Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 290148
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
848 PM EST FRI NOV 28 2014

.UPDATE...

THE REGION OF LIGHT SNOW HAS BEEN SLOWLY LIFTING NORTHEASTWARD
DURING THE EVENING...WITH LOCATIONS SOUTH OF A LANSING TO DETROIT
LINE DRY AT THE MOMENT. THE MID LEVEL FRONTAL FORCING RESPONSIBLE
FOR THIS EVENINGS SNOW WILL PERSIST WHILE CONTINUING TO TRACK TO
THE NORTHEAST THIS EVENING. THE FORCING HAS NOT BEEN TOO STRONG OR
PERSISTENT...LEADING TO FLUCTUATING CONDITIONS BETWEEN FLURRIES
AND LIGHT SNOW. AVAILABLE REPORTS THUS FAR SUGGEST A HALF INCH OR
LESS OF ACCUMULATION THIS EVENING. WITH TEMPS IN THE 20S
HOWEVER...THIS HAS STILL LED TO SLICK ROADS.

UPSTREAM RADAR RETURNS STRETCHING FROM NORTH CENTRAL WISCONSIN
INTO SOUTHERN LAKE MI ARE OCCURRING WITHIN A SECOND REGION OF
ENHANCED FRONTAL FORCING /AT A LOWER LEVEL ALONG THE FRONTAL
SLOPE/. THE 00Z GRB SOUNDING SHOWED FAIRLY RESPECTABLE DEEP LAYER
MOISTURE AND STEEP MID LEVEL LAPSE RATES. THIS LOWER TROPOSPHERIC
FGEN WILL TRAVERSE SE MI OVERNIGHT. A DEEPER REGION OF LOW STATIC
STABILITY ABOVE THE FRONTAL SLOPE AND HIGHER MOISTURE /850-700MB
SPECIFIC HUMIDITY AROUND 3 G/KG/ SUGGESTS THERE WILL BE AN
OPPORTUNITY FOR SOME HEAVIER PRECIPITATION RATES. THE BRIEF
NATURE OF THE FORCING AIDED BY UPSTREAM RADAR DOES NOT SUPPORT
ANYTHING TOO PROLONGED. SO OVERNIGHT SNOW ACCUMULATIONS UP TO AN
ADDITIONAL INCH STILL SEAM REASONABLE. MOST OF THE FORCING IS
EXPECTED TO OCCUR WHILE THE COLUMN IS ALL SUBFREEZING. MID LEVEL
WARM AIR WILL HOWEVER NUDGE INTO SE MI BETWEEN 09Z AND 10Z...AND MAY
LEAD TO SOME SLEET /POSSIBLY A VERY BRIEF PERIOD OF FREEZING
RAIN/. THE STRONGEST MID LEVEL WARMING IS EXPECTED TO OCCUR TOWARD
12Z SAT...BY WHICH TIME THE FORCING AND DEEP LAYER MOISTURE SHOULD
BE DEPARTING TO THE EAST.

OVERALL...THE GOING FORECAST LOOKS FAIRLY REPRESENTATIVE. JUST A
FEW MINOR ADJUSTMENTS WILL BE MADE WITH THE EVENING UPDATE.


&&

.AVIATION...ISSUED 613 PM EST FRI NOV 28 2014

//DISCUSSION...

THE REGION OF LIGHT SNOW WHICH DEVELOPED OVER THE AREA THE LAST FEW
HOURS WILL SLOWLY LIFT TO THE NORTHEAST OF THE TERMINALS THIS
EVENING. THE INTENSITY OF THE SNOW WILL FLUCTUATE BETWEEN LIGHT
AND JUST FLURRIES...LEADING TO A HIGH VARIABILITY IN BOTH CEILINGS
AND VISIBILITIES. LATER IN THE EVENING...SOME IMPROVEMENT IN
CONDITIONS WILL OCCUR AS THIS REGION OF LIGHT SNOW LIFTS TO THE
NORTHEAST OF THE TERMINALS. ANOTHER REGION OF LIGHT SNOW IS
FORECAST TO DEVELOP AFTER 07Z TONIGHT /ENDING JUST PRIOR TO
DAYBREAK/...WHICH AGAIN WILL LEAD TO WIDE VARIATIONS IN
CONDITIONS. TOTAL SNOWFALL FROM THIS EVENING AND OVERNIGHT SHOULD
AMOUNT TO LESS THAN AN INCH AT THE TERMINALS.

