Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 050211
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1011 PM EDT WED MAY 4 2016

.UPDATE...

THE PERSISTENT MID LEVEL DEFORMATION WHICH IMPACTED THE SAGINAW
VALLEY AND PORTIONS OF CENTRAL AND WESTERN LOWER MI TODAY HAS BEEN
BREAKING DOWN AND SHIFTING SOUTH INTO INDIANA THIS EVENING. THIS
HAS BEEN THE RESULT OF THE UPPER LOW DRIFTING SOUTHWARD ALONG THE
IN/OH BORDER. A STREAM OF MOIST ISENTROPIC ASCENT CONTINUES TO
FEED THE REMNANT DEFORMATION REGION...SUSTAINING SOME LIGHT
SHOWERS FROM METRO DETROIT TO FLINT/OWOSSO. THE UPPER LOW WILL
CONTINUE SOUTH DURING OVERNIGHT. THIS WILL ALLOW THE REMNANT
SHOWERS TO SLIDE SOUTH...EXITING THE FORECAST AREA LATE IN THE
NIGHT. A FORECAST UPDATE WILL BE ISSUED SIMPLY TO REFINE THE END
TIMING OF THE SHOWERS.

&&

.AVIATION...ISSUED 652 PM EDT WED MAY 4 2016

THE BAND OF RAIN WHICH HAS BEEN NEARLY PERSISTENT FROM METRO DETROIT
THROUGH SAGINAW THIS AFTERNOON HAS BEEN EXPANDING TOWARD THE NORTH
AND EAST OVER THE LAST SEVERAL HOURS AS THE CIRCULATION AROUND THE
ASSOCIATED UPPER LOW BROADENS. THIS REGION OF RAIN WILL START
TRACKING BACK TOWARD THE SOUTH WITHIN THE NEXT HOUR OR SO AS THE
UPPER LOW DROPS SOUTH ACROSS THE OHIO VALLEY. THE SFC LOW /EXTENDING
FROM ROUGHLY DTW TO OZW AS OF 22Z/ WILL ALSO SLOWLY PUSH SOUTH THIS
EVENING AND IS EXPECTED TO SLIDE SOUTH OF TOLEDO AROUND 06Z. THERE
HAS BEEN A REGION OF IFR CIGS JUST WEST AND NORTH OF THE SURFACE
LOW...WITHIN A LOW LEVEL THERMAL TROUGH. THIS POOL OF COLDER LOW
LEVEL AIR WILL SLIDE SOUTH THIS EVENING. SO ASIDE FROM MBS /WHICH IS
GETTING SOME ADDED MOISTURE FLUX OFF THE BAY/...THE PROBABILITY IN A
BRIEF PERIOD OF IFR CIGS WILL DECREASE SUBSTANTIALLY DURING THE
COURSE OF THE EVENING. MVFR AND/OR LOW END MVFR CIGS WILL PERSIST
WITHIN THE RAINFALL. AS THE LOW TRACKS SOUTH...DRY AIR ADVECTION
FROM THE NORTHEAST WILL SUPPORT RISING CEILINGS ONCE THE BACK EDGE
OF THE RAIN EXITS THE TERMINALS. THE DEGREE OF WARM AND DRY LOW
LEVEL AIR NOW ADVECTING ACROSS LAKE HURON FROM ONTARIO CASTS SOME
DOUBT ON POTENTIAL LOW CLOUD REDEVELOPMENT LATE TONIGHT. THIS
ALONG WITH THE SUPPORT OF THE 18Z GUIDANCE SUGGESTS HOLDING VFR
CONDITIONS THROUGH THURS MORNING FOR THE TIME BEING.

