Hail in Minnesota, July 29 to 30, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DULUTH MN
856 PM CDT SAT JUL 29 2006

.UPDATE...
LATEST 18Z MODEL RUNS...SPCLY THE SMOOTH GFS TELLS THE STORY ATTM.
A 700 MB CAP...WITH TEMPS ABOVE 10C...IS NOW APPROACHING OUR AREA
AND WILL SURROUND IT TONIGHT BEFORE OVERSPREADING EVEN THE ARROWHEAD
EARLY SUNDAY. MEANWHILE...1000 TO 700 MOISTURE POCKET OF AOA 80
PCT REMAINS OVER THE ARROWHEAD AND EXTENDS SOUTHEASTWARD ALONG THE
ENTIRE MI/WI BORDER...OUTSIDE OF THE CAP. THIS MOISTURE REMAINS
THROUGH SUNDAY...BUT BECOMES CAPPED DURING THE DAY. MEANWHILE...AT
LOW LEVELS...A MARINE AIR MASS...WITH SFC TEMPERATURES AS LOW AS
15C...HAS PUSHED WESTWARD AND SOUTHWARD. THE ONLY UNCAPPED AREA
UNDERRUN BY THE CHILLY MARITIME AIRMASS IS IN THE CURRENT LINE OF
THUNDERSTORMS AND TO THE NORTHEAST OF IT. THE VERY HOT AND HUMID
AIR MASS IS OVERRUNNING THE MARITIME AIR FROM THE WEST SOUTHWEST
AND UNDERRUNNING THE CAP...BREAKING OUT OVER THE ARROWHEAD ATTM.
WE DO NOT ANCPT SEVERE WEATHER WITH PARTICULAR LINE...SLOWLY
MOVING NORTHEAST...SINCE DOWNBURSTS WOULD HAVE TO DO WORK TO
PENETRATE THE MARITIME AIRMASS AND IMPACT THE GROUND...DECREASING
THEIR STRENGTH. AND WITH THE VERY HIGH FREEZING LEVEL AND WITH THE
INCREASINGLY HIGH ALTITUDE BASE OF THE HOT AIR...SIGNIFICANT HAIL
IS BECOMING LESS AND LESS LIKELY. ADDITIONALLY...THERE IS NO
HISTORY OF HAIL WITH THESE STORMS...VINDICATING THAT PHILOSOPHY
ATTM. AGAIN...THE BOUNDARY ALONG WHICH THE CONVECTION IS FIRING IS
NOT AT THE SURFACE...BUT IS A CERTAIN CRUCIAL DEPTH OF THE QUITE
DENSE AND SLOWLY RETREATING MARINE AIR MASS.

SO...WE RETAINED SCATTERED THUNDERSTORMS WITH CHANCE POPS ACROSS
OUR ENTIRE AREA...TO BLEND WITH NEIGHBORING AREAS...CONFORM TO
PRINTOUT MODELS...AND TAKE ACCOUNT OF ISOLATED CONVECTION JUST TO
THE SOUTHWEST WHERE THE CAP IS NOT YET AS STRONG AS OVER AREAS
SOUTH AND WEST OF OUR FORECAST AREA. HOWEVER...WE ANCPT THE LINE
TO CONTINUE DRIFTING VERY SLOWLY NORTHEAST...WITH CELLS MOVING
EAST-SOUTHEAST AS THE FLOW AT THE BOTTOM OF THE HOT LAYER MOVES.

IT REMAINS TO BE SEEN HOW QUICKLY TEMPERATURES ARE ABLE TO RISE IN
THE DULULTH AREA AND FURTHER NORTH AND EAST IF THE MARINE AIR MASS
PROVES STUBBORN AND SLOW TO RETREAT ON SUNDAY.

