539
FXUS63 KAPX 190341
AFDAPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
1041 PM EST SAT JAN 18 2025
KEY MESSAGES
- TURNING MUCH COLDER, PERHAPS DANGEROUSLY SO, WITH PERIODS OF
LAKE EFFECT SNOW THROUGH THE START OF THE WEEK.
- TEMPERATURES BEGIN TO MODERATE THE SECOND HALF OF THE WEEK.
UPDATE
ISSUED AT 1038 PM EST SAT JAN 18 2025
SYNOPSIS: COLD AIR OUTBREAK UNDERWAY ACROSS THE GREAT LAKES IN THE
WAKE OF A COLD FRONT THAT CROSSED MICHIGAN LAST NIGHT. 01Z SURFACE
ANALYSIS SHOWS A SHARP LAKE AGGREGATE TROUGH LYING ACROSS SOUTHERN
LAKE SUPERIOR AND ACROSS THE KEWEENAW PENINSULA. SUB-ZERO COLD HAS
SPREAD AS FAR SOUTH AS PARTS OF SOUTH DAKOTA/CENTRAL MINNESOTA...AND
AROUND MOST OF THE NORTH SHORE OF LAKE SUPERIOR. MULTI-BAND LAKE
CONVECTION CONTINUES OVER THE LAKES...STRONGEST BAND OVER CENTRAL
UPPER ALONG LAKE AGGREGATE CONVERGENCE AXIS OFF LAKE SUPERIOR.
SOME GOOD BANDS ACROSS WHITEFISH BAY INTO NORTHWEST CHIPPEWA COUNTY
THOUGH LACK OF CASMR RADAR DATA LEAVING A COVERAGE HOLE OVER EASTERN
LAKE SUPERIOR. BANDING INTO NORTHWEST LOWER HAS BEEN A BIT MORE
DIFFUSE SO FAR THIS EVENING. 00Z APX SOUNDING SHOWS A SUBSIDENCE
INVERSION RIGHT AT 800MB/-21C...STILL A GOOD BIT OF THE DGZ WITHIN
THE CBL BUT CLOUD BASES ARE HIGH (ABOVE 3000FT) SO THE DEPTH OF THE
DGZ WITHIN THE CLOUD LAYER IS PROBABLY NOT MUCH. INVERSION HEIGHT
OVER EASTERN LAKE SUPERIOR PROBABLY CLOSER TO 750MB/-27C BUT MORE
CLOUD DEPTH WITHIN THE DGZ HELPING WITH SNOWFALL INTENSITY.
FORECAST UPDATE: COLD AIR SPILLING AROUND THE EASTERN SIDE OF LAKE
SUPERIOR WILL CONTINUE TO DEFORM THE SURFACE PRESSURE PATTERN...WITH
MESOSCALE RIDGING EAST OF LAKE SUPERIOR AND HEATING INDUCED
TROUGHING TAKING ON A MORE NORTHWEST-SOUTHEAST ORIENTATION (I.E.,
MORE CLIMATOLOGICAL). EMBEDDED SHORT WAVE TROUGHS WILL CONTINUE TO
ROTATE THROUGH THE MEAN POSITIVE TILT LONG WAVE TROUGH AXIS
EXTENDING FROM HUDSON BAY SOUTHWEST INTO THE SOUTHERN PLAINS. DEEP
LAYER COLD ADVECTION CONTINUES WITH 850MB TEMPERATURES FALLING BELOW
-20C AND 500MB TEMPERATURES AT OR BELOW -40C.
