Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 131941
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
341 PM EDT SAT SEP 13 2014

.SHORT TERM...THIS EVENING AND TONIGHT

MID/LATE AUTUMN MAINTAINS A FIRM GRASP ON THE CENTRAL GREAT LAKES
REGION...WITH TEMPERATURES STRUGGLING IN THE 50S. MOISTURE...
MANIFEST IN A STOUT COLD SEASON STRATOCU LAYER...REMAINS WELL
ENTRENCHED BENEATH A SUBSIDENCE REINFORCED INVERSION AROUND 4KFT.
THE HIGH DEGREE OF ABSOLUTE MOISTURE WILL STILL TAKE SOME TIME TO
DISPERSE AND ERODE THROUGH CLOUD LAYER MIXING PROCESSES. BRISK
NORTHWEST WINDS WILL SLOW AS THE PRESSURE GRADIENT RELAXES THROUGH
THE EVENING.

EXPECTATION IS FOR SKIES TO TRY TO CLEAR FOR A TIME WINDOW FROM LATE
EVENING INTO THE OVERNIGHT HOURS. HOWEVER...LATEST GUIDANCE SUITE
/ESPECIALLY 13.12 NAM AND MORE SO THE 13.18 RAP/ OFFERS PLENTY OF
DOUBT THAT RESIDUAL LOW-LEVEL MOISTURE /BOTH 925&850MB/ WILL
DISAPPEAR. THIS NEAR SURFACE MOISTURE COUPLED WITH ENCROACHING
UPSTREAM HIGH CLOUDS WILL EFFECTIVELY REDUCE THE NET OUTGOING
RADIATIVE FLUX ACROSS SOUTHEAST MICHIGAN. IT WILL CERTAINLY BE A
CHILLY NIGHT FOR MID-SEPTEMBER /ESPECIALLY ACROSS INTERIOR PORTIONS
OF THE THUMB/. HOWEVER...NOT EXPECTING WIDESPREAD SURFACE FROST
FORMATION GIVEN THE QUESTIONABLE DURATION OF FORCING...MOIST GROUND
AND SURFACE LAYER FROM LAST NIGHT/S RAIN...HIGH GREEN FRACTION AND
SOIL TEMPERATURES STILL AROUND 60F. WILL OFFER A DEPICTION MORE IN
LINE WITH RAW GUIDANCE SOURCES THAN THE MUCH COOLER MOS VALUES.

&&

.LONG TERM...SUNDAY THROUGH FRIDAY

BROAD TROUGHING OVER THE MIDWEST AND GREAT LAKES WILL HOLD THROUGH
MID WEEK WITH A REINFORCING SHORTWAVE MONDAY EVENING. HEIGHTS WILL
BEGIN TO CLIMB OVER THE AREA LATER IN THE WEEK AS NORTHERN STREAM
JET RETREATS INTO CANADA ALLOW WEST COAST RIDGE TO BLEED EASTWARD.
SO SEASONALLY COOL AIRMASS WILL HOLD FOR A FEW MORE DAYS BEFORE
GRADUAL WARMING OCCURS.

MODELS HAVE BEEN STRUGGLING THE PAST FEW DAYS WITH THE POTENCY OF
THE RESIDENT AIRMASS AND ITS MOISTURE CONTENT...GIVING TOO MUCH
CREDIT TO THE DRIER AIR WITHIN THE DOME OF HIGH PRESSURE BUILDING
INTO THE REGION. TO THAT NOTE...HAVE GONE MORE PESSIMISTIC FOR
SUNDAY WITH HIGH TEMPS AND CLOUD COVER. SOME HIRES...AS WELL AS THE
NAM...IS PICKING UP ON THE LL MOISTURE BEING TRAPPED UNDER THE STOUT
INVERSION. WILL NOT TAKE MUCH TO GET A GOOD CU FIELD GOING WHICH
SHOULD HAVE A HARD TIME MIXING OUT AS THE HIGH WILL REINFORCE THE
INVERSION. SO FEEL PRETTY CONFIDENT THAT WE WILL END UP WITH MOSTLY
CLOUDY SKIES FOR MOST OF THE AFTERNOON. ADDING PERSISTENCE
FORECASTING TO THE MIX WOULD SUGGEST HEDGING TO THE LOW SIDE OF
GUIDANCE FOR MAX TEMPS AS WE HAVE BEEN STRUGGLING MIGHTILY TO EVEN
GET NEAR 60 DEGREES THE LAST COUPLE DAYS. IN ADDITION...UPSTREAM OBS
SHOW COOLER TEMPS PREVAILING OVER THE VAST MAJORITY OF SITES WITHIN
THE INFLUENCE OF THE SFC HIGH.

