000 FXUS63 KDTX 170221 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1021 PM EDT FRI MAY 16 2008 .UPDATE... THE LATEST WATER VAPOR LOOP SHOWS A WELL DEFINED SHORT WAVE MOVING INTO WESTERN UPPER MICHIGAN. REGIONAL RADAR DATA SHOWS A BAND OF SHOWERS AHEAD OF THIS FEATURE...ROUGHLY ALONG A SURFACE TROUGH AXIS OVER WESTERN UPPER MI AND NORTHERN WI. THE 00Z GRB SOUNDING DID SHOW A LITTLE HIGHER MOISTURE IN THE MID LEVELS IN COMPARISON TO DTX AND APX. THE MID LEVEL THETA E ADVECTION AND ISENTROPIC ASCENT IS LEADING TO A SECOND AREA OF SHOWERS CURRENTLY MOVING ACROSS NORTHWEST LOWER MI. THIS REGION OF ISENTROPIC ASCENT IS EXPECTED TO BRUSH THE NORTHERN SAGINAW VALLEY AND THUMB OVER THE NEXT COUPLED OF HOURS. FAIRLY DECENT QG FORCING AND EXIT REGION JET DYNAMICS IS STILL EXPECTED TO OVERSPREAD SE MI LATE TONIGHT AS THE MID LEVEL WAVE ROTATES ACROSS THE NORTHERN LAKES. THUS THE CURRENT FORECAST WHICH HAS AN IN INCREASE IN POPS AFTER 06Z STILL LOOKS ON TRACK. ONLY MINOR ADJUSTMENTS WILL BE MADE TO SKY COVER AND MIN TEMPS IN THE UPDATE. && .PREV DISCUSSION...ISSUED 708 PM EDT FRI MAY 16 2008 AVIATION... CLOUD BASES ARE GENERALLY ABOVE 6K FT THIS EVENING ALONG A WEAKENING SURFACE TROUGH AXIS ACROSS THE THUMB REGION. THIS IS A RESULT OF FAIRLY DRY LOWER LEVELS...PER RECENT TAMDAR SOUNDINGS OUT OF DTW. THE SURFACE TROUGH AXIS CURRENTLY OVER THE ARROWHEAD OF MINNESOTA IS FORECAST TO MOVE INTO THE SAGINAW VALLEY AROUND 09Z...THEN INTO METRO DETROIT BETWEEN 12Z AND 15Z. DEEPER MOISTURE ALONG THIS BOUNDARY AS WELL AS STRONGER LARGE SCALE FORCING WILL PROVIDE A BETTER CHANCE FOR SOME SHOWERS EARLY SAT MORNING. MODEL SOUNDINGS STILL SUGGEST THAT CEILINGS AND VISIBILITIES WILL REMAIN PREDOMINATELY IN THE VFR CATEGORY AS THIS TROUGH MOVES THROUGH. PREV DISCUSSION...ISSUED 358 PM EDT FRI MAY 16 2008 SHORT TERM...THROUGH TONIGHT BAND OF MID CLOUDS OVER CENTRAL LOWER MICHIGAN WILL SLIDE DOWNWARD THROUGH SOUTHEAST MICHIGAN LATE THIS AFTERNOON AND EVENING AS THE AXIS OF A SURFACE TROUGH MOVES ACROSS LAKE HURON AND WEAKENS. MODELS CONTINUE TO HINT THERE MAY BE A FEW SHOWERS OUT OF THIS BAND THIS EVENING...BUT WITH VERY MINIMAL FORCING AND VERY DRY AIR BELOW 9000 FEET WILL CONTINUE DRY FORECAST WITH INCREASING CLOUDS. BEHIND THIS BAND...WILL SEE A BRIEF BREAK IN CLOUD COVERAGE BEFORE CLOUDS INCREASE ONCE AGAIN AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. SURFACE LOW PRESSURE SYSTEM WILL MOVE INTO CENTRAL ONTARIO LATE TONIGHT AS THE FIRST IN A SERIES OF STRONG UPPER SHORTWAVES RACES DOWN INTO THE NORTHERN GREAT LAKES. PRECIPITATION IS EXPECTED TO DEVELOP AFTER MIDNIGHT AS A COLD FRONT APPROACHES SOUTHEAST MICHIGAN. BEST CHANCES FOR PRECIPITATION WILL BE FROM 06Z-14Z AS MODELS SHOW A GOOD BAND OF MOISTURE AND ISENTROPIC ASCENT (295-300K) PROGRESSING SOUTHEASTWARD ACROSS THE FORECAST AREA DURING THIS TIMEFRAME...WITH SOME HELP FROM LEFT EXIT REGION DYNAMICS. WITH AMPLE CLOUD COVER AND SOME WIND...TEMPERATURES OVERNIGHT WILL REMAIN FAIRLY MILD...FALLING TO ONLY AROUND 50. LONG TERM...SATURDAY THROUGH FRIDAY MODEL SOLUTIONS ARE A BIT DIFFERENT (TODAY AS COMPARED TO THIS TIME YESTERDAY) IN REGARDS TO THE SURFACE LOW PASSING NORTH OF THE LAKES REGION AND THE COLD FRONT THAT IT SENDS SOUTHEAST THROUGH THE AREA. THIS LOW IS NOW MUCH FURTHER NORTH AND HENCE THE