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000
FXUS63 KDTX 211138
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
738 AM EDT TUE MAY 21 2013

.UPDATE...

DESPITE A MID LEVEL SHORTWAVE AND SUPPORT FROM THE LOW LEVEL
JET...MORNING CONVECTION HAS NOT HELD TOGETHER WELL AS IT HAS
TRAVELLED THROUGH SOUTHEAST MICHIGAN THIS MORNING. AS THE 06Z RUNS
COME IN THEY ARE KEEPING ADDITIONAL CONVECTION TO THE NORTH AND
SOUTH OF THE AREA WHERE THE BETTER DYNAMICS ARE...IN STARK
CONTRAST TO THE 00Z RUNS WHICH BLANKETED THE AREA WITH RAIN ALL
DAY. WATER VAPOR IMAGERY SHOWS SOME VALIDITY TO THIS THINKING AS
THE JET STREAM TO THE NORTH PULLS STORMS OVER THE NORTHERN GREAT
LAKES AND ACTIVITY TO THE SOUTH SHOWS SIGNS OF STAYING OVER THE
SOUTH. IT APPEARS SOUTHEAST MICHIGAN COULD BE IN BETWEEN ACTIVITY
TO THE NORTH AND SOUTH TODAY THE WAY WATER VAPOR IMAGERY IS
SHAPING UP. GIVEN THESE FACTORS WILL TONE DOWN POPS FROM
CATEGORICAL TO LIKELY...HOWEVER GOING BELOW THIS THRESHOLD WOULD
BE A MISTAKE WITH THE AMOUNT OF INSTABILITY THAT IS FORECAST TO
DEVELOP DURING THE AFTERNOON HOURS. FURTHER ADJUSTMENTS TO THE
FORECAST WILL BE MADE AS NECESSARY.

&&

.AVIATION...ISSUED 727 AM EDT TUE MAY 21 2013

//DISCUSSION...

THE REGION OF THUNDERSTORMS THAT MOVED IN FROM ILLINOIS HAS HAD
LITTLE EFFECT OVER THE TAF SITES...AND WILL ONLY BRING SOME SHOWERS
TO KMBS EARLY THIS MORNING. THE EXTENT OF CLOUD COVER FROM THIS
COMPLEX WHICH MAY LINGER INTO THE AFTERNOON RAISES CONSIDERABLE
UNCERTAINTY WITH RESPECT TO THE CHANCES AND TIMING OF THUNDERSTORMS
LATER IN THE THIS AFTERNOON. BEST CHANCES FOR THUNDERSTORMS WILL BE
THIS AFTERNOON...THEREFORE WILL PUT A TEMPE GROUP IN THE 19-23Z TIME
FRAME WHEN THUNDERSTORMS ARE MOSTLY LIKELY TO OCCUR. A BREAK IN THE
ACTIVITY IS EXPECTED OVERNIGHT AS ONE OF THE SURFACE LOWS TRACKS
THROUGH THE NORTHERN GREAT LAKES.

FOR DTW...TIMING OF THUNDERSTORMS LATER IN THE DAY REMAINS HIGHLY
UNCERTAIN...THE BEST POTENTIAL WILL BE IN THE 19-23Z TIME FRAME WITH
MAX HEATING.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN THUNDERSTORMS THIS AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 342 AM EDT TUE MAY 21 2013