FOR DTW...ALTHOUGH THE STEADIER RAIN HAS BEEN LIFTING NORTH OF
METRO...THE SHOWERS WILL FOCUS BACK TOWARD THE SOUTH ACROSS THE
AIRPORT BEFORE ENDING AROUND OR SHORTLY AFTER 04Z. WITH THE MID
LEVEL COLD POOL SLIDING SOUTH OF THE REGION...THE POTENTIAL FOR
THUNDERSTORMS THIS EVENING IS QUITE LOW. AS THE LOW PUSHES INTO
TOLEDO IN THE 05Z TO 06Z TIME FRAME...A WIND SHIFT TOWARD THE NORTH
WILL LIFT CLOUD BASES.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN CEILINGS BELOW 5000 FT THIS EVENING. LOW OVERNIGHT AND
  THURSDAY MORNING. MEDIUM THURSDAY AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 350 PM EDT WED MAY 4 2016

DISCUSSION...

WATER VAPOR IMAGERY NOW SHOWS A NICE CYCLONIC CIRCULATION OVER
SOUTHEAST MICHIGAN THIS AFTERNOON...A RESULT OF UPPER ENERGY CLOSING
OFF OVER THE AREA. AS THE LOW CLOSED OFF TODAY THE BAND OF
PRECIPITATION WRAPPED INTO IT...TAKING ON MORE OF A NORTHWEST TO
SOUTHEAST ORIENTATION. BAND OF PRECIPITATION IS EXPECTED TO REMAIN
ORIENTATED FROM THE SAGINAW VALLEY DOWN TOWARDS THE DETROIT AREA
THROUGH THE EARLY EVENING BEFORE STARTING TO SINK SOUTHWARD AS THE
UPPER LOW MOVES INTO THE OHIO VALLEY. DRIER AIR...ABUNDANT IN THE
MID-LEVELS...WILL FILL IN BEHIND THE SYSTEM THROUGH THE LATE
EVENING...ENDING CHANCES FOR PRECIPITATION. A FEW HUNDRED J/KG OF
CAPE REMAIN OVER THE AREA PER LATEST SPC ANALYSIS...WITH INSTABILITY
RESULTING FROM THE COLD POOL FROM THE UPPER LOW OVERRIDING DIURNAL
HEATING IN THE BOUNDARY LAYER. THIS HAS BEEN JUST ENOUGH TO KICK OFF
A FEW THUNDERSTORMS TODAY...WITH LOW FREEZING LEVELS SUPPORTING PEA-
SIZED HAIL IN THE STRONGEST STORMS. SOME DRIER AIR IN THE LOW-LEVELS
HAS ALSO ALLOWED FOR A FEW WIND GUSTS UP TO 40 MPH. POTENTIAL FOR
THUNDERSTORMS WILL CONTINUE THROUGH THE EVENING BEFORE THERMAL
PROFILES STABILIZE.

FORECAST FOR TONIGHT IS A LITTLE CHALLENGING AS THERE IS SOME
QUESTION AS TO HOW MUCH STRATUS WILL STICK AROUND OR REDEVELOP UNDER
A LOW-LEVEL INVERSION. FORECAST SOUNDINGS SO FAR TODAY HAVE COME IN
DRIER THAN PREVIOUS RUNS (NAM/RAP IN PARTICULAR)...LENDING SOME
DOUBT TO HOW LONG CLOUDS WILL STICK AROUND BEHIND DEPARTING LOW
PRESSURE. LOW-LEVEL MOISTURE WILL BE HARD TO SCOUR OUT SO
QUICKLY...AND WITH LOW-LEVEL FLOW FROM THE NORTHEAST OFF LAKE HURON
AND NORTHERLY SURFACE WINDS OF 5-10 KNOTS...WILL FAVOR A STATUS DECK
TONIGHT OVER FOG.

