Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 250739
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
339 AM EDT MON AUG 25 2014

.SHORT TERM...TODAY AND TONIGHT

THE SFC HIGH PRESSURE NOW EXTENDING ACROSS THE ERN GREAT LAKES WILL
BUILD INTO THE MID ATLANTIC TODAY AS THE SFC COLD FRONT OVER THE
UPPER MIDWEST ADVANCES INTO WISCONSIN AND WRN UPPER MI. THIS WILL
CAUSE THE LOW LEVEL FLOW TO VEER TOWARD THE SOUTH ACROSS SRN MI. THE
EXCEPTION WILL BE ALONG THE LAKES ERIE/ST CLAIR/HURON SHORELINE
WHERE HI RES SOLUTIONS SUGGEST A CONTINUED SE COMPONENT TO THE
SURFACE WINDS. AREAS OF STRATUS HAVE BEEN EXPANDING ACROSS THE
FORECAST AREA EARLY THIS MORNING AS THE LOW LEVELS REMAIN VERY
MOIST. THE STRATUS IS NOT NEARLY AS EXTENSIVE AS THIS TIME YESTERDAY
MORNING. THE SOUTHERLY FLOW SHOULD ALSO PROMOTE ENOUGH WARMING FROM
THE BOUNDARY LAYER THROUGH 900MB TO MIX OUT THE MORNING STRATUS MORE
EFFECTIVELY THAN YESTERDAY. LOW TO MID LEVEL WARMING TODAY AND VERY
MOIST LOW LEVELS SHOULD LIMIT THE MIXING DEPTHS...WHICH SUPPORT HIGH
TEMPS GENERALLY IN THE MID TO UPPER 80S DESPITE 850MB TEMPS PUSHING
+19C THIS AFTERNOON. HIGHS WILL BE SUPPRESSED TO THE LOW 80S ALONG
THE LAKESHORES DUE TO THE MORE SE WIND DIRECTION. THE UPPER 60 TO
LOW 70 SFC DEWPOINTS BLANKETING IN/OH WILL HOWEVER PROGRESS INTO SE
MI BY AFTERNOON...PUSHING HEAT INDICES TOWARD THE 90 DEGREE MARK. AN
INCREASE IN THE S-SW FLOW ABOVE THE BOUNDARY LAYER TONIGHT COMBINED
WITH THE HIGH SFC DEWPOINTS WILL LEAD TO A WARM AND MUGGY NIGHT
/TEMPS ONLY DROPPING OFF TO AROUND 70/.

A STRENGTHENING MID LEVEL CAP IS STILL EXPECTED TO SUPPRESS
CONVECTION THROUGH THE AFTERNOON DESPITE THE BUILDUP OF MODERATE
INSTABILITY. SEVERAL HI RES SOLUTIONS SUGGEST THE DEVELOPMENT OF
SOME TROUGHING IN THE LEE OF LAKE MI THIS AFTERNOON. THE POTENTIAL
FOR SOME WEAKENING OF THE CAP LATE IN THE DAY AND A SLIGHT INCREASE
IN THE W-SW MID LEVEL WIND FIELD WILL PROVIDE A LOW CHANCE OF SOME
CONVECTION MOVING INTO THE FORECAST AREA /MAINLY THE SAGINAW VALLEY/
DURING THE EVENING. OTHERWISE...CHANCES FOR CONVECTION /AGAIN MAINLY
ACROSS THE SAGINAW VALLEY/ LOOK SLIGHTLY BETTER DURING THE OVERNIGHT
AS THE COLD FRONT AND AXIS OF STEEPER MID LEVEL LAPSE RATES MOVES
INTO NORTHERN MI AND CNTL LAKE MI. OVERALL FORCING ALONG THIS
BOUNDARY IS EXPECTED TO BE FAIRLY WEEK. THE WESTERLY FLOW ALOFT AND
HIGH DEGREE OF ELEVATED INSTABILITY DOES SUGGEST THE POSSIBILITY OF
SOME UPSTREAM CONVECTION ADVANCING INTO SE MI DURING THE OVERNIGHT.
WHILE ELEVATED INSTABILITY IS EXPECTED TO BE QUITE GOOD TONIGHT
/0-3KM MU CAPE AROUND 2K J/KG/...THE LACK OF LARGER SCALE SUPPORT
SUGGEST COVERAGE OF CONVECTION WILL NOT BE ENOUGH TO WARRANT A
SLIGHT RISK. SOME ISOLATED STRONG TO SEVERE STORM CAN NOT BE RULED
OUT HOWEVER GIVEN THE DEGREE OF INSTABILITY.

