Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 191700 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 100 PM EDT SAT APR 19 2014 .AVIATION...
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//DISCUSSION... CLEAR SKIES BELOW 15K FT WILL PERSIST THROUGH THE TAF PERIOD DUE TO LINGERING DRY AIR ASSOCIATED WITH DEPARTING SFC HIGH PRESSURE. FOR DTW...A LAKE BREEZE OFF LAKE ERIE IS EXPECTED TO ADVANCE INLAND DURING THE AFTERNOON. THE PASSAGE OF THIS LAKE BREEZE ACROSS METRO WILL TURN THE WINDS FROM EASTERLY TO SOUTHEASTERLY. THIS IS EXPECTED TO OCCUR AROUND 20Z. //DTW THRESHOLD THREATS... * NONE
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&& .PREV DISCUSSION...ISSUED 332 AM EDT SAT APR 19 2014 SHORT TERM...TODAY AND TONIGHT FIRST THINGS FIRST...FOG/STRATUS POTENTIAL EARLY THIS MORNING. THERE IS A NARROW BAND OF STRATUS EXTENDING FROM JACKSON TO DETROIT AND AND UP THROUGH MOUNT CLEMENS. THIS BAND IS ON THE EDGE OF THE 925MB THETA E BOUNDARY THAT SANK SOUTH THROUGH THE AREA LAST EVENING AND STALLED OVER THAT AREA. CIGS HAVE SLOWLY BEEN INCREASING AS DRY AIR TAKES ITS TOLL ON THE LIMITED MOISTURE. THERE IS STILL A POSSIBILITY FOR PATCHY FOG TO DEVELOP...MAINLY IN THE THUMB AS ONSHORE FLOW ADVECTS MOIST AIR BELOW A STRENGTHENING INVERSION. OBS HAVE NOT BEEN TOO FAVORABLE THUS FAR KEEPING A DEWPOINT DEPRESSION AROUND 2-5 DEGREES FOR THE MOST PART BUT THERE ARE SOME DIPPING TO AROUND A DEGREE. WITH MODELS SHOWING IMPROVING CONDITIONS FOR A BRIEF WINDOW EARLY THIS MORNING WILL KEEP THE MENTION OF PATCHY FOG IN THE FORECAST FOR NOW. SUNRISE WILL QUICKLY PUT AN END TO ANY FOG THAT DOES TRY TO FORM. THE REST OF THE DAY WILL BE PLEASANT WITH TEMPERATURES ABOUT 5 DEGREES BELOW NORMAL FOR MORE LOCATIONS...ESPECIALLY THE LAKE HURON/ERIE SHORELINE AREA. SFC HIGH PRESSURE SYSTEM CENTERED OVER NORTHERN ONTARIO WILL CONTINUE ITS MARCH EASTWARD THROUGH THE DAY REACHING THE EAST COAST BY SUNDAY...WHILE A MID LEVEL RIDGE AXIS WILL PASS OVER MI /AROUND 00Z SUNDAY/. SE MI WILL FALL ON THE SOUTHERN PERIPHERY OF THIS DOME OF HIGH PRESSURE RESULTING IN EASTERLY/NORTHEASTERLY FLOW OFF THE LAKES THROUGH THE DAY. WITH LAKE TEMPERATURES STILL IN THE LOW 40S...THIS ONSHORE FLOW WILL PREVENT TYPICAL SFC HEATING FROM THE MID APRIL SUN EVEN WITH CLEAR SKIES. QUESTION IS HOW FAR INLAND DOES THIS MARINE INFLUENCE MAKE IT? CURRENT THINKING IS THAT AREA WEST OF I-75 WILL GET A BIT MORE INFLUENCE FORM THE SUN ALLOWING THEM TO REACH INTO THE UPPER 50S. SPLIT FLOW PATTERN DEVELOPING IN THE LONGWAVE PATTERN WILL BEGIN TO ADVECT WARMER AIR INTO THE REGION TONIGHT WHICH WILL COMBAT THE EARLY RADIATIONAL COOLING KEEPING TEMPERATURES IN THE MID 30S. LONG TERM...SUNDAY THROUGH NEXT FRIDAY A VIGOROUS SHORTWAVE WILL TRACK EAST ALONG POLAR JET STREAM ACROSS SOUTHERN CANADA...REACHING JAMES BAY BY SUNDAY EVENING. WITH