940
FXUS63 KDTX 152058
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
358 PM EST WED JAN 15 2025
KEY MESSAGES
- LIGHT SNOW WORKS ACROSS THE AREA BETWEEN 1AM AND 1PM THURSDAY.
ACCUMULATIONS BETWEEN A HALF INCH TO 2 INCHES POSSIBLE. HIGHEST
AMOUNTS ARE EXPECTED IN THE THUMB.
- INCREASING CHANCES FOR PRECIPITATION EARLY SATURDAY, WITH AT LEAST
MINOR SNOW ACCUMULATIONS POSSIBLE FOR PORTIONS OF SE MICHIGAN.
THERE IS STILL UNCERTAINTY IF SOME AREAS WILL SEE A RAIN-SNOW MIX
WITH THIS SYSTEM.
- ARCTIC AIR IS EXPECTED ACROSS SOUTHEAST MICHIGAN MONDAY THROUGH
WEDNESDAY.
- OVERNIGHT LOWS WILL DROP BELOW ZERO DEGREES WITH WIND CHILLS TO -
15 F OR LOWER EACH MORNING. HIGH TEMPERATURES WILL STRUGGLE TO
CLIMB ABOVE ZERO DEGREES.
DISCUSSION
THINNING STRATOCUMULUS AND FLURRY ACTIVITY WILL DWINDLE THROUGH THE
REMAINDER OF THE AFTERNOON IN FAVOR OF THE DRIER AIRMASS THAT
BRIEFLY TAKES RESIDENCE THIS EVENING. FOR AREAS THAT RECEIVED A
BOOST FROM SOLAR INSOLATION, HIGH TEMPERATURES WERE ABLE TO BREAK
INTO THE MID 20S TODAY. EVEN THESE WARMER READINGS STILL FALL SHORT
OF NORMAL HIGHS BY ABOUT 5 TO 7 DEGREES. CLEAR SKIES CARRY INTO THE
LATE EVENING, WITH THE PRESENT SNOWPACK AND CLOUD-FREE TROPOSPHERE
AFFORDING PEAK RADIATIONAL COOLING CONDITIONS. OVERNIGHT LOW
TEMPERATURES ARE EXPECTED TO OCCUR BEFORE MIDNIGHT (WELL BEFORE THE
DIURNAL MINIMUM) AS CLOUD COVER FILLS IN SHORTLY THEREAFTER,
INSOLATING SURFACE TEMPERATURES FOR THE REMAINDER OF THE NIGHT. SOME
SPOTS MAY DIP INTO THE SINGLE DIGITS WHILE MOST SEEN LOW TEMPS IN
THE LOW TEENS BEFORE REBOUNDING INTO THE MID TEENS BY DAYBREAK.
ANOTHER GLANCING OPPORTUNITY FOR WIDESPREAD LIGHT SNOW OCCURS LATE
TONIGHT-THURSDAY AS A CLIPPER SYSTEM DIVES INTO THE GREAT LAKES
REGION. THIS SYSTEM WILL ADVECT MOISTURE INTO A PRE-EXISTING LOW
LEVEL ISENTROPIC SLOPE, AND WHILE RADAR RETURNS MAY INITIALLY LOOK
LEAN OR JUST BE VIRGA, SHOULD SEE FULL COLUMN SATURATION BY ABOUT
07Z TONIGHT. BY THIS TIME, THE STRONGEST OF THE WARM ADVECTIVE
FORCING WILL BE EAST OF I-75, BUT THE INBOUND HEIGHT FALL CENTER
WILL SUPPORT A BROADER/LIGHTER SNOW TO THE WEST OF THE INTERSTATE AS
WELL. THESE SYSTEMS ARE TYPICALLY ONLY ABLE TO SQUEEZE OUT 1-2" OF
SNOW SINCE THEY LACK MOISTURE DEPTH AND DURATION, BUT ONE
INTERESTING FEATURE OF THIS SYSTEM IS THE VERY STRONG ELEVATED
CONVECTIVE INSTABILITY ABOVE THE WARM FRONT (700-500MB LAPSE RATES
OF 7.5-8.0 C/KM). WHILE THE COLD POOL IS ONLY OVERHEAD FOR A FEW
HOURS OVER ANY ONE LOCATION, IF THE UNSTABLE LAYER IS SATURATED
SNOWFALL RATES MAY OVERACHIEVE. THIS WOULD BE IN ADDITION TO AN
ALREADY VERY EFFICIENT THERMODYNAMIC PROFILE WHERE SNOW-LIQUID RATES
ARE OVER 15:1 AND THE ISOTHERMAL LAYER IS JUST 1-2 DEGREES WARMER
THAN THE PEAK DENDRITIC GROWTH ZONE. AN OVERACHIEVING SCENARIO HAS
NOT SHOWN UP IN THE ENVELOPE OF DETERMINISTIC/ENSEMBLE DATA, SO
SNOWFALL GRIDS ARE REPRESENTATIVE OF THE MOST LIKELY OUTCOME: 1"
WEST OF I-75 AND 2" TO THE WEST, LOCALLY HIGHER AMOUNTS IN THE
THUMB. THIS SETUP SHOULD BE WATCHED CLOSELY HOWEVER FOR
OVERACHIEVEMENT POTENTIAL, ESPECIALLY SINCE SNOWFALL TIMING IS
FAVORED AROUND THE MORNING COMMUTE.
