Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 070518
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
118 AM EDT MON JUL 7 2014


.AVIATION...

//DISCUSSION...

EXTENSIVE AREA OF SHOWERS AND THUNDERSTORMS WILL CONTINUE TO IMPACT
MBS/FNT THROUGH 08Z...BRINGING PERIODIC MVFR/IFR CONDITIONS IN
MODERATE/HEAVY RAINFALL.  RECENT RADAR TRENDS LEND SUPPORT FOR
ONGOING CONVECTIVE ACTIVITY TO THEN SHIFT INTO PTK 07Z-09Z.
CONFIDENCE IN THUNDERSTORM OCCURRANCE DOES DIMINISH FOR THE DETROIT
CORRIDOR...WITH SOME POTENTIAL FOR THE OVERALL COVERAGE TO BE
CONSIDERABLY LESS AS NOCTURNAL COOLING GRADUALLY PROVIDES GREATER
STABILITY.  OVERALL...GREATEST POTENTIAL WILL EXIST 09Z-12Z IN
DETROIT...AND WILL RETAIN A DEFINED MENTION UNTIL TRENDS SUGGEST
OTHERWISE.   COLD FRONTAL PASSAGE WILL BRING A GENERAL DRYING TREND
FOR MONDAY WITH SOME INCREASE IN WESTERLY WINDS ANTICIPATED.  SOME
LINGERING LOWER STRATUS WILL EXIST BEFORE THIS DRYING TAKES A
GREATER HOLD INTO THE AFTERNOON.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING AOB 5000 FEET TONIGHT THROUGH MONDAY
  MORNING.

* MEDIUM CONFIDENCE IN THUNDERSTORM OCCURANCE AND TIMING.

&&

.PREV DISCUSSION...ISSUED 403 PM EDT SUN JUL 6 2014

SHORT TERM... REST OF TODAY AND TONIGHT

OBSERVATIONAL TRENDS IN COMPOSITE RADAR OVER THE MIDWEST...COUPLED
WITH HOURLY MESO ANALYSIS...IS SHOWING THE RESULTS OF MLCAPE
BUILDING TO ABOUT 1500 J/KG OVER WISCONSIN. THIS IS WHERE SURFACE
HEATING AND SURFACE CONVERGENCE IS MAXIMIZED ON THE WESTERN EDGE OF
THE LOW CLOUD PATTERN AND WARM FRONT/COLD FRONT INTERSECTION. EXPECT
CONVECTION IN THIS AREA WILL CONTINUE TO GROW THROUGH PEAK HEATING
WITH A BOOST OF LARGER SCALE VERTICAL MOTION SUPPORT FROM THE UPPER
WAVE AND JET MAX MOVING IN FROM CENTRAL CANADA. THE INCREASED SHEAR
IN THE WIND PROFILE WILL HELP ORGANIZE THESE STORMS DURING THE
EVENING INTO A LINE THAT WILL HAVE SOME STAYING POWER AS INSTABILITY
BUILDS OVER LOWER MICHIGAN. THIS WILL OCCUR FIRST IN THE LEE OF LAKE
MICHIGAN OVER SW LOWER WHERE LEE SIDE SURFACE CONVERGENCE COULD
GENERATE SOME DISCRETE STORMS ALONG THE WARM FRONT OUT AHEAD OF THE
LINE MOVING IN FROM WISCONSIN. THERE IS LESS CONFIDENCE IN WARM
FRONTAL DEVELOPMENT CONSIDERING CLOUD COVER REMAINING OVER LOWER
MICHIGAN WILL LIKELY DELAY ONSET OR REDUCE COVERAGE COMPARED TO
MODEL TIMING...BUT THIS REQUIRES CLOSE MONITORING AS EARLY EVENING
CONVECTIVE DEVELOPMENT ALONG THE WARM FRONT WILL HAVE SEVERE
POTENTIAL DUE TO THE USUAL WARM FRONTAL CONTRIBUTIONS TO THE LOW
LEVEL HODOGRAPH. THE EVENTUAL MCS FROM WISCONSIN WILL ALSO HAVE
SEVERE POTENTIAL BUT BOTH SCENARIOS WILL FACE A WEST TO EAST
GRADIENT OF INSTABILITY THAT WILL RUN FROM 0-1KM MLCAPE AS HIGH AS
2000 J/KG OVER THE MIDWEST TO LESS THAN 1000 OVER PORTIONS OF SE
MICHIGAN AFTER MIDNIGHT.

