Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 061129
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
729 AM EDT FRI MAY 6 2016


.AVIATION...

SURFACE HIGH PRESSURE IN PLACE TODAY WILL PROVIDE MOSTLY CLEAR SKIES
AND LIGHT WINDS DURING THE DAY. LAKE BREEZE DEVELOPMENT ACROSS METRO
DETROIT IS EXPECTED LATE FRIDAY AFTERNOON CONSIDERING THE WEAK SFC
GRADIENT. MID/HIGH CLOUDS WILL THEN BE ON THE INCREASE AHEAD OF A
COLD FRONT TONIGHT.

//DTW THRESHOLD PROBABILITIES...

* NONE

&&

.PREV DISCUSSION...ISSUED 401 AM EDT FRI MAY 6 2016

DISCUSSION...

THE OMEGA BLOCK OVER NORTH AMERICA WILL BECOME PROGRESSIVELY LESS
AMPLIFIED OVER THE NEXT 48 HOURS AS A DYNAMIC UPPER LEVEL LOW
PRESSURE SYSTEM/STRONG HEIGHT FALLS DIGS OUT OF THE ARCTIC DIRECTLY
INTO THE HEART OF THE UPPER LEVEL RIDGE AXIS.

BEFORE THIS UPPER LEVEL PATTERN WILL BREAK DOWN...THE DYNAMIC UPPER
LEVEL LOW PRESSURE SYSTEM WILL CAUSE A STOUT SHORTWAVE RIDGE AXIS
TO SETTLE INTO THE WESTERN AND CENTRAL GREAT LAKES. CLASSIC
SPRINGTIME CONDITIONS WITH VERY LOW HUMIDITY/LARGER DEWPOINT
DEPRESSIONS. A FORECAST SOUNDING ANALYSIS POINTS TO TWO SEPARATE
ARTIFACTS OF PRIOR SUBSIDENCE IN THE COLUMN BOTH OF WHICH ARE IN
THE MID TO UPPER LEVELS. SO...THESE INVERSIONS COMBINED WITH NIL
SURFACE HUMIDITY WILL LEAD TO A PICTURE PERFECT DAY. A GOOD
AMOUNT OF MID-HI CLOUD ALTOCUMULUS/ALTOSTRATUS IS WORKING DUE
SOUTHWARD EARLY THIS MORNING ACROSS THE NORTHERN GREAT LAKES.
THERE IS AT LEAST SOME PARTIAL CONCERN THESE CLOUDS COULD
COMPLICATE MATTERS FOR THE SUNNY FORECAST/FULL INSOLATION.
HOWEVER...AT THIS JUNCTURE DO NOT WANT TO SWING THE FORECAST FOR
SOME HIGH CLOUD...WHICH APPEARS TO HAVE GREATER SUPPORT TO THE
WEST OF THE CWA. WITH THE MAY SUNSHINE RAISED TEMPERATURES A
DEGREE OR TWO ACROSS THE BOARD...WITH HIGHS TODAY ECLIPSING THE 70
DEGREE MARK FOR ALL AREAS EXCEPT NEAR THE LAKE/RIVER SHORELINES.

