Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 191048 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 548 AM EST FRI DEC 19 2014 .AVIATION... //DISCUSSION... LIGHT NORTHERLY WINDS WILL ATTEMPT TO CLEAR THE LOW MVFR CLOUDS IN PLACE OVER THE MAJORITY OF SOUTHEAST MICHIGAN. HOWEVER...THE EDGE OF THE CLOUD SHIELD IS EXPECTED TO RESIDE ACROSS THE SOUTHERN TAF SITES ...DTW/YIP/DET...THIS AFTERNOON...MAKING FOR A LOW CONFIDENCE FORECAST. EVEN IF SKIES SCATTER OUT OVER THE SOUTHERN SITES...THERE IS A DECENT CHANCE OF THE LOW CLOUDS RETURNING DURING THE OVERNIGHT HOURS AS WINDS ATTEMPT TO BECOME LIGHT SOUTHWEST. HIGHER CONFIDENCE FORECAST FARTHER NORTH ACROSS MBS AND FNT WHERE MOSTLY CLEAR SKIES ARE EXPECTED TO PREVAIL. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT THROUGH AT LEAST NOON...LOWER CONFIDENCE THEREAFTER. && .PREV DISCUSSION...ISSUED 314 AM EST FRI DEC 19 2014 SHORT TERM...TODAY AND TONIGHT THE 00Z DTX SHOWED A SATURATED 850 MB LAYER...WITH A TEMP/DEW PT OF -10 C. FARTHER NORTH...A DRAMATIC DIFFERENCE...AS APX REVEALED AN 850 MB DEW PT DEPRESSION OF 31 C. AN UPPER WAVE SEEN OVER EASTERN ONTARIO TRACKING INTO THE EASTERN GREAT LAKES TODAY WILL CONTINUE TO HELP WITH THE DRY PUSH TO THE SOUTH...BUT CONFIDENCE IN CLEARING DIMINISHES AS ONE HEADS SOUTH OF THE M-59 CORRIDOR...AS 00Z NAM STILL INDICATING ENOUGH 950-925 MB MOISTURE/RH LINGERING...AS THE LOW LEVEL FLOW WILL BE CALM TO VERY LIGHT. SURFACE TROUGH/CONVERGENCE SEEN SINKING SOUTH AND EXITING LENAWEE AND MONROE COUNTIES SHORTLY AFTER 12Z...AND THUS SHOULD END THE FREEZING DRIZZLE THREAT AS THE DRIER AIR TAKES HOLD. NAM SOUNDINGS SHOWING SHALLOW MOISTURE LAYER WITHIN THE 1-2 KFT LAYER THROUGH TONIGHT (I- 94 CORRIDOR AND POINTS SOUTH)....AS THE LOW LEVEL INVERSION INCREASES/SHARPENS UP. CURRENT TRENDS/CLEARING LINE ARE MATCHED UP FAIRLY WELL WITH THE NAM...AND WILL THUS MAINTAIN A GOOD DEAL OF CLOUDS TOWARD THE OHIO BORDER. EVEN WITH SUNSHINE FARTHER NORTH TODAY...SURFACE HIGH IN PLACE WILL LIMIT THE MIXING DEPTHS...AS MID DECEMBER INSOLATION WILL PROBABLY BE ONLY GOOD FOR LOW/MID 30S...IN LINE WITH 925 MB FORECASTED TEMPS OF -4 TO -6 C. GUIDANCE TEMPS FOR TONIGHT CALL FOR UPPER TEENS NORTH TO LOWER 20S SOUTH DUE TO THE LINGERING CLOUDS. LONG TERM...SATURDAY THROUGH THURSDAY UPPER LEVEL PATTERN WILL REMAIN QUASI-ZONAL THROUGH THE WEEKEND AS UPPER TROUGHING OVER NEW ENGLAND SHIFT NORTHEAST AND THE BEGINNINGS OF THE NEXT UPPER TROUGH OVER THE ROCKIES/PLAINS JUST GET UNDERWAY. WHILE PRECIPITATION CHANCES WILL REMAIN MINIMAL THROUGH THE WEEKEND AS HIGH PRESSURE EAST THROUGH THE OHIO VALLEY AND GREAT LAKES...THE CLOUD FORECAST WILL REMAIN TRICKY AS A SERIES OF WEAK UPPER LEVEL DISTURBANCES RACES THROUGH THE RELATIVELY FLAT UPPER LEVEL FLOW. THIS SHOULD MAINTAIN A GENERAL PARTLY TO MOSTLY CLOUDY FORECAST. TEMPERATURES REALLY WON/T CHANGE TOO MUCH...PERHAPS MODERATING A FEW DEGREES WITH HIGHS RANGING IN THE LOWER/MID 30S AND LOWS IN THE MID 20S. AFOREMENTIONED PLAINS TROUGHING BEGINS TO AMPLIFY SIGNIFICANTLY EARLY NEXT WEEK AS A STEADY STREAM OF NORTHERN PACIFIC JET ENERGY WORKS EAST/SOUTHEAST FROM THE PACIFIC NORTHWEST/BRITISH COLUMBIAN COAST INTO THE MIDDLE