Marine Thunderstorm Winds in Lake St. Clair, April 20, 2003

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
308 PM EDT SUN APR 29 2003

MODELS THROUGH THE SHORT TERM ARE IN REASONABLE AGREEMENT...AND
QUITE WELL IN AGREEMENT WITH EARLIER FORECAST PACKAGE...SO WILL
CONCUR AND NOT CHANGE EXISTING FORECAST MUCH AT ALL. AT 500
MB...INITIAL LOBE TO SWING THROUGH THIS EVENING...WITH MAIN TROUGH
THEN PASSING THROUGH MONDAY AND MONDAY EVENING...WITH MORE VORTICITY
MAXIMA...THEN FINALLY NUDGED TO THE EAST. AT THE SURFACE...FIRST
FRONT/TROUGH MOVING THROUGH THIS EVENING WITH SLIGHT VEERING OF
WINDS...THEN MAIN FRONT LATE MONDAY USHERING IN MUCH CHILLIER AIR
MASS...WITH CYCLONIC CURVATURE LINGERING INTO TUESDAY BEFORE RIDGE
FINALLY BUILDS IN. THUNDERSTORM POTENTIAL SHOULD END WITH PASSAGE OF
THIS EVENING TROUGH...MORE SEVERE CERTAINLY NOT OUT OF THE QUESTION
GIVEN PAST HALF HOUR PENNY HAIL AT DTX AND EXPLOSIVE ISOLATED
DEVELOPMENT ONGOING PLUS FAIRLY RAPID DESTABILIZATION OCCURRING OVER
IN.

850 TO 500 MB DRY SLOT SHOWN BY MODELS PUNCHING IN THIS
EVENING...WITH MORE WRAPAROUND MOISTURE SWINGING IN MONDAY AFTERNOON
AND PIVOTING ON OUT TUESDAY MORNING...WITH LOW MOISTURE SEEN QUITE
PLENTIFUL UNTIL THEN TO SUPPORT LOWER CLOUDS.

PRECIPITATION TYPE...WILL MENTION POSSIBILITY OF SNOW MIX LATE
MONDAY NIGHT INTO TUESDAY MORNING...SUPPORTED BY ETA MODEL SOUNDINGS
THOUGH DEPTH OF MOISTURE ONLY TO NEAR MINUS 10C MAKES ICE
NUCLEATION FAIR AT BEST...ALSO SUPPORTED BY ESPECIALLY ETA 1000 TO
850 MB THICKNESSES BELOW 1300 METERS.

OMEGA LIFT MODEST IN LOW TO MID LEVELS LINGERING INTO THIS
EVENING...THEN SLIGHT AT TIMES UNTIL GENUINE SUBSIDENCE SETTLES IN
TUESDAY. OTHERWISE AS FOR DYNAMICS...850 TO 500 MB QVECTOR
CONVERGENCE SLIGHT TONIGHT...AND OCCASIONALLY THEREAFTER THROUGH
MONDAY NIGHT. SURFACE CONVERGENCE SLIGHT THIS EVENING...MODEST AGAIN
MONDAY AFTERNOON AND NIGHT. ALSO A BIT OF 250 MB/850 MB
DIVERGENCE/CONVERGENCE COUPLING TONIGHT. 850 TO 500 MB
FRONTOGENETICAL FORCING ALSO PROVIDING A MODEST BOOST TO RAIN
CHANCES THIS EVENING AND AGAIN SOMEWHAT ON MONDAY.

