Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 042003 CCA
AFDDTX

AREA FORECAST DISCUSSION...CORRECTED FINAL PARAGRAPH
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
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.

&&

.AVIATION...ISSUED 141 PM EDT WED MAY 4 2016

UPPER LOW AND SURFACE LOW WERE SPINNING OVER SOUTHWEST LOWER
MICHIGAN THIS AFTERNOON AND WILL SLOWLY EXIT SOUTHEAST OVERNIGHT.
IN THE MEANTIME SEVERAL BAND OF SHOWERS WERE SPIRALLING AROUND
THESE LOWS ACROSS SOUTHEAST MI. THERE WERE EMBEDDED THUNDERSTORMS
TOO. EXPECT THIS TO CONTINUE THROUGH THE AFTERNOON...BUT SHOW A
DECREASE TOWARD 00Z AS BOTH THE LOWS SPIN AWAY AND INSTABILITY
DECREASES. WINDS WILL BE STRONG ENOUGH AROUND THIS LOW EARLY...10
TO 15 KTS AND THE DIRECTION WILL BE DIFFICULT GIVEN THE LOW
PASSING CLOSE TO THE DETROIT AREA TAFS. ALSO EXPECT SOME MVFR
CEILINGS AND VISIBILITIES IN THE SHOWERS.

SOME SHOWERS WILL LINGER INTO THE EVENING BUT BY 03Z ALL TAF SITES
WILL BE DRY. CEILINGS FROM 4000 TO 6000 FEET EXPECTED THROUGH MUCH
OF THE NIGHT. SOME SUGGESTION OF STRATUS WITH RECENT RAINS AND
NORTHEAST FLOW OFF OF THE GREAT LAKES AND HAVE A TEMPO GROUP FOR
THE NORTHERN TAF SITES AROUND DAYBREAK. THURSDAY WILL HAVE MORE
DRYING WITH SCATTERED CUMULUS AND A NORTH WIND AROUND 10 KTS.

FOR DTW...THUNDER THREAT HAS ALREADY ROTATED NORTH AND EAST OF DTW
FOR THE AFTERNOON. STILL BANDS OF SHOWERS WILL MOVE IN FOR MVFR
VISIBILITIES AND CEILING THROUGH THE AFTERNOON. AFTER 02Z SHOWERS
END AND CEILINGS IMPROVE TO 4000 TO 6000 FEET AND BECOME SCATTERED
BY DAYBREAK.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN CEILINGS AT OR BELOW 5000 THROUGH 05Z.

* LOW IN THUNDERSTORMS IMPACTING THE AREA THROUGH 21Z.

&&

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

$$

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


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