Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 310358
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1158 PM EDT SAT MAY 30 2015

.AVIATION...

CONCENTRATED AREAS OF HEAVY RAIN WILL CONTINUE TO EVOLVE OVER THE SE
MICHIGAN TERMINALS BUT WILL BE MORE INFREQUENT COMPARED TO EARLIER
IN THE NIGHT. COVERAGE AND INTENSITY WILL THEN BUILD UP TO A PEAK
AROUND SUNRISE AND LAST THROUGH THE MORNING...MAINLY FROM PTK TO THE
DTW CORRIDOR...AS A STRONG WAVE OF LOW PRESSURE SLIDES ALONG THE
FRONT STALLED OVER CENTRAL OHIO. THE POTENTIAL FOR THUNDERSTORMS HAS
SHIFTED SOUTH WITH THE FRONT BUT THE HEAVY RAIN WILL COMBINE WITH
GUSTY WIND FROM THE NORTHEAST TO EFFECTIVELY HAMPER AVIATION
OPERATIONS AT ALL LOCATIONS. THE WIND WILL BE ESPECIALLY GUSTY AT
MBS WHERE GUSTS COULD REACH 30 KNOTS OFF SAGINAW BAY. OTHERWISE...
CEILING AND VISIBILITY WILL VARY WIDELY FROM BORDERLINE MVFR/VFR AT
MBS TO IFR AT DTW. IMPROVED CEILING CONDITIONS WILL SPREAD NORTH TO
SOUTH OVER THE AREA AND RETURN ALL LOCATIONS TO VFR AS RAIN ENDS BY
SUNDAY EVENING.

FOR DTW... BORDERLINE MVFR/IFR RESTRICTION WILL PERSIST THROUGH THE
NIGHT AS WAVES OF RAIN SHOWERS MOVE IN FROM OHIO AND INDIANA. HEAVY
RAINFALL WILL BECOME MORE PERSISTENT TOWARD SUNRISE AND THROUGH THE
MORNING AS STRONG LOW PRESSURE SLIDES THROUGH CENTRAL OHIO.
LOCALIZED FLOODING REMAINS POSSIBLE. THE LOW PRESSURE SYSTEM WILL
ALSO SUPPORT STRONG NORTHEAST WIND AT THE TERMINAL THROUGH MUCH OF
THE DAY. IMPROVEMENT IN BOTH CEILING AND WIND CONDITIONS IS EXPECTED
DURING SUNDAY EVENING.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CEILING 5000 FEET OR LESS.

* LOW POTENTIAL FOR THUNDERSTORMS... BUT HIGH FOR HEAVY RAINFALL.

&&

.PREV DISCUSSION...ISSUED 1055 PM EDT SAT MAY 30 2015

UPDATE...

A FLOOD WATCH REMAINS IN EFFECT TONIGHT THROUGH SUNDAY AFTERNOON.
NO CHANGES ARE PLANNED TO THE COVERED AREA OR VALID TIME. THE
UPDATE WILL MAINLY FRESHEN TIMING AND MASSAGE 6 HOURLY QPF FOR THE
REST OF TONIGHT THROUGH SUNDAY MORNING WITH THE NEXT MAIN SURGE
OF RAINFALL SET TO OCCUR LATE TONIGHT THROUGH SUNDAY MORNING. AN
ADDITIONAL 1 TO 2 INCHES LOOKS REACHABLE WITH ABOUT 1 INCH
OCCURRING DURING THE 3 AM TO NOON TIME PERIOD.

THE LATE EVENING SURGE OF HIGHER INTENSITY SHOWERS IS BEING
SUPPORTED BY A SMALLER SCALE WAVE TRACKING ALONG THE ELEVATED
PORTION OF THE FRONT...BUT BELOW 850 MB. THERE IS ALSO A WELL
DEFINED REGION OF ISENTROPIC LIFT INTO THE ENTRANCE REGION OF A
LARGE 150 KNOT UPPER JET OVER EASTERN CANADA. EXPECT THIS WILL
PRODUCE ANOTHER 0.25-0.5 INCH OF RAINFALL IN SURGES DURING THE
EARLY OVERNIGHT.

