Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 291513
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1113 AM EDT SAT AUG 29 2015

.UPDATE...

A WEAKENING MCV EMBEDDED WITHIN THE LARGER SCALE UPPER TROUGH IS
PROPPING UP A PATTERN OF SHOWERS OVER LOWER MICHIGAN HEADING INTO
THE AFTERNOON. A CONVINCING TREND IN WARMING CLOUD TOPS ALONG THE
LEADING EDGE...COMBINED WITH SUBSTANTIAL DRY AIR BELOW 600 MB IN
THE 12Z DTX SOUNDING...SUPPORTS MESOSCALE MODEL SUGGESTIONS OF A
DIMINISHING TREND AS THE RAIN PATTERN MOVES EASTWARD. THIS TREND
IS ONLY SYMPTOMATIC OF THE LEADING BAND OUTRUNNING THE SUPPORT OF
SEVERAL FAVORABLE INGREDIENTS THAT WILL REMAIN IN PLACE THROUGH
THE DAY. THE LARGER SCALE ENTRANCE REGION OF THE UPPER JET AND
UPPER TROUGH AXIS WILL CONTINUE TO SUPPORT LOW TO MID LEVEL
MOISTURE TRANSPORT/THETA-E ADVECTION THROUGH THE DAY OVER LOWER
MICHIGAN. WHILE NOT AS EFFECTIVE DURING THE DAY...THE RESULTING
ISENTROPIC LIFT WILL CONTINUE TO GENERATE ELEVATED INSTABILITY AND
CLUSTERS OF SHOWERS FROM CLOSER TO THE SURFACE WARM FRONT OVER
INDIANA/ILLINOIS NORTHEASTWARD OVER SE MICHIGAN. THIS WILL MAKE
SHOWERS LIKELY MOST AREAS THROUGH THE AFTERNOON AND LEAVE
THUNDERSTORM POTENTIAL LIMITED BY THE LACK OF SURFACE BASED
INSTABILITY DUE TO THE ONGOING CLOUDS AND SHOWERS...AND WHILE THE
SURFACE WARM FRONT REMAINS SOUTH OF THE MICHIGAN BORDER THROUGH
THE DAYTIME HEATING CYCLE. FOR NOW...THE MORNING FORECAST UPDATE
WILL NUDGE POPS INTO THE LIKELY CATEGORY ALL AREAS AND MAINTAIN
THE SUBDUED POSITION ON THUNDERSTORM POTENTIAL.

&&

.AVIATION...ISSUED 737 AM EDT SAT AUG 29 2015

EXPECTING SCATTERED-NUMEROUS SHOWERS WITH CEILINGS TRENDING LOWER TO
AROUND 5000 FEET THIS AFTERNOON...WITH LOW VFR CEILINGS THEN HOLDING
INTO TONIGHT. MVFR CONDITIONS WILL BE POSSIBLE IN ANY SHOWERS.
GREATEST SHOWER COVERAGE OVER MBS/FNT THIS MORNING...TRENDING SOUTH
TO DTW-DET-YIP THIS EVENING. THERE IS ALSO A SLIGHT CHANCE OF A
THUNDERSTORM...BUT THE RISK IS CERTAINLY TOO LOW TO INCLUDE IN TAFS.
AS DRIER AIR BEGINS TO WORK IN FROM THE NORTH TONIGHT...FOG AND/OR
LOW CEILINGS ARE POSSIBLE NEAR SUNRISE...BUT MAINLY JUST AT MBS.

FOR DTW...CONFIDENCE IN CEILINGS AOB 5KFT WILL INCREASE WITH TIME
THIS AFTERNOON AND ESPECIALLY THIS EVENING. EXPECTATION IS FOR
LOW VFR CEILING TO PERSIST THROUGH SUNDAY MORNING.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN CIGS AOB 5KFT LATE THIS AFTERNOON THROUGH SUNDAY
  MORNING.

