Heavy Snow in Michigan, December 13 to 14, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1252 AM EST FRI DEC 13 2013

.AVIATION...

//DISCUSSION...

MVFR CONDITIONS WILL PERSIST THROUGH THE NIGHT FOR MOST TAF SITES AS
LAKE EFFECT STRATUS HOLDS OVER THE AREA. THE MOISTURE CONTINUES TO
CHANNEL IN UNDER THE FAIRLY STRONG INVERSION AND SURFACE DEWPOINTS
IN THE TEENS WILL DO LITTLE TO WORK AGAINST THIS. MBS LOOKS LIKE IT
MAY BE INTO VFR FOR A WHILE AS CEILINGS UPSTREAM ARE ALL IN THE
5-6KFT RANGE WITH LOWER LAKE MOISTURE HOLDING FURHTER TO THE SOUTH.

FOR DTW...THE DRY SOUTHWEST FLOW HAS BROUGHT THE CLEARING LINE NORTH
THROUGH THE SITE FOR AT LEAST A LITTLE WHILE. THERE LOOKS TO BE A
RESURGENCE IN LAKE EFFECT CLOUDS PUSHING EASTWARD SO WILL MONITOR TO
SEE IF IT MAKES IT BACK OVER THE AIRPORT. FOR THE TIME BEING WITH
THE CLOUD/CLEARING LINE SO CLOSE...WILL TEMPO IN A BKN GROUP FOR A
COUPLE HOURS. THE NEXT LOW PRESSURE SYSTEM WILL BRING SNOW TO THE
AREA STARTING AROUND 06Z SATURDAY.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE WITH CEILINGS BELOW 5000 FT FOR THE NEXT FEW HOURS
WITH MEDIUM CONFIDENCE THROUGH THE REST OF THE TAF CYCLE.

* HIGH CONFIDENCE PRECIPITATION TYPE WILL BE SNOW SATURDAY.

&&

.PREV DISCUSSION...ISSUED 957 PM EST THU DEC 12 2013

UPDATE...

THE 00Z DTX SOUNDING SHOWED A DEEP INVERSION BASED NEAR 3500 FT
AGL. THE SOUNDING WAS SUGGESTIVE OF SUPERSATURATION WITH RESPECT
TO ICE AROUND -16C. THIS LIKELY AIDED THE FLARE UP IN FLURRIES
EARLIER THIS EVENING. MID LEVEL SUBSIDENCE IS LOWERING THIS
INVERSION AND AS A RESULT THE AMOUNT OF FLURRIES HAVE DIMINISHED
ACROSS THE AREA. WESTERLY FLOW OFF LAKE MI SHOULD STILL SUSTAIN
AMPLE STRATUS THROUGH THE NIGHT...WITH THE EXCEPTION BEING MONROE
AND LENAWEE COUNTIES DUE TO THE MORE SW FLOW NEAR THE STATE LINE.
THESE CLOUDS SHOULD HOLD TEMPS NEARLY STEADY THROUGH THE NIGHT.
MID LEVEL FGEN NOW OVERSPREADING NRN WI WILL ADVANCE INTO THE TRI
CITIES AND THUMB TOWARD MORNING. THE VERTICAL RESPONSE SHOULD BE
QUITE WEAK GIVEN THE STRONGLY STABLE MID LEVELS...RESULTING ONLY
IN FLURRIES OR LIGHT SNOW SHOWERS. OVERALL THE GOING FORECAST IS
IN GOOD SHAPE. JUST SOME MINOR ADJUSTEMENTS TO TEMPS AND POPS WILL
BE MADE.

PREV DISCUSSION...ISSUED 327 PM EST THU DEC 12 2013

SHORT TERM...TONIGHT

NORTHWEST STEERING FLOW WILL CONTINUE TO ALLOW A STRATO-CU DECK TO
SPREAD SOUTHEAST THROUGHOUT THE REGION. MUCH OF THE AREA SAW SOME
PEEKS OF SUNSHINE THIS AFTERNOON, BUT THERE WAS VERY LITTLE
CONVECTIVE ELEMENT TO THE CLOUD FIELD. DEWPOINT DEPRESSIONS FOR THE
DETROIT METRO AREA ARE NEAR 15F, SO MUCH OF THE STRATO CU WILL
CONTINUE TO DISINTEGRATE AS IT TRIES TO PROGRESS SOUTHEASTWARD.

