Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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045
FXUS63 KDTX 180403
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1203 AM EDT MON MAY 18 2015


.AVIATION...

A WARM FRONT LIFTED THROUGH THE AREA BRINGING A SLIGHT CHANGE IN
CONDITIONS FOR TONIGHT VS PREVIOUS TWO NIGHTS. THOUGH WE CONTINUE TO
BE VERY MOIST IN THE LOW LEVELS...THE WINDS IN THE WARM SECTOR HAVE
STAYED A BIT HIGHER TONIGHT WHICH HAS MITIGATED SOME FOG POTENTIAL
FOR THE EARLY OVERNIGHT PERIOD. WITH SOME CLEARING SPREADING NORTH
TO SOUTH...AND AMPLE MOISTURE...EXPECT A LOW STRATUS DECK TO DEVELOP
TOWARD MORNING WITH ONLY PATCHY LIGHT FOG. VFR RETURNS EARLY MONDAY
BEFORE DIURNAL CU FILLS BACK IN. SOME SHOWERS/THUNDERSTORMS COULD
DEVELOP WITH AFTERNOON HEATING AND A COLD FRONT APPROACHING BUT WILL
HOLD OFF ON ANY MENTION THIS FORECAST DUE TO LOW COVERAGE
EXPECTATIONS. COLD FRONT WILL SWEEP THROUGH THE AREA THIS EVENING
AROUND 02-06Z SWITCHING SW WINDS TO NW.

FOR DTW...CLEARING BEHIND THE CURRENT AREA OF SHOWERS WILL ALLOW
SOME LOW MVFR STRATUS TO DEVELOP...BUT SHOULD NOT LAST TOO LONG ONCE
DIURNAL MIXING COMMENCES. A CHANCE OF SHOWERS AND THUNDERSTORMS LATE
THIS AFTERNOON/EVENING BUT HIRES MODELS PAINT A VERY SCATTERED
PICTURE WITH BETTER MOISTURE OFF TO THE EAST SO WILL HOLD OFF ON
INCLUDING PRECIP IN TAFS. NOTABLE WIND SHIFT THIS EVENING WITH THE
FRONTAL PASSAGE AROUND 04Z.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM FOR CIG AOB 5000 FEET EARLY THIS MORNING AND AGAIN THIS
  AFTERNOON.

* LOW FOR A THUNDERSTORM TODAY AND TONIGHT.

&&

.PREV DISCUSSION...ISSUED 1030 PM EDT SUN MAY 17 2015

UPDATE...
ADJUSTMENTS MADE TO POP/WX GRIDS TO ACCOUNT FOR ONGOING CONVECTIVE
ACTIVITY AND FUTURE CONCERNS. THE WEAKENING RIBBON OF SYNOPTIC
FORCING...VORT EMANATING FROM THE STRONG PARENT LOW OVER
MN...COINCIDING WITH A DECENT DEEP LAYER THETA RIDGE IS CURRENTLY
WORKING THROUGH SE MI. NUMEROUS SHOWERS AND THUNDERSTORMS
DEVELOPED TOWARD THE END OF THE DIURNAL CYCLE WHICH HAVE BEEN
TRUDGING SLOWLY NE THROUGH THE EVENING. THE BULK OF THIS ACTIVITY
WILL CONTINUE FOR A FEW MORE HOURS UNTIL THE FORCING EXITS OFF TO
THE NORTH AND EAST. ACTIVITY COULD CONTINUE A BIT LONGER ACROSS
THE SOUTH AS THE FORCING BENDS BACK TO THE SW WITH ADDITIONAL
ENERGY RIDING NORTHWARD ALONG IT. HIRES MODELS CONTINUE TO
DECREASE THE ACTIVITY ACROSS SE MI THOUGH KEEPING THE ENERGY
FURTHER SOUTH. THAT TREND PLUS REGION RADAR SEEM TO WARRANT A
DECREASE TO CHANCE POPS AFTER MIDNIGHT.

