Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 082304
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
704 PM EDT TUE JUL 8 2014


.AVIATION...

//DISCUSSION...

A SPIKE IN MIXING DEPTHS LATE THIS AFTERNOON LED TO A BRIEF PERIOD
OF GUSTY WINDS /AROUND 30 KNOTS/. THE WIND SPEEDS WILL RAPIDLY DROP
BELOW 12 KNOTS BY 01Z DUE TO BOTH THE LOSS OF DIURNAL MIXING AND
WEAKENING IN THE WESTERLY GRADIENT. RECENT SATELLITE DATA SHOW THE
LOSS IN HEATING ALREADY HAVING AN EFFECT ON THE SHOWERS AND CLOUD
COVER...BOTH OF WHICH WILL CONTINUE TO DECREASE DURING THE COURSE OF
THE EVENING. A SECONDARY COLD FRONT NOW LOCATED ACROSS NORTHERN
MICHIGAN IS FORECAST TO ADVANCE FROM NORTH TO SOUTH ACROSS THE SE MI
TERMINALS BETWEEN 03Z AND 09Z. SHALLOW POST FRONTAL COLD AIR
ADVECTION AND RESIDUAL LOW LEVEL MOISTURE WILL PROVIDE A CHANCE FOR
SOME LOW CLOUDS TO DEVELOP LATE TONIGHT/EARLY WED MORNING.

FOR DTW...THE LATER ARRIVAL OF THE COLDER LOW LEVEL AIR AND SLOWER
PUSH OF DRIER AIR INTO METRO DETROIT SUGGESTS THE POTENTIAL FOR MVFR
BASED STRATUS AT METRO WILL OCCUR MORE TOWARD WED MORNING.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN CEILINGS BELOW 5000 FT LATE TONIGHT THROUGH
WED MORNING.

&&

.PREV DISCUSSION...ISSUED 410 PM EDT TUE JUL 8 2014

SHORT TERM... REST OF TODAY AND TONIGHT

THE PASSAGE OF THE PRIMARY COLD FRONT THROUGH THE REST OF SE
MICHIGAN WILL MAINTAIN A CHANCE OF SHOWERS AND THUNDERSTORMS IN THE
FORECAST UNTIL EVENING. THERE IS ALSO POTENTIAL FOR REMNANTS OF
ACTIVITY MAKING IT IN FROM WISCONSIN AS IT SURVIVES THE TRIP OVER
LAKE MICHIGAN. ALL ACTIVITY WILL HAVE A STRONG DIURNAL DEPENDENCY
DURING THE EVENING AND SO THE CHANCE FOR THUNDER IS LIMITED TO THE
LATE AFTERNOON/EARLY EVENING AS SURFACE BASED CAPE DROPS OFF FROM
ABOUT 1000 J/KG. A WELL DEFINED UPPER CIRCULATION IS ALSO ASSOCIATED
WITH THE UPSTREAM CONVECTION WHICH COULD HELP CARRY REMNANT SHOWERS
INTO THE TRI CITIES MORE EASILY DURING THE EVENING.

THERE IS YET ANOTHER UPPER LEVEL CIRCULATION OVER NORTHWEST ONTARIO
INDICATED IN WV SATELLITE IMAGERY DURING THE MID AFTERNOON. SURFACE
PRESSURE FALLS FOLLOWING THIS LARGER FEATURE WILL FORCE THE COLD
FRONT TO STALL JUST SOUTH OF THE OHIO BORDER AFTER MIDNIGHT WITH THE
ELEVATED PORTION OF THE FRONTAL ZONE REMAINING OVER LOWER MICHIGAN.
THERE IS LOOSE MODEL AGREEMENT THAT MOISTURE WILL REMAIN ADEQUATE
FOR CLOUDS TO REDEVELOP AS THE UPPER CIRCULATION PIVOTS OVERHEAD
DURING THE NIGHT. THERE IS ALSO AN ENTRY LEVEL CHANCE OF SHOWERS IN
THE FORECAST NEAR THE OHIO BORDER AND SLIGHTLY HIGHER TOWARD THE TRI
CITIES AND NORTHERN THUMB. EXPECT THE UPPER CIRCULATION AND
ASSOCIATED COLD POOL TO GENERATE SOME MID LEVEL LIFT AND SPREAD
ADDITIONAL COLD ADVECTION ALOFT OVER THE FRONTAL ZONE LINGERING OVER
OUR AREA BELOW 700 MB. THE BEST INTERACTION WILL BE AT POINTS NORTH
THROUGH SUNRISE WEDNESDAY.

LONG TERM...

