908
FXUS63 KDTX 210850
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
350 AM EST SAT DEC 21 2024
KEY MESSAGES
- LAKE EFFECT SNOW SHOWERS MAY BRUSH THE SHORELINE OF THE EASTERN
THUMB THIS MORNING, BRINGING A CHANCE FOR MINOR ACCUMULATIONS AND
POCKETS OF BLOWING SNOW.
- COLD THIS WEEKEND WITH DAYTIME TEMPERATURES IN THE 20S. SUNDAY
MORNING LOWS WILL RANGE FROM AROUND 0 DEGREES IN THE SAGINAW VALLEY
TO AROUND 10 DEGREES IN DETROIT.
- NEXT CHANCE FOR SNOW AND RAIN ARRIVES ON MONDAY WITH MINOR
ACCUMULATIONS POSSIBLE.
DISCUSSION
A MID-LEVEL SHORTWAVE IMPULSE IS PASSING OVER LAKE HURON AT PRESS
TIME, CAUSING A LOCAL SUBTLE VEERING TO LOW-LEVEL OVERLAKE FLOW.
THIS WILL MAINTAIN AN OPPORTUNITY FOR THE PERSISTENT LAKE EFFECT
SNOW BANDING TO BRUSH THE NORTHERN AND EASTERN SHORELINE COMMUNITIES
OF THE THUMB AT TIMES THIS MORNING. BASED ON THE CURRENT RADAR
PRESENTATION AND LATEST HI-RES RUNS GENERALLY BACKING OFF OF GREATER
IMPACTS, WILL ALLOW THE WINTER WEATHER ADVISORY TO EXPIRE AT 4 AM.
MINOR ACCUMULATIONS UP TO AN INCH OR TWO AND BLOWING SNOW WILL BE
POSSIBLE FOR LOCALIZED AREAS THAT DO SEE ANY OF THE SNOW BAND MOVE
ONSHORE.
A PATTERN OF RISING HEIGHTS AND NVA COMMENCES TODAY PROMOTING DEEP
SUBSIDENCE AND RAPID DRYING OF THE UPPER AND MID LEVELS. LOW-LEVEL
WIND DIRECTION WILL REMAIN OUT OF THE NORTH AND NORTHWEST WHICH WILL
CONTINUE TO ADVECT IN A PLUME OF LAKE MOISTURE BENEATH THE LOWERING
SUBSIDENCE INVERSION, BRINGING INTERVALS OF CLOUDS AND POSSIBLY EVEN
SOME FLURRIES AS THE TOP OF THE BOUNDARY LAYER FLIRTS WITH THE DGZ.
A SEASONABLY COLD AIR MASS WILL SETTLE IN TODAY - THE COLDER CORE
/850MB TEMP OF -19C OBSERVED UPSTREAM AT PICKLE LAKE, ON/ WILL JUST
MISS US TO THE NORTH, BUT 850MB TEMPS REACHING ABOUT -17C TODAY WILL
LIMIT HIGHS TO THE LOWER TO MID 20S. A SURFACE RIDGE WILL EASE IN,
CAUSING THE NORTHERLY WINDS TO GO NEARLY CALM TONIGHT. THIS, THE
FRESH SNOW COVER, AND CLEARING SKIES SET THE STAGE FOR A VERY COLD
NIGHT WITH TEMPS CRATERING TO WITHIN A FEW DEGREES OF 0 - COLDEST IN
THE SAGINAW VALLEY WHERE 21.01Z NBM HIGHLIGHTS A 35% PROBABILITY FOR
SUB-ZERO READINGS SUNDAY MORNING. THE ARCTIC HIGH PRESSURE HOLDS
COLD BUT DRY CONDITIONS THROUGH SUNDAY WITH HIGHS AGAIN IN THE 20S.
MONDAY PRESENTS THE NEXT CHANCE FOR WIDESPREAD PRECIP AS A LOW
TRACKS FROM THE MIDWEST DIRECTLY INTO LOWER MI. THE PARENT WAVE WILL
BE OF PACIFIC ORIGIN AND ADVECT A MILD AND MOIST AIR MASS IN AHEAD
OF IT. LATEST DETERMINISTIC GUIDANCE HAS TRENDED TOWARD A COMPROMISE
BETWEEN THE PREVIOUSLY MORE PROGRESSIVE ECMWF AND MORE AMPLIFIED GFS
SOLUTIONS. ENSEMBLE PROGS FAVOR SNOW AS THE DOMINANT PTYPE, BUT AS
THE DAY GOES ON AND TEMPERATURES EDGE UP INTO THE MID 30S A MIX WITH
OR CHANGEOVER TO RAIN WILL BECOME LIKELY ACROSS THE SOUTH. QPF ON
THE ORDER OF A FEW HUNDREDTHS TO 0.20" AND THE WARMING PROFILES WILL
SUPPORT ACCUMULATIONS OF AN INCH OR TWO IN THE NORTH AND MAINLY JUST
MINOR SLUSHY ACCUMULATIONS AROUND METRO DETROIT AND SOUTH. THE BULK
OF THE PRECIP WILL OCCUR WITHIN THE WARM ADVECTIVE WING OF THIS
SYSTEM DURING THE DAY MONDAY WITH LIGHT SNOW OR DRIZZLE FOLLOWING
FOR SOME AREAS INTO MONDAY NIGHT. WILL NOTE THAT THERE IS AN
IMPRESSIVE FGEN SIGNATURE AND QPF BULLSEYE WITH THIS SYSTEM ACROSS
NORTHERN MI AND IF THIS FORCING TRENDS SOUTHWARD, WE WILL NEED TO
ADJUST SNOWFALL AMOUNTS HIGHER FOR OUR NORTHERN COUNTIES.
