Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 191103
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
703 AM EDT FRI SEP 19 2014

.AVIATION...

//DISCUSSION...

PATCHY MVFR FOG AND VFR CEILING WILL BE POSSIBLE IN THE DTW
CORRIDOR OFF THE WEST END OF LAKE ERIE...BUT LATEST SATELLITE
TRENDS SUGGEST LITTLE TO NO IMPACT AT KDTW. ELSEWHERE...FAVORABLE
RADIATING CONDITIONS HAVE RESULTED IN PATCHY MVFR/ISOLATED IFR
VSBYS ACROSS SOUTHEAST MICHIGAN...THOUGH AREA TAF SITES HAVE
LARGELY BEEN SPARED. ANY EARLY MORNING VSBY RESTRICTIONS WILL END
WITHIN A COUPLE HOURS OF SUNRISE...GIVING WAY TO CLEAR SKIES AND
SOUTHERLY WINDS BETWEEN 5 AND 10 KNOTS. INCREASING GRADIENT SHOULD
BE ABLE TO MAINTAIN A STEADY SOUTHWEST WIND AROUND 5 KNOTS THROUGH
TONIGHT.

//DTW THRESHOLD THREATS...

*NONE

&&

.PREV DISCUSSION...ISSUED 348 AM EDT FRI SEP 19 2014

SHORT TERM...TODAY AND TONIGHT

PROGRESSIVE UPPER PATTERN WILL FORCE THE SURFACE HIGH PRESENTLY TO
OUR NORTHEAST TO TRANSLATE WELL OFF THE ATLANTIC COAST TONIGHT. AS A
RESULT, SOUTHERLY RETURN FLOW WILL GET UNDERWAY EARLY IN THE DAY
WITH A GRADUAL SHARPENING OF THE SURFACE PRESSURE GRADIENT EXPECTED
IN RESPONSE TO UPSTREAM HEIGHT FALLS. 00Z GUIDANCE INDICATES A
LAKE-ENHANCED SOUTHEASTERLY FETCH TO THE LOW-LEVEL WIND ACROSS MUCH
OF SE MICHIGAN FOR THE DAYTIME HOURS. THIS WILL RESULT IN A RATHER
SLOW RETREAT OF THE SHALLOW AND COOL AIRMASS PRESENTLY IN PLACE
ACROSS THE NORTHEAST HALF OF THE AREA. UNDER FULL SUN, HOWEVER, THE
TEMPERATURE GRADIENT WILL NOT COMPARE TO YESTERDAY`S. THIS IS
REFLECTED IN THE HIGH TEMPERATURE FORECAST WHICH RANGES FROM LOW 60S
IN THE EASTERN THUMB TO NEAR 70 FOR WESTERN AREAS AWAY FROM THE LAKE
SHADOW. FULL DECOUPLING IS UNLIKELY TONIGHT AS THE GRADIENT RAMPS UP
AHEAD OF THIS WEEKEND`S WAVE, MAINLY AFTER 06Z. AS A RESULT, CLEAR
SKIES AND A VERY DRY COLUMN MAY ALLOW FOR SOME DECENT COOLING EARLY
BEFORE TEMPERATURES STABILIZE OR EVEN SLOWLY RISE FOR THE REMAINDER
OF THE NIGHT. OTHER THAN A STRAY SHOWER IN THE SAGINAW VALLEY, ALL
LOCATIONS WILL REMAIN DRY AS THE BETTER LOW-LEVEL WESTERLIES REMAIN
UPSTREAM.

LONG TERM...

