Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 202019
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
319 PM EST THU NOV 20 2014

.SHORT TERM...THIS EVENING AND TONIGHT

THE ONGOING SNOW SHOWERS ACROSS PORTIONS OF THE FORECAST AREA HAVE
BEEN THE RESULT OF LAKE EFFECT OFF LAKE MI...SUSTAINED THIS FAR EAST
BY STRONG WSW FLOW WITHIN AN ENHANCED W-E BOUNDARY LAYER CONVERGENCE
AXIS. CONVECTIVE UPDRAFTS HAVE BEEN WITHIN THE GOOD DENDRITIC GROWTH
LAYER...SO FLAKE SIZE HAS BEEN RESPECTABLE. A LONGER LIVED HEAVY BAND
OF SNOW IMPACTED LOCATIONS ALONG AN AXIS FROM SRN SHIAWASSEE/SRN
GENESEE/NRN OAKLAND COUNTIES INTO THE PORT HURON AREA EARLIER TODAY.
SPOTTER REPORTS SUGGEST A SOLID 3 TO 5 INCHES FELL IN THESE AREAS.
WHILE ACCUMULATIONS HAVE BEEN MUCH LESS OUTSIDE OF THIS REGION...THE
INTENSE SNOW SHOWERS HAVE STILL BEEN LEADING TO SPORADIC REDUCTIONS
IN VISIBILITIES AND A QUICK DUSTING OF ACCUMULATION. WINDS HAVE ALSO
INCREASED THIS AFTERNOON /WITH SOME GUSTS OVER 30 MPH REPORTED/
WHICH HAS BEEN CAUSING SOME BLOWING SNOW AND MINOR DRIFTING IN THE
ADVISORY AREA.

ONGOING MID LEVEL COLD AIR ADVECTION AND DAYTIME HEATING HAS BEEN
LIFTING CONVECTIVE DEPTHS THIS AFTERNOON. THIS HAS ACTUALLY RESULTED
IN SOME DISRUPTION TO THE MORE ORGANIZED BANDING. DEEPER MIXING HAS
ALSO LED TO A MORE UNIFORM WESTERLY SURFACE WIND ACROSS SRN
MI...WEAKENING THE CONVERGENCE IN THE BOUNDARY LAYER. THE PREVAILING
WESTERLY FLOW WILL STILL FOCUS THE MORE WIDESPREAD SNOW SHOWER
ACTIVITY ACROSS THE ADVISORY AREA THROUGH EVENING RUSH HOUR. VEERING
OF THE LOW LEVEL FLOW TOWARD THE NORTHWEST DURING THE COURSE OF THE
NIGHT WILL FOCUS THE MORE NUMEROUS SNOW SHOWERS SOUTH OF THE I-
96/969 CORRIDOR LATER THIS EVENING. THERE WILL BE AN OVERALL
WEAKENING TREND TO LAKE EFFECT DURING THE NIGHT UNDER CONTINUED LOW
LEVEL DRY AIR ADVECTION AND LOWERING CONVECTIVE DEPTHS AS A RESULT
OF INCREASING LARGE SCALE SUBSIDENCE. THIS WILL DIMINISH THE OVERALL
COVERAGE OF SNOW SHOWERS. A TRANSITION TOWARD MORE DOMINATE BANDING
IS POSSIBLE PRIOR TO DAYBREAK...WHICH MAY IMPACT FAR SOUTHERN
COUNTIES LATER TONIGHT. THIS IS A FAIRLY LOW CONFIDENCE
SCENARIO...SUGGESTING HOLDING JUST MINOR ADDITIONAL ACCUMULATIONS
TONIGHT ATTM. THE VEERING OF THE FLOW TOWARD THE NORTHWEST AND LOW
LEVEL DRY AIR ADVECTION WILL LEAD TO SOME CLEARING DURING THE COURSE
OF THE NIGHT /ESPECIALLY ACROSS THE SAGINAW VALLEY AND THUMB/. THIS
AND A GRADUAL WEAKENING GRADIENT WILL OFFER AN OPPORTUNITY FOR GOOD
RADIATIONAL COOLING /SUPPORTING MIN TEMPS IN THE SINGLE DIGITS TO
LOWER TEENS/.

