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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 181736
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
136 PM EDT SAT MAY 18 2013


.AVIATION...

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

PERSISTENT FLOW OFF OF THE CENTRAL GREAT LAKES AGGREGATE IS
ALLOWING SURFACE HIGH PRESSURE TO HOLD ON ACROSS SOUTHEASTERN
MICHIGAN. DRY AIR IN THE LOWEST 6 KFT AGL HAS BEEN THE STORY OF
RECENT DAYS AND WILL NOT BE GOING ANYWHERE ANYTIME SOON. MAIN
SHEARING DEFORMATION AXIS THAT IS IN PLACE OVER CENTRAL LOWER
MICHIGAN...SAGINAW BAY AND THUMB WILL LIFT NORTHWARD TODAY IN
RESPONSE TO BUILDING UPPER LEVEL HEIGHTS/LONGWAVE RIDGE AXIS.
THEREFORE...EXPECT VFR CONDITIONS WITH PERHAPS SOME MESSY MID TO
HIGH CLOUD AT TIMES. WILL BE WATCHING SOME LOWER LEVEL MOISTURE
LIFT ANTICYCLONICALLY OUT OF OHIO TONIGHT AND INTO PORTIONS OF
SOUTHEASTERN MICHIGAN. THIS WILL NEED TO BE MONITORED....NOT
EXPECTING CLOUD BUT CERTAINLY COULD ADD A MOISTURE ADVECTION
COMPONENT THAT MAY BRING SOME HZ TOWARDS MORNING.

//DTW THRESHOLD THREATS...

* NONE
-- End Changed Discussion --

&&

.PREV DISCUSSION...ISSUED 339 AM EDT SAT MAY 18 2013

SHORT TERM...TODAY AND TONIGHT

MID/UPPER LEVEL RIDGING WILL CONTINUE TO BUILD INTO THE REGION TODAY
WHILE WE REMAIN ON THE WESTERN EXTENT OF A DOME OF HIGH PRESSURE AT
THE SFC CENTERED OVER EASTERN CANADA. EASTERLY WINDS WILL PERSIST
THROUGH TONIGHT DUE TO THE SFC HIGH. THE CONTINUED FEED OF DRY
CONTINENTAL AIR WILL KEEP DEWPOINTS IN THE 40S ONCE AGAIN. MODEL
SOUNDINGS IN FAIRLY GOOD AGREEMENT WITH THE 00Z DTX SOUNDING WITH
THE DEPTH OF DRY AIR IN THE BOUNDARY LAYER CURRENTLY AROUND 9KFT.
THE 700MB WARM FRONT LIFTED THROUGH FRIDAY AFTERNOON AND MODELS SHOW
THE WEAKER 925 MB FRONT WILL FOLLOW NORTHWARD THROUGH TODAY. HARD TO
FIND ANY ADDITIONAL SUPPORT TO HELP THIS KICK OFF ANY SHOWERS THIS
AFTERNOON. MODELS KEEP MOST OF THE SHOWERS OVER THE OHIO VALLEY
WHERE SFC MOISTURE IS MUCH HIGHER. THE LIKELY RESULT WILL END UP
BEING A LOWERING OF THE CLOUD DECK TO AROUND 6-7KFT. WEAK WAA WILL
ALLOW TEMPS TO REBOUND A FEW MORE DEGREES TODAY INTO THE MID/UPPER
70S WITH COOLER TEMPS FOR AREAS IN THE LAKE SHADOW.

LONG TERM...SUNDAY THROUGH FRIDAY

STABILIZING INFLUENCE OF UPPER RIDGING SHOULD HELP KEEP THE AREA DRY
ON SUNDAY. ALTHOUGH A SURFACE WARM FRONT WILL LIFT NORTH THROUGH THE
CWA EARLY ON SUNDAY...DRY CONDITIONS ARE EXPECTED TO CONTINUE
DESPITE MUCAPE VALUES APPROACHING 1000 J/KG DURING THE AFTERNOON
HOURS GIVEN THE VERY DRY AND IN PLACE AND STABILIZING EFFECT OF
DOWNWARD MOTION FROM THE UPPER LEVEL RIDGE. THE PASSAGE OF THE WARM
FRONT WILL BRING WARMER AIR TO THE REGION...WITH DAYTIME HIGHS
AROUND THE 80 DEGREE MARK AWAY FROM LAKE HURON.

