Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 151812
AFDDTX

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

.UPDATE...

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. 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.

&&

.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.

&&

.PREV DISCUSSION...ISSUED 359 AM EDT MON SEP 15 2014

SHORT TERM... TODAY AND TONIGHT

SOUTHEAST MICHIGAN FIRMLY POSITIONED THIS MORNING ALONG THE SOUTHERN
PERIPHERY OF NORTHERN STREAM MID LEVEL TROUGHING...AND AT THE
WESTERN EDGE OF SLOWLY EXITING SURFACE RIDGING.  LINGERING INFLUENCE
OF THE EXISTING RIDGING AXIS AND ATTENDANT PLUME OF DEEPER AMBIENT
DRY AIR WILL REMAIN A PREVALENT FEATURE THROUGH THE FIRST HALF OF
THE DAY...PARTICULARLY SOUTH OF THE I-69 CORRIDOR WHERE SOME EARLY
DAY SUN IS LIKELY PER RECENT SATELLITE TRENDS.  TO THE NORTH...A
LEAD SHORTWAVE AND ATTENDANT 100 KNOT UPPER JET STREAK BENDING
ACROSS NORTHERN LOWER WILL CONTRIBUTE TO A MORE PROGRESSIVE ONSET
OF THICKER/INCREASING CLOUD COVER.  ASSOCIATED FRONTAL ZONE TIED TO
THE LOWERING HEIGHT FIELD WILL STRENGHTEN THROUGH THE MID LEVELS AS
THIS PROCESS UNFOLDS...THE FRONTAL ZONE SHIFTING INTO THE SAGINAW
VALLEY/THUMB BY MIDDAY.  THIS WILL RESULT IN AN INCREASING CHANCE
FOR SHOWER DEVELOPMENT INITIALLY ALONG THIS CORRIDOR.

STRONGER FORCING WILL AWAIT THE ARRIVAL OF THE INBOUND COMPACT WAVE
NOW DIGGING ACROSS THE DAKOTAS.  SOLID CORRIDOR OF CVA TIED TO THIS
SYSTEM WILL TRANSLATE ACROSS SE MICHIGAN 21Z-03Z LATE TODAY.  WEAK
LOW LEVEL CYCLOGENESIS UPSTREAM WILL INITIATE A PERIOD OF STRONGER
THETA-E ADVECTION COINCIDENT WITH THIS TIMING.  THIS IN COMBINATION
WITH THE HIGH DEGREE OF MID LEVEL ASCENT EXPECTED IN THE PRESENCE
OF FAVORABLE ENTRANCE UPPER JET SUPPORT WILL LEAD TO THE EXPANSION
IN SHOWER COVERAGE OVER THE AREA DURING THIS TIME. HIGH END POPS
REMAIN IN ORDER FOR THIS TIME WINDOW. SUFFICIENT STABILITY THROUGH
THE COLUMN WILL CONTINUE TO PRECLUDE A MENTION OF THUNDER TODAY.

LIGHT PRE-FRONTAL SOUTHWEST FLOW WILL CONTRIBUTE SLIGHTLY TOWARD
MODERATING THE EXISTING AIRMASS...WITH THE BOTH THE TIMING AND
EXTENT OF CLOUD COVER APPLYING A COUNTER TO THIS RESPONSE.  OVERALL
A MODESTLY MIXED PROFILE INTO A 900 MB LAYER CARRYING 7-9C TEMPS
CONTINUES TO SUPPORT A HIGH DISTRIBUTION RANGING FROM MID 60S
SOUTH TO AROUND 60 NORTH.

STEADY POST FRONTAL LOW LEVEL COLD AIR ADVECTION ENSUES THROUGH THE
LATTER HALF OF TONIGHT.  CONTINUED MOIST RH FIELDS AS THIS PROCESS
UNFOLDS SUGGESTS THE CLEARING OF THE RESIDUAL LOW STRATUS WILL TAKE
SOME TIME...LIKELY UNTIL CLOSER TO DAYBREAK ACROSS THE SOUTH. LOWS
TONIGHT WITHIN THE LOWER TO MIDDLE 40S RANGE.

