779
FXUS63 KDTX 181448
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
948 AM EST WED DEC 18 2024
KEY MESSAGES
- LIGHT WET SNOW ENDS WEST TO EAST BY EARLY AFTERNOON LEAVING CLOUDS
AND A STRAY SNOW SHOWER THROUGH THIS EVENING.
- TEMPERATURES IN THE MID 30S LIMIT SNOW ACCUMULATIONS TO A SLUSHY
COATING ON OBJECTS AND UNPAVED SURFACES.
- A LARGER AND STRONGER LOW PRESSURE SYSTEM BRINGS POTENTIAL FOR
MORE WIDESPREAD ACCUMULATING SNOW STARTING LATE THURSDAY AND
CONTINUING THROUGH FRIDAY.
- MUCH COLDER CONDITIONS ARE EXPECTED FOR THE WEEKEND.
UPDATE
THE SNOW EVENT FOR TODAY IS PROCEEDING SLIGHTLY AHEAD OF SCHEDULE
AND IN LINE WITH INTENSITY EXPECTATIONS. IT HAS SET UP INTO LIGHT
STRIATED BANDS WITH A NARROW CORRIDOR OF GREATER INTENSITY REDUCING
VISIBILITY TO AROUND 1 MILE. SURFACE T/TD/TW ARE GENERALLY HOLDING
AT OR ABOVE FREEZING LEADING TO JUST A MELTING SNOW ON PAVED
SURFACES AND A HINT OF WET ACCUMULATION ON GRASSY SURFACES. THE
GOVERNING SHORT WAVE AND UPPER JET SHEAR EASTWARD AND CARRY THIS
PATTERN OUT OF SE MI SHORTLY AFTER THE NOON HOUR, SLIGHTLY AHEAD OF
SCHEDULE. CLOUDS ARE LEFT BEHIND FOR THE REMAINDER OF THE AFTERNOON
AND A STRAY SNOW SHOWER BECOMES POSSIBLE BY EVENING. THERE IS BRIEF
LAKE EFFECT ACTIVATION AS NW LOW LEVEL FLOW DEEPENS COLD AIR ACROSS
THE GREAT LAKES UNTIL LARGER SCALE SUBSIDENCE SHALLOWS CONVECTIVE
DEPTH TOWARD MIDNIGHT.
PREV DISCUSSION
ISSUED AT 626 AM EST WED DEC 18 2024
AVIATION...
MODEST INCREASE IN MOISTURE DEPTH WILL MAINTAIN A SHORT WINDOW FOR
SOME POCKETS OF LIGHT SNOW, POSSIBLY MIXED WITH RAIN, TO DEVELOP
THROUGH THE MID-LATE MORNING HOURS. UPSTREAM OBSERVATIONAL TRENDS
GENERALLY LEND TOWARD MAINTAIN MVFR CONDITIONS AS THIS PROCESS
UNFOLDS. OTHERWISE, EXTENSIVE LOW STRATUS REMAINS ENTRENCHED THROUGH
THE PERIOD WITHIN MODEST WEST-NORTHWEST FLOW. PROBABILITY FOR SOME
IMPROVEMENT IN CLOUD BASE WILL INCREASE LATE TODAY OR INTO THE
EVENING, ALLOWING RECOVERY INTO VFR DURING THIS TIME.
FOR DTW...POTENTIAL FOR A MIX OF LIGHT/MELTING SNOW AND RAIN REMAINS
POSSIBLE THIS MORNING.
DTW THRESHOLD PROBABILITIES...
* HIGH FOR CEILING AT OR BELOW 5000 FEET THIS EVENING. HIGH
WEDNESDAY.
* HIGH FOR PRECIPITATION TYPE A MIX OF RAIN AND MELTING SNOW.
PREV DISCUSSION...
ISSUED AT 423 AM EST WED DEC 18 2024
DISCUSSION...
