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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 180345
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1145 PM EDT MON JUN 17 2013


.AVIATION...

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

SEVERAL THUNDERSTORMS HAVE PUSHED THE SURFACE COLD FRONT SOUTH OF
THE TAF SITES...HOWEVER THE MID LEVEL COLD FRONT CONTINUES TO
GENERATE SHOWERS AS IT SLOWLY SINKS SOUTH. SHOWERS MAY CONTINUE FOR
ANOTHER HOUR OR TWO BEFORE INSTABILITY COMPLETELY WANES AS THE FRONT
HEADS SOUTH. IT APPEARS INSTABILITY HAS FALLEN ENOUGH TO CREATE A
NEAR NIL THREAT FOR THUNDER AS THE REMAINING ACTIVITY TRACKS THROUGH
FROM FNT SOUTHWARD...WITH MBS CLEAR OF ANY SHOWER THREAT. COLD AND
DRY ADVECTION COUPLED WITH A TIGHT PRES GRADIENT LATER ON TUESDAY
WILL BRING WIND GUSTS OVER 20KT WITH VFR CONDITIONS EXPECTED.

FOR DTW...THE PROBABILITY FOR THUNDERSTORMS TO IMPACT THE TERMINAL
WITH THE COLD FRONTAL PASSAGE CONTINUES TO BE VERY LOW...WITH A
CONTINUED THREAT FOR SHOWERS THROUGH 09Z.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE IN CEILINGS BELOW 5000 FT THROUGH 09Z.

* LOW CONFIDENCE IN THUNDERSTORM POTENTIAL THROUGH 09Z.
-- End Changed Discussion --

&&

.PREV DISCUSSION...ISSUED 401 PM EDT MON JUN 17 2013

SHORT TERM...THIS AFTERNOON AND TONIGHT

MAIN CONCERN FOR THE SHORT TERM WILL BE CONVECTION INITIATING THIS
AFTERNOON AND PERSISTING INTO EVENING AS LIFT/FORCING FROM SHORTWAVE
NOW SHIFTING INTO WESTERN GREAT LAKES PROVIDES SUPPORT FOR ACTIVITY
THAT FIRES ALONG SURFACE FRONT DRAPED FROM THE SAGINAW VALLEY INTO
THE THUMB REGION.

LEAD SURFACE TROUGH NEAR THE MICHIGAN/OHIO STATE LINE WILL CUT OFF
THE REGION FROM THE BEST BOUNDARY LAYER MOISTURE/INSTABILITY...BUT
STRONG SOLAR INSOLATION DURING THE REMAINDER OF THE AFTERNOON WILL
ALLOW FOR MODEST INSTABILITY EVEN IN AREAS WHERE SURFACE DEW POINTS
WILL BE LIMITED TO THE MID/UPPER 50S. GIVEN BULK WIND SHEAR VALUES
OF 45 KNOTS IN STRONG WEST/NORTHWEST FLOW REGIME...EXPECT SOME
DEGREE OF ORGANIZATION TO THE SHOWERS/THUNDERSTORMS THAT DEVELOP AS
THE INFLUENCE OF THE UPPER LEVEL WAVE INCREASES STEADILY DURING PEAK
HEATING/INSTABILITY OF THE AFTERNOON. THE ACTIVITY WILL ALSO BE
AIDED BY INCREASE LOW LEVEL CONVERGENCE AS NORTHEAST FLOW FROM
DEVELOPING LAKE BREEZE FROM LAKE HURON WILL AUGMENT THE PUSH OF THE
SYNOPTIC FRONTAL BOUNDARY SOUTHWARD THROUGH THE CWA.

STEEP LAPSE RATES THROUGH AT LEAST 650 MB IN WELL MIXED NORTHWEST
FLOW WILL PROVIDE A FAVORABLE ENVIRONMENT FOR GUSTY WINDS WITHIN
THUNDERSTORM DOWNDRAFTS. ALSO...RELATIVELY LOW FREEZING LEVEL WITH
LACK OF ANY SIGNIFICANT UPPER RIDGING OVER AREA WILL BE FAVORABLE
FOR SOME HAIL DEVELOPMENT.