LONG TERM...TUESDAY THROUGH SUNDAY

THE WEEK AHEAD WILL BE DOMINATED BY FAST NORTHWESTERLY FLOW ALOFT
WITH GENERAL RIDGING AT THE SURFACE. SOUTHEASTERN MICHIGAN CAN
EXPECT AN EXTENDED DURATION OF BELOW NORMAL TEMPERATURES WITH HIGHS
EACH DAY REGISTERING IN THE 60S. A VERY STABLE MIDDLE TROPOSPHERE IS
PROGGED ACCORDING TO FCST BUFFER SOUNDINGS WHICH WILL MAKE IT
DIFFICULT FOR THE COLUMN TO SUPPORT PRECIPITATION GIVEN VERY DRY
AUTUMN SFC DEWPOINTS. THE ONE EXCEPTION MAY BE ALONG A SHALLOW
SURFACE FRONT THAT WILL SLIP INTO THE NORTHERN GREAT LAKES DURING
THE MIDDLE OF THE WEEK...POSSIBLY DROPPING INTO THE SAGINAW BAY
REGION FOR WEDNESDAY AFTERNOON. ATTM...THE MODELS ARE FORECASTING A
SHALLOW LAYER OF SATURATED UNSTABLE LAPSE RATES THAT IS GOOD FOR A
LOW CHANCE POPS ACROSS THE NORTHERN CWA. THE FRONT IS EXPECTED TO
WASH OUT...LEADING TO A CONTINUATION OF QUIET AND VERY COMFORTABLE
WEATHER FOR THURSDAY AND FRIDAY.

TUESDAY...THE ONE QUESTION IS WHAT SORT OF SKY FRACTION WILL EXIST
IN THE WAKE OF THE MONDAY NIGHT SYSTEM. THE COLUMN IS AGAIN SHOWING
A DEVELOPING INVERSION BETWEEN 7-12Z WITH A BASE AT ROUGHLY 6 KFT
AGL. THIS IS REMINISCENT TO THE SUNDAY MORNING CASE WITH THE MODELS
AT THIS VANTAGE POINT SHOWING NO SATURATION OR HIGH MOISTURE
CONTENT. BUT AS WE WITNESSED...THAT ALL CHANGED AS TIME APPROACHED
ZERO. WILL SIDE WITH THE DATA THAT IS AVAILABLE...AND WILL BE LIGHT
ON CLOUD COVER FOR TUESDAY. HIGH TEMPERATURES ARE EXPECTED TO REACH
THE LOWER TO MIDDLE 60S...OR APPROXIMATELY 10 DEGREES BELOW NORMAL.

MARINE...

SURFACE RIDGING WILL RETREAT OUT OF THE CENTRAL GREAT LAKES
TODAY...ALLOWING FOR A VERY WEAK SURFACE TROUGH AND FRONTAL SYSTEM
TO ADVANCE INTO THE REGION FOR TONIGHT. THE TROUGH WILL BE VERY FAST
MOVING AND WILL NOT PROVIDE MUCH SUPPORT IN DEVELOPING A STRONG
FRONTAL BOUNDARY. THEREFORE...SURFACE WINDS WILL ONLY INCREASE
MODESTLY OUT OF THE NORTH TONIGHT DUE TO A WEAK PRESSURE GRADIENT.
HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE WEST FOR MUCH OF
THE WORK WEEK...WITH ONLY BENIGN WIND AND WAVES FOR THE TIME OF YEAR
EXPECTED THROUGH FRIDAY.

&&

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

&&

$$

UPDATE.......SF
AVIATION.....SF
SHORT TERM...MR
LONG TERM....CB
MARINE.......CB


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





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