Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 191424
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1024 AM EDT SAT JUL 19 2014

.UPDATE...
UPPER WAVE CAN BE SEEN ON WATER VAPOR LIFTING ACROSS EXTREME
SOUTHEAST MICHIGAN AND LAKE ERIE. MODEL SOLUTIONS CONTINUE TO
FOCUS MID-LEVEL DEFORMATION (850-500MB) WRAPPING AROUND THE NORTH SIDE OF
THE SYSTEM OVER FAR EASTERN MICHIGAN FROM LATE MORNING THROUGH
AFTERNOON. SHOWER COVERAGE HAS BEEN NOT SO IMPRESSIVE THUS FAR HOWEVER
DESPITE THE INFLUX OF MOISTURE EARLIER TODAY...PW ON DTX SOUNDING
WAS 1.13 INCHES AND SURFACE DEWPOINTS ARE NOW CREEPING INTO THE
LOW 60S. WILL MAKE ONLY SMALL CHANGES TO THE FORECAST THIS MORNING
HOWEVER...AS DAYTIME HEATING MAY BOOST COVERAGE OF SHOWERS. A FEW
RUMBLES OF THUNDER MAY ALSO BE POSSIBLE OVER THE EASTERN-MOST
COUNTIES.

&&

.AVIATION...ISSUED 701 AM EDT SAT JUL 19 2014

//DISCUSSION...

AN UPPER LEVEL DISTURBANCE WILL BRING INCREASED MOISTURE AND A
CHANCE OF SHOWERS TO THE DETROIT AREA TERMINALS TODAY. THE MOISTURE
WILL PIVOT INTO FAR SOUTHEASTERN MICHIGAN FROM THE SOUTH AND
EAST...PLACING KDTW ON THE FRINGE OF THE RAIN SHIELD THIS MORNING.
WITH RADAR OBSERVED PRECIPITATION AND VIRGA...WENT AHEAD AND
CONVERTED THE TEMPO INTO A PREVAILING GROUP. EXPECTATIONS ARE FOR
MORE OF A SHOWERY NATURE TO THE PRECIPITATION. THE MOISTURE WILL
LIFT TOWARD THE SOUTHERN LAKE HURON BASIN BY THIS
AFTERNOON...STRIPPING TO THE EAST BY LATE THIS AFTERNOON. A SURFACE
RIDGE AXIS WILL THEN BECOME ESTABLISHED OVER SOUTHEASTERN MICHIGAN
THROUGHOUT THE REMAINING PORTIONS OF THE WEEKEND.

AT KDTW...THE MOST LIKELY TIMEFRAME FOR PRECIPITATION TO REACH THE
GROUND WILL BE BETWEEN 14-18Z.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CIGS BELOW 5KFT FOR TODAY.

&&

.PREV DISCUSSION...ISSUED 336 AM EDT SAT JUL 19 2014

SHORT TERM...TODAY AND TONIGHT

A RELATIVELY LARGE WAVELENGTH UPPER LEVEL DISTURBANCE IS CENTERED
OVER THE OHIO RIVER VALLEY THIS MORNING. THIS POTENTIAL VORTICITY
ANOMALY RESIDES IN A WEAK SPOT OF LOWER HEIGHTS EXTENDING FROM THE
NORTHEASTERN UNITED STATES BACK TO THE SOUTHWEST. THERE IS JUST
ENOUGH LARGE SCALE FORCING WITH THE MIDLEVEL TROUGH AXIS TURNING TO
A NEGATIVE TILT AND A FAVORABLE WEAK JET CONFIGURATION ALOFT TO
ORGANIZE A GOOD AMOUNT OF DEEP COLUMN DEFORMATION. THIS DEFORMATION
IS FLANKING THE ENTIRE NORTHERN HALF OF THE UPPER LEVEL LOW AND IS
RESPONSIBLE FOR THE HIGH AMOUNT OF CLOUD AND BATCHES OF
PRECIPITATION TO THE SOUTH OF MICHIGAN.

THE DEFORMATION IS PROGGED TO LIFT NORTHWARD...PIVOTING BACK TO THE
NORTHWEST THROUGH THE MORNING AND INTO THE AFTERNOON. THE
DEFORMATION ALONG WITH SYSTEM RELATIVE ISENTROPIC ASCENT WILL BRING
THE POTENTIAL FOR PRECIPITATION TODAY ALONG THE SOUTHEASTERN EDGE OF
THE CWA. THE QUALITY OF MOISTURE THAT WILL SETTLE INTO THE AREA IS
DIFFICULT TO PIN DOWN...WITH LITTLE INTRA-MODEL CONTINUITY AND EVEN
LESS WHEN LOOKING AT INTER-MODEL COMPARISONS. THE REGIONAL SURFACE
OBSERVATION TREND THIS MORNING HAS BEEN ONE TO SHOW PRECIPITATION
STRUGGLING ALONG THE NORTHWESTERN PERIPHERY OF THE RAIN
SHIELD...WITH MANY LOCATIONS COMING UNDER THE FORECASTED QPF. WITH
THIS IN MIND IN ADDITION TO THE THE DTX HI-RES AND DTX HI-RES
ENSEMBLE OUTPUT STRUGGLING TO GENERATE MUCH OF ANYTHING...LOWERED
POPS DOWNWARD WHILE ESTABLISHING A SHARPER GRADIENT TO THE
PRECIPITATION CHANCES FOR THE WESTERN COUNTIES. AT THIS TIME...LIKELY
POPS SEEM MORE THAN GENEROUS FOR AREAS ALONG LAKE ST CLAIR/LAKE ERIE
AND THE RIVERS. THE PRECIPITATION SHOULD LIFT SOUTH TO NORTH...EXITING
THE SOUTHERN LAKE HURON BASIN BY 21Z. IN LIGHT OF THE THERMODYNAMIC
PROFILE AND THE FORECASTER SHOWALTER INDICES DISTRIBUTION TRIMMED THE
THUNDER MENTION TO THE FAR EASTERN SECTIONS OF THE CWA. THE HIGH END
OF THE FCST QPF RANGE IS AT .10 INCH.

