347
FXUS63 KDTX 210459
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1159 PM EST FRI DEC 20 2024
KEY MESSAGES
- A WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR THE EASTERN THUMB
UNTIL 4 AM. LAKE EFFECT SNOW SHOWERS WILL BRING THE CHANCE FOR NEW
ACCUMULATIONS OF 1 TO 2 INCHES WITH BLOWING SNOW.
- COLD THIS WEEKEND WITH DAYTIME TEMPERATURES IN THE 20S AND MORNING
LOWS IN THE SINGLE DIGITS, DOWN TO ZERO DEGREES ACROSS THE TRI-
CITIES.
- NEXT CHANCE FOR SNOW AND RAIN ARRIVES ON MONDAY.
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.
PREV DISCUSSION
ISSUED AT 933 PM EST FRI DEC 20 2024
UPDATE...
BASED ON ENVIRONMENT CANADA EXETER (CASET) RADAR TRENDS WITH
CELLULAR CONVECTION BRUSHING THE SHORELINE/M 25 YET THIS EVENING, 30
MPH ALONG THE LAKESHORE CAUSING BLOWING SNOW, AND A SECONDARY
VORTICITY MAXIMUM THAT IS SET TO DIG DIRECTLY INTO THE HURON COUNTY
AND EASTERN THUMB 06-09Z THE DECISION WAS MADE TO EXTEND THE WINTER
WEATHER ADVISORY THROUGH 4 AM. LITTLE CONFIDENCE EXISTS ON ADDITIONAL
SNOW AMOUNTS AS GREATER NWP SIGNAL IS TO PUSH THE BANDING OUT INTO
THE SOUTHERN BASIN OF LAKE HURON. DID EDIT THE GRIDS TO INCLUDE
BLOWING SNOW.
PREV DISCUSSION...
ISSUED AT 319 PM EST FRI DEC 20 2024
DISCUSSION...
FOR THIS AFTERNOON AND EVENING... LOW-LEVEL FLOW HAS CONTINUED TO
BACK FROM NORTHEAST TO NORTH-NORTHWEST, SHIFTING LAKE EFFECT SNOW
AWAY FROM THE TRI-CITIES, SO THE WINTER WEATHER ADVISORY (WWA) HAS
BEEN CANCELLED. THE BETTER OVER-LAND INSTABILITY NOW RESIDES ALONG
THE THUMB, AND INLAND ACROSS THE NORTHERN METRO AND URBAN METRO
REGION, ALONG A WEAK FRONTAL BOUNDARY. ALONG THE LAKESHORE ITSELF
WHERE A WWA REMAINS IN EFFECT THROUGH 10 PM, THE CONTINUED BACKING
OF FLOW WILL SUPPORT THE POSSIBILITY OF A CONVECTIVELY ENHANCED SNOW
BAND THAT WILL FEED OFF THE UNSTABLE WATERS OF THE SOUTHERN LAKE
HURON BASIN, PRODUCING EFFICIENT MOISTURE FLUX OFF THE LAKE WITH
CONVECTIVE DEPTHS EXTENDING WELL PAST 10KFT, SUPERSATURATED W.R.T
ICE. THIS WILL PROVIDE A BRIEF 1-3 HOUR WINDOW FOR SOME HIGHLY
LOCALIZED SNOW SHOWERS, CAPABLE OF PRODUCING SNOW RATES AROUND 1"/HR.
BASED ON EARLIER RADAR OBSERVATIONS, HI-RES MODELING OVERDID BANDING
POTENTIAL FOR THE NORTHERN TRI-CITIES THIS AFTERNOON, SO THERE IS
UNCERTAINTY REGARDING POTENTIAL STRENGTH OF ANY LAKE INDUCED SNOW
SHOWERS. ADDITIONAL SNOW TOTALS OF 1-3" REMAIN POSSIBLE, PENDING
WHERE ANY SNOW BANDING ALIGNS AND IF 10KFT+ CONVECTIVE DEPTHS ARE
REALIZED. THE CASET RADAR DOES HAVE A BAND OVER SANILAC COUNTY AT
THIS TIME. THE WWA REMAINS IN EFFECT FOR THE THUMB DOWN TO ST. CLAIR
COUNTY UNTIL 10PM. FURTHER INLAND, POOLED UP LAKE MOISTURE ALONG THE
FRONTAL ZONE WILL BE SUFFICIENT ENOUGH TO SUPPORT MORE WIDESPREAD
LIGHT SNOW INTO THE EARLY EVENING, BEFORE OVER-LAND INSTABILITY
QUICKLY WANES THROUGH THE EVENING. NEW ACCUMULATION WILL LIKELY BE
CONFINED TO GRASSY SURFACES AS ROAD TEMPERATURES ARE HOLDING IN THE
MID 30S THANKS TO THE WEAK DECEMBER SOLAR INSOLATION.
