Severe Thunderstorm Warning 76, NWS Gaylord, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
320 PM EDT THU SEP 19 2002

UPPER TROUGH AXIS REMAINS CENTERED OVER THE CENTRAL US...WITH
NORTHERN CIRCULATION CENTER AND ASSOCIATED COLD FRONT
APPROACHING THE WESTERN LAKES AND THE UPPER MS RIVER VALLEY...
WHILE THE BROAD SOUTHERN CIRCULATION CENTER WAS LOCATED OVER THE
SOUTHERN/WESTERN PLAINS. PER IR/WATER VAPOR IMAGERY TRENDS...
A SIGNIFICANT SHORTWAVE WAVE WAS EMERGING FROM THE PARENT TROUGH AND
WAS PUSHING N/NE THROUGH WARM CONVEYOR BELT/AXIS OF DEEP MOISTURE
AHEAD OF THE COMPLEX UPPER TROUGH...AND THIS WAVE WAS RESPONSIBLE
FOR SHOWERS/THUNDERSTORMS THAT WERE BLOSSOMING OVER THE S/SW LAKES.
FARTHER UPSTREAM...WATER VAPOR IMAGERY DEPICTED ANOTHER UPPER TROUGH
AMPLIFYING OVER SW CANADA.

BC TROUGH WILL DIG INTO THE NORTHERN PLAINS TONIGHT/FRIDAY...AND
DOWNSTREAM TROUGH WILL RESPOND BY LIFTING TOWARD THE NE...EVENTUALLY
PULLING A COLD FRONT THROUGH THE FORECAST AREA. FORECAST ATTENTION
FOCUSES ON POPS AND TIMING OF PRECIPITATION/COLD FROPA
AS THIS OCCURS.

GIVEN APPROACHING SHORTWAVE AND ASSOCIATED UPSTREAM RADAR
TRENDS...WILL RAISE POPS TO CATEGORICAL TONIGHT AS SUGGESTED BY 12Z
ETA/AVN/UKMET...WITH PRECIPITATION COVERAGE INCREASING STEADILY FROM
SW TO NE THROUGH THE EARLY EVENING. WITH BREAKS IN CLOUD SHIELD
ALLOWING ENOUGH INSOLATION TO PUSH CAPES TO AROUND 1000 J/KG ACROSS
NORTHERN LOWER MICHIGAN...AROUND 1500 J/KG ACROSS SOUTHERN
COUNTIES...AND GIVEN RELATIVELY STRONG UNIDIRECTIONAL WIND FIELDS
(SW WINDS AROUND 40 KNOTS IN THE 850-500 MB LAYER) AND FORCING
ASSOCIATED WITH APPROACHING WAVE...ISOLATED SEVERE WEATHER IS
POSSIBLE THIS EVENING.

LATER TONIGHT...12Z ETA/AVN SUGGEST THAT NORTHERN SHORTWAVE
WILL PUSH THE SURFACE BOUNDARY AND SLIGHTLY DRIER AIR INTO THE
EASTERN UP OVERNIGHT...AND THIS MAY TEMPORARILY REDUCE PRECIPITATION
COVERAGE THERE. HOWEVER...WEAKENING LOW LEVEL WIND FIELDS WITHIN
FRONTAL TROUGH MAY CREATE CONDITIONS FAVORABLE FOR DENSE FOG.

FRIDAY...MID US TROUGH WILL CONTINUE TO LIFT NE...AND PLUME OF DEEP
MOISTURE WILL REMAIN OVER THE FORECAST AREA FOR A GOOD PORTION OF
THE DAY...JUSTIFYING CATEGORICAL POPS ACROSS NORTHERN LOWER MI.
EVEN ACROSS EASTERN UPPER MICHIGAN...ANY EARLY DRYING SHOULD GIVE
WAY TO ANOTHER SURGE OF MOISTURE/INCREASED PRECIP COVERAGE AS UPPER
LOW APPROACHES...SO WILL ALSO CARRY CATEGORICAL POPS THERE.

