Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 191653
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1153 AM EST WED NOV 19 2014

.UPDATE...

OVERALL EVOLUTION OF TODAY`S SNOWFALL IS ON TRACK WITH SOME LAST
MINUTE TWEAKS TO ACCUMULATIONS. LIGHT SNOW HAS OVERSPREAD THE AREA
LATE THIS MORNING WITHIN A REGION OF ORGANIZED DEEP LAYER SYSTEM
RELATIVE ISENTROPIC ASCENT. NARROW BAND OF ENHANCED CONVERGENCE/FGEN
ON THE LEAD EDGE OF THE THETA-E RIDGE WILL REPRESENT THE ONLY
RESPECTABLE SNOWFALL RATES OF THE DAY. MAIN CHANGE TO THE FORECAST
THIS MORNING WAS TO DRASTICALLY REDUCE INHERITED SNOW RATIOS TO A
MORE REALISTIC 11:1, AS AN EVENT AVERAGE, AS SNOW HAS HAD A GRAINY
NATURE TO IT FOR MOST OF THE MORNING. CURRENT THINKING IS THAT
ACCUMULATIONS WILL GENERALLY FINISH RIGHT AROUND AN INCH AS A RESULT
OF THE OVERALL POOR RATIOS. THE EXCEPTION WILL BE WITHIN THE BAND OF
MODERATE SNOWFALL WHICH IS PRESENTLY LIFTING THROUGH THE METRO AREA.
ENHANCED ASCENT WITHIN THIS BAND WILL LIKELY LEAD TO BRIEFLY
IMPROVED RATIOS AND WILL ACCOUNT FOR THE BULK OF TODAY`S
ACCUMULATION. THE MODERATE SNOWFALL SHOULD NOT LAST MUCH MORE THAN
AN HOUR AT ANY ONE LOCATION. GRIDS AND ZONES HAVE BEEN UPDATED.

&&

.AVIATION...ISSUED 541 AM EST WED NOV 19 2014

//DISCUSSION...

LAKE EFFECT SNOW SHOWERS WILL LINGER FROM KFNT TO KMBS THIS MORNING
AS A BROADER AREA OF LIGHT SNOW OVERSPREADS ALL TERMINALS WITH LIFT
FROM SYNOPTIC SCALE SHORTWAVE. THIS -SN WILL FOCUS IN THE 15Z-20Z
TIME FRAME WITH MVFR TO OCCASIONAL IFR CONDITIONS. ONCE THIS AREA OF
-SN SHIFTS EAST OF THE REGION...LAKE EFFECT SNOW SHOWERS WILL ALIGN
BACK INTO THE KFNT/KPTK TERMINALS DURING THE EVENING WITH A GENERAL
TREND TO PARTLY CLOUDY SKIES OVERNIGHT WITH ONLY LINGERING FLURRIES.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT INTO TONIGHT.

* HIGH CONFIDENCE IN PTYPE OF SNOW.

&&

.PREV DISCUSSION...ISSUED 357 AM EST WED NOV 19 2014

SHORT TERM...TODAY AND TONIGHT

ONGOING LIGHT LAKE EFFECT SNOW SHOWER ACTIVITY WILL PERSIST THIS
MORNING OVER THE SAGINAW VALLEY WITH THE OCCASIONAL FLURRY REACHING
AS FAR SOUTH AS I 69. THIS ACTIVITY WILL EDGE NORTHWARD WITH TIME A
LOW LEVEL FLOW BACKS TO THE SOUTH IN ADVANCE OF APPROACHING LOW
PRESSURE WHICH WILL PIVOT THROUGH THE CENTRAL GREAT LAKES TODAY.

AS THIS LOW LIFTS FROM LAKE MICHIGAN INTO NORTHERN LOWER MICHIGAN IT
WILL FORCE A FRONTAL BOUNDARY EAST TROUGH SOUTHEAST LOWER MICHIGAN.
FORCING ALONG THIS FRONT WILL PRODUCE A WIDESPREAD AREA OF LIGHT
SNOW BY MIDDAY...WHICH WILL QUICKLY SHIFT EAST/NORTHEAST OUT OF THE
AREA BY LATE AFTERNOON/EVENING EVENING AS THE AFOREMENTIONED LOW
PRESSURE REFORMS ALONG THE NORTHERN SHORES OF LAKE HURON. ONE TO
PERHAPS TWO INCHES OF SNOW WILL BE POSSIBLE WITH THIS SYSTEM AS THIS
QUICK BURST OF SNOW DEVELOPS DURING THE DAY.