UNCERTAINTY ON SEVERE POTENTIAL IS COUNTERED BY CONFIDENCE IN
COVERAGE AS THE LOW LEVEL JET RAMPS UP OVER THE REGION AFTER
MIDNIGHT. ASSOCIATED MOISTURE TRANSPORT IS SHOWN TO BE STRONG ENOUGH
TO BUILD A LOW LEVEL THETA-E RIDGE IN THE SURFACE TO 700 MB LAYER
THAT WILL IN ITSELF GENERATE SHOWERS AND THUNDERSTORMS. THIS WILL BE
REQUIRED TO MAINTAIN THE MODEST MLCAPE ADVERTISED IN THE MODEL DATA
AND WILL BE AVAILABLE FOR CONTINUED SUPPORT FROM THE SOUTH
FRINGES OF THE UPPER WAVE THAT WILL BE STRONG ENOUGH TO MAINTAIN
AREAL COVERAGE WORTHY OF HIGH END LIKELY POPS BEFORE THE PATTERN
EXITS BY SUNRISE MONDAY.

LONG TERM...MONDAY THROUGH SATURDAY

MODELS HAVE BEEN SHOWING GOOD RUN TO RUN CONSISTENCY WITH THE
OVERALL PATTERN EVOLUTION THROUGH MID WEEK. THEY ARE HOWEVER
STRUGGLING TO COME IN LINE WITH IMPORTANT SMALLER SCALE FEATURES
LIKE THE PLACEMENT AND TIMING OF A SHORTWAVE AND SFC LOW ON A COLD
FRONT PASSING THROUGH THE AREA EARLY ON TUESDAY. MORE TO COME ON
THAT.

BROAD TROUGHING OVER THE EASTERN CONUS WILL AMPLIFY AS RIDGING OVER
THE WEST COAST STRENGTHENS STEERING THE STRONG JET STREAM OVER THE
REGION. THE UPPER LEVEL TROUGH WILL LOOK TO CLOSE OFF AS IT
STRENGTHENS BEFORE BEING FORCED EASTWARD BY THE NEXT STRONG WAVE MID
TO LATE WEEK. THIS NW FLOW WILL GUIDE A SERIES OF SHORTWAVES AND
FRONTS THROUGH THE GREAT LAKES. THE FIRST FRONT WILL BE WORKING
THROUGH THE AREA DURING THE DAY MONDAY. THOUGH THE PREFRONTAL LINE
OF CONVECTION WILL USHER MOST OF THE RICH THETA E AIR OUT OF THE
AREA AND RESULT IN A PERIOD OF SUBSIDENCE...THERE WILL BE SOME LOWER
THETA E PRESENT INTO THE AFTERNOON WHILE THE TROUGH WORKS THROUGH.
WITH SOME DAYTIME HEATING ERODING THE LL CAP...MAY BE ABLE TO
MUSTER UP A FEW SHOWERS OR THUNDERSTORMS BEFORE THE FROPA. THE FRONT
WILL PASS LATE ENOUGH IN THE DAY TO ALLOW DECENT HEATING BACK INTO
THE 80S AGAIN.

