Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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498
FXUS63 KDTX 051957
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
357 PM EDT THU MAY 5 2016

.DISCUSSION...

NORTHERLY LOW LEVEL FLOW HAS MAINTAINED A SUPPLY OF COOL AIR OVER
LOWER MICHIGAN TODAY AHEAD OF HIGH PRESSURE ADVANCING FROM THE
MIDWEST AND NORTHERN GREAT LAKES. DESPITE THIS...DAYTIME HEATING HAS
ALLOWED TEMPERATURES TO REACH NORMAL VALUES FOR EARLY MAY WHICH
SEEMS LIKE A BIG IMPROVEMENT COMPARED TO RECENT DAYS. THE COOL AND
RELATIVELY MOIST BOUNDARY LAYER RESPONDED TO EARLY MAY SURFACE
HEATING WITH GENEROUS COVERAGE OF CUMULUS BY MID AFTERNOON. THE MAIN
CONCERN FOR THE SHORT TERM HAS BEEN WITH RECONCILING BULLISH SHOWER
DEPICTIONS FROM JUST ABOUT ALL MESOSCALE MODELS FOR THIS AFTERNOON
INTO EVENING COMPARED WITH DRY CONDITIONS OFFERED BY SYNOPTIC MODELS
OTHER THAN THE GFS. A CASE CAN BE MADE FOR AN ISOLATED SHOWER...
ESPECIALLY OVER INTERIOR SECTIONS OF LOWER MICHIGAN WHERE SURFACE
CONVERGENCE HAS THE BEST CHANCE OF FOCUSING MOISTURE UNDER WEAKLY
CYCLONIC/NEUTRAL FLOW ALOFT BEFORE LARGER SCALE MID LEVEL SUBSIDENCE
TAKES OVER. MODEL SOUNDINGS ARE LESS SUPPORTIVE WITH A GENERAL
INDICATION OF CONVECTIVE CLOUD DEPTH SHRINKING WITH TIME THROUGH
PEAK HEATING. THIS IS SHOWN EVEN IN THE MOST AGGRESSIVE HRRR
DEPICTIONS AS THE ADVANCING UPPER RIDGE SUPPORTS SUBSIDENCE AND MID
LEVEL WARMING. SATELLITE AND RADAR OBSERVATIONAL EVIDENCE SUPPORTS
ISOLATED DEVELOPMENT FARTHER WEST AND NEAR THE OHIO BORDER UNTIL
SURFACE HEATING WANES WITH SUNSET.

A WEDGE OF SUBSIDENCE WILL PERSIST OVER SE MICHIGAN THROUGH FRIDAY
WITH SOME MID CLOUD NEARBY TO THE WEST OFF THE FLANK OF THE RIDGE.
THESE CLOUDS WILL BE ASSOCIATED WITH A MODEST MID LEVEL THETA-E
GRADIENT THAT IS SUPPORTING CLOUDS AND EVEN SOME CONVECTION TODAY
OVER THE UPPER MIDWEST/WESTERN GREAT LAKES. MODEL DEPICTIONS SUGGEST
FORCING WILL BE LESS EFFECTIVE AND REMAIN MAINLY TO OUR WEST THROUGH
THE DAY. SO AFTER CLEAR SKY OVERNIGHT ALLOWS FOR A CHILLY START TO
MORNING TEMPS...EXPECT FRIDAY HIGHS TO MAKE THE ADVERTISED RUN
TOWARD 70 WITH THE HELP OF MORE EARLY MAY SUNSHINE.

THE ABOVE MENTIONED MID CLOUD PATTERN WILL WILL BE DIRECTED OVERHEAD
ON BACKING FLOW ALOFT FRIDAY NIGHT AND IN ADVANCE OF THE NEXT
FRONTAL SYSTEM SATURDAY. MID LEVEL MOISTURE TRANSPORT WILL HELP
BUILD SOME ELEVATED INSTABILITY THAT WILL BECOME SURFACE BASED
DURING THE DAY. THE NAM PRODUCES SURFACE BASED CAPE AROUND 1700 J/KG
BUT WITH DEWPOINT IN THE LOWER 60S WHICH SEEMS LIKE THE UPPER END OF
THE RANGE AT THIS POINT SINCE THE NEAREST 60 DEGREE OBSERVATION IS
AT KEY WEST TODAY. THE FRONTAL SYSTEM OTHERWISE STILL APPEARS FULLY
CAPABLE OF LIKELY POPS/NUMEROUS SHOWERS IN MODEL SOLUTIONS. THERE IS
ALSO REASONABLE AGREEMENT ON TIMING WITH A MID MORNING PASSAGE IN
THE TRI CITIES AND A MID AFTERNOON PASSAGE IN THE DETROIT AREA THAT
IS MORE FAVORABLE FOR THUNDERSTORM DEVELOPMENT DURING PEAK HEATING.
POST FRONTAL DRY NORTHERLY FLOW IS THEN EXPECTED ALL AREAS BY SUNSET
SATURDAY EVENING.

