Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 241655
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1255 PM EDT SUN AUG 24 2014

.AVIATION...

//DISCUSSION...

LOW LEVEL MOISTURE (IFR CEILINGS THIS MORNING) HAVE BEEN SLOWING
LIFTING...AND MVFR/LOW VFR CEILINGS EARLY THIS AFTERNOON SHOULD
CONTINUE TO LIFT AND SCT OUT DURING THE LATE AFTERNOON HOURS INTO
THE EVENING HOURS. THE PROSPECTS FOR FOG AND/OR LOW CLOUDS TONIGHT
IS MUDDLED WITH STRETCHED OUT UPPER LEVEL SHORTWAVE...WHICH MAY BE
SUFFICIENT TO MAINTAIN SOME VFR/MID CLOUDS...HELPING TO MITIGATE
THE DENSE FOG/LOW CLOUD THREAT. HOWEVER...VERY WEAK WIND
FIELDS/SOUTHEAST FLOW OFF LAKE ERIE WILL CERTAINLY ARGUE FOR
FOG/IFR CONDITIONS REDEVELOPING...POTENTIALLY LIFR...ESPECIALLY
DTW/YIP.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING AOB 5000 FT DURING EARLY
  AFTERNOON...LOW CONFIDENCE LATE IN THE
  AFTERNOON/EVENING...HIGH CONFIDENCE OVERNIGHT INTO MONDAY MORNING.

* LOW CONFIDENCE FOR CEILING BELOW 200 FEET AND/OR FOR VISIBILITY
  BELOW 1/2SM EARLY MONDAY MORNING.

&&

.PREV DISCUSSION...ISSUED 326 AM EDT SUN AUG 24 2014

SHORT TERM...TODAY AND TONIGHT

LONGWAVE PATTERN CONSISTS OF HIGH AMPLITUDE RIDGE OVER THE MIDWEST
AND GREAT LAKES WITH DEEP TROUGHS OVER BOTH THE ATLANTIC AND PACIFIC
COASTS. A STRONG WAVE EJECTING OUT OF THE WEST COAST TROUGH WILL
LIFT FROM THE NORTHERN PLAINS THIS MORNING TO WESTERN ONTARIO BY
MONDAY MORNING. THIS WILL BARREL INTO THE RIDGE...FORCING IT INTO A
POSITIVE TILT ACROSS THE GREAT LAKES WITH THE RIDGE AXIS TRAVERSING
THE AREA THIS AFTERNOON/EVENING. THIS WILL OCCUR AT THE END OF THE
DIURNAL CYCLE WHICH WILL LIMIT THE AMOUNT OF ADDITIONAL SFC HEATING
WE RECEIVE TODAY. ALSO HINDERING HEATING TODAY WILL BE CLOUD COVER
AS WE WILL AGAIN HAVE TO BURN OFF THE FOG/LOW STRATUS ACROSS THE
REGION...WHICH TOOK WELL INTO THE AFTERNOON HOURS ON SATURDAY. MODEL
SOUNDINGS SHOW SOME WAA IN THE 750-900 MB LAYER BUT EASTERLY FLOW IN
THE BL FROM THE HIGH PRESSURE SYSTEM OVER SOUTHERN ONTARIO/QUEBEC
WILL KEEP THIS MOSTLY LOCKED ABOVE THE INVERSION. THE SFC WINDS
BEGIN VEERING MORE SOUTHERLY OVERNIGHT AS THE PRESSURE PATTERN
SHIFTS WHICH WILL RESULT IN A BOOST IN OVERNIGHT TEMPERATURES TO
MID/UPPER 60S.

MOST MODELS HAVE BEEN DRY FOR TODAY AND TONIGHT FOR SEVERAL RUNS IN
A ROW NOW BUT A HANDFUL ARE NOW GIVING MORE CREDIT TO A WAVE
DRIFTING THROUGH MID MI THIS AFTERNOON. HIRES MODELS ACKNOWLEDGE THE
WAVE BUT KEEP THE AREA DRY WITH HIGH PRESSURE HOLDING MORE FIRMLY AS
THE LOW LIFTS UP AND AROUND THE RIDGE. WILL LEAN MORE ON THE HIRES
KEEPING THE FORECAST DRY AT THIS POINT WHILE WE WAIT FOR THE FEATURE
TO SHOW ITSELF ON RADAR/SATELLITE.

WE WILL ONCE AGAIN HAVE TO DEAL WITH SOME FOG IN THE OVERNIGHT
PERIOD AS THE LOW LEVEL MOISTURE STILL LINGERS AND THE RIDGE AXIS
OVERHEAD ALLOWS WINDS TO GO LIGHT AND VARIABLE. DIFFERENCE TONIGHT
WILL BE THAT THERE MAY BE SOME MID CLOUDS OVER THE AREA FROM THE
WEAKENING SHORTWAVE MENTIONED ABOVE AND GRADIENT FLOW WILL BECOME
SOUTHWESTERLY BY MORNING LIMITING NOCTURNAL COOLING EFFECTS.

