Severe Thunderstorm Warning 3, NWS Marquette, MI

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE MARQUETTE MI
1005 PM EDT TUE JUL 01 1997

SHORT TERM CONCERN IS FOG NR LK SUP. LATEST SFC CHART SHOWS RDG OF
HI PRES NOSING SWWD FROM CNTRL ONTARIO INTO CNTRL U.P. GOES-8 INDICATES
FOG/STRATUS SPRDG SWWD IN LGT NELY FLOW. AT 01Z...FOG EXTENDED INLAND
ABOUT 10-20 MILES FROM LK FROM KEWEENAW TO WHITEFISH PT. FOG OVR WRN
LK SUP IS CLINGING CLOSER TO SHORELINE WITH LESS PENETRATION INLAND.
GOES-8 LOOP INDICATES BACK EDGE OF STRATUS AREA MAKING STEADY PROGRESS
SWWD AS WELL...WITH BACK EDGE ALREADY NR NRN TIP OF KEWEENAW. AS DEEP
LO PRES IN NRN PLAINS MOVES EWD THIS EVNG...LOOK FOR WINDS TO SHIFT A
BIT MORE TO E AND SE. SO XPCT PROGRESS OF FORWARD AND BACK EDGES OF
FOG MASS TO SLOW DOWN A BIT. FURTHER INLAND...SFC OBS/GOES-8 INDICATE
DIURNAL CU BEGINNING TO DSPT. TEMPS AT 01Z RANGE FROM 55 TO 60 NR LK SUP
TO ARND 75 AT IMT.

FOCUS FOR LATER TNGT WL SHIFT TO THREAT OF TSRA. SCNTRL MN CURRENTLY
GETTING HIT HARD WITH SEVERE TSRA...AND TORNADO WATCH BOX NOW UP IN
WRN WI TIL 06Z. TSRA FRMG IN AREA OF IMPRESSIVE THETA E RDG AND LO LVL
MSTR CNVGC WITH SLY LLJ UNDER EXIT RGN OF WLY H3 JET MAX. MPX SDNG
SHOWS A TORNADIC LOOKING HODOGRAPH WITH ADAP CHARTS INDICATING LI ARND
-10 OVR SRN MN/SWRN WI. IN NRN MN...DLH 88D SHOWS A MORE GENERAL AREA
OF SHRA WITH IMBEDDED TSRA IN A MORE STABLE AIRMASS UNDER INFLUENCE OF
ELY FLOW OFF LK SUP.

ADAP...00Z GRB SDNG AND GOES-8 DERIVED STABILITY INDICES SHOW A STABLE
AIRMASS OVR U.P. ASSOCIATED WITH RDG OF HI PRES MENTIONED ABV. A SHARP
GRADIENT OF STABILITY IS NOTED OVR NRN WI ON ADAP CHARTS...AND GOES-8
LOOP SHOWS A TENDENCY FOR COLDEST CLD TOPS TO MOVE MORE ESEWD TOWARD
GREATER INSTABILITY OVR SCNTRL WI. ALTHOUGH MODELS FCST U.P. TO FALL
INTO LEFT EXIT OF H3 JET AND AN AXIS OF QVECTOR CNVGC/ UVV AND THETA-E
MAX/MSTR CNVGC TO MOVE INTO SW COUNTIES ARND 06Z AND THEN TO MQT-ESC BY
12Z...THINK MOST SGNFT TSRA WL REMAIN S OF U.P. WHERE GREATEST
INSTABILITY WL REMAIN. MAGNITUDE OF LLJ ALSO FCST TO DCRS AS SYS
SPREADS EWD. PROGGED SNDG AND HODOGRAPH FOR IMT AT 12Z SHOWS A CAPE OF
ONLY ABOUT 300-500 J/KG WITH MUCH LESS WIND SHEAR THAN UPSTREAM
ATTM--HELICITY ABOUT 110 AND EHI NARND 0.5. WL RESTRICT MENTION OF GUSTY
WINDS WITH TSRA TO WI BORDER COUNTIES WHERE LWR LVLS NOT EXCESSIVELY
STABILIZED BY FLOW OFF LK SUP. ABSENCE OF SOLAR HTG WL ALSO HINDER CHCS
OF SVR TSRA.

KC