A WEAK COLD FRONT WILL THEN DROP THROUGH THE STATE LATE MONDAY AS A
FAST MOVING MID LEVEL SHORTWAVE DROPS THROUGH THE UPPER TROUGH WHICH
WILL BRING US OUR NEXT CHANCE OF PRECIPITATION. IT WILL BE RUNNING
UP AGAINST THE DEEP LAYER OF DRY AIR FROM THE HIGH WHICH WILL DELAY
THE START OF PRECIP FALLING. RAIN WILL BEGIN IN THE AFTERNOON ACROSS
THE SAGINAW VALLEY ALONG THE FRONT BUT WILL DROP SOUTH THROUGH THE
EVENING BRINGING HIGH CHANCE POPS ACROSS THE REST OF THE AREA.
REFINED TIMING TO BRING HIGHEST CHANCES FROM ABOUT 21Z-03Z AS THE
SHORTWAVE COMBINES WITH THE FRONT OVER THE AREA AT THAT TIME. SKIES
WILL ATTEMPT TO CLEAR OUT BEHIND THE SYSTEM LATER MONDAY NIGHT WITH
CAA KICKING IN...850MB TEMPS FALLING TO AROUND 3C...WHICH WILL ALLOW
TEMPS TO DROP INTO THE MID 40S AFTER THE FRONT PASSES.

WEDNESDAY THROUGH SATURDAY: HIGH PRESSURE WILL BE THE DOMINANT
WEATHER FEATURE THROUGH THE PERIOD WITH DRY CONDITIONS ANTICIPATED
THROUGH THE WEEKEND. TEMPERATURES SHOULD REMAIN BELOW AVERAGE...
ESPECIALLY THROUGH FRIDAY WITH HIGHS HOLDING IN THE LOW TO MID
60S. ON SATURDAY...TEMPS EDGE TOWARD NORMAL WITH HIGHS IN THE LOW
70S.

&&

.MARINE...

HIGH PRESSURE BUILDING INTO THE AREA WILL LEAD TO IMPROVING
CONDITIONS ACROSS THE EASTERN GREAT LAKES TONIGHT. THE WEAKER
GRADIENT IS ALREADY BEING FELT OVER THE LAKES CAPPING GUSTS AROUND
20 KNOTS WHICH WILL DECREASE FURTHER OVERNIGHT. WAVES WILL QUICKLY
DROP OFF AS WELL THROUGH THE EVENING FOLLOWING THE TREND OF THE
WINDS. THE HIGH WILL BE CENTERED OVER MI BY SUNDAY MORNING BEFORE
GETTING NUDGED TO THE EAST/SOUTHEAST BY AN APPROACHING COLD FRONT.
THIS FRONT WILL PRODUCE SHOWERS MONDAY AND MONDAY NIGHT BEFORE HIGH
PRESSURE RETURNS FOR THE MIDWEEK PERIOD.

&&

.AVIATION...ISSUED 1250 PM EDT SAT SEP 13 2014

//DISCUSSION...

PERSISTENT MVFR CEILINGS WILL CONTINUE TO SLOWLY LIFT. PLENTY OF
CLOUD RE-ENFORCEMENTS UPSTREAM ACROSS NORTHERN LOWER MICHIGAN WILL
HELP MAINTAIN COVERAGE THROUGH THE BALANCE OF THE AFTERNOON...
HOWEVER CEILINGS WILL CONTINUE TO DRIFT UPWARD. EXPECTATIONS ARE FOR
THE CLOUDS TO THIN THROUGH THE EVENING HOURS...BUT CONFIDENCE IN
COMPLETE DISSIPATION IS LESS THAN PREVIOUSLY ADVERTISED. LOOKING
LIKE DIURNAL CLOUD DEVELOPMENT WILL HAPPEN SUNDAY...COMMENCING BY
LATE MORNING. OTHERWISE...MARGINALLY GUSTY NORTHWEST WINDS WILL
TEMPER THROUGH THE AFTERNOON ONCE TEMPERATURES STABILIZE AROUND
DAYTIME MAXES. WINDS WILL RELAX SUBSTANTIALLY AFTER SUNSET.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET THROUGH THIS AFTERNOON.
* MODERATE CONFIDENCE IN CEILINGS BELOW 5000 FEET SUNDAY AFTERNOON.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
     HURON INCLUDING OUTER SAGINAW BAY...UNTIL 4 PM SATURDAY.

LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...
     SMALL CRAFT ADVISORY...UNTIL 4 PM SATURDAY.

&&

$$

SHORT TERM...MANN
LONG TERM....DRK/DE
MARINE.......DRK
AVIATION.....MANN


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






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