Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 290348
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1148 PM EDT TUE JUL 28 2015


.AVIATION...

LIGHT WINDS AND CLEAR SKIES BELOW 10K FT WILL PERSIST THROUGH
ROUGHLY 11 OR 12Z UNDER THE INFLUENCE OF HIGH PRESSURE OVER THE ERN
GREAT LAKES. INCREASING MOISTURE WILL ARRIVE AROUND OR JUST PRIOR TO
DAYBREAK. THIS WILL RESULT IN THE ARRIVAL OF SOME CLOUDS BASED BELOW
10K FT AND MAY TOUCH OFF AN ISOLATED SHOWER/TSTM. THE BETTER CHANCES
FOR THUNDERSTORMS WILL OCCUR DURING THE MID-LATE AFTERNOON WED AHEAD
OF A COLD FRONT.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN THUNDERSTORMS WED AFTERNOON AND EVENING.

&&

.PREV DISCUSSION...ISSUED 253 PM EDT TUE JUL 28 2015

SHORT TERM...THROUGH TONIGHT

UPPER RIDGE AXIS WITH H500 HEIGHTS IN EXCESS OF 588DM WILL CONTINUE
TO PROVIDE LARGE SCALE SUBSIDENCE OVER THE AREA...MAINTAINING WARM
TEMPERATURES AND QUIET CONDITIONS THROUGH THE REMAINDER OF TODAY.
THE RIDGE WILL BEGIN TO FLATTEN AND SHIFT EAST TONIGHT IN RESPONSE
TO A LARGE UPPER LOW LIFTING THROUGH MANITOBA. THIS WILL TURN UPPER
FLOW MORE WESTERLY AND ALLOW MORE CIRRUS TO SPREAD INTO THE AREA
THIS EVENING AND TONIGHT...AS IT STREAMS IN AHEAD OF THE APPROACHING
LOW AND OFF STORMS THAT DEVELOP AND STAY TO OUR WEST.

DOME OF WARM AIR OVER THE AREA AND BLANKET OF HIGH CLOUDS WILL KEEP
MIN TEMPS ABOUT 5 DEGREES ABOVE NORMAL...IN THE 60S ACROSS SOUTHEAST
MICHIGAN...SIMILAR TO SLIGHTLY WARMER THAN LAST NIGHT.

LONG TERM...

ELEVATED DEWPOINTS IN THE LOW TO MID 70S AND ANALYZED PWATS IN
EXCESS OF 2 INCHES OVER THE MIDDLE AND UPPER MS VALLEY ARE
INDICATIVE OF VERY MOIST AIRMASS THAT HAS BEEN DRAWN NORTH IN
ADVANCE OF THE CYCLONE LIFTING INTO MANITOBA THIS EVENING. ZONAL
FLOW DEVELOPING OVER THE PACIFIC NORTHWEST TONIGHT WILL ENSURE THIS
LOW REMAINS PROGRESSIVE DESPITE BEING DEEP AND CLOSED OFF. EXISTING
RESERVOIR OF HIGH MOISTURE CONTENT WILL BECOME INCREASINGLY STRUNG
OUT AS THE LOW LIFTS TOWARD HUDSON BAY ON WEDNESDAY. A PARTIAL
COVERAGE OF SHOWERS WITH SOME EMBEDDED THUNDER IS EXPECTED TO
DEVELOP ALONG THE LEAD EDGE OF THE MOISTURE GRADIENT AS THE ARRIVAL
OF SIGNIFICANT MID-LEVEL MOISTURE SUFFICIENTLY LOWERS LFCS TO
SUPPORT SOME SURFACE BASED CONVECTION. HOWEVER, DIFFERENTIAL WAA AND
MOISTURE TRANSPORT WILL ALSO SUPPORT WIDESPREAD LOW CLOUDS WHICH
WILL SEVERELY LIMIT POTENTIAL FOR DESTABILIZATION. GIVEN
PROGRESSIVE/NARROW NATURE OF THETA-E RIBBON AND POOR FORCING
ENVIRONMENT, EXPECT NOTHING MORE THAN A SHORT-LIVED SHOWER THREAT
TRAVERSING WEST TO EAST WORTHY OF A 30-40 POP.

