Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 252045
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
345 PM EST THU DEC 25 2014

.SHORT TERM... AFTERNOON AND TONIGHT

SOUTHWEST WIND GUSTING AROUND 25 MPH ADDED SOME BITE TO OTHERWISE
MILD TEMPERATURE CONDITIONS AROUND SE MICHIGAN DURING THE AFTERNOON.
EXPECT THE WIND TO DIMINISH BUT NOT DROP OFF COMPLETELY TONIGHT AS A
RIDGE OF SURFACE HIGH PRESSURE SLIDES THROUGH LOWER MICHIGAN BUT ITS
CENTER REMAINS OVER THE TENNESSEE VALLEY. THIS WILL MAINTAIN ENOUGH
GRADIENT TO KEEP WIND IN THE 5-10 MPH RANGE THROUGH THE NIGHT WHICH
WILL ONLY ALLOW TEMPERATURES TO SETTLE BACK TOWARD 30F UNDER A BLEND
OF LOWER CLOUDS DIMINISHING AND HIGHER CLOUDS INCREASING DURING THE
NIGHT. NO PRECIPITATION.

TODAY`S OBSERVATION SUITE SHOWS A BROAD UPPER LEVEL RIDGE OVER THE
EASTERN U.S. WITH STRONG CONFLUENT FLOW ALOFT OVER THE NORTHERN
GREAT LAKES. THIS LARGE SCALE PATTERN ALOFT WILL ENSURE DRY
CONDITIONS ACROSS THE GREAT LAKES AND CONTINUE TO SUPPORT THE BROAD
AREA OF SURFACE HIGH PRESSURE EXTENDING FROM UPPER OHIO VALLEY ALL
THE WAY ACROSS THE GULF TO NEAR THE YUCATAN. GULF MODIFIED CP AIR IS
JUST NOW MAKING INLAND PROGRESS ALONG THE TEXAS COAST AND IS
BECOMING PART OF LOW TO MID LEVEL THETA-E ADVECTION THAT WILL FUEL
MID AND HIGH CLOUD DEVELOPMENT OVER THE MIDWEST AND LOWER MICHIGAN
DURING THE NIGHT RATHER THAN MAINTENANCE OF STRATUS. THE SETUP FOR A
REVERSAL OF THE STRATUS CLEARING TREND OR RENEWED STRATUS
DEVELOPMENT IS OTHERWISE FAVORABLE IN TERMS OF THE WIND FIELD WITH
STEADY GRADIENT FLOW AT THE SURFACE COMBINED WITH INCREASING FLOW
ABOVE THE BOUNDARY ON THE EASTERN FRINGES OF THE LOW LEVEL JET
DEVELOPING OVER THE PLAINS. THE GAP OF DRY AIR IN THE BOUNDARY LAYER
BETWEEN THE GREAT LAKES STRATUS AND GULF RETURN FLOW IS THEN
EXPECTED TO HELP THE CLEARING TREND CONTINUE THROUGH THE EVENING
WITH THE LOWER CLOUDS EXCHANGED FOR MID AND HIGH VARIETIES UNTIL
GULF MOISTURE CATCHES UP LATER FRIDAY MORNING.

&&

.LONG TERM...

BROAD RIDGING ANCHORED IN THE SUBTROPICS IS BUILDING ACROSS THE
SOUTHEASTERN THIRD OF THE UNITED STATES AS A DEEP LONGWAVE TROUGH
DIGS INTO THE SOUTHWESTERN UNITED STATES. DEVELOPING SOUTHWEST
GRADIENT WILL ENSURE MILD CONDITIONS THROUGH FRIDAY AND PROMOTE THE
DEVELOPMENT OF AN INVERSION LIKELY TO TRAP A GOOD DEAL OF BOUNDARY
LAYER MOISTURE DURING PEAK HEATING. AS A RESULT, PLENTY OF LOW
CLOUDS ARE EXPECTED TO HANG AROUND THROUGH THE DAY AS TEMPS CLIMB
WELL INTO THE 40S. THE TROUGH OVER THE SOUTHWEST US IS PROGGED TO
EJECT IN A COUPLE OF PIECES, THE FIRST OF WHICH WILL ENHANCE THE JET
OVERHEAD LATE FRIDAY AND INCREASE ISENTROPIC ASCENT, BUT SHOULD DO
LITTLE ELSE AS THE BETTER FGEN BAND RESIDES FURTHER NORTH.
ISENTROPIC ASCENT THEN BEGINS TO INCREASE LATE FRIDAY NIGHT THROUGH
SATURDAY MORNING AS THE LOW-LEVEL FLOW BEGINS TO RAMP UP AND
MOISTURE TRANSPORT WITHIN THE BOUNDARY LAYER INCREASES. WILL MOVE
FROWARD WITH MENTION OF DRIZZLE THROUGH THE NIGHT BUT HOLD OFF ON
SHOWER MENTION UNTIL THE ARRIVAL OF BETTER FORCING ASSOCIATED WITH
THE SECOND PORTION OF THE ENERGY. LOWS FRIDAY NIGHT WILL REMAIN
QUITE MILD FOR THE TIME OF YEAR...AROUND 40 DEGREES. WAS COMFORTABLE
GOING SEVERAL DEGREES ABOVE THE GUIDANCE AS THE NWP TEND TO
UNDERESTIMATE THE IMPACTS OF NOCTURNAL WARM ADVECTION DURING THE
WINTER. THERE IS STRONG MODEL CONSENSUS THAT THE SURFACE LOW
ATTENDANT TO SATURDAY`S UPPER WAVE WILL TRACK NORTH OF THE AREA,
LEAVING THE CWA IN THE WARM SECTOR, VOID OF ANY SNOW THREAT. THE
BULK OF PRECIP WILL REMAIN WELL TO THE NORTHWEST WITHIN THE
DEFORMATION ZONE, THOUGH IT MAY SCRAPE THE SAGINAW VALLEY TO THE
TUNE OF A TENTH OR TWO OF LIGHT RAIN ON SATURDAY EVENING. RAPIDLY
STRENGTHENING UPPER JET WILL THEN SUPPORT A BAND OF COLD FRONTAL
SHOWERS AS THE LOW LIFTS TO THE NORTHWEST. COLD ADVECTION WILL DROP
TEMPS INTO THE 30S SATURDAY NIGHT.