SHORT TERM...TODAY AND TONIGHT

LINE OF THUNDERSTORMS CURRENTLY OVER NORTHERN ILLINOIS IS SLOWLY BUT
SURELY MARCHING NORTHEAST DURING THE EARLY MORNING HOURS. THE MAIN
QUESTION THIS MORNING IS HOW WELL THIS ACTIVITY WILL HOLD TOGETHER
AS IT TRACKS THROUGH SOUTHEAST MICHIGAN. HI-RES MODEL RUNS ARE IN
GENERAL AGREEMENT IN BRINGING THE SYSTEM THROUGH BETWEEN 09-13Z.
THAT IS WHERE THE AGREEMENT ENDS AS THE HRRR LIFTS THE BEST
THUNDERSTORM ACTIVITY NORTH THROUGH NORTHERN LOWER MICHIGAN WHILE
THE WRF MAINTAINS THE LINE OF STRONG THUNDERSTORMS AS IT TRACKS
THROUGH SOUTHEAST MICHIGAN...MAINLY NORTH OF THE M-59 CORRIDOR. THE
EVOLUTION OF THE JET STREAM WOULD VALIDATE THE HRRR SOLUTION AS IT
LIFTS THE 100+ KNOT JET NORTH OVER THE NORTHERN GREAT LAKES...TAKING
THE UPPER LEVEL DIVERGENCE AFFORDED BY THE RIGHT ENTRANCE REGION OF
THE JET WITH IT. HOWEVER LOWER LEVELS LEND CREDENCE TO THE WRF
SOLUTION AS THE MAIN SHORTWAVE DRIVING THE NORTHERN EDGE OF THE
CONVECTION IS PROGGED TO GO DIRECTLY THROUGH SOUTHEAST MICHIGAN WITH
THE NOSE OF THE 35 KNOT 850 MB LOW LEVEL JET POINTED OVER SOUTHEAST
MICHIGAN. DESPITE THE LOSS OF UPPER LEVEL JET SUPPORT...THE LOWER
LEVEL DYNAMICS POINT TO AN ACTIVE MORNING ACROSS SOUTHEAST MICHIGAN
WITH THE LINE OF CONVECTION EXPECTED TO SURVIVE THE TRIP AND TRACK
THROUGH THE AREA. THIS ACTIVITY WILL STILL HAVE QUITE A BIT OF
INSTABILITY TO WORK WITH AS MUCAPE VALUES REMAIN AT 1000 TO 1500
J/KG DURING THE EARLY MORNING HOURS. SEVERE WEATHER THREAT FROM THIS
MORNINGS CONVECTION WILL MAINLY BE A WIND THREAT...AS UPSTREAM
OBSERVATIONS SHOW LITTLE THREAT FROM LARGE HAIL...ALTHOUGH SMALL TO
NEAR SEVERE HAIL IS A POSSIBILITY.

AFTER THIS INITIAL ACTIVITY THE PICTURE BECOMES VERY MUDDLED AS THE
NWP MODELS KEEP SHOWERS AND THUNDERSTORMS GOING FOR MUCH OF THE DAY.
THIS SCENARIO IS CERTAINLY PLAUSIBLE AS ANOTHER JET STREAK LIFTS
FROM THE SOUTHWEST AND MAKES ITS WAY OVER THE GREAT LAKES REGION. AS
A RESULT THE AREA WILL BE IN THE PATH OF SEVERAL SHORTWAVES ROTATING
AROUND THE MAIN MID LEVEL LOW PRESSURE SYSTEM TAKING UP RESIDENCE
OVER THE MISSOURI VALLEY. WITHOUT A KEY FEATURE INDICATING THERE
WILL BE A SUBSTANTIAL BREAK FROM THE ACTION...DO NOT PLAN ON
DEVIATING MUCH FROM THE PREVIOUS FORECAST HIGH POPS THROUGH THE
DAYTIME HOURS.

