Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 251928
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
328 PM EDT FRI JUL 25 2014

.SHORT TERM...THROUGH TONIGHT

MAIN CHALLENGE IN THE SHORT TERM IS OVERALL COVERAGE AND TIMING OF
PRECIPITATION EARLY SATURDAY MORNING.  CLOUDS FROM LAST NIGHT/EARLY
MORNING CONVECTION OVER THE UPPER MISSISSIPPI VALLEY HAS BEEN
STREAMING IN OVER THE AREA SINCE THIS MORNING.  ANY PRECIPITATION
RELATED TO THIS HAS QUICKLY DIMINISHED...ESPECIALLY GIVEN THE AMOUNT
OF DRIER AIR IN THE ATMOSPHERE AND THE FACT THAT SE MI WAS STILL
UNDER THE INFLUENCE OF THE HIGH PRESSURE OFF TO THE EAST.  THE DRIER
AIR WAS PREVALENT ON THE 12Z DTX SOUNDING AND THE LATEST
OBSERVATIONS SUPPORT THIS AS SHOWERS CONTINUE TO DIMINISH OVER FAR
WESTERN MICHIGAN. ONLY THING THAT MAY BE SEEN IS SOME VIRGA AS
CLOUDS OVERSPREAD THE AREA.  CLOUDS WILL CONTINUE TO HANG AROUND AND
ONCE AGAIN INCREASE LATE TONIGHT AHEAD OF THE NEXT SYSTEM IN
ASSOCIATION WITH THE WARM FRONT.  THE DIURNAL CU FIELD THAT IS
CURRENTLY OVER THE AREA WILL DISSIPATE WITH THE LOSS OF HEATING THIS
EVENING WITH ONLY HIGH CLOUDS STICKING AROUND.  THE MAIN STORY WILL
BE THE INCREASING RAIN/THUNDERSTORM CHANCES WITH THE WARM
FRONT.  ENTRANCE REGION OF THE UPPER LEVEL JET WILL BE ENCROACHING
ON SOUTHERN LOWER MICHIGAN OVERNIGHT WHICH WILL ASSIST IN STARTING
TO CREATE BETTER OVERALL DYNAMICS.  THIS WILL CARRY INTO THE WEEKEND
AS THE CHANCE FOR UNSETTLED WEATHER CONTINUES. SOUTHERLY WINDS WILL
BRING IN BETTER MOISTURE OVERNIGHT AS PWAT VALUES SLOWLY INCREASE TO
AROUND 1.5 INCHES BY SATURDAY MORNING. THE BEST ISENTROPIC ASCENT
STILL LOOKS TO BE BETWEEN 06-09Z AS THE LOW LEVEL JET GETS GOING.
LATEST HIRES MODELS DO NOT HAVE PRECIP COMING IN UNTIL CLOSER TO 10Z
WITH THE BETTER CHANCES LOOKING TO BE OVER THE NORTHERN CWA.
OVERALL...THE ONLY CHANGE TO THE GRIDS WAS TO ACCOUNT FOR THE LATER
ONSET OF PRECIP.  GIVEN CLOUD COVER...LOW TEMPS WILL NOT DROP TOO
MUCH WITH LOWS IN THE LOWER 60S.

&&

.LONG TERM...

PLENTY OF 12Z MODEL (NAM/GFS) INITIALIZATION ISSUES WHEN LOOKING AT
UPSTREAM RAOBS OVER THE CENTRAL/NORTHERN PLAINS EXTENDING NORTHEAST
IN THE WESTERN GREAT LAKES...AS SHARP TEMP/MOISTURE GRADIENTS EXIST
AT 850/700 MB. IN ADDITION...BASED ON WATER VAPOR IMAGERY...THE
UPPER LEVEL LOW OVER ALBERTA/SASKATCHEWAN LOOKS TO BE SHEARING APART
A BIT MORE AGGRESSIVELY THAN THE MODELS SUGGEST. WE ARE LEFT WITH
THE STRONG JET CORE IN PLACE OVER THE NORTHERN PLAINS DIVING
SOUTHEAST INTO THE WESTERN OHIO VALLEY...WHICH LOOKS TO BE THE MOST
LIKELY LOCATION (MAX INSTABILITY) OF THE NEXT ORGANIZED CONVECTION
DURING SATURDAY...AS WE CONTINUE TO BE PARTIALLY UNDER THE INFLUENCE
OVER THE MASSIVE UPPER LEVEL LOW OVER EASTERN CANADA...WHICH
EVENTUALLY DIRECTS THE REMNANT MID LEVEL COLD POOL/CIRCULATION OVER
WESTERN CANADA THROUGH LOWER MICHIGAN LATER SUNDAY. STILL...THERE IS
ROOM FOR SUBTLE UPPER LEVEL DISTURBANCE TO TRACK THROUGH MICHIGAN
DURING SATURDAY WITH SURFACE TROUGH IN PLACE TO TAP INTO LIKELY
MODERATE INSTABILITY...MLCAPES OF 2000+ J/KG AND SEVERE THREAT
REMAINS CONDITIONAL ON ACTIVITY DEVELOPING...WITH THE MORE THAN
ADEQUATE WIND FIELDS (0-6 KM BULK SHEAR OF 45 KNOTS). 700 MB TEMPS
WARMING TOWARD 10 C MAY BE JUST ENOUGH TO CAP ACTIVITY
HOWEVER...AND/OR WE WILL BE IN THE SHADOW OF THE PREVIOUSLY
MENTIONED ACTIVITY OVER THE OHIO VALLEY...AND HAVE ACTUALLY LOWERED
POPS SLIGHTLY...AS NOT FULLY CONVINCED THE 70 SURFACE DEGREE DEW PTS
WILL MAKE IT INTO THE CWA WITH THE DISRUPTION IN MOISTURE TRANSPORT.
850 MB TEMPS IN THE MID TEENS SUPPORT MID 80S...BUT CLOUD CONCERNS
AND LOW LEVEL MOISTURE INCREASE WORTHY OF SHAVING A COUPLE DEGREES.

