Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 270213
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1013 PM EDT FRI SEP 26 2014

.UPDATE...

EVENING OBSERVATIONS AND INCOMING SHORT RANGE MODEL OUTPUT
CONTINUES TO BE MONITORED FOR TRENDS IN FOG DEVELOPMENT. THE FIRST
ITEM OF NOTE IS THAT...WHILE LAND BASED WIND OBSERVATIONS GO
CALM...MARINE OBSERVATIONS SUPPORT MODEL DEPICTIONS OF A GREATER
NORTHEAST WIND COMPONENT AT 925 MB AND BELOW. THIS ADDS SOME
CONFIDENCE TO A WEAKER ADVECTIVE COMPONENT AND THE MORE OPTIMISTIC
FORECAST FOR THE DETROIT METRO AREA AS LAKE ERIE IS LESS LIKELY TO
MODIFY THE MOISTURE PROFILE. IT DOES BRING LAKE HURON AND SAGINAW
BAY MORE INTO THE PICTURE FOR THE THUMB AND TRI CITIES BUT WITH
LIMITED INLAND EXTENT DUE TO THE OVERALL WEAK WIND FIELD. OTHERWISE...
SURFACE OBSERVATIONS ARE ON ABOUT THE SAME OR SLIGHTLY SLOWER PACE
OF COOLING COMPARED TO LAST NIGHT...AND MODEL FORECAST SOUNDINGS
INDICATE A SHALLOWER MOISTURE PROFILE COMPARED TO LAST NIGHT...
ESPECIALLY AT DTW. THAT BEING SAID...THE DATA STILL FEELS LIKE AN
AREAS OF FOG FORECAST...BUT WITH THE POTENTIAL FOR TROUBLE SPOTS
REMAINING NORTH OF M-59...AND POSSIBLY INCLUDING PORTIONS OF MONROE
COUNTY NEAR LAKE ERIE.

&&

.AVIATION...ISSUED 705 PM EDT FRI SEP 26 2014

//DISCUSSION...

THE EVENING FORECAST HOLDS THE LINE ON FOG EXPECTATIONS FOR THE
OVERNIGHT THROUGH MID SATURDAY MORNING WITH A GENERAL PATTERN OF
MVFR RESTRICTION IN THE DTW AREA TO IFR AT FNT AND MBS. PERSISTENT
SURFACE HIGH PRESSURE COVERING THE GREAT LAKES WILL GOVERN AN
OTHERWISE FAVORABLE AVIATION WEATHER PATTERN AS MORNING FOG BREAKS
INTO SUNNY SKY AND LIGHT EASTERLY WIND SATURDAY AFTERNOON INTO
EVENING.

//DTW THRESHOLD THREATS...

* NONE.

&&

.PREV DISCUSSION...ISSUED 348 PM EDT FRI SEP 26 2014

SHORT TERM...TONIGHT

A CENTROID OF THE PLANETARY WAVELENGTH ANTICYCLONE WILL ROLL OVER
THE MID-MISSISSIPPI LOWER HEIGHT ANOMALY TONIGHT AND EMERGE OVER
PORTIONS OF ONTARIO AND QUEBEC BY SATURDAY MORNING. PERSISTENCE IS
IN ORDER WITH CLEAR SKIES AND LIGHT WINDS.