OBSCURE QUASI-ZONAL PATTERN AT MID-LEVELS WILL PROVIDE A RETURN OF
NORMAL TEMPERATURES FOR THE EXTENDED PERIOD. STRONG ANTI-CYCLONE
RIDING THE LEE EDGE OF THE ROCKIES EARLY NEXT WEEK WILL AFFECT A
LARGE PORTION OF THE CONUS...WITH LIGHT NORTH WINDS IN THE GREAT
LAKES. A 500MB WAVE AND LOBE OF CONCENTRATED VORTICITY MAXIMA
LOOKS TO CROSS THE REGION LATE TUESDAY WHICH MAY SPARK SOME LIGHT
SNOW SHOWERS...OTHERWISE NO TANGIBLE PRECIP THREAT THROUGH THE
PERIOD.

&&

.MARINE...

WINDS AND WAVES WILL CONTINUE TO DIMINISH THROUGH TONIGHT WITH LIGHT
TO MODERATE WINDS PERSISTING INTO EARLY SATURDAY. A LOW LIFTING
ACROSS THE NORTHERN LOWER PENINSULA WILL BRING FRESH SOUTHERLY WINDS
SATURDAY FOLLOWED BY A SHIFT TO NORTHWEST WINDS BEHIND THE COLD
FRONT SATURDAY NIGHT. NORTHWEST GUSTS ON SATURDAY NIGHT ARE FORECAST
TO REMAIN BELOW THE GALE THRESHOLD.

&&

.AVIATION...ISSUED 1238 PM EST THU DEC 25 2014

HIGH PRESSURE ADVANCING FROM THE MIDWEST THROUGH THE GREAT LAKES
WILL BRING IMPROVING SKY CONDITIONS AND DIMINISHING WIND TONIGHT...
AND ENSURE DRY WEATHER THROUGH FRIDAY. A CLEARING TREND TONIGHT WILL
BE PRECEDED BY BORDERLINE MVFR/VFR CEILING DURING THE AFTERNOON THAT
WILL TEND TO SINK BACK BELOW 2000 FEET BEFORE THE CLEARING LINE
ARRIVES. THE WESTERN EDGE OF CLOUDS MOVING OUT OF ILLINOIS AT PRESS
TIME IS ON PACE TO REACH SE MICHIGAN DURING THE EVENING LEAVING JUST
PATCHY HIGH CLOUDS IN PLACE THROUGH FRIDAY MORNING. RELATIVELY MILD
AIR FOR THIS TIME OF YEAR WILL BE SUBJECT TO SOME STRATUS
REDEVELOPMENT AFTER MIDNIGHT. THIS IS HINTED IN MODEL DATA BUT NEEDS
SOME OBSERVATIONAL SUPPORT BEFORE BEING ADDED TO THE FORECAST...
ESPECIALLY CONSIDERING CLEAR SKY OVER THE MID MISSISSIPPI VALLEY
DURING THE AFTERNOON.

FOR DTW... MVFR CEILING WILL BE THE PREVAILING CONDITION THROUGH MID
EVENING. A DOWNWARD TREND BELOW 2000 FEET IS MORE LIKELY THAN ANY
MEANINGFUL TIME OF VFR...SUGGESTED BY RECENT OBSERVATIONS...UNTIL
THE CLEARING LINE EXITING ILLINOIS AT PRESS TIME REACHES THE
TERMINAL. AFTER CLEARING...CONDITIONS WILL BE MONITORED OVER THE
OHIO VALLEY FOR POTENTIAL STRATUS REDEVELOPMENT AFTER MIDNIGHT
THROUGH FRIDAY MORNING.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CEILING BELOW 5000 FEET THROUGH EARLY EVENING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.

&&

$$

SHORT TERM...BT
LONG TERM....JVC/MM
MARINE.......JVC
AVIATION.....BT


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



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