Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 231105
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
705 AM EDT SAT AUG 23 2014


.AVIATION...

//DISCUSSION...

WIDELY VARIABLE CONDITIONS ACROSS THE REGION TO START OUT THE TAF
CYCLE AS AN AREA OF DENSE FOG IS DRIFTING SOUTHWEST OFF LAKE HURON
AND BUTTING UP AGAINST A BAND OF HIGHER CLOUDS ACROSS ACROSS FAR
SOUTHERN/CENTRAL MI. THIS IS RESULTING IN ALL FLIGHT CATEGORIES
RANGING FROM LIFR TO VFR. THE INTERFACE OF THESE DIFFERING
CIGS/VSBYS HAPPENS TO ALIGN ITSELF FROM LAN TO DTW WHICH AFFECTS
FNT/PTK/DTW/YIP. WENT A LITTLE PESSIMISTIC FOR THE EARLY PART OF THE
DAY AS MOST MODELS WANT TO HOLD ONTO A CIG THROUGH THE AFTERNOON
BEFORE HIGH PRESSURE CAN HELP ERODE IT AWAY. MAY BE ABLE TO AMEND
AND SCATTER THEM OUT FASTER LATER THIS MORNING. THE OTHER ISSUE WILL
BE THE POSSIBLE RETURN OF FOG TONIGHT. WINDS WILL BE MORE EASTERLY
WHICH MAY PRESENT MORE OF A MVFR/IFR STRATUS DECK BUT A PERSISTENCE
FORECAST FAVORS FOG SO WENT MVFR FOR BOTH CIGS AND VSBYS AS A MIDDLE
GROUND FOR NOW.

FOR DTW...DENSE FOG IS APPROACHING THE AIRPORT BUT IT LOOKS LIKE THE
VFR CIGS WILL HOLD THROUGH THE MORNING AND MITIGATE THE FOG CONCERNS
NOTED EARLIER. WOULD NOT BE SURPRISED TO SEE SOME PATCHY FOG BEFORE
14Z.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE CEILINGS BELOW 5000FT INTO THE AFTERNOON BUT LOW
CONFIDENCE ON TIMING THEM SCATTERING OUT.

* MEDIUM CONFIDENCE IN CEILINGS BELOW 5000FT RETURNING TONIGHT.

&&

.PREV DISCUSSION...ISSUED 346 AM EDT SAT AUG 23 2014

SHORT TERM...TODAY AND TONIGHT

A STRONG 100+ KNOT JET ENTERING THE NW CONUS WILL HELP TO NUDGE THE
LONGWAVE PATTERN A BIT TO THE EAST. IT WILL ALSO DEEPEN THE TROUGH
OVER THE ROCKIES THUS AMPLIFYING THE RIDGE ALIGNED WITH THE
MISSISSIPPI RIVER. THE RIDGE WILL START TO MOVE INTO THE AREA WHICH
WILL INCREASE 500 MB HEIGHTS FROM 585DAM FRIDAY AFTERNOON TO 588DAM
THIS AFTERNOON. AT THE SFC...HIGH PRESSURE CENTERED OVER QUEBEC HAS
BEEN PRODUCING WEAK NORTHEASTERLY FLOW THE LAST TWO DAY AND WILL
DRIFT SW CLOSER TO THE REGION. THIS WILL USHER IN INCREASINGLY DRIER
AIR ALOFT WHILE VEERING FLOW MORE EASTERLY. THE AMPLE MOISTURE AT
THE SFC WILL NOT GO ANYWHERE BUT THE MORE EASTERLY FLOW WILL RESULT
IN LESS MOISTURE ADVECTION OFF LAKE HURON WHICH WILL KEEP DEWPOINTS
MORE IN THE MID 60S VS THE 70S WE HAVE HAD THE LAST COUPLE DAYS.
EXPECT A GOOD COVERAGE OF CU TODAY WITH THE DIURNAL CYCLE TAPPING
INTO THIS SFC MOISTURE BUT WE SHOULD REMAIN DRY AS THE AMPLIFYING
RIDGE DRAWS THE DEEPER RIBBON OF MOISTURE BACK TO THE WEST. FOG WILL
BE A CONCERN ONCE AGAIN TONIGHT AS THE RIDGE AXIS DRAWS NEARER AND
CLEARING SKIES PROMOTE COOLING. DIFFERENCE WITH TONIGHT WILL BE THE
EASTERLY SFC FLOW WHICH WILL SHUT OFF THE MOISTURE ADVECTION OFF
LAKE HURON. THIS COULD LEAD TO A LOW STRATUS DECK OVER THE AREA VS
FOG BUT AT THIS TIME WILL KEEP WITH PERSISTENCE AND MENTION FOG.

LONG TERM...SUNDAY THROUGH FRIDAY

THE AXIS OF A HIGH AMPLITUDE SUBTROPICAL RIDGE WILL BE CENTERED OVER
LOWER MI ON SUNDAY. DRY CONDITIONS WILL BE ENSURED BY WARM MID LEVEL
TEMPS AND STABLE EASTERLY FLOW IN THE LOW LEVELS RESULTING FROM THE
SFC HIGH PARKED OVER THE ERN GREAT LAKES. MORNING FOG AND/OR STRATUS
ALONG WITH THE EASTERLY LOW LEVEL FLOW WILL CUT INTO DAYTIME
HEATING. THUS DESPITE 500MB HEIGHTS OF 589 DM...AFTERNOON HIGHS ARE
EXPECTED TO ONLY RANGE FROM THE UPPER 70S NEAR THE GREAT LAKES TO
LOWER 80S INLAND.

