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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 171945 CCA
AFDDTX

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

.SHORT TERM...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

.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.

&&

.AVIATION...ISSUED 1251 PM EDT FRI MAY 17 2013

//DISCUSSION...

HIGH PRESSURE TO THE NORTH AND AN ABUNDANCE OF LOW-LEVEL DRY AIR
WILL SUSTAIN LIGHT/STABLE EASTERLY FLOW AND VFR CONDITIONS THROUGH
THE TAF PERIOD. CONVECTIVE ACTIVITY OVER WISCONSIN IS NOT EXPECTED
TO SURVIVE ITS TREK EAST, ALTHOUGH PERIODS OF MID/HIGH CLOUDS ABOVE
5KFT CAN BE EXPECTED AS THE ASSOCIATED CLOUD COVER IS DRAWN
EASTWARD. FAR NORTH AND WEST LOCATIONS SUCH AS KMBS MAY SEE A BRIEF
PERIOD OF LIGHT RAINFALL OUT OF THIS ACTIVITY WITH NO RESTRICTION TO
VISIBILITY, WHILE REMAINING LOCATIONS WILL STAY DRY WITH PASSING MID
AND HIGH CLOUDS. IMPROVING MID-LEVEL MOISTURE QUALITY WILL BRING A
CHANCE FOR A CEILING BELOW 5KFT BY MORNING, BUT CONFIDENCE REMAINS
QUITE LOW AS STABILITY AND DRY AIR IN THE LOWEST 6KFT ARE EXPECTED
TO REMAIN LARGELY DOMINANT.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE IN CEILINGS BELOW 5KFT ON SATURDAY MORNING

&&

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

&&

$$

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


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