Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 281704
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
104 PM EDT MON JUL 28 2014

.AVIATION...

//DISCUSSION...

NORTHWEST FLOW WILL BRING LOW LEVEL DRYING TO THE TAF SITES THIS
EVENING AND TONIGHT WITH AFTERNOON CUMULUS DECK GIVING WAY TO JUST
SOME SCATTERED CUMULUS AND MID LEVEL CLOUDINESS FOR THE OVERNIGHT
HOURS BEFORE 5-7KFT CLOUDS INCREASE TOWARDS DAYBREAK.  THESE CLOUDS
WILL CONTINUE TO THICKEN AND LOWER SOME TUESDAY MORNING WITH
SCATTERED SHOWERS DEVELOPING FROM NORTHWEST TO SOUTHEAST BY LATE
MORNING AND CONTINUING THROUGH THE AFTERNOON.  THERE IS A LOW RISK
OF A FEW EMBEDDED THUNDERSTORMS DURING THE AFTERNOON...BUT
CONFIDENCE NOT HIGH ENOUGH TO INCLUDE IN THIS TAF PACKAGE.

WINDS:  NORTHWESTERLY WINDS 12G20KTS WILL DIMINISH TO 5-10KTS FROM
THE WEST THIS EVENING AND CONTINUE THROUGH THE OVERNIGHT.  FOR THE
DAY TUESDAY EXPECT WEST-NORTHWEST WINDS TO INCREASE TO 10-15KTS BY
LATE MORNING.

//DTW THRESHOLD THREATS...

HIGH CONFIDENCE CEILINGS BELOW 5000 FEET THROUGH 23Z.

MEDIUM CONFIDENCE CEILINGS BELOW 5000 FEET LATE MORNING THROUGH THE
AFTERNOON TUESDAY.

&&

.UPDATE...

HAVE SLOWED CLEARING TREND THIS MORNING AS MVFR STRATUS IS HOLDING
TOUGH ACROSS MUCH OF THE AREA.  THERE ARE SOME BREAKS ALONG A
FNT-ADG LINE...WHICH INDICATE THE DIRECTION WE/RE HEADED AND EXPECT
A VERY GRADUAL THINNING TREND TO CURRENT CLOUD COVER.  THUS...WHILE
MORNING/EARLY AFTERNOON TEMPERATURES WERE LOWERED TO ACCOUNT FOR
SLOWER THAN NORMAL WARMING...HAVE MAINTAINED GOING HIGHS WITH
EXPECTED AFTERNOON SUNSHINE.  NO OTHER SIGNIFICANT CHANGES NEEDED AT
THIS TIME.

&&

.PREV DISCUSSION...ISSUED 345 AM EDT MON JUL 28 2014

SHORT TERM... TODAY AND TONIGHT

EARLY MORNING SATELLITE IMAGERY SHOWS THE UPPER LOW SPINNING AWAY
FROM SE MICHIGAN BUT STILL ABLE TO SUPPORT A PATTERN OF SHOWERS
AROUND THE NORTHWEST FLANK OF THE SYSTEM. MODEL ANALYSIS FIELDS
INDICATE THIS IS ASSOCIATED WITH A WELL-DEFINED DEFORMATION AXIS
WRAPPING AROUND THE SYSTEM WHICH WILL EFFICIENTLY WRING OUT
REMAINING MOISTURE FOR A FEW MORE HOURS. RADAR TRENDS SUPPORT MODEL
DEPICTIONS OF THE PATTERN LEAVING THE TRI CITIES DRY AT PRESS TIME
AND THEN SLIDING SOUTHWARD AND SHRINKING EASTWARD ON A PACE TO EXIT
THE REST OF THE AREA AROUND 8 AM.

THE CONTINUED EASTWARD DEPARTURE OF THE LOW WILL BOLSTER NORTHERLY
SURFACE WIND AND COLD ADVECTION THAT IS ALREADY IN PROGRESS ACROSS
LOWER MICHIGAN. THE 00Z MODEL SOLUTIONS ARE CONSISTENT WITH THE LAST
SEVERAL RUNS SHOWING A POCKET OF 850 MB AIR AT ABOUT 5C RECOVERING
TO ABOUT 7C DURING THE AFTERNOON. SOUNDING ANALYSIS TRANSLATES THAT
INTO HIGHS MOSTLY IN THE UPPER 60S WITH A BOUNDARY LAYER MIXING TO
800 MB. THIS IS ABOUT 15 DEGREES BELOW NORMAL HIGHS THAT ARE STILL
IN THE LOWER 80S DURING THE LAST WEEK OF JULY...BUT ONLY APPROACHING
THE RECORD LOWEST MAX TEMP AT DTW WHICH IS 68/1926 WHILE FNT AND
MBS ARE IN THE LOWER TO MID 60S.

HIGH CLOUDS STRIPPING AWAY REVEAL SOME BREAKS IN THE STRATUS OVER
LOWER MICHIGAN DURING THE EARLY MORNING. THERE COULD BE SOME
EXPANSION OF OPEN SKY FOR A FEW HOURS POST SUNRISE BUT THESE WILL
QUICKLY FILL IN AS SURFACE HEATING RAMPS UP BY LATE MORNING. MODEL
SOUNDINGS INDICATE ENOUGH MOISTURE FOR A GENEROUS CU RESPONSE BUT
WITH ENOUGH MID LEVEL SUBSIDENCE TO PREVENT SHOWERS. EXPECT THE
AFTERNOON CLOUD PATTERN TO LINGER LONG ENOUGH INTO THE EVENING TO
BLEND IN WITH MID AND HIGH CLOUDS ARRIVING WITH THE NEXT UPPER LEVEL
HEIGHT FALL CENTER IN NORTHERLY FLOW ALOFT. THE APPROACH OF THE
UPPER WAVE WILL ALSO SHARPEN SURFACE PRESSURE GRADIENT ENOUGH TO
MAINTAIN A 5-10 KNOT WIND THROUGH THE NIGHT. THE COMBINATION OF
CLOUDS AND WIND WILL THEN PREVENT TEMPERATURES FROM REACHING FULL
RADIATIONAL COOLING POTENTIAL AND KEEP MIN TEMPS IN THE 50S WITH THE
EXCEPTION OF THE USUAL COOL SPOTS THAT COULD TOUCH THE UPPER 40S BY
SUNRISE TUESDAY.

