Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 151948
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
348 PM EDT MON SEP 15 2014

.SHORT TERM... TONIGHT

THE MAIN MOISTURE/850-700 MB THETA-E AXIS AHEAD OF THE COLD FRONT IS
SOUTH OF THE MICHIGAN BORDER...WHICH HAS DRAWN CONCERN ABOUT THE
COVERAGE OF SHOWERS ALONG THE FRONT AS IT TRACKS THROUGH SOUTHEAST
MICHIGAN EARLY THIS EVENING. HOWEVER...THE UPPER WAVE OVER WISCONSIN
REMAINS FORMIDABLE...AND WITH THE CURRENT UPSTREAM RADAR COVERAGE
AND EXPECTED QUICK RAMP OF 700-500 MB FGEN/MID LEVEL COOLING OVER
SOUTH HALF OF THE CWA...PLANNING ON MAINTAINING THE CURRENT
INHERITED HIGHER POPS...WHICH IS ALSO SUPPORTED BY 17Z HRRR.
THE MAX QPF LOCATION OF THE 12Z GFS LOOKS PRETTY GOOD...BUT IS
LIKELY WAY OVERDONE IN MAGNITUDE. SHOWERS LOOK TO BE TAPERING OFF
FROM NORTHEAST TO SOUTHEAST SHORTLY AFTER 00Z...WITH PRONOUNCED
SURFACE RIDGE ARRIVING SHORTLY AFTER MIDNIGHT. ENOUGH MOISTURE
AROUND IN THE LOW LEVELS TO INTRODUCE UNCERTAINTY WITH THE EXACT
AMOUNT OF CLEARING. BANKING ON JUST ENOUGH DRIER AIR FEEDING IN AND
LIGHT WINDS TO KEEP FOG MENTION OUT OF THE FORECAST AS TEMPS
EXPECTED TO FALL INTO THE 40S...PER BLENDED GUIDANCE. NAM SURFACE
DEW PTS IN THE LOWER 50S AT 9Z APPEAR TO BE TOO HIGH.

&&

.LONG TERM... TUESDAY THROUGH NEXT MONDAY

SURFACE HIGH PRESSURE WILL BE FIRMLY CENTERED OVER IOWA/MISSOURI
TUESDAY MORNING WITH A RIDGE EXTENDING INTO LOWER MICHIGAN. DRY
CONDITIONS WILL BE ENSURED BY THIS HIGH PRESSURE FEATURE AND
LINGERING MID LEVEL SUBSIDENCE TRAILING TODAY`S SYSTEM...BUT THE
CLOUD FORECAST WILL BE LESS STRAIGHTFORWARD OR AT LEAST LESS
OPTIMISTIC THAN WHAT MIGHT BE EXPECTED WITH HIGH PRESSURE TAKING
CONTROL. AS MENTIONED IN THE PREVIOUS DISCUSSION...THIS PAST WEEKEND
DEMONSTRATED HOW MUCH INFLUENCE THE WARM GREAT LAKES WATER CAN HAVE
ON THE CLOUD PATTERN IN THESE EARLY SEASON COOL AIR MASSES THAT ARE
NOT DEVOID OF BOUNDARY LAYER MOISTURE BELOW THE SUBSIDENCE
INVERSION. THIS IS EXPECTED TO BE IN PLAY AGAIN TUESDAY WITH A
COUPLE OF SUBTLE DIFFERENCES MAINLY TIED TO MODEL TIMING ON THE
SOUTHWARD PLACEMENT OF THE LOW LEVEL THERMAL TROUGH AND BROAD
ANTICYCLONIC LOW LEVEL FLOW. THESE ELEMENTS ADD SOME UNCERTAINTY TO
THE PROSPECTS FOR NOCTURNAL STRATOCU MIGRATING INTO OUR AREA FROM
NORTHERN LOWER AFTER SUNRISE. HOWEVER...THERE IS MORE CONFIDENCE IN
LOW LEVEL COLD ADVECTION COMBINING WITH DAYTIME SURFACE HEATING TO
FILL IN REMAINING OPEN SKY DURING THE LATE MORNING THROUGH THE
AFTERNOON. FORECAST SOUNDINGS ACROSS ALL MODEL RUNS INDICATE STEEP
LAPSE RATES BELOW 800 MB WITH ENOUGH MOISTURE FOR GENEROUS COVERAGE
OF SHALLOW CUMULUS. THE RESULTING PARTLY SUNNY SKY AND LOW LEVEL
COLD ADVECTION WILL LIMIT MAX TEMPS TO THE LOWER AND MID 60S VS THE
LOWER HALF OF THE 70S THAT IS NORMAL FOR MID SEPTEMBER.

A SIGNIFICANT DIURNAL COMPONENT IN THE TUESDAY AFTERNOON CLOUD
PATTERN WILL GIVE WAY TO A CLEARING TREND WITH SUNSET TUESDAY
EVENING. THIS WILL OPEN THE DOOR TO A COLD NIGHT AS SURFACE HIGH
PRESSURE BECOMES CENTERED OVER INDIANA AND OHIO AND FOSTERS STRONG
RADIATIONAL COOLING WITH LIGHT WIND UNDER MOSTLY CLEAR SKY. LATE
DEVELOPING WESTERLY FLOW BELOW 850 MB WILL BE ON THE TRAILING FLANK
OF THE LOW LEVEL THERMAL TROUGH AND THUS REPRESENT WARM ADVECTION...
TOO WEAK AND LATE TO DISRUPT RADIATIONAL COOLING BUT ENOUGH TO
LESSEN CONCERN FOR STRATOCU FROM LAKE MICHIGAN. ABOUT THE ONLY OTHER
CLOUD POTENTIAL IS ASSOCIATED WITH THE NEXT SHORT WAVE EMBEDDED IN
THE BROAD LONG WAVE TROUGH OVER EASTERN CANADA. MODEL CONSENSUS
INDICATES THIS WILL BE TOO LATE TO PROVIDE MORE THAN THIN CIRRUS
TOWARD SUNRISE WEDNESDAY.

