Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 140757
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
357 AM EDT SUN SEP 14 2014

.SHORT TERM...THIS EVENING AND TONIGHT

SURFACE HIGH PRESSURE CENTERED NEAR DOWNTOWN DETROIT WILL RETREAT TO
THE NORTHEASTERN UNITED STATES BY THIS LATE THIS EVENING. WHILE THE
PRESSURE GRADIENT WILL BEGIN THE DAY DIFFUSE...A WELL DEVELOPED
SURFACE TROUGH ADVANCING INTO THE LAKE SUPERIOR REGION WILL ALLOW
SOUTHWESTERLY GRADIENT FLOW TO BE ON THE INCREASE ESPECIALLY NEAR
SAGINAW BAY DURING THE AFTERNOON. FLOW ALOFT WILL CONTINUE TO BE
CHARACTERIZED BY ZONAL FLOW IN THE WAKE OF YESTERDAYS SYSTEM WITH
MOISTURE PROGS CONTINUING TO SUPPORT DEEP DRY AIR IN PLACE OVER THE
REGION. THE EXCEPTION WILL LIKELY BE A MODEST INCREASE IN LOWER
TROPOSPHERE RH AS MOISTURE IS ADVECTED INTO THE STATE AHEAD OF THE
AFOREMENTIONED SURFACE TROUGH. THIS WILL LIKELY LEAD TO A HEALTHY
CUMULUS RESPONSE WITH DAYTIME HEATING TODAY. THE INHERITED FORECAST
WAS QUITE AGGRESSIVE WITH SKY FRACTION AND WILL NOT CHANGE IT TOO
MUCH. FORECAST REASONING FOR TEMPERATURES TODAY IS MIXED WITH A COOL
START AND SUNSHINE EARLY. DECIDED A DEGREE LESS THAN MOS
GUIDANCE...WITH TEMPERATURES MAKING A RUN FOR 60 DEGREES.

LEAD SHORTWAVE ENERGY ATTENDANT TO JET ENERGY ALOFT IN THE ZONAL
CORE WILL STREAM INTO THE NORTHERN GREAT LAKES/STRAITS AND NORTHERN
LAKE HURON THIS EVENING. THE COMBINATION OF CVA AND WARM AIR
ADVECTION IMPACTING THE AREA WILL LEAD TO SOME INCREASING
PRECIPITATION CHANCES ACROSS FAR NORTHERN LOWER MICHIGAN.
HOWEVER...THERE IS HIGH CONFIDENCE THIS WILL STAY OUT OF THE CWA
THROUGH 12Z MONDAY.

&&

.LONG TERM...MONDAY THROUGH SATURDAY

SOUTHERN EXTENSION OF A MODESTLY ACTIVE NORTHERN STREAM FLOW WILL
CONTINUE TO DICTATE CONDITIONS LOCALLY THROUGH THE UPCOMING WORK
WEEK.  A LEAD UPPER WAVE CURRENTLY SEEN ON WATER VAPOR LIFTING
ACROSS MANITOBA WILL TRANSLATE EAST ALONG THE US/CANADIAN BORDER
THROUGH TONIGHT...ACCOMPANIED BY A 100 KNOT UPPER JET STREAK.
TRAILING WAVE STILL OVER THE NORTHWEST TERRITORIES WILL QUICKLY
ENTER THE PICTURE OVER THE NEXT 24 HOURS...EFFECTIVELY AUGMENTING
THE EXPANDING MAIN HEIGHT FALL CENTER FORECAST TO SPILL INTO THE
GREAT LAKES ON MONDAY.  TIMING OF THE ATTENDANT FRONTAL PASSAGE
REMAINS CENTERED FROM MID AFTERNOON THROUGH THE EVENING HOURS.  A
NOTABLE INCREASE IN FORCING WILL COMMENCE THROUGH THIS TIME...AS
FRONTAL CONVERGENCE STRENGTHENS IN THE PRESENCE OF BRIEF FAVORABLE
RIGHT ENTRANCE REGION UPPER JET SUPPORT AND A STRONG BUT BRIEF
UPTICK IN CVA.  MODEST MID LEVEL MOISTURE ADVECTION WILL BE
SUFFICIENT TO SUPPORT SHOWER DEVELOPMENT AS THIS FORCING FIELD
PROPAGATES THROUGH THE REGION.  THIS PROCESS WILL LIKELY BE SLOW AT
THE ONSET GIVEN THE STRENGTH OF THE EXISTING DRY LAYER...WITH THE
RESPONSE EVEN SLOWER AT THE LOWEST LEVELS /DEWPOINTS STRUGGLE TO
REACH 50F/.  THIS IN COMBINATION WITH AN EXTENSIVE CANOPY OF HIGH
CLOUD WILL MINIMIZE THE OPPORTUNITY FOR BETTER PRE-FRONTAL
DESTABILIZATION.  AT THIS STAGE...THIS WILL CONTINUE TO PRECLUDE A
MENTION OF THUNDER.