LATE TONIGHT AND OVERNIGHT, THE UPPER-LEVEL TROUGH AXIS WILL MOVE
OVER THE CONTINENTAL NORTHEAST WITH HIGH PRESSURE THEN FILTERING IN
OVER THE GREAT LAKES. COLD AIR ADVECTION WILL BE ONGOING THROUGH THE
EARLY MORNING HOURS IN THE WAKE OF THE COLD FRONT, HOWEVER,
INCREASING SUBSIDENCE AND ADVECTION OF DRY AIR LOOKS TO SUPPRESS LAKE
EFFECT SNOW SHOWERS WITH SHRINKING CONVECTIVE DEPTHS. FLURRIES
REMAIN POSSIBLE AS SHALLOW MOISTURE HOLDS THROUGH THE MORNING. THE
EXCEPTION TO THIS WILL BE ALONG THE LAKE HURON SHORELINE, WHERE NNW
KEEPS THE LAKE HURON CONNECTION OPEN. THE VAST MAJORITY OF MODEL
OUTPUT HOLDS SNOW BAND PRODUCTION JUST OFFSHORE OR CLIPS A PORTION
OF HURON COUNTY FROM ROUGHLY HURON CITY TO HARBOR BEACH (NAM). THE
NSSL EXHIBITS A LITTLE MORE BACKED FLOW WHICH EXTENDS SNOW CHANCES
THROUGH SANILAC. NBM PROBABILITIES GREATER OR EQUAL TO 1" REMAIN
AROUND 20-30% THROUGH 7AM TOMORROW MORNING. ADDITIONAL SNOW CHANCES
ARE POSSIBLE WITHIN THE NORTHERN THUMB TOMORROW AFTERNOON, BUT
SHALLOW DEPTHS IN THE SOUNDING WILL BE A MAJOR LIMITING FACTOR TO
SNOW PRODUCTION, LIMITING NEW ACCUMULATION TO AN INCH OR LESS.
OTHERWISE, THIS WEEKEND WILL OFFER BELOW NORMAL TEMPERATURES.
DAYTIME HIGHS WILL STAY CAPPED IN THE 20S AND THE LOWS LEADING INTO
SUNDAY WILL DROP IN THE SINGLE DIGITS TO NEAR OR JUST BELOW 0 IN THE
TRI-CITIES THANKS TO EFFICIENT RADIATIONAL COOLING FROM CLEAR SKIES.
DRY AIR DOES BRING INCREASING CHANCES FOR EXTENDING PERIODS OF
SUNSHINE, ESPECIALLY FOR SUNDAY AS SE MI IS CLIPPED BY THE WESTERN
PERIPHERY OF A 1037 HIGH PRESSURE SYSTEM.
A CLIPPER SYSTEM WILL BRING THE NEXT CHANCE FOR WINTRY PRECIPITATION
BY MONDAY INTO EARLY TUESDAY MORNING. THE AMPLIFICATION OF THE
INCOMING WAVE WILL HAVE IMPACTS ON INITIAL P-TYPE. DEEPER TROUGHING
WEST OF LAKE MICHIGAN RELATIVE TO ENSEMBLE MEAN WILL ALLOW FOR MORE
AGGRESSIVE ADVECTION OF WARMER AIR DOWNSTREAM INTO THE GREAT LAKES,
BRINGING RAIN/SNOW CHANCES, OR SOME BETTER CHANCES FOR RAIN CLOSER
TO THE MI/OH BORDER. A PROGRESSIVE WAVE WILL FAVOR SNOW CHANCES,
WHICH THE MAJORITY OF EPS ENSEMBLES FAVOR AT PRESENT TIME. BEHIND
THE WAVE, A DIFFUSE HIGH PRESSURE SYSTEM WILL BUILD IN OVER MICHIGAN
CHRISTMAS EVE THROUGH CHRISTMAS. THIS FAVORS A DRY FORECAST AS WEAK
THERMAL ADVECTION FILTERS IN WARMER AIR FROM THE PLAINS INTO THE
REGION. TEMPERATURES RETURN TO NORMAL VALUES MON-WED, WITH HIGH
CONFIDENCE FOR ABOVE NORMAL TEMPERATURES TOWARDS THE END OF THE WEEK.
MARINE...
CLIPPER PEELS AWAY FROM THE GREAT LAKES THIS EVENING WITH LAKE
EFFECT SNOW SHOWERS CONTINUING OVER SOUTHERN LAKE HURON IN ITS WAKE.
THIS ACTIVITY LIKELY PERSISTS THROUGH THE MOST OF SATURDAY AS
MODERATE (20-25KT) NORTHERLY FLOW LIKEWISE CONTINUES. FOR AREAS
OUTSIDE OF SOUTHERN HURON, WINDS BETWEEN 15-20KTS ARE FAVORED. SMALL
CRAFT ADVISORIES REMAIN IN EFFECT THROUGH SATURDAY EVENING AROUND
THE THUMB NEARSHORE WATERS DUE TO THIS ONSHORE FLOW AND SUBSEQUENT
HIGHER WAVE ACTION. ARCTIC HIGH PRESSURE EXPANDS OVER THE CENTRAL
GREAT LAKES LATTER HALF OF THE WEEKEND BRINGING COLDER, BUT DRIER
AND CALMER CONDITIONS.
DTX WATCHES/WARNINGS/ADVISORIES
MI...WINTER WEATHER ADVISORY UNTIL 4 AM EST SATURDAY FOR MIZ049-055-063.
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 10 PM EST SATURDAY FOR LHZ421-441>443.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
AVIATION.....CB
UPDATE.......CB
DISCUSSION...AM
MARINE.......KDK
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AT WWW.WEATHER.GOV/DETROIT.
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