112  
FXUS63 KDTX 111050  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
550 AM EST MON DEC 11 2017  
 
   
AVIATION
 
 
CEILINGS SHOULD HOVER IN 3-4KFT RANGE THIS MORNING AND LOWER THIS  
AFTERNOON AS FIRST PATCH OF LIGHT SNOW SPREADS OVER AREA WITHIN LEAD  
AREA OF ISENTROPIC LIFT. LIGHT/VARIABLE WINDS TO BECOME LIGHT SOUTH.  
SNOW WILL PEAK THIS EVENING AS FGEN FORCING INCREASE WITH PASSAGE OF  
THIS SYSTEM. DIFFICULT FORECAST TO PLACE NARROW BAND OF STRONGEST  
FGEN, BUT LOOKS TO BE IN THE KFNT/KPTK AREA 00Z-06Z WITH SLIGHTLY  
LIGHTER SNOW ON EITHER SIDE. STILL, IFR VSBYS CAN BE EXPECTED ACROSS  
AREA WITH IFR OR BORDERLINE IFR CIGS. COLD FRONT WILL SWEEP THE SNOW  
OUT OF AREA 07-09Z, WITH GUSTY NW FLOW TO 30 KNOTS OR SO DEVELOPING  
IN ITS WAKE LATE TONIGHT. CIGS WILL LIFT BACK TO MVFR/LOWER VFR  
WITHIN THIS DRIER NW FLOW.  
 
FOR DTW...PERIOD OF -SN TO DEVELOP AROUND 17Z WITH POTENTIAL FOR  
HEAVIER SNOW BAND IN THE 00Z-01Z TIME FRAME. AT THIS TIME, THIS BEST  
FGEN BANDING APPEARS MORE LIKELY JUST NORTH OF THE TERMINAL, BUT IT  
WILL BE VERY CLOSE. GENERALLY EXPECT MVFR CONDITIONS BY MIDDAY WITH  
FIRST BATCH OF -SN WITH IFR VSBYS NEAR IFR CIGS THIS EVENING WITH  
BETTER SNOW RATES. GUSTY NW WINDS TO 30 KNOTS AND BY AROUND 09Z WITH  
COLD FROPA.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* HIGH CONFIDENCE FOR CEILINGS BELOW 5000 FEET THROUGH TONIGHT,  
LOWER ON TUESDAY.  
 
* HIGH CONFIDENCE IN PRECIP TYPE BEING SNOW THIS FORECAST.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 255 AM EST MON DEC 11 2017  
 
DISCUSSION...  
 
