Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 300758
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
358 AM EDT THU APR 30 2015

.SHORT TERM...TODAY AND TONIGHT

THE TIGHT MIDLEVEL POTENTIAL VORTICITY ANOMALY AND ACCOMPANYING
MIDLEVEL COLD POOL CONTINUES TO DROP STRAIGHT SOUTHWARD ALONG THE
EASTERN SHORELINE OF LAKE MICHIGAN THIS MORNING. CONVERGENCE OF THE
MASS FIELD IMMEDIATELY ALONG THE FORWARD EASTERN FLANK OF THIS COLD
POOL AND INCREASING EASTERLY SYSTEM RELATIVE FLOW HAS RESULTED IN
POSITIVE CONTRIBUTIONS OF BOTH TILTING AND MIDLEVEL STRETCHING
DEFORMATION. THE COMBINED FORCING HAS RESULTED IN A WIDESPREAD
COVERAGE OF SHOWERS OVER SOUTHEASTERN MICHGIAN FOR MUCH OF THE
NIGHT. THE RECENT TREND OF THE RADAR OUTPUT HAS BEEN FOR A FOCUS OF
THE RAIN SHOWERS DOWN TO DETROIT AND THE RIVERS. RADAR ECHOES HAVE
BEEN HOLDING STEADY IN ADDITION TO BANDS OF CONTINUED CLOUDTOP
COOLING IN IR IMAGERY. ALTHOUGH RADAR ESTIMATES LIKELY CONTAIN SOME
BRIGHTBAND CONTAMINATION...SOME AREAS OVER WAYNE AND MONROE COUNTIES
WILL LIKELY REPORT RAINFALL AMOUNTS OF GREATER THAN .5 INCH. AS A
RESULT...INCREASED POPS TO CATEGORICAL THROUGH 12Z.

MODEL DATA SUPPORTS BOTH CENTERING AND CONTRACTING THE STRETCHING
DEFORMATION AXIS OVER EXTREME EASTERN PORTIONS OF THE CWA AROUND
12Z...BEFORE SLOWLY PIVOTING TO THE SOUTHWEST DURING THE LATE
MORNING HOURS. ALL THINGS CONSIDERED...THE SOLUTION SPACE OF THE
NAM/RUC/ECWMF AND HRRR HAVE THE MOST TRUSTWORTHY OF OUTPUT WITH
REGARDS TO QPF PLACEMENT. THEREFORE...EXPECT A WIDESPREAD COVERAGE
OF RAIN SHOWERS TO HOLD FIRM THROUGH 14 OR 15Z...BEFORE SCATTERING
OUT. SOME HI RESOLUTION CONVECTION ALLOWING NWP ALONG WITH THE HRRR
IS ADVERTISING A SOLUTION FOR A RAIN SHOWER CHANCE ONCE AGAIN DURING
THE LATE AFTERNOON. THE SOLUTIONS ARE SUGGESTING THAT RAIN ACTIVITY
OVER PORTIONS OF PENNSYLVANIA RESIDE WITHIN A MOISTURE AXIS THAT
WILL GET DRAWN NORTHWARD AND THEN ADVECTED WESTWARD TOWARND THE LAKE
MICHIGAN PV ANOMALY. THEREFORE...IT IS THIS ACTIVITY THAT COULD
BACKDOOR ACROSS THE DETROIT RIVER/LAKE ST CLAIR SOMETIME AFTER 20Z
THIS AFTERNOON. CURRENT RADAR MOSAIC SHOWS THIS SHOWER ACTIVITY TO
BE STRUGGLING EARLY THIS MORNING...AND WILL ONLY ACCOUNT FOR THIS
WITH A CHANCE POP BETWEEN 16-00Z. WITH THE OPAQUE CLOUD...TRENDED
HIGH TEMPERATURES DOWNWARD A COUPLE OF DEGREES FOR THE SOUTHERN
1/3RD OF THE CWA.

SUBSIDENCE WILL WRAP BACK INTO SOUTHEASTERN MICHIGAN QUICKLY AFTER
00Z TONIGHT. THIS IS EXPECTED TO PUSH ANY REMAINING PRECIPITATION
POTENTIAL TO SOUTH OF THE OHIO/MICHIGAN STATELINE. WILL ACTUALLY SEE
SOME MINOR WARM AIR ADVECTION OVERNIGHT...KEEPING LOWS IN THE 40S
FOR MANY LOCATIONS (RIGHT AROUND AVERAGE).

&&

.LONG TERM...

WARMER WEATHER WILL DEVELOP LATE THIS WEEK INTO THE WEEKEND AS THE
CURRENT UPPER LOW MOVES TO THE EAST COAST AND BEYOND AND UPPER LEVEL
HEIGHTS BEGIN TO BUILD OVER THE AREA AS THE MAIN WESTERLIES REFOCUS
OVER THE NORTHERN PLAINS AND SOUTHERN CANADA AND UPPER TROUGHING
OVER THE GREAT LAKES IS REPLACED BY MODEST ZONAL FLOW. WITH THE
STORM TRACK SO FAR NORTH INTO THE WEEKEND...MAINLY DRY WEATHER IS
EXPECTED INTO MUCH OF SUNDAY WITH TEMPERATURES BUILDING FROM THE MID
60S FRIDAY TO 70 OR BETTER FOR MOST LOCATIONS BOTH SATURDAY AND
SUNDAY.

