FXUS63 KDTX 090518
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1218 AM EST WED DEC 9 2009
.AVIATION...
SNOW IS IN THE PROCESS OF MIXING WITH AND CHANGING TO RAIN IN THE
DETROIT AREA. THIS CONDITION WILL SPREAD NORTHWARD TO PONTIAC AND
FLINT DURING THE EARLY MORNING HOURS BUT EXPECT SNOW TO REMAIN THE
PRIMARY TYPE AT SAGINAW. WITH MBS AS AN EXCEPTION, THE TRANSITION
TO RAIN WILL EASE AVIATION CONDITIONS IN TERMS OF PRECIPITATION
BUT MILD AIR MOVING IN FROM THE SOUTH WILL KEEP CEILING AND
VISIBILITY IN THE IFR/LIFR RANGE AS THE LOW MOVES THROUGH CENTRAL
LOWER MICHIGAN.
THE MAIN STORY FOR THE DAYTIME HOURS WILL BE THE WIND. THE DRY
SLOT OF THIS LOW PRESSURE SYSTEM WILL REDUCE THE PRECIPITATION TO
SPOTTY LIGHT RAIN SHOWERS OR DRIZZLE DURING THE DAYLIGHT HOURS.
IMPROVEMENT IN CEILING AND VISIBILITY WILL COME AT THE EXPENSE OF
SOUTHWEST WINDS GUSTING TO 40 KNOTS WITH A FEW GUSTS NEAR 50 KNOTS
POSSIBLE AS COLD AIR SPILLS BACK INTO THE REGION. THE GUSTY
CONDITIONS WILL THEN LAST WELL INTO THE EVENING WHILE TURNING
TOWARD THE WEST. THIS WIND DIRECTION AND THE COLD AIR WILL DIRECT
SNOW SHOWERS INTO THE AREA FROM LAKE MICHIGAN, MAINLY TOWARD
PONTIAC AND FLINT.
&&
.PREV DISCUSSION...ISSUED 931 PM EST TUE DEC 8 2009
UPDATE...
CONDITIONS ARE UNFOLDING THIS EVENING IN SUPPORT OF THE WINTER
WEATHER HEADLINES IN EFFECT. WE WILL MAINTAIN THESE HEADLINES AS
THEY ARE THROUGH THE NIGHT, ESPECIALLY CONSIDERING THE
EFFECTIVENESS OF THE INITIAL BURST OF SNOW MOVING IN FROM
NORTHWEST OHIO THAT IS REDUCING VISIBILITY TO A HALF MILE AT TIMES
FROM TOLEDO TOWARD ADRIAN. EXPECT THIS INITIAL BURST TO SPREAD
NORTHWARD THROUGH THE DETROIT METRO AREA AND INTO THE FLINT, PORT
HURON, AND TRI CITIES/THUMB REGIONS DURING THE NIGHT.
FORCING FOR THIS ACTIVITY WILL REMAIN SUPPORTED BY STRONG ISENTROPIC
LIFT/THETA-E ADVECTION BELOW 700 MB IN A LOW STABILITY ENVIRONMENT
AS THE STRONG LOW PRESSURE SYSTEM CONTINUES TO DEVELOP AND MOVE
TOWARD LOWER MICHIGAN FROM MISSOURI. THE RESULTING STRONG VERTICAL
MOTION RESPONSE AND HIGH PRECIPITATION RATES WILL MAINTAIN A BELOW
FREEZING TEMPERATURE PROFILE DUE TO WET BULB COOLING, AT LEAST FOR
A FEW HOURS DURING THE INITIAL BURST. WITH THE EXCEPTION OF THE
TRI CITIES, THIS WILL BE FOLLOWED BY A GREATER MIX OF RAIN AND
SNOW, WITH A BRIEF PERIOD OF SNOW PELLETS/SLEET, AS PRECIPITATION
RATES DIMINISH AFTER MIDNIGHT AND AS WARMER AIR IS DRIVEN INTO THE
REGION. THE LOW VISIBILITY DURING THE HEAVIER SNOW AND WINTRY MIX
DURING THE TRANSITION TO RAIN WARRANT THE HEADLINES FOR THIS EARLY
SEASON EVENT. CONSIDERING AIR TEMPERATURES ARE HOLDING MOSTLY IN
THE MID 30S, SNOW ACCUMULATION UP TO 2 INCHES ON GRASSY SURFACES
LOOKS GOOD IN THE DETROIT METRO AREA WITH A SLUSHY INCH ON PAVED
SURFACES. WE WILL CONTINUE TO EVALUATE ACCUMULATION EXPECTATIONS
FOR POINTS NORTH DURING THE NIGHT BUT THOSE NUMBERS LOOK GOOD AS
WELL BASED ON THE LATEST OBSERVATIONS.