GIVEN THE TRACK OF THIS SYSTEM...THE NEXT SHOT OF RE-ENFORCING COLD
AIR RUSH BACK INTO THE AREA ON WEST/SOUTHWEST WINDS AND BRING A
CONTINUATION OF SNOW SHOWERS TONIGHT AS LAKE EFFECT ACTIVITY
REFORMED OFF OF LAKE MICHIGAN. AT THIS TIME...ACCUMULATIONS FROM
THIS ACTIVITY ARE EXPECTED TO REMAIN AT AN INCH OR LESS...AND FOCUS
IN THE I 69 TO M 59 CORRIDORS ONCE AGAIN.

TEMPERATURES WILL REMAIN WELL BELOW AVERAGE AS HIGHS ONLY CLIMB INTO
THE 25-30 DEGREE F RANGE TODAY AND LOWS FALL BACK INTO THE TEENS
AGAIN TONIGHT...EVEN WITH AN ABUNDANCE OF CLOUD COVER AND SNOW
SHOWER ACTIVITY THROUGH THE HEART OF THE CWA.

LONG TERM...THURSDAY THROUGH NEXT TUESDAY

SOME RELIEF TEMPERATURE WISE IS ON THE WAY FOR THE WEEKEND BUT THE
COLD LOOKS TO RETURN EARLY NEXT WEEK. THE PERSISTENT LONGWAVE TROUGH
CONSUMING MUCH OF THE EASTERN CONUS WILL BECOME DISPLACED BY BROAD
RIDGING AS SPLIT FLOW TAKES THE POLAR JET UP INTO NORTHERN CANADA.
THE WEAKER SOUTHERN STREAM WILL BECOME INVIGORATED BY A STRONG 150+
KNOT JET DIVING INTO THE SW CONUS BY SATURDAY NIGHT. THIS WILL SPIN
UP A SFC LOW OVER TEXAS WHICH WILL THEN GET PULLED NORTHWARD THROUGH
THE GREAT LAKES BRINGING MILD TEMPERATURES AND RAINFALL. TROUGHING
AND COLD AIR WILL FILL BACK INTO THE REGION IN THE WAKE OF THIS
LOW...BUT NOT QUITE AS COLD AS WE HAVE BEEN DEALING WITH.

ON THURSDAY...COLD AND GUSTY WESTERLY FLOW WILL OCCUR THROUGH THE
DAY BEHIND A COLD FRONT THAT PASSED THROUGH ON WEDNESDAY EVENING.
YET ANOTHER MID LEVEL SHORTWAVE WILL TRACK THROUGH THE TROUGH
USHERING YET ANOTHER ARCTIC COLD POOL INTO THE REGION. THE COLUMN
WILL COOL THROUGHOUT THE DAY WITH 850MB TEMPS FALLING TO AROUND -17C
BY EVENING...WHICH SHOULD HOLD THROUGH THE OVERNIGHT. THIS WILL BE
MORE THAN SUFFICIENT TO KEEP LAKE EFFECT SNOW SHOWERS GOING OFF LAKE
MI. THE COLD AIR ALOFT WILL STRENGTHEN LL LAPSE RATES TO NEAR -9C/KM
UP TO 800 MB. THIS WILL MIX DOWN STRONG WINDS POSSIBLY GUSTING TO
NEAR 30 MPH THROUGH THE AFTERNOON. THESE WINDS WILL HELP THE LAKE
EFFECT TRACK ACROSS THE STATE INTO SE MI. HIRES MODELS SEEM TO
INDICATE A FRACTURING OF THE DOMINATE SNOW BAND LEADING TO A LARGER
FOOTPRINT AND THUS LOWER CONFIDENCE IN WHERE THE BEST SNOWFALL WILL
OCCUR BUT A SATURATED COLUMN UP TO THE INVERSION AROUND
800MB...ALMOST COMPLETELY WITHIN THE DGZ...HELPS INCREASE CONFIDENCE
THAT OUR WESTERN COUNTIES WILL SEE SOME SNOW. WILL KEEP A HIGH
CHANCE POP GOING FOR THE TYPICAL CORRIDOR AFFECTED BY THIS SCENARIO.
ONE SHOULD ALSO NOTE THAT THE GUST WINDS AND COLD TEMPERATURES WILL
LEAD TO WIND CHILL VALUES ONCE AGAIN HOLDING IN THE SINGLE DIGITS.

