Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 190833
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
433 AM EDT TUE AUG 19 2014

.SHORT TERM...TODAY AND TONIGHT

A LOW PRESSURE SYSTEM CURRENTLY OVER NORTHERN WISCONSIN WILL SLOWLY
TRACK EAST OVER NORTHERN LOWER MICHIGAN BY TONIGHT. MOISTURE HAS
SURGED AHEAD OF THIS APPROACHING LOW...AS EVIDENCED BY SURFACE DEW
POINTS IN THE LOWER 60S ACROSS SOUTHEAST MICHIGAN. SHOWERS AND
THUNDERSTORMS ARE ONGOING THIS MORNING ACROSS WESTERN MICHIGAN...IN
ASSOCIATION WITH A LOW LEVEL THETA-E RIDGE SURGING EASTWARD.
ALTHOUGH CURRENT ACTIVITY IS RATHER DIFFUSE...THE FORCING IS THERE
TO CONTINUE A CHANCY POP DURING THE MORNING HOURS.

LATER THIS AFTERNOON ANOTHER LOW LEVEL THETA-E SURGE TRACKS THROUGH
THE STATE AS THE MID LEVEL TROUGH KICKS OUT A SHORTWAVE THAT TRACKS
THROUGH THE CENTRAL GREAT LAKES REGION. THE DYNAMICS WILL HAVE AN
UNSTABLE ATMOSPHERE TO WORK WITH AS MLCAPE VALUES REACH 1000 TO 1500
J/KG...ESPECIALLY ACROSS THE SOUTHERN CWA SOUTH OF M-59. WHILE MODEL
SOUNDINGS SHOW A RATHER WEAK WIND PROFILE...0-6 KM BULK SHEAR VALUES
GET UP TO AROUND 30 KNOTS. THE STORMS THAT MOVE THROUGH DURING THE
AFTERNOON ARE PROGGED TO BE THE STORMS THAT ARE CURRENTLY OVER
WISCONSIN...WHICH AT TIMES HAVE SEVERE. GIVEN THE TIMING...WHICH
WILL BE DURING PEAK HEATING AND THE DYNAMICS THERE IS A SLIGHT
CHANCE SOME OF THESE STORMS COULD BE SEVERE ALONG AND SOUTH OF THE
M-59 CORRIDOR WITH DAMAGING WINDS OF 60 MPH AND TO A LESSER EXTENT
HAIL OF PENNY TO QUARTER SIZE. THE ENVIRONMENT WILL BE RICH WITH
MOISTURE...WITH LONG SKINNY CAPE PROFILES AND PWAT VALUES OF 1.5 TO
1.8 INCHES. THIS COUPLED WITH THE EXPECTED SLOW STORM MOTION AROUND
20 MPH WILL ONCE AGAIN BRING THE THREAT FOR FLOODING TO SOUTHEAST
MICHIGAN DURING THE AFTERNOON AND EVENING HOURS.

AS THE MAIN FORCING HEADS EAST PRECIPITATION CHANCES WILL BE ON THE
DOWNWARD TREND DURING THE OVERNIGHT HOURS...WITH LINGERING SHOWERS
AND A FEW THUNDERSTORMS BEHIND THE MAIN FORCING AS A COLD FRONT
UNDERGOES OCCLUSION OVER THE CENTRAL GREAT LAKES. WITH THE LOSS OF
DAYTIME HEATING AND THE MAIN FORCING OFF TO THE EAST THE POTENTIAL
FOR SEVERE WEATHER IS NOT EXPECTED TO LAST MUCH INTO THE EVENING
HOURS.

&&

.LONG TERM...

THE MIDWEEK PERIOD IS A DIFFICULT FORECAST WITH THE SLOW MOVING LOW
PRESSURE SYSTEM PASSING THROUGH. TIMING OF PRECIPITATION REMAINS AN
ARDUOUS TASK WITH HIGH DEPENDENCE ON PRIOR CONVECTIVE EVOLUTION.

