Severe Thunderstorm Warning 59, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1035 PM EDT THU JUL 8 1999

...BEST CONVECTION WILL STAY NORTH OF GRR CWA BUT SOME ACTION STILL
POSSIBLE...

TWO MAIN FOCUS AREAS FOR THUNDERSTORMS TONIGHT.  THE FIRST IS THE
LIFT OVER THE WARM FRONT.  RUC ANAL SHOWS 40 TO 50 KNOT 850 WINDS
BRINGING  16 TO 18C DWPT AIR OVER THE WARM FRONT.  THE BEST 850 THTE
CONVERGENCE IS OVER NRN WI AND LATER TONIGHT OVER NRN LWR MI.  IS
OVER THE NRN PART OF MI WHERE THE BEST DPVA WILL BE... WHERE THE
BEST WIND SHERE WITH HEIGHT WILL BE/ GRB SOUNDING AT 00Z HAD
HELICITY VALUES OVER 700  MEANWHILE... NEAR SW LWR MI... 850 ANAL
AT 00Z SHOWS STRONG DRY ADVECTION AS ILX SOUNDING HAD 49C BETWEEN
THE TEMP AND DWPT.  THIS WILL KEEP THE STORMS OVER THE NRN MOST PART
OF OUR CWA THROUGH 06Z AT LEAST.

THIS BRINGS ME TO THE SECOND REASON FOR TSTSMS... THAT IS THE COLD
FRONT CURRENTLY MVG THROUGH WRN WI.  THE 00Z RUC IS FASTER THEN THE
12Z MODELS ON BRINGING THE FRNT INTO SW MI AND MY 12HR CONTINUITY ON
THE FRONT SIDES WITH THE RUC... SO AFTER 06Z... THERE WILL BE AN
INCREASE IN MOISTURE THROUGH THE SOUNDING AS THE FRONT MOVES INTO
THE AREA.  ON THE OTHER HAND... 700 TEMPS RISE TO OVER 10C... AND
500 TEMPS RISE TO NEAR 6C... SO SOME CAPING AT THOSE LEVELS.  EVEN
SO... RUC SOUNDING AT 12Z SHOWS NEARLY 1000 J/KG WITH STORM TOPS
NEAR 50000 FT... ABOUT 5000 FEET ABOVE THE TROP.  ADD TO THIS THE 40
TO 50 KNOTS OF WIND ABOVE 2000 FT... AND IT IS NOT OUT OF THE
QUESTION SOME GUSTY WINDS ARE POSSIBLE... MAYBE EVEN TO SEVERE
LEVELS. HAIL THREAT MINIMAL SINCE WET BULB ZERO FCST TO BE ABOVE
13000 FT TONIGHT.

SO... WILL KEEP OCCASSIONAL SHOWERS/TSTMS WITH LOCALLY HEAVY RAIN IN
FCST OVER NRN PART OF CWA AND WILL INCREASE POP TO LIKELY OVR CTNL
PART OF CWA AND STILL CARRY CHANCE OVER SE PART OF CWA OVERNIGHT.

.GRR...NONE.

WDM