Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 012009
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
409 PM EDT TUE SEP 1 2015

.SHORT TERM...THROUGH TONIGHT

UPPER RIDGE AXIS THAT WAS OVER MICHIGAN AT THE START OF THE DAY
CONTINUES TO SHIFT EAST TOWARDS THE EASTERN GREAT LAKES. THE RIDGE
WILL CONTINUE TO LOSE AMPLITUDE THROUGH TONIGHT IN RESPONSE TO UPPER
ENERGY RIDING THROUGH NORTHERN CANADA. THIS WILL OPEN THE DOOR FOR
THE WEAK SHORTWAVE OVER EASTERN SOUTH DAKOTA TO LIFT INTO THE
WESTERN GREAT LAKES TONIGHT. WEAK SURFACE TROUGHING AHEAD OF THIS
FEATURE WILL KEEP A LIGHT SOUTHWESTERLY GRADIENT OVER THE AREA
TONIGHT. THIS MAKES THE FOG/STRATUS FORECAST A LITTLE MORE
CHALLENGING FOR TONIGHT...AS ANY LIGHT WIND WOULD FAVOR STRATUS OVER
FOG. WILL CONTINUE TO HIGHLIGHT AREAS OF FOG TONIGHT AND MONITOR
TRENDS. IF WE DECOUPLE...WE MAY END UP WITH SOME DENSE FOG ONCE
AGAIN.

MEANWHILE...UPPER LOW WILL CONTINUE TO TRACK FROM INDIANA INTO OHIO
TONIGHT. GFS/NAM INDICATING A WEAK PUSH OF THETA-E LATE THIS
AFTERNOON/EVENING INTO MICHIGAN AS THIS FEATURE PASSES TO OUR SOUTH.
CAN SEE THIS SHOWING UP ON SATELLITE IMAGERY AS AN ENHANCEMENT IN
THE CLOUDS OVER SOUTHWEST MICHIGAN AND NORTHERN INDIANA...AND THIS
COINCIDES NICELY WITH WHERE SHOWERS AND THUNDERSTORMS HAVE STARTED
TO DEVELOP. EXPECT THIS ACTIVITY TO MIGRATE EAST WITH THE THETA-E
PUSH. DID ALSO SEE ONE QUICK SHOWER POP UP ALONG THE LAKE BREEZE
BOUNDARY (PRIOR TO 3 PM) OVER WASHTENAW COUNTY EARLIER THIS
AFTERNOON...A SCENARIO WHICH WILL CONTINUE TO REMAIN POSSIBLE OVER
THE FAR SOUTHEAST PART OF MICHIGAN THROUGH THE HEATING CYCLE. WILL
CONTINUE TO MENTION LOW POPS ALONG/SOUTH OF THE M-59 CORRIDOR...FOR
THE REMAINDER OF TODAY AND INTO TONIGHT AS SURFACE HEATING AND
FALLING HEIGHTS OVER THE AREA TRY TO ERODE A WEAK CAP IN
PLACE...LAKE BREEZE BOUNDARIES CONTINUE TO WORK SLOWLY INLAND AND AS
ADDITIONAL MOISTURE WORKS IN TONIGHT. SLOW STORM MOTION WOULD BRING
A THREAT FOR HEAVY DOWNPOURS. SPC ANALYSIS SHOWS 1000-1500 J/KG OF
SB CAPE...SO CANNOT RULE OUT A STRONG WIND GUST EITHER.

WARM AND MOIST AIRMASS WILL REMAIN IN PLACE OVERNIGHT...WITH BOTH
TEMPERATURES AND DEWPOINTS STAYING IN THE MID 60S TO NEAR 70.

&&

.LONG TERM...

A WEAK 500MB CIRCULATION OVER INDIANA TODAY PRODUCING SOME SHOWER
AND THUNDERSTORM ACTIVITY WILL BE JUST SOUTH OF THE STATE WEDNESDAY
MORNING AS IT CONTINUES TO DISSIPATE WHILE DRIFTING EASTWARD. THIS
WILL WARRANT A CHANCE FOR A SHOWER OR THUNDERSTORM IN THE FAR
SOUTHEAST CORNER.

REST OF WEDNESDAY AND INTO THURSDAY HAS A UPPER LEVEL RIDGE BUILDING
AND EXPANDING OVER THE CENTRAL U.S. WARMING LOW TO MID LEVELS AND
INCREASING DEWPOINTS TO AROUND 70 WEDNESDAY WILL PRODUCE AFTERNOON
CAPES APPROACHING 2K JOULES BUT ALONG WITH A MODERATELY STRONG CAP
NEAR 700MB. THIS SHOULD KEEP CONVECTION IN CHECK FOR THE MOST PART
BUT WILL STILL CARRY A LOWER CHANCE AS ANY STRONG LAKE BREEZE OR
MESOCALE BOUNDARY COULD BE SUFFICIENT TO BREAK THE CAP LATE
AFTERNOON EVENING.  THE BETTER CHANCE LIES IN THE SAGINAW VALLEY AND
THUMB AS A BACK DOOR COLD FRONT DEVELOPS AS SURFACE HIGH PRESSURE
STRENGTHENS OVER EASTERN CANADA IN RESPONSE TO BUILDING RIDGE OVER
THE CENTRAL U.S.  TEMPERATURES AND DEW POINTS SLIGHTLY LOWER BEHIND
THIS FRONT BUT ENOUGH SURFACE CONVERGENCE COULD PRODUCE A FEW
SHOWERS OR THUNDERSTORMS DEPENDING ON HOW STRONG MID LEVEL CAP IS.

