612  
FXUS63 KDTX 182304  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
604 PM EST FRI JAN 18 2019  
 
   
AVIATION
 
 
VFR TO OCCASIONAL MVFR CIGS (I-94) WILL HOLD MUCH OF THE EVENING.  
CONDITIONS WILL DETERIORATE AFTER MIDNIGHT TO IFR AS A NARROW BAND  
OF FGEN SUPPORTS LIGHT TO MODERATE SNOW DEVELOPMENT FOR THE REST OF  
THE NIGHT. DEVELOPING NORTHEAST FLOW WILL BE SUFFICIENTLY DRY TO  
LIMIT VSBY REDUCTIONS ACCUMULATION NORTH OF PTK (OTHER THAN PERHAPS  
KMBS WHERE POTENTIAL LAKE ENHANCEMENT WILL BE POSSIBLE IN NE FLOW)  
LULL IN SNOW EXPECTED AS FGEN MOVES OUT OF THE DETROIT AREA SAT  
MORNING BEFORE PRIMARY WAVE GLANCES TO THE SOUTHEAST. CONDITIONS  
WILL TREND BACK TO VFR WITH GUSTY NORTHEAST WIND AS SNOW TAPERS OFF  
DURING SATURDAY AFTERNOON.  
 
FOR DTW...FLOW WILL BACK TO THE NE 00Z-02Z WITH GUSTS TO 20 KNOTS OR  
MORE AS GRADIENT TIGHTENS ON SATURDAY. BIMODAL PEAK INTENSITY 9-12Z  
AND AGAIN 15-18Z FOR SNOW STILL SEEMS REASONABLE GIVE RECENT HIRES  
MODEL RUNS.  
   
DTW THRESHOLD PROBABILITIES
 
 
 
* HIGH FOR CIG AOB 5KFT  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 325 PM EST FRI JAN 18 2019  
 
DISCUSSION...  
 
ROUND OF ACCUMULATING SNOWFALL ON PACE TO TRACK ACROSS SOUTHEAST  
MICHIGAN OVERNIGHT INTO SATURDAY. WINTER WEATHER ADVISORY IN EFFECT  
ALONG/SOUTH OF THE M-59 CORRIDOR.  
 
DEEPER LAYER NORTHWEST FLOW BRIEFLY ENTRENCHED ACROSS SOUTHEAST  
MICHIGAN LATE THIS AFTERNOON, AS THE LOCAL AREA RESIDES IMMEDIATELY  
NORTH OF AN ELEVATED FRONTAL ZONE CURRENTLY DRAPED ACROSS THE  
NORTHERLY OHIO VALLEY. LOW LEVEL FLOW VEERS TO NORTHEASTERLY WITH  
TIME OVERNIGHT, WHILE AN EMERGING CORRIDOR OF ISENTROPIC ASCENT  
DOWNSTREAM OF STRONG HEIGHT FALLS DRAWS THE 850-700 MB FRONTAL SLOPE  
BACK INTO THE REGION. THIS BOUNDARY WILL PROVIDE THE INITIAL FOCUS  
FOR ASCENT TONIGHT, ACTING UPON A LIMITED WINDOW OF FAVORABLE UPPER  
JET SUPPORT AND MODEST MOISTURE ADVECTION WITHIN THE BROADER SYSTEM  
RELATIVE ISENTRIPIC LIFT. THIS WILL SUPPORT THE DEVELOPMENT OF A  
WEST-EAST ELONGATED AXIS OF ACCUMULATING SNOW OVERNIGHT. LATEST MODEL  
GUIDANCE CONTINUES TO PROJECT THE MOST ACTIVE PORTION OF THE FRONT  
BECOMING ALIGNED BETWEEN THE OHIO BORDER AND I-96. OVERALL  
ENVIRONMENT LESS THAN IDEAL FOR A MORE ROBUST FGEN RESPONSE,  
PLACEMENT OF THE STRONGEST FORCING DISPLACED OUTSIDE THE FAVORABLE  
SNOW GROWTH REGION AND A MOIST LAYER BELOW 700 MB CHARACTERIZED BY  
TEMPERATURES WARMER THAN -10C. THIS SUGGESTS THE OVERNIGHT ACTIVITY  
WILL BE DEFINED BY SMALLER FLAKE SIZE AND GENERALLY AVERAGE SNOW  
RATIOS IN THE 9-12:1 RANGE. POTENTIAL FOR SOME DEGREE OF DRYING GIVEN  
THE NORTHEAST FLOW MAY ALSO PROVE A LIMITING FACTOR WITH NORTHWARD  
EXTENT, ALTHOUGH THERE ARE SOME HINTS WITHIN THE HI RES GUIDANCE THAT  
MIXING DEPTH REMAINS SUFFICIENT TO MAINTAIN SOME MOISTURE FLUX OFF  
LAKE HURON.  
 