EASTERN UPPER...STRONG FRONTOGENESIS ALONG THE EASTERN SHORE OF LAKE
SUPERIOR AND RESULTANT UPWARD FORCING ENHANCING SNOW BANDS INTO THE
SAULT REGION THIS EVENING. THIS WILL CONTINUE THROUGH
MIDNIGHT...BUT THEN DRAINAGE FLOW IS EXPECTED TO DEVELOP OFF THE
HIGHER TERRAIN EAST OF LAKE SUPERIOR AND ALLOW WINDS TO VEER TO A
MORE EASTERLY COMPONENT WHICH IS EXPECTED TO PUSH HEAVIER SNOW BANDS
SLOWLY WESTWARD ACROSS WHITEFISH BAY AND NORTHWEST CHIPPEWA COUNTY
DURING THE EARLY MORNING HOURS...PERHAPS EVEN SPINNING OFF A
MESOVORTEX. CURRENT HEADLINES ARE PROBABLY SUFFICIENT AS HEAVIER
SNOW IS EXPECTED TO PUSH WEST OF THE SAULT SHORTLY AFTER MIDNIGHT
AND FOCUS ON NORTHWEST CHIPPEWA COUNTY WHERE 4 TO 8 INCHES OF SNOW
IS POSSIBLE DURING THE OVERNIGHT. SO ONGOING WINTER WEATHER
ADVISORY WILL CONTINUE. ANTICIPATE SUB-ZERO COLD TO SPILL ACROSS
THE ST. MARY'S RIVER OVERNIGHT...WITH LOWS IN THE 0 TO -10 RANGE
EXPECTED
NORTHERN LOWER: BANDS WILL CONTINUE OFF LAKE MICHIGAN OVERNIGHT WITH
THINGS GETTING PROGRESSIVELY COLDER IN THE THERMODYNAMIC PROFILE BUT
NO SIGNIFICANT CHANGES IN CBL DEPTH ANTICIPATED. SO ACCUMULATIONS
OVERNIGHT SHOULD BE LIGHT GIVEN CURRENT ACTIVITY...AROUND AN INCH OR
SO CENTERED IN THE AREA BETWEEN GRAND TRAVERSE AND LITTLE TRAVERSE
BAY.
SHORT TERM /THROUGH SUNDAY/
ISSUED AT 302 PM EST SAT JAN 18 2025
PATTERN SYNOPSIS/PATTERN FORECAST:
MUCH ADVERTISED SHOT OF BARELY MODIFIED AIR OF ARCTIC ORIGIN NOW
MAKING STEADY SOUTHEAST PROGRESS ACROSS THE NORTHERN GREAT LAKES
EARLY THIS AFTERNOON...WITH FALLING TEMPERATURES INTO THE TEENS AND
20S. CULPRIT BEHIND SUCH AN UNPLEASANT DELIVERY IS ONE HIGHLY
AMPLIFIED UPPER LEVEL FLOW REGIME...CONSISTING OF ANAMOUSLY STRONG
WESTERN RIDGING (THE NORTHERN EXTENT OF WHICH IS POKING UP WELL
NORTH OF THE ARCTIC CIRCLE) AND INCREASINGLY DEEP DOWNSTREAM
TROUGHING. NORTHERN MICHIGAN OBVIOUSLY DOMINATED BY THE LATER,
SUPPLYING A DIRECT PIPELINE TO THAT ARCTIC AIR. PASSAGE OF LEAD
SHORTWAVE TROUGH HAS ENDED ALL SYNOPTICALLY-DRIVEN PRECIPITATION,
WITH PURE LAKE PROCESSES NOW DOMINATING IN POST-FRONTAL INTENSE COLD
AIR ADVECTION REGIME. DESPITE LACK OF ANY SYNOPTIC SCALE MOISTURE
CONTRIBUTION, SIMPLE BREADTH OF THE OVER-WATER THERMAL GRADIENT IS
FORCING LAKE SNOW GENERATION IN FAVORED NORTHWEST FLOW AREAS. AS IS
OFTEN THE CASE IN SUCH A SET-UP, MOST ORGANIZED BANDS ARE ROTATING
OFF THE LAKE SUPERIOR GIVEN MUCH LONGER PARCEL RESIDENCE TIME TO
DRIVE LOW LEVEL AIRMASS MODIFICATION.
COLD AIR ADVECTION CONTINUES RIGHT THROUGH THE BEGINNING STAGES OF
THIS WEEK, EVENTUALLY DRIVING TEMPERATURES TO DANGEROUSLY COLD
LEVELS AND CONTINUING TO BRING LAKE SNOWS TO THOSE FAVORED SNOW BELT
LOCATIONS.
PRIMARY FORECAST CONCERNS:
TEMPERATURE TRENDS AND LAKE SNOW EVOLUTION THROUGH MONDAY.