WARM AIR WILL CONTINUE TO STREAM IN BEHIND THE WARM FRONT EARLY IN
THE WORK WEEK AS SOUTHERLY WINDS BRING A MARKED INCREASE IN MOISTURE
ACROSS SOUTHERN MICHIGAN. THE INCREASED MOISTURE AS WELL AS THE
SHIFT EAST IN THE UPPER LEVEL RIDGE WILL BRING AN INCREASE IN RAIN
CHANCES TO SOUTHEAST MICHIGAN AS THE WEEK PROGRESSES. ALTHOUGH AN
UPPER LEVEL LOW WILL SIT OFF TO THE WEST DURING THE EARLY PART OF
THE WEEK...SEVERAL EMBEDDED SHORTWAVES WILL TAKE ADVANTAGE OF THE
INCREASED INSTABILITY OF 1000 TO 2000 J/KG MONDAY AND TUESDAY. THE
UPPER LEVEL DYNAMICS AND INSTABILITY WILL BRING THE POSSIBILITY FOR
SEVERAL ROUNDS OF SHOWERS AND THUNDERSTORMS TO THE AREA. DESPITE THE
DECENT CAPE VALUES...SHEAR WILL BE VERY WEAK IN THE LOW LEVELS WITH
A RATHER UNIMPRESSIVE HODOGRAPH AND MEAGER HELICITY VALUES. MONDAY
LOOKS TO BE THE WARMEST DAY OF THE UPCOMING WEEK WITH HIGH
TEMPERATURES GETTING INTO THE LOWER TO MIDDLE 80S ACROSS MUCH OF THE
CWA.

ALTHOUGH MODEL DIFFERENCES STILL EXIST...THERE APPEARS TO BE MORE
AGREEMENT IN HANDLING THE CUT OFF LOW OUT TO THE WEST AS IT
PROGRESSES EAST DURING THE MIDDLE OF THE WEEK. THE GFS AND ECMWF
SOLUTIONS MERGE THIS LOW WITH THE NORTHERN STREAM LOW OVER HUDSON
BAY...ABSORBING THE LOW AS A POSITIVELY TILTED TROUGH TRACKING
THROUGH THE CENTRAL GREAT LAKES REGION. ALTHOUGH THUNDERSTORMS ARE
STILL POSSIBLE DURING THE MIDDLE OF THE WEEK...THE BEST INSTABILITY
WILL BE WELL TO THE SOUTH. HOWEVER THE SYSTEM WILL HAVE ENOUGH
MOISTURE TO PRODUCE SOME HEAVY RAIN SHOWERS DURING THE MIDDLE OF THE
WEEK AS THE SURFACE LOW TRACKS THROUGH THE SOUTHERN GREAT LAKES
REGION.

CANADIAN HIGH PRESSURE BUILDS IN BEHIND THE LOW LATE IN THE
WEEK...BRINGING DRY CONDITIONS AND MUCH COOLER DAYTIME HIGHS IN THE
60S TO SOUTHEAST MICHIGAN.

MARINE...

EASTERLY FLOW WILL CONTINUE THROUGH TONIGHT AS WE REMAIN UNDER THE
INFLUENCE OF HIGH PRESSURE OVER CANADA. THE FAVORABLE FETCH WILL
ALLOW WAVES TO BE SLIGHTLY HIGH OVER WESTERN LAKE ERIE...BUT A
DECREASING TREND WILL KEEP THEM BELOW SMALL CRAFT ADVISORY CRITERIA.
WINDS WILL VEER TO SOUTHERLY BY SUNDAY NIGHT BEFORE INCREASING
NEXT WEEK AS LOW PRESSURE LIFTS OUT OF THE PLAINS. THIS LOW WILL
BRING A CHANCE OF THUNDERSTORMS MONDAY THROUGH AT LEAST WEDNESDAY
AND WILL BE ACCOMPANIED BY A MODEST INCREASE IN SOUTHERLY WINDS BY
MONDAY AFTERNOON. A MID-WEEK WIND SHIFT TO NORTHERLY CAN THEN BE
EXPECTED AS A COLD FRONT PUSHES ACROSS AREA WATERS.

&&

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

&&

$$

AVIATION.....CB
SHORT TERM...DRK
LONG TERM....KURIMSKI
MARINE.......DRK


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