PREV DISCUSSION...ISSUED 407 PM EST TUE DEC 8 2009
SHORT TERM...TONIGHT
POTENT UPPER LEVEL SHORTWAVE EJECTING EAST OF THE ROCKIES THIS
AFTERNOON. TREMENDOUS UPPER DIFFLUENCE AND STRENGTHENING ELEVATED
WARM AIR ADVECTION DOWNSTREAM OF THIS SYSTEM GENERATING POCKETS OF
LIGHT SNOW AS FAR EAST AS SOUTHERN LOWER MI. STRONGER FORCING STILL
RESIDES UPSTREAM IN CLOSER PROXIMITY OF A BROAD SFC LOW STILL
ORGANIZING ACROSS THE SOUTHERN PLAINS. THIS LOW STILL EXPECTED TO
UNDERGO RAPID INTENSIFICATION THIS EVENING/TONIGHT...AROUND 18 MB
DEEPENING IN 12 HOURS...WHILE QUICKLY LIFTING NORTHEAST. LATEST
SHORT TERM MODEL GUIDANCE HOLDING CONSISTENT IN BRINGING THE LOW
NEAR CHICAGO/SOUTHERN END OF LAKE MICHIGAN BY 12Z.
INCREASING MOIST ISENTROPIC ASCENT/WARM AIR ADVECTION WILL ALLOW
AN EXPANDING AREA OF PRECIPITATION TO SPREAD ACROSS THE REGION
TONIGHT. BEST LIFT AND DEEPEST MOISTURE ARRIVES BETWEEN 06-12Z
FOCUSED ALONG A GOOD 850-700 MB THETA-E GRADIENT AND WITHIN AN
AREA OF FAVORABLE JET COUPLING/SOLID DIFFLUENCE. LATEST MODEL
THERMAL PROFILES STILL SUPPORT AN INITIAL BURST OF SNOW...ALTHOUGH
MARGINAL BOUNDARY LAYER CONDITIONS WILL ALLOW A MIX TO DEVELOP
QUICKLY NEAR THE OHIO BORDER AND ACROSS AREAS ALONG THE LAKESHORE.
THE DEEPENING WARM AIR ADVECTION WILL EFFECTIVELY SHIFT THE THERMAL
PROFILE TOWARD A RA/SN MIX AND THEN ALL RAIN FROM SOUTH TO NORTH
THROUGH THE NIGHT. EXCEPTION WILL BE ACROSS THE TRI-CITIES WHERE
THE EVENT WILL REMAIN PREDOMINATELY SNOW THROUGH SUNRISE.
GOING HEADLINES WILL CONTINUE WITH THE AFTERNOON FORECAST PACKAGE.
GIVEN THE QUICKER TRANSITION IN PTYPE FROM M-59 SOUTH...EXPECT
MARGINAL ADVISORY WORTHY ACCUMULATIONS /2 INCHES OR LESS/...BUT WILL
RETAIN THE HEADLINE GIVEN THE POTENTIAL FOR A QUICK MODERATE BURST
RESULTING IN THE FIRST ACCUMS OF THE SEASON. THE DEGREE OF
AVAILABLE MOISTURE /3-4 G/KG OF SPECIFIC HUMIDITY/ AND LARGE SCALE
ASCENT STILL POINT TOWARD SEEING AMOUNTS OF 3 INCHES OR MORE
NORTHWEST OF AN OWOSSO TO SANDUSKY LINE...WITH THE HIGH END AMOUNTS
APPROACHING 6 INCHES ACROSS NORTHERN MIDLAND/BAY COUNTIES.
DAYTIME TEMPERATURES MADE IT INTO THE MID 30S FOR MUCH OF THE CWA
TODAY THOUGH THEY REMAINED SLIGHTLY LOWER WHERE AN ENHANCED CLOUD
FIELD/BRIEF SNOW BURST MOVED THROUGH THIS AFTERNOON. TEMPS WILL DROP
TO AROUND 30 FOR MOST LOCATIONS EARLY TONIGHT BUT WILL THEN STEADILY
CLIMB OVERNIGHT DUE TO SOUTHERLY WAA FROM THE APPROACHING LOW. THIS
WILL CAUSE THE PRECIP TO SWITCH FROM SNOW TO A MIX THEN OVER TO ALL
RAIN FROM SOUTH TO NORTH STARTING AROUND 00Z.
LONG TERM...