THE MID LEVEL RIDGE AXIS WILL BE FORCED EAST OF THE STATE ON MONDAY
AS A DEEP UPPER LOW TRACKS FROM THE NRN PLAINS INTO NRN ONTARIO. THE
LOW LEVEL FLOW WILL IN TURN VEER TOWARD THE S-SW WHICH WILL ADVECT
WARMER AIR INTO SE MI /850MB TEMPS FORECAST TO REACH +18C/...
ALLOWING DAYTIME HIGHS TO RISE INTO THE UPPER 80S TO NEAR 90. THE
VEERED LOW LEVEL FLOW WILL ALSO LIFT THE POOL OF LOW 70 DEWPOINTS
NOW RESIDING OVER IL/IN INTO SE MI...RAISING HEAT INDICES INTO THE
LOW 90S. THE MODEL SOLUTIONS DO HINT AT A WEAKENING FRONTAL BOUNDARY
BEING DRIVEN INTO LOWER MI LATE MON/MON NIGHT IN RESPONSE TO THE
UPPER LOW PASSING ACROSS NRN ONTARIO. THE WEAK NATURE OF THE FORCING
AND A MID LEVEL CAP WILL BE LARGE LIMITING FACTORS FOR CONVECTIVE
INITIATION AND THUS SUPPORT THE CURRENT DRY FORECAST.

TRENDS AMONG THE 00Z MODEL SUITE HAVE BEEN TOWARD HIGHER MID LEVEL
HEIGHTS OVER SRN MI ON TUESDAY AS THE FORECAST AREA REMAINS ON THE
NORTHERN PERIPHERY OF THE SUBTROPICAL RIDGE. THE MODEL SOLUTIONS
SUGGEST THE POSSIBILITY OF THE AREA BEING IMPACTING BY UPSTREAM
CONVECTION BY TUES AFTERNOON. CONFIDENCE ON THIS IS QUITE LOW AND
NOT ENOUGH TO INCREASE POPS AT THIS TIME. CONTINUED SW FLOW DOES
SUGGEST THE POTENTIAL FOR TUES TO BE ANOTHER HOT AND HUMID DAY /MOS
GUIDANCE TEMPS HAVE ALSO TRENDED UPWARD/. THE CHANCE OF CONVECTION
WILL INCREASE DURING THE MID WEEK PERIOD /TUES NIGHT THROUGH
THURSDAY/ AS SEVERAL MID LEVEL SHORT WAVE IMPULSES ARE EXPECTED TO
EJECT OUT OF THE CENTRAL PLAINS AND TRAVERSE THE GREAT LAKES. MODEL
SOLUTIONS DIVERGE CONSIDERABLY WITH RESPECT TO THE PROGRESSION OF
THE LONGER WAVELENGTH TROUGH. THE FORECAST WILL CONTINUE TO LEAN
TOWARD THAT OF THE ECMWF WHICH HAS BEEN A BIT MORE CONSISTENT AND
HAS SOME SUPPORT FROM THE CANADIAN. THIS SOLUTION SLIDES A LOW LEVEL
BAROCLINIC ZONE ACROSS LOWER MI BY MID WEEK AND SUGGESTS THE
POSSIBILITY FOR SEVERAL ROUNDS OF CONVECTION. HEAVY RAINFALL WILL BE
A CONCERN WITH THIS PATTERN AND WILL BE SOMETHING TO MONITOR AS
FORECAST CONFIDENCE INCREASES OVER THE NEXT COUPLE OF DAYS.

MARINE...

EAST-NORTHEAST WINDS WILL PERSIST THROUGH THE DURATION OF THE
WEEKEND AS HIGH PRESSURE REMAINS CENTERED ACROSS THE EASTERN GREAT
LAKES. OVERALL...WINDS WILL REMAIN LIGHT ALTHOUGH SOME GUSTS OVER 12
KNOTS ARE POSSIBLE FROM TIME TO TIME ACROSS SAGINAW BAY WHERE THE
WATER IS WARM AND WINDS GET FUNNELED INTO THE BAY. THE HIGH WILL
DRIFT EAST BY MONDAY ALLOWING WINDS TO VEER TOWARD THE SOUTH. WARMER
AIR WILL OVERSPREAD THE REGION WHICH WILL INCREASE THE STABILITY
OVER THE LAKES...KEEPING THE WIND SPEEDS IN CHECK.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...DENSE FOG ADVISORY...MIZ049-MIZ054-MIZ055-MIZ062-MIZ063...UNTIL 9
     AM SATURDAY.

LAKE HURON...
     DENSE FOG ADVISORY...LHZ361-LHZ362-LHZ363...UNTIL 5 PM SATURDAY.

     DENSE FOG ADVISORY...LHZ421-LHZ441-LHZ442-LHZ443-LHZ462-LHZ463-
     LHZ464...UNTIL 1 PM SATURDAY.

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

&&

$$

AVIATION.....DRK
SHORT TERM...DRK
LONG TERM....SC
MARINE.......SC


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






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