&&

.LONG TERM...TUESDAY THROUGH SUNDAY

THE ONCE AMPLIFIED LONGWAVE PATTERN HAS BECOME FAIRLY ZONAL WITH THE
BULK OF THE JET ENERGY TRAVELING ALONG THE US/CANADA BORDER. THE
FLOW BECOMES LOCKED TO OUR NORTH THROUGH THE END OF THE WEEK AS AN
UPPER LOW CUTOFF OVER THE ROCKIES SLOWLY DRIFTS INTO THE CENTRAL
PLAINS BEFORE BEING GETTING A PUSH FROM A TROUGH SWINGING THROUGH
THE WESTERN CONUS. THIS PATTERN HAS THE POTENTIAL TO BE FAIRLY WET
AS SEVERAL KEY FEATURES PASS THROUGH THE GREAT LAKES. THE FEATURES
BEING A COLD FRONT ON TUESDAY...A STATIONARY FRONT THURSDAY NIGHT
INTO SATURDAY...AND FINALLY THE CUTOFF UPPER LOW SUNDAY AND MONDAY.
THERE WILL OF COURSE BE BREAKS IN THE ACTION WHICH WILL BE GOAL TO
PIN DOWN.

FIRST ORDER OF BUSINESS WILL BE TO ASSESS TUESDAY/TUESDAY NIGHTS
COLD FRONTAL PASSAGE AND ANY SEVERE POTENTIAL. THE FRONT IS TIED TO
A BROAD AREA OF SFC LOW PRESSURE WHICH IS DEEPENING AS IT TRACKS NE
THROUGH QUEBEC. FRONTAL FORCING WILL BE WEAK BY THE TIME IT REACHES
SE MI AS THE LOW IS QUITE REMOVED AND IT WILL BE RUNNING INTO THE
RIDGE OVER THE SE CONUS WHICH FOLDED OVER EARLIER IN THE WEEK. THE
RIDGE WILL CAUSE THE FRONT TO CHANGE ORIENTATION FROM N/S TO MORE
W/E DURING THE LATE EVENING/OVERNIGHT PERIOD TUESDAY. MODELS HAVE
BEEN CONSISTENT WITH DEVELOPING CONVECTION ALONG THE FRONT BUT THE
NATURE AND COVERAGE OF CONVECTION ARE IN QUESTION. INSTABILITY WILL
BE MORE THAN ADEQUATE WITH MODELS AVERAGING AROUND 2000 K/KG IN THE
MOISTURE RICH AIRMASS AHEAD OF THE FRONT. AS WE GET DEEPER INTO THE
PREFRONTAL SW FLOW...THE DEWPOINTS WILL RISE FROM THE MID 60S INTO
THE LOW 70S. THE 700MB CAP SHOULD KEEP CONVECTION TO A MINIMUM
THROUGH THE EARLY PART OF THE DAY LEAVING THE FRONT TO CROSS THE
AREA NEAR PEAK HEATING. BULK SHEAR IS ON THE LOW SIDE...AROUND 20
KNOTS...WHICH WILL HELP KEEP STORMS AT BAY BUT WILL BE ENOUGH FOR
SOME STRONG TO SEVERE STORMS. THE CAVIOT TO ALL OF THIS IS THE
POTENTIAL FOR AN EARLY MORNING MCS FROM OVERNIGHT CONVECTION
UPSTREAM TO CROSS THE AREA. MODELS ARE ADVERTISING A CONVECTIVELY
INDUCED WAVE TO TRACK THROUGH SOUTHERN MI. THE EXTENT OF THIS
CONVECTION AND CLOUD COVER WILL DICTATE HOW THE ATMOSPHERE CAN
RECOVER FOR THE FRONTAL PASSAGE. NOT COUNTING ANYTHING OUT AT THIS
POINT.