LONG TERM...MONDAY THROUGH SATURDAY

THE HIGH AMPLITUDE RIDGE AXIS EXTENDING ACROSS THE GREAT LAKES WILL
FLATTEN AS THE UPPER LOW NOW CHURNING OVER THE NRN ROCKIES LIFTS
INTO NRN ONTARIO ON MONDAY. THIS WILL CAUSE THE ERN GREAT LAKES SFC
HIGH TO EXIT EAST OF THE REGION...VEERING THE LOW LEVEL FLOW TOWARD
THE SOUTH. POTENTIAL MORNING FOG AND LOW CLOUDS AS WELL AS SOME
MID/HIGH LEVEL MOISTURE WILL SUPPORT A CONSERVATIVE APPROACH TO
AFTERNOON HIGHS DESPITE 850MB TEMPS FORECAST TO HIT +19C. THE 00Z
MODEL SUITE SUGGEST LOCALS NEAR THE LAKESHORES WILL HOLD ONTO A MORE
SE COMPONENT TO SFC WINDS...SUPPORTING HIGHS IN THE MID 80S. FARTHER
INLAND TEMPS SHOULD APPROACH THE 90 DEGREE MARK. THE SOUTHERLY FLOW
WILL BRING NEAR 70F SFC DEWPOINTS INTO SRN MI...LEADING TO HEAT
INDICES IN THE LOW 90S.

MODEL SOUNDINGS SHOW THAT WARMING NEAR 850MB WILL SUFFICIENTLY CAP
THE ATMOSPHERE ON MONDAY AND SUPPORTS THE CURRENT DRY FORECAST. THE
UPPER LOW PASSING NORTH OF THE REGION WILL DRIVE A SFC COLD FRONT
INTO NRN LOWER MI MON NIGHT. SLIGHTLY ENHANCED LOW LEVEL INFLOW AND
MODERATE TO HIGH INSTABILITY OVER THE REGION MAY ALLOW SOME
CONVECTIVE INITIATION ALONG THE FRONT...POSSIBLY MAKING IT INTO SE
MI. THE FRONT WILL ATTEMPT TO DROP INTO SRN MI ON TUESDAY. FORCING
ALONG THE FRONT MAY STRUGGLE TO OVERCOME THE CAPPING INVERSION.
THERE IS HOWEVER A CONTINUED CHANCE FOR UPSCALE GROWTH TO CONVECTION
UPSTREAM WHICH COULD SLIDE ACROSS SRN MI WITHIN THE WESTERLY FLOW.
MODERATE TO HIGH INSTABILITY AND VERY GOOD CAPE DENSITY WILL POSE
THE RISK FOR SOME STRONG TO POSSIBLY SEVERE STORMS. ASSUMING
CONVECTION DOES NOT BECOME WIDESPREAD...BETTER MIXING POTENTIAL
UNDER WESTERLY FLOW AND 850MB TEMPS AROUND +20C WILL SUPPORT
FORECAST HIGHS NEAR 90 ON TUES. LOW LEVEL MOISTURE POOLING ALONG THE
SFC FRONT WILL LEAD TO SFC DEWPOINTS IN THE LOW 70S...PLACING HEAT
INDICES WELL INTO THE 90S.

ADDITIONAL MID LEVEL HEIGHT FALLS ACROSS NRN ONTARIO TUES NIGHT WILL
FURTHER SUPPRESS THE MID LEVEL RIDGE SOUTH OF THE REGION AND WILL
PLACE A LOW LEVEL BAROCLINIC ZONE ACROSS THE UPPER MIDWEST AND GREAT
LAKES REGION. MID LEVEL SHORT WAVE PERTURBATIONS WITHIN THE WESTERLY
FLOW WILL SUPPORT CONTINUED CHANCES OF CONVECTION OVER SE MI TUES
NIGHT INTO WED. THE TRENDS NOTED IN THE ECMWF AND CANADIAN
/INCLUDING THE LATEST 00Z RUNS/ SHOW THE INSTABILITY AXIS SLIDING
SOUTH OF MI ON WED WITH HIGH PRESSURE BUILDING ACROSS LOWER MI BY
THURS. THIS IS THE RESULT OF GREATER HEIGHT FALLS ACROSS ERN CANADA
AND A TREND TOWARD SLOWING THE EASTWARD PROGRESSION OF ANOTHER UPPER
LOW OVER THE ROCKIES. THESE TRENDS ARE SUPPORTING A COOLER AND DRIER
FORECAST WED NIGHT THROUGH THURS.

MARINE...

A MOIST EASTERLY FLOW RESULTING FROM HIGH PRESSURE ACROSS THE
EASTERN GREAT LAKES WILL SUSTAIN SOME AREAS OF FOG /ESPECIALLY IN
THE COLDER OPEN WATERS OF LAKE HURON/ TODAY INTO MONDAY MORNING. THE
LOW LEVEL WINDS WILL THEN TURN MORE TOWARD THE SOUTH ON MONDAY AS A
COLD FRONT APPROACHES THE NORTHERN GREAT LAKES. VERY WARM AIR
LIFTING INTO THE AREA AHEAD OF THIS FRONT WILL KEEP STABILITY VERY
HIGH OVER THE LAKES AND THUS KEEP WINDS AND WAVES IN CHECK. THE
FRONT WILL SLOWLY PROGRESS FROM NORTHERN LAKE HURON MONDAY NIGHT
INTO THE OHIO VALLEY ON WEDNESDAY. THIS FRONT WILL SUSTAIN A CHANCE
OF STRONG STORMS AS IT TRACKS ACROSS THE REGION.

&&

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

&&

$$

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


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