STRONG DYNAMIC FORCING TIED TO THE EASTWARD PROPAGATING HEIGHT FALL  
CENTER WILL PASS SOUTH OF LOWER MICHIGAN ON SATURDAY, AS THE  
ATTENDANT SURFACE LOW MAINTAINS A TRAJECTORY INVOF THE OHIO RIVER.  
THERE WILL BE A SEVERAL HOUR WINDOW OF DEEPER MID LEVEL FORCING TIED  
TO RENEWED FAVORABLE UPPER JET DYNAMICS AND WEAK CVA IN THE PRESENCE  
OF THE EXISTING BOUNDARY - CENTERED 14Z-18Z SATURDAY. GREATEST  
POTENTIAL EXISTS DURING THIS TIME FOR A PERIOD OF SNOWFALL RATES  
NEAR .5"/HOUR, MAINLY SOUTH OF THE I-96 CORRIDOR. OTHERWISE, EVENT  
CHARACTER WILL BE THAT OF A LONGER DURATION OF LIGHT ACCUMULATING  
SNOW. THE LONGER RESIDENCE TIME AND PROSPECTS FOR A BRIEF PERIOD OF  
HEALTHIER RATES WILL SOLIDIFY HIGHER ACCUMULATION TOTALS FROM METRO  
DETROIT SOUTHWARD. THE PREVAILING NORTHEAST TRAJECTORY MAY OFFER A  
BRIEF LAKE BAND OFF SAGINAW BAY FOR THE TRI-CITIES DURING THIS TIME.  
SNOWFALL TAPERS OFF NORTHWEST TO SOUTHEAST DURING THE AFTERNOON AS  
ASCENT QUICKLY DIMINISHES AND MOISTURE DEPTH SHRINKS. THIS OCCURS AS  
NORTHEAST WINDS MODESTLY STRENGTHEN, LIMITING THE WINDOW FOR A  
GREATER COMPONENT OF BLOWING SNOW.  
 
STRONG COLD AIR ADVECTION ENSUES SATURDAY NIGHT IN THE WAKE OF THIS  
SYSTEM, AS LOW LEVEL FLOW TURNS NORTHERLY BENEATH INCREASING UPPER  
LEVEL TROUGHING. THIS PROCESS COMBINED WITH A FIRM 15-20 MPH WIND  
WILL BRING WIND CHILL SUNDAY MORNING DOWN INTO THE -5 TO -10 RANGE.  
INBOUND ARCTIC AIR CHARACTERIZED BY 850 MB TEMPERATURES OF -20 TO  
-22C THEN TAKES RESIDENCE THROUGH THE REMAINDER OF THE WEEKEND. THE  
OVERALL STRENGTH AND TIMING OF THE ADVECTIVE PROCESS POINTS TO  
LIMITED DIURNAL RECOVERY POTENTIAL ON SUNDAY, LEAVING TEMPERATURES  
PARKED IN THE TEENS THROUGH THE DAY. COLDEST CONDITIONS EXPECTED  
SUNDAY NIGHT, INFLUENCED A DIMINISHING PRESSURE GRADIENT AS SURFACE  
RIDGING BUILDS IN. ASSUMING LAKE STRATUS IS NOT PROBLEMATIC,  
POTENTIAL FOR WIND CHILL TO APPROACH ADVISORY LEVELS /-15/ MONDAY  
MORNING. THE COLD NORTHERLY FLOW OVER THE LONG LAKE HURON FETCH WILL  
ELICIT SOME DEGREE OF A LAKE RESPONSE DURING THIS TIME, BUT THE  
OVERALL SCALE AND VIGOR MAY PROVE LIMITED BY INCREASING DEPTH OF DRY  
AIR WITH TIME. FORECAST CONTINUES TO CALL FOR SOME MINOR  
ACCUMULATION THROUGH THE PERIOD WITHIN THOSE FAVORED LAKE EFFECT  
AREAS ALONG THE EASTERN THUMB.  
 
