Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 261606
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1206 PM EDT TUE AUG 26 2014

.UPDATE...

A MINOR UPDATE TO THE FORECAST WILL BE ISSUED MOMENTARILY TO
CLEAN UP THE GRIDS PER LATEST OBSERVATIONS. THE FORECAST FROM THE
MORNING PACKAGE IS IN VERY GOOD SHAPE AND MUCH OF THE REASONING
OFFERED IN THE PREVIOUS DISCUSSION REMAINS VALID.

BEEN WATCHING TWO AREA OF CONVECTION THIS MORNING...THE FIRST
PERCOLATING IN A RELATIVELY UNORGANIZED FASHION OVER SW MI/NW IN
AND THE SECOND ADVANCING FAIRLY RAPIDLY INTO SOUTHCENTRAL PORTIONS
OF WI AND EXTREME NORTHERN IL. BOTH AREAS APPEAR TO BE TIED TO A
SHORTWAVE RIDGE STRUCTURE THAT WILL ROLL THROUGH SOUTHEASTERN
MICHIGAN THIS AFTERNOON. THIS RIDGE IS THE FEATURE RESPONSIBLE
FOR THE SUBSIDENCE BUBBLE HAMMERED IN THE PREVIOUS FORECAST
DISCUSSION. LATEST MODEL GUIDANCE IS SUPPORTIVE OF THIS LOW
POTENTIAL VORTICITY ANOMALY TO FOLD OVER DIRECTLY IN THE STATE. THE
EASTWARD CONVECTIVE ACTIVITY IS RESIDING ON THE EASTERN FACE OF
THE SHORTWAVE RIDGE IN AN AREA OF ANTICYCLONIC CURVATURE/UPPER
LEVEL SUBSIDENCE. THE WI/IL ACTIVITY IS SHOWING MORE
ORGANIZATION...NESTLED ONTOP OF OR SLIGHTLY WEST OF THE SHORTWAVE
RIDGE FEATURE. IT IS THIS LOCALIZED FORCING THAT COMMANDS MORE
ATTENTION FOR THE POTENTIAL OF SHOWERS AND THUNDERSTORMS LATE THIS
AFTERNOON/EARLY EVENING.

MOVING FORWARD...THE EASTERN SHOWERS AND TSTORMS ARE IN A PRIME
NORTHERLY CORFIDI COMPONENT ZONE. THIS IS NOT SURPRISING THEN TO
SEE THE THUNDERSTORM ACTIVITY EXHIBITING A GREATER SOUTHERLY
PROPAGATION BEHAVIOR THE PAST HOUR OR SO. WHILE IT REMAINS
POSSIBLE THAT SOME OF THIS CONVECTION COULD GRAZE THE FAR SOUTHERN
PORTION OF THE CWA DURING THE EARLY TO MID AFTERNOON HOURS...MID
CHANCE OR SCATTERED POPS ARE REASONABLE FOR THE SETUP. THE SECOND
AREA HAS MORE GOING FOR IT...PRIMARILY BEING HARBORED WITHIN A
MINOR MIDLEVEL HEIGHT FALL BULLSEYE. BEING SO FAR REMOVED FROM THE
PARENT FEATURE NEAR JAMES BAY...THE HEIGHT FALLS ARE PRIMARILY A
MESOSCALE FEATURE. SINCE IT IS WORKING IN THE BACKGROUND OF AN
UPPER LEVEL RIDGE AND SYNOPTIC SCALE DESCENT IT WILL NEED TO PROVE
ITSELF THIS AFTERNOON TO JUSTIFY RAISING POPS OR CHANGE THE TONE
OF THE CONVERSATION WITH REGARDS TO COVERAGE. THIS IS NOT TO
MENTION THAT OVERALL MOISTURE QUALITY WITHIN THE WARM SECTOR IS
DISJOINTED AND MESSY. IT IS NOT UNTIL LATE DAY MATURATION OF
DIURNAL LOW LEVEL MIXING THAT WILL PROVIDE EROSION OF 870-800MB
CAPPING. SO THE BEST TIMEFRAME IN A RELATIVE SENSE REMAINS 21-02Z
FOR MUCH OF SOUTHEASTERN MICHIGAN.

