Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 031639
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1239 PM EDT THU SEP 3 2015

.UPDATE...

DUAL SHORTWAVES OVER THE WESTERN AND CENTRAL GREAT LAKES WILL
REMAIN THE SOLE FORCING MECHANISMS THROUGH THE NEXT 18 HOURS. THE
SMALL MCS IMPACTING LOWER MICHIGAN IS TIED TO THE FIRST LOWER
COLUMN PV ANOMALY...THE SECOND IS THE SHORTWAVE CIRCULATION THAT
IS NOW DROPPING INTO THE BACKSIDE OF THE GEOPOTENTIAL HEIGHT
WEAKNESS OVER FAR NORTHERN WISCONSIN. AT THE BIG PICTURE...LOWER
DELTA X SOLUTIONS/GLOBAL MODELS SUGGEST A PHASING OF THE TWO
SHORTWAVES AND A SUBSEQUENT STALLING OF THE COMBINED PV ANOMALY
LATE THIS AFTERNOON AND TONIGHT.

THE MCS THAT HAS BEEN PUSHING ACROSS THE NORTHERN CWA CONTINUES TO
MAKE SOME PROGRESS EASTWARD. A LINEAR EXTRAPOLATION OF REGIONAL Z
MOSAIC CONTINUES TO SUPPORT SOME SLIGHT SOUTHWARD DRIFT WITH TIME
ON THE TRACK OF THE MCS. THIS SOUTHWARD DRIFT SHOULD AT LEAST BE
PARTIALLY SUPPORTIVE BY ADDITIONAL OUTFLOW DEVELOPMENT ALONG THE
SOUTHERN FLANK. THERE HAS BEEN SOME MODEST...CONTINUED DEVELOPMENT
DURING THE PAST FEW HOURS. NWP GUIDANCE WITH A BULLISH HRRR AND
BOTH NAM/ECMWF SUPPORT BRING ADDITIONAL CONVECTIVE DEVELOPMENT FOR
ALL OF SOUTHEASTERN MICHIGAN DURING THE AFTERNOON HOURS. GIVEN THE
LACK OF AN AGGRESSIVE SOUTHERN PROGRESSION TO THE
STRATUS/CIRRUS/CU DECK EXPECTATIONS ARE FOR THE
INSTABILITY/BUOYANCY GRADIENT TO REMAIN DRAPED THROUGH FAR
SOUTHERN SECTIONS OF THE CWA. THE FORECAST IS SKEWED ON THE
AGGRESSIVE SIDE WITH RESPECT TO RAIN AND THUNDERSTORM ACTIVITY
THIS LATER THIS AFTERNOON AND EVENING. THERE DOES REMAIN A SLIVER
OF DOUBT THAT THUNDERSTORMS WILL FILL IN COMPLETELY ACROSS FAR
SOUTHERN LOWER MICHIGAN AND IMPACT DETROIT METRO DIRECTLY. STORM
BEHAVIOR TODAY IS EXPECTED TO REMAIN MORE OF A PULSE TYPE NATURE
WITH PERHAPS SOME EMBEDDED LINE TYPE FEATURES. THEREFORE...A LOW
END DAMAGING WIND GUST THREAT EXISTS THIS AFTERNOON AND WILL
PERHAPS BE A CIRCUMSTANCE OF CONSTRUCTIVE CELL MERGERS OR
PRECIPITATION LOADING EFFECTS.

A CONCERNING POTENTIAL WILL CONTINUE TO BE A HEAVY RAINFALL
THREAT...ESPECIALLY UNDER THE DIRECTION OF ADVERTISED PHASING AND
STALLING OUT OF PV MAX OVERHEAD. PWATS ARE AT APPROXIMATELY 1.8
INCHES. SOME SAMPLED RAINFALL RATES EARLIER OFF OF RADAR BASED
PRECIPITATION PRODUCT SUGGESTS 1.25 INCHES OF RAINFALL IS
POSSIBLE IN ROUGHLY 40 MINUTES. WILL BE MONITORING ACTIVITY THIS
AFTERNOON FOR ANY TRAINING OR STATIONARY BEHAVIOR OF THUNDERSTORMS.