SEVERE WEATHER POTENTIAL THIS AFTERNOON WILL HINGE ON THE ABILITY TO
GET A BREAK IN THE CONVECTION. THIS WINDOW WILL NOT HAVE TO BE
LARGE...AS EVIDENCED YESTERDAY...WITH A BRIEF BREAK ALLOWING
TEMPERATURES AND CAPES TO RISE SIGNIFICANTLY IN A SHORT PERIOD OF
TIME. MODELS SHOW MUCAPE VALUES RANGING FROM 500 TO 1000 J/KG WITH A
FAIRLY STEADY STREAM OF CONVECTION DURING THE DAY. AFTERNOON
SUNSHINE COULD EASILY BOOST THESE VALUES TO AROUND 1500 J/KG GIVEN
THE LATE MAY SUN ANGLE AND THE VERY WARM AIR IN THE LOW LEVELS. IN
ADDITION TO THE INSTABILITY...0-6 KM BULK SHEAR VALUES ARE A GOOD 30
TO 40 KNOTS TODAY...MEANING THE POTENTIAL FOR STRONG TO SEVERE
THUNDERSTORMS PRODUCING DAMAGING WINDS AND LARGE HAIL ARE A
POSSIBILITY. CLOSER INSPECTION OF THE HODOGRAPH AND LOW LEVEL CAPE
SHOW ISOLATED TORNADOES WILL ALSO BE A THREAT...ESPECIALLY IF WE CAN
GET SOME SUNSHINE...AS 0-3KM CAPE VALUES REACH 150 TO 200 J/KG AND
STORM RELATIVE HELICITY VALUES GET TO 150 TO 200 M2/S2. ALL OF THIS
ACTIVITY MAKES FORECASTING HIGH TEMPERATURES TODAY QUITE
CHALLENGING. EVEN WITH ALL OF THE ACTIVITY WE SHOULD BE ABLE TO GET
INTO THE LOW 80S AWAY FROM THE GREAT LAKES...HOWEVER A FEW MID 80S
ARE A DISTINCT POSSIBILITY IF THE AFOREMENTIONED BREAK IN THE
ACTIVITY OCCURS.

OVERNIGHT MODELS ARE HINTING AT A BREAK IN THE CONVECTION AS THE
SECONDARY JET STREAM MOVES OFF TO THE NORTH WITH NVA PROGGED AT THE
500 MB LEVEL AS THE SURFACE LOW LIFTS OVER THE SOO. EVEN WITH THESE
FACTORS THERE IS ABUNDANT LOW LEVEL MOISTURE ACROSS SOUTHEAST
MICHIGAN...SO A COMPLETELY DRY FORECAST IS NOT IN THE CARDS AND
NEITHER IS A CONTINUATION OF THE HIGH POPS FROM TODAY. WITH ALL
THESE FACTORS IN MIND WILL MAINTAIN CHANCY POPS DURING THE OVERNIGHT
HOURS. ABUNDANT CLOUD COVER AND THE REGION STILL IN THE WARM SECTOR
WILL ONCE AGAIN LEAD TO A MILD NIGHT WITH OVERNIGHT LOWS EXPECTED IN
THE 60S.

LONG TERM...WEDNESDAY THROUGH MONDAY

UPPER LEVEL TROUGHING WILL KEEP MENTION OF SHOWERS AND THUNDERSTORMS
AROUND INTO THURSDAY WHICH IS WHEN THE MAIN TROUGH AXIS PASSES EAST
OF THE AREA ALLOWING HEIGHTS TO BUILD. MEANWHILE...COMPLEX SFC LOW
PRESSURE SYSTEM WILL WORK THROUGH LOWER MI ON WEDNESDAY AND THURSDAY
BEFORE A STRONG CANADIAN HIGH PRESSURE SYSTEM DROPS INTO THE GREAT
LAKES AND EXPANDS ACROSS MUCH OF THE EASTERN CONUS FOR THE HOLIDAY
WEEKEND. THIS WILL LEAD TO A DRY BUT COOL WEEKEND.