CHALLENGING FORECAST AS PHASING/MERGING 6 HR HEIGHT FALLS TAKES  
PLACE OVER THE CENTRAL/EASTERN GREAT LAKES THIS EVENING/TONIGHT.  
LEAD SYMMETRIC UPPER WAVE CLEARLY SEEN ON WATER VAPOR IMAGERY  
TRACKING THROUGH EASTERN NORTH DAKOTA, WITH FULL HEAD OF THE STEAM  
TOWARD THE SOUTHEAST. MEANWHILE, STRONG PV ANOMALY DESCENDING FROM  
WESTERN HUDSON BAY/NORTHERN MANITOBA, WITH TROUGH AXIS DROPPING INTO  
WESTERN GREAT LAKES EARLY THIS EVENING, HELPING TO DRAW THE LEAD  
WAVE OVER THE WESTERN OHIO VALLEY THIS AFTERNOON NORTHEAST. STILL  
CONFLICTING SIGNALS IN THE VARIOUS MODELS ON WHICH FGEN BAND WILL BE  
MOST ACTIVE THIS EVENING. THE LOW LEVEL ONE TOWARD THE OHIO BORDER  
OR THE MID LEVEL FGEN FARTHER NORTH TOWARD THE I-69 CORRIDOR. 12Z  
EURO ENSEMBLE MEMBERS ALSO EXHIBITED/REVEALED THIS HIGH VARIABILITY  
WITH RESPECT TO THE MAX QPF AXIS PLACEMENT AS WELL. AS POINTED OUT  
BY DAY SHIFT, THE LONGER THE TWO SYSTEMS STAY SEPARATE, THE BETTER  
CHANCE THE SNOW AXIS WILL RESIDE FARTHER SOUTH, NEAR OHIO BORDER  
(SEE ARW/NMM), BUT IF PHASING OCCURS SOONER AND LOW DEEPENS RAPIDLY,  
BETTER CHANCE THE HIGHER SNOW AXIS WILL BE FARTHER NORTH, ALONG AND  
POSSIBILITY NORTH OF THE I-69 CORRIDOR (SEE 00Z NAM/GFS). FIRST  
THINGS FIRST TODAY, LEAD ISENTROPIC ASCENT/WARM ADVECTION/MOISTURE  
ADVECTION (2.5 G/KG OF SPECIFIC HUMIDITY AT 700 MB) TO LIFT THROUGH  
SOUTHEAST MICHIGAN DURING THE DAY (AROUND NOON), WHICH SHOULD BE  
SUFFICIENT FOR UP TO 1 INCH OF SNOW, AS WARMING THERMAL PROFILES IN  
THE 850-700 MB LAYER DIMINISHES THE SNOW TO LIQUID RATIOS TO  
TRADITIONAL 12:1. MORE INTENSE SNOWFALL RATES ARRIVING THIS EVENING  
WITH MID LEVEL FGEN FLAREUP, AND BRIEF DEFORMATION BEFORE SYSTEM  
HEADS OFF INTO THE EASTERN GREAT LAKES. THE 00Z REGIONAL GEM SPREADS  
THE QPF OUT A BIT MORE DURING THE EVENING, AS TROWAL/700 MB THETA-E  
AXIS SINKS SOUTHEASTWARD AS IT PULLS AWAY, WITH THE AGGRESSIVE DRY  
ARCTIC AIR ARRIVING BETWEEN 7-12Z. AS FAR AS SNOWFALL AMOUNTS GO,  
INCLUDING THE LIGHT SNOW FROM THE DAYTIME HOURS, 1-4 INCH TOTALS  
STILL SEEM REASONABLE, AND WILL FAVOR THE EURO SOLUTION HIGHLIGHTING  
THE MIDDLE TIER (M-59/I-69) COUNTIES WITH HIGHEST TOTALS. THIS  
SCENARIO ALSO HAS SUPPORT FROM THE 6Z RAP13 THROUGH 3Z TUESDAY. AN  
ADVISORY MAY BE NEEDED AS 3 INCHES IN SIX HOURS IS POSSIBLE, BUT DUE  
TO UNCERTAINTY WITH THE EXACT PLACEMENT AND BULK OF ACTIVITY NOW  
LOOKING TO COME JUST AFTER THE EVENING COMMUTE, WILL DEFER TO DAY  
SHIFT TO PULL THE TRIGGER IF NEED BE. AS STATED EARLIER, QUICKER  
PHASING/DEEPENING WOULD TEND TO PUT THE THUMB UNDER THE GUN FOR  
HIGHER AMOUNTS TONIGHT, BUT IT APPEARS THE SYSTEM WILL COME TOGETHER  
JUST A BIT TOO LATE TO EXPECT MUCH MORE THAN 4 INCHES. PERHAPS MORE  
CONCERNING IS THE POSSIBILITY OF INTENSE LAKE HURON BAND(S) ON  
TUESDAY BACKING/GLANCING THE NORTHERN TIP OF THE THUMB REGION FROM  
PORT AUSTIN TO HARBOR BEACH AREA. BASED OFF 00Z NAM 925 MB  
LIFT/CONVERGENCE, GOING TO BE A REAL CLOSE CALL, AND CERTAINLY WILL  
BE HIGHLIGHTING THE POTENTIAL FOR ACCUMULATING SNOW ALONG THE  
EASTERN SHORELINE IN HWO.  
 