NO SURPRISES OR CHANGES TO THE SATURDAY FORECAST ARE NEEDED. MODELS
ARE IN STRONG AGREEMENT THAT COLD FRONTAL PRECIPITATION SWILL SLIP
SOUTHWARD INTO THE SAGINAW BAY REGION AFTER 12Z SATURDAY...THEN
PROGRESS SOUTHWARD DURING THE DAY...EXITING FAR SOUTHEASTERN
MICHIGAN SHORTLY/BEFORE OR AFTER 21Z SATURDAY. SO THE NARRATIVE IS
ONE OF SOME MIDDAY RAIN/TSTORM CHANCES BUT NOT AN ALL DAY
SOAKING/MISERABLE DAY. BASIN AVERAGED PRECIPITATION IS RELATIVELY
LIMITED DUE TO PROGRESSIVE FRONTAL FORCING. MIDLEVEL LAPSE
RATES...PARTICULARLY 700-600MB...WILL STEEP ENOUGH TO SUPPORT A
CHANCE OF THUNDERSTORMS WITH THE CONVECTIVE SHOWERS FROM LATE
FRIDAY NIGHT THROUGH SATURDAY AFTERNOON. THE SUBJECT OF POTENTIAL
CONVECTIVE VIGOR FOR SATURDAY AFTERNOON HINGES SOLELY ON SURFACE
DEWPOINTS. THE ALWAYS BULLISH NAM IS SUGGESTING SURFACE DEWPOINTS
APPROACHING 60 DEGREES F WHICH YIELDS AS MUCH AS 1500 J/KG. THIS
IS A BORDERLINE UNREALISTIC FORECAST WITH A NORTHWEST FLOW EVENT
AND THE DOWNRIGHT LACK OF ANY TRUE GOMEX MOISTURE. THE PREVIOUS
DISCUSSION PROBABLY FRAMED IT BEST SAYING ONE HAS TO GO TO KEY
WEST TO GET THAT LEVEL OF MOISTURE CONTENT. CONSENSUS OF MOS IS
MUCH MORE REASONABLE IN THE LOWER 50S. FREEZING HEIGHTS ARE
RELATIVELY ELEVATED...SO SKINNY CAPE PROFILES WILL STRUGGLE TO
SUPPORT HAIL. ATTM...NOT EXPECTING SEVERE WEATHER...BUT 0-6KM
SHEAR WILL BE HIGH ENOUGH TO SUPPORT SOME STORM ORGANIZATION
ESPECIALLY IF CAPE CAN REACH 1000 J/KG. HIGHS SATURDAY ARE
EXPECTED TO REACH THE LOWER 70S OVER THE SOUTHERN CWA...UPPER 60S
ELSEWHERE.

UPPER LEVEL TROUGHING AND COOL NORTHWEST FLOW WILL BE OVERHEAD FOR
SUNDAY. AN ABUNDANCE OF CYCLONIC VORTICITY WORKING THROUGH THE
TROUGH ALWAYS CATCHES ONES ATTENTION...BUT DEEP COLUMN DRYING AND
UPPER LEVEL CONFLUENT FLOW APPEARS TO BE ENOUGH TO KEEP CONDITIONS
DRY. AN EXCEPTION MAY BE OVER THE THUMB...CLOSER TO THE MIDLEVEL
COLD AIR POCKET. MODELS SUGGEST THERE IS SOME POTENTIAL FOR HIGH
BASED INSTABILITY SHOWERS/SPRINKLES DURING THE AFTERNOON HOURS.
HAVE INCLUDED AN ISOLATED/SLIGHT CHANCE.

THE LATEST FORECAST INFORMATION SUGGESTS THE MAIN UPPER LEVEL TROUGH
AXIS WILL PIVOT OUT OF THE CENTRAL GREAT LAKES AND BECOME REPLACED
BY RISING GEOPOTENTIAL HEIGHTS AND AN UPPER LEVEL RIDGE AXIS. THIS
WILL MAINTAIN DRY WEATHER TO THE START THE WORK WEEK. MODELS HAVE
BEEN AGGRESSIVE IN BRINGING SHOWERS IN ON MONDAY. HAVE SOME SERIOUS
RESERVATIONS ON THE OVERALL POTENTIAL FOR THIS GIVEN THE AMOUNT OF
LOW LEVEL DRY AIR THAT WILL NEED TO BE OVERCOME ON THE FRONT END.
THE BETTER POTENTIAL FOR LIGHT PRECIPITATION WILL BE MONDAY NIGHT AS
ISENTROPIC ASCENT INCREASES AND CERTAINLY ON TUESDAY WITH DEEPER
CYCLONIC FLOW.

MARINE...

LIGHT WINDS TODAY WILL GIVE TO SOUTHERLY WINDS TONIGHT AHEAD OF A
COLD FRONT...BUT STILL BELOW 20 KNOTS. THIS FRONT WILL TRIGGER
SHOWERS AND THUNDERSTORMS TOMORROW...WITH A WIND SHIFT TO THE
NORTHWEST BEHIND THE FRONT. WINDS LOOK TO PEAK OUT AROUND 25 KNOTS
SATURDAY EVENING...THEN BECOMING LIGHT AGAIN ON SUNDAY...OUT OF THE
WEST. LIGHT AND VARIABLE WINDS ON MONDAY...WITH WARM FRONT THEN
LIFTING NORTH MONDAY NIGHT...TRIGGERING ANOTHER ROUNDS OF SHOWERS
AND POSSIBLE THUNDERSTORMS.

&&

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

$$

AVIATION.....SF
DISCUSSION...CB
MARINE.......SF

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


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