Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 051949
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
349 PM EDT TUE MAY 5 2015

.SHORT TERM...TONIGHT

OBSERVATIONAL DATA INCLUDING REGIONAL RADAR MOSAIC AND WATER VAPOR
IMAGERY SHOWS THE INITIAL SURGE OF LARGE SCALE FORCING AND
WIDESPREAD PRECIPITATION PUSHING EASTWARD ACROSS THE LOWER
PENINSULA. THE BACK EDGE OF THIS ACTIVITY IS NOW ACROSS FAR WESTERN
SECTIONS OF LOWER MICHIGAN. LINEAR EXTRAPOLATION OF REFLECTIVITY
SUPPORTS THIS BACK EDGE TO PUSH ACROSS THE CWA IN THE 22-01Z
TIMEFRAME. BEEN MONITORING THE SOUTHWEST FLANK OF THE FORCING OVER
PORTIONS OF NORTHERN INDIANA/NORTHERN ILLINOIS FOR SHOWER/TSTORM
REDEVELOPMENT. NWP GUIDANCE HAS SUGGESTED IT IS DEVELOPMENT OVER
THIS AREA THAT WILL HAVE A SHOT AT TRACKING INTO FAR SOUTHERN LOWER
MICHIGAN BETWEEN THE SAME TIME PERIOD. A SUPPRSSED FRONTAL BOUNDARY
WELL SOUTH OF THE STATE LINE LIMITS THE POTENTIAL FOR THUNDER THIS
EVENING.

THE QUESTION FOR TONIGHT IS THEN CENTERED ON THE OVERALL POTENTIAL
FOR PRECIPIATION. SUBSIDENCE IN THE WAKE OF THIS COMPLEX WILL
EVENTUALLY LEAD TO A PERIOD OF PRECIPATION WEAKENING. A LOOSE MODEL
CONSENSUS EXISTS WITH THE SOLUTION...WITH INTRA MODEL CONTINUITY
EVEN BOUNCING AROUND A LITTLE BIT. LARGE SCALE FORCING WILL REMAIN
FAIR...WITH 925-700MB DEFORMATION QUITE HIGH IN A ZONE ACROSS THE
CENTRAL CWA. LARGE WAVELENGTH RIDGE AMPLIFICATION IS EXPECTED TO
TAKE PLACE WHICH WILL LOWER TROPOSPHERIC CONVERGENCE TO THE
HEIGHTNED DEFORMATION. AS A RESULT...EXPECTATIONS ARE FOR CONTINUED
RAIN SHOWER CHANCE DURING THE OVERNIGHT. DISAGREEMENT EXISTS WITH
WHERE EXACTLY THIS STATIONARY BOUNDARY WILL RESIDE. CONTINUE TO
FAVOR SECTIONS OF THE CWA FROM THE NORTHERN SUBURBS OF DETROIT/I 59
CORRIDOR NORTHWARD TO I 69.  AT THE END OF THE PERIOD...RIDGE
AMPLIFICATION WILL BEGIN TO PUSH THE FRONTAL ZONE NORTHWARD AS A
WARM FRONT. WITH THE LACK OF UNCERTAINTY AND LIGHTER COVERAGE OF
RAIN/SHOWERS IN HI-RESOLUTION MODELS...LOWERED POPS INTO THE CHANCE
TO LIKELY CATEGORY. THE CONDITIONAL ASPECT OF TONIGHT...DOES SUPPORT
SOME LOCALLY HIGHER QPF FOR THOSE AREAS THAT SEE MULTIPLE ROUNDS OF
PRECIPATION.

