-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 161812
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
212 PM EDT THU MAY 16 2013


.AVIATION...

-- Changed Discussion --
//DISCUSSION...

THE AVIATION FORECAST DECISION POINT IS A LAKE BREEZE PUSH THAT WILL
RELEASE OFF OF THE ADJACENT LAKE AGGREGATE BEGINNING AT/AROUND
22-23Z. HAVE TIMED AN ABRUPT WINDSHIFT FROM 300 TO 030 AT THE
SOUTHERN FOUR SITES.

CANADIAN SURFACE HIGH PRESSURE NOSING INTO SOUTHEASTERN MICHIGAN
TODAY IS CHARACTERIZED BY A VERY STABLE ATMOSPHERIC COLUMN THROUGH 9
KFT AGL. WILL WATCH A WEAK MIDLEVEL IMPULSE SLIDE SOUTHEASTWARD OUT
OF WISCONSIN ACROSS THE CENTRAL TERMINAL SITES DURING THE LATE
AFTERNOON HOURS. THERE IS ENOUGH MIDLEVEL INSTABILITY TO SUPPORT
SOME ACCAS STREAMERS...OTHERWISE DEEP AMBIENT DRY AIR WILL MAKE THIS
OF LITTLE CONSEQUENCE AT THE SURFACE.

//DTW THRESHOLD THREATS...

* THE WIND DIRECTION IS EXPECTED TO SHIFT ABRUPTLY FROM 290-300 TO
030 AT APPROXIMATELY 2330-0000Z THIS EVENING. WIND SPEEDS POST LAKE
BREEZE WILL BE ABOVE 10 KNOTS.
-- End Changed Discussion --

&&

.PREV DISCUSSION...ISSUED 333 AM EDT THU MAY 16 2013

SHORT TERM...TODAY AND TONIGHT

SOUTHEAST MICHIGAN WILL LIE ALONG THE SOUTHERN PERIPHERY OF A
SLIGHTLY SUPPRESSED MID LEVEL HEIGHT FIELD WORKING AROUND THE CLOSED
CIRCULATION NOW OVER WESTERN QUEBEC.  WEAK SURFACE/THERMAL TROUGHING
WILL EMERGE IN RESPONSE TODAY...A THIN CONVERGENCE ZONE ENHANCED BY
DEVELOPING LOW LEVEL ANTICYCLONIC/NORTHEAST FLOW ALONG THE FRONT
FACE OF A SPRAWLING HIGH PRESSURE CENTER SQUEEZING SOUTHEAST INTO
THE UPPER PENINSULA.  THIS FEATURE WILL LIKELY TRANSLATE INTO AN
AREA OF AGITATED CU GROWTH DURING PEAK HEATING.  HOWEVER PROSPECTS
FOR PRECIPITATION DEVELOPMENT APPEAR EXTREMELY LIMITED GIVEN THE
DEARTH OF AVAILABLE LOW LEVEL MOISTURE.  BOTH NAM AND GFS NEAR
SURFACE MOISTURE PARAMETRIZATION CONTINUES TO BE AN ISSUE...AGAIN
ALLOWING SURFACE DEWPOINTS TO INCORRECTLY INCREASE INTO THE LOWER
AND MIDDLE 50S.  THIS RESULTS IN ERRONEOUSLY HIGHER LOW LEVEL
INSTABILITY/ASCENT...CONTRIBUTING TO THE GENERATION OF SOME HIGH
BASED SHOWERS.  WHILE A VERY LOW PROBABILITY DOES EXIST FOR A SHOWER
OR TWO TO DEVELOP...CONTINUE TO FAVOR A DRY FORECAST TODAY GIVEN THE
LIMITED OPPORTUNITY.

OTHERWISE PLENTY OF SUNSHINE WORKING INTO A RELATIVE PERSISTENT
THERMAL PROFILE /850 MB TEMPS OF LOWER TEENS/ WILL ALLOW
TEMPERATURES TO PUSH THE UPPER 70S TO AROUND 80 DEGREE MARK IN MANY
LOCALES.  EXCEPTION WILL BE ACROSS THE THUMB...WHERE THE DIURNAL
RESPONSE WILL BE CUT SHORT SLIGHTLY BY THE EMERGING NORTHEAST
FLOW/LAKE BREEZE WORKING OFF THE COOL LAKE HURON WATERS.  WEAK
SFC-850 MB COOLING COMMENCES THROUGH THE EVENING AS THE SHALLOW
FRONTAL STRUCTURE SLIDES SOUTHWEST.  THIS WILL EFFECTIVELY TRIM
SEVERAL DEGREES OFF LOWS...READINGS LOW TO MID 40S NORTH TO UPPER
40S SOUTH.

