Severe Thunderstorm Warning 31, NWS Detroit, MI

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
345 PM EDT SAT JUN 9 2001

SHORTWAVE...READILY SEEN ON VISIBLE SATELLITE IMAGES...MOVING
GRADUALLY SOUTHEAST ACROSS THE NORTHERN GREAT LAKES THIS AFTERNOON.
DESPITE SURFACE DEW POINTS FROM THE UPPER 40S TO MID 50S ALONG AND
SOUTH OF THE PATH OF THE COMMA CLOUD...ENOUGH ELEVATED INSTABILITY
EXISTS WITH INCREASING THETAE AIR TO ACCOMMODATE CONTINUING SHOWERS
AND ISOLATED THUNDERSTORMS ACROSS THE SAGINAW VALLEY AND THE TIP OF
THE THUMB.  ALSO HELPING ARE A 45KT JETLET AT 500MB SEEN ON THE 12Z
GRB RAOB AND WEAK UPPER DIVERGENCE.  THE UPPER-LEVEL WAVE IS
FORECAST TO SLOWLY MOVE SOUTHEAST MAINLY ACROSS LAKE HURON
OVERNIGHT.  THE CURRENT RAIN MAY DIMINISH AS IT WORKS IT WAY TOWARD
FAR SOUTHEAST MICHIGAN...WITH BUFKIT MODEL SOUNDINGS FROM THE ETA
NEAR DETROIT SHOWING INCREASING STABILITY THIS EVENING ABOVE 850MB.
HOWEVER...OTHER SHOWERS AND THUNDERSTORMS CURRENTLY DEVELOPING OVER
NORTHERN WISCONSIN MAY LIVE INTO FAR SOUTHEAST MICHIGAN LATE TONIGHT
AS ELEVATED INSTABILITY IS SHOWN TO INCREASE AGAIN.  THE AVN MORE SO
THAN THE ETA FORECASTS RELATIVELY DECENT FRONTOGENESIS LATE
TONIGHT...AND WITH INCREASES IN THETAE AT BOTH 850MB AND 700MB AND
THE NEARBY SHORTWAVE...CHANCE POPS ARE WARRANTED EVEN IN THE FAR
SOUTHEAST.  MOST OF THE SHORT-TERM MODELS SHOW WEAK QPF OVER FAR
SOUTHEAST MICHIGAN IN THE 12Z SUNDAY TIME FRAME.  THANKS TO SOME
AFTERNOON RAIN AND DEW POINTS RISING INTO THE UPPER 50S OVER
NORTHERN MICHIGAN THIS AFTERNOON...WILL MENTION SOME LIGHT FOG LATE
FOR THE SAGINAW VALLEY AND THE THUMB.

AVN REALLY RAMPS UP A STRONG SHORTWAVE ACROSS NORTHERN MICHIGAN
SUNDAY.  THIS WAVE...CURRENTLY OVER THE ROCKIES...WILL WORK ITS WAY
EAST INTO THE GREAT LAKES SUNDAY.  THE ETA IS NOT AS STRONG...AND
CONSEQUENTLY...IT IS FASTER WITH HIGH UVV.  REGARDLESS...IT WOULD
APPEAR THE CHANCES FOR STORMS ARE PRETTY GOOD FROM MID AFTERNOON
SUNDAY THROUGH ABOUT 09Z MONDAY...WHEN DRIER AIR SHOULD START
WORKING IN FROM THE NORTHWEST.  FINE FRONTOGENESIS ON BOTH THE AVN
AND ETA ARE PROGGED...A LITTLE MORE BEYOND 00Z MONDAY ON THE AVN...
AND WITH THE STRENGTH OF THE UPPER WAVE AND INFO FROM DAY 2 SPC
DISCUSSION WILL LEAN JUST A TOUCH TOWARD THE AVN AND HAVE HIGHER
POPS FOR THE SUNDAY NIGHT PERIOD.  SEVERE A POSSIBILITY WITH 850MB
WINDS PROGGED AROUND 35KTS ON THE ETA AND THE APPROACH OF THE LEFT
EXIT REGION OF A 70KT 250MB JET.  INSTABILITY IS NOT TREMENDOUS...
GENERALLY AROUND 1000 J/KG...AND DEW POINTS ON MOS DO NOT GO MUCH
ABOVE THE LOWER 60S...BUT IF MID 60S CAN APPROACH SOUTHEAST
MICHIGAN...INSTABILITY WOULD BE A BIT HIGHER THAN FORECAST BY THE
BUFKIT ETA MODEL SOUNDINGS.

