Severe Thunderstorm Warning 52, NWS Detroit, MI

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
325 PM EDT SUN JUL 29 2001

WATER VAPOR IMAGERY CONTINUED TO HELP US TRACK A SHORT WAVE OVER THE
WESTERN GREAT LAKES AND INTO LOWER MICHIGAN THIS AFTERNOON, AND
VISIBLE IMAGERY SHOWED A LOT OF CU AROUND THE AREA AT PRESS TIME.
THERE WERE SOME PATCHES OF CLOUDLESS SKY FOR A WHILE EARLIER IN THE
AFTERNOON AS AC/AS DISSIPATED OR MOVED EAST. THESE DIFFERENTIAL
HEATING ZONES HAVE MOSTLY FILLED IN WITH CU NOW, BUT ARE STILL NOTED
AS A POSSIBLE FOCUSING MECHANISM FOR SHOWERS AND THUNDERSTORMS,
ALONG WITH INDICATED LAKE BREEZE BOUNDARIES AND THE WEAK SURFACE
REFLECTION FROM THE UPPER SHORT WAVE. AFTER SCATTERED ACTIVITY
TONIGHT, IT WILL BE DRY AND INCREASINGLY WARM AND HUMID TOWARD MID
WEEK.

RADAR TRENDS OVER WESTERN LOWER INDICATED THAT THE SHORT WAVE WAS
DOING A GOOD JOB OF ERODING ANY REMAINING CAPPING INVERSION. THE 12Z
DTX SOUNDING SHOWED A WELL-DEFINED INVERSION AROUND 600 MB THIS
MORNING, BUT ANALYSIS INDICATED THAT A SURFACE PARCEL OF 85/65 WOULD
BE ABLE TO BREAK THE CAP. AS MENTIONED IN THE MORNING DISCUSSION,
SOUNDING MODIFICATION ALONE OFTEN OVERFORECASTS CONVECTION WITH THIS
TYPE OF CAPPING INVERSION, BUT THE PRESENCE OF THE SHORT WAVE IS
MAKING THE DIFFERENCE BY ERODING THE CAP WITH VERTICAL MOTION. THIS
IN TURN CAUSES THE MID LEVELS TO COOL AND FREES UP THE CONVECTION
EVEN MORE. THAT PROCESS, COMBINED WITH SURFACE BOUNDARIES AS A
FOCUS, CONTINUES TO REQUIRE THE MENTION OF SHOWERS AND THUNDERSTORMS
THIS EVENING. THE LATEST KDTX RADAR DATA SHOWS SOME OF THIS
CONVECTION OCCURRING NOW ALONG THE LAKE ERIE LAKE BREEZE FROM
DETROIT OVER TO ANN ARBOR AND ADRIAN. WILL CONTINUE TO INCLUDE
MONROE COUNTY IN THAT GROUP FOR THE POTENTIAL OF SE DRIFT TO ANY NEW
CONVECTION. PLAN TO USE SCATTERED WORDING EVERYWHERE NOW THAT THERE
IS RADAR EVIDENCE IN SW LOWER AS WELL.

LAPS DATA INDICATES CAPE AVERAGING AROUND 2000 J/KG THIS AFTERNOON
WITH THE FREEZING LEVEL UP AROUND 13 KFT. THE HIGH FREEZING LEVEL
AND WEAK WIND FIELD WILL MINIMIZE SEVERE POTENTIAL BY LIMITING THE
CONVECTION TO GARDEN VARIETY PULSE STORMS. THEN THE LOSS OF DAYTIME
HEATING AND THE UPPER RIDGE BUILDING IN FROM THE WEST WILL BRING AN
END TO THE PRECIP BY MIDNIGHT AND CLOUDS WILL BE ON THE DECREASE.
THE RIDGE WILL CONTINUE TO BUILD THROUGH THE DAY ON MONDAY WITH
SURFACE HIGH PRESSURE EXTENDING INTO LOWER MICHIGAN FROM ONTARIO.
FORECAST SOUNDINGS AND RH PROGS SUGGEST THERE WILL BE ENOUGH LOW
LEVEL MOISTURE FOR CU FORMATION, BUT IT WILL STAY SCATTERED IN THE
ANTICYCLONIC LOW LEVEL FLOW PATTERN. MOSTLY SUNNY WILL WORK FINE
FOLLOWED BY CLEAR SKIES MONDAY NIGHT.

THE UPPER RIDGE WILL CONTINUE TO BUILD ON TUESDAY AND GUIDE ANY
CONVECTIVE DEBRIS TO OUR NORTH, OR FORCE IT TO THIN OVER OUR AREA.
SLIGHTLY INCREASED SOUTHERLY LOW LEVEL FLOW WILL START RAMPING UP
THE HUMIDITY AND GETTING TEMPS INTO THE UPPER 80S. GUIDANCE TEMPS IN
THE UPPER 80S LOOK GOOD.

HEADING INTO THE MIDDLE OF THE WEEK, THE WARMING TREND WILL PEAK ON
WEDNESDAY AS THE 12Z AVN SHOWS 500 MB HEIGHTS UP AROUND 597 DM, WITH
MEX AND FMR GUIDANCE TEMPS AROUND 90. CONFIDENCE IS HIGH THAT
AFTERNOON READINGS WILL BE IN THE 90 TO 95 DEGREE RANGE WEDNESDAY
AFTERNOON. THE EXTENDED MODELS ALL INDICATE THAT THE UPPER AIR
PATTERN WILL BE PROGRESSIVE ENOUGH TO BRING A SHORT WAVE INTO THE
GREAT LAKES BY THURSDAY AND COOL THINGS OFF A LITTLE, BUT THE
STRENGTH OF THE UPPER RIDGE AND A SLIGHT REX BLOCK SHOWN OVER
EASTERN CANADA AND THE ATLANTIC COAST ON WEDNESDAY PROVIDES SOME
CONCERN ABOUT THE TIMING OF A COOL-DOWN. THERE IS STILL GOOD MODEL
AGREEMENT ON THE SHORT WAVE BEING STRONG ENOUGH TO KNOCK DOWN THE
RIDGE AND ALLOW IT TO RETROGRADE WEST HEADING INTO THE WEEKEND. PLAN
TO KEEP THE CHANCE OF THUNDERSTORMS GOING FOR BOTH THURSDAY AND
FRIDAY TO ALLOFW FOR TIMING THAT IS SLOWER THAN THE AVN/MRF ON THE
ASSOCIATED SURFACE TROF AND COLD FRONT MOVING INTO SE MICHIGAN.
COOLER HIGH PRESSURE FROM CENTRAL CANADA WILL EVENTUALLY SETTLE IN
FOR THE WEEKEND.

.DTX...NONE.

BT