SNOWFALL RATES BEGIN TO TAPER OFF AFTER 15Z THURSDAY (10AM EST) WITH
THE LOSS OF BROAD ISENTROPIC FORCING, ALTHOUGH A MORE LOCALIZED
POCKET OF FORCING IS EXPECTED TO HOLD ON IN THE THUMB WHICH MAY
RESULT IN AN ADDITIONAL DUSTING OF SNOW TO BRING TOTALS ABOVE THE 2"
MARK. ELSEWHERE, SHALLOW, BUT WELL-MIXED BOUNDARY LAYER CONDITIONS
WILL MAINTAIN LAKE EFFECT SNOW SHOWERS WITH ADDITIONAL MINOR
ACCUMULATIONS OF DRY/FLUFFY SNOW POSSIBLE. THE PARENT LOW PRESSURE
SYSTEM DRAWS A COLD FRONT ACROSS THE REGION DURING THE AFTERNOON,
WITH VEERED WINDS OUT OF THE NORTHWEST FURTHER LOWERING SNOW SHOWER
CHANCES FOR THE AFTERNOON-EVENING.
FRIDAY AND SATURDAY WILL BE THE WARMEST DAYS OF THE FORECAST PERIOD
WITH HIGHS IN THE MID 30S, IN ADVANCE OF AN ORGANIZED LOW PRESSURE
SYSTEM THAT WILL IMPACT SE MICHIGAN FRIDAY NIGHT-SATURDAY. A COUPLED
UPPER LEVEL JET STRUCTURE WILL INDUCE CYCLOGENESIS OVER THE
MISSISSIPPI RIVER VALLEY FRIDAY AFTERNOON, WITH THE PRECIPITATION
SHIELD ADVANCING TOWARD SE MICHIGAN FRI NIGHT. NEARLY ALL ENSEMBLE
MEMBERS IN THE LREF GUIDANCE PRODUCE SOME DEGREE OF ACCUMULATING
SNOW FOR PORTIONS OF THE CWA BY SATURDAY MORNING, BUT THERE ARE
STILL DISAGREEMENTS ON SYNOPTIC FEATURE PLACEMENT, RAIN-SNOW LINE
PLACEMENT, ETC. SO NAILING DOWN EXACT SNOWFALL RANGES IS A BIT
PREMATURE. FOR AT LEAST SOME REFERENCE ON THE MAGNITUDE OF THIS
SYSTEM, ENSEMBLE QPF AMOUNTS RANGE BETWEEN ABOUT 0.1-0.3".
A STRONG COLD FRONT WILL CLEAR OUT PRECIPITATION SATURDAY, BUT USHER
IN THE COLDEST AIR OF THE SEASON. BY EARLY NEXT WEEK H8 TEMPERATURES
WILL DROP BELOW -30 C FOR MUCH OF THE UPPER MIDWEST. NEARLY ALL
ENSEMBLE MEMBERS MONDAY-WEDNESDAY SUPPORT OVERNIGHT LOWS BELOW ZERO
DEGREES, WITH WIND CHILLS APPROACHING ADVISORY CRITERIA (-15 F OR
LOWER). NOT MUCH RELIEF IS EXPECTED DURING THE DAY EITHER, WITH HIGH
TEMPERATURES BARELY CLIMBING ABOVE ZERO.
