Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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685
FXUS63 KDTX 272326
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
726 PM EDT WED APR 27 2016


.AVIATION...

THE PRIMARY FORECAST ITEM REMAINS TIMING THE ONSET TO PRECIPITATION
AS THE INCREASE IN MIDLEVEL FRONTAL FORCING AND MOISTURE ADVECTION
LIFTS INTO SOUTHEASTERN MICHIGAN. THERE IS A GOOD CONSENSUS AMONGST
THE DETERMINISTIC AND HIRES MODELS (SANS HRRR) THAT SUPPORTS
SLOWER TIMING...AFTER 10Z FOR THE DETROIT TERMINALS. LINEAR
EXTRAPOLATION OF PRECIPITATION UPSTREAM AND HIRES SOLUTIONS DO
SUGGEST A GOOD AMOUNT OF VIRGA LATER TONIGHT AHEAD OF THE 10Z
HOUR...BUT DEPTH OF DRY AIR IN THE LOWER TROPOSPHERE WILL LIMIT
RAIN FROM REACHING THE GROUND. THERE IS A GOOD SIGNATURE IN THE RH
PROGS ON ISENTROPIC SURFACES THAT KEEPS SATURATION/CLOUD ABOVE
4000 FT AGL WITH SOME INCREASE IN RH DOWN LOW DUE TO THE ATTEMPT
AT SATURATING FROM RAIN FALLING INTO THE LAYER. AS IT STANDS...THE
MOISTURE PROFILE SUPPORTS VFR CIGS THROUGHOUT THE ENTIRE PERIOD.
THERE IS SOME QUESTION AS TO HOW LONG 3500 TO 5000 FT CIGS WILL
PERSIST ACROSS THE CENTRAL CWA...NORTH OF THE DETROIT TERMINALS
WITH STRETCHING DEFORMATION STALLING OVERHEAD. THIS PERSISTENCE OF
THE MVFR MAY ONLY BE ACCENTUATED AT THE END OF THE PERIOD BY THE
APPROACHING MIDLEVEL LOW CIRCULATION.

FOR DTW...RAIN AND MVFR VISIBILITIES ARE EXPECTED TO START IMPACTING
THE TERMINAL AFTER 10Z...WITH SHOWER EXPECTED TO LIFT NORTH BY THE
START OF THE AFTERNOON AS DRIER AIR MOVES IN AT THE MID LEVELS.
EASTERLY WINDS WILL CONTINUE THROUGH THE TAF PERIOD.


//DTW THRESHOLD PROBABILITIES...

* HIGH WITH CEILINGS FALLING BELOW 5000 FEET THURSDAY MORNING AND
  REMAINING THERE THROUGH 00Z.

&&

.PREV DISCUSSION...ISSUED 345 PM EDT WED APR 27 2016

DISCUSSION...

AMPLE SUNSHINE CAN BE EXPECTED THE REST OF THE AFTERNOON AND EARLY
EVENING UNDER CONTINUED LOW LEVEL DRY AIR ADVECTION ASSOCIATED WITH
THE SFC RIDGE EXTENDING FROM NRN ONTARIO INTO THE EASTERN GREAT
LAKES. A BAND OF SHOWERS NOW EXTENDS FROM IOWA INTO SRN INDIANA.
THESE ARE RESULTING FROM MID LEVEL FRONTAL FORCING ASSOCIATED WITH
THE UPPER LOW NOW CENTERED OVER ERN NEBRASKA. THE 12Z MODEL SUITE
ARE IN STRONG AGREEMENT IN SHOWING THE UPPER LOW EJECTING OUT INTO
THE WRN GREAT LAKES ON THURSDAY...THEN DAMPENING INTO AN OPEN WAVE
AS IT TRACKS ACROSS THE SRN GREAT LAKES LATE THURS NIGHT/EARLY FRI
MORNING. THIS WILL SLOWLY DRIVE THE MID LEVEL FRONT INTO FAR SW
LOWER MI TONIGHT...THEN ACROSS SE MI ON THURSDAY.

MODEL CROSS SECTIONS GENERALLY SUGGEST THE MID LEVEL FRONTAL
CIRCULATION SLOWLY LIFTING FROM SOUTH TO NORTH ACROSS THE FORECAST
AREA DURING THE DAY THURSDAY. SYSTEM RELATIVE ASCENT IS FORECAST TO
BE QUITE GOOD ALONG THE FRONTAL SLOPE. THE 12Z UPPER AIR ANALYSIS
COMBINED WITH THE LATEST WATER VAPOR LOOP SUPPORT AMPLE MOISTURE
WITHIN THE MID LEVEL FRONTAL SLOPE. WHILE THE NEAR STATIONARY HIGH
PRESSURE SYSTEM TO THE NORTH OF THE STATE WILL MAINTAIN A FEED OF
DRY AIR UNDER LOW LEVEL NE FLOW...THE DEGREE OF MOISTURE TRANSPORT
INTO THE MID LEVEL FRONT WILL BE ADEQUATE IN OVERCOMING THE DRY AIR.
THIS WILL SUPPORT FAIRLY HIGH CHANCES OF RAIN SHOWERS ON THURSDAY.
STEEPER MID LEVEL LAPSE SOUTH OF THE MID LEVEL FRONT WILL SUPPORT A
CHANCE FOR SOME ELEVATED THUNDERSTORMS FOR METRO DETROIT/ANN ARBOR
AND SOUTH THURS. WHILE MODEL SOLUTIONS GENERALLY AGREE THAT THE PUSH
OF ISENTROPIC ASCENT ALONG THE MID LEVEL FRONT WILL LIFT ALL THE WAY
INTO CENTRAL MI AND THE NRN THUMB THURS AFTERNOON...THE DEGREE OF
ELEVATED INSTABILITY FARTHER SOUTH RAISES CONCERNS THAT THE MORE
ACTIVE PORTION OF THE FRONT WILL REMAIN FOCUSED SOUTH. THUS JUST
CHANCE TYPE POPS WILL BE MAINTAIN ACROSS THE SAGINAW VALLEY AND
THUMB ON THURS...WITH HIGHER POPS TO THE SOUTH. MODEL SOUNDINGS
SUGGEST THE MID LEVEL FRONT WILL FRACTURE THURSDAY NIGHT. ALTHOUGH A
POOL OF RELATIVELY HIGH MID LEVEL MOISTURE WILL REMAIN IN PLACE
ACROSS SE MI INTO FRI MORNING. LIFT ASSOCIATED WITH THE REMNANT MID
LEVEL WAVE ALONG WITH THIS LINGERING MOISTURE WILL SUSTAIN A CHANCE
OF SHOWERS THURS NIGHT THROUGH THE FIRST OF THE DAY FRIDAY BEFORE
THE UPPER WAVE EXITS TO THE EAST. IF THE MID LEVEL WAVE REMAINS MORE
OF A CLOSED FEATURE...THERE IS A CHANCE FOR SOME MID LEVEL
DEFORMATION ENHANCEMENT WHICH WOULD SUPPORT A LITTLE MORE ORGANIZED
RAINFALL.

