Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 110829
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
429 AM EDT FRI APR 11 2014

.SHORT TERM...TODAY AND TONIGHT

A VERY WEAK SURFACE HIGH WILL DRIFT ACROSS SOUTHEASTERN MICHIGAN
THIS MORNING. POSITIONING AND TIMING OF THE WEAK ANTICYCLONE
SUGGESTS THAT FORCING IS PURELY THAT OF LOW LEVEL COLD AIR ADVECTION
THAT OCCURRED BEHIND THE DEPARTING FRONT. THE SURFACE HIGH AND 300MB
RIDGE AXIS WILL EVENTUALLY PASS EAST OF THE CWA TODAY WHICH WILL
ALLOW SOUTHERLY FLOW TO BUILD BACK INTO THE CWA. OVERALL WIND
POTENTIAL IS A DIFFICULT FORECAST. THE REASON IS MIXING DEPTHS ARE
EXPECTED TO REACH 6000 FT. ON THE OTHER HAND...RAW MODEL OUTPUT
ALONG WITH THE EXPECTED WEAK SURFACE PRESSURE GRADIENT SUGGESTS
WINDS WILL BE HARD PRESSED TO REACH 10 KNOTS. THE INBOUND HIGH CLOUD
NOW ADVANCING THROUGH WISCONSIN IS ANOTHER COMPLICATING MATTER. NOT
SEEING ENOUGH TO GO AGAINST GUIDANCE AND WILL FORECAST 10 TO 15 MPH
WITH SLIGHTLY HIGHER VALUES FOR THE SAGINAW VALLEY. LOOKING FOR
OVERACHIEVING HEIGHT TEMPERATURES TODAY WITH THE HIGH MIXING HEIGHTS
AND MODEL LOW BIAS. SURFACE HIGHS ARE EXPECTED TO REACH THE LOW TO
MIDDLE 60S.

A DEEPER TROUGH AXIS 500-300MB WILL EVENTUALLY PASS OVER THE CENTRAL
GREAT LAKES BY THIS EVENING. A SHORTWAVE COLLECTED WITHIN THE MID TO
UPPER LEVEL WINDSHIFT IS EXPECTED TO TRACK DIRECTLY THROUGH THE CWA
BETWEEN 00-06Z. MODELS HAVE BEEN ADVERTISING SOME LIGHT QPF
POTENTIAL PRIMARILY WITH THE CVA AND SOME WARM AIR ADVECTION ALOFT.
SOUNDINGS ARE NOT SUPPORTIVE...WITH A TOTAL LACK OF MOISTURE AND
ACTUALLY LOWERING SUBSIDENCE IN THE 10-19 KFT AGL LAYER. MODELS
TYPICALLY UNDERACHIEVE IN NOCTURNAL WAA ALOFT SCENARIOS AND WILL KEEP
THE SLIGHT CHANCE GOING FOR THE SAGINAW VALLEY. IN THIS
CASE...OVERACHIEVING WOULD ONLY BE MEASURING A FEW HUNDREDTHS.

&&

.LONG TERM...SATURDAY THROUGH THURSDAY

AN APPROACHING LOW PRESSURE SYSTEM WILL BRING INCREASING CHANCES FOR
RAIN DURING THE WEEKEND AS A WARM FRONT LIFTS NORTH THROUGH
SOUTHEAST MICHIGAN ON SATURDAY. AS THE LOW APPROACHES FROM THE WEST
THIS BOUNDARY WILL SERVE AS THE FOCUS FOR HEAVY RAIN SHOWERS DURING
THE WEEKEND AS THE WARM MOIST AIR BRINGS THE CHANCE FOR
THUNDERSTORMS ALONG WITH THE CHANCE FOR RAIN SHOWERS WITH THE AREA
WELL IN THE WARM SECTOR. ANOTHER LOW PRESSURE SYSTEM TRACKING
THROUGH THE GREAT LAKES ON MONDAY WILL BRING ANOTHER ROUND OF HEAVY
RAIN ON MONDAY WITH COLD AIR FILTERING IN BEHIND THE DEPARTING LOW
MONDAY NIGHT AND TUESDAY. THESE MULTIPLE ROUNDS OF HEAVY RAIN WILL
BRING FLOODING CONCERNS TO SOUTHEAST MICHIGAN...HOWEVER THE FLOODING
WILL BE DEPENDENT ON THESE MULTIPLE ROUNDS. IF THE FIRST ROUND DOES
NOT MATERIALIZE OR THE SECOND ROUND IS FURTHER WEST FLOODING WILL BE
AT A MINIMUM...THEREFORE WILL WAIT TO SEE HOW THESE ROUNDS SET UP
BEFORE THINKING ABOUT ANY HEADLINES FOR FLOODING.