&&

.LONG TERM...

THE SURGE OF STRONG PACIFIC ENERGY TAKING AIM ON THE PACIFIC
NORTHWEST OVER THE NEXT 24 HOURS HAS DEAMPLIFIED THE WEST COAST
RIDGE RESULTING IN A TRANSITION TO ZONAL FLOW ACROSS THE CONUS. THE
ZONAL REGIME WILL SPREAD INTO THE GREAT LAKES, FLOODING THE MID-
LEVELS WITH WARMER AIR, UPON THE DEPARTURE OF TODAY`S TROUGH.
BETWEEN 12Z FRIDAY AND 12Z SATURDAY, H85 TEMPERATURES OVER SOUTHEAST
MICHIGAN WILL RISE ABOUT 20 DEGREES AS THE MID-LEVEL CLIMB ABOVE
FREEZING BY SATURDAY MORNING. SHORTWAVE RIDGING EMBEDDED IN THE
DEVELOPING ZONAL FLOW WILL BUILD INTO THE AREA DURING THE DAY FRIDAY
AND EASE THE SURFACE HIGH OVER THE OHIO VALLEY EAST. RETURN FLOW AT
THE SURFACE WILL BE OF LITTLE HELP WITH ARCTIC AIR ENTRENCHED OVER
THE EASTERN US. TEMPERATURES WILL REMAIN IN THE UPPER TEENS/LOW 20S
TOMORROW THROUGH TOMORROW NIGHT. AS A RESULT, A STRONG INVERSION
WILL BEGIN TO TAKE SHAPE ON FRIDAY NIGHT AS THE SHORTWAVE OVER THE
INTERMOUNTAIN WEST EJECTS OUT OVER THE GREAT LAKES. ISENTROPIC
ASCENT AND A QUICK HIT OF PV ADVECTION 09Z-15Z SATURDAY MORNING WILL
SUPPORT AT LEAST A SCATTERED COVERAGE OF SHOWERS LIFTING THROUGH THE
AREA. CURRENT INDICATIONS ARE THAT THIS PRECIPITATION MAY FALL AS
FREEZING RAIN. SHORT DURATION AND LACK OF MAINTENANCE FOR SUB-ZERO
WET BULBING AT THE SURFACE LIMIT CONCERNS, BUT THE POTENTIAL FOR
SOME LIGHT ICING IS EVIDENT.

WEAK ISENTROPIC ASCENT WILL THEN BE ONGOING THROUGH THE DAY SATURDAY
AS A 100KT JET DEVELOPS OVERHEAD IN RESPONSE TO THE DEEPENING LONGWAVE
TROUGH UPSTREAM. THIS WILL HELP ORIENT A MID-LEVEL BAROCLINIC ZONE
ACROSS THE AREA WHICH WILL SERVE AS A FOCUS FOR ONGOING
PRECIPITATION DURING THE DAY. DRY MID-LEVELS SUGGEST THAT DRIZZLE,
AS OPPOSED TO SHOWERS, WILL BE WORTH KEEPING AN EYE ON. EITHER WAY,
TEMPERATURE RECOVERY DURING THIS TIME WILL BE IMPORTANT TO WATCH AS
AN ADDITIONAL FREEZING PRECIP THREAT COULD THEORETICALLY EVOLVE.
HOWEVER, THE SOLID SOUTHERLY GRADIENT COMBINED WITH THE NAM`S
TENDENCY TO HOLD ONTO LOW-LEVEL COLD AIR A BIT TOO LONG HELP
ALLEVIATE THAT CONCERN AT THIS TIME.

GLOBAL NWP REMAINS IN DECENT AGREEMENT WITH THE REST OF THE
FORECAST WITH SLIGHT DIFFERENCES IN TIMING AND LOCATION OF A
SURFACE LOW AS IT LIFTS NORTHWARD FROM THE SOUTHERN PLAINS TO
NORTHERN LOWER MICHIGAN SUNDAY MORNING TO MONDAY MORNING. WE REMAIN
ON THE WARM SIDE OF THE SYSTEM WITH A GOOD FEED OF MOISTURE SO A
RAINY PERIOD CAN BE EXPECTED...WITH THE HIGHEST POPS CENTERED ON
LATE SUNDAY TO EARLY MONDAY. SOME DISAGREEMENT EXISTS ON HOW FAST
THE UPPER WAVE AND ATTENDANT SURFACE LOW AND FORCING LIFT IN SUNDAY
SO THE DAY MAY NOT BE A COMPLETE WASHOUT...BUT WILL REFINE TIMING
WITH FUTURE FORECASTS. THE COLD FRONT MOVES THROUGH LATER MONDAY
USHERING A COLDER AIRMASS BACK IN SO THE WARMING TREND LOOKS TO BE
SHORT LIVED.
.