FIRST OFF WE WILL ADDRESS CONVECTIVE POTENTIAL FOR WEDNESDAY. THE
GFS POORLY INITIALIZES THE SFC LOW OVER THE NORTHERN PLAINS SO WILL
LEAN MORE TOWARD THE ECMWF/NAM/GEM REGIONAL. THE UPPER LEVEL LOW
THAT HAS BEEN SITTING OVER THE NORTHERN PLAINS FOR A FEW DAYS NOW
WILL PHASE WITH A NORTHERN STREAM TROUGH DIGGING SOUTH THROUGH
MANITOBA/ONTARIO ON WEDNESDAY. THIS WILL LEAD TO A MORE PROGRESSIVE
SYSTEM FINALLY. WITH THE CLOSED NATURE OF THE UPPER LOW...A FEW SFC
LOWS HAVE BEEN ROTATING AROUND EACH OTHER THE LAST TWO DAYS. AS THE
WAVE OPENS FURTHER AND THE UPPER JET TURNS WEST/EAST ACROSS NORTHERN
MI...THE MAIN SFC LOW WILL RELEASE AND TRACK ACROSS NORTHERN LOWER
MI THROUGH THE DAY WEDNESDAY. THIS WILL BE A BROAD WEAKENING LOW BUT
WILL PRESENT ISENTROPIC ASCENT AND WILL KEEP THE THETA E RIDGE UP
INTO SE MI. FOCUS WILL BE PLACED ON A SOUTHERN STREAM SHORTWAVE THAT
WILL ROUND THE BASE OF THE TROUGH AND TARGET LOWER MI WEDNESDAY
AFTERNOON. MODEL CONSENSUS SHOWS A SFC LOW CLIPPING EXTREME SE MI.
THIS WILL OPEN THE DOOR FOR ADDITIONAL HEATING AND MOISTURE INTO
THAT AREA DURING PEAK AFTERNOON HEATING WITH THE EASTWARD TRACKING
UPPER LEVEL JET MORE SQUARELY OVERHEAD. CONVECTIVE PARAMETERS ARE ON
THE DECLINE FROM MONDAY AND TUESDAY BUT THERE WILL STILL BE 500 TO
1000 J/KG OF TALL SKINNY MUCAPE WITH A COLD/COOL FRONT PASSING
THROUGH THE AREA IN THE EVENING. OVERALL WEDNESDAY LOOKS LIKE IT
WILL BE COMPOSED OF WIDESPREAD SHOWERS AND THUNDERSTORMS WITH A
CHANCE OF ORGANIZED CONVECTION ACROSS THE EXTREME SE PORTION OF THE
CWA.

UPPER LEVEL TROUGH AXIS WILL BE OVER WESTERN LOWER MI WEDNESDAY
NIGHT PROVIDING BROAD AREA OF LIFT ALOFT WITH THE BACK END OF THE
SFC LOW STILL LINGERING. THIS WILL KEEP SHOWERS AND THUNDERSTORMS
OVER MUCH OF LOWER MI THROUGH THE OVERNIGHT. THE AXIS WILL SWEEP
THROUGH SE MI EARLY ON THURSDAY LEADING TO A CLEARING TREND IN THE
SHOWERS THROUGH THE DAY FROM NW TO SE. MAIN BAROCLINIC ZONE THATS
BEEN LINGERING ACROSS THE NORTHERN GREAT LAKES WILL SURGE SOUTH ON
THURSDAY WITH STRONG CANADIAN HIGH PRESSURE RIGHT BEHIND IT. WITH
BUILDING HEIGHTS ALOFT...CLOUDS WILL CLEAR OUT BUT THAT WILL NOT BE
REALIZED IN TEMPERATURES. 850 MB TEMPS IN THE LOW SINGLE DIGITS WILL
ONLY ALLOW HIGH TEMPS TO REACH AROUND 60F BOTH THURSDAY AND FRIDAY
WITH LOWS AROUND 40. A SLOW WARMING TREND THROUGH THE WEEKEND WILL
ONLY ALLOW TEMPS TO REBOUND TO NEAR 70 FOR MONDAY AND TUESDAY.
THOUGH IT WILL BE COOL...AT LEAST IT LOOKS TO STAY DRY THOUGHT THE
HOLIDAY WEEKEND.

MARINE...

MODEST SOUTHERLY WINDS WILL REMAIN IN PLACE TODAY AND WEDNESDAY AS A
LOW PRESSURE SYSTEM SLOWLY LIFTS EAST OUT OF THE UPPER MIDWEST.  A
WARM AND UNSTABLE ENVIRONMENT WILL BRING A CHANCE OF THUNDERSTORMS
DURING THIS TIME.  WINDS WILL SHIFT TO THE NORTH ACROSS ALL WATERS
BY THURSDAY MORNING...AS THE LOW AND TRAILING COLD FRONT PUSH OFF TO
THE EAST. THESE CONDITIONS WILL PUSH WINDS AND WAVES CLOSE TO SMALL
CRAFT CRITERIA ON THURSDAY OVER LAKE HURON.

&&

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

&&

$$

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


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