451
FXUS63 KDTX 172359
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
659 PM EST TUE DEC 17 2024
KEY MESSAGES
- A PATTERN OF LIGHT AND WET SNOW IS ON SCHEDULE TO DEVELOP LATE
TONIGHT INTO WEDNESDAY MORNING WITH TEMPERATURES NEAR FREEZING.
- TEMPERATURES RISE A FEW DEGREES ABOVE FREEZING DURING WEDNESDAY
MORNING LIMITING SNOW ACCUMULATION TO A SLUSHY COATING MAINLY ON
OBJECTS AND UNPAVED SURFACES. A MORE LOCALIZED REGION OF UP TO AN
INCH IS POSSIBLE NEAR THE I-69 CORRIDOR.
- 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.
AVIATION
LOW LEVEL COLD AIR BELOW A MIDLEVEL INVERSION HAS SUPPORTED
EXTENSIVE MVFR STRATUS AT 2.0 KFT AGL ACROSS LOWER MICHIGAN. WARM
ADVECTION IS ANTICIPATED LATE THIS EVENING WHICH WILL 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.
PREV DISCUSSION
ISSUED AT 357 PM EST TUE DEC 17 2024
DISCUSSION...
A CLOUDY BUT DRY AND MILD WEATHER DAY IS UNFOLDING ACROSS LOWER MI
AS ABOVE NORMAL TEMPERATURES REACH FOR HIGHS NEAR 40 MADE TO FEEL
EVEN LESS HARSH AS GUSTY WEST WIND SUBSIDED. THE WIND CONTINUES TO
DIMINISH HEADING INTO THIS EVENING IN THE WEAKENING PRESSURE
GRADIENT ACROSS THE GREAT LAKES AHEAD OF THE NEXT FRONT AND LOW
PRESSURE SYSTEM. CLOUDS AND DRY WEATHER THEN CONTINUE FOR THE BULK OF
TONIGHT IN A TRANSITION TOWARD INFLUENCE FROM THAT SYSTEM EXPECTED
TO ARRIVE WITH LIGHT SNOW JUST GETTING STARTED AROUND SUNRISE.
TRENDS IN THE 17/12Z MODEL CYCLE MAINTAIN LIGHT LIQUID EQUIVALENT
QPF OF GENERALLY LESS THAN 0.10 INCH FOR THIS SNOW EVENT.
ACCUMULATION POTENTIAL IS FURTHER LIMITED BY STILL RELATIVELY WARM
TEMPERATURES JUST SETTLING TO LOWS WITHIN A FEW DEGREES EITHER SIDE
OF FREEZING BY WEDNESDAY MORNING WHICH ARE THEN PROJECTED TO WARM
INTO THE MID 30S BEFORE THE SNOW ENDS EARLY AFTERNOON. MODEL
SOUNDINGS INDICATE THE SURFACE BASED WARM LAYER/FREEZING LEVEL MAKING
A RUN TOWARD THE 1000 FT THRESHOLD FOR RAIN/SNOW MIX BY LATE MORNING
WHILE THE REST OF THE TEMPERATURE PROFILE IS SUFFICIENTLY COLD AND
SATURATED THROUGH THE DGZ. A BRIEF PERIOD OF STRONGER ISENTROPIC
ASCENT WITHIN THE EVENT TIME WINDOW ALREADY ONLY ABOUT 6 HOURS WILL
HELP WITH A BRIEF UPTICK IN RATE AS IT OVERLAPS ADEQUATE MOISTURE
JUDGING BY 850-700 MB SPECIFIC HUMIDITY IN THE RANGE OF 2-3 G/KG
WITHIN THE MOISTURE AXIS. THETA-E GRADIENT ALIGNMENT WITH THE UPPER
JET AXIS ALSO SUGGESTS BRIEF BANDING IS POSSIBLE ON THE MESOSCALE BUT
CONSTRAINED BY A HIGHER STABILITY PROFILE SHOWN IN CROSS SECTIONS.
ALL THIS TO SAY THE GRASSY 1 INCH OR LESS OF WET ACCUMULATION LOOKS
GOOD IN OUR GOING FORECAST.
THE WEDNESDAY GREAT LAKES SHORT WAVE LATCHES ON TO THE COLD FRONT
TRAILING A LARGER LOW PRESSURE SYSTEM IN QUEBEC AND BOTH MOVE EAST OF
LOWER MI WEDNESDAY EVENING. DRY AND COLDER NW FLOW FOLLOWS TO CARRY
TEMPERATURES DOWN INTO THE MID 20S BY THURSDAY MORNING. BROAD AND
STRONG CONFLUENT NW FLOW ALOFT PROMOTES STRONG MID LEVEL SUBSIDENCE AND
SHALLOW BOUNDARY LAYER CONVECTIVE DEPTH DURING THE NIGHT. THIS REDUCES
LAKE EFFECT TO A CLOUD COVER FORECAST AS SURFACE HIGH PRESSURE BRIEFLY
SETTLES OVERHEAD BY THURSDAY MORNING.
