Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 011627
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1227 PM EDT MON SEP 1 2014

.UPDATE...

MOST OF SOUTHEAST MICHIGAN REMAINS SHROUDED IN LOW AND MID-LEVEL
CLOUDS EARLY THIS AFTERNOON, ALTHOUGH THE LATEST TRENDS ON VISIBLE
INDICATE THAT THE STRATUS DECK HAS BEGUN TO EVOLVE TOWARD A
DIURNALLY FORCED CU FIELD. AS A RESULT, TEMPERATURES HAVE RISEN INTO
THE MID TO UPPER 70S FROM WESTERN LOWER MI NORTHEASTWARD INTO THE
THUMB WHILE DEWPOINTS REMAIN LOCKED IN AROUND 70 DEGREES.

THE STOUT 600MB CAP INDICATED ON THIS MORNING`S SOUNDING REMAINS THE
ONLY IMPEDANCE, ALBEIT A POTENTIALLY SIGNIFICANT ONE, TO WIDESPREAD
SEVERE WEATHER THIS AFTERNOON. CAP NOTWITHSTANDING, THERMODYNAMIC
PROFILES ARE IMPRESSIVE. MODERATE DESTABILIZATION IS STILL FAVORED
GIVEN THE ABUNDANCE OF LOW-LEVEL MOISTURE AND SURFACE TEMPERATURES
ALREADY PUSHING UPPER 70S AT NOON. 0-6KM BULK SHEAR FEATURING
VEERING THROUGH THE LOWEST 1.5KM AGL AND AFOREMENTIONED DEGREE OF
DESTABILIZATION WILL SUPPORT AN INITIAL CONVECTIVE MODE OF
SUPERCELLS. ANY SUPERCELLS WILL CARRY TORNADIC POTENTIAL GIVEN
FAVORABLE THERMODYNAMIC PROFILES FOR STRETCHING IN THE LOWEST
LEVELS, VEERED SFC-1KM WIND PROFILES, AND REASONABLY LOW LCLS OF
700-900M. UNIDIRECTIONAL MID-LEVEL WIND PROFILE AND PLENTY DRY AIR
WOULD THEN SUPPORT A QUICK EVOLUTION TOWARD DOWNDRAFT MODULATED
CONVECTION AND A CORRESPONDING EVOLUTION TOWARD DYNAMIC BOWS EARLY
IN THE CONVECTIVE CYCLE. GIVEN THE HIGH FREEZING LEVELS, THE LACK
OF MESOCYCLONE FORCING WITHIN BOWS WILL TEND TO LIMIT THE THREAT
TO WIND ONLY.

IN SPITE OF THE RIPE ENVIRONMENT, CAPPING LOOMS LARGE. THE 12Z NAM12
ALLOWS ENCROACHING HEIGHT FALLS TO USHER IN SUFFICIENT MID-LEVEL
COOLING SUPPORTIVE OF STRONG, DEEP CONVECTION THROUGH THE
EARLY/MID AFTERNOON. AT THE SAME TIME, THE LAST SEVERAL RUNS OF
THE RAP IS CONSIDERABLY SLOWER COOLING THE COLUMN AND LIMITS ANY
SEVERE THREAT TO THE SAGINAW VALLEY AREA WHERE MID-LEVEL
COOLING/FORCING WILL BE MAXIMIZED. THE SOLUTION SPACE REMAINS WIDE
OPEN AND CONFIDENCE IN SEVERE WX IS CORRESPONDINGLY LOW. AT THIS
POINT, EVEN COVERAGE OF CONVECTION SEEMS TO BE IN QUESTION,
PARTICULARLY IF THE LATEST NON NAM GUIDANCE IS TO BE BELIEVED. IN
PURSUIT OF CLARITY, AN 18Z SOUNDING IS FORTHCOMING.

&&

.AVIATION...ISSUED 703 AM EDT MON SEP 1 2014

//DISCUSSION...

FOG AND STRATUS IN THE WARM AND HUMID AIR OVER SE MICHIGAN WILL
PRESENT LIFR/IFR CONDITIONS AS THE FIRST CONCERN FOR AVIATION
INTERESTS. INCREASING SOUTH TO SOUTHWEST WIND AND SURFACE HEATING
WILL HELP LIFT THE FOG AND MIX THE LOW CLOUDS DURING THE MORNING.
THUNDERSTORMS WILL THEN BECOME THE MAIN CHALLENGE DURING THE
AFTERNOON AND TONIGHT. TWO ROUNDS OF STORMS ARE LIKELY TO AFFECT
THE ENTIRE TERMINAL CORRIDOR...FIRST DURING THE MID AFTERNOON TO
MID EVENING DURING THE WARMEST PART OF THE DAY...AND THEN FROM
LATE EVENING THROUGH THE OVERNIGHT AS A COLD FRONT MOVES SLOWLY
ACROSS SE MICHIGAN. THE MAIN AREA OF RAIN WILL BE ON TRACK TO EXIT
TO THE SOUTH AND EAST BY SUNRISE TUESDAY LEAVING BEHIND ANOTHER
ROUND OF FOG AND STRATUS BEHIND THE COLD FRONT.