THE PERTINENT FORECAST CONCERN IS OVERALL FOG POTENTIAL. NOTICED IN
MODEL DATA FROM YESTERDAY THAT MOISTURE RESPONSIBLE FOR FOG WAS
ACTUALLY TERRESTRIAL MOISTURE THAT WAS IN PLACE SOUTH OF LAKE ERIE
PRIOR TO SUNDOWN. THIS WAS THEN LIFTED NORTHWARD AND EITHER PIVOTED
OR DUCTED WESTWARD TOWARD SOUTHEASTERN MICHIGAN AFTER 9Z. FOR
TONIGHT...MODELS ARE SUGGESTING THAT DRIER AIR IS IN PLACE OVER THE
EASTERN LAKE ERIE BASIN AND WILL BE THE AIRMASS OF INTEREST AFTER 9Z
TONIGHT FOR AREAS SOUTH OF M 59 INCLUDING THE DETROIT METRO. IF THE
MODEL DATA CAN BE TRUSTED...SURFACE TEMPERATURE AND DEWPOINT SPREAD
MAY BE RELATIVELY HIGH WHICH COULD THEN LIMIT THE AMOUNT OF SURFACE
VISIBILITY RESTRICTIONS TOMORROW MORNING. RICHER SURFACE THETA E
CONTENT OVER ONTARIO IS SHOWN TO SLIDE WESTWARD DURING THE NOCTURNAL
RELEASE OF THE BOUNDARY LAYER. THIS MOISTURE IS SHOWN TO ADVECT INTO
THE NORTHERN CWA...WITH NOT MUCH OF AN INTERACTION WITH AREA LAKES.
CURRENT THINKING HAS GREATEST LIKELIHOOD FOR FOG OCCURRING NORTH OF
M 59 ACROSS THE NORTHERN CWA WHERE SHALLOW RADIATIONAL FOG SHOULD BE
LIKELY. THE GOING FORECAST HAS AREAS OF FOG FOR ALL AREAS AND
SUBSEQUENT SHIFTS CAN DETAIL AS OBSERVATIONAL TRENDS BECOME
ESTABLISHED.

LONG TERM...SATURDAY THROUGH FRIDAY

SURFACE HIGH PRESSURE WILL MAINTAIN DRY AND MILD WEATHER ACROSS THE
CENTRAL GREAT LAKES THROUGHOUT THE WEEKEND. THE ONLY CAVEAT WILL BE
THE POTENTIAL FOR PATCHY FOG DURING THE EARLY MORNING HOURS...WHICH
MAY TAKE A FEW HOURS TO BURN OFF IN SOME LOCATIONS DUE TO THE WEAK
BOUNDARY LAYER FLOW IN PLACE WITH THIS HIGH PRESSURE SYSTEM. SUNNY
SKIES ON SATURDAY WILL BE REPLACED BY SOME INCREASING UPPER LEVEL
CLOUDS ON SUNDAY AS CLOSED LOW PRESSURE SYSTEM OVER IOWA BECOMES AN
OPEN WAVE AND BEGINS A MOVE TOWARDS THE REGION. OTHERWISE...EXPECT
TEMPERATURES TO CLIMB INTO THE MIDDLE 70S ON AVERAGE ACROSS THE CWA
WITH THE COOLEST READINGS...LOW 70S...IMMEDIATELY DOWNWIND OF LAKE
HURON AND ERIE AND THE MILDEST READINGS...UPPER 70S...IN DOWNSLOPE
REGION FROM THE GENESEE INTO SAGINAW VALLEY REGION FROM FLINT INTO
THE TRI-CITIES AS LIGHT SOUTHEAST FLOW PREVAILS.

A COLD FRONT LOOKS TO DROP SOUTHWARD TOWARD LOWER MICHIGAN ON MONDAY
NIGHT...BUT THE BAROCLINIC ZONE BECOMES MUCH WEAKER AS IT APPROACHES
THE CWA. THIS WILL BE OUR FIRST CHANCE FOR -RA IN SOME TIME...BUT
DOES NOT APPEAR TO PAN OUT OTHER THAN A FEW SPRINKLES. FOLLOWING
THAT WAVE...UPPER LEVEL RIDGING WILL RETURN AND MAINTAIN DRY
CONDITIONS THROUGH THURSDAY. MODELS DIFFER ON TIMING OF THE NEXT LOW
AND COLD FRONT...BUT A MORE SUBSTANTIAL THREAT FOR RAIN WILL BE IN
THE THURSDAY NIGHT TO FRIDAY TIMEFRAME.

MARINE...

MARINE CONDITIONS WILL REMAIN BENIGN AS HIGH PRESSURE REMAINS
CENTERED NEAR THE AREA...MAINTAINING LIGHT WINDS AND LIMITED
WAVE DEVELOPMENT.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

UPDATE.......BT
AVIATION.....BT
SHORT TERM...CB
LONG TERM....DG/MM
MARINE.......DG


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








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