FXUS63 KDTX 041458 AAB AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1100 AM EDT WED AUG 4 2004 .UPDATE... DRIER AIR STARTING TO MAKE A MOVE INTO THE SAGINAW VALLEY. THE THREAT OF SHOWERS HAS ENDED FOR THE TRI CITIES...AND WILL COME TO AND END FOR THE THUMB AND FLINT AREAS EARLY THIS AFTERNOON. 12Z ETA SEEMS TO HAVE A HANDLE ON THE RH FIELDS...BUT NOT SO MUCH THE QPF. FORECAST UPDATE WILL HAVE SOME TIMING UPDATES OF THE CLEARING AND RAIN...ESPECIALLY FOR THE NORTH HALF OF THE CWA. WILL ALSO TAKE OUT THUNDER. CERTAINLY NOTHING IN THIS MORNINGS SOUNDING OR FORECAST SOUNDING TO INDICATE ANY SORT OF ELEVATED CAPE OR STEEP LAPSE RATES. STILL COULD BE A RUMBLE OF THUNDER IN THE FAR SOUTH...CLOSER TO THE FRONT AND INSTABILITY...BUT WILL STILL TAKE OUT THE THUNDER MENTION FOR THE ENTIRE CWA. OTHER UPDATES NEEDED WILL BE TEMPS. CLOUDS SHOULD HANG TOUGH SOUTH OF A PORT HURON TO HOWELL LINE. NORTH OF THAT LINE...ENOUGH SUN TO REACH FORECAST HIGHS. TO THE SOUTH HOWEVER...CLOUDS AND RAIN WILL KEEP TEMPS DOWN. THEREFORE WILL LOWER TEMPS FOR METRO DETROIT. RBP && .PREV DISCUSSION... 00Z RAOBS/WATER VAPOR LOOP SHOW UPPER LOW OVER QUEBEC WITH A TROUGH DROPPING INTO THE NORTHERN GREAT LAKES. ANOTHER SHORTWAVE OVER THE DAKOTAS...WITH A CONVECTIVELY INDUCED VORT NEAR THE MID MISSISSIPPI VALLEY. SURFACE ANALYSIS SHOWS LOW OVER KANSAS WITH A FRONT EXTENDING NORTHEAST THROUGH ILLINOIS TO FAR SOUTHERN LOWER MICHIGAN. REGIONAL RADARS SHOW A MULTITUDE OF CONVECTION UPSTREAM...FORMERLY SEPARATED INTO TWO DISTINCT MCS/S BUT NOT MORE WIDESPREAD. MAIN FORECAST FOCUS CONTINUES TO REVOLVE AROUND TODAY...WITH PRECIP AND HEAVY RAIN POTENTIAL THE MAIN CONCERN. ETA/GFS BOTH STILL HAVE FEEDBACK ISSUES...BUT NOT NECESSARILY AS BAD AS EARLIER RUNS. ETA REMAINS MORE CONSISTENT COMPARED TO EARLIER RUNS REGARDING THE TRACK OF THE SURFACE LOW /WHICH IS NOT GOOD/. HOWEVER THE GFS AND CANADIAN BOTH HAVE TRENDED FARTHER SOUTH WITH THE WAVE. ETA DID NOT CAPTURE THE FIRST MCS THAT SWEPT ACROSS NORTHERN ILLINOIS OVERNIGHT. THIS SYSTEM ATE UP SOME OF THE LINGERING INSTABILITY...AS WELL AS ENHANCED/PUSHED THE BAROCLINIC ZONE FARTHER SOUTH WITH ITS OUTFLOW. UPSTREAM COMPLEX OVER IOWA HAD BEEN TRACKING ALMOST DUE SOUTH INTO MISSOURI...BUT HAS BEGUN TO TURN TO THE SOUTHEAST INTO THE UNSTABLE AIR ACROSS SOUTHERN ILLINOIS. THIS WOULD BRING THE MORE STRATIFORM PRECIP NORTH OF THE COMPLEX THROUGH SOUTHERN LOWER...BUT WITH THE MAIN BAROCLINIC ZONE AND HIGHEST QPF SOUTH OF THE STATE. THIS IS CONTRARY TO THE ETA FORECAST...WHICH BRINGS MAIN BULLSEYE OF LIFT FROM THIS SYSTEM INTO SOUTHERN LAKE MICHIGAN AND EVENTUALLY ACROSS SOUTHEAST MICHIGAN. GIVEN RECENT TRENDS AND OVERALL SETUP...WOULD EXPECT THE HIGHEST QPF TO FALL FARTHER SOUTH ACROSS INDIANA AND OHIO. THIS IS ALSO IN LINE WITH LATEST NCEP QPF AND EXCESSIVE RAINFALL GRAPHICS. FOR TODAY...EXPECT A COUPLE ROUNDS OF WIDESPREAD PRECIP...HOWEVER FIRST ONE WILL BE WINDING DOWN AROUND FORECAST ISSUANCE. LONG-LIVED SQUALL LINE IS ONLY NOW BEGINNING TO WEAKEN ACROSS CENTRAL LOWER/EASTERN INDIANA AS IT MOVES INTO A MORE STABLE AIRMASS. LARGE AREA OF STRATIFORM PRECIP EXTENDS ACROSS MUCH OF LOWER MICHIGAN... HOWEVER DRY AIR HAS BEEN A LIMITING FACTOR FARTHER NORTH. TIGHT 850MB THETA-E GRADIENT DEPICTED ACROSS