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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