Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 281633
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1133 AM EST FRI NOV 28 2014

.UPDATE...

EARLY INDICATIONS...BASED ON RADAR TRENDS AND INITIAL 12Z MODEL
GUIDANCE SUGGEST THAT THE LIGHT SNOW EVENT EXPECTED OVER THE CWA
WILL BE DELAYED SLIGHTLY. WHILE FLURRIES AND LIGHT SNOW SHOWERS
ARE STILL EXPECTED TO SPREAD INTO THE AREA THIS AFTERNOON...A
WEDGE OF VERY DRY AIR...NOTED FROM 850-600MB ON THE 12Z KDTX
SOUNDING WILL LIMIT PRECIPITATION WITH THIS INITIAL PUSH OF
MOISTURE WITHIN BROAD ISENTROPIC LIFT PATTERN UNDER LEFT EXIT
REGION OF 100-120KFT H3 JET STREAK. AS NOTED...RADAR TRENDS
SUPPORT THIS IDEA AS ACTIVITY TO THIS POINT HAS FADED STEADILY IN
ITS TRANSIT ACROSSES LOWER MICHIGAN. BETTER FGEN FORCING AIDED BY
THE JET STREAK WILL EVENTUALLY OVERCOME THIS AND ALLOW FOR SOME
LIGHT ACCUMULATIONS DURING THE LATE AFTERNOON...PARTICUARLY FROM
THE SAGINAW VALLEY ON EAST ALONG THE I 69 CORRIDOR.

THIS DOES NOT MEAN THAT OVERALL SNOW AMOUNTS ARE EXPECTED TO BE
LESS THAN ORIGINALLY EXPECTED. THE AFOREMENTIONED JET STREAK HAS A
SLIGHT ANTI-CYCLONIC SHAPE TO IT AS IT ARCHS ACROSS THE AREA.
THIS...IN GENERAL...SHOULD SUPPORT A BETTER POCKET OF LIFT WITHIN
THE RIGHT ENTRANCE REGION...WHICH WILL CROSS THE AREA OVERNIGHT.

12Z MODEL SOLUTIONS SEEM TO PICK UP ON THIS AND BRING THE MOST
PERSISTENT LIGHT SNOW TO THE AREA FROM EVENING INTO THE OVERNIGHT
HOURS AS STRONG WARM AIR ADVECTION PATTERN CONTINUES TO PROVIDE
ADDITIONAL LIFT/MOISTURE COINCIDENT WITH THIS JET SUPPORT. BETWEEN
STRUGGLING EASTWARD EXPANSION FROM INITIAL EVAPORATION...AND THE
SECOND AREA OF LIFT OVERNIGHT...THE EVENT IS ESSENTAILLY PUSHED
FORWARD IN TIME BY 2-4 HOURS...WITH 1-2 INCHES STILL EXPECTED
THROUGH A FAIR PORTION OF THE CWA WITH LOCAL AMOUNTS PERHAPS
APPROACHING 3 INCHES WITHIN STRONGEST FGEN BANDING OVER THE MID
CWA...ROUGHLY THE I 69 TO M 59 CORRIDORS. CONVERSELY...WOULD
EXPECT THE AREAS SOUTH OF I 94 AND ALSO OVER THE NORTHERN THUMB
TO RECEIVE THE LEAST AMOUNT OF SNOW...LIKELY LESS THAN AN INCH IN
SOME INSTANCES.

WILL BE ISSUING AN UPDATE BY NOON TO BETTER ALIGN THE FORECAST TO
THESE EXPECTATIONS. TIMING WILL BE ADJUSTED MOST...BUT LOCATION
WILL ALSO BE REFINED EVER SO SLIGHTLY.

&&

.AVIATION...ISSUED 605 AM EST FRI NOV 28 2014

//DISCUSSION...

SOME LINGERING LAKE EFFECT CLOUDS BETWEEN 3500-4000 FEET WILL STREAM
OVER THE AREA THIS MORNING. THESE WILL PRIMARILY BE SCATTERED IN
NATURE...BUT A TERMINAL SITE COULD SEE SOME PERIODS OF BKN SKIES.
VFR CONDITIONS ARE EXPECTED TO PREVAIL THIS AFTERNOON AS DRIER AIR
ARRIVES FROM THE WEST. A WARM FRONT WILL THEN LIFT THROUGH SOUTHEAST
MICHIGAN LATE TODAY AND TONIGHT...SPREADING SNOW AND MVFR CEILINGS
INTO SOUTHEAST MICHIGAN STARTING BETWEEN 20-23Z. THE BEST SNOWFALL
AND LOWEST VISIBILITIES (IFR TO MVFR) WILL BE THIS EVENING AS AN
UPPER LEVEL DISTURBANCE RIDES OVER THE FRONT...ENHANCING LIFT. THERE
IS SOME UNCERTAINTY TO WHERE THE HEAVIEST SNOW WILL FALL...AND HOW
LONG INTO THE NIGHT IT WILL LAST. FURTHER REFINEMENTS TO THE TAFS
ARE LIKELY AS THIS EVENT BEGINS TO UNFOLD. AT THIS TIME...IT APPEARS
THE TERMINALS WILL RECEIVE BETWEEN 1.0 AND 2.0 INCHES. LOW-LEVEL DRY
AIR WILL WORK INTO THE AREA SATURDAY MORNING BEHIND THE
FRONT...ALLOWING CEILINGS TO RISE BACK UP TO VFR.