THE COLD FRONT TRAILING THE CENTRAL CANADIAN LOW PRESSURE SYSTEM
TODAY WILL BECOME THE FOCUS FOR SECONDARY LOW DEVELOPMENT DURING
SATURDAY. THE SHORT WAVE ALOFT WILL FEED OFF INCREASING LARGE SCALE
HEIGHT FALLS DUE TO CONTINUED LONG WAVE AMPLIFICATION DURING THE
DAY. THE SURFACE REFLECTION IS MODEST ALONG THE FRONT IN MODEL DATA
NEAR THE NORTH SHORE OF LAKE SUPERIOR BY 12Z WEDNESDAY BUT EFFECTIVE
AT MAINTAINING ENHANCED SOUTHWEST FLOW AND MOISTURE TRANSPORT WITHIN
THE WARM SECTOR EXTENDING FROM LOWER MICHIGAN INTO THE CENTRAL
PLAINS. MODEL ANALYSIS FIELDS INDICATE HYBRID GULF/TROPICAL MOISTURE
LEAKING NORTHWARD THROUGH THE HIGH PLAINS INTO THE FRONTAL SYSTEM
BECOMING MIXED IN WITH THE INCREASINGLY DYNAMIC UPPER WAVE AND JET
AXIS. EXPECT THIS TO RESULT IN GENEROUS COVERAGE OF NOCTURNAL/LOW
LEVEL JET SUPPORTED SHOWERS OVER THE MIDWEST AND NORTHERN GREAT
LAKES TO START SATURDAY MORNING HAVING THE BEST CHANCE TO AFFECT THE
TRI CITIES BEFORE NOON. A VERY SHARP LOW LEVEL THETA-E GRADIENT
OUTLINES A STRONG WARM FRONT THAT WILL SPREAD QUICKLY THROUGH THE
GREAT LAKES AND POSITION THE LOW LEVEL MOISTURE AXIS DIRECTLY OVER
SE MICHIGAN DURING THE AFTERNOON AND EVENING. SHOWERS WILL THEN
BECOME LIKELY WHEN COMBINED PEAK HEATING AND THE APPROACHING COLD
FRONT. THUNDERSTORM POTENTIAL WILL BE SOLID WITH SURFACE DEWPOINT
RISING INTO THE 60S AND 850 MB DEWPOINT AROUND 12C...BUT SEVERE
POTENTIAL LIKELY MUTED BY SKINNY CAPE PROFILES/WEAK MID LEVEL LAPSE
RATES AVERAGING ABOUT 1000 J/KG AND 6.5 C/KM RESPECTIVELY. THIS WILL
REQUIRE MONITORING HOWEVER AS THE WIND PROFILE WILL BE STRONG WITH
SOME VEERING IN THE LOW LEVELS DURING THE AFTERNOON EVOLVING MORE
UNIDIRECTIONAL DURING THE EVENING AND PUSHING NEAR 50 KNOTS OF 0-6KM
BULK SHEAR BEFORE MIDNIGHT. TEMPERATURE OVERACHIEVEMENT IS ALREADY
BUILT INTO THE FORECAST FOR SATURDAY AFTERNOON CALLING FOR HIGHS IN
THE MID TO UPPER 70S.

THE LEADING COLD FRONT/PRE-FRONTAL TROUGH WILL SWEEP THE LOW LEVEL
MOISTURE AXIS EASTWARD BY SUNDAY MORNING LEAVING LESS BUT ADEQUATE
MOISTURE FOR SHOWERS ALONG AND AHEAD OF THE PRIMARY COLD FRONT
THROUGH SUNDAY AFTERNOON. THE FRONT WILL BE SWEPT THROUGH THE REGION
BY A COMPACT UPPER WAVE TRAILING THROUGH THE GREAT LAKES IN THE
NORTHWEST FLOW ALOFT. THIS SYSTEM LOOKS PLENTY STRONG ENOUGH TO
WRING OUT LINGERING BOUNDARY LAYER MOISTURE DURING AFTERNOON PEAK
HEATING BUT EXITING QUICKLY BY EVENING TO ALLOW SURFACE HIGH
PRESSURE TO TAKE CONTROL SUNDAY NIGHT THROUGH MONDAY.

THE EASTERN PACIFIC LONG WAVE TROUGH IS POSITIONED FARTHER
WEST/OFFSHORE OF THE WEST COAST BY WEDNESDAY IN THE NEW GLOBAL
MODEL SOLUTIONS. THIS ALLOWS A SLIGHTLY FARTHER WEST AXIS
POSITION OF THE BROAD LONG WAVE RIDGE TAKING UP MOST OF CENTRAL
NORTH AMERICA. THE SHORT WAVE CAUGHT UP IN THIS LARGE SCALE
PATTERN WILL ALSO BE FORCED SLOWER ACROSS THE PLAINS AND ALLOW
MAINTENANCE OF A DRY FORECAST FOR THE MIDWEEK PERIOD IN THE GREAT
LAKES. THE FARTHER WEST LONG WAVE RIDGE POSITION DOES PAVE THE WAY
FOR A WEAK COLD FRONT TO SETTLE THROUGH THE GREAT LAKES TUESDAY IN
BACKDOOR FASHION BUT APPEARS MOISTURE STARVED IN THE MODEL DATA
AND WASHES OUT ENOUGH FOR JUST A MODEST REINFORCEMENT OF COOLER
AIR.

MARINE...

SOUTHWEST FLOW WILL INCREASE STEADILY THROUGH THE DAY AND PERSIST
TONIGHT THROUGH SATURDAY. THIS WILL OCCUR AHEAD OF THE NEXT COLD
FRONT THAT WILL SUPPORT A PATTERN OF SHOWERS AND THUNDERSTORMS AS IT
SWEEPS THROUGH THE REGION SATURDAY AFTERNOON AND NIGHT. ALTHOUGH
WARM AIR WILL STREAM INTO THE REGION WITHIN THE SOUTHWEST FLOW...
STABILITY MAY STILL NOT BE HIGH ENOUGH TO PREVENT STRONG WIND GUSTS
OVER SAGINAW BAY AND THE OPEN WATERS OF LAKE HURON. THE NEED FOR
SMALL CRAFT ADVISORIES WILL BE MONITORED AS THE SYSTEM EVOLVES
THROUGH THE DAY. THE COLD FRONT WILL THEN BRING A NEW ROUND OF
COOLER AIR SUNDAY WHICH WILL LINGER WITH HIGH PRESSURE TO START NEXT
WEEK.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

AVIATION.....JVC
SHORT TERM...JVC
LONG TERM....BT
MARINE.......BT


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