Severe Thunderstorm Warning 53, NWS Marquette, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MARQUETTE MI
340 PM EDT MON AUG 25 2003

BIGGEST FORECAST CONCERN IS CONVECTIVE POTENTIAL TONIGHT.

STRONG RIDGE ALOFT CONTINUES OVER THE CENTRAL U S...WITH WLY FLOW
ALONG THE NORTHERN TIER STATES. WV IMAGERY SHOWS DEEPER TROUGH
SWINGING THROUGH NRN SASKATCHEWAN. SHORTWAVES EMBEDDED W/IN WLY FLOW
HAVE KICKED OFF CONVECTION FROM CENTRAL MN TO SRN WI. SFC HIGH/LAKE
BREEZE REGIME HAS DOMINATED WX OVER THE U P TODAY...THOUGH SOME
-SHRA HAVE WORKED THEIR WAY INTO THE FAR WEST OF LATE. SATELLITE
IMAGERY SHOWS CU FIELDS DEVELOPING ALONG CONVERGENT LAKE BREEZE
BOUNDARIES IN THE CENTRAL AND EAST...WITH A SMALL CELL PRODUCING
-SHRA AT KERY AT 1430Z. OTHERWISE...MID/HIGH CLOUD HAVE INCREASED
FROM THE WEST THIS AFTN.

MANY FACTORS APPEAR TO BE IN PLACE FOR A ROUND OF CONVECTION
TONIGHT. RUC/12Z RAOBS SHOW STRONGER H5 FLOW (50KT OR GREATER) TO
OUR NW WHICH WILL PUSH THROUGH TONIGHT. CONVECTION TO OUR WEST LINES
UP WELL WITH H8 THETA-E ADVECTION AND ALONG AXIS OF HIGHER H8-H5
DTHETA/DZ...WHICH MOVE INTO THE WRN U P THIS EVENING. THOUGH CURRENT
CONVECTION IN WI WILL LIKELY STAY TO OUR SOUTH PER RUC LLJ WINDS...
H8 TROF/CONVERGENCE WILL SHARPEN IN THE MN ARROWHEAD BY 00Z THEN
TRACK THROUGH THE U P AT THE NOSE OF DEVELOPING 25-30KT LLJ. THOUGH
CLOUD COVER IN WEST HAS LIMITED SBCAPES THIS AFTN...ETA SOUNDINGS
SHOW ELEVATED CAPES OF 1000-2000 J/KG TONIGHT AS THE TROF PASSES.
WIND PROFILE IS ALSO FAVORABLE AND SHOWS 55-60 KT OF SHEAR THROUGH
6KM. SHALLOWNESS OF EXPECTED SFC INVERSION COMBINED WITH STRONG MID
LEVEL FLOW SUGGEST SEVERE WIND CONCERNS. WBZERO HEIGHTS OF 10K-11KFT
ARE FAVORABLE FOR HAIL AS WELL. THOUGH CURRENT SFC PATTERN IS
MESSY...WITH MAIN WARM FRONT WELL TO OUR SOUTH...INITIATION OF LAKE
BREEZES SHOULD ONLY ENHANCE THE BAROCLINIC ZONE FOR THIS EVENING.
OVERALL...WILL KEEP W/ ISOLD/SCT POPS THIS EVENING (LAKE BREEZE
SHRA)...THEN PICK THINGS UP TO NUMEROUS TSRA OVERNIGHT FROM WEST TO
EAST. BEST FORCING LOOKS TO EXIT THE EAST BY AROUND 08-10Z TOMORROW.

HAVE DECIDED TO MENTION SLGT CHC TSRA NEAR LAKE MICHIGAN SHORE TUE
AFTN. MODIFIED MESOETA SOUNDINGS FOR 88/64 YIELD NEARLY 2K J/KG OF
CAPE IN AN AREA WHICH SHOULD HAVE SOME DEGREE OF LLVL CONVERGENCE
AND LINGERING HIGHER THETA-E AIR...DESPITE FACT THAT THE MAIN FRONT
WILL HAVE PASSED. Q-VECTOR DIVERGENCE AND DRYING ALF WILL BE BIG
INHIBITORS...BUT THE K-INDEX AT KMNM IS STILL FORECAST TO BE 33 AT
18Z.

SFC HIGH BUILDS FOR BENIGN AND COOLER PERIOD TUE NIGHT AND WED.
THEN...DEEP SFC LOW DEVELOPS IN NRN PLAINS AHEAD OF NEXT STRONG
SHORTWAVE. ETA/GFS SHOW PERIOD OF STRONG ISENTROPIC LIFT AND H8
THETA-E ADVECTION INTO THU...WITH H8 TEMPS WARMING TO 20C IF YOU
BELIEVE THE ETA...SO HAVE BUMPED POPS UP TO 50 WITH THIS DYNAMIC-
LOOKING SYSTEM. STRONG CAA/ISENTROPIC DOWNGLIDE ON ITS BACK SIDE
WILL BRING MUCH COOLER WX AND WINDY CONDITIONS LATE THU AND FRI.
WINDS/WAVES ON SUPERIOR LOOK TO BE AN ISSUE BY FRI AS H8 TEMPS DROP
TO NEAR ZERO. OTHERWISE...WILL KEEP CHC SHRA GOING FRI AFTN AS TROF
AXIS ALF SWINGS THROUGH THE AREA...ENHANCED BY SFC-H8 DELTA-TS WHICH
MAY APPROACH 15C OVER LAKE SUPERIOR. IT WILL BE A TASTE OF FALL.

FOR THE REMAINDER OF THE EXTENDED (SAT-MON) HAVE OPTED TO INCLUDE
LOW CHANCE POPS FOR SHRA ALL THREE DAYS AS WE REMAIN IN CYCLONIC
FLOW AT THE SFC AND ALF...W/ LOW PRESSURE CENTERED NEAR HUDSON BAY.
H5 TEMPS OF NEAR 20C WILL PROVIDE DIURNAL INSTABILITY...AND
SHORTWAVES ROTATING AROUND PARENT LOW WILL BE FACTOR THOUGH
IMPOSSIBLE TO TIME AT THIS POINT. GFS SHOWS H8 TEMPS RISING NO
HIGHER THAN 5C THROUGH THE PERIOD...SO IT WILL REMAIN FALL-LIKE.

.MQT...NONE.

JKL

MIZ001>007-009>014-084-085-261200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE MARQUETTE MI
530 AM EDT MON AUG 25 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL UPPER
MICHIGAN.

.DAY ONE...TODAY AND TONIGHT

ISOLATED INLAND THUNDERSTORMS ARE POSSIBLE LATE THIS AFTERNOON AND
EVENING. MORE NUMEROUS THUNDERSTORMS ARE EXPECTED OVERNIGHT. SOME OF
THESE STORMS COULD BECOME SEVERE WITH DAMAGING WINDS AND LARGE HAIL.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THUNDERSTORMS ARE POSSIBLE EARLY TUESDAY OVER SOUTH AND EAST UPPER
MICHIGAN. MORE THUNDERSTORMS ARE POSSIBLE THURSDAY THROUGH FRIDAY
MORNING...AND AGAIN EARLY SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT.

ADDITIONAL WEATHER INFORMATION MAY BE OBTAINED AT THE FOLLOWING URL:

HTTP://WWW.CRH.NOAA.GOV/MQT (ALL LOWER CASE)

JLB