&&

.AVIATION...ISSUED 732 AM EDT THU SEP 3 2015

EXTREMELY MOIST AND UNSTABLE ENVIRONMENT TODAY WILL PROVIDE A
FAVORABLE ENVIRONMENT FOR SHOWER AND THUNDERSTORM DEVELOPMENT
AREAWIDE.  WHILE THERE REMAINS SOME UNCERTAINTY AS TO POTENTIAL
COVERAGE...CONFIDENCE IS HIGH ENOUGH TO INCLUDE A SPECIFIC MENTION
TO HIGHLIGHT THE MOST LIKELY PERIOD FOR THUNDERSTORMS.  OUTSIDE OF
THUNDERSTORMS...EXPANDING COVERAGE OF DIURNAL VFR CU CENTERED ON THE
AFTERNOON/EVENING PERIOD.  THE MOIST LOW LEVEL CONDITIONS AND
PROSPECTS FOR WET GROUND WITH RECENT RAINFALL WILL BRING A GREATER
POTENTIAL FOR FOG DEVELOPMENT TONIGHT.  POSSIBILITY EXISTS FOR ONE
OR MORE TERMINALS TO DROP INTO LIFR DURING THE EARLY MORNING
PERIOD...CONFIDENCE TOO LOW YET TO INCLUDE BUT WILL HIGHLIGHT WITH
IFR VSBY RESTRICTIONS.

FOR DTW...GREATEST POTENTIAL FOR THUNDERSTORMS CENTERED WITHIN THE
18Z-00Z WINDOW...ALTHOUGH A LOWER PROBABILITY WILL EXIST RIGHT
THROUGH THURSDAY NIGHT.

//DTW THRESHOLD PROBABILITIES...

* LOW FOR CIG AOB 5KFT THIS AFTERNOON AND EVENING

* MEDIUM FOR THUNDERSTORMS THIS AFTERNOON AND EVENING

&&

.PREV DISCUSSION...ISSUED 333 AM EDT THU SEP 3 2015

SHORT TERM...TODAY AND TONIGHT

ATTENTION OVER THE NEXT 24 TO 36 HOURS CENTERS ON THE INBOUND SLOWLY
MOVING MID LEVEL WAVE CURRENTLY CENTERED ACROSS THE LAKE MICHIGAN
CORRIDOR.  LITTLE VARIATION IN THE UNDERLYING LOW LEVEL
THERMODYNAMIC PROFILE HEADING INTO TODAY...WITH SE MICHIGAN FIRMLY
ENTRENCHED WITHIN A MOISTURE RICH LOW LEVEL ENVIRONMENT /LOWER 70S
DEWPOINTS/.  AS NOTED YESTERDAY...THIS WILL AGAIN TRANSLATE INTO
SUBSTANTIAL LOW LEVEL INSTABILITY (2500+ J/KG SBCAPE) WITHIN A VERY
STEEP LAPSE RATE ENVIRONMENT. INCREASING DPVA AND AN ACCOMPANYING POCKET
OF COOLER MID LEVEL TEMPERATURES WILL CONTRIBUTE AN ADDITIONAL
COMPONENT OF DESTABILIZATION AND MORE FOCUSED ASCENT FOR TODAY.
THIS ENVIRONMENT SEEMS CONDUCIVE FOR A MORE SIZABLE EXPANSION IN
CONVECTIVE COVERAGE LOCALLY...AND WORTHY OF A NUDGE UPWARD IN
POPS...PARTICULARLY FOR THE AFTERNOON/EVENING PERIODS. THE HIGH
MOISTURE CONTENT AND CORRESPONDING POTENTIAL FOR SIGNIFICANT
PRECIPITATION LOADING WITHIN THE DEEPEST CONVECTIVE CELLS WILL
AGAIN PRESENT THE POTENTIAL FOR STRONGER WIND GUSTS...WITH AT
LEAST AN OUTSIDE POSSIBILITY THAT AN ISOLATED STORM OR TWO CAN
GENERATE A PEAK GUST NEARING SEVERE LIMITS. SOLID HEAVY RAINFALL
THREAT GIVEN LIKELY LIMITED STORM MOTION WITHIN THIS HIGH CAPE
ENVIRONMENT. HIGHS TODAY A TOUCH LOWER WITH THE ENSUING EXPANSION
IN CONVECTION/CLOUD COVER LIKELY UNDERCUTTING THE HEATING
POTENTIAL SLIGHTLY. READINGS TOPPING OUT IN THE LOWER AND MIDDLE
80S...HEAT INDICES APPROACHING 90.