&&

.MARINE...

NORTHWEST WINDS GUSTING TO GALES WILL GRADUALLY EASE THROUGH TONIGHT
AS HIGH PRESSURE BUILDS INTO THE GREAT LAKES. ALL GALE WARNINGS AND
SMALL CRAFT ADVISORIES ARE THEREFORE SCHEDULED TO EXPIRE
INCREMENTALLY THROUGH THE NIGHT AS WINDS AND WAVES SUBSIDE. A
MODERATE SOUTHWEST BREEZE WILL THEN DOMINATE THROUGH FRIDAY BEFORE
DEPARTURE OF HIGH PRESSURE TO THE EAST TRIGGERS AN INCREASE IN WINDS
AGAIN ON FRIDAY NIGHT. SOUTHWESTERLY GUSTS TO GALES OR NEAR GALES
WILL BE POSSIBLE FRIDAY NIGHT THROUGH THE FIRST HALF OF
SATURDAY...MAINLY OVER THE CENTRAL SW TO NE AXIS OF LAKE HURON.

&&

.AVIATION...ISSUED 1204 PM EST THU NOV 20 2014

//DISCUSSION...

LOW LEVEL CONVERGENCE HAS ENHANCED SNOW SHOWERS OFF LAKE MICHIGAN
AND BROUGHT THEM WELL INLAND INTO SE MI. INCREASED LOW LEVEL
INSTABILITY HAS FRACTURED SOME OF THE MORE PERSISTENT SNOW BANDS.
WHAT THIS MEANS IS THAT THERE WILL BE INTERVALS OF BREAKS AND BRIEF
INTENSE SNOW SHOWERS...IMPACTING MAINLY FNT AND PTK THROUGH THE
AFTERNOON. VISIBILITIES WITHIN SOME OF THE HEAVIER SNOW SHOWERS WILL
BE REDUCED TO LESS THAN A QUARTER MILE. THE LOW LEVEL WINDS WILL
VEER TOWARD THE W-NW THIS EVENING...PUSHING THE HIGHER CONCENTRATION
SNOW BANDS FARTHER SOUTH AND LEADING TO SOME CLEARING FROM NORTH TO
SOUTH.

FOR DTW...THROUGH THE AFTERNOON...THE MORE WIDESPREAD AND INTENSE
SNOW SHOWERS WILL REMAIN NORTH OF METRO. THE WINDS WILL TURN MORE
TOWARD THE WEST-NORTHWEST THIS EVENING /AFTER 00Z/ AND THIS MAY
BRING SOME OF THE HIGHER INTENSITY SNOW SHOWERS INTO METRO...
POSSIBLY LEADING TO SOME MINOR ACCUMULATIONS. CONTINUED VEERING OF
THE WINDS OVERNIGHT SHOULD PUSH LINGERING SNOW SHOWERS SOUTH OF
METRO AFTER MIDNIGHT.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5KFT.

* LOW CONFIDENCE IN BRIEF INTERVALS OF VISIBILITY BELOW A HALF MILE
  IN SNOW THIS EVENING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR MIZ060>063-
     068>070.

LAKE HURON...GALE WARNING UNTIL 3 AM EST FRIDAY FOR LHZ362-363-441-462-463.

     SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR LHZ421-442-
     443.

     GALE WARNING UNTIL 7 PM EST THIS EVENING FOR LHZ361.

LAKE ST CLAIR...SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR LEZ444.

     LOW WATER ADVISORY UNTIL 4 AM EST FRIDAY FOR LEZ444.

&&

$$

SHORT TERM...SC
LONG TERM....JVC/DT
MARINE.......JVC
AVIATION.....SC


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



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