VERY MINIMAL THERMAL ADVECTION FOLLOWS THE MONDAY SYSTEM AS HIGH
PRESSURE BUILDS INTO THE AREA FOR THE CHRISTMAS HOLIDAY. A COMPLEX
UPPER AIR PATTERN AND MULTIPLE WAVE INTERACTIONS DURING THE MID-WEEK
RESULTS IN A LOWER CONFIDENCE FORECAST AS A PAIR OF SOUTHERN STREAM
WAVES ATTEMPT TO LIFT INTO THE GREAT LAKES. THERE IS HOWEVER
RELATIVELY HIGH CONFIDENCE IN A WARMING TREND THROUGH THE WEEK WITH
HIGHS LIKELY TO REACH THE 40S ACROSS THE AREA BY FRIDAY PER LATEST
NBM. HIGHER THAN AVERAGE TEMPERATURES ARE VERY LIKELY TO PERSIST
THROUGH THE END OF THE MONTH AS THE LATEST 6-10 AND 8-14 DAY
TEMPERATURE OUTLOOKS FROM CPC HIGHLIGHT SE MI WITHIN AN 85% AND 78%
CHANCE, RESPECTIVELY FOR THOSE TIME PERIODS, FOR ABOVE NORMAL TEMPS.
MARINE
NORTHERLY FLOW CONTINUES TODAY IN THE WAKE OF YESTERDAY'S CLIPPER
WITH STRONGEST WINDS OCCURING OVER THE SOUTHERN HALF OF LAKE HURON.
GUSTS IN THESE WATERS WILL BE ABLE TO REACH 25-30KTS WITH 20-25KTS
POSSIBLE OVER THE REST OF THE CENTRAL GREAT LAKES. SMALL CRAFT
ADVISORIES REMAIN IN EFFECT THROUGH THIS EVENING AROUND THE THUMB
DUE TO THESE WINDS/WAVES. LAKE EFFECT SNOW SHOWERS REMAIN POSSIBLE
OVER SOUTHERN HURON UNTIL LATE EVENING WHEN ARCTIC HIGH PRESSURE
BEGINS TO BECOME ESTABLISHED OVERHEAD. HIGH PRESSURE INFLUENCE IS
SHORTLIVED BRINGING LIGHTER WINDS AND DRIER CONDITIONS UNTIL MONDAY
MORNING WHEN A COMPACT PLAINS LOW IS SET TO TRACK ACROSS THE GREAT
LAKES. MODERATE SOUTHERLY FLOW (20-30KTS) AND WIDESPREAD SNOW
ACCOMPANIES THIS SYSTEM MONDAY-MONDAY NIGHT.
PREV DISCUSSION
ISSUED AT 1159 PM EST FRI DEC 20 2024
AVIATION...
DIFFERENTIAL ANTICYCLONIC VORTICITY ADVECTION AND BACKING WIND
TRAJECTORIES HAS LEAD TO CONSIDERABLE DRY AIR ADVECTION AND CLEARING
DURING THE LATE EVENING. A SECONDARY TROUGH AXIS AND ABSOLUTE
VORTICITY MAY LEAD TO SOME DEVELOPMENT OF LOW VFR IN VICINITY OF LAKE
HURON EARLY THIS MORNING. MVFR DIURNAL STRATOCUMULUS IS ANTICIPATED
FOR MOST OF SOUTHEAST MICHIGAN BY LATE MORNING SATURDAY.
FOR DTW...VFR CONDITIONS EXPECTED THE REMAINDER OF TONIGHT.
DTW THRESHOLD PROBABILITIES...
* CEILINGS ABOVE 5000 FT TONIGHT. CEILINGS BELOW 5000 FT SATURDAY.
DTX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR LHZ421-
441>443.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
DISCUSSION...TF
MARINE.......KDK
AVIATION.....CB
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