Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 182341
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
641 PM EST THU DEC 18 2014

.AVIATION...

//DISCUSSION...

DEEP PLUME OF LOW LEVEL MOISTURE TUCKED BENEATH A STRONG INVERSION
WILL HOLD FIRM TONIGHT.  RECENT OBSERVATIONS AND RADAR DATA CONTINUE
TO DISPLAY A COMBINATION OF LIGHT FREEZING DRIZZLE AND SNOWFLAKES
WITHIN THE RESULTANT LOW STRATUS FIELD.  THE OVERALL COVERAGE PER
LATEST TRENDS DO SUPPORT A TEMPO INCLUSION PRIOR TO MIDNIGHT FROM
FLINT SOUTHWARD.   CEILINGS AT FNT/PTK WILL FLUCTUATE WITHIN IFR/LOW
MVFR THROUGH THIS TIME...LOWER MVFR ELSEWHERE.  DRIER AIR WILL BEGIN
TO ERODE THIS MOIST LAYER FROM ABOVE THROUGH THE EARLY MORNING
PERIOD.  THIS WILL BRING A DIMINISHING TREND TO THE LIGHT
PRECIPITATION COVERAGE...ALTHOUGH THE EXISTING MVFR STRATUS WILL
LIKELY STRUGGLE TO SCATTER UNTIL WELL INTO FRIDAY.

FOR DTW...THERE WILL CONTINUE TO BE THE POTENTIAL FOR A LIGHT
MIXTURE OF FREEZING DRIZZLE AND SNOW EARLY TONIGHT.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE CEILINGS REMAIN BELOW 5000 FT THROUGH FRIDAY
  MORNING.

* HIGH CONFIDENCE THAT PRECIPITATION TYPE WILL BE A MIXTURE OF LIGHT
  FREEZING DRIZZLE AND SNOW THROUGH MIDNIGHT.

&&

.PREV DISCUSSION...ISSUED 355 PM EST THU DEC 18 2014

SHORT TERM...TONIGHT

FREEZING DRIZZLE AND LIGHT SNOW ACROSS SOUTHEAST MICHIGAN IS SLOWLY
BECOMING LESS WIDESPREAD AS THE AFTERNOON PROGRESSES. THE MAIN
CONCERN FOR TONIGHT WILL BE TIMING THE ENDING OF THE FREEZING
DRIZZLE AND WHETHER CLOUDS WILL STICK AROUND. WHILE CURRENT
SATELLITE IMAGERY IS SHOWING DRIER AIR SLOWLY PROGRESSING SOUTHWARD
OUT OF CANADA...PROGRESSION IS REALLY SLOW AND CURRENTLY NOT
ANTICIPATING THE DRY SURGE TO REACH SOUTHEAST MICHIGAN UNTIL CLOSER
TO DAYBREAK FRIDAY MORNING. WITH THE LOW LEVEL MOISTURE STICKING
AROUND OVERNIGHT...LOW LEVEL STRATUS IS EXPECTED TO REMAIN OVER THE
CWA. THE CLOUDS WILL KEEP TEMPERATURES FROM DROPPING TOO MUCH
OVERNIGHT AND HAVE THEREFORE OPTED TO SIDE ON THE WARMER SIDE OF
MODEL GUIDANCE FOR LOWS. EXPECT MID 20S ACROSS THE METRO DETROIT
AREA AND LOW TO MID 20S FOR THE REST OF THE CWA.

IN ADDITION...WHILE DRIZZLE IS DIMINISHING THE FORECASTED STRATUS
COULD RE-INITIATE DRIZZLE FOR THE EARLY PART OF THE EVENING. CURRENT
MODEL SOUNDINGS SHOW A WELL SATURATED BOUNDARY LAYER WITH LIGHT
WINDS OVER SOUTHEAST MICHIGAN THROUGH MOST OF THURSDAY EVENING WHICH
COULD HELP IN THE RE-DEVELOPMENT OF LIGHT DRIZZLE. AS TEMPERATURES
FALL BELOW FREEZING AFTER SUNSET...THE DRIZZLE COULD BECOME FREEZING
DRIZZLE AND MIX WITH SNOW ONCE AGAIN. HOWEVER...CONFIDENCE IN THIS
OCCURRING IS LOW AT THIS FORECAST ISSUANCE AND HAVE ONLY INCLUDED
FREEZING DRIZZLE IN THE FORECAST THROUGH 00Z /7PM/ THURSDAY. WILL
HAVE TO MONITOR OVER THE NEXT SEVERAL HOURS TO SEE IF DRIZZLE STARTS
TO DEVELOP.