WEDNESDAY NIGHT...THIS FRONT WILL SLOWLY WORK THROUGH THE FORECAST
AREA. THOUGH NIGHT TIME...WITH DEWPOINTS AROUND 70 THERE WILL STILL
BE DECENT INSTABILITY AND SOME NOCTURNAL WEAKENING OF THE CAP. WILL
STILL CARRY A CHANCE FOR A SHOWER OR STORM AS THE FRONT MAKES ITS
WAY SOUTHWARD.

THURSDAY...DEWPOINTS WILL GRADUALLY LOWER AS SLIGHTLY DRIER AIR
CONTINUES TO ADVECT IN ALSO DECREASING SURFACE INSTABILITY.
HOWEVER...MODELS ALL SUGGEST A SHORTWAVE DEVELOPING OVER NEBRASKA
TONIGHT AND STRENGTHENING AS RIDGE AXIS DOES.  THIS SHORTWAVE WILL
ENTER THE STATE AROUND 12Z THURSDAY.  GFS/NAM MOVE IT ACROSS
SOUTHERN LOWER MICHIGAN DURING THE DAY WHILE DISSIPATING.
CANADIAN/EURO STRENGTHENS IT A LITTLE MORE THEN KEEPS IT CUTOFF OVER
CENTRAL LOWER THURSDAY INTO FRIDAY.  AT THIS POINT WITH THE
SHORTWAVE NOT IN EXISTENCE YET...WILL JUST KEEP A CHANCE FOR SHOWERS
OR THUNDERSTORMS THURSDAY AND THURSDAY NIGHT UNTIL SHORTWAVE
ACTUALLY DEVELOPS AND A BETTER HANDLE ON IT CAN BE ESTABLISHED.

ALL INDICATIONS ARE THAT MUCH ABOVE-NORMAL TEMPERATURES WILL
CONTINUE INTO AT LEAST EARLY NEXT WEEK AS EXPANSIVE LARGE-SCALE
RIDGING DOMINATES THE EASTERN CONUS. DETERMINISTIC MODELS INDICATE A
WEAKNESS IN THE RIDGE OVER THE WESTERN GREAT LAKES FRIDAY WHICH
COULD SPAWN ISOLATED/SCATTERED CONVECTIVE DEVELOPMENT IN A
MARGINALLY UNSTABLE ENVIRONMENT. OTHERWISE...HOT AND HUMID THROUGH
THE WEEKEND INTO MONDAY WITH H85 TEMPS AROUND 18C.

&&

.MARINE...

WARM AND HUMID AIR OVER THE CENTRAL GREAT LAKES WILL PROMOTE LIGHT
WINDS AND POSSIBLE FOG AT TIMES. A WEAK COLD FRONT PASSING THROUGH
WEDNESDAY NIGHT WILL BRING THE RISK OF SHOWERS AND
THUNDERSTORMS WEDNESDAY AFTERNOON THROUGH THURSDAY. LIGHT SOUTHERLY
WINDS TODAY INTO TOMORROW WILL SHIFT TO A NORTHERLY DIRECTION BEHIND
THE FRONT AS WE HEAD INTO WEDNESDAY NIGHT...CONTINUING INTO THURSDAY.

&&

.AVIATION...ISSUED 142 PM EDT TUE SEP 1 2015

AN UPPER LEVEL LOW PRESSURE SYSTEM WILL SEND ADDITIONAL MOISTURE
INTO LOWER MICHIGAN TODAY AND TONIGHT AS IT SLOWLY TRACKS EAST
ACROSS THE OHIO VALLEY. THIS WILL ALLOW A SCT-BKN CU DECK TO FILL IN
OVER THE AREA. ISOLATED SHOWERS AND THUNDERSTORMS MAY ALSO DEVELOP
THIS AFTERNOON/EARLY EVENING...BUT POTENTIAL IS LOW. THERE IS SOME
QUESTION AS TO WHETHER ADDITIONAL MOISTURE ADVECTION OVERNIGHT WILL
ALLOW THIS DECK TO REMAIN DESPITE LOSS OF SUPPORT FROM DIURNAL
HEATING. WILL LEAN TOWARDS THE DECK SCATTERING OUT AS BEST FORCING
AND DEEPER MOISTURE SHOULD REMAIN SOUTH OF THE MICHIGAN STATE LINE.
AREAS OF FOG AND LOW STRATUS ARE EXPECTED TO DEVELOP AGAIN OVERNIGHT
WITH HIGH DEWPOINTS AND LIGHT WINDS. WILL CONTINUE TO HIGHLIGHT A
PERIOD OF IFR DEVELOPING AFTER ABOUT 08Z. CANNOT RULE OUT LIFR OR
EVEN VLIFR CONDITIONS TOWARDS SUNRISE...HOWEVER CONFIDENCE WITH
LOCATION IS VERY UNCERTAIN. SIMILAR TO THE PAST FEW DAYS...FOG/LOW
STRATUS SHOULD MIX OUT AROUND 14Z WITH THE ONSET OF DAYTIME HEATING.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM FOR CIG AOB 5KFT THROUGH 00Z.

* LOW FOR THUNDERSTORMS IMPACTING THE DTW AIRSPACE.

* LOW FOR VISIBILITY BELOW 1/2 MILE OR CIGS BELOW 200 FEET.

&&

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

$$

SHORT TERM...HLO
LONG TERM....DRC/DT
MARINE.......DRC
AVIATION.....HLO


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


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