LIGHT SNOW HAS STARTED TO FILL IN ACROSS THE SAGINAW VALLEY AND
THUMB REGIONS THIS MORNING AS A RESULT OF AN ELEVATED RESPONSE TO H7
FRONTOGENESIS. HAVE SEEN A GENERAL WEAKENING TREND TO THIS BAND
UPSTREAM, AND A LOT OF WHAT IS SHOWING UP ON KGRR/KDTX RADAR RIGHT
NOW IS VIRGA. NONETHELESS, AS THIS BAND SNOWS INTO DRIER AIR BELOW
SHOULD SEE A PERIOD OF LIGHT SNOW THIS MORNING. WHILE CURRENT
TEMPERATURE READINGS ARE IN THE MID 30S, WET BULBING MAY ALLOW MINOR
ACCUMULATIONS UP TO A HALF INCH EARLY ON BEFORE TEMPERATURES REBOUND
ABOVE FREEZING THIS AFTERNOON. WILL SEE SNOW TAPER OFF THIS
AFTERNOON AS THE PARENT TROUGH DROPS SOUTHEAST. DAYTIME HIGHS SETTLE
IN THE MID TO UPPER 30S WITH CLOUDS STICKING AROUND EVEN AS SNOW
COMES TO AN END.
A MORE ORGANIZED OPPORTUNITY FOR ACCUMULATING SNOW ARRIVES THURSDAY
NIGHT-FRIDAY AS A WEAKENING CLIPPER SYSTEM DIVES INTO THE GREAT
LAKES. TWO PHASES OF THIS SYSTEM WILL EXIST, THE FIRST PHASE BEING A
LEAD ARM OF ISENTROPIC ASCENT/WARM ADVECTION THAT WILL HAVE GREATEST
MOISTURE DEPTHS NORTH OF I-96. BROAD AND STEADY ASCENT RESULTS IN
LIGHT ACCUMULATING SNOW EXPANDING WEST TO EAST ACROSS THE NORTHERN
HALF OF THE CWA LATE THURSDAY AFTERNOON. SOUTHERLY FLOW AHEAD OF THE
CLIPPER WILL MAINTAIN A FEED OF DRY LOW LEVEL AIR INTO THE METRO
DETROIT AREA, WHICH WILL LIMIT ACCUMULATION POTENTIAL ACROSS THE
SOUTH FOR MOST OF THURSDAY EVENING. THE SECOND PHASE OF THIS SYSTEM
RESULTS IN A BROADER AREA OF SNOW EXPANDING ACROSS ALL OF SE
MICHIGAN AFTER 06Z (1AM FRIDAY) IN RESPONSE TO THE APPROACHING
SURFACE LOW AND VORT MAX. THE BULK OF 00Z AND 06Z GUIDANCE BRINGS
THE SURFACE LOW ACROSS SOUTHERN LAKE MICHIGAN EARLY FRIDAY MORNING,
WITH CORRESPONDING H8 AND H7 CIRCULATIONS TRACKING RIGHT ACROSS SE
MICHIGAN. COMBINATION OF MOISTURE FLUX OFF OF LAKE MICHIGAN AND
FOCUSED ASCENT SATURATE THE COLUMN ENOUGH TO COMPENSATE FOR
DWINDLING PURE SYNOPTIC MOISTURE. THIS KICKS OFF A MORE MEANINGFUL
PERIOD OF ACCUMULATING SNOW THAT WILL PEAK AROUND THE MORNING
COMMUTE, WITH APPROXIMATELY 1-3" OF NEW SNOW ACCUMULATION POSSIBLE
BY 18Z FRIDAY. THERE ARE SOME OUTLIER SOLUTIONS (18.03Z RAP AND
18.00Z HRRR) THAT KEEP THE SURFACE LOW MUCH FURTHER NORTH (OVER THE
UPPER PENINSULA OF MICHIGAN), WHICH COULD BE A FAILURE POINT OF THIS
FORECAST. THIS TREND WILL NEED TO MONITORED IN SUBSEQUENT MODEL
CYCLES.