QUIETER WEATHER WILL TAKE US INTO THE OVERNIGHT BUT WILL NOT LAST
LONG AS THE NEXT STRONG WAVE ENTERS THE TROUGH. THIS WAVE LOOKS TO
HAVE SEVERAL FAVORABLE PARAMETERS LINING UP FOR IT WHILE IT PASSES
THROUGH THE GREAT LAKES. IT WILL TAKE A SOUTHERN TRACK THROUGH THE
LOWER GREAT LAKES NEAR THE MI/OH BORDER LATE MONDAY NIGHT AND INTO
TUESDAY. IT WILL HAVE FAVORABLE LEFT EXIT REGION DYNAMICS OVERHEAD
WITH AN 850MB LL JET RAMPING UP TO AROUND 40 KNOTS YIELDING STRONG
BULK SHEAR OF 40+ KNOTS. GOOD SW FLOW WILL ADVECT ANOTHER MOISTURE
RICH AIRMASS INTO SOUTHERN MI AS WELL. LAPSE RATES WILL NOT BE TOO
GREAT BUT WILL BE FAVORABLE IN THE MID LEVEL. THE QUESTION REMAINS
WHERE WILL THE SFC LOW ACTUALLY DEVELOP? MODELS ARE ALL OVER THE
BOARD ANYWHERE FROM MID MI TO THE OHIO VALLEY ALONG THE STALLED
BAROCLINIC ZONE CLOSER TO THE BETTER INSTABILITY. THIS WILL MAKE A
BIG DIFFERENCE IN HOW THE SYSTEM PLAYS OUT AND HOW STRONG THE STORMS
OVER THE AREA WILL BE. EVEN IF THE PRESSURE FALLS SPLIT AS MODELS
HINT AT...ANY PRESSURE FALLS OVER THE AREA WITH THE WAY THE OTHER
PARAMETERS LINE UP SHOULD BE ABLE TO PRODUCE SOME CONVECTION OVER
THE AREA.

WINDS WILL BECOME NORTHERLY BEHIND THIS COLD FRONT ALLOWING COOLER
AIR TO FILTER INTO LOWER MI. WITH RAIN AND CLOUDS TO START THE
DAY...AND CAA DROPPING 850MB TEMPS TO NEAR 10C BY EVENING...EXPECT
HIGH TEMPS TO HOLD IN THE MID/UPPER 70S WITH HIGHER VALUES TO THE
SOUTH WHERE IT WILL TAKE THE FRONT LONGER TO PUSH THROUGH. LINGERING
TROUGH WITH POTENTIAL FOR ANOTHER WEAK SHORTWAVE TO PASS OVERHEAD
WILL KEEP A SLIGHT CHANCE POP IN THE FORECAST OVERNIGHT.

POST-FRONTAL AIRMASS ON WEDNESDAY WILL SPORT STABILITY AND COLD AIR
ADVECTION. THIS WILL BRING MAX TEMPS DOWN TO ABOUT 10 DEGREES BELOW
CLIMO. THESE VALUES MAY ALSO HOLD TRUE FOR THE OVERNIGHT AS HIGH
PRESSURE...LIGHT WINDS...AND LOW RH VALUES WILL BE FAVORABLE FOR
RADIATIONAL COOLING. RETURN FLOW FROM SURFACE HIGH BEGINS ON
THURSDAY...BUT WITH SINGLE DIGIT H85 TEMPS...EXPECT ANOTHER COOL AND
SUNNY DAY. WARMING TREND FRI-SUN WITH SHOWERS POSSIBLE ON THE WEEKEND.

MARINE...

INCREASED SOUTHWEST FLOW WILL RESULT IN WINDS GUSTING TO NEAR 20
KNOTS FOR ALL MARINE ZONES THROUGH MONDAY MORNING. CHANNELING WINDS
THROUGH SAGINAW BAY WILL PRODUCE SLIGHTLY HIGHER WINDS THUS THE
SMALL CRAFT ADVISORY WILL CONTINUE. GUSTS OVER LAKE ERIE WILL
APPROACH SMALL CRAFT CRITERIA JUST AHEAD OF THE FRONT BUT LOOK TO
STAY JUST BELOW THUS FAR. AN APPROACHING COLD FRONT WILL BRING A
CHANCE OF THUNDERSTORMS LATE TONIGHT THROUGH EARLY MONDAY.
ADDITIONAL THUNDERSTORMS WILL BE POSSIBLE ON TUESDAY AS ANOTHER COLD
FRONT SWEEPS THROUGH.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...SAGINAW BAY...UNTIL 10 AM MONDAY.

LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....MR
SHORT TERM...BT
LONG TERM....DRK/MM
MARINE.......DRK

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



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