FOR DTW...THE MOST SIGNIFICANT SNOWFALL APPEARS TO HAVE OCCURRED THE
LAST TWO HOURS...AS THE BACK EDGE OF THE ACCUMULATING SNOW SHOULD BE
EXITING TO THE NORTHEAST BETWEEN 00Z AND 01Z. THERE WILL BE WARMING
ALOFT OVERNIGHT. SO THE SECOND ROUND OF LIGHT SNOW OVERNIGHT WILL
HAVE A LITTLE MORE WATER CONTENT TO IT. THERE IS A SMALL CHANCE OF A
BRIEF PERIOD OF LIGHT FREEZING RAIN ON THE BACK EDGE OF THE SNOW
/ROUGHLY AROUND 09 OR 10Z/. THE CHANCES OF THIS ARE QUITE LOW...SO
NO INCLUSION WILL BE MADE INTO THE 00Z TAF CYCLE.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN CEILINGS BELOW 5000 FT TONIGHT AND SATURDAY
  MORNING.

* HIGH CONFIDENCE PRECIPITATION TYPE WILL BE ALL SNOW THROUGH 09Z
  SATURDAY...WITH LOW CONFIDENCE OF FREEZING RAIN BETWEEN 09Z AND
  12Z.

&&

.PREV DISCUSSION...ISSUED 240 PM EST FRI NOV 28 2014

SHORT TERM...THIS AFTERNOON AND TONIGHT

FORECAST HAS PLAYED OUT PRETTY MUCH AS EXPECTED THUS FAR AS DRIER
AIR FROM 850-600MB HAS QUELLED LIGHT SNOW SHOWERS TO THIS POINT.
RADAR TRENDS DO SUGGEST THAT THIS LAYER IS GRADUALLY SATURATING AND
VARIOUS ENHANCED FGEN BANDS ARE BEGINNING TO BRING LIGHT SNOW INTO
PORTIONS OF THE AREA. THIS UPTICK IN SNOW SHOWER ACTIVITY SHOULD
PERSIST INTO THIS EVENING...PARTICULARLY FROM M 59 NORTH WHERE THE
BREAK BETWEEN THIS INITIAL SURGE OF LIFT/MOISTURE AND THE NEXT
PERIOD OF ENHANCED LIFT...THIS EVENING INTO TONIGHT...ASSOCIATED
WITH STRONG WARM AIR ADVECTION AND LIFT FROM RIGHT ENTRANCE OF JET
STREAK IS SHORTER. THIS IS SUPPORTED SO FAR BY REGIONAL RADAR LOOP
FROM THE GREAT LAKES INTO THE UPPER MIDWEST AS THE TRAJECTORY OF NEW
LIGHT SNOW DEVELOPMENT OVER MINNESOTA AND WISCONSIN SEEMS TO AIM
MORE AT THE NORTHERN HALF OF THE CWA. WILL MAINTAIN THE SAME GENERAL
SNOWFALL TOTALS FROM LATE TODAY INTO LATE TONIGHT WITH 1 TO 2 INCHES
EXPECTED THRU THE MIDDLE OF THE CWA AND LESSER AMOUNTS SOUTH OF I
94. THERE STILL MAY BE LOCAL AMOUNTS APPROACHING 3 INCHES IN THE
GENERAL VICINITY OF THE I 69 CORRIDOR...ESPECIALLY IF SOME LOCATIONS
RECEIVE ON THE ORDER OF HALF AN INCH PRIOR TO 00Z.

THE OTHER ASPECT OF THIS SYSTEM THAT NEEDS TO BE MENTIONED IS THE
POTENTIAL FOR A BRIEF PERIOD OF LIGHT FREEZING DRIZZLE FROM LATE
TONIGHT. AS THE MAIN BAND(S) OF LIGHT SNOW END LATE TONIGHT...AND
DEEPER MOISTURE IS STRIPPED AWAY...THERE WILL BE A 2-4 HOUR PERIOD
WHERE SURFACE TEMPERATURES WILL HOVER IN THE 29-32F RANGE BEFORE
THE PRECIPITATION SUBSIDES COMPLETELY.

GIVEN THE FACT THAT SURFACES WILL BE WET AND/OR SNOW COVERED FROM
OVERNIGHT LIGHT SNOW...DO NOT EXPECT THIS TO BE TOO BIG OF AN
ISSUE AT THIS TIME. WILL REMAIN FOCUSED ON THE SNOW POTENTIAL
MORE SO FOR THIS FORECAST PACKAGE...WITH THE ASSUMPTION THAT THE
MAIN BANDS OF LIGHT PRECIPITATION REMAIN ALL OR MOSTLY SNOW LATE
TONIGHT BEFORE TAPERING OFF QUICKLY EARLY SATURDAY MORNING. GIVEN
THE FACT THAT SNOW ACCUMULATIONS OF 1 TO 2 INCHES WILL BE THE RULE
OVER ROUGHLY A 15-18 HOUR TIME FRAME...NO HEADLINE IS ANTICIPATED
AT THIS TIME.

LONG TERM...