COLD FRONT WILL LAG BEHIND AND IS SHOWN BY THE 12Z NAM TO ENCROACH
ON THE SAGINAW VALLEY BY 00Z. THIS REPRESENTS AN OPPORTUNITY FOR
SECONDARY DEVELOPMENT IN THE EVENING. IF A SEVERE THREAT IS TO
MANIFEST ITSELF, IT WILL BE WITH THIS SECOND ROUND. HOWEVER, LIMITED
INSTABILITY, WANING FRONTAL CONVERGENCE, AND THE SETTING SUN WILL
CONSIDERABLY LIMIT POTENTIAL HERE. INSTEAD, EXPECTATION LEANS MORE
TOWARD BRIEFLY RENEWED CONVECTIVE COVERAGE EXHIBITING LIMITED
ORGANIZATION.

WELL-MIXED WESTERLY FLOW AROUND THE NORTHERN PERIPHERY OF SURFACE
HIGH PRESSURE DEVELOPS ON THURSDAY BENEATH INCREASING CONVERGENCE
ALOFT. MUCH COOLER COLUMN ON THURSDAY WILL BE COMPENSATED FOR BY
DEEP ADIABATIC MIXING TO 850MB TEMPS OF 15C WHICH WILL STILL SUPPORT
HIGHS IN THE MID TO UPPER 80S. MAIN CHANGE FROM RECENT DAYS WILL BE
SUBSTANTIALLY LOWER DEWPOINTS IN THE MID 50S ALONG WITH GUSTY
WESTERLY WIND OF 25 KTS WITHIN TIGHT GRADIENT FLOW.

GENERAL BROAD TROUGHINESS ADVERTISED BY 12Z DETERMINISTIC MODELS AND
GEFS MEAN FRIDAY INTO THE WEEKEND AS THE GREAT LAKES REGION LIES ON
THE SOUTHERN PERIPHERY OF A NEARLY STATIONARY UPPER LOW OVER HUDSON
BAY. UPPER FLOW LOOKS TO REMAIN FAIRLY STRONG WITH SHORTWAVES MOVING
THROUGH THE UPPER LONGWAVE TROUGH. THIS ALONG WITH BEHAVIOR OF
UPSTREAM CONVECTION WILL CAUSE TIMING OF PRECIP TO REMAIN DIFFICULT
AT THIS TIME HORIZON. BOTTOM LINE IS THAT PRECIP CANNOT BE RULED OUT
FRIDAY INTO THE WEEKEND BUT WITH NO SIGNAL AT THIS POINT THAT FAVORS
A WIDESPREAD EVENT. RATHER LOW PWAT VALUES ARGUE FOR KEEPING POPS
LOW AS SUPERBLEND DOES. TEMPS EXPECTED TO REMAIN NEAR SEASONAL NORMS.

MARINE...

MODERATE SOUTHERLY FLOW WILL DEVELOP ON WEDNESDAY IN ADVANCE OF AN
APPROACHING FRONT ALTHOUGH STABLE NATURE OF WARM SOUTHERLY FLOW WILL
LIMIT WIND GUST POTENTIAL TO 20 KTS OR LOWER. MODERATE SW FLOW WILL
PERSIST THROUGH WEDNESDAY NIGHT WITH GUSTS INCREASING TO AS HIGH AS
25 KNOTS. SMALL CRAFT ADVISORIES FOR WIND MAY BE NEEDED DURING THIS
TIME. LIGHT GRADIENT WILL SETTLE IN FOR THE EXTENDED PERIOD FAVORING
WINDS 10 KNOTS OR LESS FRIDAY AFTERNOON INTO SUNDAY.

&&

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

$$

AVIATION.....SC
SHORT TERM...HLO
LONG TERM....JVC/DT
MARINE.......JVC


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