AN INCREASE IN THE NORTHEAST GRADIENT AND INCREASE IN MID/HIGH LEVEL
CLOUDS TONIGHT WILL LIMIT RADIATIONAL COOLING...SUPPORTING MINS IN
THE 30S AND 40S...WITH THE COLDEST READINGS ACROSS THE THUMB. THE
POTENTIAL FOR RAIN...AMPLE CLOUD COVER AND A DRY NORTHEAST SFC FLOW
SUGGEST ANOTHER COOL DAY WITH HIGHS LIKELY STUCK IN THE 40S ON
THURS. THE DEPARTURE OF THE UPPER WAVE TO THE EAST ON FRIDAY WILL
OFFER A POTENTIAL FOR SOME LATE DAY CLEARING. THIS WILL SUPPORT FCST
HIGHS INTO THE 50S DESPITE THE CONTINUED NORTHEAST FLOW.

THE MEDIUM RANGE MODEL SUITE SUGGEST ANOTHER INFLUX OF MID LEVEL
MOISTURE INTO THE SOUTHERN GREAT LAKES OVER THE WEEKEND. THIS IS
ASSOCIATED WITH ANOTHER DAMPENING MID LEVEL WAVE FORECAST TO LIFT
FROM THE HIGH PLAINS ACROSS THE OHIO VALLEY. THERE REMAINS
CONSIDERABLE DIFFERENCES WITH RESPECT TO TIMING THE BEST CHANCES FOR
RAIN. MOST PROBABLE TIMING BASED ON THE 12Z SUITE IS LATE SATURDAY
INTO EARLY SUNDAY. RELATIVELY COOL CONDITIONS FOR THE END OF
APRIL/EARLY MAY WILL PERSIST UNDER CONTINUED LIGHT NE FLOW THIS
WEEKEND INTO EARLY NEXT WEEK.

MARINE...

HIGH PRESSURE WILL REMAIN IN PLACE OVER THE NORTHERN GREAT LAKES AND
CANADA INTO THE WEEKEND. LOW PRESSURE SLOWLY TRACKING ACROSS THE
OHIO VALLEY WILL CAUSE NORTHEAST WINDS TO INCREASE LATE TONIGHT AND
THURSDAY. WHILE WIND SPEEDS ARE NOT EXPECTED TO BE PARTICULARLY
STRONG...THE PERSISTENT NORTHEAST WIND DIRECTION AND LONG FETCH OVER
THE LENGTH OF THE LAKES WILL CAUSE WAVE HEIGHTS TO BUILD OVER
SOUTHERN LAKE HURON AND WESTERN LAKE ERIE. WAVE HEIGHTS ARE EXPECTED
TO BUILD BETWEEN 3 AND 5 FEET IN THESE AREAS...AND SMALL CRAFT
ADVISORIES ARE IN EFFECT FROM EARLY THURSDAY MORNING INTO THURSDAY
EVENING. HIGH PRESSURE WILL EXPAND BACK INTO THE CENTRAL GREAT LAKES
THURSDAY NIGHT...ALLOWING WINDS AND WAVE HEIGHTS TO DECREASE. HIGH
PRESSURE WILL THEN REMAIN OVER THE REGION INTO SATURDAY...KEEPING
THE WEATHER QUIET.

THUNDERSTORMS WILL ALSO BE POSSIBLE OVER LAKE ST CLAIR AND WESTERN
LAKE ERIE THURSDAY AS THE AREA OF LOW PRESSURE TRACKS THROUGH THE
OHIO VALLEY. THESE STORMS ARE NOT EXPECTED TO BE SEVERE.

HYDROLOGY...

AN AREA OF RAINFALL WILL LIFT NORTHWARD THROUGH SOUTHEAST MICHIGAN
THURSDAY AS LOW PRESSURE TRACKS ACROSS THE OHIO VALLEY. TOTAL
RAINFALL HAS THE POTENTIAL TO REACH 0.25 INCHES FROM THE FLINT AREA
SOUTHWARD. MOST OF THE RAIN WILL FALL BEFORE 5 PM.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY FROM 8 AM TO 10 PM EDT THURSDAY FOR LHZ421-422-
     441-442.

LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY FROM 6 AM TO 5 PM EDT THURSDAY FOR LEZ444.

&&

$$

AVIATION.....CB
DISCUSSION...SC
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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