Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 010429
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1229 AM EDT SUN MAY 1 2016


.AVIATION...

LATEST REGIONAL MOSAIC TRENDS SUGGESTS THE HEIGHT OF THE RAINFALL
EVENT IS NOW AT PRESS TIME. THE COMBINATION OF THE LOW LEVEL JET
AXIS VEERING ACROSS THE STATE AND RIGHT ENTRANCE REGION DYNAMICS
PULLING EASTWARD OUT OF ONTARIO WILL CAUSE THE MAIN SWATH OF RAIN TO
LIFT NORTH AND EAST OUT OF SOUTHEASTERN MICHIGAN WITH TIME. WILL SEE
A TRANSITION TO DRIZZLE WITH THE DRY SLOT LIFTING INTO THE STATE.
THERE IS NOW INCREASING CONCERNS FOR LIFR TO POSSIBLY EVEN VLIFR
CEILING HEIGHTS AS A POSSIBILITY. CONFIDENCE IS LOW ATTM ON CEILING
HEIGHTS BELOW 500 FT AGL. THE BAND WILL EVENTUALLY LIFT NORTH OF
SAGINAW BAY DURING THE MID MORNING HOURS. LACK OF ANY POSITIVE
SURFACE PRESSURE TENDENCIES WILL LIMIT ADVECTIONS ON SUNDAY. THIS
WILL KEEP A MVFR CEILING IN PLACE OVER THE STATE. TIMING FOR THE
ONSET OF THE NEXT RAINFALL EVENT IS EXPECTED TO BE DURING THE MID
EVENING HOURS SUNDAY.


FOR DTW...WATCHING FOR THE POSSIBILITY OF VLIFR CONDITIONS IN LOW
CIG HEIGHTS. ATTM...CONFDIENCE REMAINS LOW. BACK EDGE OF THE
PRECIPITATION SHIELD IS NOW WORKING TOWARDS DETROIT. EXPECTING A
TRANSITION TO DRIZZLE WITH THE DRY SLOT LIFTING OVERHEAD. MVFR CIGS
TO PERSIST ALL OF SUNDAY WITH RAINFALL LIFTING BACK TOWARDS DETROIT
BY/AROUND 05Z SUNDAY EVENING.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CIGS BELOW 5000 FT AGL THROUGHOUT THE ENTIRE TAF
  FORECAST PERIOD.

* LOW FOR A CEILIGN HEIGHT OF AT/LESS THAN 200 FT AGL.

* VERY LOW FOR A THUNDERSTORM TO IMPACT DTW.

&&

.PREV DISCUSSION...ISSUED 1021 PM EDT SAT APR 30 2016

UPDATE...

THERE IS A CLASSIC PRESENTATION OF OVERRUNNING/ELEVATED WARM
FRONTAL DYNAMIC PRECIPITATION ON REGIONAL REFLECTIVITY MOSAIC
THIS EVENING OVER MUCH IF NOT ALL OF THE UPPER MIDWEST/GREAT LAKES.
THE WIDE BAND OF RAIN HAS NOW FULLY ENCOMPASSED THE CWA WITH -RA
REPORTING RIGHT THROUGH THE THUMB AND SAGINAW BAY. HIGHER Z ECHOES
AND HEAVIER RAIN RATES ARE IN PLACE OVER SW MICHIGAN. THIS
ACTIVITY IS NEAR A PSEUDO-TRIPLE POINT THAT IS BEING FORCED
DIRECTLY BY THE NOSE OF THE LOW LEVEL JET. ADDITIONALLY...THERE
IS SOME PHASING OF THIS MIDLEVEL FORCING WITH STRONG UPPER LEVEL
RIGHT ENTRANCE REGION DYNAMICS TO THE UPPER LEVEL JET AXIS OVER
PORTIONS OF ONTARIO/QUEBEC. MODELS SHOW THE LOW
LEVEL JET CYCLING/STRENGTHENING THIS EVENING WHILE IT
VEERS/ROTATES ACROSS THE CWA. IT IS THIS SPECIFIC FORCING THAT IS
CURRENTLY INDUCING A FRONTAL WAVE RESPONSE IN ADDITION TO THE LOW
LEVEL JET.

THE NET RESULT IS FOR RAINFALL RATES TO INCREASE FOR A
PERIOD THIS EVENING AS THE TRIPLE POINT AND -DIV CENTROID WORKS
ITSELF ACROSS THE AREA. IMMEDIATELY TO THE SW...OVER OVER NORTHERN
INDIANA AND SOUTHERN LAKE MICHIGAN IS A DRY SLOT THAT WILL LIFT
NORTHWARD FOR LATER TONIGHT. THE MODELS ARE ALL VERY STRONG WITH
THIS DRY SLOT. INTRODUCED A DRIZZLE MENTION FOR AREAS AFTER 09Z
TONIGHT. ALL IN ALL...THE FORECAST HAS BEEN/IS/REMAINS IN GREAT
SHAPE.

