Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211958
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
358 PM EDT THU AUG 21 2014

.SHORT TERM...TONIGHT

A FEW LIGHT SHOWERS HAVE STARTED TO BUILD ACROSS SOUTHEAST
MICHIGAN...BUT HAVE FIZZLED OUT AS QUICKLY AS THEY DEVELOPED DUE TO
SIGNIFICANT AMOUNT OF SUBSIDENCE ACROSS THE REGION. NOT EXPECTING
MUCH IN THE WAY OF THUNDERSTORM DEVELOPMENT THE REST OF THE
AFTERNOON...HOWEVER A WARM FRONT ACROSS THE NORTHERN OHIO RIVER
VALLEY WILL BRING AN INCREASED CHANCE OF RAIN SHOWERS TO SOUTHEAST
MICHIGAN THIS EVENING. PRECIPITATION CHANCES WILL BEGIN NEAR THE
OHIO BORDER AND SLOWLY MOVE NORTHWARD AS THIS FRONT LIFTS SLOWLY
ACROSS THE CWA.

RAIN SHOWERS SHOULD CONTINUE OVERNIGHT AS MODELS ARE CONTINUING TO
INDICATE AN MCS /MESOSCALE CONVECTIVE SYSTEM/ TO DEVELOP OVER THE
WESTERN GREAT LAKES. THIS MCS WILL TRACK SOUTHEASTWARD TOWARDS
SOUTHEAST MICHIGAN. CURRENT THINKING IS THAT THE BULK...INCLUDING
THE MOST DAMAGING WIND GUSTS AND SEVERE POTENTIAL...OF THE MCS WILL
TRACK SOUTH OF THE CWA RESULTING IN JUST RAIN SHOWERS ACROSS
SOUTHERN MICHIGAN. HAVE LEFT IN LIKELY POPS ACROSS THE SOUTHERN TWO
TIERS OF COUNTIES TO ACCOUNT FOR ANY DEVIATION ON THE TRACK OF THE
MCS. CURRENT SPC OUTLOOK HAS PULLED BACK ON THE SLIGHT RISK ACROSS
SOUTHERN MICHIGAN...ADDING TO THE CONFIDENCE IN THE CURRENT SOUTHERN
TRACK OF THIS MCS. WITH MOST OF THE SIGNIFICANT THUNDERSTORM
DEVELOPMENT TRACKING SOUTH...THE MAJOR CONCERN FOR SOUTHEAST
MICHIGAN WILL BE THE HEAVY RAIN POTENTIAL. CURRENT MODELS ARE
SHOWING PWAT VALUES IN THE 1.5 TO 2.0 INCH RANGE. THIS WILL RESULT
IN NEARLY AN INCH OR SLIGHTLY MORE OF RAIN TO FALL OVER A SHORT
AMOUNT OF TIME. AT THIS TIME...FLOODING ISSUES ARE NOT A CONCERN.
THIS WILL HAVE TO BE MONITORED CLOSELY AS THE EVENT PROGRESSES AS
LITTLE RAIN FALLING OVER AN ALREADY SATURATED GROUND/URBAN AREAS
COULD QUICKLY RESULT IN FLOODING CONCERNS ACROSS METRO DETROIT AND
SOUTHEAST MICHIGAN.

OTHERWISE...CLOUD COVER OVERNIGHT FROM THE DEVELOPING MCS SHOULD
RESULT IN FAIRLY OVERCAST SKIES KEEPING TEMPERATURES ON THE MILD
SIDE. LOWS SHOULD BE IN THE UPPER 60S IN THE METRO DETROIT AREA AND
SLIGHTLY COOLER IN THE MID 60S ACROSS THE REST OF THE CWA. THIS IS
SLIGHTLY ABOVE AVERAGE FOR THIS TIME OF YEAR WHERE LOWS ARE NORMALLY
IN THE LOW 60S FOR DETROIT AND THE UPPER 50S FOR FLINT AND SAGINAW.

&&

.LONG TERM...

