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000
FXUS63 KDTX 291711
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
111 PM EDT TUE JUL 29 2014


.AVIATION...

//DISCUSSION...

ENHANCED LOW LEVEL MOISTURE IN THE VICINITY OF A SURFACE TROUGH
SLOWLY PUSHING ACROSS SE MI AND VERY COLD AIR ALOFT WILL LEAD TO
DIURNAL ENHANCEMENT IN CLOUDS AND SHOWERS THIS AFTERNOON. THE DEGREE
OF LOW LEVEL MOISTURE DOES SUGGEST SOME MVFR BASED CLOUDS...
ESPECIALLY WITHIN THE SHOWERS. THERE IS LIKELY TO BE WIDE VARIATIONS
IN CLOUD BASES ACROSS THE AREA WITH AN OVERALL TREND TOWARD
HIGHER CIGS LATER IN THE DAY AS DIURNAL HEATING LIFTS THE
CONVECTIVE CLOUD BASES. THE LOSS OF DAYTIME HEATING THIS EVENING
SHOULD RESULT IN A DIMINISHING TREND TO THE CONVECTION. THE COLD
AIR ALOFT WILL CERTAINLY MAINTAIN A RISK OF LATE AFTERNOON
THUNDERSTORMS. THE INSTABILITY IS NOT EXTREMELY HIGH...SO
CONFIDENCE OF THUNDERSTORMS IMPACTING THE TERMINALS IS TOO LOW TO
MENTION IN THE TAFS.

FOR DTW...THE SFC TROUGH AXIS AND BETTER MOISTURE AND THUS THE
CONVECTIVE POTENTIAL WILL NOT ARRIVE INTO METRO DETROIT UNTIL LATE
THIS AFTERNOON /AROUND 21Z/. THE LATER ARRIVAL OF THE HIGHER LOW
LEVEL MOISTURE INTO METRO WILL SUPPORT SLIGHTLY HIGHER CLOUD BASES
THAN FARTHER NORTH BUT STILL INTO THE 3500 TO 5000 FT CATEGORY.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN CEILING AOB 5000 FEET IN SHOWERS DURING THE
  AFTERNOON.

* LOW CONFIDENCE IN AN ISOLATED THUNDERSTORM DURING THE AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 1107 AM EDT TUE JUL 29 2014

UPDATE...

THE LEAD EDGE OF THE CLOUD FIELD NOW ADVANCING INTO METRO DETROIT
MARKS A GRADIENT IN LOW LEVEL MOISTURE MOVING FROM NORTHWEST TO
SOUTHEAST ACROSS THE AREA. THE SHOWERS WITHIN THIS REGION OF
MOISTURE HAVE THUS FAR BEEN VERY LIGHT AND WIDELY SCATTERED.
COVERAGE OF SHOWERS WILL INCREASE THIS AFTERNOON DURING THE PEAK
IN THE DIURNAL HEATING CYCLE. COLDER AIR ALOFT WILL CONTINUE
ARRIVING FROM THE NORTH DURING THE AFTERNOON. COVERAGE AND
INTENSITY OF SHOWERS SHOULD INCREASE BY EARLY AFTERNOON ACROSS THE
SAGINAW VALLEY AND THUMB. METRO DETROIT AND POINTS SOUTH SHOULD
SEE THIS INCREASE MID-LATE AFTERNOON WITH THE SLOWER ARRIVAL OF
THE LOW LEVEL MOISTURE AND COLDER AIR ALOFT. A SURFACE
TROUGH...NOW MOVING ACROSS THE SAGINAW VALLEY WILL ALSO TRAVERSE METRO
DETROIT LATER THIS AFTERNOON. THE ADDED LOW LEVEL CONVERGENCE WILL
CERTAINLY ENHANCE COVERAGE OF LATE DAY CONVECTION. THE GOING
FORECAST STILL HAS A GOOD REPRESENTATION OF EXPECTED AFTERNOON AND
EVENING CONDITIONS. OTHER THAN SOME VERY MINOR ADJUSTMENTS TO FCST
MAX TEMPS...NO CHANGES WILL BE MADE TO THE GOING FORECAST.