SOUTHEASTERN MICHIGAN WILL REMAIN INFLUENCED BY NORTHWESTERLY FLOW
ALOFT IN THE WAKE OF TODAYS DEEPENING LOW PRESSURE SYSTEM AS THE
MAIN MID TO UPPER LEVEL TROUGH AXIS REMAINS LAGGED BACK ACROSS THE
GREAT LAKES REGION. THIS SLOW EXIT WILL RESULT FROM ACCOMMODATING
SEPARATE BUT PHASING UPPER LEVEL SHORTWAVES THAT WILL POUR INTO THE
LOWERED HEIGHT ANOMALY. MODELS SHOW THE MERGED LOW CIRCULATION
CENTER AND IMPRESSIVE COLD POOL ALOFT PASSING THROUGH THE IMMEDIATE
VICINITY PRIOR TO 18Z...BUT GENERALLY REMAINING JUST NORTH AND EAST
OF THE DTX CWA. ONE SHOULD ALWAYS BE LEARY OF COLD POOLS AND THE
PRIOR DISCUSSION ALLUDES TO THIS. LOOKING THROUGH LATEST NWP
SOLUTIONS...ALSO AGREE WITH PRIOR SHIFT THAT PRECIPITATION AND
THUNDER CHANCES ARE LOW. MODEL SOUNDINGS WITH A LACK OF ANY
CONVECTIVE INSTABILITY OR NEUTRAL ENVIRONMENTAL LAPSE RATES THROUGH
THE -15 TO -20C LAYER ALONG WITH A POSITIVE SHOWALTER DISTRIBUTION
IN THE ECMWF PAINTS A REAL DIRE PICTURE. DID REMOVE MORNING
POPS...AS IT APPEARS WILL NEED TO MIX OUT/REACH CONVECTIVE TEMPS.
FORCING OVERALL IS NOT VERY COLLOCATED...WITH LOW AND MIDLEVELS OUT
OF PHASE. BEST POTENTIAL FOR PRECIPITATION SHOULD COME ALONG A
POSSIBLE DEWPOINT MAXIMUM/RIBBON THAT SHOULD SET UP FROM THE TRI
CITIES SOUTHEASTWARD TOWARDS PORT HURON. TEMPERATURES ARE EXPECTED TO
RANGE IN THE MID TO UPPER 70S...WITH MUCH DRIER HUMIDITY.

VERY STRONG FORCING FOR SUBSIDENCE WILL EXIST OVER LOWER MICHIGAN ON
THURSDAY WITH A DRAMATIC RECOVERY IN GEOPOTENTIAL HEIGHTS. NWP
SOUNDINGS ARE SUPPORTIVE OF ACTIVE SUBSIDENCE IN THE 800-500MB LAYER
WHICH WILL YIELD A DRY AIRMASS. EXPECT COOL CONDITIONS AS
TEMPERATURES WILL RISE JUST OVER 70 DEGREES...BUT DEWPOINTS WILL BE
IN THE LOW 50S...POSSIBLY EVEN SOME UPPER 40S FOR AREAS IN THE NORTH.

HIGH PRESSURE WILL REMAIN OVER SOUTHEAST MICHIGAN FRIDAY THROUGH
EARLY SATURDAY. A COLD FRONT WILL TRACK ACROSS THE GREAT LAKES ON
SATURDAY AND SUNDAY BRINGING A CHANCE OF RAIN SHOWERS AND
THUNDERSTORMS TO THE AREA THROUGH MOST OF THE WEEKEND. ANOTHER COLD
FRONT ASSOCIATED WITH A LOW PRESSURE SYSTEM OVER NORTHERN ONTARIO
WILL TRACK ACROSS SOUTHEAST MICHIGAN ONCE AGAIN IN THE BEGINNING OF
NEXT WEEK. THIS LOW AND COLD FRONT WILL KEEP RAIN CHANCES ACROSS THE
AREA THROUGH THE REMAINDER OF THE EXTENDED PERIOD. HIGH TEMPERATURES
WILL REMAIN IN THE UPPER 70S TO LOW 80S THROUGH SUNDAY BEFORE
DROPPING INTO THE LOW TO MID 70S ON MONDAY AND TUESDAY AFTER THE
PASSAGE OF THE COLD FRONT.

MARINE...

LAND BASED SURFACE WINDS THIS AFTERNOON RANGING BETWEEN 20-25 KNOTS
HAS PROMPTED THE EXPANSION OF THE SMALL CRAFT ADVISORY FOR ALL
NEARSHORE WATERS OF LAKE HURON...LAKE ST CLAIR...AND THE MICHIGAN
WATERS OF LAKE ERIE. THE WINDS ARE EXPECTED TO RELAX THIS EVENING AS
DIURNAL HEATING PROCESSES WANE. WINDS WILL CONTINUE OUT OF THE WEST
WEDNESDAY...BUT WILL BE UNDER 15 KNOTS...AS COOLER AIR SETTLES OVER
THE CENTRAL GREAT LAKES. HIGH PRESSURE OVER THE REGION THURSDAY WILL
ASSURE THE LIGHT WINDS AND LOW WAVES CONTINUE...RIGHT INTO FRIDAY.

&&

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

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
     HURON INCLUDING SAGINAW BAY...UNTIL 10 PM TUESDAY.

LAKE ST CLAIR...
     SMALL CRAFT ADVISORY...UNTIL 10 PM TUESDAY.

MI WATERS OF LAKE ERIE...
     SMALL CRAFT ADVISORY...UNTIL 10 PM TUESDAY.

&&

$$

AVIATION.....SC
SHORT TERM...BT
LONG TERM....CB/RK
MARINE.......CB


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