WHAT IS OF HIGHER CERTAINTY IS THE AMOUNT OF CLOUDS THAT ARE EXPECTED
ACROSS ALL OF THE CWA EXCEPT THE FAR NW/TRI CITIES. THE INHERITED
FORECAST HAD THIS WELL IN HAND. THE OPAQUE CLOUD WILL HAVE A MAJOR
IMPACT ON TEMPERATURES...COMBINING WITH AN EASTERLY FLOW TRAJECTORY
TO BRING COOL CONDITIONS. HIGHS ARE ONLY EXPECTED TO REACH THE LOW
70S EAST...TO 80 DEGREES FOR FAR NORTHERN SHIAWASSEE COUNTY
NORTHWARD.

LONG TERM...SUNDAY THROUGH FRIDAY

REBOUNDING HEIGHTS IN THE WAKE OF THE DEPARTING MID LEVEL SHORT WAVE
LIFTING INTO QUEBEC ON SUNDAY WILL BUILD A MID LEVEL CAPPING
INVERSION OVER SE MI. AMPLE DAYTIME INSOLATION WILL BOOST MIXING
DEPTHS ENOUGH TO SUPPORT AFTERNOON HIGHS INTO THE LOW 80S OVER MOST
OF THE FORECAST AREA. A STRENGTHENING OF THE SUBTROPICAL RIDGE OVER
THE SRN ROCKIES/PLAINS WILL OCCUR EARLY IN THE WORK WEEK. A MID
LEVEL RIDGE AXIS IS EXPECTED TO EXTEND FROM THIS BUILDING HIGH INTO
THE SOUTHERN GREAT LAKES MON INTO TUES. THE CORRESPONDING INCREASE
IN THE MID LEVEL HEIGHT FIELD SHOULD EFFECTIVELY CAP SE MI TO
CONVECTION...THUS SUPPORTING A DRY FORECAST. A SLOW MOVING FRONTAL
BOUNDARY OVER THE NRN PLAINS AND SFC HIGH PRESSURE ANCHORED OVER THE
EAST COAST WILL LEAD TO INCREASING S-SW FLOW MON INTO TUES. THE
RESULTING LOW LEVEL WARM AIR ADVECTION WILL BOOST AFTERNOON HIGHS
INTO THE MID/UPPER 80S MON AND NEAR 90 BY TUES. SFC DEWPOINTS WILL
GRADUALLY RISE TO THE MID/UPPER 60S WITHIN THE SOUTHERLY
FLOW...LEADING TO MORE SUMMER-LIKE CONDITIONS AS COMPARED TO THE
LAST WEEK.

THE LAST SEVERAL RUNS OF THE MEDIUM RANGE MODEL SUITE INDICATE SHORT
WAVE ENERGY SLIDING INTO THE GREAT LAKES BY MID WEEK AND ERODING THE
MID LEVEL RIDGE AXIS OVER THE OHIO VALLEY/SRN GREAT LAKES. IN
FACT... AN AMPLIFICATION OF THE LONG WAVE PATTERN IS FORECAST...
FEATURING A SLIGHT RETROGRESSION OF THE SUBTROPICAL RIDGE AND LONG
WAVE TROUGH AMPLIFICATION OVER ERN CANADA AND THE ERN US BY LATE
NEXT WEEK. THE 00Z ECMWF HAS TRENDED TOWARD MORE PROGRESSIVE WITH
SHORT WAVE ENERGY AND THE ASSOCIATED SFC COLD FRONT MID WEEK...MORE
IN LINE WITH THE GFS AND CANADIAN. THIS SUGGEST THE BEST POTENTIAL
FOR CONVECTION WILL BE WEDNESDAY AND COOLER AND DRIER POST FRONTAL
AIR WILL FILTER INTO THE AREA BY THE END OF THE FORECAST PERIOD.

MARINE...

A WEAK E-SE GRADIENT WILL ACCOMPANY AN UPPER LEVEL LOW LIFTING
ACROSS THE EASTERN GREAT LAKES REGION TODAY. THE GRADIENT WILL RELAX
BEHIND THIS FEATURE TONIGHT...LEADING TO LIGHT AND RATHER VARIABLE
WINDS DURING THE LATER HALF OF THE WEEKEND. A GRADUAL INCREASE IN
THE SOUTHERLY GRADIENT WILL OCCUR MONDAY AND TUESDAY. LOW LEVEL WARM
AIR ADVECTION WILL LEAD TO HIGH STABILITY OVER THE LAKES...SO THE
WINDS ARE EXPECTED TO REMAIN MAINLY BELOW 15 KNOTS.

&&

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

&&

$$

UPDATE.......HLO
AVIATION.....CB
SHORT TERM...CB
LONG TERM....SC
MARINE.......SC


YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).





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