DETAILS:
PURE LAKE EFFECT SNOW PROCESSES CONTINUE TONIGHT AND SUNDAY. LAKE
INDUCED CLOUD TEMPERATURE PROFILES CONTINUE TO COOL, RESULTING IN
COMPLETE LOSS OF THE DENDRITIC GROWTH LAYER (FAVORING MUCH LESS
EFFICIENT SNOW ACCUMULATING BUT VERY EFFICIENT VISIBILITY
RESTRICTING POWDERY TYPE SNOW). ONE EXCEPTION TO THIS MAY BE ACROSS
THE SNOW BELTS OF EASTERN UPPER MICHIGAN WHERE TREMENDOUS LATENT
HEAT RELEASE FROM LAKE SUPERIOR MAY ALLOW THE BOTTOM PORTIONS OF THE
LAKE CLOUDS TO REMAIN IN THE UPPER ECHELON OF THE DGZ. STEADY
STRENGTHENING OF LAKE AGGREGATE TROUGHING WILL ALSO HELP DRIVE
ENHANCED LOW LEVEL CONVERGENCE INTO NORTHWEST CHIPPEWA COUNTY FOR A
TIME THIS EVENING...ALTHOUGH EVENTUAL MATURATION OF ONTARIO INDUCED
LAND BREEZE WILL LIKELY PUNT BETTER SNOWS INTO CENTRAL UPPER
MICHIGAN THROUGH LATER TONIGHT AND SUNDAY. UPSHOT TO THE ABOVE...
LOOKING AT ADVISORY LEVEL PRODUCING SNOWS ACROSS NORTHWEST CHIPPEWA
COUNTY BY EARLY SUNDAY MORNING. LESSER AMOUNTS EXPECTED FOR THE SNOW
BELT LOCATIONS SOUTH OF THE BIG BRIDGE THROUGH SUNDAY, ALTHOUGH WITH
SOME TRAVEL IMPACTS EXPECTED GIVEN VIS RESTRICTION QUALITIES OF
THOSE EXPECTED FINE SNOW FLAKES.
DOWNWARD TEMPERATURE SPIRAL WILL CONTINUE, ALTHOUGH THE LAKES WILL
FORCE SIGNIFICANT MODIFICATION TO THE LOW LEVEL ENVIRONMENT.
LOOKING AT LOWS TONIGHT MOSTLY IN THE SINGLE DIGITS ABOVE ZERO
ACROSS NORTHERN LOWER MICHIGAN. EXPECT READINGS TO DROP ON THE
NEGATIVE SIDE OF ZERO BY A FEW DEGREES ACROSS EASTERN SECTIONS OF
UPPER MICHIGAN OWNING TO THAT ONTARIO LAND BREEZE. WIND CHILL VALUES
WILL BE SEVERAL DEGREES COLDER, WITH VALUES PERHAPS BRIEFLY
APPROACHING COLD WEATHER ADVISORY LEVELS BY EARLY SUNDAY MORNING
NEAR THE ST. MARY'S RIVER. HIGHS ON SUNDAY EXPECTED TO ONLY "WARM"
INTO THE UPPER SINGLE DIGITS AND TEENS. AGAIN, WITH WIND CHILL
READINGS SEVERAL DEGREES COLDER YET (BUT ABOVE HEADLINE CRITERIA).
LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/
ISSUED AT 302 PM EST SAT JAN 18 2025
PATTERN SYNOPSIS: FORECAST PERIOD BEGINS WITH DEEP LONG-WAVE
TROFFING OVER MOST OF NORTH AMERICA, WITH UPSTREAM RIDGING INTO THE
GULF OF ALASKA. THIS PATTERN SUPPORTS A CONTINUED FLOW OR
ARCTIC/MODIFIED ARCTIC AIR INTO THE EASTERN 2/3 OF THE LOWER 48
STATES FOR MUCH OF THE FIRST HALF OF THE WEEK. A SHORT-WAVE TROF
TOPS THE GULF OF ALASKA RIDGE MONDAY, HELPING TO DEAMPLIFY THE
FLOW OVER NORTH AMERICA FOR A TIME. THE REMNANTS OF THIS WAVE
ARE FORECAST TO CROSS THE UPPER GREAT LAKES IN THE
WEDNESDAY/THURSDAY TIMEFRAME WITH THE STRONG COLD AIR FLOW
SUBSIDING FOR A TIME AS THIS WAVE APPROACHES AND IN ITS WAKE.
ANOTHER SHORT-WAVE TOPPING THE GULF OF ALASKA RIDGE IS FORECAST
TO ARRIVE TOWARD THE END OF NEXT WEEK.
