-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 180033
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
833 PM EDT FRI MAY 17 2013

.UPDATE...

-- Changed Discussion --
A UPDATE TO THE GRIDS/ZONES WAS ISSUED TO INCREASE THE CHANCES OF
LIGHT RAIN ACROSS THE SAGINAW VALLEY AND THUMB REGION. MID
TROPOSPHERIC FRONTOGENESIS HAS BEEN RATHER PERSISTENT AND HAS
RESULTED IN SEVERAL OBS REPORTING LIGHT RAIN OR SPRINKLES. THE
FGEN SHOULD PERSIST THROUGH 06Z TONIGHT BEFORE WANING LATE AS
SHORT WAVE RIDGING OVERSPREADS LOWER MI CAUSING THE MID LEVEL
FRONTAL CIRCULATION TO WEAKEN.
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
ISSUED 702 PM EDT FRI MAY 17 2013

//DISCUSSION...

STRONG HIGH PRESSURE PARKED ACROSS ERN ONTARIO AND QUEBEC WILL
MAINTAIN A FEED OF LOW LEVEL DRY AIR INTO SE MI UNDER PERSISTENT
EAST-SOUTHEASTERLY WINDS. THIS WILL SUSTAIN CLEAR SKIES BELOW 8000
FT THROUGH SAT MORNING. GIVEN THIS DRY LOW LEVEL AIR...THE RADAR
RETURNS NOW BLANKETING CENTRAL MI ARE MOSTLY LIGHT RAIN OR SPRINKLES.

//DTW THRESHOLD THREATS...

* NONE.
-- End Changed Discussion --

&&

.PREV DISCUSSION...ISSUED 329 PM EDT FRI MAY 17 2013

SHORT TERM...TONIGHT

THE COMPACT AREA OF SHOWER AND OCCASIONAL THUNDERSTORM ACTIVITY OVER
CENTRAL/NORTHERN WISCONSIN WILL BE SUPPORTED THROUGH TONIGHT AS THE
JET OVER SOUTHERN ONTARIO STRENGTHENS IN RESPONSE TO LARGE SCALE
AMPLIFICATION. THE RESULTING NARROW CORRIDOR OF 300K FGEN AND MOIST
ISENTROPIC ASCENT THAT HAS BEEN SUPPORTING THESE SHOWERS WILL REMAIN
TIED TO THE SLOWLY EVOLVING LARGE SCALE PATTERN AND WILL THEREFORE
ESSENTIALLY REMAIN ANCHORED OVER NORTHERN WISCONSIN THROUGH THE
REMAINDER OF THE SHORT TERM PERIOD, ONLY SLOWLY LIFTING NORTHEAST
WITH TIME. SO FAR THIS AFTERNOON, NOTHING MORE THAN DRIZZLE HAS BEEN
OBSERVED ACROSS THE SAGINAW VALLEY. THIS IS EXPECTED GIVEN THAT THE
DEARTH OF LOW-LEVEL MOISTURE IN PLACE OVER SOUTHEAST MICHIGAN CONTINUES
TO BE SUPPORTED BY SYNOPTIC SCALE RIDGING AND ENHANCED BY THE LAKE
AGGREGATE. THE BEST CHANCE FOR MEASURABLE RAINFALL WILL COME TOWARD
MORNING IN THE SAGINAW VALLEY...PERHAPS EVEN THE WESTERN
THUMB...WHEN ADDITIONAL ENERGY SHEARS TOWARD LOWER MI AND ENHANCES
THE LOW-LEVEL FORCING FIELD. STILL FEEL THAT NOTHING BETTER THAN A
LOW CHC POP IS WARRANTED AT THIS TIME. INHERITED FORECAST LOWS IN
THE UPPER 40S REMAIN ROUGHLY ON TRACK AND NOT DISSIMILAR TO WHAT HAS
BEEN OBSERVED THE LAST FEW NIGHTS. HOWEVER, THE ABUNDANCE OF CLOUD
DEBRIS ADVECTING ACROSS THE PENINSULA THIS EVENING WARRANTS AN
UPWARD BOOST OF A COUPLE DEGREES.