LATER PERIODS...
RATHER GOOD AGREEMENT OVERALL AMONG MODELS UNTIL LATE WEEK. AT 500
MB...EASTERN TROUGH CLOSES OFF AGAIN AND PERSISTS IN NORTHEASTERN
USA/EASTERN CANADA INTO THE WEEKEND...AS A LOW COMING EAST OUT OF
CENTRAL PLAINS WEAKENS. 500 MB RIDGING OVERHEAD BY SUNDAY AS PER
GFS. MODELS GENERALLY SHOW SURFACE RIDGE PREVAILING. MAIN QUESTION
IS HOW FAR NORTH AND ITS EXTENT OF INFLUENCE OF SURFACE WAVE
ASSOCIATED WITH UPPER LOW MOVING OUT OF THE CENTRAL PLAINS. GFS
TENDING TO BE CONSIDERABLY FARTHER SOUTH WITH THIS LOW THAN OTHER
MODELS...ESPECIALLY COMPARED TO ETAXX WHICH BRINGS LOW JUST SOUTH OF
GREAT LAKES FRIDAY NIGHT AND SATURDAY...SOME MODEL TIMING
DIFFERENCES AS WELL. GIVEN MODEL UNCERTAINTY...WILL MENTION CHANCE
OF SHOWERS FRIDAY...OTHERWISE DRY FOR THE WEDNESDAY THROUGH SUNDAY
PERIOD...GOING CLOSE TO GFS MOS TEMPERATURES.

.DTX...NONE.

EXPERIMENTAL GRAPHICAL FORECASTS ARE AVAILABLE ONLINE AT
HTTP://WWW.CRH.NOAA.GOV/DTX  (ALL LOWER CASE)

DWD

MIZ047>049-053>055-060>063-068>070-075-076-082-083-210900-

HAZARDOUS WEATHER OUTLOOK...RETRANSMITTED
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
508 AM EDT SUN APR 20 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST LOWER MICHIGAN.

.DAY ONE...TODAY AND TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS THIS MORNING OVER ALL OF
SOUTHEAST MICHIGAN...BUT SEVERE WEATHER IS NOT EXPECTED WITH THIS
ACTIVITY. THE STRONGEST STORMS WILL BE CAPABLE OF PEA SIZE HAIL AND
WIND GUSTS TO 35 MPH AS THEY MOVE NORTHEAST AT 40 MPH.

THUNDERSTORMS ARE LIKELY THIS AFTERNOON OVER THE ENTIRE AREA...AND
THERE IS A CHANCE SOME MAY REACH SEVERE LIMITS. THE MAIN HAZARD WITH
ANY SEVERE THUNDERSTORMS THIS AFTERNOON WILL BE DAMAGING WIND GUSTS
IN EXCESS OF 60 MPH. HAIL TO THREE QUARTER INCH IS ALSO POSSIBLE AS
THE STORMS MOVE NORTHEAST AT 55 MPH. THE BEST CHANCE OF SEVERE
WEATHER WILL BE FROM 1 PM TO 7 PM TODAY.

ANY THUNDERSTORMS THIS MORNING WILL BE THE RESULT OF WARM AND MOIST
AIR MOVING INTO THE REGION ON SOUTHERLY WINDS. THE STORMS THIS
AFTERNOON WILL DEVELOP ALONG A COLD FRONT MOVING THROUGH LOWER
MICHIGAN. THEY WILL INCREASE IN COVERAGE AND INTENSITY AS
TEMPERATURES RISE OVER OUR AREA...IN THE WARMER AIR TO THE EAST OF
THE COLD FRONT. THE STORMS WILL MOVE INTO CANADA SHORTLY AFTER
SUNSET THIS EVENING.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

AFTER A PERIOD OF BELOW NORMAL TEMPERATURES THROUGH MID WEEK...
THERE IS A CHANCE OF THUNDERSTORMS AGAIN ON FRIDAY AS WARMER AIR
STARTS A RETURN TO THE REGION.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON.

&&

STAY TUNED TO NOAA WEATHER RADIO...OR LOCAL MEDIA OUTLETS...FOR THE
LATEST FORECAST INFORMATION FROM THE NATIONAL WEATHER SERVICE. YOU
CAN ALSO OBTAIN THE LATEST FORECAST ON THE NATIONAL WEATHER SERVICE
WEB SITE HTTP://WWW.CRH.NOAA.GOV/DTX/ (ALL LOWER CASE)

BT