FOR DTW...SNOW AND MVFR CEILINGS/VIS LOOK TO SPREAD INTO THE AREA
AROUND 22Z. A PERIOD OF IFR VISIBILITIES COULD DEVELOP IF A HEAVIER
BAND OF SNOW SETTLES IN OVER THE TERMINAL THIS EVENING.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET LATE FRIDAY AFTERNOON
  THROUGH EARLY SATURDAY MORNING.

* HIGH CONFIDENCE PRECIPITATION TYPE WILL BE ALL SNOW THROUGH 12Z
  SATURDAY.

&&

.PREV DISCUSSION...ISSUED 342 AM EST FRI NOV 28 2014

SHORT TERM...TODAY AND TONIGHT

DRIER AIR AND A RIDGE OF SURFACE HIGH PRESSURE EXTENDING UP INTO
LOWER MICHIGAN HAS ALLOWED LAKE EFFECT SHOWERS TO TAPER OFF...EVEN
ALLOWING FOR SOME BREAKS IN THE CLOUDS. THE TREND FOR LOWER CLOUDS
TO BREAK SHOULD CONTINUE THROUGH THE EARLY MORNING HOURS AS A VERY
DRY AIRMASS ARRIVES (PER 00Z GRB RAOB) AND INVERSION HEIGHTS
CONTINUE TO LOWER OVER THE LAKE...TEMPERING THE LAKE EFFECT
RESPONSE. HIGHER CLOUDS WILL HOWEVER BEGIN TO ARRIVE AHEAD OF THE
NEXT SYSTEM.

MODELS ARE A LITTLE DIVIDED WITH HOW A SMALL SNOW EVENT WILL UNFOLD
FROM LATE THIS AFTERNOON INTO TONIGHT. UPPER ENERGY OFF THE WEST
COAST AND OVER BRITISH COLUMBIA WILL CONTINUE TO DROP SOUTH AND EAST
INTO THE PACIFIC NORTHWEST AND NORTHERN ROCKIES TODAY AND
TONIGHT...ALLOWING A LARGE AREA OF SURFACE LOW PRESSURE TO DEVELOP
OVER THE ROCKIES AND PLAINS. THIS WILL PUSH THE RIDGE OVER THE AREA
EAST...AND SEND AN ELEVATED WARM FRONT NORTHWARD INTO LOWER MICHIGAN
LATE THIS AFTERNOON AND TONIGHT. LEAD SHORTWAVE ENERGY EJECTING OUT
OF THE SYSTEM OVER THE WEST WILL MEANWHILE TRACK ACROSS
MICHIGAN...OVER THE TOP OF THE FRONTAL BOUNDARY. ISENTROPIC
ASCENT...AND A LITTLE UPRIGHT FORCING FROM FGEN...LOOK TO OVERCOME
DRY AIR IN THE BOUNDARY LAYER BY EVENING ALLOWING LIGHT SNOW TO
SPREAD INTO THE AREA. FORCING SHOULD BE AIDED BY STEEPENING MID-
LEVEL LAPSE RATES THIS EVENING AND OVERNIGHT AS COOLER AIR ALOFT
SLIDES IN WITH THE UPPER WAVE. THIS IS WHEN THE BEST SNOWFALL SHOULD
OCCUR.

MODELS ARE A LITTLE DIVIDED ON WHERE OVER SOUTHEAST MICHIGAN THE
SHORTWAVE WILL MEET UP WITH THE FRONT...AND FURTHER ADJUSTMENTS TO
THE FORECAST REMAIN POSSIBLE AS THE DAY UNFOLDS. NAM SOLUTION
CURRENTLY LOOKS TO BE THE FURTHEST NORTH (AND MOST AGGRESSIVE WITH
QPF)...WHILE THE OPERATIONAL GFS HAS TRENDED THE FURTHEST
SOUTH...NOW FOCUSING BETTER PRECIPITATION SOUTH OF THE M-59
CORRIDOR. GEM/EURO/PARALLEL GFS/AND SPC WRF SOLUTIONS ALL LIE
SOMEWHERE IN THE MIDDLE...AND PREFERENCE IS GIVEN TO THIS CONSENSUS.
DID EXPAND HIGHER BAND OF POPS AND SNOW FROM PREVIOUS FORECAST
SLIGHTLY SOUTHWARD...ON ACCOUNT OF 00Z MODEL TRENDS AND CONSIDERING
RADAR RETURNS FURTHER SOUTH INTO IOWA/ILLINOIS THAN PREVIOUSLY
ANTICIPATED THIS MORNING. EXPECTING TO SEE BETWEEN 0.5-1.5 INCHES OF
SNOW ACROSS MOST OF SOUTHEAST MICHIGAN...MOSTLY BETWEEN 4 PM AND
MIDNIGHT...WITH SOME LIGHT SNOW SHOWERS THEN CONTINUING OVERNIGHT AS
THE 850-925MB FRONTAL BOUNDARY CONTINUES TO LIFT THROUGH SOUTHEAST
MICHIGAN. PRECIPITATION TYPE IS EXPECTED TO REMAIN ALL SNOW...WITH
00Z FORECAST SOUNDINGS AND THERMAL PROFILES NOW KEEPING THE LAYER OF
ABOVE-FREEZING AIR ALOFT TO OUR SOUTHWEST BY SUNRISE.