A SHORT LIVED UPPER LEVEL RIDGE AND HIGH PRESSURE WILL KEEP THE AREA  
DRY ON MONDAY. CHANGES COME BACK INTO PLAY ON TUESDAY, AS ANOTHER  
LOW MOVES UP FROM THE SOUTHWEST. WHILE STILL A FEW DAYS OUT, MODELS  
ARE HINTING AT RAIN/SNOW COMING IN AS SOUTHERLY FLOW LOOKS TO BRING  
IN SOME WARMER AIR. HOWEVER, THE TRACK OF THE SYSTEM WILL LIKELY  
SHIFT AND THUS WILL BE WATCHED AS TIME GETS CLOSER. TEMPERATURES ON  
MONDAY WILL BE THE COLDEST NEXT WEEK, WITH HIGHS ONLY MAKING IT UP  
INTO THE TEENS. AFTER MONDAY, TEMPS START TO REGULATE BACK TO THE  
UPPER 20S TO 30S.  
 
MARINE...  
 
WEAKENING NORTHWEST WINDS TODAY WILL GIVE WAY TO INCREASING  
NORTHEAST WINDS THIS EVENING AS LOW PRESSURE TRACKS WELL SOUTH OF  
THE GREAT LAKES REGION ON SATURDAY. SNOW, ALONG WITH NORTHEAST WINDS  
OF 20 TO 30 KNOTS ARE EXPECTED DURING THE DAY, AS MUCH COLDER AIR  
FILTERS INTO THE REGION OVER THE WEEKEND. BRIEF GUSTS TO  
MARGINAL GALES ARE POSSIBLE OVER WESTERN LAKE ERIE AND SOUTHERN LAKE  
HURON. WINDS WILL REMAIN STRONG INTO SUNDAY AS THEY BACK AROUND TO  
THE NORTH, WITH HEAVY FREEZING SPRAY LIKELY OVER OPEN WATERS OF LAKE  
HURON. COLD AIRMASS WILL PERSIST ON MONDAY, BUT WINDS WILL BECOME  
MUCH LIGHTER AND SHIFT TO THE SOUTHEAST.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...WINTER WEATHER ADVISORY FROM 2 AM TO 4 PM EST SATURDAY FOR  
MIZ068>070-075-076-082-083.  
 
LAKE HURON...HEAVY FREEZING SPRAY WARNING UNTIL 1 AM EST MONDAY FOR LHZ362-363-  
462.  
 
HEAVY FREEZING SPRAY WARNING FROM 7 PM SATURDAY TO 1 AM EST MONDAY  
FOR LHZ442-443-463-464.  
 
HEAVY FREEZING SPRAY WARNING FROM 1 AM SATURDAY TO 1 AM EST MONDAY  
FOR LHZ421-441.  
 
SMALL CRAFT ADVISORY UNTIL 7 AM EST MONDAY FOR LHZ421-441>443.  
 
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY FROM 7 AM SATURDAY TO 10 AM EST SUNDAY FOR  
LEZ444.  
 

 
 

 
 
AVIATION.....DG  
DISCUSSION...MR/SP  
MARINE.......JVC  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT.  
 
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