Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 221048 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 548 AM EST MON DEC 22 2014 .AVIATION...
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VFR CONDITIONS WILL HOLD INTO MID/LATE AFTERNOON BEFORE MVFR TO LOWER VFR STRATUS DECK BEGINS TO EXPAND BACK OVER THE TERMINALS AS MOISTURE GRADUALLY INCREASES IN ADVANCE OF DEVELOPING STORM SYSTEM OVER THE MID MISSISSIPPI VALLEY. SOUTHERLY FLOW WILL INCREASE THIS EVENING INTO TONIGHT WITH MVFR TO OCCASIONAL IFR CIGS POSSIBLE AS LIGHT SHOWERS EXPAND NORTH THROUGH THE AREA IN THE 04Z-08Z TIME FRAME. WINDS WILL REMAIN FROM THE EAST/SOUTHEAST THROUGH THE TAF PERIOD. FOR DTW...CEILINGS ABOVE 10KFT WILL CONTINUE INTO THIS AFTERNOON BEFORE STRATUS AOB 5000 FEET EXPANDS INTO TERMINAL 21Z-00Z. CIGS WILL LOWER FURTHER OVERNIGHT AS -SHRAS SPREAD INTO AREA BETWEEN 06Z AND 08Z. WHILE MVFR CONDITIONS WILL BECOME COMMON...OCCASIONAL IFR CIGS WILL ALSO BE POSSIBLE LATE TONIGHT. EAST/SOUTHEAST WINDS WILL BECOME SOUTHEAST NEAR 10 KNOTS BY TUESDAY MORNING. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILINGS ABOVE 5000 FEET THROUGH 22Z TODAY. * HIGH CONFIDENCE IN CEILINGS AOB 5000 FEET AFTER 00Z TONIGHT.
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&& .PREV DISCUSSION...
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ISSUED 348 AM EST MON DEC 22 2014 SHORT TERM...TODAY THROUGH TONIGHT AMPLIFYING UPPER TROUGH OVER THE PLAINS/MIDWEST WILL LEAD TO AN EVER INCREASING DEGREE OF MOISTURE OVER THE AREA LATE TODAY INTO TONIGHT AS BROAD SOUTHWEST FLOW REGIME BECOMES ESTABLISHED IN ADVANCE OF THIS SYSTEM. INITIAL THETA-E SURGE WILL WORK INTO THE AREA IN THE 03Z-06Z TIME FRAME THIS EVENING AND EXPAND TO ENCOMPASS THE ENTIRE CWA OVERNIGHT. HAVE ADJUSTED THE RAIN FORECAST TO INCLUDE MORE DEFINITION AS RAIN CHANCES WILL INCREASE STEADILY FROM SOUTHWEST TO NORTHEAST ACROSS LOWER MICHIGAN DURING THE EVENING AND THEN CONTINUE OVERNIGHT FOR MUCH OF THE AREA AS HIGHER THETA-E AIR GRADUALLY DISLODGES ALREADY MODIFIED POLAR AIRMASS IN PLACE. ESSENTIALLY...PRECIPITATION CHANCES WERE LOWER FOR THE EVENING HOURS...PARTICULARLY FROM THE NORTHEAST HALF OF THE CWA INTO LAKE HURON AND INCREASE SLIGHTLY OVERNIGHT TO ACCOUNT FOR LIKELY TO CATEGORICAL RAIN CHANCES AREA-WIDE IN THE 06Z TO 12Z PERIOD. HIGHS TODAY WILL CLIMB INTO THE MID/UPPER 30S AS EXTENSIVE CLOUD COVER WILL OFFSET WARM AIR ADVECTION PATTERN. EAST TO SOUTHEAST SURFACE FLOW WILL ALSO LIMIT WARMING TODAY INTO PARTS OF THIS EVENING. WITH HIGHS REMAINING IN THE 30S IN MOST LOCATIONS...LOW TEMPERATURES WILL MOST LIKELY FALL BACK TO NEAR FREEZING IN SOME LOCATIONS...AT LEAST OVER THE THUMB...THIS EVENING BEFORE STEADY TO RISING TEMPERATURES ENSUE OVERNIGHT. ONLY MINOR ADJUSTMENTS TO THE FORECAST WERE MADE IN THIS REGARD. LONG TERM... ENERGETIC FLOW DIVING SOUTHEAST FROM THE GULF OF ALASKA...THROUGH THE ROCKIES...AND INTO THE SOUTHERN PLAINS THIS MORNING. THE SUPPLY OF UPPER LEVEL PV IS PLENTIFUL...WITH THE FLOW QUICKLY BUCKLING AND LEADING TO CLOSED 500 MB LOW OVER THE CENTRAL CONUS TONIGHT. NO SIGNIFICANT INITIALIZATIONS ERRORS NOTED TO LATCH ONTO. STILL ISSUES WITH THE AMOUNT OF ENERGY AND TIMING OF 500 MB COLD POOL WORKING THROUGH THE BACKSIDE OF THE LONGWAVE TROUGH INTO TEXAS ON TUESDAY...WITH DIFFERENCES ON THE STRENGTH AND PLACEMENT OF THE SECONDARILY LOW PRESSURE SYSTEM SPINNING UP BETWEEN 00Z NAM/GFS/CANADIAN AND EURO. LEAD SHEARING OUT/ELONGATED UPPER WAVE WORKING THROUGH THE WESTERN GREAT LAKES WILL LAY THE