Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 210351
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1151 PM EDT SAT SEP 20 2014


.AVIATION...

//DISCUSSION...

A GRADUAL EXPANSION OF IFR STRATUS HAS BEEN OCCURRING IN THE WAKE OF
THE EVENING STORMS. LOW LEVEL MOISTURE AND A DEVELOPING INVERSION
SHOULD CAUSE CONTINUED LOW STRATUS DEVELOPMENT INTO THE MORNING.
ANOTHER UPPER LOW RAPIDLY APPROACHING FROM THE WEST AND A RENEWED
SURGE OF INSTABILITY WILL LEAD TO INCREASING CHANCES FOR
THUNDERSTORMS DURING THE MORNING INTO EARLY AFTERNOON. ALTHOUGH
THERE WILL BE A GOOD CHANCE FOR STORMS ANYTIME AFTER 09Z...THE MOST
PROBABLE TIME PERIOD WILL BE AHEAD OF THE COLD FRONT. THE FRONT WILL
ENTER MBS BY 12Z...BUT WILL LIKELY SLOW AS IT WORKS ACROSS METRO
DETROIT LATE MORNING AND EARLY AFTERNOON AS THE UPPER WAVE SLOWS.

FOR DTW...

THERE CERTAINLY IS A POTENTIAL FOR STORMS TO LIFT UP FROM THE
SOUTH AND IMPACT METRO EARLY THIS MORNING. CHANCES OF THIS ARE
QUITE LOW ATTM. THE BEST INSTABILITY AND LOW LEVEL CONVERGENCE
WILL OCCUR DURING THE AFTERNOON.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE CEILINGS WILL BE BELOW 5000 FT THROUGH THE TAF
PERIOD.

* MEDIUM CONFIDENCE ON THUNDERSTORMS SUN MORNING AND SUN
  AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 913 PM EDT SAT SEP 20 2014

UPDATE...

STRONG MID LEVEL SUBSIDENCE NOW OVERSPREADING SE MI IN THE WAKE OF
THE EARLIER CONVECTIVE ACTIVITY WILL SUPPRESS ADDITIONAL SHRA/TSTM
DEVELOPMENT FOR THE REST OF THE EVENING AND FIRST HALF OF THE
OVERNIGHT. THERE HAS BEEN CONVECTIVE DEVELOPMENT ALONG A COLD
FRONT OVER NORTHERN LOWER MI. THIS FRONT WILL PUSH ACROSS THE
SAGINAW VALLEY AND THUMB REGION LATE TONIGHT INTO EARLY SUN
MORNING. THE 00Z GRB SOUNDING SHOWED FAIRLY STEEP MID LEVEL LAPSE
RATES...SUPPORTING GOOD ELEVATED INSTABILITY. THE SECONDARY MID
LEVEL WAVE NOW TRAVERSING MN THIS EVENING WILL PROVIDE ANOTHER
ROUND OF LARGE SCALE ASCENT LATE TONIGHT INTO SUN MORNING. COOLING
ALOFT ASSOCIATED WITH THIS WAVE WILL IN TURN STEEPEN THE MID LEVEL
LAPSE RATES OVER SE MI. THUS ADDITIONAL CONVECTION IS POSSIBLE
LATE ACROSS THE NORTH HALF OF THE FORECAST AREA WITH THE APPROACH
OF THE FRONT. THE CHANCES FOR SHRA/TSTM WILL THEN INCREASE FURTHOR
SOUTH SUNDAY MORNING INTO AFTERNOON AS THE FRONT PUSHES THROUGH
AND THE UPPER WAVE PASSES OVERHEAD. AN UPDATED FORECAST PACKAGE
REFLECTING THIS WILL BE FORTHCOMING.

PREV DISCUSSION...ISSUED 314 PM EDT SAT SEP 20 2014

SHORT TERM...THIS AFTERNOON AND TONIGHT

SEVERAL OUTFLOW BOUNDARIES FROM OVERNIGHT CONVECTION WELL TO THE
WEST ARE TRACKING ACROSS LOWER MICHIGAN. HOWEVER...18Z DTX SOUNDING
SHOWS A RATHER ROBUST CAP IN THE 875-850MB AREA...WHICH WILL LIKELY
TAKE QUITE SOME TIME TO TOTALLY ERODE. MODELS...INCLUDING PRIMARY
AND PARALLEL HRRR RUNS TODAY...SUGGEST CONVECTION WILL EVENTUALLY
FILL IN ALONG BOTH OUTFLOW BOUNDARY SINKING SOUTH/SOUTHEAST THROUGH
THE CWA AND ALSO ALONG VORTICITY SPOKE FURTHER WEST ASSOCIATED WITH
LEFTOVER WEAK MCV. GIVEN CAPPING...AND THE LACK OF SIGNIFICANT
INSTABILITY...EXPECT THIS ACTIVITY TO REMAIN RATHER DISORGANIZED AND
SUB-SEVERE FOR THE MOST PART.

WILL STILL WATCH FOR THE POTENTIAL OF A FEW SEVERE STORMS AS WIND
FIELDS ARE DECENT...INCREASING FROM 25-30 KNOTS H85-H7 TO 50 KNOTS
AT H5. WITH ADDITIONAL HEATING...TEMPERATURES AROUND 80F DETROIT
SOUTH...OVER THE SOUTHERN CWA AND A LACK OF NOTABLE DEEP LOW LEVEL
MOISTURE...INVERTED-V SOUNDINGS MAY ASSIST IN GUST POTENTIAL GIVEN
THE ABOVE ATMOSPHERIC WIND SPEEDS.