LONG TERM...SATURDAY THROUGH NEXT FRIDAY

STABILIZING INFLUENCE OF UPPER RIDGING SHOULD HELP KEEP THE AREA DRY
THROUGH SUNDAY. MODELS SHOW A WEAK ELEVATED WARM FRONT (NEAR 925MB)
OVER SOUTHERN MICHIGAN TO START THE DAY LIFTING NORTHWARD INTO LAKE
HURON BY AFTERNOON. WITH NO UPPER SUPPORT...ONLY WEAK ISENTROPIC
ASCENT...AND VERY DRY AIR EXPECTED BELOW 6000 FEET...WILL CARRY A
DRY FORECAST. WOULD NOT BE SURPRISED TO SEE A FEW SPRINKLES
HOWEVER...BUT NOT MUCH WORTH MENTIONING AT THIS POINT. DO EXPECT
PLENTY OF MID AND HIGH LEVEL CLOUDS HOWEVER. SURFACE FRONT SHOULD
LIFT THROUGH LATE SATURDAY NIGHT INTO EARLY SUNDAY...BUT AGAIN
EXPECT DRY CONDITIONS. EXPECT A GRADUAL WARMING TREND OVER THE
WEEKEND AS WARMER AIR ARRIVES...WITH EASTERLY FLOW OFF THE COLD
WATERS OF THE GREAT LAKES KEEPING TEMPERATURES COOLER OVER THE EAST
SIDE OF THE STATE. SOUTHERLY FLOW ON SUNDAY WILL HELP BRING
TEMPERATURES NEAR TO ABOVE 80 BY AFTERNOON.

CHANCES FOR RAIN THEN START TO INCREASE LATE SUNDAY NIGHT INTO THE
FIRST HALF OF MONDAY AS THETA-E SURGE OCCURS AS A WEAK LOW LEVEL JET
NOSES UP INTO LOWER MICHIGAN. FORECAST COMPLEXITY THEN INCREASES
BEYOND THAT...WITH MODELS DIVERGING SIGNIFICANTLY WITH THE PATTERN
OVER THE UPPER MISSISSIPPI RIVER VALLEY AND GREAT LAKES BY TUESDAY.
WILL BE WATCHING THE EVOLUTION...BOTH IN REAL LIFE AND IN THE
MODELS...OVER THE NEXT FEW DAYS AS THE LOW NEAR SOUTHERN CALIFORNIA
AND THE STRONG UPPER WAVE OFF BRITISH COLUMBIA INTERACT AND
EVENTUALLY MERGE OVER THE COUNTRY`S MID-SECTION. THIS SYSTEM IS THEN
FORECAST TO SLOWLY MOVE ACROSS THE GREAT LAKES/OHIO VALLEY THROUGH
MIDWEEK. FOR MONDAY...GFS AND EURO INDICATE EITHER A WARM FRONT OR
OCCLUSION MOVING ACROSS LOWER MICHIGAN DURING THE AFTERNOON AS
SURFACE LOW PRESSURE MOVES INTO SOUTHERN MINNESOTA. MODELS ALSO SHOW
A STRONG COLD FRONT POISED NORTH OF LAKE HURON. BOTH THESE FEATURES
WILL INCREASE SOUTHERLY FLOW OVER THE AREA...AND DEPENDENT ON CLOUD
COVER AND CONVECTIVE ACTIVITY...COULD LEAD TO A VERY WARM DAY ACROSS
SOUTHEAST MICHIGAN WITH TEMPERATURES WELL INTO THE 80S. WENT A
LITTLE CONSERVATIVE WITH TEMPS FOR NOW AS GOOD AMOUNT OF MOISTURE
AND INSTABILITY ALONG WITH A CONVECTIVE TRIGGER WILL MORE THAN
LIKELY PRODUCE ROUNDS OF CONVECTION AND CLOUDS ACROSS THE REGION.
ROUNDS OF SHOWERS AND THUNDERSTORMS ARE THEN EXPECTED TO CONTINUE
THROUGH AT LEAST EARLY THURSDAY AS THE FRONT NORTH OF LAKE HURON
SINKS SOUTHWARD...AND POTENTIALLY STALLS OVER THE GREAT LAKES AS
RECENT MODEL RUNS HAVE SHOWN. UNCERTAINTY WITH TIMING GREATEST
THUNDERSTORM THREAT AND POPS OVERALL CENTERS AROUND DIFFERENT TRACKS
THE LOW MAY TAKE OVER THE GREAT LAKES/OHIO VALLEY...AND WHEN THE
STRONG COLD FRONT OVER CANADA WILL DROP DOWN THROUGH THE AREA.
CANNOT RULE OUT SEVERE WEATHER MONDAY THROUGH WEDNESDAY...BUT IT`S
REALLY TOO EARLY TO PIN DOWN THE DETAILS.

COOLER AND QUIET CONDITIONS WILL THEN RETURN FOR THE END OF THE WEEK
BEHIND THE SYSTEM...WITH MAX TEMPERATURES FALLING BELOW NORMAL FOR
THURSDAY AND FRIDAY.

MARINE...

GENTLE TO MODERATE EASTERLY BREEZE 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. UNTIL THEN...SIGNIFICANT WAVE HEIGHTS WILL GENERALLY REMAIN
AT OR BELOW 2 FEET WITH THE EXCEPTION OF THE MICHIGAN WATERS OF LAKE
ERIE WHERE SIG WAVES OF UP TO 3 FEET WILL BE COMMON THROUGH SATURDAY
NIGHT.

&&

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

&&

$$

UPDATE.......SC
AVIATION.....SC
SHORT TERM...JVC
LONG TERM....HLO
MARINE.......JVC


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