FOR DTW... A STRAY SHOWER OR THUNDERSTORM WILL BE POSSIBLE DURING
THE MORNING AND EARLY AFTERNOON BUT THE MAIN WINDOW FOR STORMS AND
POSSIBLE SEVERE WEATHER REMAINS LATE AFTERNOON THROUGH EARLY EVENING
FOR DTW.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING BELOW 5000 FEET DURING THE MORNING.

* MEDIUM CONFIDENCE IN THUNDERSTORM TIMING AND COVERAGE.

&&

.PREV DISCUSSION...ISSUED 405 AM EDT MON SEP 1 2014

SHORT TERM... TODAY AND TONIGHT

THUNDERSTORMS AND THE POTENTIAL FOR SEVERE WEATHER WILL BE THE
PRIMARY SUBJECT OF THE FORECAST FOR TODAY AND TONIGHT AS INGREDIENTS
COME TOGETHER FOR AN ACTIVE AFTERNOON AND EVENING AROUND SE
MICHIGAN. A FEW ELEVATED SHOWERS OR WEAK THUNDERSTORMS WILL BE
POSSIBLE DURING THE MORNING AS THE WARM SECTOR OF THE BROAD LOW
PRESSURE SYSTEM BUILDS INTO LOWER MICHIGAN. EXPECT THIS TO BE
FOLLOWED BY SURFACE BASED STORMS LIKELY INITIATING IN THE LEE OF
LAKE MICHIGAN EARLY TO MID AFTERNOON AND PROGRESSING THROUGH SE
MICHIGAN AS THE LEADING EDGE OF THE UPPER WAVE/MCV REMNANTS INTERACT
WITH THE LOW LEVEL MOISTURE AXIS DURING PEAK HEATING. A SECOND ROUND
OF STORMS IS THEN LIKELY TO INITIATE ALONG AND AHEAD OF THE COLD
FRONT AND FOLLOW THE AFTERNOON STORMS THROUGH OUR AREA MID EVENING
THROUGH THE OVERNIGHT.

EARLY MORNING IR SATELLITE IMAGERY INDICATES STRONGLY WARMING CLOUD
TOPS ASSOCIATED WITH THE UPSTREAM CONVECTION WHICH SUPPORTS THE
DISSIPATING TREND ADVERTISED IN MODEL DATA AND THE SCENARIO OF NEW
DEVELOPMENT OVER LOWER MICHIGAN DURING THE DAY. THIS DISSIPATING
TREND IS HAPPENING SOON ENOUGH TO ALLOW DEBRIS CLOUDS TO ERODE
AND/OR GET CARRIED TO OUR WEST AND NORTH BY THE SOUTHWEST FLOW
ALOFT. THAT LEAVES JUST PATCHY MID CLOUDS...ALONG WITH AREAS OF FOG
AND LOW STRATUS...AS A MINIMAL OBSTRUCTION TO STRONG SURFACE HEATING
TO START THE DAY. IT THEN SEEMS REASONABLE TO ASSUME MAX TEMPS OF
80-85 WILL BE REACHABLE WITH SURFACE DEWPOINT AROUND 70 CARRYING
0-1KM LAYER CAPE TOWARD 1500 J/KG. A SURFACE PARCEL AT 85/72
GENERATES SURFACE BASED CAPE NEAR 2500 J/KG AS A WORST CASE
SCENARIO. THESE VALUES ARE PLENTY HIGH ENOUGH TO INTERACT WITH A
STRENGTHENING UNIDIRECTIONAL WIND PROFILE INCREASING TO NEAR 40 KNOTS
OF BULK SHEAR IN THE 0-6KM LAYER...WITH MOST OF THAT IN THE 0-3KM
LAYER. THIS WILL ALLOW DISCRETE CELLS TO DEVELOP SUPERCELL CHARACTER
EARLY ON WITH SPLITS AND MERGERS GROWING UPSCALE INTO LINEAR SEGMENTS
AS CONVECTION MATURES LATE AFTERNOON INTO EARLY EVENING. DAMAGING
WIND WILL BE THE PRIMARY HAZARD. LARGE HAIL WILL BE POSSIBLE BUT
LIKELY LIMITED TO ONLY THE STRONGEST MESO ENHANCED UPDRAFTS DUE TO
HIGH FREEZING LEVEL. IT IS ALSO IMPORTANT TO NOTE THAT MODEL
SOUNDINGS INDICATE CAPE EXCEEDING 300 J/KG IN THE LOWEST 3 KM ALONG
WITH 0-3 KM HELICITY AROUND 200 M2/S2 AND LCL BETWEEN 3500 AND 4000
FT. THESE ARE FAVORABLE PARAMETERS FOR TORNADOGENESIS.

