Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 212331
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
731 PM EDT MON APR 21 2014


.AVIATION...

//DISCUSSION...

A STEADY INCREASE IN MOISTURE ALONG AN APPROACHING COLD FRONT WILL
SUPPORT AN EXPANDING REGION OF SHOWERS TONIGHT.  EXISTENCE OF A
STRONG LOW LEVEL DRY LAYER WILL MAINTAIN VFR INITIALLY AS POCKETS OF
LIGHT SHOWERS ENTER SE MICHIGAN LATE THIS EVENING.  INCREASING
COVERAGE WILL EVENTUALLY RESULT IN MVFR CONDITIONS.  THERE REMAINS
AN ISOLATED RISK FOR THUNDERSTORMS...BUT THE EXPECTED LIMITED
COVERAGE WILL PRECLUDE A SPECIFIC MENTION UNLESS NEAR TERM TRENDS
DICTATE.   COOLER AIR WILL SPREAD OVER THE REGION DURING TUESDAY
ALLOWING FOR A GENEROUS COVERAGE OF DIURNAL STRATOCU...CEILINGS
LIFTING FROM MVFR TO VFR AS THE MIXED LAYER DEEPENS WITH TIME.  A
GUSTY NORTHWEST WIND WILL EMERGE AS HEATING/MIXING ENSUES...PEAK
GUST POTENTIAL IN THE 25 TO 28 KNOT RANGE DURING THE AFTERNOON.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN CEILING BELOW 5000 FEET TONIGHT THROUGH
TUESDAY MORNING.

&&

.PREV DISCUSSION...ISSUED 350 PM EDT MON APR 21 2014

SHORT TERM... THIS AFTERNOON THROUGH TONIGHT

MODERATE SOUTHWEST WIND OVER LOWER MICHIGAN IS HELPING CARRY WARM
AIR INTO THE REGION DURING THE AFTERNOON. COMBINE THE WARM SOUTHWEST
FLOW WITH THIN SPOTS IN THE HIGH CLOUDS AND WE GET MAX TEMPS MAKING
A RUN AT 80...ESPECIALLY AT INLAND LOCATIONS. THESE NUMBERS ARE WELL
ABOVE NORMAL VALUES THAT ARE AROUND 60 THIS TIME IN APRIL BUT BELOW
RECORDS THAT AVERAGE MID AND UPPER 80S. NO DOUBT THE AIR MASS IS
WARM BUT IT IS ALSO DRY INITIALLY WITH SURFACE DEWPOINT STRUGGLING
TO RISE INTO THE 40S IN DEEP BOUNDARY LAYER MIXING. THE EXCEPTION IS
IN THE SAGINAW VALLEY AND NORTHERN THUMB WHERE DEWPOINT IS PUSHING
50. THIS IS THE FIRST SIGN OF IMPROVED MOISTURE CONDITIONS FOR
SHOWER DEVELOPMENT LATE TODAY AND TONIGHT. IT MARKS THE LEADING EDGE
OF A LOW LEVEL THETA-E RIDGE SURGING NORTHWARD INTO THE WESTERN
GREAT LAKES AND MEETING UP WITH A STALLED FRONT OVER UPPER AND
NORTHERN LOWER MICHIGAN AT MID AFTERNOON. RADAR INDICATIONS OF
SURFACE BASED CONVECTION IN THAT AREA WILL CONTINUE TO EVOLVE
THROUGH LATE AFTERNOON WITH A FEW SHOWERS ABLE TO BRUSH MIDLAND AND
BAY COUNTIES BEFORE BEING SWEPT NORTHWARD.

THE LATE AFTERNOON ACTIVITY SUGGESTS THE STAGE IS BEING SET FOR
INCREASING COVERAGE OF SHOWERS WITH A FEW THUNDERSTORMS TONIGHT OVER
SE MICHIGAN AS THE FRONT SETTLES THROUGH THE REGION. UPSTREAM
OBSERVATIONS INDICATE SURFACE DEWPOINT SOLIDLY IN THE UPPER 50S OVER
WISCONSIN AND ILLINOIS WITH MODEL FIELDS INDICATING 850 MB DEWPOINT
RISING INTO THE UPPER SINGLE DIGITS(C). THIS REPRESENTS THE MAIN ARM
OF THE LOW LEVEL MOISTURE AXIS HAVING BOTH ADEQUATE MAGNITUDE AND
DEPTH FOR EFFECTIVE INTERACTION WITH THE COLD FRONT...ESPECIALLY
WHEN COMBINED WITH A BOOST OF LARGER SCALE LIFT FROM THE MAIN UPPER
TROUGH AND ENTRANCE REGION OF THE UPPER JET AS THEY BECOME FAVORABLY
POSITIONED OVER THE GREAT LAKES. THIS FORCING WILL TAKE THE PLACE OF
WANING SURFACE BASED INSTABILITY AS THE MOISTURE AXIS SETTLES OVER
LOWER MICHIGAN TOWARD MIDNIGHT. THE RESULT WILL BE A CORRIDOR OF
SHOWERS ABOUT THE WIDTH OF THE SURFACE TO 850 MB FRONTAL ZONE HAVING
ENOUGH COVERAGE FOR ENTRY LEVEL CATEGORICAL POPS DURING LATE EVENING
INTO THE OVERNIGHT BUT EXITING TO THE EAST BEFORE SUNRISE TUESDAY.