NO SUBSTANTIAL CHANGES FROM THE PREVIOUS COUPLE OF FORECAST
PACKAGES. AMPLIFICATION OF THE SUBTROPICAL RIDGE OVER THE SOUTHERN
UNITED STATES IS STILL FORECAST TO RESULT IN SIGNIFICANT WARMING OF
THE COLUMN OVER SE MICHIGAN HEADING INTO THE WEEKEND. H85 TEMPS BOTH
FRI AND SAT WILL BE PUSHING THE UPPER TEENS, WHICH WILL SUPPORT HIGH
TEMPERATURES AT LEAST IN THE LOW 80S. THERE IS SOME UNCERTAINTY
REGARDING THE POTENTIAL MIXING DEPTHS ON FRIDAY OWING TO UNCERTAIN
EVOLUTION OF TONIGHT`S CONVECTION, WHICH CORRESPONDINGLY TEMPERS
EXPECTATIONS FOR FRIDAY`S MAX TEMPS. PERHAPS THE PRIMARY REASON FOR
ABSTAINING FROM PUSHING FOR HIGHER DAYTIME HIGHS, HOWEVER, IS
ACTUALLY MORE OF A CREDIT TO EXPECTED EASTERLY WINDS AT THE SURFACE
AROUND THE SOUTHERN PERIPHERY OF HIGH PRESSURE OVER QUEBEC. THE
PREVIOUS FORECAST HANDLED THIS WELL AND NO CHANGES WERE NECESSARY.
EVEN WITH THE TEMPERED EXPECTATION FOR HIGH TEMPERATURES, THE LACK
OF ANY NOTEWORTHY EXCHANGE OF AIRMASS WILL ENSURE STICKY DEWPOINTS
IN THE MID 60S TO NEAR 70 EACH AFTERNOON. LIKEWISE, THERE REMAINS
SOME CONCERN OVER COOLING POTENTIAL AT NIGHT DUE TO ANTECEDENT MOIST
BOUNDARY LAYER CONDITIONS. AGREE WITH PREVIOUS DISCUSSION THAT THE
PRESENCE OF THETA-E GRADIENT INVOF THE LOWER PENINSULA IMMEDIATELY
DOWNSTREAM OF THE UPPER RIDGE AXIS AND RESIDENT MOIST AIRMASS MAKE
IT ESSENTIALLY IMPOSSIBLE TO RULE OUT SHOWER/T-STORMS DURING ANY ONE
PERIOD. HOWEVER, UNTIL A WELL-DEFINED OPPORTUNITY FOR DEVELOPMENT
PRESENTS ITSELF, THE BEST APPROACH REMAINS TO LEAVE THE FORECAST DRY.

SUNDAY THROUGH THURSDAY: RAIN CHANCES WILL LIKELY HANG AROUND
THROUGH MUCH OF NEXT WEEK AS A SERIES OF SHORTWAVES TRACK OVER
SOUTHEAST MICHIGAN. MODEL AGREEMENT IS STILL QUITE LOW AND HAVE
THEREFORE ONLY PUT IN LOW CHANCE POPS INTO THE FORECAST THROUGH
THURSDAY. TIMING AND COVERAGE OF THE RAIN WILL BE BETTER DEFINED
AS MODELS GET A BETTER HANDLE ON THESE DISTURBANCES. TEMPERATURES
WILL REMAIN FAIRLY CONSISTENT WITH HIGHS IN THE LOW 80S AND LOW
TEMPERATURES IN THE MID TO UPPER 60S THROUGH THE PERIOD.

&&

.MARINE...

A WEAK PRESSURE GRADIENT WILL MAINTAIN LIGHT WINDS ACROSS THE WATERS
THROUGH THE FIRST HALF OF THE WEEKEND. THERE IS A CHANCE FOR
THUNDERSTORMS FOR ALL MARINE AREAS LATE TONIGHT INTO EARLY
FRIDAY...AND SEVERE WEATHER IS NOT OUT OF THE QUESTION DURING THIS
TIME...ESPECIALLY FOR LAKE SAINT CLAIR AND LAKE ERIE. MODERATE
SOUTHEAST FLOW WILL DEVELOP BY SUNDAY BUT WIND GUSTS WILL REMAIN AT
A MINIMUM.

&&

.AVIATION...ISSUED 112 PM EDT THU AUG 21 2014

//DISCUSSION...

SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON AND
INTO THE EARLY EVENING. SOUTHERN TAF SITES WILL MAINLY BE IMPACTED
IN THE LATE AFTERNOON WHILE FNT AND MBS WILL NOT SEE RAIN UNTIL
EARLY EVENING. WINDS WILL REMAIN FAIRLY LIGHT /5 TO 10 KTS/
HOWEVER...WINDS COULD INCREASE QUICKLY IN ANY THUNDERSTORMS THAT
DEVELOP. STEADY RAIN SHOWERS ARE EXPECTED TO CONTINUE THROUGH THE
OVERNIGHT HOURS WITH SOME LIGHT FOG DEVELOPING DROPPING VISIBILITIES
DOWN TO AROUND 2 SM. RAIN SHOWERS WILL GRADUALLY DIMINISH AFTER 12Z
FRIDAY.

//DTW THRESHOLD THREATS...

* MODERATE CONFIDENCE THAT THUNDERSTORMS WILL OCCUR THIS AFTERNOON
AND EARLY EVENING.

* HIGH CONFIDENCE THAT CEILINGS WILL REMAIN BELOW 5000 FT THROUGH
FRIDAY MORNING.

&&

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

&&

$$

SHORT TERM...RK
LONG TERM....JVC/DE
MARINE.......JVC
AVIATION.....RK


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





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