Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 271045
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
645 AM EDT THU AUG 27 2015


.AVIATION...

STRATUS WILL BRING BKN-OVC MVFR CIGS TO KPTK NORTH THIS MORNING AND
MAY EDGE SOUTH INTO THE I-94 TERMINALS AS WELL. AS THE MORNING
PROGRESSES...CIGS SHOULD LIFT GRADUALLY WITH A TREND TO BKN AND THEN
SCT CLOUDS AS LOW LEVEL MIXING PROGRESSES WITH DIURNAL HEATING. BY
EARLY THIS EVENING...EXPECT GENERALLY CLEAR SKIES. WINDS WILL REMAIN
LIGHT...5 KNOTS OR LESS...THROUGHOUT THE FORECAST PERIOD AS HIGH
PRESSURE BUILDS ACROSS THE REGION.

FOR DTW...SCT LOW LEVEL CLOUDS WILL MOST LIKELY BECOME BKN FOR SOME
TIME TODAY AS LOW LEVEL MOISTURE EDGE SOUTHWARD INTO AREA. INITIAL
CIGS MAY BE 3KFT OR LESS...BUT 4KFT SHOULD BE THE RULE INTO THIS
AFTERNOON.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN CEILINGS AOB 5KFT 14Z-21Z TODAY.

&&

.PREV DISCUSSION...ISSUED 235 AM EDT THU AUG 27 2015

SHORT TERM...TODAY AND TONIGHT

SURFACE HIGH PRESSURE WILL CONTINUE TO DRIFT SLOWLY EASTWARD THROUGH
THE AREA TODAY AND THEN CENTER OVER THE EASTERN GREAT LAKES TONIGHT.
STRATUS HAS BEEN EVER SO STEADILY ERODING AS DRIER AIR ASSOCIATED
WITH THIS HIGH FILTERS INTO THE AREA. GENERALLY EXPECT THIS SLUGGISH
TREND TO CONTINUE INTO THE EARLY MORNING HOURS...BUT LOW LEVEL
MOISTURE WILL LIKELY BE SUFFICIENT ENOUGH TO FORM A SCATTERED TO
BROKEN CUMULUS OR STRATO-CU DECK FROM MID MORNING INTO MID TO LATE
AFTERNOON BEFORE FINALLY CLEARING OUT FOR GOOD BETWEEN 21Z-01Z.

WILL MAINTAIN RELATIVELY COOL CONDITIONS TODAY AS BOUNDARY LAYER
MIXING WILL BE WEAK UNDER THE SURFACE RIDGE...AND SOLAR INSOLATION
WILL BE MODEST GIVEN PERIODS OF BROKEN DIURNAL CU/STRATO-CU. HIGHS
IN THE LOWER 70S STILL SEEMS ON TRACK FOR MOST OF AREA WITH PERHAPS
A POCKET OF UPPER 60S OVER THE THUMB WHERE CLOUDS WILL BE SLOWEST TO
BREAK UP. WITH GENERALLY CLEAR SKIES THEN PERSISTING FROM THIS
EVENING INTO THE OVERNIGHT HOURS...LOWS SHOULD FALL WELL INTO THE
50S IN MANY LOCATIONS...ONLY HOLDING IN THE UPPER 50S WITHIN THE
CORE URBAN HEAT ISLAND OF METRO DETROIT.

LONG TERM...FRIDAY THROUGH WEDNESDAY

SURFACE RIDGE OF HIGH PRESSURE WILL HAVE FRIDAY START MOSTLY SUNNY.
SHOULD BE SOME CU TO DEVELOP IN THE AFTERNOON AS A FAIRLY DENSE CI
SHIELD MOVES IN LATE ON FRIDAY AHEAD OF THE NEXT SYSTEM. STILL
ENOUGH SUN TO GO WITH THE WARMER MET GUIDANCE NUMBERS.