THE DEGREE OF INSTABILITY REMAINS IN QUESTION BECAUSE OF THE MESSY
NATURE OF THE WARM SECTOR THETA E FIELDS. LATEST NAM WITH
FORECASTED SBCAPES IS UPWARDS OF 3300 J/KG WHILE THE GFS IS
AROUND 2300 J/KG. REGARDLESS OF THE NUMBER...CONVECTIVE
INSTABILITY WILL BE SUPPORTIVE OF A CONDITIONAL STRONG TO SEVERE
THUNDERSTORM RISK. THE PRESENCE OF SOME REMNANT CAPPING IN THE
AFOREMENTIONED LAYER ALONG WITH THE BACKGROUND SUBSIDENCE ALSO
SUPPORTS A MID CHANCE POP FOR LATE THIS AFTERNOON THROUGH 00Z
ALONG WITH A CONDITIONAL MENTION OF STRONG TO SEVERE
THUNDERSTORMS.


&&

.AVIATION...ISSUED 700 AM EDT TUE AUG 26 2014

//DISCUSSION...

AN INFLUX OF GREATER INSTABILITY HAS TRIGGERED SOME THUNDERSTORMS
OVER SW LOWER MI AND LAKE MI. THE INSTABILITY WILL RAPIDLY INCREASE
ACROSS SE MI THIS AFTERNOON IN ADVANCE OF A SLOW MOVING COLD
FRONT...EXPECTED TO TRACK ACROSS MBS BY MID AFTERNOON AND METRO
DETROIT JUST PRIOR TO 00Z. ALTHOUGH THE BUILDING INSTABILITY MAY
INITIATE SOME ISOLATED STORMS AT ANY TIME TODAY...THE MOST PROBABLE
TIME PERIOD FOR CONVECTION WILL LATE THIS AFTERNOON WITH THE
APPROACH OF THE COLD FRONT. THE HIGHEST INSTABILITY...LATER ARRIVAL
OF THE FRONT AND POTENTIAL IMPACTS FROM UPSTREAM STORMS WILL TARGET
PTK AND METRO DETROIT FOR THE BETTER CHANCES FOR STORMS. THE CHANCES
AT FNT AND MBS LOOK A BIT LOW TO INCLUDE IN THE TERMINALS AT THIS
TIME. IN THE MEANTIME...FOG WILL DIMINISH OVER THE NEXT COUPLE OF
HOURS AND GIVE WAY TO AN MVFR STRATO CU FIELD.

FOR DTW...WITH THE FRONT NOT PASSING THROUGH UNTIL LATE
AFTERNOON/EARLY EVENING...THE BEST CHANCES FOR STORMS WILL BE AFTER
21Z. THE RISK WILL THEN QUICKLY END AFTER 00Z AS DRIER AND MORE
STABLE AIR ARRIVES IN THE WAKE OF THE FRONT.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN THUNDERSTORM POTENTIAL THIS AFTERNOON AND
EARLY THIS EVENING.

* MEDIUM CONFIDENCE IN CEILINGS AOB 5000 FT TODAY.

&&

.PREV DISCUSSION...ISSUED 338 AM EDT TUE AUG 26 2014

SHORT TERM...TODAY AND TONIGHT

A WARM AND MUGGY START TO THE DAY CAN BE EXPECTED THIS MORNING AS
SFC DEWPOINTS CONTINUE TO HOVER AROUND 70F...KEEPING SFC TEMPS IN
THE LOW 70S OVER MOST OF THE AREA. THE 07Z SURFACE ANALYSIS SHOWS A
COLD FRONT EXTENDING FROM ERN UPPER MI TO ERN KS. THE HIGH CLOUDS
HAVE BEEN STEADILY DECREASING OVERNIGHT AND THUS FAR NOT MUCH
STRATUS HAS DEVELOPED. SO THE PROSPECTS FOR AT LEAST A LITTLE MORE
SUN DURING THE FIRST HALF OF THE DAY /NOT TO MENTION A BETTER
POTENTIAL FOR LOW LEVEL MIXING UNDER STRONGER W-SW FLOW/ SHOULD
BOOST DAYTIME HIGHS INTO THE MID TO UPPER 80S. THE LATEST SURFACE
OBS AND RECENT SPC MESO ANALYSIS SHOW A PLUME OF HIGHER LOW LEVEL
MOISTURE /925MB DEWPOINTS OF 20-22C/ EXTENDING INTO SRN WI AHEAD OF
THE FRONT. THIS MOISTURE WILL FUNNEL INTO SE MI THIS AFTERNOON AND
SHOULD SUSTAIN SFC DEWPOINTS IN THE 68-73 DEG RANGE DESPITE BETTER
LOW LEVEL MIXING POTENTIAL. THUS HEAT INDICES ARE EXPECTED TO RISE
INTO THE 90S.