DRIER AIR MOVES IN FOR MONDAY...BUT 850MB MOISTURE RETREAT LAGS OVER
FAR SOUTHEAST MICHIGAN INTO THE EARLY AFTERNOON.  WILL LEAVE IN A
LOW CHANCE POP FOR THE FAR SOUTHEAST CORNER FOR MONDAY.  NORTH...
CURRENT THINKING IS THAT MID-LEVEL DRY AIR SHOULD PROVIDE FOR ENOUGH
OF A CAP TO RESTRAIN ANY SHOWER OR THUNDERSTORM DEVELOPMENT DESPITE
CAPE VALUES PROGGED TO EEK OVER 1000 J/KG EARLY IN THE AFTERNOON.
ANOTHER UPPER WAVE HEADED TOWARD SOUTHEAST MICHIGAN MONDAY NIGHT
WITH INCREASING MOISTURE LOOKS TO GIVE ANOTHER CHANCE OF NOCTURNAL
THUNDERSTORMS LATE.  MOS TEMPERATURES IN THE SHORT TERM FAIRLY CLOSE
AND GENERALLY FOLLOWED.

SUMMER-LIKE CONDITIONS LOOK TO BE THE RULE FOR MOST OF THE EXTENDED
PERIOD AS BUILDING HEIGHTS AND A DEVELOPING SOUTHERLY SURFACE FLOW
ARE FORECAST TO PROVIDE FOR INCREASING TEMPERATURES AND HUMIDITY BY
MID-WEEK.  THE ETAXX...MRF...AND NEW AVN ALL SUGGEST A WARM FRONT
SLOWLY MOVING BACK NORTH ACROSS SOUTHERN MICHIGAN LATE TUESDAY.
THOUGH THE BEST MID AND UPPER-LEVEL FORCING APPEARS TO BE JUST NORTH
OF SOUTHEAST MICHIGAN...AS THE TEMPERATURE AND LOW-LEVEL MOISTURE
RISE...THERE MAY BE ENOUGH INSTABILITY TO RESULT IN A FEW SHOWERS
AND STORMS ALONG THE NORTHWARD-MOVING SURFACE BOUNDARY.  THIS
SURFACE FRONT IS FORECAST BY THE ETAXX AND MRF TO BE IN THE FAR
NORTHERN GREAT LAKES BY WEDNESDAY AFTERNOON...THOUGH THE NEW AVN
TRENDS THAT A LITTLE SLOWER.  850MB TEMPERATURES WEDNESDAY ARE
PROGGED CLOSE TO 20C...BUT SOME MID-LEVEL DRY AIR ALONG WITH 700MB
TEMPERATURES FORECAST IN THE LOWER TEENS ON THE ETAXX/MRF WOULD
PROVIDE FOR A GOOD CAP.  THE CANADIAN MODEL SHOWS LITTLE SURFACE
GRADIENT WEDNESDAY...WHICH YIELDS SOME CONCERN ABOUT LAKE BREEZES
HELPING TO INITIATE ISOLATED...AFTERNOON THUNDERSTORMS NEAR THEM.
HOWEVER...THE ETAXX AND MRF INDICATE MORE OF A SURFACE GRADIENT
WHICH...IF VERIFIED...WOULD SERIOUSLY DIMINISH THAT THREAT.  IN
ADDITION...THE NEW AVN MODEL ONLY FORECASTS 700MB TEMPERATURES
WEDNESDAY INTO THE HIGH SINGLE FIGURES...SO THE CAP MAY NOT BE AS
STRONG AS INDICATED BY 00Z RUNS OF THE EXTENDED MODELS.  IN SOME
AREAS WEDNESDAY...WITH JUST A FEW CLOUDS AND 850MB TEMPERATURES
APPROACHING 20C...SOME AFTERNOON HIGHS COULD PUSH 90.  APPROACH OF
THE NEXT COLD FRONT FOR FRIDAY WILL SLOWLY ERODE HIGH MID-LEVEL
TEMPERATURES FOR LATE IN THE WORK WEEK...BRINGING AN INCREASE IN THE
POTENTIAL FOR THUNDERSTORMS ESPECIALLY INTO FRIDAY WITH THE COLD
FRONTAL PASSAGE.  TEMPERATURES SHOULD STILL APPROACH 80 FRIDAY...AND
HIGH LOW-LEVEL MOISTURE WITH COOL TEMPERATURES ALOFT WOULD ALLOW FOR
AMPLE INSTABILITY FRIDAY AFTERNOON.  DRIER CONDITIONS ARE FORECAST
SATURDAY AS SURFACE HIGH PRESSURE BUILDS IN WITH MORE COMFORTABLE
WEATHER.

.DTX...NONE.

DJF