&&

.PREV DISCUSSION... (ISSUED 308 PM CDT SAT JUL 29 2006)

DISCUSSION...MAIN FORECAST FOCUS IS ON PENDING SEVERE WEATHER
EVENT FOR THIS EVENING THROUGH TOMORROW MORNING. CURRENT SURFACE
ANALYSIS SHOWS E/W ORIENTED BOUNDARY STRETCHING ACROSS SOUTHERN
NORTH DAKOTA AND ACROSS CENTRAL MINNESOTA INTO THE ARROWHEAD.
ABUNDANT LOW LEVEL MOISTURE CURRENTLY ADVECTING NORTHWARD TO THE
SOUTH OF SURFACE BOUNDARY. DESPITE AFTERNOON MIXING...AXIS OF
LOWER 70S DEWPOINTS EXTENDS INTO SOUTHERN AND WEST CENTRAL
MINNESOTA. ARC OF SHOWERS AND A FEW THUNDERSTORMS CONTINUES NORTH
OF SURFACE BOUNDARY PER 88D MOSAIC AND VISIBLE SATELLITE IMAGERY
THIS AFTERNOON. THUS FAR...THERMAL CAP HAS HELD THROUGH THE DAY
WITH NO SIGNIFICANT FORCING PRESENT. SURFACE AND DIFFERENTIAL
HEATING ALONG CLOUD LINE MAY STILL BE ENOUGH TO TRIGGER CONVECTION
THIS LATE AFTERNOON EVENING. 0-6KM DEEP LAYER SHEAR OF 40 TO 50 KT
WILL SUPPORT AN INITIAL SUPER-CELLULAR STRUCTURE...POSSIBLY
ENHANCING HAIL SIZE. OTHERWISE...THE MAIN SEVERE THREAT LOOKS TO
OCCUR WITH THE ONSET OF DEVELOPING SOUTHERLY LOW LEVEL JET. AXIS
OF INSTABILITY PUSHES INTO AND VEERS ACROSS THE FA WITH THE LOW
LEVEL JET. DIFFERENTIAL THETA-E ADVECTION SHOULD TRIGGER
THUNDERSTORMS TO THE WEST OF CWA...WHICH ARE EXPECTED TO THEN
FOLLOW THE THICKNESS CONTOURS/MEAN FLOW OVERNIGHT THROUGH MUCH OF
MINNESOTA AND INTO NORTHWEST WISCONSIN. CONVECTION INITIATION
LOOKS POSSIBLE ALONG MUCH OF THE BOUNDARY GIVEN THE BROAD LOW LEVEL
JET AND PRESENCE OF AMPLE MOISTURE...AS WELL ENHANCED LIFT FROM
APPROACHING SHORT WAVE ATOP THE RIDGE. FAST MID-LEVEL FLOW WITH
GOOD DEEP LAYER SHEAR WILL LIKELY SUPPORT A PROGRESSIVE MCS WITH
EMBEDDED SUPERCELL STRUCTURE OVERNIGHT. BOTTOM LINE...GOOD SET UP
FOR ANOTHER ROUND OF SEVERE WEATHER WITH DAMAGING WINDS AND LARGE
HAIL OVERNIGHT INTO SUNDAY MORNING.

SURFACE WARM FRONT WILL CONTINUE TO LIFT NORTHWARD AS STRONG
SOUTHERLY FLOW AND WARM AIR ADVECTION CONTINUES SUNDAY. THE AXIS
OF UPPER RIDGE SHIFTS SLIGHTLY EASTWARD FOR SUNDAY AS
WELL...LEAVING THE EDGE OF THE THERMAL CAP ACROSS NORTHERN
MINNESOTA/WISCONSIN. INSTABILITY AND SHEAR REMAIN FAVORABLE FOR
SEVERE CONVECTION OVER FA...ESPECIALLY SUNDAY AFTERNOON AND
EVENING. THE FOCUS WILL JUST SHIFT A BIT NORTHWARD TOMORROW.
SUNDAY AND MONDAY WILL ALSO BRING A RETURN TO OPPRESSIVE HEAT TO
THE NORTHLAND. THE SOUTHERN HALF OF THE CWA WILL BE APPROACHING
HEAT ADVISORY CRITERIA SUNDAY /HEAT INDICES OF 105-115F/ AND WILL
LIKELY HIT CRITERIA MONDAY.