SO...AS THE PREVIOUS FORECAST OUTLINED NICELY...THERE WILL BE A
CHANCE FOR SEVERAL SEVERE STORMS FROM THIS AFTERNOON INTO THE EARLY
EVENING AS ACTIVITY GRADUALLY EXPANDS AS INSTABILITY MAXES OUT WITH
LATE DAY HEATING. WHILE THE MAIN WINDOW FOR ACTIVE STORMS WILL EXIST
THROUGH 00Z-01Z...LINGERING CONVECTION WILL MOST LIKELY PERSIST OVER
SOME PARTS OF THE AREA INTO THE 04Z-06Z TIME FRAME AS LIFT FROM THE
TRAILING ENTRANCE REGION OF UPPER JET SHIFTS OVER THE AREA.

ANY REMAINING ACTIVITY WILL END QUICKLY AFTER MIDNIGHT AS FRONTAL
BOUNDARY PUSHES SOUTH OF THE AREA...AUGMENTED BY THE AGEOSTROPHIC
CIRCULATION ON THE TAIL END OF THE UPPER JET. BUILDING HIGH PRESSURE
WILL BRING RELATIVELY COOL TEMPERATURES INTO MUCH OF THE CWA...WITH
LOW TEMPERATURES NEAR 50 OVER THE NORTHERN CWA...AND MID 50S FOR A
GOOD PORTION OF THE AREA.

LONG TERM...TUESDAY THROUGH SUNDAY

AN ANTICYCLONE OF CANADIAN ORIGIN WILL BECOME ESTABLISHED OVER THE
GREAT LAKES IN WELL ORGANIZED CONFLUENCE ALOFT. THE SURFACE HIGH
WILL MAINTAIN A CENTERING OVER LAKE HURON THROUGH WEDNESDAY NIGHT.
AS THIS SURFACE HIGH PASSES EAST NWP SUGGESTS A STRONG SURFACE RIDGE
WILL THEN PERSIST OVER THE LAKE AGGREGATE THROUGH FRIDAY. A FINE
STRETCH OF EARLY SUMMER WEATHER IS EXPECTED WITH CONDITIONS THAT ARE
NOTABLY COOL. SURFACE TEMPERATURES TUESDAY SHOULD FAIL TO CLIMB OUT
OF THE 60S FOR THE THUMB...WITH READINGS IN THE HEAT ISLAND ABLE TO
REACH THE MID 70S DUE TO FULL JUNE INSOLATION. TUESDAY NIGHT WILL BE
DOWNRIGHT COOL WITH GUIDANCE SUGGESTING WIDESPREAD LOWER TO MIDDLE
40S WHICH WILL BE SOME 15 TO 17 DEGREES COOLER THAN NORMAL.

RETURN FLOW WILL EVENTUALLY COLLAPSE UPON THE REGION BY THIS
WEEKEND. CLEAN SHOWALTER INDICES ANALYSIS SUGGESTS THAT A
THERMODYNAMIC PROFILE CONDUCIVE FOR PRECIPITATION WILL ARRIVE ON
SATURDAY. IT IS AT THIS TIME THAT SOUTHEASTERN MICHIGAN MAY BECOME
IN LINE WITH POSSIBLE MCS TRACK THAT WILL BE CRESTING AN INBOUND MID
TO UPPER LEVEL RIDGE.

MARINE...

APPROACHING SHORTWAVE WILL INDUCE WEAK SURFACE LOW PRESSURE ALONG
FRONTAL BOUNDARY DRAPED THROUGH THE CENTRAL GREAT LAKES. SHOWER AND
THUNDERSTORM DEVELOPMENT WILL INCREASE AS THIS PROCESS TAKES PLACE
DURING PEAK HEATING LATE TODAY...WITH CONVECTION PERSISTING INTO
THIS EVENING AS JET SUPPORT SHIFTS OVERHEAD.

NORTHEAST FLOW WILL INCREASE OVERNIGHT INTO EARLY TUESDAY IN THE
WAKE OF THIS SYSTEM...BUT ONLY TOP OUT AROUND 15 KNOTS...SO WHILE
WAVES WILL BUILD OVER SOUTHERN LAKE HURON IN PARTICULAR...EXPECT
CONDITIONS TO REMAIN UNDER SMALL CRAFT ADVISORY CRITERION FOR THE
NEARSHORE ZONES...PEAKING AT 2-4 FEET OVER FAR SOUTHERN LAKE HURON.

ONCE THIS SLIGHTLY ENHANCED FLOW SUBSIDES BY MIDDAY TUESDAY...HIGH
PRESSURE WILL BRING FAVORABLE MARINE CONDITIONS FOR THE REMAINDER OF
THE WEEK AS WINDS BECOME LIGHT AND VARIABLE.

&&

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

&&

$$

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


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