FOR WEDNESDAY...THE FRONT WILL HAVE PASSED THE AREA AND WILL STALL
ACROSS THE NORTHERN OHIO VALLEY. MODELS ARE SHOWING SHORTWAVE RACING
ACROSS SOUTHERN CANADA REACHING DOWN INTO NORTHERN MI. THE POST
FRONTAL AIRMASS WILL USHER IN A GOOD DEAL OF COOL AIR...850MB TEMPS
DROPPING FROM 19C WED 00Z TO 10C THURS 00Z...INTO THE BL WHICH WILL
STRENGTHEN THE CAP 700-850MB LAYER WHICH MAY BE ENOUGH TO SUPPRESS
CONVECTION AND RESULT ONLY IN A MID CLOUD DECK. WILL LEAN THIS WAY
AND KEEP THE DAY DRY AT THIS POINT.

THE STATIONARY BOUNDARY DRAPED TO OUR SOUTH WILL LIFT BACK INTO THE
AREA LATE THURSDAY AS THE CUTOFF LOW APPROACHES. SHORTWAVES EJECTING
OUT OF THE TROUGH WILL HAVE A CHANCE TO PRODUCE SEVERAL ROUNDS OF
PRECIP LATE THURSDAY THROUGH SATURDAY. WILL CARRY CHANCE POPS FOR
NOW AND TIME INDIVIDUAL WAVES AS IT DRAWS NEARER. THE UPPER LOW WILL
THEN DRIFT THROUGH THE REGION LATE IN THE WEEKEND RESULTING IN
CONTINUED CHANCES OF POPS WITH MODELS NOW SPINNING UP A SFC LOW
ALONG WITH IT.

&&

.MARINE...

LOW LEVEL WINDS WILL VEER TO THE SOUTH TODAY OUT AHEAD OF A COLD
FRONT WHICH WILL IS OVER THE NORTHERN GREAT LAKES CURRENTLY AND WILL
SWEEP THROUGH THE EASTERN GREAT LAKES ON TUESDAY. A VERY WARM
AIRMASS IS LIFTING INTO THE AREA AHEAD OF THE FRONT WHICH WILL
INCREASE STABILITY OVER THE COOL LAKES KEEPING WINDS AND WAVES AT A
MINIMUM. THE FRONT WILL SLOWLY DROP THROUGH THE REGION TUESDAY AND
WILL POSSIBLY BE ACCOMPANIED BY STRONG TO SEVERE STORMS. THE FRONT
WILL STALL OUT JUST TO THE SOUTH OF THE SOUTHERN GREAT LAKES THROUGH
MID WEEK.

&&

.AVIATION...ISSUED 1206 AM EDT MON AUG 25 2014

//DISCUSSION...

LATE EVENING SURFACE OBSERVATIONS BEGAN TO SHOW SE SURFACE WIND
DROPPING OFF ENOUGH TO ALLOW SOME COOLING AND SOME LIGHT FOG FORMING
IN PRONE AREAS. EXPECT THIS WILL CONTINUE IN BETWEEN A DISORGANIZED
PATTERN OF VFR STRATOCU THAT WILL COME AND GO ENOUGH TO POSSIBLY
PREVENT LIFR CEILING/IFR VISIBILITY. MBS HAS THE BEST POTENTIAL TO
BENEFIT FROM THAT THROUGH SUNRISE. A SHORT PERIOD OF MVFR CEILING IS
LIKELY DURING THE MORNING AS SURFACE HEATING CHURNS THE BOUNDARY
LAYER BEFORE BASES LIFT TO VFR BY AFTERNOON THROUGH MONDAY EVENING.

FOR DTW... SURFACE WIND LIGHT FROM THE SOUTHEAST WILL SWEEP EXTRA
MOISTURE INTO THE TERMINAL REGION TO MAINTAIN FOG POTENTIAL AND/OR
LIFR STRATUS TOWARD SUNRISE...ESPECIALLY IF VFR CEILING REMAINS WEST
AND NORTH. INCREASING SOUTHERLY FLOW DOES POINT TO A FASTER RATE OF
IMPROVEMENT BY AFTERNOON COMPARED TO RECENT DAYS.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING AOB 5000 FT DURING THE MORNING.

* LOW CONFIDENCE IN CEILING BELOW 200 FEET AND/OR VISIBILITY BELOW
  1/2SM EARLY MORNING.

&&

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

&&

$$

SHORT TERM...SC
LONG TERM....DRK
MARINE.......DRK
AVIATION.....BT


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





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