OF THE CONUS. INITIALLY...THIS WILL LEAD TO AN EXPANDING SHORTWAVE RIDGE INTO THE EASTERN CONUS...WHICH WILL BRING A MORE NOTABLE MODERATION IN TEMPERATURES MONDAY AND TUESDAY AS HIGHS CLIMB BACK TO 40 DEGREES OR BETTER. PRECIPITATION CHANCES WILL STEADILY INCREASE DURING THIS TIME FRAME AS MOISTURE STREAMS INTO AREA WITHIN EXPANDING SOUTHWEST FLOW REGIME IN ADVANCE OF THE DEVELOPING STORM SYSTEM OVER THE PLAINS. OTHER THAN AN INITIAL MIX OF LIGHT RAIN/SNOW MONDAY AS COLD AIR IS DISLODGED...EXPECT MAINLY RAIN MONDAY NIGHT INTO TUESDAY AS PRECIPITATION CHANCES...IN GENERAL...MARKEDLY INCREASE. FROM THAT POINT FORWARD...THE FORECAST BECOMES EVER MORE DIFFICULT TO PIN DOWN AS THE UPPER TROUGH TO THE WEST PIVOTS INTO AREA AS A NEGATIVELY TILTED FEATURE. THIS SHOULD LEAD TO A GRADUAL TRANSITION BACK TO A RAIN/SNOW MIX AND THEN SNOW AS COLDER AIR WORKS EAST INTO AREA WITH THIS EXPANDING TROUGH. PRECIPITATION CHANCES WILL REMAIN RATHER HIGH AS THIS TROUGH WORKS INTO THE AREA. TO COMPLICATE MATTERS FURTHER...MEDIUM RANGE MODELS REMAIN SOMEWHAT SPLIT AS TO HOW SIGNIFICANT A SOUTHERN STREAM SHORTWAVE WILL BE AS IT LIFTS INTO THE DEVELOPING UPPER TROUGH OVER THE AREA. HOWEVER...GIVEN FACT THAT 00Z ECMWF/CANADIAN GEM NOAM BOTH DEVELOP A RATHER ROBUST STORM OVER OR NEAR THE AREA BY WEDNESDAY AS THIS SOUTHERN ENERGY PHASES INTO NORTHERN STREAM TROUGH...CONFIDENCE IS PERHAPS INCREASING SLIGHTLY THAT A NOTEWORTHY STORM WILL WORK INTO/NEAR THE AREA BY MIDWEEK. WHILE GFS DOES NOT SHARE THIS SOLUTION ATTM...AT LEAST HALF OF THE ENSEMBLE MEMBERS DO TO A SIGNIFICANT DEGREE. SUCH A SOLUTION WOULD BRING AN EXPANDING PRECIPITATION SHIELD INTO THE AREA ON WEDNESDAY WITH A MIXTURE OF RAIN/SNOW CHANGING TO SNOW WITH TIME AS THE SYSTEM INTENSIFIES AND LIFTS NORTH/NORTHEAST INTO THE EASTERN GREAT LAKES/NORTHEAST CONUS INTO WEDNESDAY NIGHT. WHILE THE ECMWF/NOAM CMC DO HAVE RATHER OMINOUS REPRESENTATIONS OF THIS POTENTIAL WINTER STORM...A NUMBER OF SCENARIOS STILL REMAIN QUITE PLAUSIBLE...RANGING FOR MINIMAL SOUTHERN DEVELOPMENT OF THIS TROUGH TO THE SOUTHERN ENERGY SHIFTING EAST OF THE APPALACHIANS AND THEN LIFTING UP/NEAR THE EASTERN SEABOARD. GIVEN THE UNCERTAINTY OF A DAY 6 FORECAST...WILL NOT ADJUST FORECAST TOO ANY GREAT DEGREE WITH THIS FORECAST PACKAGE. SUFFICE IT TO SAY THAT THE MIDWEEK PERIOD NEXT WEEK DOES APPEAR TO BE RATHER ACTIVE FOR THE AREA AS COMPARED TO THE CURRENT WEATHER REGIME. MARINE... SURFACE HIGH PRESSURE IS FORECASTED TO BUILD INTO THE AREA DURING THE DAY TODAY AND THEN DRIFT EAST ACROSS THE CENTRAL AND EASTERN GREAT LAKES OVER THE WEEKEND. THIS WILL LEAD TO EXCEEDINGLY CALM CONDITIONS FOR THIS TIME OF YEAR...AT LEAST INTO MUCH OF SUNDAY. SOUTHERLY WINDS WILL THEN BEGIN TO INCREASE ON THE BACKSIDE OF THIS HIGH SUNDAY INTO MONDAY. EVEN SO...RATHER AGREEABLE MARINE CONDITIONS ARE EXPECTED INTO EARLY NEXT WEEK AS WINDS/WAVES ONLY INCREASE MARGINALLY WITHIN THIS DEVELOPING SOUTH/SOUTHEAST FLOW. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MICHIGAN WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....SF SHORT TERM...SF 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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