUE TO TRACK NE ALONG THE THERMAL RIDGE IN NW WIS THIS
EVENING...DIMINISHING AFTER SUNSET.

FORECAST FOCUS TURNING TO THUNDERSTORMS OVERNIGHT AS ON SUNDAY AS
A LOW PRESSURE SYSTEM AND DEVELOPING COLD FRONT AFFECT THE REGION.
SOME OF THE STORMS COULD BE SEVERE SUNDAY AFTERNOON IN NORTHERN
WISCONSIN.

OVERNIGHT...SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP AS A
50 KT SW LLJ ENTERS THE ERN HALF OF THE CWA. THE FOCUS FOR ACTIVITY
OVERNIGHT AND SUNDAY MORNING WILL BE ALONG A STRONG THERMAL BOUNDARY
AHEAD OF COLD FRONT IN WRN AND NRN MN. MINOR CHANGES TO POPS
OVERNIGHT.  ALTHOUGH NAM/GFS ARE IN SIMILAR AGREEMENT WITH THE
PLACEMENT OF THE FRONT AND THE MAX QPF OVERNIGHT...THE GFS IS
STRONGER AND DEEPENS THE SFC FRONT INTO A 998 LOW IN NC MN BY SUNDAY
MORNING. DUE TO THE POOR HANDLING OF THE LINE OF STORMS
TODAY...SIGNIFICANT FURTHER SE THAN MODELS DEPICTED...DECREASED
CONFIDENCE IN THE MODELS PLACEMENT OF THE QPF OVERNIGHT.

TOMORROW...THE COLD FRONT WILL PUSH SE ACROSS NW MN SUNDAY
MORNING...DECREASING THE CHANCE FOR ADDITIONAL TSTMS BEHIND IT. MUCH
DRIER AIR AND CAA WILL FILTER INTO NW MN BY SUNDAY AFTERNOON. THE
EXTEND OF THE DRY AIR IS STILL SOMEWHAT UNCERTAIN...BUT THE GFS AND
NAM ARE BRINING IT FURTHER SE INTO THE CWA BY SUNDAY AFTERNOON. THIS
DRY AIR WILL DECREASE THE CHANCE FOR THE NW THIRD OF THE CWA TO SEE
ANY STORMS SUNDAY AFTERNOON AND EVENING. THE MODELS ARE ALSO
TRENDING WITH A FASTER FROPA SUNDAY AND SUNDAY NIGHT. ADJUSTED POPS
TO REFLECT THEES TRENDS.

STORMS ARE LIKELY TO FIRE SUNDAY AFTERNOON AND EVENING...GENERALLY
ALONG AND SOUTH OF A LINE FROM CASS LAKE...TO HIBBING...AND INTO THE
MN ARROWHEAD. THE STRONGER STORMS ARE EXPECTED ACROSS ALL OF WI AND
INTO SW MN...WHERE THERE IS A SLIGHT RISK FOR SEVERE THUNDERSTORMS.

MUCAPE VALUES SUNDAY AFTN/EVEN ARE EXPECTED TO MAX OUT BETWEEN 1000
AND 1500 J/KG...WHILE 0-3KM SRH VALUES ARE PROGGED TO RANGE FROM
100-200 J/KG...WHICH SHOULD BE SUFFICIENT FOR THE DEVELOPMENT FOR
ISOLATED SEVERE THUNDERSTORMS. REFER TO THE THE DAY TWO SPC OUTLOOK
FOR FURTHER DETAILS.

THE FRONT WILL MOVE EAST OF OUR FA SUNDAY NIGHT...ALTHOUGH SOME
SHOWER ACTIVITY SHOULD LINGER ACROSS OUR ERN ZONES THROUGH MONDAY
MORNING. HIGH PRESSURE WILL BUILD ACROSS THE UPPER MIDWEST MONDAY
AND MONDAY NIGHT...RESULTING IN A DRYING TREND. TEMPERATURES WILL
REMAIN ABOVE NORMAL THIS WEEKEND...WITH COOLER TEMPS THEN EXPECTED
FOR NEXT WEEK ASSOCIATED WITH THE AFOREMENTIONED HIGH PRESSURE
SYSTEM FROM CANADA.

&&

POINT TEMPS/POPS...
DLH  47  64  41  57 /  50  70  70  10
INL  49  62  37  49 /  80  60  10  10
BRD  55  65  43  62 /  80  70  70  10
HYR  55  71  44  60 /  10  60  80  10
ASX  53  70  42  57 /  10  70  70  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...

MN...NONE.
WI...NONE.
LS...NONE.

KDW/GSF