LONG TERM...TUESDAY THROUGH SUNDAY

COOL CYCLONIC FLOW WILL PERSIST OVER THE CENTRAL GREAT LAKES FROM
TUESDAY INTO FRIDAY AS THE UPPER LOW REMAINS OVER ONTARIO AND
QUEBEC. WEAK UPPER SHORTWAVES PIVOTING AROUND THE LOW WILL
OCCASIONALLY BRUSH ACROSS THE AREA...BRINGING QUICK SHOTS OF
MOISTURE. DAYTIME HEATING WILL HELP US DESTABILIZE EACH DAY WITH
SURFACE HEATING COMBINING WITH COOL AIR ALOFT (H850 TEMPS RUNNING
JUST BELOW 10C THROUGH THIS PERIOD) TO STEEPEN LAPSE RATES.
TEMPERATURES WILL ALSO RUN A BIT BELOW NORMAL...WITH HIGHS ONLY IN
THE 70S (COMPARED TO AVERAGE HIGHS IN THE LOW 80S).

FOR TUESDAY...MODELS HAVE BEEN CONSISTENT WITH DROPPING A VERY WEAK
UPPER WAVE DOWN FROM CANADA...BRINGING A SURGE OF LOW/MID LEVEL
MOISTURE WITH IT. THE SHORTWAVE AND ASSOCIATED SURFACE TROUGH ARE
PROGGED TO WORK ACROSS THE AREA DURING PEAK HEATING. MODEL FORECAST
SOUNDINGS LACK A CAP AND SHOW LAPSE RATES FROM THE SURFACE TO 500MB
RANGING BETWEEN 7 AND 9 C/KM. THIS SHOULD PROVIDE SCATTERED TO
NUMEROUS SHOWERS ACROSS THE AREA...WITH A LITTLE BETTER COVERAGE
EXPECTED NORTH OF M-59...CLOSER TO THE UPPER WAVE AND COOLER AIR
ALOFT. FREEZING LEVELS ARE EXPECTED TO RUN AROUND 9000 FEET WITH THE
COOLER AIRMASS OVERHEAD. WHILE THE POTENTIAL FOR THUNDERSTORMS WILL
BE LOW...THUNDERSTORMS OR EVEN MORE VERTICALLY DEVELOPED SHOWERS
THAT DEVELOP WILL BE CAPABLE OF SMALL HAIL.

CANADIAN UPPER LOW WILL LIFT NORTH FOR THE WEEKEND...BUT MEDIUM
RANGE MODELS ARE STILL IN STRONG AGREEMENT WITH KEEPING SOME
TROUGHING THROUGH THE GREAT LAKES. WHILE SHOWERS AND THUNDERSTORMS
WILL STILL BE POSSIBLE...WE SHOULD SEE SOME MODERATION IN
TEMPERATURES INTO THE UPPER 70S OR NEAR 80 FOR HIGHS.

MARINE...

GUSTY WINDS WILL PERSIST TODAY BEHIND A COLD FRONT...AND AS THE
CENTRAL GREAT LAKES BECOMES SITUATED BETWEEN LOW PRESSURE TRACKING
THROUGH THE EASTERN GREAT LAKES AND HIGH PRESSURE BUILDING OVER THE
PLAINS AND UPPER MIDWEST. GUSTS UP TO 30 KNOTS WILL BE POSSIBLE OVER
THE SOUTHERN HALF OF LAKE HURON TODAY...IN ADDITION TO LARGE WAVES.
A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE NEARSHORE WATERS OF
LAKE HURON....INCLUDING ALL OF SAGINAW BAY. FURTHER SOUTH OVER LAKE
ST CLAIR AND LAKE ERIE...GUSTS SHOULD STAY MOSTLY BETWEEN 18 AND 23
KNOTS...HOWEVER A FEW GUSTS TO 25 KNOTS CAN BE EXPECTED. WIND SPEEDS
WILL DECREASE TONIGHT AS LOW PRESSURE OVER THE EASTERN GREAT LAKES
STARTS TO LIFT NORTH AND ALLOWS THE SURFACE PRESSURE GRADIENT OVER
MICHIGAN TO RELAX.

THE CENTRAL GREAT LAKES WILL THEN REMAIN IN COOL CYCLONIC FLOW
THROUGH THE MID-WEEK PERIOD. THIS WILL PROVIDE CHANCES FOR SHOWERS
AND A FEW THUNDERSTORMS...BUT WINDS SHOULD BECOME FAIRLY LIGHT
(UNDER 15 KNOTS) AS ONLY WEAK TROUGHING REMAINS OVER THE AREA.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...BEACH HAZARDS STATEMENT...MIZ048-MIZ049-MIZ055-MIZ063...UNTIL 8 PM
     MONDAY.

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
     HURON INCLUDING SAGINAW BAY...UNTIL 8 PM MONDAY.

LAKE ST CLAIR...NONE.

MI WATERS OF LAKE ERIE...NONE.

&&

$$

UPDATE.......ARNOTT/APX
AVIATION.....ARNOTT/APX
SHORT TERM...BT
LONG TERM....HLO
MARINE.......HLO


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