&&

.LONG TERM...WEDNESDAY THROUGH NEXT TUESDAY

THE REMNANT MID LEVEL FRONTAL BOUNDARY OVER SE MI WILL BE LIFTED
NORTHWARD TO THE SAGINAW VALLEY AND THUMB BY EARLY WED AFTERNOON.
THIS WILL OCCUR AS A MID LEVEL RIDGE AXIS EXPANDS FROM THE SRN OHIO
VALLEY INTO THE SRN GREAT LAKES. THE CORRESPONDING INCREASE IN MID
LEVEL SUBSIDENCE WILL ERODE ANY RESIDUAL MID LEVEL FRONTAL
CIRCULATION AND WILL LEAD TO A DECREASE IN LINGERING SHOWERS ALONG
THIS FRONT DURING THE LATE MORNING INTO EARLY AFTERNOON. DIURNAL
HEATING WILL ALSO DECREASE THE DEPTH OF THE LOW LEVEL INVERSION AND
WILL OFFER THE OPPORTUNITY FOR A DECREASE IN THE CLOUD COVER DURING
THE AFTERNOON /ESPECIALLY ACROSS THE SRN HALF OF THE FORECAST AREA/.
ONCE CLOUDS DIMINISH...TEMPS WILL QUICKLY RISE INTO THE 70S /THICKER
CLOUDS ACROSS THE TRI CITIES AND THUMB MAY HOWEVER KEEP THESE LOCALS
IN THE 60S/. MODEL SOLUTIONS DEVELOP SOME LATE DAY CONVECTION
ASSOCIATED WITH MODEST SFC BASED INSTABILITY FROM ADRIAN/MONROE INTO
SW LOWER MI ALONG A REMNANT SURFACE BOUNDARY. MODEL SURFACE
DEWPOINTS APPEAR TO BE A LITTLE ON THE HIGH SIDE. GIVEN THIS AND
WITH A BUILDING MID LEVEL CAP...NOTHING MORE THAN A SLIGHT CHANCE OF
LATE DAY CONVECTION APPEARS WARRANTED ATTM.

THE BOUNDARY LAYER WILL DECOUPLE WED NIGHT WITH THE MID LEVEL RIDGE
OVERHEAD AND WEAK SFC GRADIENT IN PLACE. BOTH NAM AND GFS SUGGEST
SFC DEWPOINTS WILL HOLD IN THE 50S...LEADING TO THE POTENTIAL FOR
SOME FOG LATE WED NIGHT/EARLY THURS MORNING. THE MID LEVEL RIDGE
AXIS WILL PUSH OFF TO THE EAST ON THURSDAY WHILE A SHORT WAVE
IMPULSE LIFTS ACROSS THE NRN PLAINS. THIS WILL ESTABLISH A LOW LEVEL
S-SW FLOW ACROSS SE MI ON THURS WHICH WILL PERSIST AND ACTUALLY
STRENGTHEN ON FRIDAY. THIS WILL ADVECT A MORE SUMMER-LIKE AIRMASS
INTO SE MI...WITH HIGHS LIKELY SURPASSING THE 80 DEGREE MARK. BOTH
GFS AND ECMWF TRY TO DRIVE A WEAK SFC BOUNDARY INTO LOWER MI FRI
AFTERNOON. THIS AND THE POTENTIAL FOR SOME WEAK SHORT WAVE IMPULSES
LIFTING INTO THE AREA FROM THE SOUTHWEST AND BUILDING INSTABILITY
WILL SUPPORT A CHANCE OF CONVECTION LATE FRI INTO FRI NIGHT.

FRONTAL BOUNDARY WILL CONTINUE TO SAG INTO THE REGION SATURDAY AS
CONTINUED SHORTWAVE ENERGY EMBEDDED IN UPPER SWLYS AUGMENT FORCING
FOR ASCENT. 12Z GLOBAL MODELS DIFFER WITH THEIR DEPICTION OF FRONTAL
PROGRESSION SATURDAY INTO EARLY NEXT WEEK LEADING TO RELATIVELY LOW
PREDICTABILITY IN TIMING ROUNDS OF PRECIP. FOR INSTANCE...12Z GFS
PUSHES THE FRONT THROUGH THE REGION LATE SATURDAY...WHILE 12Z ECMWF
BASICALLY STALLS THE FRONT ACROSS LOWER MICHIGAN. FORMER SOLUTION
WOULD LEAD TO A COOLER/DRIER SAT NIGHT/SUNDAY AND VICE VERSA FOR THE
LATTER. AT THIS POINT WILL PLAY MIDDLE OF THE ROAD WITH CHANCE POPS
FOR THE WEEKEND /IN COLLABORATION WITH NEIGHBORS/ UNTIL BETTER
PREDICTABILITY IS SHOWN BY THE MODEL SUITE. DESERT SW CUTOFF UPPER
LOW IS FORECAST TO OPEN UP AND PROGRESS INTO THE UPPER MIDWEST EARLY
NEXT WEEK...WARRANTING CONTINUED CHANCES OF SHOWERS/TSTORMS.

