476  
FXUS63 KDTX 202314  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
614 PM EST SAT DEC 20 2014  
   
AVIATION
 
 
//DISCUSSION...  
 
CEILING HEIGHTS WILL BE HIGHLY VARIABLE THROUGH MUCH OF THE  
FORECAST. UPPER LEVEL WAVE LIFTING ACROSS LOWER MICHIGAN HAS  
PROVIDED ENOUGH SUBSIDENCE TO SCOUR OUT THE MVFR CEILINGS  
IMMEDIATELY IN IT/S WAKE. FARTHER UPSTREAM NEAR LAKE MICHIGAN...MVFR  
CEILINGS REESTABLISH...HOWEVER FARTHER SOUTHWEST THE CEILING LIFTS  
BACK TO ABOVE 5KFT. THE SLOW MOVING CLOUD SHIELDS WILL SPELL  
PERIODS OF SEVERAL HOURS OF EACH VARIETY OF CEILING CONDITION.  
WINDS WILL REMAIN A NON-CONCERN THROUGH THE FORECAST PERIOD.  
 
FOR DTW...CEILING NEAR 3KFT WILL BREAK IN THE NEXT COUPLE OF HOURS.  
EXPECT A RETURN TO SUB 3KFT CEILINGS AND SOME LIGHT FOG AROUND  
MIDNIGHT FOR SEVERAL HOURS...BEFORE GIVING WAY TO UNRESTRICTED  
CEILINGS PRIOR TO DAYBREAK.  
 
//DTW THRESHOLD THREATS...  
 
* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET EARLY THIS EVENING.  
MEDIUM CONFIDENCE OVERNIGHT.  
 

 
   
PREV DISCUSSION
 
ISSUED 324 PM EST SAT DEC 20 2014  
 
SHORT TERM...THIS EVENING AND TONIGHT  
 
A MID LEVEL SHORT WAVE IMPULSE SHOWN ROTATING ACROSS INDIANA ON  
THE LATEST WATER VAPOR LOOP WILL TRACK INTO OHIO THIS EVENING...  
SPREADING MID LEVEL HEIGHT FALLS ACROSS SE MI. DESPITE SOME WEAK  
RADAR RETURNS OVER NW INDIANA/SW MI THIS AFTERNOON...A WEDGE OF  
EXTREMELY DRY AIR IN THE 900-800MB LAYER OVER SE MI AND OVERALL  
WEAK NATURE OF THE LARGE SCALE ASCENT WILL SUPPORT THE CURRENT DRY  
FORECAST THIS EVENING. MID AND HIGH CLOUDS WILL HOWEVER CONTINUE  
TO INCREASE DURING THE REMAINDER OF THE AFTERNOON AND EVENING.  
THESE HIGHER BASED CLOUDS WILL DEPART TO THE NORTH AND EAST  
OVERNIGHT AS THE SHORT WAVE SLIDES INTO PENNSYLVANIA.  
 
THERE WILL BE SOME WEAK COLD AIR ADVECTION NEAR 850MB TONIGHT. THIS  
IS NOT EXPECTED TO BE ENOUGH TO ERODE THE DEEP LOW LEVEL INVERSION  
OVER THE AREA. WHILE THE LOSS OF A DIURNAL COMPONENT MAY LEAD TO  
SOME DECREASE IN THE LOW CLOUD COVERAGE THIS EVENING...THE  
DEVELOPMENT OF A LIGHT W-SW LOW LEVEL FLOW OVERNIGHT WILL CAUSE SOME  
OF THE LOW CLOUDS ACROSS WRN LOW MI TO SLIDE INTO THE FORECAST AREA  
UNDER THIS INVERSION. THE EXPECTED CLOUD COVERAGE AND NEAR NEUTRAL  
SUB 925MB THERMAL ADVECTION TONIGHT WILL SUPPORT MIN TEMPS ON THE  
WARM SIDE OF MOS /MID TO UPPER 20S/. THE POTENTIAL FOR A BRIEF  
PERIOD OF CLEAR SKIES IN THE SAGINAW VALLEY AND THUMB WILL HOWEVER  
SUPPORT FCST MIN TEMPS DOWN INTO THE UPPER TEENS/LOW 20S.  
 
LONG TERM...SUNDAY THROUGH NEXT FRIDAY  
 
THE EXTENDED PERIOD STARTS OFF QUIET BUT LATER IN THE WEEK A PAIR OF  
LOW PRESSURE SYSTEMS LOOK TO TARGET THE REGION AS STRONG JET LEVEL  
ENERGY WORKS ACROSS THE COUNTRY. A 160+ KNOT JET IS BEGINNING TO  
MOVE ASHORE OVER THE FAR NW CONUS TODAY WHICH WILL DEVELOP A TROUGH  
OVER THE CENTRAL CONUS SUNDAY AND THEN AMPLIFY IT THROUGH THE  
BEGINNING OF THE WORK WEEK.  
 
