Severe Thunderstorm Warning 40, NWS Marquette, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MARQUETTE MI
420 PM EDT TUE AUG 8 2000

12Z RAOBS/LATEST WV LOOP SHOWS WNWLY FLOW ACRS THE NRN TIER STATES E
OF MEAN SUBTROPICAL RDG OVR SW. SVRL IMPORTANT SHRTWVS EMBEDDED IN
FLOW. THE FIRST WHICH BROUGHT PCPN THIS MRNG IS NOW MOVG INTO NRN
LWR MI PER LATEST RUC ANAL/WV IMAGERY. WRN EDGE OF PCPN JUST CLRG
ERY ATTM PER 88D LOOP AND WL BE OUT OF ENTIRE AREA BY ZN ISSUANCE
TIME. BUT LGT ENELY FLOW IN WAKE OF SHRTWV HAS ENVELOPED CWA IN LK
STABILIZED AIRMASS (PER MOST RECENT MSAS LI ANAL) AND LO CLD. SRN
EDGE OF LO CLD ACRS NRN WI...WHERE MOST CURRENT MSAS ANAL ALSO SHOWS
LLVL CNVGC AND MAX PRES FALLS IN NW WI. NXT SYS OF CONCERN IS
VIGOROUS JET MAX DIGGING SE OVR SCNTRL CAN AS DEPICTED ON WV LOOP.
POTENT LINE OF TSRA HAS DVLPD OVR NE MN...DESPITE VERY STABLE 12Z
INL SDNG AND UNIMPRESSIVE H85 WNDS/MSTR...IN LEFT EXIT OF THIS JET.
WNWLY H5 WNDS 55 TO 60 KTS. TENDENCY FOR CNVCTN HAS BEEN TO DVLP
MORE SEWD TOWARD GREATER INSTABILY/LLVL CNVGC/PRES FALLS IN NW WI AS
DEPICTED ON MOST RECENT MSAS...BUT ECHOES APPEAR TO BE HOLDING
TOGETHER RATHER WELL AS THEY APRCH WRN LK SUP. A FEW TSRA DVLPG BEHIND
MAIN LINE AS WELL...SFC DWPTS REMAIN IN UPR 50S WELL BEHIND LINE.

MAIN FCST CONCERNS TNGT INCLUDE TSRA THREAT. 12Z ETA FCST MN TSRA TO
WEAKEN AS IT HIT LK MODIFIED AIRMASS. NEW MESOETA SUGS CNVCTN WL
REMAIN MORE ORGANIZED...IN LINE WITH RADAR TRENDS SHOWING ACTIVITY
REMAINING MORE POTENT THAN WHAT 12Z ETA SUGD. WL GO WITH NMRS
SHRA/TSRA DVLPG ACRS WCNTRL CWA AS LEFT EXIT OF UPR JET CONTINUES TO
PRESS EWD AND GOING CNVTN INTERACTS WITH BNDRY OF LK MODIFIED
AIRMASS ACRS NRN WI. WL ALSO MENTION PSBL GUSTY WNDS/LARGE HAIL ACRS
SRN TIER WHERE MOST RECENT MSAS SHOWS LI TO -4 AND MESOETA FCSTG
CAPES TO 1500 J/KG. AS UPR JET CONTS EWD...H7-3 QVECTOR DVGC/UPR CNVGC
IN LEFT ENTRANCE OF SYS AFFECTS NW CWA OVRNGT...SO WL END PCPN LATE
THERE. ERN ZNS SHUD REMAIN IN MORE NWLY FLOW BEHIND EXITING LO AND
THUS REMAIN MORE STABLE. SO JUST GOING WITH CHCY POPS THERE. GIVEN
LINGERING HI DWPTS EVEN BEHIND CNVCTN...WL GO WITH LINGERING LO
CLDS/FOG AND MIN TEMPS ABV MOS.

CWA TO BE IN LEFT ENTRANCE/UPR DVGC OF DIGGING JET MAX TMRW. BUT
WITH LINGERING LLVL MSTR/NWLY CYC FLOW AND PRES TROF ACRS SCNTRL
ZNS...FCST SDNG FOR ESC FOR 78/61 SHOWS 1000 J/KG. SO WL MAINTAIN
CHCY POPS FOR ECNTRL ZNS AS IN GOING FCST. SOLAR HTG SHUD LIFT LO
CLD INTO MORE CUMULOFORM SKY. NWLY FLOW OFF LK SUP SHUD STABILIZE
WRN ZNS ENUF TO REMOVE MENTION OF PCPN. FCST H85 TEMPS SUGS MAX
TEMPS HIER THAN MOS...XCPT FOR AREAS DOWNWND OF LK SUP.

AS SFC PRES RDG BLDS INTO CWA TMRW NGT...XPCT CLRG SKIES. BUT
LINGERING HIER DWPTS AND LGT WND FLOW SUGS PTCHY FOG WL DVLP. XPCT
CU TO DVLP ON THU WITH LINGERING LLVL MSTR AND H85 THERMAL TROF IN
UPR TROF DVLPG OVR NE. MIXING OF FCST H85 TEMPS SUG HI TEMPS ON WARM
SIDE OF MOS.

EXTENDED MODELS SHOW GRT LKS TROF LIFTING OUT ON FRI WITH UPR RDG/
SFC HI BLDG OVR CWA. MIXING OF FCST H85 TEMPS WITH A GOOD DEAL OF
SUNSHINE ON FRI SUPPORT MEX GUIDANCE TEMPS...COOLER THAN PREVIOUS
FCST. RETURN FLOW TO SET UP ON SAT. ALTHOUGH TEMPS WL REBOUND WITH A
GOOD DEAL OF SUNSHINE AND RISING H85 TEMPS...WL PUSH BACK MENTION OF
PCPN CHCS TO SAT NGT OVR W GIVEN FCST HI HGTS/ACYC FLOW AND DISTANCE
TO COLD FNT ASSOCIATED WITH SHRTWV MOVG THRU ZONAL FLOW ALF IN
ONTARIO. ARPCH OF THAT SHRTWV/COLD FNT SUN AS UPR HGTS BEGIN TO FALL
ACROSS ONTARIO PER ECMWF AND MRF ENSEMBLES WL TRIGGER BETTER CHC OF
SHRA/TSRA ON SUN. SINCE MAJORITY OF MRF ENSEMBLE MEMBERS SHOW LWR
HGTS/MORE WNWLY FLOW ALF VS OPERATIONAL MRF AND MEAN ERN TROF OVR E
HAS BEEN QUITE PERSISTENT THIS SUMMER...WL HEDGE TOWARD ECMWF
SCENARIO OF STRGR COLD FNT APRCH ON MON AND MAINTAIN CHC OF SHRA/
TSRA AND MORE DRYING/COOLING ON TUE W-E.

COORDINATED WITH APX.

.MQT...NONE.

KC