PREV DISCUSSION...ISSUED 403 PM EDT SUN MAY 17 2015

SHORT TERM... AFTERNOON AND TONIGHT

CLUSTERS OF SHOWERS DEVELOPED DURING MID AFTERNOON WITHIN THE
PRIMARY THETA-E RIDGE ADVANCING INTO LOWER MICHIGAN. THE COMBINATION
OF THIS DEEPER MOISTURE AND PEAK SURFACE HEATING WILL LIFT MLCAPE TO
ABOUT 1000 J/KG AS TEMPERATURES SETTLE INTO THE LOWER 80S WITH
EFFECTIVE PARCEL DEWPOINT GENERALLY IN THE MID 60S. THIS WILL RESULT
IN INCREASED AREAL COVERAGE OF SHOWERS WITH A FEW THUNDERSTORMS
DURING THE LATE AFTERNOON INTO EARLY EVENING...ENOUGH TO NUDGE POPS
INTO THE LIKELY CATEGORY ALONG AND SOUTH OF I-96.

THE LATE AFTERNOON SHOWERS AND STORMS WILL BE DRIVEN PRIMARILY BY
BOUNDARY LAYER INSTABILITY DUE TO SURFACE HEATING. THIS WILL
TRANSITION INTO A MORE STRONGLY FORCED PATTERN OF ASCENT AS THE
EASTERN FRINGE OF THE UPPER LOW OVER THE NORTHERN PLAINS DRIFTS
TOWARD LOWER MICHIGAN TONIGHT. THE AFTERNOON CONVECTIVE DEVELOPMENT
OVER WISCONSIN PROVIDES A TRACER FOR THE LEADING EDGE OF THE MORE
FAVORABLE LARGE SCALE ENVIRONMENT. THE ONGOING CONVECTION WILL
LIKELY NOT REACH SE MICHIGAN IN ITS LATE AFTERNOON FORM. RATHER
EXPECT NEW DEVELOPMENT OR EXPANSION WITHIN THE THETA-E RIDGE OVER
LOWER MICHIGAN AS IT INTERACTS WITH THE UPPER LOW DURING THE LATE
EVENING INTO THE OVERNIGHT. CONVECTION WILL NOT BE SURFACE BASED BY
THEN BUT THE PROFILE AROUND 1000 J/KG WILL ALSO NOT YET BE
EXHAUSTED. THE COMBINATION OF AN ADEQUATE AMOUNT OF INSTABILITY...
THE MOISTURE AXIS...AND INCREASED DYNAMIC SUPPORT ADDS CONFIDENCE TO
MODEL MOISTURE/QPF DEPICTIONS...ENOUGH FOR LIKELY POPS UNTIL THE
MOISTURE AXIS IS DRIVEN EASTWARD BY SUNRISE MONDAY.

LONG TERM...TUESDAY THROUGH SATURDAY

MONDAY...VERTICALLY STACKED LOW PRESSURE OVER THE NORTHERN GREAT
LAKES WITH MEAN FLOW GENERALLY PARALLEL TO MAIN FRONTAL BOUNDARIES
SIGNIFIES A SLOW APPROACH OF THE MAIN COLD FRONT TOWARDS
SOUTHEASTERN MICHIGAN. THE CWA WILL CONTINUE TO RESIDE WITHIN THE
WARM SECTOR MONDAY. MOS CONSENSUS ALONG WITH TRENDS TODAY SUPPORT
TEMPERATURES RISING INTO/THROUGH THE LOW 80S. PURE MIXING OF THERMAL
PROGS SUGGESTS LOW 80S...BUT MID MAY INSOLATION IS ALMOST ALWAYS
GOOD FOR OVERACHIEVEMENT.