FRIDAY AFTERNOON/EVENING...MODELS DISAGREE WHETHER ANOTHER
WAVE/SURGE OF MOISTURE WITH PUSH INTO THE REGION AND WILL LINGER
INTO THE EVENING (ETA/AVN)...OR WHETHER DEEP WARM CONVEYOR BELT
MOISTURE WILL PROGRESS STEADILY EAST...LEAVING ONLY WRAP AROUND
MOISTURE BY FRIDAY EVENING. THIS FORECAST WILL LEAN TOWARD A SLOWER
SOLUTION...WITH LIKELY POPS CARRIED OVER INTO THE 3RD PERIOD.

GIVEN PWATS EXCEEDING 1.50 INCHES...DEEP MOISTURE EXTENDEING WELL
UPSTREAM AND POTENTIAL FOR BACKBUILDING (850 MB WINDS VIRTUALLY AS
STRONG AS 700-500 MB WINDS THROUGH THIS EVENING) AND TRAINING
CONVECTION...WILL MENTION LOCALLY HEAVY RAIN TONIGHT...AND WILL
CONTINUE MENTION OF HEAVY RAIN FRIDAY AS PLUME OF DEEP MOISTURE
PROGRESSES ONLY SLOWLY EASTWARD.

WITHIN DEEP CYCLONIC FLOW REGIME...WHERE COLD ADVECTION WILL PUSH
850 MB TEMPS TO +5C TO +7C ACROSS THE N/W BY LATE SATURDAY AFTERNOON
AND TO AROUND 0C ACROSS THE N/W SUNDAY...CONDITIONS WILL BECOME
INCREASINGLY FAVORABLE FOR LAKE ENHANCED SHOWERS...SO WILL CONTINUE
CHANCE POPS THROUGH THE WEEKEND.

UPPER TROUGH REMAINS OVER THE LAKES MONDAY THROUGH THURSDAY...WITH
BELOW NORMAL TEMPS AND WITH PERIODIC SHORTWAVES/SURFACE BOUNDARIES
ROTATING THROUGH THE LAKES. PER PASSAGE OF SHORTWAVE/SECONDARY COLD
FRONT (AND LAKE ENHANCEMENT AS 850 MB TEMPS FALL TOWARD 0C) WILL
CONTINUE A CHANCE OF SHOWERS MONDAY AND TUESDAY. MODELS DISAGREE
CONCERNING TIMING OF NEXT SHORTWAVE WEDNESDAY/THURSDAY...WITH 0Z
EXTENDED AVN FASTEST. WILL MAINTAIN CONTINUITY WITH PREVIOUS
FORECAST AND WILL DELAY NEXT CHANCE FOR SHOWERS UNTIL THURSDAY.

.APX...NONE.

ROWLEY

MIZ016>036-041-042-200200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GAYLORD MI
410 PM EDT TUE SEP 10 2002

...SEVERE WEATHER IS POSSIBLE ACROSS PORTIONS OF NORTHERN LOWER
MICHIGAN THIS AFTERNOON AND EVENING...

* THREAT AREA...NORTHERN LOWER MICHIGAN SOUTHWEST OF A LINE FROM
CHEBOYGAN TO TAWAS CITY

* DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.
  SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING.

* HAZARDOUS WEATHER THREAT...THUNDERSTORM WIND GUSTS TO 70 MPH.
  ISOLATED THUNDERSTORMS MAY PRODUCE HAIL TO 1 INCH IN DIAMETER.

* TIME OF HAZARDOUS WEATHER THREAT...THROUGH 10 PM.

* FOR INFORMATION REGARDING ONGOING...POSSIBLY HAZARDOUS WEATHER
  CONDITIONS PLEASE REFER TO WWW.CRH.NOAA.GOV/APX/ (ALL LOWER CASE).

IF LATER INFORMATION FURTHER SUPPORTS THIS HAZARDOUS WEATHER
THREAT...APPROPRIATE WATCHES AND/OR WARNINGS WILL BE ISSUED. STAY
TUNED TO NOAA WEATHER RADIO OR YOUR LOCAL MEDIA FOR THE LATEST
WEATHER INFORMATION.

SULLIVAN