LONG TERM...FRIDAY THROUGH WEDNESDAY

THE UPPER LEVEL PATTERN OVER THE UPPER MIDWEST AND GREAT LAKES
STATES WILL DEAMPLIFY TO THE POINT THAT PSEUDO ZONAL FLOW WILL BE
THE PRIMARY SETUP THROUGH MUCH OF THE UPCOMING WEEKEND. THE MAIN
WESTERLY JET AXIS WILL RESIDE OVER THE SOUTHEASTERN UNITED STATES
WITH VERY NOISY SHORTWAVE ENERGY PASSING WITHIN A FADING MIDLEVEL
COL STRUCTURE. HIGH COLUMN STABILITY SEEMS TO BE THE PRIMARY DRIVER
OF A SURFACE ANTICYCLONE THAT WILL PASS DIRECTLY THROUGH
SOUTHEASTERN MICHIGAN. DEAMPLIFIED FLOW WEAK SHORTWAVE ENERGY AND
RESULTS IN VERY QUIET WEATHER THAT MAINTAINS A STATUS QUO FROM A
TEMPERATURE AND PRECIPITATION PERSPECTIVE.

THERE WILL STILL BE SOME FORECAST DIFFICULTY IN THE EXPECTED
PATTERN...PRIMARILY THAT OF CLOUDS AND CLOUD TRENDS. MODEL DATA IS
VERY AGGRESSIVE WITH A SOUTHWARD PUSH OF DRY AIR LATE
TONIGHT...MAKING INROADS OVER MANY AREAS PRIOR TO SUNRISE. PATTERN
RECOGNITION AND OBSERVATIONAL DATA SUGGESTS OTHERWISE...THE HEAVY
LOOK OF SHEARING OCCURRING ALONG A MIDLEVEL CONVERGENCE BOUNDARY
THAT IS SUPPORTING THE SURFACE TROUGH AND CONTINUATION OF
REFLECTIVITY FINELINE. THE PROBLEM WITH THIS SURFACE TROUGH IS
THAT IT CONTINUES TO HOLD ON STRONGER THAN ANY OF THE MODEL
SOLUTIONS HAVE BEEN SUPPORTING. RH AND SPECIFIC HUMIDITY ANALYSES
SUGGESTS THAT CLEARING MAY BE DOWN TO THE M59 CORRIDOR BY SUNRISE
WITH CLOUDS SOLIDLY LOCKED IN OVER THE CENTRAL DETROIT METRO AREA
SOUTHWARD. THE CLEARING TREND MAY THEN ACCELERATE FOR THESE
SOUTHERN LOCATIONS AS WE HEAD INTO FRIDAY EVENING. FINALLY...COULD
BE LOOKING AT A PERIOD OF CLEAR SKIES FRIDAY NIGHT AND INTO THE
FIRST PART OF SATURDAY. LONGWAVE HEIGHT REBOUND AND WIND DIRECTION
CHANGE TO THE SOUTH BY LATE SATURDAY SUPPORTS THE RETURN OF
ORGANIZED MOISTURE ADVECTION AND CLOUDS.

ACTIVE WEATHER IS EXPECTED FOR THE REMAINDER OF THE FORECAST. THIS
WILL OCCUR AS A STRONG PACIFIC JET ENTERS THE PACIFIC
NORTHWEST...DEEPENS THE LONGWAVE TROUGH OVER THE CENTRAL CONUS...AND
EVENTUALLY CAUSES THE TROUGH TO BECOME NEGATIVELY TILTED AS THE JET
ENERGY ROUNDS THE BASE OF THE TROUGH TOWARD CHRISTMAS EVE. AT THE
SURFACE...A WEAKER LOW PRESSURE SYSTEM WILL EVOLVE OVER THE NORTHERN
PLAINS MONDAY/TUESDAY...EVENTUALLY GETTING ABSORBED BY A POTENTIALLY
STRONGER STORM LIFTING NORTHWARD FROM THE DEEP SOUTH. STILL LOTS OF
POSSIBLE SOLUTIONS AS TO HOW/WHERE THIS INTERACTION TAKES PLACE SO
THE DETAILS ARE FAR FROM BEING CLEAR. AT THIS POINT WILL HIGHLIGHT
THE POTENTIAL FOR IMPACTFUL WEATHER CENTERED AROUND
TUESDAY/WEDNESDAY. IMPACTS IN TERMS OF PRECIPITATION WILL BE MOST
LIKELY DURING THE MONDAY NIGHT THROUGH WEDNESDAY TIME FRAME.
MODEL CONSENSUS...WEAK AS IT IS AT THIS POINT...SUGGESTS WE HAVE A
BETTER CHANCE OF BEING ON THE WARMER SIDE OF THIS SYSTEM MONDAY
NIGHT THROUGH TUESDAY NIGHT...WITH COLDER AIR AND BREEZY CONDITIONS
BY CHRISTMAS EVE.

MARINE...

HIGH PRESSURE WILL BUILD INTO THE AREA TONIGHT...MAINTAINING
RELATIVELY RELAXED NORTHERLY WINDS FOR THE TIME OF YEAR. THE SURFACE
HIGH IS FORECASTED TO DRIFT ACROSS THE CENTRAL GREAT LAKES THIS
WEEKEND WITH SOUTHERLY FLOW EVENTUALLY RETURNING ON SUNDAY.

&&

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

$$

AVIATION.....MR
SHORT TERM...RK
LONG TERM....CB/DT
MARINE.......CB


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