489
FXUS63 KDTX 200453
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1153 PM EST WED FEB 19 2025
KEY MESSAGES
- WIDESPREAD LIGHT SNOW LATE TONIGHT LASTS THROUGH THE MORNING AS A
LOW PRESSURE SYSTEM PASSES TO OUR SOUTH BUT REACHES UP INTO
MICHIGAN. GENERALLY AROUND A HALF INCH OF SNOW IS EXPECTED.
- NORTHERLY WINDS MAY PUSH A LAKE EFFECT SNOW BAND OFF LAKE HURON
INTO THE NORTHERN AND EASTERN THUMB WHICH COULD RESULT IN SOME
ADDITIONAL SNOW ACCUMULATIONS.
- TEMPERATURES OF 5 TO 10 DEGREES BELOW NORMAL WILL HOLD THROUGH THE
REMAINDER OF THE WEEK.
AVIATION
LIGHT SNOW IS INCREASING COVERAGE AND INTENSITY ON SCHEDULE AS
MIDWEST LOW PRESSURE SLIDES JUST SOUTH OF THE MI BORDER LATE
TONIGHT. CLOUD CEILING HOVERS AROUND THE MVFR THRESHOLD GIVEN
MAINTENANCE OF THE NW CLOUD LAYER WIND COMBINED WITH THE CENTRAL
GREAT LAKES SURFACE TROUGH. ALONG WITH THE CLOUDS, BRIEF MVFR
VISIBILITY QUICKLY DROPS INTO IFR AS SNOW SPREADS ACROSS THE
TERMINAL CORRIDOR DURING PEAK INTENSITY AND THEN BACKS OFF INTO MVFR
DURING THE MORNING. SNOW ENDS WHILE MVFR CEILING LINGERS IN A
RENEWED NW WIND FIELD THIS AFTERNOON AND THURSDAY EVENING.
FOR DTW... A PERIOD OF LIGHT SNOW AVERAGES IFR VISIBILITY DURING THE
LATE NIGHT GRADUALLY IMPROVING TO MVFR THROUGH MUCH OF THE MORNING.
PROJECTIONS ARE FOR EVENT TOTAL ACCUMULATION AROUND 0.5 INCH.
DTW THRESHOLD PROBABILITIES
* HIGH FOR CEILING AT OR BELOW 5000 FEET TONIGHT AND THURSDAY.
* HIGH FOR SNOW AS PRECIPITATION TYPE TONIGHT AND THURSDAY.
PREV DISCUSSION
ISSUED AT 955 PM EST WED FEB 19 2025
UPDATE...
THE EVENING UPDATE CHECKS ON THE PROGRESS OF LIGHT SNOW STILL
EXPECTED TO SPREAD OVER SOUTHERN LOWER MI LATER TONIGHT. UPSTREAM
OBSERVATIONS INDICATE A LARGE AREA OF MOSTLY VIRGA FILLING IN WITH
SNOW REACHING THE SURFACE FROM ABOUT AZO TO FWA AND WEST, WHICH IS
IN LINE WITH MODEL SOLUTIONS AT THIS POINT IN THE EVENING. A ROBUST
MID LEVEL CIRCULATION SHOWN IN SATELLITE IMAGERY ALSO SUPPORTS RECENT
MODEL UPDATES AND AVAILABLE 00Z DATA THAT PROJECT STEADY EXPANSION
OF SNOW INTO SE MI AFTER MIDNIGHT. HINTS OF ELEVATED INSTABILITY
SHOW UP IN MODEL THETA-E CROSS SECTIONS WITHIN A STRONG
DCVA/DEFORMATION HYBRID OF MID LEVEL FORCING ADDING CONFIDENCE IN
THE TREND. MOISTURE REMAINS THE LIMITING FACTOR AS SPECIFIC HUMIDITY
AVERAGES SUB 1 G/KG IN THE 850-700 MB LAYER, ALSO IN LINE WITH THE
HIGH POP/LOW QPF SCENARIO ALREADY SET UP IN THE FORECAST. MODEL
SOUNDINGS ARE DEEPLY SUPERSATURATED WHICH COULD ALLOW FOR SPOTTY
"OVERACHIEVEMENT" BUT STILL LESS THAN 1 INCH ACROSS THE AREA, JUST
ENOUGH TO PREVENT PEAK SPEED DURING THE MORNING COMMUTE.
THE OTHER AREA TO MONITOR IS THE THUMB SHORELINE WHERE THE LAKE
AGGREGATE SURFACE TROUGH COULD BE PULLED ONSHORE THE MID LEVEL WAVE
TRAVERSING THE OHIO BORDER. THIS CAN SOMETIMES BE A VOLATILE
CONFIGURATION AS SYSTEM MOISTURE SEEDS A DOMINANT BAND OR STRONG
MULTIBAND LAKE EFFECT PATTERN. THE ACTIVITY IS THEN PULLED SOUTHWARD
OR WESTWARD INTO THE SHORELINE AS THE WAVE MOVES BY TO THE SOUTH. IN
TONIGHT'S CASE, CONVECTIVE DEPTH IS SURPRISINGLY LIMITED TO AROUND
5000 FT IN MODEL SOUNDINGS WHICH MATCHES ONGOING SNOW SHOWERS OVER
THE SOUTH HALF OF LAKE HURON THIS EVENING. THE FORECAST UPDATE JUST
NUDGES POPS UP INTO THE LIKELY/NUMEROUS RANGE DURING THE MORNING
WHILE MAINTAINING ADDITIONAL ACCUMULATION AROUND 1 INCH.
PREV DISCUSSION...
ISSUED AT 340 PM EST WED FEB 19 2025
DISCUSSION...