THE LATE NIGHT THROUGH MORNING SURGE WILL BE DRIVEN BY
DEFORMATION WITHIN THE NORTH FLANK OF THE LARGER UPPER WAVE MOVING
IN FROM SOUTHERN ILLINOIS AND ALONG THE SURFACE TO 850 FRONTAL
ZONE. SHARS CHARACTERISTICS WITH THIS WAVE ARE NOT REALLY THAT
SUBTLE. THE MOISTURE SUPPLY AND STRONG DYNAMIC FORCING WILL
COMBINE WITH SLIGHTLY LESS THAN CONVECTIVE INSTABILITY TO PRODUCE
EFFICIENT RAINFALL TOTALS IN A BAND THROUGH THE FLOOD WATCH AREA
THAT WILL PROBABLY LAST INTO SUNDAY AFTERNOON. AS LONG AS THE
TROWAL DOES NOT BECOME TOO CONVECTIVE/CELLULAR...THEN COVERAGE AND
INTENSITY WILL BE GREAT ENOUGH TO WARRANT THE FLOOD WATCH.

PREV DISCUSSION...ISSUED 349 PM EDT SAT MAY 30 2015

SHORT TERM...TONIGHT

FLOOD WATCH CONTINUES.

HIGH MOISTURE CONTENT IN PLACE OVER SOUTHEAST MICHIGAN TODAY...AS
EVIDENCE BY 13 C DEW PT AT 850 MB (PER 12Z DTX SOUNDING)...SURFACE
DEW PTS IN MID/UPPER 60S...AND PW VALUES ABOVE 1.6 INCHES...PER SPC
MESOSCALE ANALYSIS. SURFACE COLD FRONT HAS PUSHED TOWARD THE OHIO
BORDER THIS AFTERNOON...BUT HAS BEEN LOSING IT SOUTHWARD MOMENTUM.
THERE WAS RIPPLE/THUNDERSTORM COMPLEX WHICH RODE THE FRONT EARLY
THIS AFTERNOON ALONG THE M-59 CORRIDOR. DTE OUTAGE MAP SUGGESTS A
FEW POWER OUTAGES DUE TO WIND DAMAGE. RAINFALL TOTALS FROM THIS
COMPLEX RANGED FROM HALF AN INCH TO ONE AND HALF INCHES IN A VERY
SHORT PERIOD. HIGH WET BULB ZERO HEIGHT CONDUCIVE TO TORRENTIAL
RAINFALL...WITH STILL ENOUGH INSTABILITY AROUND ACROSS THE SOUTH
HALF OF THE CWA TO SUPPORT TORRENTIAL PRODUCING THUNDERSTORMS INTO
EARLY EVENING HOURS. ATTENTION TONIGHT TURNS TO THE WELL DEFINED
CIRCULATION OVER EXTREME SOUTHEAST MISSOURI LIFTING NORTHEAST INTO
THE CENTRAL OHIO VALLEY TONIGHT. THIS FEATURE IS EXPECTED TO SUPPORT
BLOSSOMING RAIN SHIELD TONIGHT...DESPITE THE LOSS OF DAYTIME
HEATING...AS LOW/MID LEVEL FGEN RAMPS UP. INCREASING PRESSURE
GRADIENT AS HIGH PRESSURE OVER SOUTH CENTRAL CANADA BEGINS TO BUILD
IN WHILE SURFACE LOW TRACKS INTO OHIO VALLEY...SUPPORTING GUSTY
NORTHEAST WINDS OF 25 TO 30 MPH...LIKELY HIGHER DOWNWIND OF SAGINAW
BAY. ENOUGH LOW LEVEL DRYING IS EXPECTED NORTH OF I-69 TO SUPPORT
SHOWERS TAPERING OFF.

IT WAS DECIDED TO ISSUE A FLOOD WATCH EARLIER TODAY TO COVER
LOCALIZED FLASHY TYPE RAINFALL LATE THIS AFTERNOON...BUT ALSO TO
CAPTURE THE LONG DURATION RAINFALL TONIGHT INTO SUNDAY...AS STORM
TOTALS SHOULD RESIDE IN THE 1 TO 3 RANGE ACROSS A WIDE AREA....WITH
POTENTIAL FOR LOCALIZED HIGHER AMOUNTS. FORTUNATELY...RAINFALL HAS
BEEN LAGGING OVER THE PAST WEEK OR TWO LEADING INTO THIS EVENT...AND
6 HOUR FLASH FLOOD GUIDANCE IS RUNNING ABOVE 2 INCHES. THUS...THIS
LOOKS TO BE MORE OF URBAN TYPE FLOODING IF THERE ARE ANY ISSUES.

