Severe Thunderstorm Warning 149, NWS Gaylord, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
252 AM EDT SAT SEP 26 1998

CURRENT SFC MOIST FLUX CONVERGENCE CHART SHOWS STG MSTR POOLING IN IA
AHEAD OF 50-55 KT 850 MB JET. STREAMLINE ANAL INDICATES INITIAL WRM FNT
OVER FAR NRN WI AND ACROSS THE UPR PENINSULA...WHILE SFC PLOT SHOWS
PRIMARY WRM FNT NUDGING INTO FAR SW LWR MI WITH JUICIER AIRMASS BEHIND
IT (DPWTS APPCHNG 70F). MAIN FCST CONCERNS ACROSS NRN LWR/ERN UPR MI
WILL BE WITH POPS WITH APPCHNG SYSTEM TDA...ALONG WITH THE SEVERE
WEATHER POTENTIAL LATER TODAY FOR PTNS OF NRN LWR THAT MAKE IT INTO THE
WARM SECTOR. WILL THUS FOCUS DISCUSSION ON THE SHORT TERM (24 HRS).

00Z ETA/NGM INITIALIZED SIMILARLY...THOUGH ETA QUICKLY DIVERGES BY
06Z WITH 65-70 KT 850 JET NOSING INTO SE NB (NGM INDICATES 50-55KTS).
BASED ON OBSERVED PROFILER DATA...CURRENT THINKING IS THAT THE ETA MAY
BE A BIT OVERDONE. REGARDLESS...FAIRLY IMPRESSIVE 850-500 MB SHEAR
PROFILE ADVERTISED ACROSS NRN LWR MI LATER TDA NO MATTER WHICH MODEL OF
CHOICE.

ETA/NGM FAIRLY SIMILAR WITH COUPLING OF ENTRANCE/EXIT JETS AT UPPER
LVLS AND ASSCD UPR DIVERGENCE/LWR CONVERGENCE FIELDS (ETA A LITTLE
FARTHER S DURING THE AFTN)...WITH BOTH MODELS LIFTING THE COUPLED JET
REGION NE OF THE FCST AREA BY 00Z. DPVA ALONG WITH LAPLACIAN OF THCK
ADVECTION MAXIMIZES ACROSS ERN UPR AS EVIDENCED BY 850-500 QVEC
CONVERGENCE PROGS. 1000-300 MB LAYER AVE RH ALSO QUITE HIGH (>80 PCT)
AS PER GRIDDED DATA/MODEL SOUNDINGS. TROPICAL CONNECTION OFF THE WESTERN
MEXICO COAST NO DOUBT A PLAYER IN THIS VIA CURRENT WATER VAPOR IMAGERY.
BOTH ETA/NGM HAVE SFC LOW GOING THROUGH UPR MI ALONG STG LOW LVL
BAROCLINIC ZONE...KEEPING WRM FNT INVOF STRAITS AREA AND THUS ALLOWING
MUCH OF NRN LWR TO SNEAK INTO THE WRM SECTOR. THTA PROFILE S-N LATER IN
THE DAY ALONG THE WRM FNTL ZONE WITH 40-50 KT 850 JET AND STG MSTR FLUX
CONVERGENCE WOULD SUGGEST CSI PCPN POSSIBLE ACROSS ERN UPR. WITH THIS
IN MIND ALONG WITH THE OPTIMAL QG FORCING/MSTR PROFILE PROGGED...WOULD
HIT POPS HARDEST IN ERN UPR (CATEGORICAL...SHOWERS/TSTMS DEVELOPING).
AS FOR NRN LWR...STILL LIKE LIKELY POP MENTION GIVEN SOMEWHAT LESS
FVRBL QG FORCING AND MSTR PROFILE.

AS FOR SVR WX THREAT...MODEL SOUNDINGS/GRIDDED DATA SHOW CAPES APPCHNG
1200 J/KG WITH 0-6 KM SHEAR MAGNITUDE NEAR 20 M/S. BRN VALUES PEAK BTWN
15-20 ACROSS NRN LWR. 00Z BUFKIT DATA UNAVLBL...THOUGH ANALYSIS OF MODEL
SOUNDINGS SUGGEST A LINEAR SHEAR PROFILE SUGGESTIVE OF SPLITTING
SUPERCELLS IF CAPE IS SUFFICIENT (AS IT APPEARS TO BE FROM ETA...
THOUGH CERTAINLY CANNOT EXPECT MUCH DIURNAL CONTRIBUTION AT THE SFC
THIS TIME OF YEAR). SOME DRY AIR AT MID LVLS LATER IN THE DAY IS NOTED
WITH STEEPENING 850-500 MB THTE LAPSE RATES. THIS ALONG WITH THE
IMPRESSIVE DYNAMICAL SUPPORT COULD CERTAINLY OPEN THE DOOR FOR LARGE
HAIL AND DAMAGING WET MICROBURSTS. WILL HAVE TO KEEP AN EYE ON THE
SITUATION LATER IN THE DAY.

CD FROPA OVERNIGHT NW-SE WITH POST-FNTL SC AIDED BY INCREASING LAKE
EFFECT INSTBY ON SUNDAY AS WELL AS DIURNAL INSTBY OVER LAND. LAKE-850
DELTA TS MARGINAL THIS TIME AROUND (NEAR 14-15C). INCREASED SUBSIDENCE
AND LOW LVL DRYING DURING THE AFTN SUNDAY AS REGION BCMS UNDER LEFT
ENTRANCE REGION OF UPR JET CORE WOULD SUGGEST AT LEAST PARTIAL CLEARING
AND PTLY SUNNY CONDITIONS W TO E ACROSS THE REGION.

HURLEY

MIZ016>036-041-042-261425-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GAYLORD MI
428 AM EDT SAT SEP 26 1998

THE NATIONAL WEATHER SERVICE HAS ISSUED A SEVERE THUNDERSTORM WATCH
EFFECTIVE UNTIL 1000 AM EDT FOR THE FOLLOWING LOCATIONS...

IN LOWER MICHIGAN

   ...EMMET... CHEBOYGAN... PRESQUE ISLE... CHARLEVOIX... LEELANAU
   ...ANTRIM... OTSEGO... MONTMORENCY... ALPENA... BENZIE
   ...GRAND TRAVERSE... KALKASKA... CRAWFORD... OSCODA... ALCONA
   ...MANISTEE... WEXFORD... MISSAUKEE... ROSCOMMON... OGEMAW... IOSCO
   ...GLADWIN... ARENAC

AT 425 AM EDT...DOPPLER RADAR INDICATED A CLUSTER OF VERY STRONG
THUNDERSTORMS OVER THE OPEN WATERS OF LAKE MICHIGAN MOVING EAST
NORTHEAST AROUND 35 MPH. THESE THUNDERSTORMS THAT PRODUCED LARGE HAIL
OVER WISCONSIN AND WILL MOVE ACROSS NORTHERN LOWER MICHIGAN THIS
MORNING.

A SEVERE THUNDERSTORM WATCH MEANS SEVERE THUNDERSTORMS ARE POSSIBLE
IN AND NEAR THE WATCH AREA. PERSONS SHOULD WATCH FOR THREATENING
WEATHER AND LISTEN TO NOAA WEATHER RADIO...COMMERCIAL RADIO...OR
TELEVISION FOR FURTHER INFORMATION.

FARINA