THE DEGREE OF COLD AIR PUSHING INTO THE STATE ON SATURDAY IS MINIMIZED TO SOME DEGREE. OVERNIGHT FORECAST HAD THIS PRETTY WELL IN HAND...AND DO NOT EXPECT ANY MAJOR ADJUSTMENTS TO TEMPERATURES. ANOTHER MAJOR DIFFERENCE IN THE FORECAST IS A STRONG SHORTWAVE THAT DIVES SOUTH FROM THE ARCTIC CIRCLE IN BEHIND THIS INITIAL SYSTEM. THIS RESULTS IN ANOTHER LOW PRESSURE SWINGING AROUND THE FIRST ONE NORTHEAST OF LAKE HURON...WITH A MUCH STRONGER SURGE OF COLD AIR ON THE WAY FOR SUNDAY...WITH TEMPERATURES ONLY IN THE LOW/MID 50S IN MANY LOCATIONS. ALTHOUGH THE COLDEST SURGE OF AIR PROGRESSES SOUTHEAST OF THE AREA RATHER QUICKLY...A RELATIVELY COOL PATTERN REMAINS IN PLACE EARLY NEXT WEEK...WITH TEMPERATURES ONLY EDGING BACK INTO THE 60S MONDAY INTO TUESDAY. BY THIS TIME...THE FORECAST BECOMES UNCERTAIN AS THE CURRENT UPPER PATTERN BREAKS DOWN. BASICALLY...A STRONG UPPER LEVEL TROUGH WILL BE DIGGING INTO THE WESTERN CONUS...WHICH FORCES THE CURRENT UPPER RIDGE EAST INTO THE MISSISSIPPI VALLEY AND PARTS OF THE GREAT LAKES REGION. THE VORTEX OVER SOUTHEAST CANADA THAT WILL BE FEEDING THE COOL AIR INTO THE AREA WEAKENS SOME...BUT REMAINS STRONG ENOUGH TO INFLUENCE THE WEATHER IN SOUTHEAST MICHIGAN BY BLOCKING THE WARMER AIR THAT WILL BE ENCROACHING ON THE AREA WITH THE BUILDING RIDGE. THE BATTLE GROUND WILL BE A NEARLY STATIONARY SURFACE FRONT THAT WILL BECOME DRAPED FROM THE WESTERN GREAT LAKES SOUTHEAST INTO THE OHIO VALLEY. THE POSITIONING OF THIS FRONT WILL EVENTUALLY DETERMINE THE DEGREE OF WARMING (OR LACK THEREOF). THIS FEATURE WILL ALSO BE THE FOCUS FOR SHOWERS/THUNDERSTORMS FROM MID/LATE NEXT WEEK. WILL MAINTAIN SOMEWHAT OF A CONSERVATIVE FORECAST ATTM...ASSUMING THIS FRONTAL BOUNDARY WILL HAVE TROUBLE LIFTING COMPLETELY NORTH THROUGH THE AREA. THIS WILL FOCUS THE WARMEST AND WETTEST OF THE WEATHER JUST SOUTH/SOUTHWEST OF THE REGION. MARINE... WINDS WILL INCREASE TONIGHT AS THE PRESSURE GRADIENT TIGHTENS IN ADVANCE OF THE NEXT COLD FRONT. NORTHWEST WINDS WILL INCREASE FURTHER IN THE WAKE OF THIS FRONT ON SATURDAY...LEADING TO GUSTS AROUND 25 KNOTS OVER ALL NEARSHORE WATERS ON SATURDAY. THE SETUP IS NOT QUITE AS FAVORABLE FOR GALES OVER NORTHERN LAKE HURON...BUT IT APPEARS WEST/NORTHWEST FLOW WILL BE IDEAL OF FUNNELING OVER THE FAR NORTHERN PART OF THE LAKE...WITH SOME DEGREE OF INSTABILITY AIDING IN MIXING AS WELL. WILL UPGRADE THE WATCH TO A WARNING FOR THE TWO NORTHERN ZONES FROM LATE SATURDAY AND RUN IT INTO SUNDAY MORNING AS A SECOND STRONGER COLD FRONT SWEEPS THROUGH THE REGION. EVEN THOUGH THERE WILL BE A LULL IN WINDS EARLY SATURDAY NIGHT IN BETWEEN THE TWO COLD FRONTAL PASSAGES...SMALL CRAFT ADVISORY CONDITIONS WILL BE THE RULE OVER MOST OF THE WEEKEND...AND WILL KEEP THE ADVISORIES IN PLACE AS IS. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON... GALE WARNING...LHZ361-LHZ362...FROM 5 PM SATURDAY TO 10 AM SUNDAY. SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT HURON INCLUDING SAGINAW BAY...FROM 4 AM SATURDAY TO 8 AM MONDAY. LAKE ST CLAIR... SMALL CRAFT ADVISORY...FROM 8 AM SATURDAY TO 8 PM SUNDAY. MI WATERS OF LAKE ERIE... SMALL CRAFT ADVISORY...FROM 8 AM SATURDAY TO 8 PM SUNDAY. && $$ UPDATE.......SC AVIATION.....SC SHORT TERM...HLO LONG TERM....DG MARINE.......HLO YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).