&&

.PREV DISCUSSION...ISSUED 314 AM EDT SAT AUG 29 2015

SHORT TERM...TODAY AND TONIGHT

MERGING UPPER WAVES (NORTHERN MINNESOTA/IOWA) EARLY THIS
MORNING...WITH MAX HEIGHT FALL CENTER/RIGHT ENTRANCE REGION FORCING
OF UPPER LEVEL JET LOOKING TO TRACK THROUGH CENTRAL LOWER
MICHIGAN/LAKE HURON...SUPPORTING HIGHER BASED SHOWER ACTIVITY THIS
MORNING...MAINLY NORTH OF M-59. CONTINUED MOISTURE TRANSPORT THROUGH
THE DAY AND SHEARED OUT UPPER LEVEL PV FILAMENT/500 MB TROUGH AXIS
DRIFTING THROUGH THE AREA WILL SUPPORT CHANCE POPS FARTHER SOUTH
TOWARD THE OHIO BORDER THROUGH TONIGHT AS MAIN MOISTURE AXIS (PW
VALUES 1.5+ INCHES) ALSO FOLDS OVER INTO EAST-WEST ALIGNMENT. TEPID
DIURNAL INSTABILITY PERHAPS LEADING TO AN ISOLATED THUNDERSTORM.
SURFACE RIDGE AXIS RELUCTANT TO BUDGE DURING THE DAY...WITH WEAK
SURFACE TROUGH/WARM FRONT ATTEMPTING TO EXPAND EAST ALONG THE
SOUTHERN MICHIGAN BORDER TONIGHT...PROVIDING FOCUS FOR POSSIBLE
ACTIVITY...WITH MODEST INSTABILITY IN PLACE AS SHOWALTER INDEX
HOVERS AROUND ZERO. CLOUDS EXPECTED TO LIMIT DIURNAL SWING...HOLDING
MAXES IN THE 70S DURING THE DAY...AND LOW TO MID 60S TONIGHT.

LONG TERM...SUNDAY THROUGH FRIDAY

MID LEVEL TROUGH AXIS ANCHORED OVERHEAD SUNDAY MORNING WILL SLOWLY
EXIT TO THE EAST THROUGH THE DAY...THE LEAD EDGE OF THE INBOUND
INCREASING UPPER HEIGHT FIELD LOOMING ACROSS THE PLAINS TAKING A
PROGRESSIVE HOLD LOCALLY OVER THE NEXT 24-36 HOURS.  MOIST RESIDUAL
BOUNDARY LAYER/NEAR SURFACE CONDITIONS IN COMBINATION WITH DAYTIME
HEATING WILL YIELD A WEAKLY UNSTABLE ENVIRONMENT DURING THE DAYLIGHT
PERIOD.  MID LEVEL TROUGH POSITIONING SUGGESTS THERE MAY BE A NARROW
WINDOW FOR SOME RENEWED CONVECTIVE DEVELOPMENT WITHIN THE TRAILING
SHEAR AXIS/CYCLONIC FLOW...ALTHOUGH MOST RECENT MODEL GUIDANCE
TEMPERING THIS RESPONSE PARTICULARLY ACROSS NORTHERN SECTIONS.  WITH
PROJECTED HIGHS /80 DEGREES/ AT THE CUSP OF CONVECTIVE
TEMPERATURES...THIS POINTS TOWARD SIMPLY A LOW END
POTENTIAL/COVERAGE OF SHOWERS AND THUNDERSTORMS FOR SUNDAY.

CONDITIONS THROUGHOUT THE UPCOMING WORK WEEK WILL LARGELY BE DEFINED
BY LIGHT SOUTHWEST LOW LEVEL FLOW TUCKED BENEATH QUASI-STATIONARY
UPPER RIDGING.  THIS PATTERN WILL FAVOR A TRANSITION BACK TOWARD
ABOVE NORMAL WARMTH...WITH DAYTIME READINGS CLIMBING WELL INTO 80S
THROUGH THE WEEK.  LIMITED POTENTIAL FOR CONVECTIVE DEVELOPMENT
THROUGH THIS TIME GIVEN THE ILL-DEFINED/NEGLIGIBLE FORCING AND
WARM MID LEVEL TEMPERATURES. MID RANGE GUIDANCE DOES CENTER AN
OPPORTUNITY ON WEDNESDAY AS A WEAK IMPULSE BRIEFLY WORKS THROUGH
THE EXISTING RIDGE CENTER.

MARINE...

GENERALLY LIGHT WINDS WILL EXIST ACROSS ALL MARINE AREAS THROUGH
THE WEEKEND AS BROAD HIGH PRESSURE REMAINS IN PLACE. A LIGHT
SOUTHWEST WIND WILL CONTINUE INTO EARLY NEXT WEEK WITH HIGH
PRESSURE CENTERED OVER THE EASTERN OHIO VALLEY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

UPDATE.......BT
AVIATION.....SF
SHORT TERM...SF
LONG TERM....MR
MARINE.......MR


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


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