FOR FRIDAY NIGHT THROUGH THE WEEKEND...LITTLE CONFIDENCE IN THE
EVOLUTION OF THAT NEXT SYSTEM. THE SHORTWAVES WERE OVER THE ROCKY
MOUNTAINS EARLY THIS MORNING...GOING THROUGH ONE CONVECTIVE CYCLE AT
THIS TIME. THIS SYSTEM WILL HAVE TWO MORE CONVECTIVE CYCLES LATER
TODAY AND FRIDAY BEFORE MOVING INTO THE GREAT LAKES REGION FOR THE
WEEKEND. MODELS BARE THIS OUT AS SOLUTIONS RANGE FROM THE MORE
CONSOLIDATED UPPER FEATURES OF THE NAM AND ECMWF...THE WEAKENING
STRONGER WAVES OF THE GFS...TO THE MORE SEPARATE AND MUCH WEAKER
SHORTWAVES OF THE GEM. FOR THIS FORECAST WILL FOCUS ON LATER FRIDAY
NIGHT WITH THE FRONTAL FORCING...MOISTURE ADVECTION AND UPPER JET
SUPPORT SOMEWHERE BETWEEN THE BRIDGE AND MBS. THIS WILL HAVE THE
HIGHEST POPS IN THE NW CORNER OF THE FORECAST AREA WITH LESSER POPS
TO THE SOUTH AND EAST.

ON SATURDAY...THE SHORTWAVES WILL BE MOVING TO AT LEAST WESTERN
LOWER MICHIGAN. WITH MLCAPES FROM 500-1000 J/KG...SHOWERS AND
THUNDERSTORMS LOOK TO BE INCREASINGLY LIKELY ESPECIALLY FOR THE
AFTERNOON. WILL HAVE LIKELY POPS FOR AREAS NORTH AND WEST OF A
HARBOR BEACH TO CHELSEA LINE...AND THEN CHANCE POPS TO THE SOUTH AND
EAST.

SEVERE WEATHER NOT ANTICIPATED TO BE MUCH OF AN ISSUE AS 6KM BULK
SHEAR WILL BE AROUND 30KTS WITH THAT LIMITED INSTABILITY.
PRECIPITABLE WATERS DO INCREASE TO AT LEAST 1.5 INCHES...AND SOME
INDICATION WILL BE NORTH OF 1.75 INCHES. THE SLOWER MOVEMENT OF THE
SHORTWAVES WILL ALSO KEEP THE LOW LEVEL JET PINNED ON THE BOUNDARY
THAT WILL BE LYING FROM SOME SORT OF A WEST TO EAST LINE ACROSS
LOWER MICHIGAN.  COULD BE SOME LOCALLY HEAVY RAINFALL IN THIS
ENVIRONMENT.

THE MAIN SHORTWAVE WEAKENS AND SHEARS OUT FROM SATURDAY INTO
SUNDAY...LEAVING THE 500 MB TROF OVER THE REGION. LESS FORCING WILL
LEAD TO JUST SLIGHT CHANCE OR CHANCE POPS ON SUNDAY AND SUNDAY
EVENING WITH THE HIGHEST FOR THE SOUTHEAST HALF OF THE FORECAST
AREA.

BUILDING HEIGHTS AS THE 500 MB RIDGE SETS UP OVER THE GREAT LAKES ON
TAP FROM MONDAY THROUGH MUCH OF NEXT WEEK. FORECAST WILL GENERALLY
BE DRY AND WARM ALTHOUGH THE RIDGE CONTINUES TO BE NOT AS STRONG AS
SOME EARLIER MODEL FORECASTS. IN FACT...SOME WEAKNESS IN THE HEIGHT
FIELD TO OUR SOUTH THROUGH THE EXTENDED PERIOD MAY BE ENOUGH TO
BRING SOME AFTERNOON/EVENING THUNDERSTORMS...BUT CHANCES ARE TOO LOW
TO INCLUDE AT THIS TIME IN THE EXTENDED FORECAST.

MARINE...

LAST FEW HOURS OF INFLUENCE FROM THE HUDSON BAY LOW...WITH
CLOUDS...A FEW LIGHT SHOWERS AND A CHANCE OF WATERSPOUTS THROUGH 14Z
THIS MORNING. SURFACE HIGH PRESSURE CONTINUES TO BUILD INTO THE
CENTRAL LAKES TODAY BRINGING MORE TRANQUIL CONDITIONS. LIGHT WINDS
WILL CONTINUE AS THE SURFACE HIGH MAINTAINS CONTROL THROUGH FRIDAY
EVENING. THE NEXT LOW PRESSURE SYSTEM WILL START TO BRING STRONGER
SOUTHEASTERLY FLOW LATE FRIDAY NIGHT INTO SATURDAY.  THIS TIME FRAME
WILL ALSO BE THE NEXT CHANCE OF SHOWERS AND STORMS WITH THE
APPROACHING LOW PRESSURE SYSTEM.

&&

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

$$

AVIATION.....DG
SHORT TERM...DG
LONG TERM....RBP
MARINE.......RBP


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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).


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