Severe Thunderstorm Warning 12, NWS Detroit, MI

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1150 AM EDT SUN APR 29 2003

ONE MORE QUICK UPDATE SENT OUT TO REMOVE MENTION OF ANY TIMING AND
JUST GO WITH CATEGORICAL POPS FOR THE AFTERNOON HOURS.
SHOWERS AND THUNDERSTORMS ARE OVERSPREADING SOUTHEAST MICHIGAN AT
THIS HOUR. THIS IS GOOD NEWS...AS THIS WILL HELP STABILIZE THE
ATMOSPHERE BEFORE THE COLD FRONT PUSHES THROUGH LATE TODAY. STILL
NOT READY TO RULE OUT MARGINALLY SEVERE WINDS THIS AFTERNOON.

SF

******************EARLY MORNING DISCUSSION***********************

TIMING AND INTENSITY OF CONVECTION TODAY WILL BE THE FIRST CONCERN
FOR THIS FORECAST FOLLOWED BY, DARE I SAY, PRECIP TYPE MONDAY NIGHT.

THE 00Z SOUNDINGS AROUND THE MIDWEST SUPPORT THE FARTHER WEST LOW
LEVEL MOIST AXIS SHOWN BY THE ETA AND NGM THIS MORNING. THE GFS
LOOKS TOO FAR EAST AND TOO FAST WITH THE MOIST AXIS AND NEXT ROUND
OF CONVECTION FOR TODAY. IT SHOWS THINGS FLARING UP, AS AN EXTENSION
OF THE ONGOING CONVECTION OVER MISSOURI, BY 12Z OVER WESTERN LOWER.
THE ETA LOOKS BETTER SHOWING THE 850 MB THETA-E RIDGE FARTHER WEST
AND CLOSER TO THE SURFACE TROF WITH SOME SHOWERS DUE TO LOW LEVEL
THETA-E ADVECTION IN ADVANCE OF ANY EXTENSION OF MS VALLEY ACTIVITY.
THESE ARE OCCURRING NOW OVER SW LOWER. THE ETA ALSO SHOWS MORE OF A
DIURNAL TREND ON THE CONVECTION. PLANNING SCATTERED POPS THIS
MORNING THEN CATEGORICAL SHOWERS THIS AFTERNOON WITH THUNDER LIKELY.

SATELLITE IMAGERY AND MODEL DATA THEN INDICATE CLOUDS WILL BE SPARSE
ENOUGH FOR SOME DAYTIME HEATING TO OCCUR WITH A CHANCE AT STRONGER
THUNDERSTORM DEVELOPMENT THIS AFTERNOON, AHEAD OF THE SURFACE TROF
AND WITH A BOOST FROM THE UPPER WAVE. MODIFIED ETA FORECAST
SOUNDINGS SHOW CAPE RUNNING NEAR 1500 J/KG WITH A SURFACE PARCEL OF
73/60 AND TAKEN OFF OF THE 15Z SOUNDING, BEFORE CONVECTION APPEARS
IN THE MODEL. A CURLY-CUE IN THE HODOGRAPH SHOWS AN INFLATED 0-3 KM
SHEAR BUT APPEARS TO STILL BE AT LEAST 25 M/S AND SUFFICIENT FOR BOW
ECHO DEVELOPMENT. SOME UNCERTAINTY ARISES AFTER EXAMINING THE VVEL
FORECASTS FROM THE ETA ON THE MESO GRID WHICH SHOWS DAYTIME HEATING
TAKING MUCH OF THE DAY TO GET THINGS GOING. IT SHOWS TWO LINES OF
DEVELOPMENT WITH THE MOST INTENSE CONVECTION TO OUR EAST WITH THE
FIRST LINE AFTER 21Z. FOR NOW WILL CONTINUE WITH THE CHANCE OF
SEVERE MENTIONED IN OUR HWO.

AFTER A CHANCE OF SHOWERS THIS EVENING, THE MID AND UPPER LEVEL DRY
SLOT WILL WORK IN OVERNIGHT AND WILL USHER IN COOLER AIR ON MONDAY.
THE STRONG LATE APRIL SUN WILL COMBINE WITH THIS COLDER AIR TO
GENERATE SHOWERS OVER OUR AREA. THE TREND TOWARD LIKELY POPS IN THE
GUIDANCE NUMBERS LOOKS GOOD CONSIDERING THE DIURNAL HEATING
COMPONENT ALONG WITH POSITION OF THE UPPER TROF AND THE SURFACE COLD
FRONT.

THINGS GET EVEN MORE INTERESTING AGAIN MONDAY NIGHT AS COLD AIR
CONTINUES TO SURGE IN FROM CENTRAL CANADA. THE ETA AND GFS SHOW
CRITICAL THICKNESS THRESHOLDS BEING MET FOR SNOW AFTER MIDNIGHT AND
FORECAST SOUNDINGS ONLY SHOW A SHALLOW SURFACE LAYER ABOVE FREEZING.
FOR NOW WILL JUST MENTION A CHANCE OF RAIN AND SNOW NORTH OF FLINT
TO PORT HURON WHERE THE MOISTURE PROFILE IS A LITTLE DEEPER.

THIS MOISTURE WORKS TO OUR EAST TUESDAY MORNING WITH HIGH PRESSURE
STILL SETTING UP A DRY PATTERN FOR MID WEEK.

.DTX...NONE.

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

BT

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