THE NEXT SYSTEM EXPECTED IN THE GREAT LAKES THURSDAY NIGHT AND FRIDAY
MOVES ACROSS THE PACIFIC COAST OF CANADA TONIGHT AND ACROSS THE ROCKIES
WEDNESDAY. MODEL TRENDS OVER THE LAST 24 HOURS OF FORECASTS INDICATE
FASTER TIMING OF THE SYSTEM INTO THE NORTHERN PLAINS WEDNESDAY NIGHT
AND UPPER MIDWEST BY THURSDAY, ESPECIALLY IN THE NAM SOLUTIONS. MODEL
VARIATIONS STILL NEED TO BE SORTED OUT REGARDING THE STRENGTH AND TRACK
OF THE SYSTEM, ALTHOUGH CONSENSUS OF THE 17/12Z CYCLE FAVORS A SURFACE
LOW TRACK FROM THE UPPER MIDWEST INTO THE OHIO VALLEY WHICH, IF IT
HOLDS, PLACES SE MI IN THE FAVORABLE "CLIPPER" NORTH FLANK FOR
ACCUMULATING SNOW. THE NORTH FLANK TYPICALLY PROVIDES A LONGER EVENT
CONSISTING OF LEADING MOISTURE TRANSPORT/ISENTROPIC LIFT AND GREATER
EXPOSURE TO POTENTIAL MESOSCALE BANDING ASSOCIATED WITH MID LEVEL
TROWAL OR DEFORMATION FORCING DEPENDING ON THE INTENSITY TREND OF THE
SYSTEM AS IT PASSES THROUGH THE REGION. OVERALL FORECAST CONFIDENCE
REMAINS ON THE UPSWING FOR A WIDESPREAD 1-2 INCH ACCUMULATION ACROSS
CENTRAL AND SE MI, WITH THE USUAL LOCALLY HIGHER MESOSCALE AND/OR LAKE
ENHANCED TOTALS POSSIBLE, UNTIL THE SYSTEM EXITS FRIDAY EVENING.
POLAR HIGH PRESSURE AND INTRUSION OF COLD AIR BECOME THE STORY FOR THE
WEEKEND. GUIDANCE TEMPERATURES DROP BACK DOWN INTO THE 20S BY SATURDAY
WITH SINGLE DIGIT LOWS POSSIBLE SUNDAY MORNING. THE GOOD NEWS IS A
PROGRESSIVE LARGE SCALE UPPER AIR PATTERN INDICATED IN THE LONG RANGE
GLOBAL MODELS THAT SUGGESTS AT LEAST A MODEST TEMPERATURE REBOUND NEXT
WEEK.
MARINE...
DIFFUSE HIGH PRESSURE BUILDS IN ACROSS THE OHIO VALLEY THIS EVENING,
PROMOTING WEAKENING WESTERLY WINDS ACROSS THE CENTRAL GREAT LAKES
TONIGHT INTO WEDNESDAY. A LOW PRESSURE SYSTEM WILL THEN TRACK UP THE
OHIO VALLEY ON WEDNESDAY, AND AT THE SAME TIME A WEAK COLD FRONT
WILL SINK INTO THE GREAT LAKES. THIS BRINGS A CHANCE FOR LIGHT SNOW
THROUGH THE DAY. WINDS BEHIND THE FRONT WILL VEER NORTHWESTERLY AND
INCREASE SLIGHTLY WEDNESDAY NIGHT WITH THE LATEST FORECAST CALLING
FOR WIND SPEEDS MAINLY IN THE 15 TO 25 KNOT RANGE. COLDER AIR WILL
WORK INTO THE REGION AS HIGH PRESSURE SPREADS IN ON THURSDAY,
BRINGING ANOTHER PERIOD OF WEAKER FLOW. A CLIPPER LOW PRESSURE
SYSTEM IS STILL ON TRACK TO TREK FROM THE MIDWEST INTO THE OHIO
VALLEY ON FRIDAY, BRINGING LIKELY WIDESPREAD SNOW. NORTHERLY WIND
WILL INCREASE LATE FRIDAY IN ITS WAKE BUT WILL LIKELY REMAIN BELOW
GALES. COLDER AIR TAKES OVER THROUGH THE WEEKEND WITH A GOOD CHANCE
FOR SNOW SHOWERS OVER THE LAKES.
DTX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
AVIATION.....CB
DISCUSSION...BT
MARINE.......TF
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