WHILE MILD WEATHER WILL PERSIST INTO MUCH OF NEXT WEEK...THE CHANCE
OF RAIN...AND THUNDERSTORMS AT TIMES...WILL INCREASE AS A SERIES OF
STRONG SHORTWAVE BUCKLE THE STRONG ZONAL FLOW OVER MID NOAM SLIGHTLY
AND ALLOWS THE MEAN FRONTAL BOUNDARY DRAPED ALONG THE SWATH OF
WESTERLIES TO PUSH SOUTH INTO THE AREA SUNDAY NIGHT...WHERE IT WILL
REMAIN UNTIL MIDWEEK. BY THE END OF THE FORECAST PERIOD...A MORE
SUBSTANTIAL WESTERN UPPER TROUGH IS EXPECTED TO AMPLIFY AS SHORTWAVE
ENERGY DIGGING INTO THE PACIFIC NORTHWEST AND BRITISH COLUMBIA PICK
UP AN UPPER LOW MEANDERING OVER CALIFORNIA/FOUR CORNERS. DOWNSTREAM
OF THIS FEATURE...UPPER LEVEL HEIGHTS WILL BUILD OVER THE AREA AND
MAINTAIN MILD WEATHER GENERALLY ABOVE AVERAGE BY SEVERAL DEGREES.
DURING THIS TIME...SHOWER AND THUNDERSTORM CHANCES WILL BECOME MORE
SCATTERED AS THE FOCUS OF MORE ORGANIZED CONVECTION SHIFTS BACK
NORTH FOR AT LEAST A DAY OR TWO LATE NEXT WEEK. WITH THE TRANSITION
TO A MORE MODERATE PATTERN...THERE IS LITTLE TO NO CHANCE OF FROST
OVER FREEZING TEMPERATURES FROM THIS WEEKEND INTO MID/LATE NEXT WEEK.

&&

.MARINE...

NORTH TO NORTHEAST FLOW WILL DEVELOP TONIGHT AS AN UPPER LEVEL LOW
PRESSURE SYSTEM DROPS SOUTH THROUGH THE CENTRAL GREAT LAKES. THIS
FLOW WILL PERSIST THROUGH FRIDAY AS THE LOW PIVOTS EAST TO SOUTHEAST
TO THE MID ATLANTIC SHORELINE. WHILE WINDS WILL REMAIN RELATIVELY
LIGHT...10 TO 15 KNOT FLOW LATE THURSDAY AND THURSDAY NIGHT WITH
GUSTS TO 20 KNOTS WILL PRODUCE SOME ENHANCED WAVE DEVELOPMENT. THAT
SAID...WAVES SHOULD STILL REMAIN BELOW SMALL CRAFT CRITERION FOR THE
NEARSHORE WATERS.

NORTHERLY FLOW WILL BECOME LIGHT AND VARIABLE LATE FRIDAY AND
FRIDAY NIGHT AS A SMALL AREA OF SURFACE HIGH PRESSURE SETTLES
THROUGH THE AREA. LIGHT SOUTH FLOW WILL THEN BECOME ESTABLISHED
HEADING INTO THE WEEKEND AS THIS HIGH SHIFTS TO THE EAST.

&&

.AVIATION...ISSUED 140 AM EDT THU APR 30 2015

LOCALIZED LOW LEVEL DYNAMICS UNDER BROADER DEFORMATION FORCING HAS
RESULTED IN WIDESPREAD SHOWERS OVER SOUTHEASTERN MICHIGAN TONIGHT.
CIGS ARE STILL STRUGGLING WITH DRY AIR IN THE LOWER TROPOSPHERE.
GIVEN ADDITIONAL TIGHTENING OF THE THERMAL AND MOISTURE GRADIENTS
OVERHEAD IN ADDITION TO TOP DOWN SATURATION...MVFR CIGS ARE STILL
EXPECTED TO DEVELOP DURING THE COURSE OF THE NIGHT. THE UPPER LEVEL
WAVE RESPONSIBLE FOR THIS INCREASE IN ASCENT WILL DIVE STRAIGHT
SOUTHWARD OVER LAKE MICHIGAN TONIGHT. THE SOUTHERN TERMINALS WILL
REMAIN WITHIN A PIVOT POINT WHICH SUPPORTS A CONTINUATION OF SHOWERS
THROUGH 14-15Z. MODEL DATA THEN SUPPORTS A SIGNIFICANT DOWNTREND IN
THE COVERAGE OF SHOWERS FOR THE AFTERNOON HOURS. HOWEVER...MODELS DO
SUPPORT PESKY SHOWERS HANGING AROUND FOR THE AFTERNOON ACROSS THE
DETROIT TERMINALS AS THE MOISTURE AXIS WILL BE SLOW TO STRIP OUT.

FOR DTW...FORCING WILL MAXIMIZE OVER THE DETROIT TERMINAL OVER THE
NEXT 6 HOURS. CIGS ARE EXPECTED TO FALL AND REMAIN BELOW 5 KFT AGL
MOMENTARILLY. WIDESPREAD LIGHT RAIN SHOWERS WITH POCKETS OF MODERATE
RAINFALL ARE EXPECTED TO PERSIST TO AROUND 15Z. VFR CONDITIONS TO
RETURN LATE THURSDAY.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CIGS AOB 5KFT THIS MORNING.

* LOW FOR CIGS BACK ABOVE 5KFT BY THURSDAY AFTERNOON.

&&

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

$$

SHORT TERM...CB
LONG TERM....DG
MARINE.......DG
AVIATION.....CB


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


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