MARINE
WINDS SHIFT TO SOUTHWESTERLY AND STRENGTHEN THIS EVENING AND
OVERNIGHT IN RESPONSE TO A CLIPPER SYSTEM TRACKING SOUTHEAST INTO
THE GREAT LAKES. PEAK WINDS ARE EXPECTED DURING THE EARLY MORNING
HOURS THURSDAY WITH WIND SPEEDS OF 20 TO 25 KNOTS AND GUSTS UP TO 30
KNOTS OVER SAGINAW BAY INTO CENTRAL LAKE HURON WHERE THE SOUTHWEST
WIND HAS LONGER FETCH. LIGHT SNOW WILL ACCOMPANY THIS SYSTEM THROUGH
MUCH OF THE DAY THURSDAY. WINDS VEER TO NORTHWEST THURSDAY NIGHT,
PEAKING AROUND 20 TO 25 KNOTS, AS THE SYSTEM DEPARTS EAST. A
STRONGER SYSTEM WILL THEN TRACK JUST NORTH OF THE GREAT LAKES ON
FRIDAY, CAUSING A STRONG SOUTHWESTERLY LOW-LEVEL JET TO PASS OVER
THE REGION. MODELS CONTINUE TO SHOW A HIGH PROBABILITY FOR GALES,
AND A GALE WATCH REMAINS IN EFFECT FOR THE MAJORITY OF LAKE HURON
FROM FRIDAY AFTERNOON TO SATURDAY MORNING. THERE WILL BE POTENTIAL
FOR GUSTS TO 40 KNOTS. MILDER AIR WILL BRIEFLY ACCOMPANY THIS SYSTEM
BEFORE FRIGID ARCTIC AIR SETTLES OVER THE REGION TO START NEXT WEEK.
PREV DISCUSSION
ISSUED AT 550 AM EST WED JAN 15 2025
AVIATION...
UPSTREAM OBSERVATIONS SHOW A FAIRLY EXTENSIVE MVFR BASED STRATUS
DECK APPROACHING THE SE MI TERMINALS FROM THE WEST. ONGOING
SUBSIDENCE AND WARM AIR ADVECTION IS LOWERING THE BASE OF THE
INVERSION, WHICH WILL MAKE MVFR BASED STRATUS INCREASINGLY MORE
PROBABLE WITHIN THE FIRST COUPLE HOURS OF TAF ISSUANCE. A GRADUAL
BACKING OF THE WIND FIELDS WITHIN THE LOW LEVELS TOWARD THE SSW WEST
DURING THE AFTERNOON WILL DRIVE THE LAKE MICHIGAN MOISTURE PLUME
NORTHWARD, LEADING TO A COMPLETE CLEARING OF LOW CLOUDS. A MID LEVEL
SHORT WAVE WILL THEN ADVANCE INTO LOWER MI OVERNIGHT, RESULTING IN
NUMEROUS SNOW SHOWERS AND A RETURN OF LOW CLOUDS.
FOR DTW...METRO WILL RESIDE ALONG THE SOUTHERN PERIPHERY OF THE LAKE
STRATUS THIS MORNING THROUGH MID AFTERNOON. THE BULK OF THE MODEL
GUIDANCE SUGGESTS THE MVFR CLOUDS WILL BE EXTENSIVE ENOUGH TO SUPPORT
PREVAILING MVFR CONDITIONS INTO EARLY AFTERNOON. AS THE LOW LEVEL
FLOW BECOMES BACKED, THERE WILL BE A MORE PERSISTENT EROSION OF THE
EDGE OF THESE CLOUDS BY MID AFTERNOON, LIKELY LEADING TO THEIR
EROSION.
DTW THRESHOLD PROBABILITIES...
* HIGH FOR CEILINGS AOB 5000 FEET THIS MORNING. MODERATE THIS
AFTERNOON. LOW THIS EVENING.
* HIGH FOR PTYPE OF SNOW OVERNIGHT AND THURSDAY MORNING.
DTX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LAKE HURON...GALE WATCH FROM FRIDAY AFTERNOON THROUGH LATE FRIDAY NIGHT FOR
LHZ362-363-421-441-462>464.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
DISCUSSION...MV
MARINE.......TF
AVIATION.....SC
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