Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 292350
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
750 PM EDT TUE JUL 29 2014


.AVIATION...

//DISCUSSION...

COVERAGE OF PULSE TYPE SHOWERS AND THUNDERSTORMS ALREADY SHOWING A
DIMINISHING TREND WHICH SHOULD CONTINUE THROUGH THE EVENING HOURS.
EXPECT VFR CONDITIONS THROUGH THE TAF CYCLE WITH CIGS SCATTERING OUT
THROUGH THE OVERNIGHT FOR MOST LOCATIONS. COULD SEE CIRRUS DEBRIS
FROM UPSTREAM SYSTEM STREAM INTO THE AREA THROUGH THE NIGHT. AS THE
SHOWERS DIMINISH...ATTENTION WILL TURN TO FOG POTENTIAL FOR THE
EARLY MORNING HOURS. WITH CLOUDS DIMINISHING AND AMPLE MOISTURE AT
THE SFC DUE TO RAINFALL...RADIATIONAL COOLING COULD PRODUCE SOME FOG
BY MORNING. CLOUDS CLEARING FASTER AND EARLIER ACROSS THE NORTH WILL
PUT MBS AT THE BIGGEST RISK TO SEE FOG...LESS CONFIDENT FOR FNT AND
PTK. WILL INCLUDE A PERIOD OF MVFR VSBY FOR MBS AND MONITOR TRENDS
FOR THE OTHER SITES AS WE BEGIN NIGHTFALL.

FOR DTW...STILL A CHANCE FOR SOME SHOWERS THROUGH ABOUT 02Z AS
UPSTREAM CONVECTION DRIFTS SOUTHEASTWARD THROUGH SUNSET. VFR
CONDITIONS THROUGH TOMORROW MOST LIKELY UNLESS A SHOWER PASSES OVER
THE SITE.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN CEILING BELOW 5000 FEET IN SHOWERS DURING
THE   EVENING.

* LOW CONFIDENCE IN CEILING BELOW 5000 FEET WEDNESDAY AFTERNOON.

* LOW CONFIDENCE IN AN ISOLATED THUNDERSTORM THROUGH 03Z.

&&

.PREV DISCUSSION...ISSUED 339 PM EDT TUE JUL 29 2014

SHORT TERM... TODAY AND TONIGHT

DIURNAL CLOUDS AND CONVECTION HAVE BEEN BLOSSOMING IN THE WAKE OF
A BAND OF MID CLOUDS. THESE MID CLOUDS /ASSOCIATED WITH THE LEAD
EDGE OF A PLUME OF HIGHER LOW-MID LEVEL MOISTURE/ WILL BE EXITING TO
THE EAST OF THE AREA BY FORECAST ISSUANCE. THE COLD AIR ALOFT IS A
RESULT OF AN ANOMALOUSLY DEEP UPPER TROUGH EXTENDING ACROSS THE ERN
US. WITH 500MB TEMPS AROUND -17C OVER SE MI...MID LEVEL LAPSE RATES
WILL REMAIN STEEP WELL INTO THE NIGHT. THE 19Z SURFACE ANALYSIS
SHOWS A TROUGH AXIS EXTENDING FROM THE THUMB DOWN TO SOUTH-CENTRAL
LOWER MI. MOISTURE POOLING ALONG THIS TROUGH HAS SENT SFC DEWPOINTS
INTO THE MID TO UPPER 50S...RESULTING IN 0-1KM ML CAPE ON THE ORDER
OF 500 J/KG. THE COMBINATION OF THIS WEAK INSTABILITY AND COLD AIR
ALOFT WILL CONTINUE TO SUPPORT BRIEF SHOWERS/THUNDERSTORMS INTO THIS
EVENING THAT WILL BE CAPABLE OF PRODUCING SMALL HAIL. THE SURFACE
TROUGH WILL MOVE INTO THE ERN PORTIONS OF THE AREA /PORT HURON-
DETROIT-MONROE/ BY 21Z. THUS SCATTERED-NUMEROUS CONVECTION IS
EXPECTED TO CONTINUE DEVELOPING TOWARD THE EAST OVER THE NEXT COUPLE
OF HOURS.

THE LOSS OF DAYTIME HEATING DURING THE EVENING WILL LEAD TO A
DIMINISHING TREND IN COVERAGE AND INTENSITY OF RESIDUAL CONVECTION.
IN LIGHT OF WHAT WAS OBSERVED UPSTREAM YESTERDAY AND CONSIDERING THE
STEEP MID LEVEL LAPSE RATES...THIS PROCESS SHOULD BE GRADUAL. THE
REGIONAL WATER VAPOR IMAGE SHOWS A MID LEVEL SHORT WAVE IMPULSE OVER
WRN LAKE SUPERIOR...EMBEDDED WITHIN THE NORTHWEST FLOW. THIS WAVE
WILL TRACK ACROSS SW LOWER MI INTO NRN OHIO TONIGHT. SOME ADDED
ASCENT ASSOCIATED WITH THIS FEATURE COUPLED WITH A RESIDUAL LOW
LEVEL MOISTURE AXIS OVER FAR SRN MI WILL WARRANT A CHANCE OF
LINGERING SHOWERS/ISOLATED THUNDERSTORMS INTO THE OVERNIGHT. THERE
WILL BE SOME OPPORTUNITY FOR CLEARING TONIGHT...ESPECIALLY ACROSS
THE SAGINAW VALLEY AND THUMB. WITH SURFACE DEWPOINTS HOLDING WELL IN
THE 50S UP THROUGH THE NRN GREAT LAKES...THERE WILL BE A CHANCE OF
SOME FOG LATE TONIGHT PREDICATED UPON THE DEGREE OF RADIATIONAL
COOLING.