THE CENTRAL CWA...ALONG WHICH A FEW THUNDERSTORMS HAVE DEVELOPED OUT AHEAD OF THE MAIN BATCH. FARTHER NORTH THERE IS NO INSTABILITY TO SPEAK OF AND DRY AIR FEEDING AROUND SURFACE RIDGE OVER THE NORTHERN GREAT LAKES. EXPECT A SHARP CUTOFF IN QPF...AND WILL ONLY KEEP CHANCE RW ACROSS THE FAR NORTHERN CWA. FARTHER SOUTH THOUGH CATEGORICAL SHOULD BE BETTER. CURRENT WIDESPREAD PRECIP WILL BE OUT JUST AROUND THE TECHNICAL START OF THE FIRST PERIOD. HOWEVER NEXT AREA OF RAIN IS CURRENTLY ACROSS NORTHERN ILLINOIS. REGIONAL RADARS SHOW THESE TWO AREAS ARE BEGINNING TO FILL IN...WHICH WOULD SUPPORT NOT TRYING TO TIME A BREAK BETWEEN THE TWO. WILL WORD THE GRIDS OCCASIONAL RAIN WITH SCATTERED THUNDERSTORMS. IN ADDITION TO COVERAGE OF PRECIP...INTENSITY IS ALSO A CONCERN. A JUICY AIRMASS WITH PRECIPITABLE WATERS OBSERVED AROUND 1.75" AT 00Z...HOWEVER VALUES POOLED AROUND 2" OR MORE ARE NOT UNREASONABLE. BASED ON UPSTREAM METAR REPORTS ACROSS WISCONSIN/ILLINOIS AND RECENT WEAKENING TREND OBSERVED...WOULD EXPECT ABOUT 0.50-1.00" OF PRECIP WITH THIS FIRST COMPLEX...MAINLY ALONG AND SOUTH OF I-69. THAT MUCH RAIN SHOULD NOT CREATE TOO MUCH OF A PROBLEM...HOWEVER QUESTION REMAINS AS TO WHAT WILL FALL DURING THE REST OF THE DAY. AS MENTIONED ABOVE...EXPECT HIGHEST QPF TO FALL FARTHER SOUTH TOWARD THE OHIO VALLEY. HOWEVER BASED ON ADJUSTED MODEL GUIDANCE AND UPSTREAM OBSERVATIONS...WOULD EXPECT TO SEE ROUGHLY ANOTHER INCH OF QPF ACROSS THE SOUTHERN CWA. THIS PRESENTS MORE OF A PROBLEM...WITH UP TO 2 INCHES TOTAL ACROSS THE SOUTHERN CWA. THIS IS THE SAME AREA WHICH SAW UP TO AN INCH OF RAIN LAST NIGHT WITH THE CONVECTIVE THAT DEVELOPED OVER THE CWA. EARLIER SPOTTER REPORTS INDICATED THE HIGHEST VALUES FELL GENERALLY SOUTHEAST OF THE OFFICE /E.G. TROY BLOOMFIELD DEARBORN WYANDOTTE/. THIS RAIN CAUSED A SOME RISES ON AREA RIVERS...AND IS ALSO WHY FLASH FLOOD GUIDANCE IS LOWEST ACROSS THE SOUTHEAST. WITH THIS IN MIND...WILL ISSUE A FLOOD WATCH FOR TODAY FOR THE SOUTHERN CWA BASICALLY ALONG AND SOUTH OF M-59 /LIVINGSTON TO MACOMB/. NOT TOO SURE ABOUT THE NORTHERN TIER OF COUNTIES... ESPECIALLY SINCE MACOMB MAY RECEIVE THE LOWEST PRECIP IN THE WATCH AREA. /FARTHER EAST THE THE CWA THE DRY/STABLE AIR WILL DOMINATE LONGER...SO THEY WILL NOT SEE AS MUCH FROM THE CURRENT EARLY MORNING SYSTEM THAT CONTINUES TO WEAKEN AS IT MOVES EAST./ HOWEVER THEY ALSO HAVE ONE OF THE LOWEST FFG VALUES GIVEN EARLIER RAIN...SO IT WOULD BE PRUDENT TO INCLUDE THEM IN THE WATCH. OTHERWISE DID NOT MAKE MANY CHANGES TO THE REMAINDER OF THE FORECAST. COULD SEE SOME LINGERING PRECIP ACROSS THE SOUTHEAST CWA THIS EVENING...UNTIL THE SYSTEM FINALLY CLEARS EAST. HOWEVER GIVEN EXPECTED FARTHER SOUTH TRACK...WILL KEEP POPS BELOW MOS GUIDANCE. UPPER TROUGH OVER THE NORTHERN LAKES DIGS ACROSS THE REGION TONIGHT...CARVING OUT A LONGWAVE TROUGH OVER THE EASTERN CONUS. CANADIAN SURFACE HIGH BUILDS DOWN ACROSS THE WESTERN GREAT LAKES...LEAVING SOUTHEAST MICHIGAN IN A SOMEWHAT BRISK NORTHERLY FLOW. ETA/GFS BOTH DROP 850MB TEMPS TO 5-6C IN THERMAL TROUGH THAT CROSSES THE REGION THURSDAY NIGHT. && .DTX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ BRAVENDER EXPERIMENTAL GRAPHICAL FORECASTS ARE AVAILABLE ONLINE AT HTTP://WWW.CRH.NOAA.GOV/DTX (ALL LOWER CASE)