TRACKS SO TO SPEAK. THE TRACKS ARE ALREADY DISPLACED BY TUESDAY EVENING...AS THE NAM AND CANADIAN AVERAGE 850-700 MB TEMPERATURE DIVERGES BY A SIGNIFICANT 4 DEGREES OVER SOUTHEAST MICHIGAN. WITH NOT A WHOLE LOT OF COLD AIR TO WORK WITH...PACIFIC ORIGIN OF THE AIRMASS OVER WESTERN CANADA...WILL LEAN TOWARD THE MILDER SOLUTION...WHICH MAINTAINS THE BAROCLINIC ZONE CLOSE BY...ENOUGH FOR THE DEVELOPING WESTERN GULF COAST LOW TO HEAD TOWARD THE CENTRAL/EASTERN GREAT LAKES ON WEDNESDAY. THE PROBLEM IS...EVEN WITH A FAVORABLE SURFACE LOW TRACK JUST TO OUR SOUTH AND EAST...THE LACK OF COLD AIR/CONNECTION WITH THE POLAR STREAM... AND MILD/MOIST AIR PICKED UP FROM THE GULF OF MEXICO WILL LIKELY SUPPORT MOSTLY A RAIN EVENT. CONFIDENCE IS AVERAGE AT BEST HOWEVER. NO SNOW COVER ON THE GROUND HELPS ONE LEAN TOWARD THIS DIRECTION...AS THE DAYTIME TIMING IS ALSO A SLIGHT NEGATIVE AS WELL. SO...WILL HOLD ONTO THE CATEGORICAL RAIN FORECAST ON WEDNESDAY...DESPITE THE DRY FORECAST OUT OF THE NAM. THE STRENGTH OF THE LOW STILL REMAINS A BIT UNCERTAIN...BUT EVEN IF A DEEPER LOW MATERIALIZES (SEE EURO/CANADIAN)...NOT SURE WE WILL SEE WIND ADVISORY CRITERIA (DESPITE GOOD 23 MB RISE/FALL PRESSURE COUPLET) AS THERE SHOULD BE PRECIPITATION DRAG ISSUES AND NO GOOD DOWNWARD DESCENT...AS A PERIOD OF SNOW APPEARS LIKELY AS PRECIPITATION SHUTS OFF WEDNESDAY EVENING/NIGHT. THE 00Z EURO IS REALLY TOWING THE RAIN/SNOW LINE...WITH THE POSSIBILITY OF SEVERAL INCHES OF SNOW ACCUMULATION WITH THE DEFORMATION WEDNESDAY EVENING/NIGHT. HOWEVER...SURFACE DEW PTS ARE STILL ADVERTISED TO BE 33+ DEGREES THROUGH 6Z THURSDAY...WITH 1000-850 MB THICKNESSES IN THE 1295-1300 M RANGE. SO...NOT EXACTLY SURE WHEN ACCUMULATION WILL BEGIN TO TAKE PLACE. AT THIS POINT...WILL THE HIGHLIGHT THE POTENTIAL OF 1 TO 3 INCHES BEFORE PRECIPITATION TAPERS OFF...THUS KEEPING THE HOPES OF A WHITE CHRISTMAS ALIVE AND WELL. MARINE... A DEVELOPING LOW PRESSURE SYSTEM OVER THE PLAINS TODAY WILL SUPPORT INCREASING S-SE WINDS ACROSS LAKE HURON. THE LOW WILL SLOWLY ROTATE INTO THE WESTERN GREAT LAKES TONIGHT INTO TUESDAY. PERSISTENT LOW LEVEL WARM AIR ADVECTION WILL INCREASE OVER LAKE STABILITY AND THUS SUPPRESS PEAK WINDS FROM EXCEEDING 25 KNOTS. HOWEVER...WAVES WILL STILL LIKELY REACH AROUND 4 FEET ACROSS NEARSHORE WATERS OF NORTHERN THUMB REGION...AND HAVE ISSUED SMALL CRAFT ADVISORIES. THE SURFACE LOW WILL ACTUALLY WEAKEN AS IT LIFTS INTO THE NORTHERN GREAT LAKES ON TUESDAY. A SUBSEQUENT WEAKENING IN THE GRADIENT OVER LAKE HURON WILL LEAD TO A DIMINISHING TREND IN THE WIND AND WAVES TUESDAY INTO TUESDAY NIGHT. A SECONDARY SURFACE LOW IS FORECAST TO RAPIDLY DEEPEN AS IT MOVES FROM THE DEEP SOUTH TUESDAY NIGHT AND IN BETWEEN THE CENTRAL AND EASTERN GREAT LAKES WEDNESDAY. THIS SYSTEM WILL CONTINUE TO STRENGTHEN AS IT LIFTS NORTHEAST OF THE REGION WEDNESDAY NIGHT. COLD AIR ADVECTION IN THE WAKE OF THIS SYSTEM WILL POSE THE RISK OF GALE FORCE WINDS OVER THE LAKES WEDNESDAY NIGHT INTO THURSDAY MORNING. ENOUGH UNCERTAINTY IN THE STRENGTH AND TRACK OF THIS SYSTEM REMAINS AT THIS STAGE IN THE FORECAST TO HOLD OFF ON THE ISSUANCE OF A GALE WATCH.
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&& .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 7 PM EST TUESDAY FOR LHZ421-441-442. LAKE ST CLAIR...NONE. MICHIGAN WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....DG SHORT TERM...DG LONG TERM....SF MARINE.......SF YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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