Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 081657
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1257 PM EDT TUE JUL 8 2014

.AVIATION...

//DISCUSSION...

A PREFRONTAL TROUGH/INITIAL COLD FRONT SWEPT THE MAIN AREA OF
SHOWERS AND THUNDERSTORMS TO THE EAST OF THE TERMINAL CORRIDOR
SHORTLY AFTER NOON. SCATTERED SHOWERS AND MVFR CEILING LEFT OVER THE
REGION IS TRAILING THE BACK EDGE BUT AHEAD OF THE PRIMARY COLD FRONT
WHICH WILL ALSO EXIT TO THE SOUTH AND EAST OF THE REGION DURING MID
TO LATE AFTERNOON. A MODEST DECREASING CLOUD TREND WILL FOLLOW THE
FRONTAL PASSAGE DURING THE EVENING BUT THE COLD FRONT IS NOW
EXPECTED TO STALL JUST SOUTH OF THE OHIO BORDER DURING THE NIGHT.
THIS MAKES LOW CLOUD REDEVELOPMENT LIKELY WITH MVFR CEILING HAVING
THE BEST CHANCE OF AFFECTING THE DTW TERMINAL REGION THROUGH SUNRISE
WEDNESDAY. LIGHT BUT COOLER NW SURFACE WIND WILL THEN HELP LIFT
CEILING DURING WEDNESDAY MORNING INTO THE AFTERNOON.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING BELOW 5000 FT DURING THE AFTERNOON...
  MEDIUM CONFIDENCE WEDNESDAY MORNING.

&&

.PREV DISCUSSION...ISSUED 1055 AM EDT TUE JUL 8 2014

UPDATE...

COMPLEX INTERACTION BETWEEN THE MATURE MCV SLIDING THROUGH OHIO
AND THE COLD FRONT OVER LOWER MICHIGAN HAS ACTUALLY LESSENED THE
CONCERN FOR STORM SEVERITY AS THE PATTERN MOVES THE REST OF THE
WAY THROUGH SE MICHIGAN. THE MCV...CLEARLY ORIGINATING FROM
CONVECTION LAST NIGHT OVER MISSOURI...HELPED GENERATE ENOUGH
SHOWER AND THUNDERSTORM COVERAGE ON ITS NORTH FLANK TO KEEP
INSTABILITY IN CHECK AHEAD OF THE FRONT IN OUR AREA. COMPOSITE
RADAR IMAGERY AND SURFACE OBSERVATIONS INDICATE SHOWERS AND STORMS
FOCUSED ALONG THE FRONT BUT ONLY ABLE TO GENERATE WIND GUSTS
AROUND 30 MPH. EXPECT LOCALLY HEAVY RAINFALL AND PONDING OF WATER
ON ROADS AND IN PRONE AREAS TO BE THE MAIN CONCERNS THE REST OF
THE WAY UNTIL THE FRONT SWEEPS THE PATTERN EASTWARD. EARLY TO MID
AFTERNOON FRONTAL PASSAGE REMAINS ON TRACK WITH DRY CONDITIONS BUT
LINGERING CLOUD COVER THROUGH THE REST OF THE DAY.

PREV DISCUSSION...ISSUED 321 AM EDT TUE JUL 8 2014

SHORT TERM... TODAY AND TONIGHT

SHORTWAVE ENERGY STREAMING THROUGH THE PERIPHERY OF BROAD MID LEVEL
TROUGHING WILL TRANSLATE INTO A STEADY LOWERING OF THE HEIGHT FIELD
THROUGHOUT THE GREAT LAKES OVER THE NEXT 24 HOURS.  LEAD EDGE OF
THESE HEIGHT FALLS ANCHORING A STRONGER KINEMATIC RESPONSE WITHIN
THE MASS FIELDS...A DEEP COLUMN INCREASE NOTED UPSTREAM IN THE
ATTENDANT PRE-FRONTAL WIND FIELD.  THE ASSOCIATED INCREASE IN MID
LEVEL ASCENT...LIKELY ENHANCED VIA ONE OR MORE EMBEDDED
IMPULSES...WORKING ALONG A THIN HIGHER THETA-E PLUME CURRENTLY
ANCHORING A CONVECTIVE COMPLEX EXTENDING FROM CENTRAL LAKE MICHIGAN
INTO SOUTHWEST WISCONSIN.  THIS ENVIRONMENT WILL STEADILY ADVECT
EASTWARD AND INTO SE MICHIGAN THROUGH THE LATTER HALF OF THE MORNING
PERIOD.

THERE REMAINS SOME POTENTIAL FOR THIS LEAD CORRIDOR OF CONVECTION TO
DIMINISH IN COVERAGE YET THIS MORNING AS IT OUTPACES THE MAIN
MOISTURE GRADIENT AND SUPPORTING ASCENT.  HOWEVER FORCING REMAINS
FORECAST TO INCREASE COINCIDENT WITH MODEST THETA-E ADVECTION
THROUGH THE LATE MORNING/EARLY AFTERNOON PERIOD.  THIS CONTINUES TO
SUPPORT SOME DEGREE OF MAINTENANCE AND/OR RENEWED DEVELOPMENT
LOCALLY DURING THIS TIME...AND WILL HOLD FIRM WITH THE GOING LIKELY
POPS.  OVERALL INSTABILITY WILL CARRY SOME DEPENDENCE ON THE SCALE
AND TIMING OF ANY INBOUND PRECIPITATION AND CLOUD COVER THIS
MORNING...BUT RECENT MODEL GUIDANCE CONTINUES TO SHOW MUCAPES IN
EXCESS OF 1500 J/KG.  THIS WILL LEAVE THE DOOR OPEN FOR THE
POSSIBILITY OF A PERIOD OF MORE ORGANIZED CONVECTION TO EMERGE GIVEN
THE IMPRESSIVE WIND FIELDS...0-6 KM SHEAR VALUES IN THE 40 TO 45
KNOT RANGE.  TEMPERATURES WILL BE CAPPED BY LIMITED INSOLATION
POTENTIAL...HIGHS MID TO UPPER 70S.