THE WATER VAPOR LOOP AND LATEST RAP/NAM SOLUTIONS SUGGEST A REGION
OF ENHANCED MID LEVEL SUBSIDENCE IS NOW MOVING OVER NRN IL. THIS MID
LEVEL SUBSIDENCE BUBBLE WILL OVERSPREAD SE MI THIS MORNING AND EARLY
AFTERNOON. SO DESPITE AN INFLUX OF GOOD MID LEVEL INSTABILITY
ARRIVING FROM THE SOUTHWEST THIS MORNING...THE MID LEVEL SUBSIDENCE
WILL OFFER ENOUGH OF A LIMITING FACTOR TO CARRY JUST ISOLATED
CONVECTION THIS MORNING. MODEL SOUNDINGS INDICATE THAT AFTERNOON
DESTABILIZATION WILL BOOST 0-1KM ML CAPE UP TO 2K TO 3K J/KG. THE
COLD FRONT WILL SLOWLY TRAVERSE SE MI THIS AFTERNOON DURING PEAK
HEATING AND WILL PROVIDE SCATTERED THUNDERSTORMS ASSUMING THE
DAYTIME HEATING WILL BE ENOUGH TO OVERCOME THE CAP. A CONVECTIVELY
INDUCED MID LEVEL SHORT WAVE EMANATING OUT OF THE GROWING TSTM
COMPLEX NOW OVER THE NE/IA BORDER WILL LIKELY NOT TRACK INTO FAR SE
MI/NW OH UNTIL THIS EVENING...BY WHICH TIME THE FRONT AND
INSTABILITY AXIS SHOULD BE SOUTH OF THE FORECAST AREA. SO THE LACK
OF GOOD LARGE SCALE FORCING WILL REMAIN SUPPORTIVE OF JUST SCATTERED
TYPE POPS THIS AFTERNOON. THE UNCERTAINTY WITH THE COVERAGE OF
CONVECTION HAS ALSO PRECLUDED SE MI FROM BEING OUTLOOKED FOR SEVERE
WX. HOWEVER...STEEP LOW LEVEL LAPSE RATES SHOWN ON MODEL SOUNDINGS
AND VERY GOOD CAPE DENSITY /NOT TO MENTION THE POTENTIAL FOR A
POCKET OF MID LEVEL DRY AIR ALONG THE FRONT/ WILL POSE THE RISK OF
SEVERE WIND GUSTS ASSUMING DEEP CONVECTION CAN GET INITIATED.

THE CONVECTIVE THREAT WILL QUICKLY END DURING THE EVENING AS STRONG
HIGH PRESSURE BUILDS IN FROM THE NORTHWEST AND ADVECTS A MUCH DRIER
AIRMASS INTO SE MI. THE HI RES SOLUTIONS INDICATE A SECONDARY
FRONTAL BOUNDARY /REINFORCED BY THE LAKE HURON MARINE LAYER/ PUSHING
ACROSS THE AREA DURING THE EVENING. THE SHALLOW COLD AIR FOLLOWING
THIS SECONDARY FRONT WILL DROP NIGHTTIME LOWS INTO THE 50S AND LOW
60S TONIGHT.

LONG TERM...WEDNESDAY THROUGH MONDAY

WE WILL START OUT THE MID WEEK WITH A LOW AMPLITUDE LONGWAVE PATTERN
SET UP ACROSS THE NORTHERN CONUS WITH WEAK FLOW OVER MOST OF THE
COUNTRY. A CUTOFF UPPER LOW WILL DRIFT OUT OF THE ROCKIES ACROSS THE
CENTRAL PLAINS DURING THE END OF THE WEEK BEFORE PHASING BACK WITH
THE MEAN FLOW OVER THE MIDWEST THIS WEEKEND.