SOUTHWEST SURFACE WINDS AND NORTHWEST FLOW ALOFT HAS CREATED A
CORRIDOR OF CONVERGENCE THAT WILL KEEP SNOW SHOWERS POSSIBLE IN THE
SAGINAW VALLEY THROUGH THIS EVENING. ADDING TO THE SFC CONVERGENCE
WILL BE A COLD FRONT ENTERING THE AREA OVERNIGHT. THIS FRONT WILL
PROVIDE ELEVATED OMEGA AND RH VALUES AT LEAST AS FAR SOUTH OF I-69.
SOUTH OF THERE...THE FRONT LOSES ITS STRENGTH AND WASHES OUT AS A
WEAK STATIONARY BOUNDARY. THE RESULT WILL BE AROUND AND INCH OF SNOW
IN THE NORTHERN COUNTIES...WITH JUST TRACE AMOUNTS EXPECTED SOUTH OF
I-69.

MODELS CONTINUE TO SHOW A SHARP CUT-OFF IN THE LOW LEVEL MOISTURE
NEAR THE OH BORDER. HAVE SCATTERED OUT THE CLOUD COVERAGE IN THE
SOUTH TONIGHT WHICH SHOULD ALLOW THEM TO RADIATE CLOSE TO SINGLE
DIGITS. MOST PLACES WILL BE IN THE MID TEENS FOR LOWS WITH THE WIND
CHILL FACTOR IN THE 0 TO 5F RANGE.

LONG TERM...

THE 12Z SUITE OF GUIDANCE ARRIVES WITH SAMPLING OF THE PV ANOMALY
OVER SOUTHERN CALIFORNIA AND MARGINAL UPPER AIR SAMPLING OF PORTIONS
OF THE WEST COAST TROUGH COMPLEX AS WELL AS EMERGING SHORTWAVE
ENERGY OVER THE GULF OF ALASKA. ALL THREE FEATURES WILL COME INTO
PLAY FRIDAY NIGHT THROUGH SATURDAY AS WIDESPREAD ACCUMULATING SNOW
OVERSPREADS SOUTHEAST MICHIGAN.

A QUICK SUMMARY OF THE GUIDANCE - THE NCEP MODELS SHOWED LITTLE
CHANGE WHILE THE GEM REMAINED ON THE MORE AGGRESSIVE SIDE.
NOTEWORTHY ADJUSTMENTS WERE OBSERVED BY THE ECMWF AND UKMET WHICH
HAVE BOTH TRENDED DECIDEDLY STRONGER AND SLOWER. FOR THE PURPOSE OF
GETTING A FULL HANDLE ON THE SPECTRUM OF MODEL SOLUTIONS, IT IS
PERHAPS WORTH NOTING THAT EVEN THE EXTENDED/48HR PANELS OF THE HIGH
RESOLUTION NMM IS MORE ROBUST IN ITS SOLUTIONS. THIS LEAVES THE GFS
ON THE WEAKER END OF THE CONSENSUS AND THE NAM AN APPARENT OUTLIER
ALTOGETHER, WHICH IS EXPECTED AS THE 48+HR TIME FRAME IS NOT EXACTLY
THE NAMS WHEELHOUSE.

THERE ARE MULTIPLE CAUSES FOR THE MORE AGGRESSIVE TREND NOTED IN THE
ECMWF AND UKMET. FIRST, THE EMERGING ENERGY OVER THE NORTHERN GULF
OF ALASKA/NORTHERN FRINGE OF THE WEST COAST TROUGH IS DEPICTED ON
PLANVIEWS OF 400MB POTENTIAL VORTICITY AS BEING CONSIDERABLY MORE
COHERENT AS IT SWEEPS TOWARD THE GREAT LAKES ON SATURDAY AFTERNOON.
THIS WAS A TREND THAT WAS ACTUALLY OBSERVED TO SOME EXTENT AMONG
MULTIPLE MEMBERS OF THE 12Z SUITE. IN ADDITION, ENERGY ASSOCIATED
WITH THE DIGGING WEST COAST TROUGH APPEARS TO BE MORE CONSOLIDATED
IN THE BASE OF THE TROUGH THAT WILL BE POSITIONED OVER NEW
MEXICO/WESTERN TEXAS ON SATURDAY AFTERNOON. AS A RESULT, THE LEAD
DAMPENING PV ANOMALY THAT IS BEING EJECTED NORTHEAST - AND WHICH IS
PROGGED TO ARRIVE COINCIDENT WITH THE INITIAL SLUG OF DEEP MOISTURE
- WILL BE PULLED FURTHER TO THE NORTHWEST INSTEAD OF SHEARING OFF
THE MID-ATLANTIC COAST. THE NET EFFECT IS A CONSIDERABLY MORE ROBUST
PATTERN OF MID-LEVEL HEIGHT FALLS ACROSS THE GREAT LAKES IN THE
PRESENCE OF A PRONOUNCED INVERTED LOW-LEVEL TROUGH AS ALL FEATURES
INVOLVED LOOK A TOUCH STRONGER AND CLOSER IN PROXIMITY.