THIS INITIAL PUSH OF FORCING...AND WHATEVER CONVECTION COMES OF
IT...WILL SHIFT EAST/SOUTHEAST OF THE AREA LATE THIS AFTERNOON/EARLY
THIS EVENING. HOWEVER...HIGHER THETA-E AIR WILL CONTINUE TO SHIFT
OVER THE CWA...PARTICULARLY M 59 SOUTH...WITHIN SOUTHWEST FLOW IN
ADVANCE OF MAIN SHORTWAVE TROUGH AXIS. SO...ADDITIONAL SCATTERED
SHOWERS/EMBEDDED STORMS WILL BUILD THROUGH AREA INTO THIS EVENING.
ONCE THIS ACTIVITY EBBS LATE THIS EVENING...EXPECT RENEWED SHOWER
AND STORM DEVELOPMENT LATE TONIGHT AS MAIN UPPER LEVEL SHORTWAVE
DIGS FROM THE UPPER MISSISSIPPI VALLEY INTO THE CENTRAL GREAT LAKES.

WITH MILD...SOUTHWEST FLOW PERSISTING THROUGH THE NIGHT...MINIMUM
TEMPERATURES WILL BE RATHER MILD...HOLDING IN THE 60S IN MOST
LOCATIONS...ESPECIALLY AS FURTHER CLOUDS/PRECIPITATION PROVIDE
ADDITIONAL INSOLATION AND MINIMIZE RADIATIONAL COOLING FURTHER.

LONG TERM...

LATEST WATER VAPOR IMAGERY SHOWS A STRONG BUT PROGRESSIVE UPPER
LEVEL SYSTEM/CIRCULATION OVER SOUTHERN MANITOBA...WITH A STRONGER
EMBEDDED UPPER WAVE AT THE BASE OF THE TROUGH OVER NORTH DAKOTA. IT
IS THIS UPPER WAVE/COLD POOL (-18 TO -19 C) WHICH WILL ARRIVE OVER
SOUTHERN LOWER MICHIGAN SUNDAY MORNING. WITH SOME LEFTOVER LOW LEVEL
MOISTURE AND MORE THAN ADEQUATE MID LEVEL LAPSE RATE (6.5+ C/KM FROM
700-500 MB)...ADDITIONAL SHOWERS AND EMBEDDED THUNDERSTORMS APPEAR
LIKELY DURING SUNDAY. A SECONDARY UPPER WAVE/COLD POOL WILL FOLLOW
ON THE BACKSIDE THROUGH THE WESTERN GREAT LAKES AND INTO THE OHIO
VALLEY. DEEP NORTHERLY FLOW IN THIS SYSTEMS WAKE OVER THE CENTRAL
GREAT LAKES WILL ALLOW FOR SOLID COLD ADVECTION TO TAKE PLACE...AS
850 MB TEMPS LOWER INTO THE LOW SINGLE NUMBERS...WITH SLIGHTLY
NEGATIVE VALUES OVER LAKE HURON...PER 12Z EURO/NAM. AS SUCH...FULLY
ONBOARD WITH THE 12Z NAM 925 MB RH/LOW CLOUDS AS NORTHERLY FLOW
COMES OFF THE RELATIVELY WARM WATERS OF LAKE HURON SUNDAY NIGHT.
HAVE SUBSEQUENTLY RAMPED UP THE CLOUDS MONDAY MORNING...WHICH WILL
LIKELY TAKE MUCH OF THE DAY TO MIX OUT/ERODE...HOLDING MAXES CLOSE
TO 60 DEGREES. FAVORABLE RADIATING CONDITIONS MONDAY NIGHT EXPECTED
TO ALLOW MINS TO FALL INTO THE 40S.

STUBBORN HIGH PRESSURE AND RELENTLESS LOW RH VALUES THROUGH THE
COLUMN WILL REMAIN IN PLACE FOR THE ENTIRE EXTENDED PERIOD. FLOW
WILL CONTINUE TO BE WEAK UNDER AN OMEGA BLOCKING HIGH. TEMPERATURES
WILL TREND SLIGHTLY ABOVE NORMAL WITH NO THREAT OF PRECIPITATION.

MARINE...

WARMER AIRMASS AHEAD OF COLD FRONT...COUPLED WITH THE WEAKENING
PRESSURE GRADIENT AS THE FRONT APPROACHES IS TRANSLATING
TO WIND SPEEDS BELOW 25 KNOTS...AND WILL DROP THE SMALL CRAFT
ADVISORIES. HOWEVER...SHOWERS AND THUNDERSTORMS WILL LIKELY
DEVELOP...AND THUNDERSTORMS WILL BE STRONG TO POSSIBLY SEVERE INTO
TONIGHT. A SECONDARY UPPER WAVE AND COLD FRONT WILL LEAD TO
ADDITIONAL SHOWERS TOMORROW AND POSSIBLE THUNDERSTORMS. BRISK
NORTHERLY WINDS OF 20 TO 25 KNOTS WILL FOLLOW THIS FRONT...ALLOWING
LARGE WAVE TO BUILD OVER SOUTHERN LAKE HURON SUNDAY NIGHT INTO
MONDAY...WITH SMALL CRAFT ADVISORIES LIKELY NEED DURING THAT TIME
FRAME. HIGH PRESSURE WILL EXERT FAVORABLE INFLUENCE ON THE WATERS
DURING THE MIDDLE OF NEXT WEEK.

&&

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

&&

$$

AVIATION.....SC
UPDATE.......SC
SHORT TERM...DG
LONG TERM....SF/MM
MARINE.......SF


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






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