WING OF ISENTROPIC ASCENT SUPPORTING OVERNIGHT SNOWFALL WILL EXIT
THE CWA TO THE NORTHEAST AROUND SUNRISE SATURDAY MORNING. LEE
CYCLONE POSITIONED OVER THE FAR NORTHERN GREAT PLAINS IS THEN
FORECAST TO LIFT NORTH OF LAKE SUPERIOR TOWARD JAMES BAY SATURDAY
EVENING INTO SUNDAY AS THE UPPER WAVE OVER THE PACNW EJECTS ACROSS
SOUTH-CENTRAL CANADA. THIS WILL RESULT IN THE ESTABLISHMENT OF MOIST
RETURN FLOW OVER THE CENTRAL UNITED STATES AND A STOUT AXIS OF SUB-
1KM MOISTURE ADVECTION THAT WILL FOCUS ON SOUTHEAST MICHIGAN MIDDAY
SATURDAY THROUGH MUCH OF SUNDAY. DESPITE DRY MID-LEVELS, ONGOING
WARM ADVECTION WILL SUPPORT A BACKGROUND OF LIGHT ISENTROPIC ASCENT
BENEATH A STRENGTHENING INVERSION AND ABUNDANT LOW-LEVEL MOISTURE.
THIS WILL BE SUPPORTIVE OF A BROKEN COVERAGE OF SHOWERS OR PERHAPS
AN EXTENDED PERIOD OF DRIZZLE SAT AFTN INTO SUNDAY.

MOISTURE ADVECTION ALONE WILL FORCE SATURDAY`S HIGHS INTO THE UPPER
30S AS DEWPOINTS RISE. TEMPERATURES WILL FALL LITTLE, IF ANY,
SATURDAY NIGHT AS PERSISTENT THETA-E ADVECTION CONTINUES AND
TEMPERATURES ULTIMATELY RISE INTO THE UPPER 40S TO AROUND 50 BY
DAYBREAK SUNDAY MORNING. THE COLD FRONT ASSOCIATED WITH THE
AFOREMENTIONED CYCLONE PASSING WELL TO OUR NORTH WILL THEN TRANSIT
THE AREA LATE SUNDAY WITH A CONTINUED SHOWER/DRIZZLE THREAT IN THE
MEANTIME. HIGHS WILL BE SENSITIVE TO TIMING OF FROPA. LOW/MID 50S
SEEM A SAFE BET FOR NOW. THIS REPRESENTS AN ECMWF/GEM WEIGHTED
COMPROMISE FOR SUNDAY`S TEMPS, AS LESS CREDENCE WAS GIVEN TO THE OFT
FAST GFS/NAM. FRONTAL PASSAGE WILL LARGELY BE DRY AS SYSTEM MOISTURE
WILL BE MINIMAL, BUT THE STRENGTHENING UPPER JET CENTERED OVER THE
GREAT LAKES MAY INDUCE JUST ENOUGH DEEPER FGEN WITHIN THE PRE-
FRONTAL MOISTURE AXIS TO SQUEEZE OUT SOME PREFRONTAL SHOWERS OVER
THE SOUTHERN CWA ON SUNDAY EVENING AS ADVERTISED BY THE 12Z NAM.
STRONG COLD ADVECTION WILL CAUSE H85 TEMPS TO PLUMMET BACK TO - 10C
BY 12Z MONDAY HELPING OVERNIGHT LOWS SUNDAY NIGHT FALL BACK INTO THE
20S.

AS THE COLD FRONT EXITS THE REGION SUNDAY NIGHT...A STRONG 1044 MB
HIGH PRESSURE SYSTEM BUILDING OVER THE AREA...WILL CONTINUE TO USHER
IN COLD CANADIAN/ARCTIC AIR. THIS PATTERN IS EXPECTED TO HOLD
THROUGH THE 7 DAY FORECAST PERIOD. TEMPERATURES WILL REMAIN BELOW
NORMAL WITH LOW CHANCES FOR PRECIPITATION.

MARINE...

DEVELOPING MODERATE SOUTHERLY WINDS WILL BECOME FRESH AT TIMES
SATURDAY THROUGH SATURDAY NIGHT WITH GUSTS OCCASIONALLY APPROACHING
30 KNOTS MAINLY OVER THE SOUTHERN LAKE HURON BASIN. WINDS WILL
GRADUALLY VEER TO A MORE WESTERLY DIRECTION ON SUNDAY BEFORE RAMPING
UP OUT OF THE NORTHWEST AS A COLD FRONT TRAVERSES THE WATERS SUNDAY
EVENING. GUSTS TO NEAR-GALES OR WEAK GALES AND BUILDING WAVES ARE
LIKELY BY SUNDAY NIGHT.

&&

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

$$

UPDATE.......SC
AVIATION.....SC
SHORT TERM...DG
LONG TERM....JVC/DE
MARINE.......JVC


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



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