PRIOR TO THE ARRIVAL OF ACCUMULATING SNOW FRIDAY NIGHT, A COLD FRONT
IS STILL ON TRACK TO SAG THROUGH THE AREA DURING THE DAY ON FRIDAY.
STILL FULLY AGREE WITH THE PREVIOUS SHIFT THAT QPF IS OVERSIMULATED
HERE, BUT ALSO FEEL THAT THE COLLAPSING THERMAL GRADIENT RESULTING
FROM INCREASINGLY CONFLUENT MID-LEVEL FLOW COULD EASILY TOUCH OFF AN
FGEN RESPONSE AND HAVE THEREFORE MOVED FORWARD WITH LIGHT QPF INVOF
THE FRONT. LESS THAN ONE INCH WILL BE POSSIBLE NORTH OF M59 FRI AFTN
THROUGH MIDNIGHT. RIGHT ENTRANCE JET SUPPORT WILL THEN DEVELOP LATE
FRIDAY NIGHT AND PERSIST THROUGH SATURDAY WHILE THE CORRIDOR OF
STRONGEST HEIGHT FALLS BECOMES INCREASINGLY FOCUSED OVER THE GREAT
LAKES IN THE FASHION DESCRIBED ABOVE RESULTING IN INCREASINGLY
WIDESPREAD LIGHT TO MODERATE SNOWFALL THAT IS FORECAST TO PERSIST
FOR THE BALANCE OF THE DAYLIGHT HOURS ON SATURDAY.

AS FOR AMOUNTS, TAKEN AT FACE VALUE THE 12Z ECMWF WOULD SUPPORT 3 TO
5 ACROSS THE FAR NORTH INCREASING TO 5 TO 7 SOUTH OF 8 MILE. EVEN
THE SOMEWHAT LESS IMPRESSIVE GFS SUPPORTS SIMILAR, IF SOMEWHAT
TEMPERED VALUES. THE FORECAST HAS THEREFORE BEEN TRENDED IN THE
DIRECTION OF THE GROWING CONSENSUS. THE OFFICIAL FORECAST IS NOW
ESSENTIALLY: 2-4 NORTH OF I-69, 3-5 NORTH OF I-96, 4-6 SOUTH OF
THERE. AS FOR HEADLINES, THE LONG 18+ HOUR DURATION OF THE BULK OF
THE SNOWFALL SUGGESTS A SOLID ADVISORY EVENT. WILL AFFORD THE
MID-SHIFT THE OPPORTUNITY TO PERUSE ANOTHER MODEL CYCLE BEFORE
CONSIDERING ISSUANCE.

HIGH PRESSURE RETURNS ON SUNDAY TO THE SOUTHERN CWA WHILE A WEAK
SURFACE LOW PRESSURE SYSTEM TRACKS ACROSS THE NORTHERN GREAT LAKES.
THIS LOW COULD BRING ANOTHER CHANCE FOR SOME SNOW TO THE SAGINAW
VALLEY AND THUMB REGIONS. OTHERWISE...COLD ARCTIC AIR FILTERS IN FOR
SUNDAY NIGHT WITH LOWS IN THE SINGLE DIGITS AND WIND CHILLS DROPPING
TO BELOW ZERO FOR MOST LOCATIONS. THE COLD AIR WILL STICK AROUND
THROUGH MONDAY BEFORE SLIGHTLY WARMER AIR RETURNS /HIGHS IN THE MID
20S AND LOWS IN THE UPPER TEENS/ THROUGH MID WEEK. A SERIES OF
DISTURBANCES WILL IMPACT THE REGION THROUGH MID WEEK...EACH BRINGING
ANOTHER CHANCE OF SNOW TO THE AREA.

MARINE...