LONG TERM...

HIGH PRESSURE BUILDING INTO THE CENTRAL GREAT LAKES ON FRIDAY WILL
LEAD TO TEMPERATURES NEAR NORMAL...AS LIGHT NORTHEAST FLOW OFF
THE COOL WATERS OF LAKE HURON (UPPER 30S/LOWER 40S) AND SOME MID/HIGH
CLOUDS BOTH SERVE TO MITIGATE THE DIURNAL RESPONSE COMING OFF THE
MORNING LOWS IN THE 40S. TEMPERATURES ACROSS THE MAJORITY OF THE
CWA SHOULD BE WITHIN 2 DEGREES OF 70...WITH THE COOLER NORTHERN
THUMB REGION THE EXCEPTION.

STILL FAVORING A DRY AND NICE WEEKEND WITH TEMPERATURES WARMING AS
AMPLIFIED UPPER LEVEL RIDGE MOVES OVERHEAD. THERE IS SMALL CONCERN
AN ACTIVE WARM FRONT OVER THE WESTERN GREAT LAKES FRIDAY WILL LEAD
TO SHOWERS SPILLING OVER FRIDAY NIGHT-SATURDAY. HOWEVER...CANADIAN/EURO
AND EVEN THE GFS SUGGEST DRIER/STABLE AIR IN PLACE WILL ALLOW THE
ACTIVITY TO FALL APART AS IT TRACKS SOUTHEAST ALONG THE THICKNESS
FIELD ORIENTATION.

WILL HAVE TO KEEP EYE OUT FOR UPPER LEVEL LOW CURRENTLY OVER THE
SOUTHERN PLAINS...AS IT SLOWLY HEADS OFF TO THE NORTHEAST....BUT IS
EXPECTED TO TRACK REAL CLOSE TO THE OHIO RIVER...FAR ENOUGH SOUTH
NOT TO BE AN ISSUE FOR US.

WARMING TREND THROUGH THE WEEKEND WITH 850 MB TEMPS SEEN RISING INTO
THE MID TEENS ON SUNDAY...SUPPORTIVE OF LOWER 80S...BUT LINGERING
SOUTHEAST FLOW COMING OFF THE COOL LAKES MAY BE ENOUGH TO HOLD MAXES
IN THE UPPER 70S. INCREASING SOUTHERLY FLOW ON MONDAY WILL SUPPORT
TEMPERATURES CLIMBING EVEN MORE...AS 850 MB TEMPS REACH AT LEAST 16
C. THE PROBLEM IS THE UPPER LEVEL RIDGE AXIS SHIFTS EAST...ALLOWING
FOR AN INCREASINGLY MOIST/UNSTABLE AIRMASS TO MOVE IN...AND QUESTION
MARKS WITH TIMING AND COVERAGE OF SHOWERS AND THUNDERSTORMS SUNDAY
NIGHT-MONDAY AS UPPER LEVEL LOW ADVANCES INTO THE NORTHERN PLAINS...WITH
A POTENTIAL PIECE OF ENERGY/SHORTWAVE TROUGH BREAKING OFF TO THE
EAST.

THE UPPER LEVEL LOW IS EXPECTED TO WEAKEN AND MOVE OFF TO THE
EAST/SOUTHEAST...PROVIDING UNSETTLED WEATHER TUESDAY-WEDNESDAY TO
GREAT LAKES REGION. STILL...MEDIUM RANGE MODEL (EURO INCLUDED) HAVE
NOT BEEN VERY CONSISTENT WITH POSITION AND STRENGTH OF THIS
LOW/TROUGH...AS NEXT SYSTEM DROPPING INTO THE PACIFIC NORTHWEST
BECOMES THE MORE DOMINANT FEATURE. NOT CONFIDENT ENOUGH TO CARRY
LIKELY POPS FOR ANY SPECIFIC PERIOD TUESDAY AND BEYOND.

MARINE...

MODEST NORTHWEST WINDS TODAY WILL VEER TO NORTHEASTERLY INTO TONIGHT
IN ADVANCE OF STRONG HIGH PRESSURE BUILDING INTO THE WESTERN GREAT
LAKES.  FAVORABLE MARINE CONDITIONS WILL EXIST ON FRIDAY AS THIS
HIGH SLOWLY WORKS THROUGH THE REGION.  EXTENDED PERIOD OF LIGHTER
EASTERLY FLOW WILL EXIST THROUGH THE WEEKEND.

&&

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

&&

$$

AVIATION.....CB
SHORT TERM...MR
LONG TERM....SF
MARINE.......MR


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