BEHIND THE FRONT WE WILL COOL FROM THE 60S AND 70S BACK INTO THE 40S
TUESDAY AND WEDNESDAY AS HIGH PRESSURE BRINGS A STRETCH OF QUIET
WEATHER BACK TO THE CENTRAL GREAT LAKES. TEMPERATURES WARM UP A BIT
ON THURSDAY AS ANOTHER WARM FRONT LIFTS THROUGH THE CENTRAL GREAT
LAKES. THERE IS QUITE A BIT OF DIFFERENCE BETWEEN THE MODELS ON
THURSDAY AS THE GFS FOCUSES THE WARM FRONT FURTHER SOUTH WITH RAIN
SHOWERS WHILE THE ECMWF LIFTS THE FRONT FARTHER NORTH WITH SOUTHEAST
MICHIGAN IN THE WARM SECTOR AND DRY. GIVEN THE DIFFICULTIES OF
LIFTING A WARM FRONT THAT FAR NORTH WITH A STILL COOL GREAT LAKES
WILL PUT IN A SLIGHT CHANCE WITH THIS FORECAST ISSUANCE.

&&

.MARINE...

LIGHT FLOW WILL RULE TODAY AND TONIGHT AS A WARM FRONT LIFTS THROUGH
THE CENTRAL GREAT LAKES TONIGHT. THIS FRONT WILL SERVE AS A FOCUS
FOR SHOWERS AND THUNDERSTORMS DURING THE WEEKEND AS MODERATE
SOUTHERLY WINDS TURN SOUTHWESTERLY ON SATURDAY NIGHT. MODERATE
SOUTHERLY WINDS WILL RETURN SUNDAY NIGHT BEFORE TURNING
NORTHWESTERLY MONDAY AND MONDAY NIGHT BEHIND A COLD FRONT.

&&

.AVIATION...ISSUED 157 AM EDT FRI APR 11 2014

//DISCUSSION...

WEAK FLOW AND CLEAR SKIES IN THE POST FRONTAL ENVIRONMENT HAS LED TO
SOME FOG DEVELOPMENT OVER PORTIONS OF NORTHERN INDIANA AND NORTHERN
OHIO. NEAR SURFACE SATURATION HAS OCCURRED WHERE SURFACE DEWPOINTS
HAVE HELD ON IN THE UPPER 30S AND LOW 40S. CERTAINLY PLAUSIBLE THAT
FOG MAY CREEP NORTHWARD ACROSS THE BORDER INTO FAR SOUTHEASTERN
MICHIGAN.

WEAK SURFACE HIGH PRESSURE AND NEUTRAL TEMPERATURE ADVECTION IN THE
LOWER TROPOSPHERE WILL LEAD TO VFR CONDITIONS THROUGHOUT THE PERIOD.
HIGH CLOUD NOW ADVANCING THROUGH WISCONSIN WILL ARRIVE FOR THE
MORNING HOURS. THIS CLOUD FORCED BY WARM AIR ALOFT IS THEN EXPECTED
TO HANG AROUND FOR MUCH OF THE DAY. THE ATMOSPHERE IS EXPECTED TO
BECOME WELL MIXED THROUGH 6 KFT AGL BY THIS AFTERNOON. SOME
UNCERTAINTY EXISTS WITH REGARDS TO WIND GUST POTENTIAL...BUT ATTM
LACK OF A PRESSURE GRADIENT SUGGESTS UP TO 10 KNOTS.

FOR DTW...INTRODUCED A PERIOD THIS MORNING OF MVFR BR. CONFIDENCE IN
THE OCCURRENCE IS LOW.

//DTW THRESHOLD THREATS...

* NONE

&&

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

&&

$$

SHORT TERM...CB
LONG TERM....KURIMSKI
MARINE.......KURIMSKI
AVIATION.....CB


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






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