PREV DISCUSSION...ISSUED 323 PM EDT SAT APR 30 2016

DISCUSSION...

A GOOD AMOUNT OF MOISTURE POOLED UP OVER WESTERN OHIO VALLEY (12Z
KILX SOUNDING INDICATED 9 C DEW PT AT 850 MB) WILL CONTINUE TO
PROGRESS OFF TO THE NORTHEAST INTO SOUTHERN LOWER MICHIGAN EARLY
THIS EVENING. SOLID UPPER LEVEL DIVERGENCE/PV ADVECTION/HEIGHT FALLS
AND LOW LEVEL MOISTURE TRANSPORT/ISENTROPIC ASCENT TO SUPPORT
WIDESPREAD RAINFALL...WITH PW VALUES REACHING 1 INCH ALONG/SOUTH OF
I-69 CORRIDOR...SUPPORTIVE OF AMOUNTS REACHING AND LIKELY ECLIPSING
HALF AN INCH TONIGHT...ESPECIALLY WITH ANY CONVECTIVE ELEMENTS...AS
SHOWALTER INDEX PROGGED TO DROP BELOW ZERO JUST PAST THE SOUTHERN
MICHIGAN BORDER...BUT LITTLE IN THE WAY OF ACTUAL CAPE...SHOULD BE
HARD PRESSED TO SEE ANY THUNDERSTORMS. MID LEVEL LAPSE RATE DO
BECOME STEEP ON SUNDAY (7+ C/KM)...BUT MAINLY DUE TO THE DRYING
OCCURRING IN THE MID LEVELS...AND DON`T EXPECT MUCH SHOWER ACTIVITY
DURING THE DAY. VERY TIGHT LOW LEVEL BAROCLINIC ZONES IN PLACE (850
MB TEMPS OF 1 C OVER SAGINAW TO 10 C NEAR OHIO BORDER PER 12Z
EURO)...AND EVEN WOULD NORTHEAST SURFACE WINDS...COULD SEE FAR SOUTH
REACH AND EXCEED 60 DEGREES WITH PREVIOUSLY MENTIONED DRYING/LULL IN
ACTIVITY.

THE 00Z MODEL SUITE INDICATED A FARTHER NORTH SURFACE/LOW LEVEL
FRONTAL BOUNDARY PLACEMENT TOMORROW...WHICH LOOKS TO SET US UP FOR
ANOTHER ROUND OF RAINFALL SUNDAY EVENING....AS SECOND WAVE AND
LEFTOVER UPPER LEVEL CIRCULATION FROM THE CENTRAL PLAINS SLIDES
EAST...PROVIDING GOOD UPPER LEVEL DIVERGENCE/DEFORMATION AXIS WHICH
LOOKS TO CLIP AREAS SOUTH OF I-69 CORRIDOR. THE 12Z MODEL
NAM/GFS/CANADIAN HAVE SHIFTED BACK TO THE SOUTH A BIT...BUT 12Z EURO
REMAINS MOST AGRESSIVE/ADAMANT...AND FEEL CONFIDENT TO GO LIKELY
POPS SOUTH OF I-69 TO CATEGORICAL NEAR THE OHIO BORDER. SUBSTANTIAL
COLD ADVECTION TO TAKE PLACE BEHIND THE MERGING NORTHERN STREAM
TROUGH AXIS PASSAGE MONDAY MORNING...WITH 850 MB TEMPS STILL PROGGED
TO FALL TO ZERO...OR EVEN SLIGHTLY COLDER. NORTHEAST FLOW OFF LAKE
HURON AND EXPECTED CLOUD COVER ON MONDAY COULD PROVE SUFFICIENT TO
KEEP MAXES UNDER 60 DEGREES. IF LOW CLOUDS DISSIPATE MONDAY
NIGHT...FROST CONCERNS WILL RETURN AS TEMPERATURES POTENTIALLY
FALL BACK INTO THE 30S WITH CALM/NEARLY CALM WINDS.