LONG TERM...

LARGE UPPER LEVEL LOW CENTERED OVER THE SOUTHERN END OF JAMES BAY
WILL DRIFT SOUTHWEST...DROPPING INTO NORTHEASTERN ONTARIO BY
THURSDAY MORNING.

MULTIPLE SPOKES OF ENERGY/SHORTWAVE TROUGHS WILL BE ROTATING AROUND
THE MAIN CIRCULATION...WITH ONE MOVING THROUGH NORTHERN LOWER
MICHIGAN LATE TOMORROW/TOMORROW EVENING...AS 500 MB TEMPS FALL INTO
THE NEGATIVE UPPER TEENS TO AROUND -20 C. THERE LOOKS TO BE A SHARP
MOISTURE GRADIENT STRADDLING SOUTHERN LOWER MICHIGAN TOMORROW...AS
SEEN IN 850-700 MB THETA-E FIELDS...AND THERE IS A QUESTION MARK ON
HOW MUCH MOISTURE AND SUBSEQUENT INSTABILITY WILL BE AROUND TO
SUPPORT SHOWERS AND ISOLATED THUNDERSTORMS...AS NAM IS THE MOST
AGRESSIVE...BUT LATEST EURO HAS ALSO TRENDED MORE UNSTABLE. WITH THE
FAVORABLE LATE DAY TIMING AND MAGNITUDE OF THE MID LEVEL COLD
POOL...CERTAINLY THINK SCATTERED POPS (ESPECIALLY TOWARD OHIO
BORDER) ARE WARRANTED WITH ISOLATED THUNDERSTORMS.

THURSDAY LOOKS FAIRLY SIMILAR WITH ANOTHER PIECE OF UPPER LEVEL
ENERGY ROTATING THROUGH....WITH TIMING SENSITIVITY. 30 KNOTS OF 0-6
KM WIND SHEAR AND INVERTED V SOUNDING MAKES WIND A BIT OF A CONCERN
IF ANY THUNDERSTORM IS IN FACT ABLE TO MATERIALIZE...AS WELL AS HAIL
WITH MAX CAP DENSITY CENTERED AROUND FREEZING LEVEL. ONCE
AGAIN...NAM IS INDICATING THE MOST INSTABILITY WITH UP TO 1500 J/KG
OF CAPE.

LOW LEVEL AIRMASS WILL BE SLOWLY MODIFYING AS 850 MB TEMPS GO FROM
UPPER SINGLE NUMBERS WEDNESDAY (SUPPORTING HIGH IN THE LOWER 70S) TO
LOWER TEENS ON THURSDAY (MID/UPPER 70S).

THE LONGWAVE PATTERN WILL CONTINUE TO SLOWLY DEAMPLIFY OVER THE
REMAINDER OF THE FORECAST PERIOD...BUT IT STILL LOOKS TO FEATURE A
GENERAL RIDGE WEST/TROUGH EAST PATTERN...PRECLUDING ANY BIG
WARM-UPS. UPPER TROUGH AXIS/COLD POOL WILL STILL BE OVERHEAD FRIDAY
AND SATURDAY SO DIURNALLY ENHANCED SHOWERS WILL BE A POSSIBILITY AT
LEAST THROUGH SATURDAY. TEMPERATURES ARE EXPECTED TO BE NEAR TO
SLIGHTLY BELOW NORMAL INTO EARLY NEXT WEEK.

MARINE...

A COOL BUT LIGHT NORTHWEST WIND WILL PERSIST OVER LAKE HURON AND
LOWER MICHIGAN THROUGH TOMORROW. THE WIND WILL REMAIN LIGHT THROUGH
THE END OF THE WEEK AND TEND TO SHIFT TOWARD THE SOUTHWEST BY FRIDAY
WITH INCREASING INFLUENCE OF WEAK HIGH PRESSURE BY THE WEEKEND.
OTHERWISE THERE WILL BE A LOW CHANCE OF BRIEF SHOWERS AND ISOLATED
THUNDERSTORMS...PRIMARILY NEAR THE SHORELINES OVER LAKE ST CLAIR AND
WESTERN LAKE ERIE.

&&

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

&&

$$

AVIATION.....DRK
SHORT TERM...SC
LONG TERM....SF/DT
MARINE.......SF


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





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