LONG TERM...

COLD ADVECTION WILL BE ONGOING TO START THE PERIOD IN THE WAKE OF
THE OVERNIGHT COLD FRONT. H85 TEMPS ARE PROGGED TO FALL FROM AROUND
3C AT 12Z TO -5C BY EVENING, AND THE CORRESPONDING INCREASE IN
BOUNDARY LAYER LAPSE RATES WILL FACILITATE AN EXPANSION OF STRATOCU
DURING THE LATE MORNING/EARLY AFTERNOON HOURS PER AREA NAM SOUNDINGS
AND PLANVIEWS OF H85 RH. CLOUDS WILL BE FURTHER ENHANCED BY THE
PASSING OF A SECONDARY MID-LEVEL TROUGH AXIS, MAKING IT DIFFICULT
FOR TEMPERATURES TO RESPOND TO A DAMPENED COMPONENT OF DIURNAL
HEATING. A FEW PASSING SHOWERS WILL BE POSSIBLE ACROSS THE THUMB
WHERE SLIGHTLY BETTER MOISTURE QUALITY WILL BE IN PLACE AHEAD OF THE
TROUGH, BUT CONDITIONS WILL BE BEST CHARACTERIZED AS COOL/CLOUDY. IN
ADDITION TO TEMPERATURES STUCK IN THE LOW TO MID 50S, GUSTY WINDS
WILL PUT AN ADDITIONAL CHILL IN THE AIR WITH COLD ADVECTION/MODEST
SYSTEM RELATIVE DESCENT HELPING TO FORCE DOWN GUSTS ON THE ORDER OF
25 TO 30 KNOTS.  DEEP LAYER SUBSIDENCE ASSOCIATED WITH AN
APPROACHING UPSTREAM RIDGE WILL THEN COMBINE WITH INCREASINGLY
DISORGANIZED NEAR-SURFACE FLOW WITHIN THE BUILDING ANTICYCLONE TO
SCOUR OUT ANY LINGERING BOUNDARY LAYER CLOUD COVER BY AROUND
MIDNIGHT. LIGHT WARM ADVECTION OCCURRING IN RESPONSE TO BUILDING
HEIGHTS AND CLEAR SKIES WITHIN THE ZONE OF DEEP SYNOPTIC SCALE
SUBSIDENCE WILL ALLOW TEMPERATURES TO BEGIN REBOUNDING INTO THE 55
TO 60 DEGREE RANGE ON WEDNESDAY.

THE LOW PRESSURE SYSTEM MOVING ACROSS THE WESTERN PLAINS WILL START
INFLUENCING WEATHER CONDITIONS OVER THE GREAT LAKES REGION THURSDAY.
CLOUDS AND SCATTERED RAIN ARE EXPECTED BY AFTERNOON. RAIN BECOMES
LIKELY FOR THURSDAY NIGHT INTO EARLY FRIDAY MORNING WITH POPS ABOVE
60 PERCENT MARK. POPS BEGIN TO DWINDLE FOR FRIDAY
AFTERNOON...HOWEVER AN UPPER LEVEL TROUGH WILL ALLOW FOR AT LEAST
SOME SHOWER ACTIVITY TO PERSIST IN THE FORECAST INTO EARLY NEXT
WEEK.

MARINE...

AN APPROACHING COLD FRONT WILL BRING A CHANCE OF THE THUNDERSTORMS
TO THE WATERS THIS EVENING FOLLOWED BY DEVELOPING MODERATE NORTHWEST
FLOW LATE TONIGHT INTO TUESDAY AS COLDER AIR SPILLS INTO THE AREA.
WINDS MAY APPROACH 30 KNOTS AT TIMES BUT CONDITIONS WILL NOT BE
TERRIBLY UNSTABLE...SO GUSTINESS IS NOT EXPECTED TO ADD MUCH THE
OVERALL WIND HAZARD. SMALL CRAFT ADVISORIES MAY BE NEEDED FOR THE
EXPOSED NEARSHORE WATERS OF THE THUMB FOR WINDS...WAVES...OR BOTH BY
LATE TUESDAY. WINDS AND WAVES WILL THEN SUBSIDE LATE TUESDAY NIGHT
INTO EARLY THURSDAY BEFORE THE NEXT SYSTEM BRINGS AN INCREASE IN
SOUTHEASTERLY WINDS.

&&

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

&&

$$

AVIATION.....MR
SHORT TERM...BT
LONG TERM....JVC/DE
MARINE.......JVC


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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).






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