PREV DISCUSSION...ISSUED 358 AM EDT TUE JUL 29 2014

SHORT TERM... TODAY AND TONIGHT

A LOBE OF SHORT WAVE ENERGY WILL SLIDE OVER THE GREAT LAKES FROM
NORTHERN ONTARIO AND AFFECT THE WEATHER FOR SE MICHIGAN TODAY AND
EVEN MUCH OF TONIGHT. SATELLITE AND RADAR IMAGERY INDICATE THIS
FEATURE IS SUPPORTING SHOWER ACTIVITY IN THE ABSENCE OF ANY DIURNAL
CONTRIBUTION. THERE WERE EVEN SOME LIGHTNING STRIKES AS LATE AS
MIDNIGHT OVER NORTHERN MINNESOTA. UPPER AIR ANALYSIS OVER THE
MIDWEST AND CENTRAL CANADA SHOWS 850 DEWPOINT RUNNING AROUND
7C...ITSELF IMPRESSIVE GIVEN THE STRONG MERIDIONAL FLOW...AND MORE
THAN ENOUGH MOISTURE TO COMBINE WITH THE UPPER LEVEL COLD POOL
AVERAGING -17C AT 500 MB TO MAINTAIN SUFFICIENT ELEVATED INSTABILITY
FOR MODEST CONVECTION. DTX UPPER AIR CLIMATOLOGY POINTS OUT 850 MB
DEWPOINT IS ABOUT AVERAGE FOR LATE JULY BUT 500 MB TEMPERATURE NEAR
RECORD LOWS. MODEL OUTPUT THEN SHOWS THE UPPER WAVE SLIDING OVER
LOWER MICHIGAN DURING PEAK HEATING WHICH WILL HELP SCATTERED MORNING
ACTIVITY BECOME NUMEROUS. MODEL SOUNDINGS DEPICT A SKINNY CAPE
PROFILE THAT APPEARS UNDERDONE WHEN SURFACE HEATING IS ADDED TO WHAT
WAS FORCED IN EARLY MORNING OBSERVATIONS UPSTREAM. A 72/52 SURFACE
PARCEL YIELDS MODIFIED CAPE VALUES IN THE 500-750 J/KG RANGE WHICH
SHOULD RESULT IN SCATTERED COVERAGE OF THUNDERSTORMS AMONG NUMEROUS
SHOWERS OVER LOWER MICHIGAN DURING THE AFTERNOON THROUGH MID
EVENING. FREEZING LEVEL AVERAGING 9500 FEET IS ALSO NOTABLE AS IT
WILL MAKE ANY STRONGER UPDRAFT CAPABLE OF SOME PEA SIZE HAIL.

EARLY MORNING OBSERVATIONS ALSO TIP THE HAND FOR TONIGHT AS RESIDUAL
ELEVATED INSTABILITY WILL BE ADEQUATE FOR SHOWERS TO LINGER WELL
INTO THE OVERNIGHT HOURS. WITH LITTLE CHANGE IN THE LOW LEVEL
MOISTURE PROFILE...THE NAM OFFERS 850 MB LI NEAR -1C OVER SOUTH
SECTIONS OF OUR AREA THROUGHOUT THE NIGHT WHICH WILL BE GOOD FOR
SCATTERED SHOWER COVERAGE...AND A RUMBLE OF THUNDER...THROUGH
SUNRISE WEDNESDAY.