A LOBE OF PLANETARY VORTICITY AND A MYRIAD OF FAIRLY DISORGANIZED
SHORTWAVE ENERGY WILL STEADILY COALESCE WHILE PIVOTING THROUGH THE
UPPER MISSISSIPPI RIVER VALLEY AND CENTRAL GREAT LAKES THIS
AFTERNOON AND TONIGHT. H5 GEOPOTENTIAL CHARTS AND ABSOLUTE VORTICITY
FIELDS SUPPORT AMPLIFICATION AND MIDLEVEL LOW PRESSURE DEEPENING
THROUGH PORTIONS OF NORTHERN IN/OH BETWEEN 00-06Z TONIGHT. ALL
INDICATIONS ARE THAT WEAK AGEOSTROPHIC OR DEFORMATION RESPONSE OF
THE DEVELOPING LOW WILL PASS IMMEDIATELY SOUTH OF THE MICHIGAN BORDER
, HOWEVER, MODELS HAVE BEEN VERY CONSISTENT IN ADVECTING REMNANT
ATLANTIC MOISTURE SOUTHWARD INTO LOWER MICHIGAN FROM ONTARIO.
FORECAST 290-280KT SURFACES SIGNAL SHALLOWLY SLOPED ISENTROPIC
ASCENT BETWEEN 05-12Z WITH A MATCH IN TIMING TO DEEP SATURATION IN
THE FORECAST SOUNDINGS. SOUNDINGS SHOW DEEP MOISTURE WITH AT LEAST
A BOUNDARY LAYER CONNECTION INTO THE DENDRITIC GROWTH ZONE INTO THE
DAYLIGHT THURSDAY. MUCH OF THE DETERMINISTIC AND ENSEMBLE GUIDANCE
REMAINS LEAN ON QPF, BUT GIVEN THE SETUP QUALITATIVELY PREFERENCE IS
TO CARRY A HIGH POP (APPROXIMATELY 60%) WITH LOW QPF (SNOW
ACCUMULATION OF DUSTING OR A COUPLE OF TENTHS). GIVEN THE COLD
TEMPERATURES AND REFRIGERATED GROUND, SUSPECT THAT FLURRIES AND LIGHT
SNOW ACTIVITY WILL BE ABLE TO ACCUMULATE EFFICIENTLY FOR A LIGHT
ACCUMULATION. COLD NORTHERLY FLOW WITH SOME CYCLONIC VORTICITY
DIFFERENTIAL 1000-500MB GEOPOTENTIAL HEIGHT RISES WILL SUPPORT
SURFACE HIGH PRESSURE BUILDING THROUGH THE GREAT LAKES LATE THURSDAY
THROUGH EARLY SUNDAY. QUIET WEATHER WITH HIGH CONFIDENCE IN STRONG
STATIC STABILITY BETWEEN 4.0 AND 9.0 FT AGL. DAYTIME TEMPERATURES
WILL RANGE IN THE UPPER 20S FRIDAY AND SATURDAY, SOME 5 TO 10
DEGREES BELOW NORMAL.
VERY DISORGANIZED SHORTWAVE ENERGY IS FORECASTED TO ADVECT ALONG IN
THE WEST TO NORTHWEST FLOW THIS WEEKEND AND EARLY NEXT WEEK. PLENTY
OF OPPORTUNITY EXISTS FOR PERIODIC CHANCES AT FLURRIES, BUT WARM AIR
IS FORECASTED TO REMAIN IN PLACE DIFFERENTIALLY ALOFT. THE ONE TIME
PERIOD TO MONITOR MAY BE ON MONDAY AS THE EXIT REGION OF THE NEXT
UPPER LEVEL JET STREAK COULD ARRIVE. THE CURRENT FORECAST HAS A LOW
CHANCE FOR A RAIN/SNOW MIX WITH PACIFIC AIR MASS ALLOWING FOR
TEMPERATURES OF NEAR 40 DEGREES.
MARINE...
A WEAK SURFACE TROUGH HOLDS OVER THE CENTRAL GREAT LAKES THROUGH
THIS EVENING WITH JUST ENOUGH CONVERGENCE WITHIN THE WEAK N TO NW
FLOW TO MAINTAIN SOME POCKETS OF SNOW SHOWERS OVER LAKE HURON. AN
UPPER LEVEL DISTURBANCE PASSING OVER TONIGHT WILL THEN BRING A MORE
WIDESPREAD AREA OF LIGHT SNOW FROM LATE THIS EVENING INTO THURSDAY.
AN UPTICK IN N TO NW WIND ENSUES THURSDAY AFTERNOON INTO THURSDAY
NIGHT AS THIS SYSTEM PASSES, TOPPING OUT AROUND 20 TO 25 KNOTS. HIGH
PRESSURE BUILDS INTO THE MID-MISSISSIPPI VALLEY ON FRIDAY, EXTENDING
NORTHEAST INTO THE GREAT LAKES. THIS MAINTAINS LIGHTER WIND THAT
SHIFTS SW AND BEGINS TO INCREASE AGAIN FRIDAY NIGHT INTO SATURDAY.
MAGNITUDE AGAIN LOOKS TO TOP OUT AROUND 20 TO 25 KNOTS, BUT THERE
WILL BE A CHANCE FOR SOME 30 KNOT GUSTS OVER PARTS OF LAKE HURON
SATURDAY AFTERNOON AND EVENING AS A COLD FRONT APPROACHES FROM THE
NORTH. A CLIPPER SYSTEM WILL THEN DROP INTO THE REGION SUNDAY INTO
MONDAY BRINGING THE NEXT INCREASE IN SOUTH WINDS AHEAD OF IT.
DTX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
AVIATION.....BT
UPDATE.......BT
DISCUSSION...CB
MARINE.......TF
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