GUIDANCE TEMPS SUGGESTS TEMPERATURES FALLING INTO THE MID 40S TO
LOWER 50S SOUTH AS THE STIFF NORTHEAST WINDS OFF LAKE HURON AND LOW
LEVEL COLD ADVECTION TAKES HOLD.

LONG TERM...SUNDAY THROUGH FRIDAY

MAIN HEIGHT FALLS ASSOCIATED WITH A DYNAMIC WAVE LIFTING THROUGH
SOUTHERN ONTARIO WILL LARGELY HOLD TO THE NORTH...LEAVING THE
DAMPENING MID LEVEL TROUGH EXTENSION TO WORK INTO SE MICHIGAN OVER
THE NEXT 24 HOURS.  THIS EVOLUTION WILL HOLD THE TRAILING MID LEVEL
FRONTAL SLOPE FIRMLY ACROSS A GOOD PORTION OF SOUTHEAST MICHIGAN ON
SUNDAY.  STRONG MID LEVEL DYNAMIC RESPONSE ALREADY UNDERWAY BY EARLY
SUNDAY...ELLICITED BY INTERACTION BETWEEN THIS TROUGH AND A
STRONGER INBOUND SOUTHERN STREAM WAVE NOW LIFTING OUT OF MISSOURI.
PROLONGED STRONG MID LEVEL FRONTAL FORCING WITHIN FAVORABLE RIGHT
ENTRANCE REGION UPPER JET SUPPORT AND INCREASING DEFORMATION
CONTINUES TO LEND SUPPORT TOWARD SEEING AN EXTENDED PERIOD OF
WIDESPREAD RAINFALL IMPACTING A SIZABLE PORTION OF SOUTHEAST
MICHIGAN /OHIO BORDER TO I-69 CORRIDOR/ RIGHT THROUGH THE AFTERNOON.
THE EXISTING DEEP LAYER MOISTURE PROFILE /PW AT 1.5"...10C 850 MB
DEWPTS/ AND OVERALL MAGNITUDE AND LONGEVITY OF THIS FORCING FIELD
WILL LEAD TO SOME HIGHER END RAINFALL AMOUNTS ON THE ORDER OF AN
INCH THROUGH THE DAYLIGHT HOURS.  COLUMN CARRIES A HIGHER DEGREE OF
STABILITY RELATIVE TO TODAY/TONIGHT...SUGGESTING A LIMITED
CONVECTIVE ELEMENT TO THIS PRECIPITATION.  FLOOD WATCH NOW IN PLACE
THROUGH THE AFTERNOON ON SUNDAY ALONG AND SOUTH OF I-69 TO HIGHLIGHT
THE POSSIBLE ADDITIVE IMPACT OF THIS RAINFALL ON TOP OF THE MULTIPLE
ROUNDS EXPECTED THROUGH TONIGHT.

THE EXTENSIVE MOISTURE AND A STRENGTHENING NORTHEAST LOW LEVEL
GRADIENT WILL KEEP ANY DIURNAL TEMPERATURE RECOVERY TO A EXTREME
MINIMUM ON SUNDAY.  925 MB TEMPERATURE REMAIN PROJECTED TO HOLD AT
THE 2 TO 4C LEVEL THROUGH THE DAY.  THIS SUGGESTS TEMPERATURE
READINGS WILL STRUGGLE TO CLIMB MUCH ABOVE THE LOWER 50S...WITH SOME
LOCALES OVER THE THUMB AND TRI-CITIES IMMEDIATELY DOWNSTREAM OF THE
COLDER LAKE WATERS HOLDING IN THE 40S.  THIS WILL BE A GOOD 20 TO 25
DEGREES BELOW NORMAL FOR THE LAST DAY OF MAY.  THE INCREASING WIND
FIELD WILL CONTRIBUTE A GUST COMPONENT TO THIS RAW LOOKING
DAY...GUSTS INTO THE 20 TO 25 MPH RANGE COMMON.  SOME STRONGER GUSTS
POSSIBLE INTO THE TRI-CITIES GIVEN THE DIRECT FLOW OFF SAGINAW BAY.