SFC RIDGE WILL BE HOLDING OVER THE AREA ON SUNDAY AS AN UPPER LEVEL  
TROUGH EXITS THE AREA. THIS WILL USHER THE COLDEST AIR ALOFT TO THE  
NE BUT 500MB TEMPS STILL REMAIN LESS THAN -20C WITH 850MB TEMPS  
AROUND -3C. STILL EXPECT PLENTY OF CLOUDS AROUND AS SEVERAL UPPER  
LEVEL LOWS DRIFT THROUGH THE NORTHERN PLAINS AND SOUTHERN GREAT  
LAKES. WILL BE PESSIMISTIC WITH MOSTLY CLOUDY SKIES UNTIL  
OBS/SATELLITE SUGGEST SOME THINNING/CLEARING. BY SUNDAY  
AFTERNOON...THE SFC HIGH WILL DRIFT FAR ENOUGH EAST TO ALLOW  
SOUTHERLY FLOW TO RETURN TO THE AREA. BEFORE THE UPPER LEVELS DEEPEN  
TOO MUCH...CYCLOGENESIS WILL BEGIN OVER THE NORTHERN PLAINS  
DEVELOPING AN AREA OF LOW PRESSURE AT THE SFC OVER THE NORTHERN  
PLAINS LATE SUNDAY AND OVERNIGHT. UPPER LEVEL SHORTWAVE WILL SWING  
THROUGH THE STILL LOW AMPLITUDE TROUGH AND LIFT NE THROUGH WI. THIS  
WILL OPEN THE DOOR FOR SW FLOW TO COMMENCE THROUGHOUT THE COLUMN.  
THE INITIAL BAND OF WEAK ISENTROPIC LIFT ON THE ELEVATED FRONT WAS  
SUGGESTING SOME LIGHT PRECIP OVERNIGHT SUNDAY BUT MODELS CONTINUE TO  
HOLD THIS RIBBON OF MOISTURE FURTHER WEST AND A DRIER BL OVER SE MI  
THUS POPS WERE REMOVES SUNDAY NIGHT.  
 
THIS INITIAL SFC LOW REMAINS FAIRLY UNORGANIZED THROUGH MONDAY AS  
THE UPPER LEVEL TROUGH STILL DIGS DEEPER INTO THE GULF COAST STATES  
AND SEVERAL SHORT WAVES TRAVERSING THROUGH IT. INSTEAD OF SHOWING  
SIGNS OF STRENGTHENING...THE CENTER OF THE LOW MEANDERS SOME AS IT  
SEARCHES OUT THE STRONGER PRESSURE FALLS. DURING THE OVERNIGHT THE  
UPPER LEVEL TROUGH REALLY COMES TOGETHER SPARKING STRONGER  
CYCLOGENESIS FURTHER SOUTH ALONG THE BAROCLINIC ZONE. THIS ALLOWS  
THE DEEPER RIBBON OF MOISTURE TO DRIFT EAST OVER CENTRAL LOWER MI  
BEHIND THE ELEVATED OCCLUDED FRONT. WITH WAA THROUGHOUT THE DAY  
MONDAY...THERMAL PROFILE WILL BE ABOVE 0C FROM THE SFC TO 700MB  
WHICH WOULD RESULT IN PURE RAIN SHOWERS WITH LOW TEMPS IN THE  
MID/UPPER 30S.  
 
STORY FOR THE EXTENDED WILL BE THE DYNAMICALLY EVOLVING LOW PRESSURE  
SYSTEM SET TO IMPACT THE EASTERN THIRD OF THE CONUS TUESDAY THROUGH  
CHRISTMAS. WITH TEMPERATURES ABOVE FREEZING FOR MOST OF THE  
EVENT...SNOW WILL BE A SECONDARY OR TERTIARY IMPACT OF THE EVENT.  
FOR SOUTHEAST MICHIGAN...HIGH WINDS WILL BE THE MAIN IMPACT. A TIGHT  
SURFACE PRESSURE GRADIENT WILL BRING SWIFT WARM ADVECTION PROCESSES  
TO THE AREA AS PRESSURE RAPIDLY DROPS 12 MB PER 12 HOURS. 850 MB  
TEMPS ALSO MAKE STRONG SWINGS AS THEY INCREASE TO 8-10C WED  
AFTERNOON...THEN QUICKLY DROP TO -5C THU MORNING. THE STRONG COLD  
ADVECTION WILL HELP INCREASE WIND SPEEDS TO GUST NEAR 30 MPH ON  
CHRISTMAS. CAA WILL ALSO SWITCH PRECIP TYPE TO ALL SNOW WED EVENING.  
FROM THAT POINT ON...QPF DROPS TO A TENTH OF AN INCH OR SO...WITH  
STRONG WINDS AND MARINE INTERESTS TAKING THE FORECAST ATTENTION.  
MODEL SOLUTIONS ARE NOT IN AGREEMENT WITH STRENGTH OR PLACEMENT OF  
THE LOW...SO LOOK FOR FUTURE UPDATES ON STORM TRACK.  
 
MARINE...  
 
LIGHT WINDS WILL CONTINUE ACROSS THE MARINE AREAS THROUGH THE  
REMAINDER OF THE WEEKEND. LOW PRESSURE WILL DEVELOP AND DEEPEN OVER  
THE CENTRAL US SUNDAY NIGHT INTO MONDAY. THIS WILL LEAD TO THE  
DEVELOPMENT AND SLIGHT INCREASE IN SOUTH-SOUTHEAST WINDS THROUGH  
THIS PERIOD. SECONDARY SURFACE LOW DEVELOPMENT IS FORECAST ACROSS  
THE GULF COAST ON TUESDAY...WITH THE LOW FORECAST TO RAPIDLY  
INTENSIFY AS IT LIFTS NORTH ACROSS THE GREAT LAKES REGION WEDNESDAY.  
THIS SYSTEM HAS THE POTENTIAL TO PRODUCE GALES WEDNESDAY NIGHT AND  
THURSDAY.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LAKE HURON...NONE.  
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...NONE.  

 
 

 
 
AVIATION.....MANN  
SHORT TERM...SC  
LONG TERM....DRK/MM  
MARINE.......SC  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).  
 
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