THE DIFFUSE INNER CYCLONIC SWIRL OF THE UPPER LEVEL LOW WILL DESCEND
SOUTHEASTWARD DIRECTLY INTO LOWER MICHIGAN ON WEDNESDAY. THE CENTER
OF THE BROAD CYCLONIC CIRCULATION IS EXPECTED TO CENTER OVER FAR
NORTHERN LOWER MICHIGAN BETWEEN 18-00Z. THIS PLACES THE CWA IN A
MORE FAVORABLE AREA FOR PRECIPITATION AND HIGH MOISTURE CONTENT BY
REMAINING IN THE SOUTHWESTERLY FLOW/LOWER RIGHT QUADRANT OF THE
CIRCULATION. MODEL EQUIVALENT POTENTIAL TEMPERATURE FIELDS KEEP DEEP
MOISTURE IN PLACE AT LEAST THROUGH 21Z BEFORE A STRAIGHT WESTERLY
WIND PROFILE BEGINS TO BUDGE IN. OVERALL...FRONTAL FORCING IS WEAK
GIVEN THE HOMOGENIZED AND BAROTROPIC SYSTEM. WITH THE HUMID
AIRMASS...NOT EXPECTING THERE TO BE MUCH CAPPING BY THE TIME THE
AFTERNOON HITS. A BAND OF VORTICITY WITH AN ORIENTATION FROM NW TO
SE IS SHOWN TO LIFT INTO THE CWA...BRINGING THE BEST DEEP
CONVERGENCE SIGNAL OVER THE NORTHERN 2/3RDS OF THE CWA (PORT HURON
TO THE SAGINAW VALLEY AND THUMB). POP DISTRIBUTION IS LIKELY FOR
THAT AREA TAPERING DOWN TO A CHANCE ACROSS THE SOUTHWEST. BETTER
HEIGHT GRADIENT AND WIND CORE PUSHES INTO THE SOUTHERN CWA DURING
THE LATE AFTERNOON...LIKELY COLLOCATED WITH SOME DRIER MIDLEVEL AIR.
0-6KM BULK SHEAR VALUES ARE FORECASTED TO INCREASE UPWARDS OF 30
KNOTS WITH THIS FEATURE. IN ADDITION...THE DRIER AIR COULD LEAD TO
SOME STEEPER MIDLEVEL LAPSE RATES THAT COULD CONTRIBUTE TO
RELATIVELY HIGHER CAPE VALUES. MODELS DIFFER BUT THE NAM MAX IS
ADVERTISING ML/SB CAPES OF OVER 2000 J/KG. GIVEN SOME OF THE CWA IS
UNDER A SLIGHT RISK IN SWODY1...SEE NO REASON WHY THERE WILL NOT BE
A SEE TEXT OR SLIGHT RISK DESIGNATION FOR WEDNESDAY. A
UNIDIRECTIONAL WIND PROFILE SUPPORTS ANY LINE SEGMENTS THAT DO
BECOME ORTHOGONAL TO THE MEAN WIND WILL CARRY A HIGHER WINDGUST
THREAT. AN ADDITIONAL THREAT TO MONITOR IS HEAVY RAIN POTENTIAL DUE
TO A SLOW STORM MOTION OF ROUGHLY 25 TO 30 MPH.

DRIER LOWER TROPOSPHERIC AIR AND THE LONGWAVE RIDGE AXIS WILL
FINALLY CATCH SOUTHEASTERN MICHIGAN ON THURSDAY. THIS IS EXPECTED TO
LEAD TO QUIET WEATHER WEDNESDAY NIGHT AND THROUGH THE FIRST HALF OF
THURSDAY. VIRTUALLY NO SURFACE RIDGING TO SPEAK OF AND A
REESTABLISHMENT OF THE UPPER LEVEL RIDGE TO OUR NORTH AND EAST WILL
ALLOW WARM AIR ADVECTION TO FLOOD TO THE NORTHEAST. THIS IS ACTUALLY
EXPECTED TO OCCUR RATHER RAPIDLY. IN STARK CONTRAST TO WHAT USUALLY
OCCURS DURING THE SPRINGTIME. AS A RESULT...MOISTURE/INSTABILITY AND
WARM AIR ADVECTION WILL RETURN RATHER QUICKLY AGAIN BY THURSDAY
AFTERNOON AND FRIDAY. BRING A MID CHANCE POPS IN THURSDAY AFTERNOON
FOR THE SOUTHWESTERN 1/3RD OF THE CWA LINGERING INTO THURSDAY NIGHT.
HUMID CONDITIONS ARE EXPECTED BOTH WEDNESDAY AND THURSDAY.

&&

.MARINE...

LIGHT WINDS WILL GIVE WAY TO A MODERATE SOUTHEAST BREEZE TODAY AND
THIS EVENING AS A WEAK LOW DRIFTS TROUGH THE AREA. WINDS WILL BE THE
STRONGEST ACROSS NORTHERN LAKE HURON BUT GUSTS THERE WILL STILL
STRUGGLE TO BREAK 20 KNOTS. THIS LOW WILL ALSO BRING A CHANCE FOR
THUNDERSTORMS BOTH TODAY AND WEDNESDAY...PARTICULARLY FOR THE
SOUTHERN LAKE HURON BASIN AND POINTS SOUTH.

&&

.PREV DISCUSSION...ISSUED 346 AM EDT TUE AUG 19 2014


&&

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

&&

$$

SHORT TERM...KURIMSKI
LONG TERM....CB
MARINE.......CB


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





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