AS THE SURFACE LOW SLIDES SOUTHEAST OF THE STATE LINE, COLD
NORTHERLY FLOW WILL ACTIVATE THE LAKE AGGREGATE AND PRODUCE A LAKE
EFFECT RESPONSE OVER LAKE HURON. GIVEN THE OVERALL PROGRESSIVE
MOTION OF THE SYSTEM AND SUBTLE BACKING TREND TO THE LOW LEVEL WIND
FIELD, ANY BANDING THAT DOES FORM WOULD DRIFT OFFSHORE FRIDAY
EVENING. NONETHELESS, THIS COULD LEAD TO LOCALLY ENHANCED SNOWFALL
TOTALS (4+ INCHES) ALONG THE LAKE HURON SHORELINE.
A COLDER PERIOD OF TEMPERATURES ARRIVES FOR THE WEEKEND AS FRIDAY'S
CLIPPER SYSTEM DIVES TOWARD THE MID-ATLANTIC COAST. DAYTIME HIGHS
WILL ONLY BE IN THE LOW TO MID 20S WHILE OVERNIGHT LOWS EXHIBIT
LARGER VARIANCE IN THE LONG RANGE ENSEMBLE DATA. THE COLDEST
FORECAST LOWS THIS WEEKEND LIE WITHIN THE GEPS DATASET, WHERE THERE
IS HEALTHY SNOWPACK AND MINIMAL CLOUD COVER TO SUPPORT IDEAL
RADIATIONAL COOLING CONDITIONS AND LOWS IN THE SINGLE DIGITS. EVEN
THE MORE "MILD" ENS/GEFS SOLUTIONS HOWEVER STILL HAVE MEAN LOW
TEMPERATURES IN THE TEENS, SO EXPECT COLD MORNINGS SATURDAY THROUGH
MONDAY. LAKE EFFECT SNOW SHOWERS MAY LINGER SATURDAY MORNING, BUT
OTHERWISE STRONG SUBSIDENCE ALOFT AND A SURGE OF DRY LOW LEVEL AIR
WILL LEAVE ONLY A SHALLOW LAYER OF MOISTURE TO WORK WITH OUTSIDE OF
THE LAKESHORES.
MARINE...
A COLD FRONT EASES ACROSS THE CENTRAL GREAT LAKES TODAY, BRINGING A
LIKELY CHANCE OF LIGHT SNOW AND RAIN. LIGHT WESTERLY WINDS THROUGH
MOST OF THE DAY WILL BEGIN TO INCREASE AND VEER TO THE NORTHWEST
THIS EVENING AS THE FRONT DEPARTS. WIND SPEEDS WILL REACH THE 15 TO
25 KNOT RANGE, SENDING AN INCREASING WAVE FIELD ACROSS CENTRAL AND
SOUTHERN LAKE HURON. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE
NEARSHORE WATERS AROUND THE THUMB TONIGHT INTO THURSDAY MORNING FOR
THESE HIGHER WAVES. WINDS AND WAVES WILL DECREASE ON THURSDAY AS
HIGH PRESSURE BUILDS INTO THE REGION. FLOW FLIPS TO EASTERLY LATE
THURSDAY INTO EARLY FRIDAY AS A CLIPPER SYSTEM APPROACHES THE REGION
FROM THE MIDWEST, THEN BACKS TO NORTHERLY FRIDAY AFTERNOON AS THE
SYSTEM PASSES THROUGH THE OHIO VALLEY. THIS SYSTEM BRINGS LIKELY
WIDESPREAD SNOW AND WILL ALLOW A COLDER AIR MASS TO WORK INTO THE
REGION THROUGH THE WEEKEND. AT THIS TIME WINDS LOOK TO REMAIN BELOW
HEADLINE CRITERIA BUT ADDITIONAL SMALL CRAFT ADVISORIES WILL BE
LIKELY AROUND THE THUMB LATE FRIDAY INTO SATURDAY AS THE NORTHERLY
WIND SENDS BUILDING WAVES SOUTHWARD.
DTX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST THURSDAY
FOR LHZ421-441-442.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
UPDATE.......BT
AVIATION.....MR
DISCUSSION...MV
MARINE.......TF
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