NO SOUTHERN STREAM COMPANION TO THIS WAVE...EXPECT THE COLD FRONT THAT PUSHES SOUTH IN THE WAKE OF THIS SYSTEM TO HANG UP JUST NORTH OF THE AREA LATE THIS WEEKEND AS ZONAL UPPER FLOW REMAINS IN PLACE OVER THE GREAT LAKES. THIS WILL LIMIT RAIN SHOWER CHANCES TO THE SAGINAW VALLEY AND THUMB LATE SUNDAY/SUNDAY NIGHT...WHERE POPS WILL BE MINIMAL ANYWAY. A SECOND POLAR SHORTWAVE WILL FOLLOW IN BEHIND THIS INITIAL SYSTEM AND PHASE TO SOME DEGREE WITH A WELL DEFINED SHORTWAVE LIFTING FROM THE SOUTHWEST CONUS INTO THE CENTRAL PLAINS. TIMING ON THE EVOLUTION OF THIS SYSTEM...AS PORTRAYED BY THE 00Z MODEL SUITE...HAS SLOWED SLIGHTLY. THIS WILL ALLOW THE AREA TO REMAIN IN THE WARM SECTOR INTO A LARGE PORTION OF MONDAY AND WILL UP TEMPERATURES INTO THE LOWER 70S AS NAM12/ECMWF/GFS ARE ALL RATHER CONSISTENT IN THE POSITIONING OF THE UPPER TROUGH AXIS...WEST OF THE CWA THROUGH 00Z. WILL ALSO HAVE TO BACK OFF ON THE HIGHER SHOWER CHANCES OVER MUCH OF THE AREA UNTIL SUNDAY AFTERNOON/EVENING...AND WITH ADDITIONAL DAYTIME HEATING AND DESTABILIZATION...A MENTION OF THUNDER IS NOW WARRANTED AS LI/S DROP TO 0C OR BELOW AND SBCAPES ARE FORECAST NEARING 500 J/KG...AT LEAST BY THE NAM12. WITH A GREATER DEGREE OF NORTHERN/SOUTHERN STREAM PHASING AS THIS SYSTEM EVOLVES...AND THE RESULTANT DEEPER UPPER TROUGH HANGING BACK OVER THE GREAT LAKES...RELATIVELY COOL WEATHER WILL LINGER THROUGH THE MIDDLE OF NEXT WEEK AS HIGHS TOP OUT IN THE 50S ON AVERAGE FROM TUESDAY THROUGH THURSDAY AND LOWS DROP INTO THE 30S. A SECOND WELL PHASED STORM SYSTEM WILL THEN DEVELOP OVER THE DAKOTAS/UPPER MIDWEST AND WOBBLE INTO THE AREA AS IT OCCLUDES LATE IN THE FORECAST PERIOD. THIS WILL BRING INCREASED RAIN CHANCES AND MILDER TEMPERATURES INTO AT LEAST PARTS OF FRIDAY. NOTABLY COLDER AIR IS THEN EXPECTED TO FILTER BACK INTO THE AREA JUST BEYOND THE FORECAST PERIOD THROUGH NEXT WEEKEND...WHICH WAS CONSISTENTLY FORECAST BY MEDIUM RANGE MODELS 24 HOURS AGO AS WELL. MARINE... CONDITIONS WILL REMAIN REASONABLY QUIET INTO TONIGHT AS LIGHT EAST FLOW...AVERAGING 10 KNOTS OR SO...CONTINUES TO FILTER OFF OF STRONG HIGH PRESSURE CENTERED TO THE NORTH/NORTHEAST. TWO LOW PRESSURE SYSTEMS WILL THEN PASS NEAR THE AREA LATE THIS WEEKEND INTO EARLY NEXT WEEK. THE FIRST WILL TRACK ACROSS ONTARIO ON SUNDAY...DROPPING A COLD FRONT DOWN INTO NORTHERN LAKE HURON. THE FRONT WILL REMAIN QUASI-STATIONARY OVER THIS AREA UNTIL THE SECOND LOW PRESSURE SYSTEM DRAWS IT SOUTHWARD MONDAY AND MONDAY NIGHT. STRONGER NORTH WINDS ARE THEN POSSIBLE ACROSS THE AREA LATE MONDAY NIGHT INTO TUESDAY BEHIND THE FRONT AS COLDER AIR FILTERS BACK INTO THE AREA. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....SC SHORT TERM...DRK LONG TERM....DG MARINE.......DG YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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