Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 011947
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
347 PM EDT FRI AUG 1 2014

.SHORT TERM...THIS EVENING THROUGH TONIGHT

SCATTERED MULTICELLS ARE ONGOING ACROSS SOUTHEAST MICHIGAN AT PRESS
TIME. SO FAR, THE UPDRAFTS HAVE EXHIBITED LITTLE TO NO ORGANIZATION
AND ARE QUICK TO PRODUCE OUTFLOWS. THIS IS IN LINE WITH EXPECTATIONS
AND IN AGREEMENT WITH THE LATEST MESOANALYSIS AND SIMULATED RAP
SOUNDINGS WHICH REVEAL A RATHER LOW DENSITY CAPE PROFILE FEATURING
AROUND 1500 J/KG MLCAPE AND VIRTUALLY NO SHEAR. NO ENVIRONMENTAL
CHANGES EXPECTED OVER THE NEXT FEW HOURS, SO EXPECT THE LION`S SHARE
OF CONVECTION TO CONTINUE TO BE SUB-SEVERE, ALTHOUGH A PARTICULARLY
VIGOROUS UPDRAFT COULD PRODUCE MARGINALLY SEVERE HAIL GIVEN
PERSISTENCE OF THE FREEING LEVEL AROUND 11KFT.

NONDESCRIPT SURFACE PRESSURE PATTERN AND ASSOCIATED WEAK PRESSURE
GRADIENT WILL FAVOR QUICK DECOUPLING ONCE DIURNAL HEATING IS LOST.
THIS WILL SEPARATE MARGINALLY UNSTABLE MID-LEVELS FROM THE BOUNDARY
LAYER AND WILL EFFECTIVELY SHUT DOWN CONVECTION FOR THE REMAINDER OF
THE NIGHT. REMOVED POPS FOR THE OVERNIGHT PERIOD SAVE FOR A 3 HOUR
GRACE PERIOD 00-02Z TO ALLOW FOR THE WANE OF TODAY`S DIURNAL
ACTIVITY. OVERNIGHT LOWS WILL FALL TO AROUND 60...RIGHT AROUND
AVERAGE.

&&

.LONG TERM...SATURDAY THROUGH THURSDAY

THE OVERALL LONGWAVE PATTERN HAS CHANGED VERY LITTLE OVER THE PAST
SEVERAL DAYS. THE UPPER LEVEL TROUGH IS STILL HOLDING OVER MUCH OF
THE EAST COAST AND GREAT LAKES AND AND LOOKS TO STAY THAT WAY
THROUGH AT LEAST MID WEEK. THE CURRENT PROFILE OF THE ATMOSPHERE HAS
ALSO REACHED A STEADY STATE HAVING CHANGED LITTLE OVER THE PAST 24
HOURS AND FORECAST TO STAY SIMILAR THROUGH THE WEEKEND. THERE WILL
LIKELY BE SOME WARMING IN THE MID LEVELS AS A SHORTWAVE RIDGE
TRAVERSES THE AREA SATURDAY NIGHT AND SUNDAY MORNING BUT THE REST OF
THE PROFILE REMAINS RELATIVELY UNCHANGED. WE CONTINUE TO ADD DETAIL
TO THE FORECAST AND BASE POPS OFF MESOSCALE FEATURES AND SHORTWAVES
ROTATING ABOUT THE UPPER LOW.

FOR THE WEEKEND...THE UPPER LEVEL TROUGH AXIS WILL CROSS SE MI
DURING THE AFTERNOON. AS THIS IS GOING ON...A SHORTWAVE DIVING
THROUGH THE BACKSIDE OF THE TROUGH WILL STALL AND STRENGTHEN A BIT
OVER OHIO. MODELS ARE HINTING AT A WEAK SFC LOW TRYING TO DEVELOP
OVER OHIO PUTTING EXTREME SE MI INTO THE BUDDING DEFORMATION REGION.
WITH THE CURRENT SETUP AND INSTABILITY PRESENT...AND THE URGE TO
CONVECT WITH DIURNAL HEATING EACH AFTERNOON...THE ADDITIONAL
DEFORMATION FORCING COULD LEAD TO BETTER COVERAGE OF PRECIPITATION
OVER THAT AREA. WILL CONTINUE WITH THE CURRENT 50 POP ACROSS EXTREME
SE MI WITH LESSER 30 POP TO THE NW. PRECIP SHOULD QUICKLY SHUT OFF
LATER IN THE EVENING AS THE SHORTWAVE RIDGE BUILDS INTO THE AREA AND
WEAK SFC HIGH DRIFTING ACROSS CENTRAL MI. THIS WILL LEAVE SATURDAY
NIGHT DRY.