HIGH PRESSURE WILL BEGIN BUILDING IN THURSDAY NIGHT WHICH WILL HELP
SHUT DOWN THE LAKE EFFECT WITH DRIER AIR AND SUBSIDENCE FILLING IN
ALONG WITH A WEAKER GRADIENT AND WARMER AIR ALOFT. WILL NOT QUITE
REALIZE ANY OF THE WARMER AIR AT THE SFC YET SO EXPECT TEMPERATURES
TO LINGER IN THE 20S FOR ANOTHER DAY. THIS WILL CHANGE BY SATURDAY
THOUGH AS RIDGING BUILDING INTO THE REGION. WAA AND GOOD SW FLOW
MOIST ADVECTION BEHIND A WARM FRONT WILL HELP TEMPS REACH BACK INTO
THE UPPER 30S. ONE ISSUE STILL PENDING IS THAT THE COLDER AIR WILL
REMAIN LOCKED AT THE SFC AS THE ELEVATED FRONT WORKS NORTH THROUGH
LOWER MI. THIS TIME OF YEAR WITH A DEEP LAYER OF WARM AIR ALOFT FROM
ABOUT 1500-7000FT AND COLD AIR LOCKED AT THE SFC BENEATH THE WARM
AIR...AND WEAK FGEN AND ISENTROPIC ASCENT...ONE HAS TO CONSIDER A
PRECIP PHASE CHANGE THROUGH THE EVENT. THIS COULD POSSIBLE INTRODUCE
SOME LIGHT FREEZING RAIN/DRIZZLE BEFORE RATES INCREASE ENOUGH TO
CHANGE OVER TO PURE RAIN. THE STRENGTHENING LOW WILL THEN MOVE NORTH
BY SUNDAY BRINGING WIDEPSREAD RAIN TO THE REGION. CONFIDENCE
CONTINUES TO INCREASE WITH THE SCENARIO DUE TO SHEAR SIZE OF THE
SYSTEM. MODELS TEND TO DO A LITTLE BETTER WITH LARGER SYSTEMS
ENCOMPASSING MORE GRID POINTS. THE UPPER LOW AND TROUGH WILL THEN SIT
AND SPIN OVER THE GREAT LAKES INTO THE BEGINNING OF NEXT WEEK. THIS
WILL USHER IN YET ANOTHER ARCTIC AIRMASS BUT EARLY GUIDANCE ONLY
SUGGESTS 850MB TEMPS FALLING TO -10C SO NOT QUITE AS COLD AS WE HAVE
BEEN SEEING.

MARINE...

THE ACTIVE MARINE WEATHER PATTERN CONTINUES TONIGHT INTO THURSDAY AS
A LOW PRESSURE SYSTEM DEVELOPING OVERHEAD TODAY USHERS IN THE NEXT
ARCTIC SURGE TONIGHT INTO THURSDAY. THIS WILL AGAIN BRING GUSTY
WESTERLY WINDS TO THE EASTERN LAKES. THE SETUP DOES NOT LOOK QUIET
AS POTENT AS THIS PAST EVENT BUT WIDESPREAD GALE FORCE WINDS APPEAR
LIKELY ACROSS MUCH OF THE LAKE HURON BASIN. BEING ALMOST A FULL 24
HOURS OUT YET...CHOSE TO ISSUE A GALE WATCH AT THIS POINT. HAVE ALSO
ALLOWED CURRENT SMALL CRAFT ADVISORIES AND LOW WATER ADVISORY TO
END...AND CANCELLED THE SMALL CRAFT FOR THE OUTER SAGINAW BAY AREA
AS WAVES HAVE FALLEN BELOW CRITERIA.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...GALE WARNING FROM 7 PM THIS EVENING TO 11 PM EST THURSDAY FOR
     LHZ362-363-421-441-462>464.

     SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 11 PM EST THURSDAY
     FOR LHZ442-443.

     GALE WARNING FROM 10 PM THIS EVENING TO 1 PM EST THURSDAY FOR
     LHZ361.

     SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR LHZ421-422.

     GALE WARNING FROM 7 PM THIS EVENING TO 1 PM EST THURSDAY FOR LHZ422.

LAKE ST CLAIR...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 4 PM EST THURSDAY
     FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 4 PM EST THURSDAY
     FOR LEZ444.

&&

$$

UPDATE.......JVC
AVIATION.....DG
SHORT TERM...DG
LONG TERM....DRK
MARINE.......DRK


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



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