WEAK AND FRAGILE HIGH PRESSURE WILL LINGER OVER LOWER MICHIGAN
TUESDAY BETWEEN LOW PRESSURE OVER THE OHIO VALLEY AND THE NEXT COLD
FRONT PUSHING THROUGH NORTHERN ONTARIO. EXPECT THERE WILL AT LEAST
BE CLOUDS AROUND WITH A PORTION OF THE UPPER TROUGH SUPPORTING THE
OHIO VALLEY SURFACE TROUGH. THIS WILL PRODUCE TEMPERATURES RIGHT
AROUND NORMAL FOR EARLY MAY FOR ONE MORE DAY BEFORE THE ONTARIO
FRONT MOVES THROUGH THE GREAT LAKES WEDNESDAY. THERE IS INCREASING
EVIDENCE IN GLOBAL MODEL SOLUTIONS THAT SUPPORT CLOSING OFF THE
ASSOCIATED UPPER WAVE BY THURSDAY WHICH WILL KEEP SHOWERS AND COOLER
TEMPERATURES OVER THE REGION POSSIBLY EVEN INTO FRIDAY. THIS IS AN
UNPLEASANT WEATHER SCENARIO FOR THE SECOND HALF OF NEXT WEEK
HIGHLIGHTED BY TEMPERATURES THAT WILL STRUGGLE TO REACH GUIDANCE
VALUES IN THE LOWER TO MID 50S...ESPECIALLY FOR THURSDAY. THESE
TYPES OF CLOSED SYSTEMS OFTEN END UP BEING SLOWER TO EVOLVE THAN
MODEL FORECASTS WHICH ALSO POINTS TO A SHAKY START TO NEXT WEEKEND
AS WELL.

MARINE...

WINDS WILL INCREASE FROM THE NORTHEAST TONIGHT AS LOW PRESSURE
PASSES THROUGH THE OHIO VALLEY...AND REMAIN GUSTY OVER LAKE HURON
TOMORROW AS THE LOW MOVES INTO THE EASTERN GREAT LAKES. SMALL CRAFT
ADVISORIES REMAIN IN EFFECT LATE TONIGHT THROUGH SUNDAY FOR THE LAKE
HURON NEARSHORE WATERS...INCLUDING SAGINAW BAY...AS PERSISTENT AND
STRONG FLOW ACROSS THE LAKE ALLOWS WAVE HEIGHTS TO BUILD BETWEEN 4
AND 8 FEET. GUSTS AROUND 25 KNOTS WILL ALSO DEVELOP TONIGHT AND
CONTINUE INTO SUNDAY BEFORE LOW PRESSURE MOVES EAST AND SPEEDS
DECREASE. THIS WILL ALSO ALLOW LARGE WAVES TO SUBSIDE DURING THE
LATE EVENING. A VERY LARGE DOME OF HIGH PRESSURE CENTERED OVER THE
CENTRAL PLAINS WILL THEN KEEP WINDS FAIRLY LIGHT MONDAY INTO TUESDAY.

A BRIEF PERIOD OF GUSTY EAST-NORTHEAST WINDS IS ALSO EXPECTED THIS
EVENING...BETWEEN 6 PM AND 11 PM...OVER WESTERN LAKE ERIE AS THE
CENTER OF LOW PRESSURE DRAWS CLOSER. GUSTS MAY APPROACH 25 KNOTS FOR
SEVERAL HOURS BEFORE WINDS WEAKEN AND FINALLY TURN LIGHT FROM THE
NORTH BEFORE SUNRISE.

HYDROLOGY...

LOW PRESSURE PASSING THROUGH THE OHIO VALLEY WILL SPREAD WIDESPREAD
AND STEADY RAINFALL INTO SOUTHEAST MICHIGAN LATE THIS AFTERNOON
THROUGH TONIGHT...WITH SHOWERS THEN LINGERING THROUGH SUNDAY. THE
HEAVIEST RAIN LOOKS TO FALL BETWEEN 9 PM AND 4 AM TONIGHT. TOTAL
RAINFALL THROUGH 2 PM SUNDAY LOOKS TO EXCEED 0.25 INCHES ACROSS ALL
OF SOUTHEAST MICHIGAN...WITH TOTALS BETWEEN 0.75 AND 1.00 INCH SOUTH
OF THE M-59 CORRIDOR. THIS RAINFALL WILL PROMPT RISES ON AREA
RIVERS...CREEKS...AND STREAMS...BUT FLOODING IS NOT EXPECTED.

ANOTHER QUICK ROUND OF RAINFALL IS EXPECTED SUNDAY NIGHT ACROSS FAR
SOUTHERN MICHIGAN. LOCATIONS ALONG AND SOUTH OF I-94 MAY PICK UP AN
ADDITIONAL 0.25 INCHES OF RAIN.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY FROM 5 AM EARLY THIS MORNING TO 8 PM EDT THIS
     EVENING FOR LHZ421-422-441>443.

LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

AVIATION.....JVC
UPDATE.......CB
DISCUSSION...SF/BT
MARINE.......HLO
HYDROLOGY....HLO


YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).



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