FORECAST DETAILS: A COLD AND RATHER STAGNANT WEATHER PATTERN IS
EXPECTED ACROSS THE FORECAST AREA DURING THE SUNDAY-TUESDAY
TIMEFRAME. THIS WOULD TEND TO ARGUE FOR A PERSISTENCE FORECAST WITH
GOOD PREDICTABILITY. HOWEVER, AS IS USUALLY THE CASE WITH THE GREAT
LAKES, THERE ARE MANY COMPLICATIONS TO THE FORECAST. LAKE AGGREGATE
TROFFING IS VERY APPARENT THROUGH THE PERIOD, EXTENDING UP THE AXIS
OF LAKE HURON INTO EASTERN LAKE SUPERIOR. WHERE EXACTLY THE TROF
AXIS SETS UP AND HOW MUCH WOBBLING IT DOES WILL HAVE SIGNIFICANT
IMPACT ON HOW MUCH LAKE EFFECT SNOW FALLS IN EASTERN UPPER AND
MAINLY COASTAL NORTHEAST LOWER MICHIGAN, AND HOW COLD IT WILL GET IN
THOSE AREAS (ESPECIALLY AT NIGHT). SIGNIFICANT COLD AIR DRAINAGE
LOOKS POSSIBLE OFF NORTHERN ONTARIO INTO EASTERN UPPER AND POSSIBLY
PARTS OF NORTHERN LOWER MICHIGAN. NORTHWEST LOWER MICHIGAN APPEARS
LESS LIKELY TO BE IMPACTED BY THE LAKE AGGREGATE TROFFING WITH A
MORE GENERAL WEST TO NORTHWEST FLOW LAKE EFFECT EVENT ANTICIPATED.
FORECAST SOUNDINGS SUGGEST QUITE A BIT OF OVER-LAKE INSTABILITY,
WHICH IS NOT SURPRISING WITH THE VERY COLD AIR MASS IN PLACE AND
MOSTLY OPEN LAKES (LOW ICE COVER). INVERSION HEIGHTS ARE FORECAST TO
AVERAGE 7-9K FEET, WHICH IS PLENTY FOR GOOD LAKE CONVECTION.
HOWEVER, THE CLOUD LAYER IN MOST AREAS WILL BE QUITE COLD (MOSTLY
COLDER THAN THE DGZ) AND SHOULD ONLY SUPPORT POWDERY SNOW THAT
DOESN'T ACCUMULATE WELL. THAT BEING SAID, THIS TYPE OF SNOW CAN CUT
VISIBILITY SIGNIFICANTLY DURING HEAVIER BURSTS.
EXPECT POWDERY LAKE EFFECT SNOW ACCUMULATIONS IN PARTS OF NORTHWEST
LOWER AND EASTERN UPPER MICHIGAN FROM SUNDAY-TUESDAY. THIS WILL
LIKELY REQUIRE ISSUANCE OF WINTER WEATHER ADVISORIES AT SOME POINT,
BUT WILL WAIT UNTIL THE AREAS CAN BE TARGETED A LITTLE BETTER. COLD
WEATHER ADVISORIES ARE ALSO POSSIBLE AT TIMES SUNDAY NIGHT INTO
TUESDAY DURING A PERIOD OF SINGLE DIGIT HIGH TEMPERATURES AND SUB-
ZERO LOWS, AND WELL BELOW ZERO WIND CHILL TEMPERATURES.
THE DEEP FREEZE SUBSIDES FOR THE SECOND HALF OF THE WEEK AS THE
UPPER-LEVEL FLOW BECOMES LESS AMPLIFIED AND WE EVEN SEE MORE
SOUTHERLY LOW-LEVEL FLOW AT TIMES. TEMPERATURES RETURN TO MORE
NORMAL LEVELS FOR LATE JANUARY WITH HIGHS IN THE 20S AND LOWS AROUND
10 TO THE TEENS. TWO WEAK DISTURBANCES WHICH MAY ARRIVE AROUND
WEDNESDAY/THURSDAY AND AGAIN BY THE END OF THE WEEK SHOULD PROVIDE
MORE WIDESPREAD BUT LIGHT SNOWFALL.
AVIATION /00Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 700 PM EST SAT JAN 18 2025
SNOW SHOWERS WILL CONTINUE DOWNWIND OF THE GREAT LAKES INTO
SUNDAY...CONDITIONS MOSTLY VFR WITH SOME OCCASIONAL MVFR
CEILINGS AND VISIBILITIES.
APX WATCHES/WARNINGS/ADVISORIES
MI...WINTER WEATHER ADVISORY UNTIL 7 AM EST SUNDAY FOR MIZ086.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR LHZ345>349.
SMALL CRAFT ADVISORY UNTIL 5 AM EST SUNDAY FOR LMZ323-341-342-
344>346.
SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR LSZ322.
SMALL CRAFT ADVISORY UNTIL 5 AM EST SUNDAY FOR LSZ321.
UPDATE...JPB
SHORT TERM...MSB
LONG TERM...PBB
AVIATION...JPB
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