LATE AFTERNOON FRONTAL PASSAGE WITH STEADY BOUNDARY LAYER DRYING
HEADING INTO THE EVENING.  HEIGHTENED CYCLONIC FLOW AS THE MAIN MID
LEVEL TROUGH BASE PIVOTS ACROSS NORTHERN LOWER MI MAY PROVIDE ENOUGH
ASCENT TO KICK OFF A FEW WIDELY SCATTERED SHOWERS THROUGH THE FIRST
HALF OF THE NIGHT.  NOCTURNAL COOLING AUGMENTED BY WEAK COLD AIR
ADVECTION...LOWS LARGELY ARRIVING IN THE MIDDLE AND UPPER 50S
WEDNESDAY MORNING.

LONG TERM...

STRONG PV ANOMALY/UPPER WAVE TO ROTATE THROUGH LOWER MICHIGAN ON
WEDNESDAY...WITH NORTHWEST FLOW IN THE WAVES WAKE USHERING IN COOLER
AIR TO THE REGION TO FINISH THE WORK WEEK. THE ISSUE WITH THE UPPER
WAVE IS THE EARLY TIMING...AS CENTER/COLD POOL (-20 C AT 500 MB) IS
EAST OF SOUTHEAST MICHIGAN BY 18Z...WITH GENERAL SUBSIDENCE REGIME
TAKING OVER...COUPLED WITH THE LIMITED/SHALLOW MOISTURE IN THE FIRST
PLACE...AND THE COVERAGE/CHANCES FOR SHOWERS IS LOW...WITH THE
PROSPECT FOR THUNDERSTORMS EVEN LOWER. 850 MB DEW PTS IN THE MID TO
PERHAPS UPPER SINGLE NUMBERS TO START THE DAY (MAINLY SOUTH OF
M-59)...WILL TRY TO MIX OUT DURING THE AFTERNOON HOURS...WHICH WOULD
EFFECTIVELY END THE CHANCE.

EXPANSIVE HIGH PRESSURE (1022 MB) WILL THEN TAKE CONTROL ON
THURSDAY...RESULTING IN TEMPERATURES SOLIDLY BELOW NORMAL...AS 850
MB TEMPS HOLD UNDER 10 C ON THURSDAY.

WE BEGIN TO GET INTO THE RETURN FLOW/WARM ADVECTION PATTERN ON
FRIDAY AS THE HIGH PUSHES EAST...WITH 850 MB TEMPS RISING INTO THE
LOWER TEENS. MOISTURE ADVECTION AND SHORTWAVE TROUGH FORECASTED TO
ARRIVE FRIDAY EVENING/NIGHT...WORTHY OF CHANCE POPS.

POTENTIALLY ACTIVE JET STREAM ON TOP OF US OVER THE WEEKEND...AND
TIMING OF UPPER LEVEL DISTURBANCES THIS FAR OUT IS ALWAYS A
PROBLEM...AND CHANCES POPS THROUGH THE WEEKEND WILL HAVE TO SUFFICE.
TEMPERATURES ACTUALLY LOOK TO CLIMB THERE WAY BACK TO AROUND
NORMAL...BUT INDICATIONS FOR EARLY NEXT WEEK ARE FOR ANOTHER LARGE
UPPER LEVEL LOW TO TAKE RESIDENCE OVER ONTARIO...SENDING US BACK
INTO THE 70S FOR HIGHS.

MARINE...

LOW PRESSURE WILL TRACK ACROSS NORTHERN LOWER MICHIGAN TODAY...WITH
SOUTHWEST WINDS IN THE 10 TO 20 KNOTS RANGE EXPECTED ACROSS ALL
MARINE WATERS. THERE LOOKS TO BE A SLIGHT ENHANCEMENT ACROSS SAGINAW
BAY...AND HAVE ISSUED SMALL CRAFT ADVISORIES FOR WINDS GUSTING TO 25
KNOTS DURING THE DAY. WINDS WILL SHIFT TO THE WEST WEDNESDAY...BUT
WILL BE UNDER 15 KNOTS...AS COOLER AIR SETTLES OVER THE CENTRAL
GREAT LAKES. HIGH PRESSURE OVER THE REGION THURSDAY WILL ASSURE THE
LIGHT WINDS AND LOW WAVES CONTINUE...RIGHT INTO FRIDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...SAGINAW BAY...UNTIL 6 PM TUESDAY.

LAKE ST CLAIR...NONE.

MI WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....BT
UPDATE.......BT
SHORT TERM...MR
LONG TERM....SF
MARINE.......SF


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