POSTFRONTAL ENVIRONMENT SUNDAY SHOULD LEAD TO A QUIET WEATHER DAY
FOR MOST LOCALES AND A FEW DEGREES COOLER THAN SATURDAY. MODELS ARE
DEPICTING A WEAK SURFACE REFLECTION OF AN UPPER LEVEL IMPULSE
ROTATING THROUGH THE UPPER LEVEL TROUGH WHICH COULD ENHANCE
CLOUDINESS OR GENERATE A FEW SPRINKLES OVER THE THUMB...BUT
DEPARTURE OF DEEPER MOISTURE WILL GREATLY LIMIT THIS ACTIVITY.
MOISTURE INCREASES AGAIN LATE MONDAY AS A WARM FRONT CONNECTED TO
SLOW-MOVING LOW PRESSURE ON THE PLAINS LIFTS THROUGH. LOW CONFIDENCE
IN TIMING INDIVIDUAL PERIODS OF PRECIPITATION...BUT INDICATIONS ARE
THAT A FAIRLY WET WEEK IS POSSIBLE GIVEN NWP DEPICTIONS OF THE FRONT
STALLING OVER THE REGION.

&&

.MARINE...

GUSTY NORTH WINDS WILL CONTINUE INTO THE EARLY EVENING BEHIND
DEPARTING LOW PRESSURE. SURFACE HIGH PRESSURE EXPANDING INTO THE
GREAT LAKES WILL THEN BRING FAIRLY LIGHT WINDS TO THE AREA THROUGH
FRIDAY NIGHT. A MODEST INCREASE IN SOUTHERLY WINDS IS EXPECTED EARLY
SATURDAY BEFORE A COLD FRONT SURGES THROUGH THE REGION AND FLIPS
WINDS TO THE NORTHWEST DURING THE AFTERNOON AND EVENING. SPEEDS LOOK
TO REMAIN BELOW GALES...PEAKING AROUND 25 KNOTS OVER THE OPEN WATERS
OF LAKE HURON. WILL HAVE TO WATCH WAVE HEIGHTS OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE HURON HOWEVER AS THEY COULD BUILD IN EXCESS
OF 4 FEET...POSSIBLY NECESSITATING A SMALL CRAFT ADVISORY SATURDAY
EVENING. WEATHER ACROSS THE CENTRAL GREAT LAKES IS EXPECTED TO
REMAIN DRY THOUGH LATE FRIDAY. NUMEROUS SHOWERS AND A FEW
THUNDERSTORMS WILL THEN DEVELOP LATE FRIDAY NIGHT THROUGH SATURDAY
EVENING AS THE COLD FRONT DROPS THROUGH THE AREA.

&&

.AVIATION...ISSUED 201 PM EDT THU MAY 5 2016

ONSET OF DAYTIME HEATING HAS ALLOWED SCT-BKN CU TO DEVELOP. BEST
COVERAGE IS EXPECTED FROM PTK SOUTHWARD...WHERE MOISTURE WILL BE
SLIGHTLY GREATER BEHIND LOW PRESSURE DEPARTING TO THE SOUTHEAST. DRY
AIR IN THE MIXED LAYER WILL TRY TO LIMIT COVERAGE OF CU THIS
AFTERNOON...EVEN TOWARDS THE DETROIT-AREA TERMINALS. OVERALL
CONFIDENCE IN CEILINGS BKN BETWEEN 4500-6000 FOR MORE THAN AN HOUR
OR TWO IS NOT HIGH. CU WILL DISSIPATE THIS EVENING...LEAVING CLEAR
SKIES OVERNIGHT. NORTHERLY FLOW WILL BE THE OTHER NOTABLE WEATHER
ELEMENT THIS AFTERNOON...WITH GUSTS TO AROUND 20 KNOTS DISSIPATING
AROUND SUNSET. WINDS WILL BE LIGHT OVERNIGHT...GENERALLY 5 KTS OR
LESS.

FOR DTW...DRIER AIR MIXING INTO THE LOWER LEVELS MAY LIMIT CU
COVERAGE THIS AFTERNOON...BRINGING SOME UNCERTAINTY TO HOW LONG BKN
CEILINGS CAN LAST. ALSO EXPECT TO SEE BASES RISE FROM 4500 FEET TO
6000 FEET BY LATE AFTERNOON DUE TO THE DRIER AIR. WINDS ARE MORE
LIKELY TO HAVE A SLIGHT NORTHEAST COMPONENT THROUGH THE MID-
AFTERNOON BEFORE THEY BECOME MORE SOLIDLY OUT OF THE NORTH.

//DTW THRESHOLD PROBABILITIES...

* LOW IN CEILINGS BELOW 5000 FEET THIS AFTERNOON.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

DISCUSSION...BT/DT
MARINE.......HLO
AVIATION.....HLO


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