GRADUAL COOLING VIA DIABATIC PROCESSES AND ANY OUTFLOW WILL FAVOR A
DIMINISHING TREND TO EXISTING CONVECTIVE ACTIVITY BY EARLY TONIGHT.
HOWEVER THE UNDERLYING ENVIRONMENT WILL STILL REMAIN FAVORABLE FOR
ADDITIONAL ISOLATED-SCATTERED DEVELOPMENT THROUGHOUT THE NIGHT.
INCREASING POTENTIAL FOR FOG OVERNIGHT...MOIST NEAR SURFACE
ENVIRONMENT AUGMENTED BY THE RAINFALL AND WEAK GRADIENT.  A CORRIDOR
OF DENSE FOG FOR THE EARLY MORNING COMMUTE NOT OUT OF THE QUESTION.

LONG TERM...

MULTIPLE UPPER WAVES UPSTREAM OVER UPPER MISSISSIPPI RIVER VALLEY
THIS MORNING...WHICH WILL CONSOLIDATE OVER THE WESTERN/CENTRAL GREAT
LAKES TONIGHT INTO FRIDAY...BUT THE EXACT POSITION OF THE DEVELOPED
MID LEVEL CIRCULATION/500 MB LOW IS QUESTION...AS 00Z NAM/GFS ARE
INDICATING A FARTHER SOUTH/WEST SOLUTION...NEAR CHICAGO...WHILE
EURO/CANADIAN REMAIN STEADFAST WITH 500 MB LOW FARTHER NORTH/EAST
OVER NORTHERN LOWER MICHIGAN. EITHER WAY...CHANCE POPS STILL SEEM
WARRANTED...EVEN WITH THE STRENGTHENING HIGH PRESSURE OVER EASTERN
CANADA (1025 MB)...AS THE LOW LEVEL SOUTHEAST/EAST FLOW WILL
INCREASE A BIT...BUT THERE ACTUALLY LOOKS TO BE MODEST MOISTURE
ADVECTION FROM WESTERN PA/LAKE ERIE. MLCAPES PROGGED TO INCREASE
INTO THE 500 TO 1500 J/KG RANGE DURING FRIDAY...PER 00Z EURO.

STILL LINGERING UPPER LEVEL TROUGHINESS ON SATURDAY WITH MLCAPES
RISING INTO THE 1000-2000 J/KG RANGE TO SUPPORT LOW CHANCE POPS.
UPPER LEVEL RIDGE BUILDING OUT AHEAD OF STRONG GREAT BASIN 500 MB
LOW ON SATURDAY SHOULD EXERT A BIGGER INFLUENCE FOR THE SECOND HALF
OF THE WEEKEND...ALLOWING FOR TEMPERATURES TO HEAT UP ONCE
AGAIN...WITH 90 DEGREES LIKELY ON SUNDAY...AS SOUTH-SOUTHWEST FLOW
INCREASES OUT AHEAD OF NEXT COLD FRONT...WITH 850 MB TEMPS PROGGED
TO BE IN THE 18-19 C RANGE. UPPER LEVEL RIDGE AXIS ARRIVING SUNDAY
AFTERNOON IS EXPECTED TO PROVIDE ENOUGH MID LEVEL WARMING/SUBSIDENT
BACKDROP TO SQUELCH POTENTIAL CONVECTION. THE SAME CAN NOT BE SAID
FOR EARLY NEXT WEAK AS SOLID HEIGHT FALLS/MOISTURE PLUME/AXIS (PW
VALUES OF 2 INCHES) AND COLD FRONT TRACKS THROUGH THE GREAT LAKES
REGION.

MARINE...

STRENGTHENING HIGH PRESSURE OVER EASTERN CANADA WILL PROMOTE LIGHT
EASTERLY FLOW AS WE HEAD INTO FRIDAY. UPPER LEVEL DISTURBANCE WILL
RESULT IN SCATTERED SHOWERS AND THUNDERSTORMS THROUGH FRIDAY...WITH
A LOW CHANCE ON SATURDAY. WINDS WILL SHIFT TO THE SOUTH OVER THE
WEEKEND...BUT REMAIN LIGHT...AS VERY WARM AIR STREAMS INTO THE
REGION.

&&

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

$$

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


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



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