MAX TEMPERATURES WILL RUN LOWER TODAY IN THE WAKE OF SOME COOLER AIR
THAT PUSHED IN YESTERDAY. HIGHS ARE ONLY EXPECTED TO REACH THE MID
20S TO NEAR 30. WARM AIR ADVECTION OVERNIGHT WILL LIMIT
COOLING...ALLOWING MIN TEMPS TO FALL VERY LITTLE FROM DAYTIME
HIGHS...COOLING ONLY INTO THE MID 20S.

LONG TERM...SATURDAY THROUGH THURSDAY

WARM AIR ADVECTION WILL WORK ITS WAY TO THE SURFACE ON SATURDAY AS A
SURFACE WARM FRONT LIFTS NORTH THROUGH THE CENTRAL GREAT LAKES AS
MID LEVEL HEIGHTS CONTINUE TO RISE ACROSS THE REGION. 850 MB
TEMPERATURES ARE FORECAST TO RISE TO AROUND +10 CELSIUS ACROSS THE
SOUTHERN GREAT LAKES. DESPITE THE PASSAGE OF THE SURFACE WARM FRONT
DAYTIME TEMPERATURES ARE ONLY EXPECTED TO GET TO AROUND 40 DEGREES
AS A STRONG INVERSION TRAPS LOW LEVEL MOISTURE IN THE LOWEST FEW
THOUSAND FEET OF THE COLUMN. THIS WILL LEAD TO AN EXTENDED PERIOD OF
LIGHT RAIN OR DRIZZLE DURING THE WEEKEND. LOW TEMPERATURES ON
SATURDAY NIGHT WILL BE CLOSE TO SATURDAYS HIGHS WITH ABUNDANT CLOUD
COVER AND CONTINUED DRIZZLE PREVENTING MUCH IN THE WAY OF
RADIATIONAL COOLING. TEMPERATURES ON SUNDAY WILL RANGE FROM THE MID
40S ACROSS THE NORTH TO THE MID 50S TOWARDS THE OHIO BORDER AHEAD OF
AN APPROACHING COLD FRONT PROGGED TO TRACK THROUGH THE AREA LATE
SUNDAY AFTERNOON INTO SUNDAY EVENING. ALTHOUGH THIS FRONT WILL
BRING A STRONG PUSH OF COLD AIR THROUGH THE AREA...IT WILL NOT HAVE
MUCH IN THE WAY OF PRECIPITATION AS THE LOW WILL BE OF PACIFIC
ORIGINS AND UNABLE TO TAP INTO DEEPER GULF MOISTURE WELL TO THE
SOUTH.

BEHIND THE COLD FRONT DAYTIME HIGHS WILL COME BACK DOWN INTO THE 30S
DURING THE EARLY PART OF THE WORK WEEK AS STRONG HIGH PRESSURE OF
1040+ MB TRACKS THROUGH THE GREAT LAKES REGION.  MODEST WARM AIR
ADVECTION WILL BOOST TEMPERATURES A FEW DEGREES WEDNESDAY AND
THURSDAY ON THE BACK SIDE OF THE HIGH AS A MID LEVEL TROUGH WITH A
WEAK SURFACE REFLECTION BRINGS A SLIGHT CHANCE FOR SNOW SHOWERS TO
THE AREA DURING THE MIDDLE PART OF NEXT WEEK.

MARINE...

ALTHOUGH SURFACE WINDS HAVE DROPPED WELL BELOW HEADLINE
CRITERIA...ELEVATED WAVE HEIGHTS CONTINUE ACROSS SOUTHERN LAKE
HURON...CLIPPING THE NEARSHORE ZONES AROUND THE THUMB. THEREFORE
WILL CONTINUE THE SMALL CRAFT ADVISORIES EARLY THIS MORNING FOR
THESE AREAS.  A WARM FRONT WILL LIFT NORTH INTO THE REGION TODAY
WHICH WILL FLIP THE WINDS TO THE SOUTHWEST/SOUTH BY THIS EVENING.
WIND GUSTS OF 25 KNOTS ARE EXPECTED OVER MUCH OF LAKE HURON BEFORE
WARMER AND MORE STABLE AIR WORKS INTO THE REGION SATURDAY NIGHT.

&&

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

$$

UPDATE.......DG
AVIATION.....HLO
SHORT TERM...HLO
LONG TERM....KURIMSKI
MARINE.......KURIMSKI


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