955
FXUS63 KDTX 180923
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
423 AM EST WED DEC 18 2024
KEY MESSAGES
- LIGHT WET SNOW HAS STARTED TO IMPACT THE SAGINAW VALLEY AND THUMB
THIS MORNING, WITH POTENTIAL FOR A RAIN SNOW MIX TO DEVELOP LATER
THIS MORNING ACROSS SOUTHERN PORTIONS OF THE CWA.
- TEMPERATURES IN THE MID 30S THIS MORNING LIMIT SNOW ACCUMULATIONS
TO A SLUSHY COATING ON OBJECTS AND UNPAVED SURFACES UP TO A HALF
INCH.
- ANOTHER 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.
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.
PREV DISCUSSION
ISSUED AT 1200 AM EST WED DEC 18 2024
AVIATION...
LOW LEVEL COLD AIR BELOW A MIDLEVEL INVERSION HAS SUPPORTED
EXTENSIVE MVFR STRATUS AT 2.0 KFT AGL ACROSS LOWER MICHIGAN. WARM
ADVECTION MAY ACT TO BREAKDOWN THE MVFR CLOUD, BUT CONFIDENCE IS LOW
ON TIMING AND HOW WIDESPREAD THE LOSS OF THE LOW CLOUD WILL BE.
UPPER LEVEL DIVERGENCE BROUGHT ON BY RIGHT ENTRANCE REGION JET
DYNAMICS WILL SUPPORT A PERIOD OF LIGHT SNOW MAINLY BETWEEN 12-17Z
WEDNESDAY. THE LIGHT SNOW IS EXPECTED TO BE LIGHT ENOUGH TO SUPPORT
PREVAILING MVFR CONDITIONS. MVFR TO VFR STRATUS WEDNESDAY AFTERNOON
AND EVENING.
FOR DTW...LIGHT SNOW WILL BE POSSIBLE BETWEEN 12-17Z WEDNESDAY. THE
POTENTIAL DOES EXIST FOR MELTING SNOW OR POSSIBLY SOME RAINDROPS TO
MIX IN WITH THE RAIN.
DTW THRESHOLD PROBABILITIES...
* HIGH FOR CEILING AT OR BELOW 5000 FEET THIS EVENING. HIGH
WEDNESDAY.
* HIGH FOR PRECIPITATION TYPE AS WET SNOW TRANSITIONING TO MELTING
SNOW WEDNESDAY MORNING.
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.
DISCUSSION...MV
MARINE.......TF
AVIATION.....CB
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