SURFACE HIGH PRESSURE OVER THE TENNESSEE VALLEY WILL BATTLE WITH A
LOW DIPPING SOUTH INTO THE GREAT LAKES TONIGHT. LOW PRESSURE AND ITS
ATTENDANT COLD FRONT WILL CREATE A PRESSURE GRADIENT ACROSS LAKE
HURON. INSTABILITY CAUSED BY WARM AIR IMMEDIATELY ABOVE THE LAKE
RISING INTO THE COLD, ARCTIC AIR BEHIND THE FRONT WILL ENHANCE WIND
SPEEDS AND WAVE HEIGHTS TONIGHT. GALE WARNINGS AND HEAVY FREEZING
SPRAY WARNINGS HAVE BEEN ISSUED THROUGH TONIGHT. A FRONTAL BOUNDARY
WILL CAUSE A QUICK WIND SHIFT TO THE NORTHEAST ON FRIDAY. THIS MAY
CAUSE FUNNELING AND HIGH WAVES IN THE SAGINAW BAY. SUB-GALE WIND
GUSTS WILL ARRIVE LATE SATURDAY AND AGAIN SUNDAY NIGHT.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

AVIATION.....DRK
UPDATE.......SC
SHORT TERM...MM
LONG TERM....JVC/RK
MARINE.......JVC

YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
341 PM EST THU DEC 12 2013

MIZ075-076-082-083-132045-
WASHTENAW-WAYNE-LENAWEE-MONROE-
341 PM EST THU DEC 12 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

A LOW PRESSURE SYSTEM IS FORECAST TO TRACK THROUGH THE GREAT LAKES
REGION FRIDAY NIGHT THROUGH SATURDAY. WIDESPREAD SNOW ACCUMULATION
IS EXPECTED. THE POTENTIAL EXISTS FOR 4 TO 6 INCHES SOUTH OF THE
INTERSTATE 96 CORRIDOR.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT.

MIZ060>063-068>070-132045-
SHIAWASSEE-GENESEE-LAPEER-ST. CLAIR-LIVINGSTON-OAKLAND-MACOMB-
341 PM EST THU DEC 12 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

A LOW PRESSURE SYSTEM IS FORECAST TO TRACK THROUGH THE GREAT LAKES
REGION FRIDAY NIGHT THROUGH SATURDAY. WIDESPREAD SNOW ACCUMULATION
IS EXPECTED. THE POTENTIAL EXISTS FOR 3 TO 5 INCHES NORTH OF THE
INTERSTATE 96 CORRIDOR.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT.

MIZ047>049-053>055-132045-
MIDLAND-BAY-HURON-SAGINAW-TUSCOLA-SANILAC-
341 PM EST THU DEC 12 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

A LOW PRESSURE SYSTEM IS FORECAST TO TRACK THROUGH THE GREAT LAKES
REGION FRIDAY NIGHT THROUGH SATURDAY. WIDESPREAD SNOW ACCUMULATION
IS EXPECTED. THE POTENTIAL EXISTS FOR 2 TO 4 INCHES NORTH OF THE
INTERSTATE 69 CORRIDOR.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT.

LCZ422-423-460-LEZ444-LHZ361>363-421-422-441>443-462>464-132045-
ST. CLAIR RIVER-DETROIT RIVER-LAKE ST. CLAIR-
MICHIGAN WATERS OF LAKE ERIE FROM DETROIT RIVER TO NORTH CAPE MI-
LAKE HURON FROM 5NM EAST OF MACKINAC BRIDGE TO PRESQUE ISLE LT
BEYOND 5 NM OFF SHORE-
LAKE HURON FROM PRESQUE ISLE LIGHT TO STURGEON POINT MI BEYOND 5NM
OFF SHORE-
LAKE HURON FROM STURGEON POINT TO ALABASTER MI BEYOND 5NM OFF SHORE-
OUTER SAGINAW BAY SW OF ALABASTER TO PORT AUSTIN MI TO INNER SAGINAW
BAY-INNER SAGINAW BAY SW OF POINT AU GRES TO BAY PORT MI-
PORT AUSTIN TO HARBOR BEACH MI-HARBOR BEACH TO PORT SANILAC MI-
PORT SANILAC TO PORT HURON MI-
LAKE HURON FROM PORT AUSTIN TO HARBOR BEACH BEYOND 5NM OFF SHORE-
LAKE HURON FROM HARBOR BEACH TO PORT SANILAC BEYOND 5NM OFF SHORE-
LAKE HURON FROM PORT SANILAC TO PORT HURON BEYOND 5NM OFF SHORE-
341 PM EST THU DEC 12 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE ERIE...LAKE
HURON AND LAKE ST CLAIR.

.DAY ONE...THIS AFTERNOON AND TONIGHT

GALE WARNINGS...HEAVY FREEZING SPRAY WARNINGS...AND SMALL CRAFT
ADVISORIES ARE IN EFFECT. PLEASE SEE THE LATEST FORECAST FOR MORE DETAIL.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT.

YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).