ROUND TWO OF STORMS WILL BE TRIGGERED BY THE COLD FRONT WEST OF LAKE
MICHIGAN DURING THE LATE AFTERNOON. SEVERE POTENTIAL WITH THIS
ACTIVITY WILL BE LOWER BY THE TIME IT REACHES OUR AREA TOWARD LATE
EVENING INTO THE OVERNIGHT...BOTH DUE TO THE DOWNSIDE OF DAYTIME
HEATING AND THE PRECEDING STORMS. HEAVY RAINFALL MAY END UP BEING
THE MAIN CONCERN AS THE THE SLOW MOVING COLD FRONT ENDS UP THE FOCUS
OF LARGE SCALE SUPPORT FROM THE ENTRANCE REGION OF THE UPPER JET AND
CONTINUED LOW LEVEL MOISTURE TRANSPORT. THIS WILL DEPEND ON HOW MUCH
POST FRONTAL/ELEVATED CONVECTION IS ABLE TO OCCUR WHICH THE MODELS
SUGGEST WILL BE MINIMAL...INSTEAD FOCUSING ADDITIONAL RAINFALL ALONG
AND AHEAD OF THE FRONT THROUGH SUNRISE TUESDAY.

LONG TERM...

WARMER/ABOVE NORMAL TEMPERATURES APPEAR TO BE IN STORE FOR THE FIRST
SEVERAL DAYS OF SEPTEMBER.

BROAD UPPER LEVEL TROUGH WILL BE SWINGING THROUGH THE CENTRAL GREAT
LAKES ON TUESDAY...AND IT APPEARS THE SURFACE COLD FRONT/MOISTURE
AXIS WILL HAVE CLEARED SOUTHEAST MICHIGAN AROUND 12Z TUESDAY...WITH
A DRAMATIC DRYING TREND TAKING PLACE AS PW VALUES AROUND 2 INCHES
NEAR THE OHIO BORDER ARE JUST ABOUT CUT IN HALF TO AROUND 1 INCH.
HOWEVER...THERE IS AN EMBEDDED STRONG SHORTWAVE QUICKLY TRACKING OUT
OF EASTERN IOWA EARLY TUESDAY MORNING...AND NEED TO ACCOUNT FOR THE
POSSIBILITY OF THE FLOW OUT AHEAD OF THIS FEATURE A BIT MORE
BACKED...SLOWING THE PROGRESS OF THE FRONTAL BOUNDARY TO THE
SOUTH...AND CARRY LOW CHANCE POPS...AS DAYTIME SURFACE BASED
INSTABILITY SETS IN AS WELL...WITH AROUND 1000 J/KG TO WORK WITH PER
00Z NAM. ALTHOUGH...THE 00Z GFS IS DRIER AND DECIDEDLY MORE
ANTICYCLONIC AT THE SURFACE...WHILE THE CANADIAN IS THE WETTEST.

SHORT LIVED ENERGETIC ZONAL FLOW OVER THE NORTHERN CONUS TUESDAY
NIGHT WITH STRONGER UPPER WAVE DIVING SOUTHEAST THROUGH THE PACIFIC
NORTHWEST. HEIGHTS WILL REBOUND OVER THE EASTERN CONUS
WEDNESDAY/THURSDAY WITH FAVORABLE DEEP SOUTHWEST FLOW AROUND SURFACE
HIGH CENTERED OVER THE EASTERN SEABOARD. HIGHS THE 80S APPEAR IN
THE OFFING...AS 850 MB TEMPS RISE TOWARD 20 C ON THURSDAY...AND
REACH OR POSSIBLY SLIGHTLY EXCEED 20 C ON FRIDAY...WHICH MAKES A RUN
TOWARD A 90 DEGREE DAY A REAL POSSIBILITY. HOWEVER...A COLD FRONT
WILL PROBABLY ALREADY BE ARRIVING...SUPPORTING CLOUDS AND A GOOD
CHANCE OF SHOWERS AND THUNDERSTORMS...WHICH OF COURSE WOULD HINDER
MAXES. MUCH LOWER CHANCE OF PRECIPITATION ON THURSDAY AS WARM FRONT
LIFTS THROUGH THE WESTERN GREAT LAKES.

MARINE...

SHOWERS AND THUNDERSTORMS WILL DEVELOP THIS AFTERNOON...AND CONTINUE
TONIGHT AS A COLD FRONT MOVES THROUGH LAKE HURON AND LOWER MICHIGAN.
SOME OF THESE STORMS MAY BE SEVERE. HIGH PRESSURE WILL BUILD INTO
THE REGION BEHIND THIS FRONT ON TUESDAY...WHICH WILL REMAIN IN
CONTROL OF THE WEATHER THROUGH THURSDAY...PROVIDING FAVORABLE
BOATING CONDITIONS.

&&

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

&&

$$

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


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





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