A PERIOD OF COLD AIR ADVECTION ENSUES UNDER DEEPER POST-FRONTAL
NORTHWEST FLOW MONDAY NIGHT AND EARLY TUESDAY.  THIS WILL LEAVE A
LOW LEVEL THERMAL TROUGH MARKED BY 850 MB TEMPERATURES OF 3 TO 4C IN
PLACE FOR TUESDAY.  ENOUGH RESIDUAL MOISTURE AT THE EDGE OF BUILDING
HIGH PRESSURE TO AGAIN YIELD A BROADER STRATOCU FIELD WITH DAYTIME
HEATING.  THE EXISTING AIR MASS WILL AGAIN CONFINE HIGHS IN THE
LOWER AND MIDDLE 50S.

HIGH PRESSURE TUCKED BENEATH THE PERSISTENT WEAKLY CYCLONIC
NORTHWEST FLOW IN CONTROL ON WEDNESDAY.  LIMITED AIR MASS
MODIFICATION UNDER THIS SETUP WILL LEAVE TEMPERATURES HOVERING
SEVERAL DEGREES BELOW NORMAL.  LATEST MODEL PROJECTIONS CONTINUE TO
DIFFER ON THE DEGREE OF AMPLIFICATION OF THE EXISTING TROUGHING OVER
THE GREAT LAKES LATE WEDNESDAY INTO WED NIGHT.  THE ECMWF OFFERS A
DEEPER SOLUTION RELATIVE TO THE GFS...PROVIDING A WEAK BACKDOOR
FRONTAL PASSAGE AND A MORE PRONOUNCED WINDOW OF COLD AIR ADVECTION
IN NORTHEAST TO EASTERLY FLOW HEADING INTO THURSDAY.  A MORE SIZABLE
RECOVERY IN TEMPERATURES STILL APPEARS IN THE OFFING BY FRIDAY AND
INTO NEXT WEEKEND AS THE CENTRAL CANADA TROUGHING RELAXES AND UPPER
HEIGHTS BUILD NORTHEAST IN RESPONSE.

&&

.MARINE...

SOUTHWEST WINDS WILL EMERGE TODAY AS HIGH PRESSURE SLOWLY EXISTS TO
THE EAST.   BRIEF GUSTS TO 20 KNOTS WILL BE POSSIBLE FROM SAGINAW
BAY INTO CENTRAL LAKE HURON THIS AFTERNOON.  OTHERWISE LIGHT WINDS
AND LIMITED WAVE ACTION CAN BE EXPECTED THROUGH TONIGHT.  COLD FRONT
LIFTING ACROSS THE REGION WILL BRING THE CHANCE OF SHOWERS MONDAY
AFTERNOON AND EVENING.  SLIGHT INCREASE IN POST-FRONTAL NORTHWEST
WINDS MONDAY NIGHT AND TUESDAY.

&&

.AVIATION...ISSUED 1142 PM EDT SAT SEP 13 2014

//DISCUSSION...

PATCHY LOW VFR CEILINGS PERSIST INVOF KMBS AND KFNT BUT MAINLY CLEAR
SKIES PREVAIL ELSEWHERE. THE MOSTLY CLEAR TREND IS FORECAST TO HOLD
THROUGH THE NIGHT AS HIGH PRESSURE BUILDS IN FROM THE WEST ALTHOUGH
A BRIEF LOWER VFR CEILING CANNOT BE RULED OUT AT ANY ONE LOCATION.
THIS CLEARING WILL SUPPORT SOME POTENTIAL FOR LIGHT MVFR RADIATION
FOG DURING THE PRE-DAWN PERIOD. DIURNAL CLOUDS AROUND 4KFT WILL
RETURN BY LATE MORNING ALONG WITH EMERGENCE OF SOUTHWEST FLOW
APPROACHING 10 KTS. CLOUDS WILL GRADUALLY DISSIPATE WITH THE LOSS OF
DIURNAL HEATING SUNDAY EVENING.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET.

&&

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

&&

$$

SHORT TERM...CB
LONG TERM....MR
MARINE.......MR
AVIATION.....JVC


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






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