LARGE UPPER RIDGE WILL THEN BECOME THE DOMINANT PLAYER IN THE
WEATHER OVER SOUTHEAST MICHIGAN THURSDAY INTO FRIDAY AS IT ALLOWS
STRONG SURFACE HIGH PRESSURE CENTERED OVER THE PLAINS TO EXPAND INTO
THE AREA. THIS WILL ALLOW FOR A GRADUAL LIFTING/EROSION OF STRATUS
EARLY THURSDAY BEFORE DRYING AND DEEP LAYER SUBSIDENCE THROUGH THE
ATMOSPHERIC COLUMN SUPPORT MOSTLY CLEAR SKIES LATE THURSDAY THROUGH
FRIDAY. WARMING WILL BE TEMPERED TOMORROW BY EARLY DAY CLOUDS AND
NORTH FLOW OFF LAKE HURON...BUT STILL EXPECTING HIGHS IN THE MID 60S
FOR MOST LOCATIONS...50S CLOSE TO LAKE HURON. TEMPS WARMING TO 7-8C
AT H850 AND FULL INSOLATION SHOULD SUPPORT MAX TEMPERATURES NEAR 70
BY FRIDAY.

SURFACE FRONT ALONG THE LEADING EDGE OF INBOUND NORTHERN STREAM
HEIGHT FALLS STILL ON TRACK FOR SATURDAY. 50-60 POPS LOOK GOOD.
FORCING APPEARS STRONG...BUT DURATION OF MOISTURE RETURN IN ADVANCE
OF THE FRONT IS LIMITED...AND SYSTEM LOOKS TO BE PROGRESSIVE. HIGH
PRESSURE QUICKLY BUILDS IN THE WAKE OF THE FRONT...DRYING US OUT FOR
SATURDAY NIGHT THROUGH MONDAY. WEAK IMPULSE AND BACKDOOR FRONT
SUNDAY IS SOMETHING TO KEEP AN EYE ON BUT NOT ENOUGH EVIDENCE TO
INTRODUCE POPS.

MARINE...

MODEST NORTHEASTERLY WINDS LATE THIS AFTERNOON ACROSS SAGINAW BAY
WILL BE CLOSE TO SMALL CRAFT ADVISORY THROUGH THE EARLY EVENING BUT
SHOULD REMAIN JUST BELOW CRITERIA. THESE WIND SHOULD RELAX
OVERNIGHT. AS THE SURFACE LOW DEPARTS...NORTHERLY FLOW TAKES OVER
TONIGHT AND INCREASES TOWARD THE MORNING.  WINDS AND WAVES WILL
AGAIN GET CLOSE TO SMALL CRAFT CRITERIA FOR SOUTHERN LAKE HURON ON
THURSDAY...ESPECIALLY FOR THE AFTERNOON AND EVENING. WILL HOLD OFF
FOR NOW AND LET LATER FORECAST MAKE NECESSARY ADJUSTMENTS. HIGH
PRESSURE WILL THEN BRING TRANQUIL MARINE CONDITIONS FOR FRIDAY. THE
NEXT COLD FRONT MOVES THROUGH ON SATURDAY...BRINGING ONLY A MODEST
INCREASE TO THE WINDS ON EITHER SIDE OF THE FRONT.

HYDROLOGY...

IMPRESSIVE SMALL SCALE LOW PRESSURE OVER SOUTH CENTRAL LOWER
MICHIGAN THIS AFTERNOON WILL SLOWLY PUSH SOUTHEAST TONIGHT. BANDS OF
SHOWERS AND STORMS WILL CONTINUE TO SLOWLY WANE THROUGH THE EARLY
EVENING BEFORE ENDING LATE THIS EVENING. RAINFALL AMOUNTS HAVE BEEN
GENERALLY LESS THAN A HALF INCH THROUGH MID AFTERNOON EXCEPT UNDER A
FEW THUNDERSTORMS. EXPECT RAINFALL FOR THE REST OF THE AFTERNOON AND
EVENING TO AGAIN BE LESS THAN AN ADDITIONAL HALF INCH EXCEPT FOR A
FEW LOCAL SPOTS UNDER A THUNDERSTORM OR TWO. AFTER MIDNIGHT...DRY
CONDITIONS EXPECTED THROUGH FRIDAY.

&&

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

$$

UPDATE.......SC
AVIATION.....SC
DISCUSSION...HLO/DT
MARINE.......RBP
HYDROLOGY....RBP


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