BULK OF THE NWP SUITE IS QUIET FOR MUCH OF MONDAY...WHICH IS IN
AGREEMENT WITH AN EARLY DAY CAPPING INVERSION BETWEEN 3000-5000 KFT
AGL. THE LATE ARRIVAL 17.12Z ECMWF SUGGESTS SOME SHOWER POTENTIAL
DURING THE MORNING HOURS...BUT THE BELIEF REMAINS THAT IT WILL TAKE
INTO THE AFTERNOON BEFORE THE ATMOSPHERE CAN DESTABILIZE. MAIN
FEATURES TO WATCH FOR MONDAY AFTERNOON WILL BE THE ARRIVAL OF THE
COLD FRONT FROM THE WEST AND THE ARRIVAL OF WEAK RIGHT ENTRANCE
REGION DYNAMICS THAT WILL LIFT INTO FAR SECTIONS OF SOUTHEASTERN
MICHIGAN FROM SOUTHERN IL/IN. CENTERED THE MID LOW CHANCE POPS IN
THE NARROW TIME WINDOW OF BETWEEN 21-03Z. FORECAST SOUNDINGS ALSO
DEPICT SOME POSSIBLE RELIANCE ON TSTORM CHANCES ON LOWERING
CONVECTIVE DEPTHS DURING THE EVENING OWING FROM THE EARLY EVENING
BOUNDARY LAYER TRANSITION. TREND IN THE MODEL DATA HAS BEEN FOR LESS
INSTABILITY THAN PREVIOUSLY EXPECTED. LAPSE RATE STRUCTURES WITH
SOME AFTERNOON MIXING OUT OF NEAR SURFACE MOISTURE QUALITY SUGGESTS
THAT MLCAPE VALUES WILL BE ON THE ORDER OF ABOUT 500 J/KG. WEAK
KINEMATICS AND WIND FIELD SUPPORTS A LOW AMOUNT OF WIND SHEAR WHICH
PLACES A CONSIDERABLE AMOUNT OF DOUBT ON OVERALL STRONG-SEVERE
THUNDERSTORM RISK TOMORROW AFTERNOON. THE MARGINAL RISK DESIGNATION
WAS SHIFTED TO THE EAST IN THE LATEST SWODY2.

TUESDAY...THE TRUE COLD FRONT WILL PASS EAST OF SOUTHEASTERN
MICHIGAN MONDAY NIGHT...SETTING UP THE AREA FOR A LONG PERIOD OF
ISENTROPIC DOWNGLIDE ON TUESDAY. IMPRESSIVE COLD AIR ADVECTION WITH
850MB TEMPERATURES DROPPING TO -8C OVER NORTHERN LOWER MICHIGAN BY
00Z WEDNESDAY. FAVOR A SLIGHTLY MILDER SOLUTION FOR DAYTIMES HIGHS
ON TUESDAY...GIVEN RESIDUAL BOUNDARY LAYER THETA E CONTENT. THE
DOWNRIGHT CHILL PERIOD IS EXPECTED TO BE TUESDAY NIGHT/WEDNESDAY
MORNING WHERE FROST HEADLINES MAY BE NEEDED.

REST OF THE WEEK...THE REMAINDER OF THE WEEK IS EXPECTED TO BE QUIET
AS A STABLE HIGH ANTICYCLONE TAKES ITS TIME TO PASS THROUGH THE
AREA. MODEL DATA SHOWS A VERY STABLE PROFILE BETWEEN 5 AND 10 KFT
AGL. MODELS ARE NOW SUGGESTING SOME LOW END PRECIPITATION POTENTIAL
LATE WEDNESDAY NIGHT/THU MORNING AS AN AREA OF FAVORABLE ENTRANCE
REGION DYNAMICS PASS THROUGH THE REGION.

MARINE...

FAVORABLE MARINE CONDITIONS IN TERMS OF WINDS AND WAVES TO FINISH
THE WEEKEND. BEEN ABLE TO GET A LOOK ON SATELLITE IMAGERY TODAY. THE
FOG THAT HAD BEEN PLAGUING THE SOUTHERN LAKE HURON BASIN HAS BEEN
ADVECTED NORTHWARD TODAY INTO THE NORTHERN BASIN. WILL SHIFT THE
DENSE FOG HEADLINES TO THE NORTHERN BASIN WITH THE AFTERNOON
PACKAGE. MODEST SOUTHWESTERLY WINDS DEVELOP IN ADVANCE OF A COLD
FRONT ON MONDAY.  COLD FRONT SWEEPS THROUGH MONDAY EVENING WITH
COOLER AND DRIER CONDITIONS DEVELOPING ON WEST TO NORTHWEST FLOW FOR
THE MID WEEK PERIOD.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...DENSE FOG ADVISORY UNTIL 4 AM EDT EARLY THIS MORNING FOR LHZ361>363.

LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

AVIATION.....DRK
UPDATE.......DRK
SHORT TERM...BT
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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