STRONG WINDS AND SNOW SQUALLS WILL BECOME THE FOCUS WITH THIS
INTENSE...SLOWLY DEPARTING STORM SYSTEM LATE WEDNESDAY/WEDNESDAY
NIGHT. 12Z NAM/REGIONAL GEM BOTH REMAIN ON THE DEEPER END OF
SOLUTIONS...AS SURFACE PRESSURE DROPS TO AT LEAST 970 MB. THE GFS
REMAINS IN CATCH UP MODE...AS THE TRACK HAS BEEN GRADUALLY TRENDING
FARTHER WESTWARD EACH RUN. WITH THE FORECAST LEANED TOWARD THE
STRONGER AND SUBSEQUENT SLOWER SOLUTION...HAVE GONE AHEAD AND ISSUED
A HIGH WIND WATCH FOR THE SOUTH HALF OF THE CWA (18Z WEDNESDAY-06Z
THURSDAY). WITH A BRIEF SUBSIDENCE SURGE AND 55 KNOTS INDICATED AT
925 MB SOUTH OF EIGHT MILE...SUSTAINED WINDS OF 30 TO 35 MPH WITH
GUSTS OF 50 TO 55 MPH APPEAR TO BE A GOOD BET WITH THE POTENTIAL FOR
40 MPH SUSTAINED/GUSTS TO 60 MPH.
TEMPERATURES SHOULD HAVE NO PROBLEM CLIMBING INTO THE MID 30S TO
LOWER 40S WEDNESDAY MORNING WITH THE LOW TRACK NORTHWEST OF THE
CWA. RATHER PRONOUNCED SURFACE TROUGH HELPED OUT BY SOME LAKE
INDUCED TROUGHING WILL SWING THROUGH SOUTHERN LOWER MICHIGAN
WEDNESDAY EVENING. VERY STRONG SIGNAL SEEN IN 850 MB OMEGA
FIELDS...AS 850 MB TEMPS DROP THROUGH THE NEGATIVE TEENS OVERNIGHT.
SOUNDINGS SHOW INVERSION HEIGHTS ABOVE 700 MB WITH SATURATION AND
700 MB TEMPS FALLING INTO THE NEGATIVE LOWER TWENTIES. THE SETUP FOR
A POTENT SNOW SQUALL LINE/LOW LEVEL CONVERGENCE BAND APPEARS TO BE
VERY GOOD...AND THINKING IT WILL SET UP ALONG THE M-59 CORRIDOR.
ALTHOUGH THE GFS IS SHOWING THE BEST QPF ALONG THE I-94
CORRIDOR...THE BEST 925/850 MB LIFT AT 6Z THURSDAY IS SEEN OVER
EIGHT MILE...AND WILL ALLOW FOR A BIT BETTER LAKE
TROUGHING...ORIENTING THE BAND A BIT FARTHER NORTH. TOOK A QUICK
LOOK AT THE 18Z NAM WHICH IS ZEROING IN ON THE M-59/EIGHT MILE
CORRIDOR AS WELL. LOOKING AT AREA WIDE SNOW ACCUMULATIONS OF 1 TO 3
INCHES WITH INCREASING SNOW RATIOS (CLOSE TO 20:1 BY 12Z
THURSDAY)...WITH LOCALIZED HIGHER AMOUNTS IN THE WEST CENTRAL PART
OF THE CWA...ESPECIALLY IF THE BAND IS SLOWER TO MOVE.
LOWER INVERSION HEIGHTS SHOULD DIMINISH THE LAKE EFFECT ACTIVITY ON
THURSDAY...BUT ANOTHER INCH OR TWO WILL LIKELY FALL IN THE MID
SECTION WITH WESTERLY FLOW AND INCREASING FLUFF FACTOR TO THE SNOW.
SOLID LOW LEVEL COLD ADVECTION (925 MB TEMPS FALLING TO -12 TO -14
C) THROUGH THE DAY WILL PREVENT TEMPERATURE FROM RISING...HOLDING
AROUND 20 DEGREES.
POLAR VORTEX WILL BE DESCENDING SOUTH-SOUTHWEST INTO CENTRAL CANADA
BY SATURDAY MORNING...WITH PREDOMINATELY SPLIT ZONAL FLOW PROGGED
FOR THE CONUS (PER 12Z EUROPEAN). LONGWAVE PATTERN THEN SUPPORTS
TROUGHING OVER THE WESTERN CONUS/RIDGING EASTERN CONUS AS WE HEAD
INTO SUNDAY. NORTHERN STREAM TROUGH (EXTENSION OF POLAR VORTEX) THEN
PROGGED TO SWING THROUGH THE GREAT LAKES REGION EARLY NEXT
WEEK...RE-ENFORCING THE COLD AIR/BELOW NORMAL TEMPERATURES.