SLOW EXIT OF THE DEFORMATION INTO SUNDAY EVENING WITH AN ASSOCIATED
REDUCTION IN SHOWER COVERAGE ACROSS SOUTHEAST SECTIONS THROUGH THIS
TIME.  CLEARING OF LOW LEVEL MOISTURE LIKELY AN EVEN SLOWER
PROCESS...EXPANSION OF DRIER AIR FROM THE NORTH TAKING A GOOD
PORTION OF THE NIGHT TO MAKE BETTER INROADS.  WITH THAT...ENOUGH
MOISTURE TUCKED INTO THE INVERSION TO SUGGEST SOME PERSISTENT
STRATUS/STRATOCU MAY LINGER INTO MONDAY /PARTICULARLY SOUTH/ WITH
ENSUING DAYTIME MIXING ON MONDAY THEN WORKING TO SCOUR OUT THIS
MOISTURE.  REGARDLESS OF THE CLOUD COVERAGE...SE MICHIGAN WILL
REMAIN UNDER THE INFLUENCE OF COOL NORTHEAST FLOW SOUTH OF HIGH
PRESSURE BUILDING ACROSS ONTARIO ON MONDAY.  TEMPERATURES WILL
CONTINUE TO RUN WELL BELOW NORMAL...READINGS LARGELY MID 50S TO
LOWER 60S.

WARMING TREND IS ON TAP TUESDAY THROUGH FRIDAY AS UPPER LEVEL
HEIGHTS RISE IN THE WAKE OF THE EXITING UPPER TROUGH. HIGH PRESSURE
LOOKS TO MAINTAIN DRY CONDITIONS THROUGH AT LEAST THURSDAY. LOW
CHANCE POPS FRIDAY/FRIDAY NIGHT TO ACCOUNT FOR EURO DEPICTION OF
WELL-DEFINED SHORTWAVE MOVING THROUGH THE WESTERLIES.

MARINE...

THUNDERSTORMS WILL REMAIN POSSIBLE THROUGH TONIGHT ACROSS LAKE ST
CLAIR AND THE MICHIGAN WATER OF LAKE ERIE AS A COLD FRONT LIFTS
ACROSS THE REGION.  A POST-FRONTAL NORTHWEST WIND THIS EVENING WILL
TRANSITION TO NORTHEASTERLY AND STRENGTHEN TONIGHT AS LOW PRESSURE
TRACKS THROUGH THE OHIO VALLEY.  THE COMBINATION OF GUSTY
WINDS...ONSHORE FLOW AND CORRESPONDING BUILDING WAVE HEIGHTS WILL
RESULT IN SMALL CRAFT CONDITIONS AT ALL NEARSHORE LOCATIONS.  THE
POTENTIAL DOES EXIST FOR A PERIOD OF GALES TO EMERGE LATE TONIGHT
INTO SUNDAY ACROSS SAGINAW BAY GIVEN THE FAVORABLY LONG FETCH ON
NORTHEAST FLOW.  THIS CORRIDOR WILL BE UPGRADED TO A WARNING.
WINDS AND WAVES WILL DIMINISH SUN NIGHT INTO MONDAY AS THE LOW
DEPARTS TO THE NORTHEAST AND HIGH PRESSURE BUILDS INTO THE REGION.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...FLOOD WATCH THROUGH SUNDAY AFTERNOON FOR MIZ055-060>063-068>070-075-
     076-082-083.

LAKE HURON...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT SUNDAY NIGHT FOR LHZ441>443.

     GALE WARNING UNTIL 8 PM EDT SUNDAY FOR LHZ421-422.

LAKE ST CLAIR...SMALL CRAFT ADVISORY UNTIL 8 PM EDT SUNDAY FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT SUNDAY FOR LEZ444.

&&

$$

AVIATION.....BT
UPDATE.......BT
SHORT TERM...SF
LONG TERM....MR/DT
MARINE.......MR


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