&&

.MARINE...

A WEAK GRADIENT ASSOCIATED WITH HIGH PRESSURE OVER LAKE HURON WILL
MAINTAIN LIGHT WINDS TONIGHT RIGHT INTO THURSDAY. THE HIGH WILL THEN
DRIFT TO THE EAST BY THE END OF THE WEAK AND WILL OPEN THE DOOR FOR
SOME LIGHT SOUTHERLY WINDS LATE THURSDAY INTO FRIDAY. AND INCREASE
IN LOW LEVEL MOISTURE LATE IN THE WEEK INTO THE WEEKEND WILL ALSO
POSE THE RISK OF SOME MARINE FOG AND THE COLDER WATERS OF LAKE
HURON.

&&

.AVIATION...ISSUED 154 PM EDT TUE MAY 5 2015

THE MATURE MCS AND INITIAL SURGE OF DEEP MOISTURE IS CURRENTLY
TRACKING THROUGH SOUTHEASTERN MICHIGAN THIS AFTERNOON. LATEST DATA
SUGGESTS A CONTINUED POTENTIAL FOR SHOWERS AND THUNDERSTORMS OVER
MUCH OF THE AREA THROUGH AT LEAST THE EARLY EVENING HOURS. A
DEVELOPING WARM FRONT IS THEN EXPECTED TO SLOWLY ORGANIZE OVER
SECTIONS OF SEMICH TONIGHT. UNCERTAINTY EXISTS TO EXACTLY WHERE THIS
BOUNDARY WILL STALL OUT FOR A TIME...BUT LATEST INDICATIONS ARE
SUGGESTING THE NORTHERN DETROIT METRO AREA THROUGH THE I 69 CORRDOR.
IT IS ALONG THIS BOUNDARY THAT A POTENTIAL EXISTS FOR
CONTINUED...LONG DURATION RAIN OVERNIGHT. FOCUSED THIS RAIN MENTION
AT THE KPTK/KFNT FOR THIS TAF ISSUANCE...WILL CONTINUE TO MONITOR
THE NEED FOR THE SOUTHERN TAF SITES. THE OTHER IMPORTANT ISSUE FOR
TONIGHT WILL BE THE POTENTIAL FOR IFR/LIFR CIGS ALONG AND TO THE
SOUTH OF THE DEVELOPING FRONTAL BOUNDARY. WENT MORE AGGRESSIVE WITH
IFR/LIFR CIGS SOUTH.

FOR DTW...RAIN POTENTIAL WILL NOW SHIFT TO MORE SHOWER CHARACTER AS
THE INITIAL MATURE MCS SHIFTS NORTHWARD THROUGH THE CWA. WILL NEED
TO MONITOR PORTIONS OF NORTHERN ILLINOIS/INDIANA WHERE ADDITIONAL
SHOWER AND THUNDERSTORM DEVELOPMENT IS FORECASTED TO TAKE PLACE. IT
REMAINS POSSIBLE THIS ACTIVITY WHILE MOVING EASTWARD COULD IMPACT
PORTIONS OF FAR SOUTHERN MICHIGAN...INCLUDING THE METRO TERMINAL.
OTHERWISE TONIGHT...EXPECTATIONS AT THIS TIME ARE FOR THE WARM FRONT
TO SET UP NORTH OF THE TERMINAL...FOCUSING BEST LONG DURATION RAINS
CHANCES NORTH. LIFR CIGS TONIGHT AND TOMORROW MORNING.


//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CEILING BELOW 5000 FT TONIGHT.

* LOW FOR THUNDERSTORMS THIS EVENING AND TONIGHT

* LOW FOR CIGS TO FALL BELOW 200 FEET.

&&

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

$$

SHORT TERM...CB
LONG TERM....SC/DT
MARINE.......SC
AVIATION.....CB


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


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