MARINE...
AN INTENSE WINTER STORM WILL STRENGTHEN TONIGHT AS THE SYSTEM LIFTS
NORTHWARD THROUGH THE MID MISSISSIPPI RIVER VALLEY. THE LOW IS
EXPECTED TO DEEPEN TO 975 MB OFFSHORE OF KENOSHA WISCONSIN BY 12Z
WEDNESDAY AND TO 973 MB NEAR ALPENA MICHIGAN 00Z THURSDAY. VERY
STRONG EASTERLY WINDS WILL DEVELOP TONIGHT IN ADVANCE OF THE
LOW...WITH A COOL AIRMASS FILTERING IN FROM THE EAST. THIS WILL
RESULT IN UNSTABLE CONDITIONS/INCREASED TURBULENT MIXING DEPTHS
ACROSS LAKE HURON WITH DELTA T VALUES IN EXCESS OF -10C. THE
STRONGEST WINDS...REACHING STORM FORCE...WILL OCCUR ACROSS MUCH OF
LAKE HURON LATE TONIGHT TOWARDS DAYBREAK WEDNESDAY. A MAJOR IMPACT
OF THIS STORM WILL BE WAVE HEIGHTS WITH THE ONSHORE FLOW. WAVE
HEIGHTS IN EXCESS OF 22 FEET WILL BE POSSIBLE ACROSS THE WESTERN
WATERS OF LAKE HURON NORTH OF SAGINAW BAY. AS THE LOW CENTER TRACKS
INTO NORTHERN PORTIONS OF LAKE HURON...A LULL IN THE SURFACE WINDS
IS ANTICIPATED. A SHARP...ATTENDANT...POLAR COLD FRONT WILL THEN
SLICE THROUGH SOUTHERN LAKE HURON...LAKE ST CLAIR...AND THE MICHIGAN
WATERS OF LAKE ERIE WEDNESDAY AFTERNOON. A SECONDARY TIME PERIOD FOR
STORM FORCE WINDS WILL OCCUR ALONG AND IMMEDIATELY BEHIND THIS FRONT
FOR SOUTHERN LAKE HURON. HAVE ISSUED A GALE WARNING FOR THE
POSTFRONTAL WINDS OVER LAKE ST CLAIR AND THE MICHIGAN WATERS OF LAKE
ERIE IN EFFECT BEGINNING LATE WEDNESDAY MORNING. ATTM...THESE WIND
MAGNITUDES ARE EXPECTED TO REMAIN AT 45 KNOT GALES.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING...MIZ047-MIZ048...UNTIL 10 AM WEDNESDAY.
WINTER WEATHER ADVISORY...MIZ063-MIZ068-MIZ069-MIZ070-MIZ075-
MIZ076...UNTIL 4 AM WEDNESDAY.
HIGH WIND WATCH...MIZ063-MIZ068-MIZ069-MIZ070-MIZ075-MIZ076-MIZ082-
MIZ083...FROM 1 PM WEDNESDAY TO 1 AM THURSDAY.
WINTER WEATHER ADVISORY...MIZ082-MIZ083...UNTIL 1 AM WEDNESDAY.
WINTER WEATHER ADVISORY...MIZ055-MIZ060-MIZ061-MIZ062...UNTIL 7 AM
WEDNESDAY.
WINTER WEATHER ADVISORY...MIZ049-MIZ053-MIZ054...UNTIL 10 AM
WEDNESDAY.
LAKE HURON...
STORM WARNING...LHZ361-LHZ362...UNTIL 1 PM WEDNESDAY.
STORM WARNING...LHZ363-LHZ421-LHZ441-LHZ442-LHZ443-LHZ462-LHZ463-
LHZ464...UNTIL 1 AM THURSDAY.
GALE WARNING...INNER SAGINAW BAY...UNTIL 1 PM THURSDAY.
LAKE ST CLAIR...
GALE WARNING...FROM 10 AM WEDNESDAY TO 10 AM THURSDAY.
SMALL CRAFT ADVISORY...UNTIL 10 AM WEDNESDAY.
MI WATERS OF LAKE ERIE...
GALE WARNING...FROM 10 AM WEDNESDAY TO 10 AM THURSDAY.
SMALL CRAFT ADVISORY...UNTIL 10 AM WEDNESDAY.
&&
$$
AVIATION.....BT
UPDATE.......BT
SHORT TERM...MR/DRK
LONG TERM....SF
MARINE.......CB
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