UPPER PATTERN SHIFTS SOUTHWEST BY LATE MONDAY BEHIND UPPER RIDGE.
ASSOCIATED LOW LEVEL THERMAL BOUNDARY WILL BEGIN TO MOVE INTO THE
REGION MONDAY NIGHT. WEAK SHORT WAVES IN THE SOUTHWEST FLOW ALOFT
MAY BRING A FEW ROUNDS OF CONVECTION WITH HEAVY RAIN TUESDAY
THROUGH WEDNESDAY TO THE NORTHLAND. THE SURFACE BOUNDARY WILL BE
NEARLY PARALLEL TO THE UPPER FLOW...SUGGESTING A SLOW MOVING
SYSTEM. MOISTURE AVAILABILITY WILL REMAIN HIGH SOUTH OF THE
BOUNDARY WITH PWATS OF 2 TO 2.5 INCHES. POPS WERE RAISED
ACCORDINGLY. A MUCH DRIER AIRMASS WILL THEN MOVE IN FOR WED NIGHT
AND THURSDAY.

&&

.DLH WATCHES/WARNINGS/ADVISORIES...

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

EOM

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE DULUTH MN
753 AM CDT SAT JUL 29 2006

LSZ121-140>148-162-MNZ010>012-018>021-025-026-033>038-WIZ001>004-
006>009-301300-
BAYFIELD TO OAK POINT WI-GRAND PORTAGE TO GRAND MARAIS MN-
GRAND MARAIS TO TACONITE HARBOR MN-
TACONITE HARBOR TO SILVER BAY HARBOR MN-
SILVER BAY HARBOR TO TWO HARBORS MN-TWO HARBORS TO DULUTH MN-
DULUTH MN TO PORT WING WI-PORT WING TO SAND ISLAND WI-
SAND ISLAND TO BAYFIELD WI-OAK POINT TO SAXON HARBOR WI-
OPEN WATERS OF LAKE SUPERIOR WEST OF A LINE FROM SAXON HARBOR WI
TO GRAND PORTAGE MN-KOOCHICHING-NORTHERN ST. LOUIS-
NORTHERN COOK/NORTHERN LAKE-NORTHERN ITASCA-CENTRAL ST. LOUIS-
SOUTHERN LAKE/LAKESHORE-SOUTHERN COOK/LAKESHORE-NORTHERN CASS-
SOUTHERN ITASCA-SOUTHERN CASS-CROW WING-NORTHERN AITKIN-
SOUTHERN AITKIN-CARLTON/SOUTHERN ST. LOUIS-PINE-DOUGLAS-BAYFIELD-
ASHLAND-IRON-BURNETT-WASHBURN-SAWYER-PRICE-
753 AM CDT SAT JUL 29 2006

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHEAST MINNESOTA...
NORTHWEST WISCONSIN AND WESTERN LAKE SUPERIOR.

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS WILL REDEVELOP ACROSS PORTIONS OF NORTHEASTERN
MINNESOTA AND NORTHWESTERN WISCONSIN TODAY. THERE IS A SLIGHT RISK
OF SEVERE THUNDERSTORMS THIS AFTERNOON AND TONIGHT...MAINLY SOUTH
OF A WASKISH TO EMBARRASS...TO SILVER BAY LINE. LARGE HAIL AND
DAMAGING WINDS WILL BE THE MAIN THREAT. GUSTY NORTHEAST WINDS OF
UP TO 20 KNOTS CAN BE EXPECTED IN THE NEAR SHORE WATERS OF LAKE
SUPERIOR. AS A RESULT...THERE IS A THREAT OF RIP CURRENTS ON
THE BEACHES FROM THE TWIN PORTS ALONG THE SOUTH SHORE.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THUNDERSTORMS ARE AGAIN EXPECTED ON SUNDAY AND SUNDAY NIGHT. A FEW
STORMS COULD BE SEVERE...WITH DAMAGING WINDS AND LARGE HAIL. THERE
IS ALSO A CHANCE OF THUNDERSTORMS FROM MONDAY NIGHT THROUGH
TUESDAY NIGHT.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION MAY BE NEEDED TODAY AND TONIGHT.

DAP