WEDNESDAY WILL BE A DRY DAY AS THE COLD FRONT WILL HAVE PUSHED SOUTH
OF THE AREA WITH CAA THROUGHOUT THE DAY. AFTER FEATURING A VERY WARM
AIRMASS MONDAY AND TUESDAY...HIGH PRESSURE BUILDING IN FROM THE WEST
BEHIND THE COLD FRONT WILL HELP GENERATE NORTHERLY FLOW UNDER A
STOUT INVERSION WHICH WILL USHER IN 850MB TEMPS DOWN TO AROUND 10C
BY THE EVENING HOURS. MODELS CONTINUE TO ADVERTISE A SHORTWAVE
RACING ACROSS THE AREA THROUGH THE FIRST HALF OF THE DAY BUT HAVE
COME OFF THE IDEA OF THIS RESULTING IN PRECIPITATION AS THE SOUNDING
WILL BE TOO STABLE WITH TOO MUCH DRY AIR IN THE MID LEVEL TO RESULT
IN ANYTHING. SO WILL DROP THE SLIGHT CHANCE POPS AND GO WITH A DRY
AND COOL DAY WITH HIGH TEMPS PRIMARILY IN THE MID 70S. THE EXCEPTION
COULD BE LOCATIONS NEAR THE MI/OH BORDER WHERE THE FRONT MAY LINGER
LONG ENOUGH TO ALLOW SOME ADDITIONAL HEATING.

THURSDAY WILL AGAIN BE DRY AS THE HIGH WILL BE CENTERED OVER
NORTHERN LOWER IN THE AFTERNOON THOUGH THIS MAY CHANGE OVERNIGHT.
THE CLOSED LOW WILL BE EXITING THE ROCKIES WHILE EJECTING A
SHORTWAVE WHILE LEE CYCLOGENESIS SPINS UP A NEW CFC LOW OVER THE
PLAINS. THE LOW WILL LIFT THE OLD COLD FRONT...WHICH STALLED OVER
THE OHIO VALLEY...BACK NORTH THROUGH THE AREA AS A WARM FRONT
BEGINNING THURSDAY NIGHT. THE CLOSED LOW WILL THEN START FEELING THE
EFFECTS OF THE APPROACHING TROUGH SHEARING SW TO NE THROUGH THE
WESTERN GREAT LAKES. THIS WILL PRESENT SEVERAL OPPORTUNITIES FOR
PRECIPITATION THROUGH THE EARLY PART OF THE WEEKEND AS A SERIES OF
SHORTWAVES RIDE ALONG THE SHEAR AXIS THROUGH THE AREA. A SECOND SFC
LOW LOOKS TO THEN SPIN UP ON THE TAIL END OF THE FRONT LIFTING
THROUGH SE MI SUNDAY INTO MONDAY. THOUGH THE SETUP DOES NOT LOOK TO
GENERATE ANY SEVERE WEATHER AT THE MOMENT...TRAINING STORMS/SHOWERS
WITH PWATS APPROACHING 2 INCHES FOR THE WEEKEND COULD RESULT IN
HEAVY DOWNPOURS.

MARINE...

WARM SOUTHERLY FLOW AHEAD OF AN APPROACHING COLD FRONT HAS LEAD TO
INCREASED STABILITY OVER THE COOL LAKES KEEPING WINDS AND WAVES
MINIMAL. THE FRONT WILL DROP SOUTHEAST THROUGH THE REGION LATE THIS
AFTERNOON SWITCHING WINDS AROUND TO NORTHERLY. COLD AIR ADVECTION
WITH THIS INCREASED NORTHERLY FLOW WILL LEAD TO ELEVATED WAVE
HEIGHTS ALONG SOME OF THE LAKE HURON SHORELINE WHICH WILL
NECESSITATE A SMALL CRAFT ADVISORY. IN ADDITION...SCATTERED
THUNDERSTORMS TRIGGERED BY THE FRONT WILL BE STRONG TO POSSIBLY
SEVERE IN THE EVENING. THE FRONT WILL STALL OUT JUST TO THE SOUTH OF
THE SOUTHERN GREAT LAKES DURING THE MID WEEK PERIOD...WITH HIGH
PRESSURE ARRIVING OVER LOWER MICHIGAN ON THURSDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...OUTER SAGINAW BAY AND THE NEARSHORE WATERS
     FROM PORT AUSTIN TO HARBOR BEACH...FROM 10 PM TUESDAY TO 10 AM
     WEDNESDAY.

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

&&

$$

UPDATE.......CB
AVIATION.....SC
SHORT TERM...SC
LONG TERM....DRK
MARINE.......DRK


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






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