SATURDAY NIGHT INTO SUNDAY`S FORECAST HINGES ON THE LOCATION OF THE
NEARLY WEST-EAST MOISTURE AXIS/850-700 MB THETA-E RIDGE...AS THE 500
MB LOW DROPPING INTO THE WESTERN GREAT LAKES WILL HELP DRAW SOME OF
THE MOISTURE BACK NORTH...BUT NOT SURE HOW MUCH PAST THE OHIO BORDER
THE DEEPER MOISTURE WILL GET BEFORE THE MID LEVEL DRY SLOT PUNCHES
INTO LOWER MICHIGAN DURING SUNDAY. THAT WILL NOT END THE RAIN
CHANCES ALL TOGETHER...AS DEFORMATION AXIS SWINGS THROUGH SUNDAY
EVENING/NIGHT LIKELY PRODUCING ADDITIONAL RAINFALL. AT THE VERY
LEAST (IN LINE WITH DAY 3 SPC OUTLOOK)...THERE DOES LOOK TO BE A
SEVERE THREAT TOWARD THE OHIO BORDER AS BETTER MOISTURE/INSTABILITY
FEEDS UP FROM THE NORTHERN OHIO VALLEY...AND IT APPEARS THE TRIPLE
POINT WILL RESIDE IN THAT VICINITY.

AMPLIFIED UPPER LEVEL EASTERN NORTH AMERICAN TROUGH NEXT WEEK WILL
ASSURE BELOW NORMAL TEMPERATURES...AS -2.5 TO -3 STANDARDIZED 500 MB
HEIGHT ANOMALIES RESIDE OVER THE MID ATLANTIC STATES. WITH THE
TROUGH AXIS NEAR OR OVERHEAD...SCATTERED DIURNAL CONVECTIVE ACTIVITY
SEEMS LIKELY IN OUR NECK OF THE WOODS.

&&

.MARINE...

THERE IS AN INCREASING CHANCE OF SHOWERS AND THUNDERSTORMS OVER THE
WEEKEND...WITH THE POTENTIAL FOR SEVERE WEATHER...ESPECIALLY OVER
WESTERN LAKE ERIE. OUTSIDE OF THE THUNDERSTORMS...WINDS WE BE LIGHT.
SOUTHERLY WINDS SATURDAY...BECOMING VARIABLE ON SUNDAY AS LOW
PRESSURE TRACKS THROUGH THE AREA. BEHIND THIS LOW SUNDAY
NIGHT...NORTHERLY WINDS WILL RAMP UP...PEAKING AROUND 30 KNOTS OVER
SOUTHERN LAKE HURON ON MONDAY....AND SMALL CRAFT ADVISORIES WILL
LIKELY BE NEEDED AS LONG FETCH ALLOWS FOR GOOD WAVE BUILD UP
IMPACTING THE NEARSHORE LAKE HURON MARINE ZONES.

&&

.AVIATION...ISSUED 128 PM EDT FRI JUL 25 2014

//DISCUSSION...

DIURNAL CU FIELD WILL PERSIST THROUGH AT LEAST THE EARLY EVENING
BEFORE THOSE LOWER VFR CLOUDS SCATTER OUT.  CURRENT OBS HAVE
SHOWN INCREASED WINDS DUE TO DIURNAL HEATING AND THESE WILL DIMINISH
BY EARLY EVENING.  CLOUDS WILL HANG AROUND THROUGH THE ENTIRE TAF
CYCLE AS BOTH UPSTREAM CLOUD DEBRIS FROM PREVIOUS CONVECTION OVER
THE MIDWEST AND CLOUDS ASSOCIATED WITH THE NEXT SYSTEM CONTINUE
TO STREAM ACROSS THE AREA.  THE SCATTERED LIGHT RAIN CURRENTLY OVER
EASTERN WISCONSIN WILL ENCOUNTER DRIER AIR OVER THE AREA AND ARE
EXPECTED TO DIMINISH...ALTHOUGH VIRGA MAY BE OBSERVED. MORE
SUBSTANTIAL MOISTURE WILL BE POSSIBLE TOWARDS 12Z SATURDAY.
CONFIDENCE HOWEVER IS LOW FOR THE COVERAGE AND TIMING OF ANY
RAIN/THUNDERSTORMS FOR EARLY SATURDAY MORNING.

FOR DTW...BEST POTENTIAL FOR SHOWERS...POSSIBLY A THUNDERSTORM...
WILL BE AFTER 10Z SATURDAY MORNING WITH CEILINGS FALLING INTO THE
MVFR CATEGORY.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE WITH CEILINGS AT OR BELOW 5000 FEET INTO EARLY
FRIDAY EVENING.

* LOW CONFIDENCE IN COVERAGE AND TIMING OF SHOWERS/THUNDERSTORMS
AFTER 10Z SATURDAY.

&&

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

&&

$$

SHORT TERM...SS
LONG TERM....SF
MARINE.......SF
AVIATION.....SS


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





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