LONG TERM... WEDNESDAY THROUGH MONDAY

SHOWERS ASSOCIATED WITH THE UPPER LEVEL WAVE AND COLD POOL MOVING
OVER SE MICHIGAN TODAY AND TONIGHT WILL LINGER OVER THE REGION NEAR
THE OHIO BORDER WEDNESDAY MORNING. THE REST OF WEDNESDAY WILL THEN
COME UNDER THE INFLUENCE OF LOCALIZED SUBSIDENCE THAT WILL PRESENT A
LESS FAVORABLE ENVIRONMENT FOR SHOWERS AS DAYTIME HEATING RAMPS UP.
A CHANCE POP WILL BE MAINTAINED WEDNESDAY AND DURING THE SECOND HALF
OF THE WEEK MAINLY TO ACCOUNT FOR THE LOW PREDICTABILITY BETWEEN
UPPER LEVEL FEATURES AND THE OVERALL BACKGROUND OF INSTABILITY
SUPPORTED BY THE UPPER LEVEL TROUGH...BOTH OF WHICH MAKE IT
DIFFICULT TO RULE OUT SOME SHOWER ACTIVITY. MODEL SOLUTIONS DEPICT
UPPER LEVEL FEATURES THAT ARE SMALLER IN SCALE AND LESS ORGANIZED
COMPARED THOSE LEADING UP TO THE SYSTEM TODAY WHICH MAKES IT ONLY
POSSIBLE TO USE THEM IN A GENERAL SENSE. THERE SHOULD BE PLENTY OF
TIMING AND STRENGTH ADJUSTMENTS OVER THE NEXT FEW MODEL CYCLES WHICH
WILL ALLOW REFINEMENT OF RAIN CHANCES IN THE SHORTER TERM. ON THE
OTHER HAND...THE EXPECTATION OF BELOW NORMAL BUT SLOWLY MODERATING
TEMPERATURES REMAINS SOLID OVER THE NEXT FEW DAYS. THE LOW LEVEL
THERMAL TROUGH WILL REMAIN FIXED OVER JAMES BAY WITH PERIODIC
REINFORCEMENTS OF COOLER AIR IN DEEP NW FLOW CARRYING SLIGHTLY LESS
IMPACT EACH DAY WEDNESDAY THROUGH FRIDAY.

THE LATEST GLOBAL MODEL SOLUTIONS INDICATE A GRADUAL DEAMPLIFICATION
OF THE LONG WAVE PATTERN DURING THE WEEKEND. THERE IS QUITE A BIT OF
DISPERSION IN THE 500 MB PATTERN BY SUNDAY...BUT THE STARTING POINT
OF SUCH ANOMALOUS AMPLIFICATION DURING THE SECOND HALF OF THE WEEK
FAVORS SOLUTIONS WITH A SLOWER EVOLUTION. THE MAIN RESULT WILL BE
TEMPERATURES MAKING A RETURN TO NORMAL IN BETWEEN A CONTINUED CHANCE
OF SHOWERS.

MARINE...

A COOL BUT LIGHT NORTHWEST WIND WILL PERSIST OVER LAKE HURON AND
LOWER MICHIGAN DURING THE MID WEEK PERIOD. CLUSTERS OF SHOWERS WILL
MOVE OVER THE MARINE AREAS AND HINDER OTHERWISE FAVORABLE MARINE
CONDITIONS. THE BEST CHANCE OF RAIN WILL OCCUR TODAY AND TONIGHT
ALONG WITH A CHANCE OF THUNDERSTORMS BUT PRIMARILY NEAR THE
SHORELINES AND OVER LAKE ST CLAIR AND WESTERN LAKE ERIE. THE WIND
WILL REMAIN LIGHT THROUGH THE END OF THE WEEK AND TEND TO SHIFT
TOWARD THE SOUTHWEST BY FRIDAY WITH INCREASING INFLUENCE OF WEAK
HIGH PRESSURE BY THE WEEKEND.

&&

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

&&

$$

AVIATION.....SC
UPDATE.......SC
SHORT TERM...BT
LONG TERM....BT
MARINE.......BT


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