THE COLD FRONT TRAILING THE NORTHERN GREAT LAKES SHORT WAVE WILL
BRING A GLANCING CHANCE OF LIGHT RAIN TO THE SAGINAW VALLEY
WEDNESDAY AFTERNOON. THE FRONT WILL BE LOSING MOISTURE INTEGRITY AS
IT MOVES SOUTH BUT WILL HAVE A RESPECTABLE TEMPERATURE CONTRAST
JUDGING FROM MODEL LOW LEVEL THICKNESS AND THERMAL FIELDS. AFTER A
RUN TOWARD 70F WEDNESDAY AFTERNOON THIS FRONT WILL KICK THE LEGS OUT
OF THE WARMING TREND BY THURSDAY WITH HIGHS BACK DOWN TOWARD THE
LOWER END OF THE 60S...AND POSSIBLY CONFINED TO THE UPPER 50S IN THE
THUMB GIVEN LOW LEVEL FLOW FROM THE NORTHEAST.

AS QUICKLY AS THE SURFACE HIGH IS REINFORCED THROUGH LOWER MICHIGAN
THURSDAY...IT IS DISPLACED EASTWARD EQUALLY FAST FRIDAY IN GLOBAL
MODEL SOLUTIONS HEADING INTO THE WEEKEND. SUBSTANTIAL UPPER LEVEL
HEIGHT FALLS OVER THE GULF OF ALASKA ARE SHOWN TO INITIATE
PROGRESSION IN THE LONG WAVE TROUGH OVER EASTERN CANADA. THE SHORT
WAVE TROUGH HELPING THIS ALONG IS TRENDING STRONGER IN THE LATEST
SOLUTIONS AS IT MOVES THROUGH THE PLAINS...JUST IN TIME TO PICK UP
TROPICAL REMNANTS OF "ODILE" FROM THE FOUR CORNERS AREA. THIS WILL
SET THE STAGE FOR A WARMER BUT WETTER WEEKEND AS THE FRONTAL SYSTEM
MOVES THROUGH THE GREAT LAKES.

&&

.MARINE...

MARINE CONDITIONS WILL BE FAVORABLE IN TERMS OF WIND AND WAVES
DESPITE THE PASSAGE OF TWO COLD FRONTS DURING THE WEEK. THE FIRST
WILL BE TONIGHT WHICH WILL HAVE JUST A WEAK WIND SHIFT PASSING
THROUGH ALONG WITH THE RAIN PATTERN. THE SECOND WILL BRING A CHANCE
OF LIGHT RAIN WEDNESDAY AND RENEWED SURGE OF COOLER AIR BY THURSDAY
WITH MODEST NORTHERLY FLOW POSSIBLY RAMPING UP WAVES A BIT MORE OVER
THE RELATIVELY WARM WATER OF LAKE HURON. AFTER THAT...THE NEXT
STRONGER LOW PRESSURE SYSTEM WILL BRING WARMER AIR FRIDAY AND
SATURDAY BUT POSSIBLY STORMY CONDITIONS LATER SATURDAY AND SUNDAY AS
THE ASSOCIATED COLD FRONT MOVES THROUGH THE REGION.

&&

.AVIATION...ISSUED 1250 PM EDT MON SEP 15 2014

//DISCUSSION...

CEILINGS GRADUALLY LOWERING THIS AFTERNOON AS MID LEVELS MOISTEN UP
AND SHOWERS OVERSPREAD THE AREA. SHOWERS AND MODEST LOW LEVEL
CONVERGENCE ALONG A COLD FRONT ARE EXPECTED TO PRODUCE MVFR CEILINGS
BY EARLY EVENING. POTENTIAL FOR IFR CEILINGS WILL EXIST LATE THIS
EVENING-OVERNIGHT AS COLDER POST-FRONTAL AIR DRAINS IN DEVELOPING
NORTHWEST WINDS...WHICH LOOK TO REMAIN LIGHT (LESS THAN 10 KNOTS)
NONE-THE-LESS. CONFIDENCE IS NOT VERY HIGH IN AN EXTENDED PERIOD OF
LOWER CEILINGS...AS THE SURFACE RIDGE BUILDING INTO THE AREA IS
PRONOUNCED...AND PREFER TO BE MORE OPTIMISTIC IN THE TAFS...CLEARING
OUT/SCATTERING OUT THE CLOUDS BEFORE A QUICK DIURNAL CU UP RETURNS
LATE TOMORROW MORNING.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING BELOW 5KFT LATE THIS AFTERNOON INTO
THIS EVENING...LOWER CONFIDENCE OVERNIGHT INTO TOMORROW.

&&

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

&&

$$

SHORT TERM...SF
LONG TERM....BT
MARINE.......BT
AVIATION.....SF


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






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