Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 261948
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
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.

&&

.AVIATION...ISSUED 138 PM EDT FRI SEP 26 2014

//DISCUSSION...

DEEP HIGH PRESSURE WILL CONTINUE THE TREND OF CLEAR SKIES AND LIGHT
WINDS. PERSISTENCE CALLS FOR THE POTENTIAL OF FOG AFTER 9Z SATURDAY
MORNING. IF NEAR SURFACE MOISTURE GUIDANCE CAN BE TRUSTED...THE
POTENTIAL FOR MORE WIDESPREAD AND DENSE FOG MAY BE GREATER NORTH OF
M59 AS DRIER AIR IS FORECASTED TO ADVECT INTO FAR SOUTHEASTERN
MICHIGAN SATURDAY MORNING. GIVEN WHAT WAS OBSERVED THIS
MORNING...ANY FOG WILL LIKELY BURN OFF BETWEEN 14 AND 15Z.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE IN CIGS/VSBY BELOW 200 FT AND/OR 1/2 SM BETWEEN
9-15Z SATURDAY MORNING.

&&

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

&&

$$

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


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





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