ON SUNDAY...A SHORTWAVE WILL TRACK THROUGH ONTARIO DROPPING A
WEAKENING FRONTAL BOUNDARY INTO NORTHERN MI. IT WILL DROP SLOWLY
THROUGH THE STATE PROVIDING A FOCUS OF CONVECTION BUT IT WILL NOT
REACH SE MI TIL LATER IN THE DAY WHICH SHOULD RESULT IN A PRETTY
NICE DAY OVERALL.

REMAINDER OF PERIOD WILL BEGIN WITH A WEAK COLD FRONT DROPPING
SOUTHWARD ACROSS THE MITTEN WHICH COULD PROVIDE THE FOCUS FOR
SHOWERS AND THUNDERSTORMS...AT THIS POINT APPEARING TO FAVOR
NORTHERN POINTS. SOME UNCERTAINTY WITH WHETHER THE BOUNDARY WILL
STALL/WASH OUT OVER THE REGION ON TUESDAY /E.G. 12Z ECMWF SOLUTION/
OR BE MORE PROGRESSIVE AND CLEAR MUCH OF THE AREA /E.G. 12Z GFS
SOLUTION/. FROM WEDNESDAY THROUGH THE END OF THE WEEK THIS BOUNDARY
LOOKS TO TIGHTEN UP AND BE THE FOCUS FOR ROUNDS OF SHOWERS AND
THUNDERSTORMS. HOWEVER...TRENDS FROM THE LAST COUPLE OF GLOBAL NWP
RUNS HAVE SHIFTED THIS BOUNDARY SOUTH OF THE REGION WITH HIGH
PRESSURE BUILDING IN OVER THE WESTERN GREAT LAKES. WILL FOLLOW SUIT
FROM NEIGHBORING OFFICES AND LEAVE ENTRY LEVEL CHANCE POPS FOR THE
REMAINDER OF THE FORECAST...BUT IF THE RECENT TRENDS REMAIN STABLE
WILL HAVE TO CUT OUT POPS FOR MID/LATE WEEK.

&&

.MARINE...

A WEAK SURFACE HIGH PRESSURE SYSTEM BUILDING ACROSS THE CENTRAL
GREAT LAKES WILL PRODUCE A WEAK WIND FIELD WITH WIND SPEEDS
REMAINING AT 10 KNOTS OR LESS THROUGH THE WEEKEND...RESULTING IN
MINIMAL WAVE HEIGHTS. WIDELY SCATTERED SHOWERS/THUNDERSTORMS WILL BE
POSSIBLE DESPITE THIS HIGH PRESSURE...BUT WILL FAVOR LAND AREAS AS
LAKE BREEZE BOUNDARIES PROVIDE THE PRIMARY FOCUS DURING THE
AFTERNOON AND EARLY EVENING HOURS.

&&

.AVIATION...ISSUED 136 PM EDT FRI AUG 1 2014

//DISCUSSION...

DIURNAL CU OF THE VFR VARIETY HAS DEVELOPED EARLY THIS AFTERNOON AND
REVEALED A LINE OF CONVERGENCE DRAPED ACROSS DETROIT METRO. SHOWERS
HAVE DEVELOPED ALONG THIS LINE BUT WITH ACTIVITY SLOW TO EXPAND IN
COVERAGE OR INCREASE INTENSITY...OPTED TO OMIT MENTION FROM THE 18Z
FORECAST...ALTHOUGH A BRIEF SHOWER/TSTORM WILL BE POSSIBLE DURING
THE NEXT HOUR OR TWO. BEHIND THIS LINE, PROBABILITY FOR PRECIP WILL
DIMINISH A BIT...WITH THE CHANCE FOR TSRA ENDING WITH THE LOSS OF
DIURNAL HEATING. WINDS WILL REMAIN LIGHT OVERNIGHT WHICH WILL AID IN
PATCHY LIGHT FOG FORMATION.

FOR DTW...A BROKEN LINE OF POORLY ORGANIZED SHOWERS AND A LONE
THUNDERSTORM ARE GRADUALLY WORKING THRU THE METRO AREA. THERE WILL BE
POTENTIAL FOR BRIEF IMPACT OVER THE NEXT HOUR OR TWO, BUT PROBABLE
SHORT DURATION AND LOW CONFIDENCE IN DIRECT IMPACT PRECLUDES A
MENTION IN THE TAF ATTM. CEILINGS MAY BRIEFLY HOVER AROUND 4KFT
BEFORE LIFTING ABOVE 5KFT.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE IN CEILINGS BELOW 5000 FT TODAY AND TONIGHT.

* LOW CONFIDENCE IN THUNDERSTORMS THIS AFTERNOON.

&&

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

&&

$$

SHORT TERM...JVC
LONG TERM....DRK/DT
MARINE.......DRK
AVIATION.....JVC


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






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