FOR REST OF SOUTHEAST MICHIGAN, FLURRIES/SCATTERED LIGHT SNOW  
SHOWERS, WIND, AND COLD WILL BE THE STORY FOR TUESDAY AS 850 MB FALL  
INTO THE -18 TO -20 C RANGE. PROBABILISTIC GUIDANCE SUGGEST WIND  
GUSTS IN EXCESS OF 30 MPH, SUPPORTED BY 16-20 MB 6 HR RISE/FALL  
PRESSURE COUPLET TRACKING THROUGH EARLY TUESDAY.  
 
ALTHOUGH PARTIAL CLEARING IS LIKELY TUESDAY NIGHT, WITH THE AIRMASS  
BEING SO COLD, A FEW FLURRIES WILL LIKELY BE AROUND WITH ANY  
LINGERING 925 MB MOISTURE AROUND. WINDS COMING AROUND TO THE WEST  
WITH WARM ADVECTION PUSH LATE WEDNESDAY MAY BE SUFFICIENT FOR LIGHT  
SNOW, BUT INDICATIONS IS BULK OF THE SNOW WITH CLIPPER SYSTEM WILL  
BE PASSING SOUTH OF THE STATE WEDNESDAY NIGHT. STILL PLENTY OF  
OPPORTUNITIES FOR ADDITIONAL SNOW LATE IN THE WORK WEEK INTO THE  
WEEKEND AS ACTIVE BAROCLINIC ZONE LOOKS TO BE STRADDLING THE GREAT  
LAKES REGION WITH TEMPERATURES RESIDING FAIRLY CLOSE TO NORMAL  
VALUES.  
 
MARINE...  
 
SOUTHERLY WINDS WILL GRADUALLY INCREASE TODAY AND VEER TO THE  
SOUTHWEST IN ADVANCE OF APPROACHING COLD FRONT THIS EVENING. THE  
COLD FRONT IS QUITE STRONG AND WILL BRING MUCH COLDER AIR OVER THE  
LAKE, LEADING TO UNSTABLE CONDITIONS. WILL BE UPGRADING THE GALE  
WATCH TO A WARNING WITH SUSTAINED WINDS PEAKING NEAR GALE FORCE ON  
TUESDAY MORNING WITH GUSTS PUSHING 45 KNOTS AT TIMES. GALES WILL  
ARRIVE RATHER ABRUPTLY LATE TONIGHT IN THE WAKE OF THIS FRONT AND  
PERSIST INTO TUESDAY EVENING BEFORE SUBSIDING SOMEWHAT.  
 
THE COMBINATION OF THESE GUSTY WINDS, VERY COLD AIR AND FREQUEST  
WAVE HEIGHTS IN EXCESS OF 10 FEET WILL LEAD TO AREAS OF FREEZING  
SPRAY AS WELL ALLOW CONDITIONS SUGGEST MOST OF THIS SPRAY WILL HOLD  
IN THE MODERATE CATEGORY SO NO WARNING IS ANTICIPATED. THE HIGHEST  
WAVES MAY REACH 20 FEET OVER SO BY MIDDAY TUESDAY. AT THAT TIME,  
SNOW SQUALL ACTIVITY WILL ALSO BEGIN TO CONSOLIDATE OVER THE  
SOUTHERN BASIN OF LAKE HURON.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LAKE HURON...GALE WARNING FROM 2 AM TUESDAY TO 5 AM EST WEDNESDAY FOR LHZ362-363-  
462>464.  
 
GALE WARNING FROM 4 AM TUESDAY TO 4 AM EST WEDNESDAY FOR LHZ421-  
441>443.  
 
GALE WARNING FROM 1 AM TO 11 PM EST TUESDAY FOR LHZ361.  
 
GALE WARNING FROM 4 AM TO 4 PM EST TUESDAY FOR LHZ422.  
 
LAKE ST CLAIR...SMALL CRAFT ADVISORY FROM 3 AM TO 11 PM EST TUESDAY FOR LCZ460.  
 
MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY FROM 3 AM TO 11 PM EST TUESDAY FOR LEZ444.  
 

 
 

 
 
AVIATION.....DG  
DISCUSSION...SF  
MARINE.......DG  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT.  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MI Page Main Text Page