Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 210730
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
330 AM EDT THU AUG 21 2014

.SHORT TERM...TODAY AND TONIGHT

SOME MORNING FOG IS AGAIN POSSIBLE WITH JUICY DEW POINTS STILL IN
PLACE ACROSS SOUTHEAST MICHIGAN WITH LIGHT WINDS AND AREAS OF CLEAR
SKIES. HOWEVER FOG FORMATION WILL BE MITIGATED BY CIRRUS BLOWOFF
FROM UPSTREAM CONVECTION WHICH IS LIMITING RADIATIONAL COOLING AND
SOME SHOWERS ACROSS THE EXTREME CWA. THEREFORE DO NOT EXPECT FOG TO
BE AS BAD AS YESTERDAY MORNING WITH THE BEST CHANCE ALONG AND NORTH
OF THE I-69 CORRIDOR WHICH WILL BE FARTHER AWAY FROM THE CIRRUS.

A WARM FRONT RESIDING OVER THE NORTHERN OHIO VALLEY WILL SLOWLY LIFT
NORTH TO THE OHIO BORDER TODAY...CREEPING NORTH INTO SOUTHERN LOWER
MICHIGAN DURING THE OVERNIGHT HOURS. PRECIPITATION CHANCES WILL
INCREASE FROM SOUTH TO NORTH TODAY AND TONIGHT AS THIS FRONT LIFTS
NORTH...BRINGING WARM UNSTABLE AIR INTO SOUTHEAST MICHIGAN. ACTIVITY
TODAY AND EARLY THIS EVENING SHOULD MAINLY BE DIURNALLY DRIVEN AND
ASSOCIATED WITH THE WARM FRONT LIFTING NORTH. DESPITE MUCAPES OF
1000 TO 1500 J/KG...SEVERE WEATHER IS NOT ANTICIPATED DURING THIS
PERIOD AS THE LOW LEVEL WIND FIELD IS VERY WEAK DURING THIS PERIOD
WITH AN ALMOST STRAIGHT HODOGRAPH. HEAVY RAIN IS POSSIBLE GIVEN THE
LONG SKINNY HODOGRAPHS AND PWAT VALUES OF 1 TO 1.5 INCHES.

LATER THIS EVENING INTO TONIGHT IS A DIFFERENT STORY AS THE MODELS
DEVELOP A MESOSCALE CONVECTIVE SYSTEM OVER THE WESTERN GREAT LAKES
TODAY...BARRELING EAST SOUTHEAST ALONG THE WARM FRONT WHICH WILL BE
LAID OUT OVER THE SOUTHERN GREAT LAKES TONIGHT. THIS SYSTEM COULD
BRING SOME DAMAGING WIND GUSTS AS IT TRACKS ALONG THE WARM
FRONT...WITH THE GREATEST POTENTIAL FOR SEVERE WEATHER ALONG THE
OHIO BORDER WITH THE WARM FRONT...WHICH IS IN LINE WITH THE LATEST
SPC DAY 1 OUTLOOK. IN ADDITION TO DAMAGING WINDS...HEAVY RAIN AND
FLOODING IS A CONCERN OVER THIS SAME AREA AS PWAT VALUES SOAR TO
AROUND 2 INCHES. WILL HOLD OFF ON ANY FLASH FLOOD WATCH HEADLINES
UNTIL THE EVENT DRAWS CLOSER AND THE TRACK OF THE MCS CAN BE BETTER
ASCERTAINED.

&&

.LONG TERM...

THE CONSENSUS OF THE 21.00Z DETERMINISTIC SOLUTIONS OFFERS SOME
RESOLUTION TO WHAT HAD BEEN A NOISY AND CLOUDED PROGRESSION INTO THE
AMPLIFYING LONGWAVE RIDGE. IN SHORT...THE EASTWARD MIGRATION OF THE
UPPER LEVEL RIDGE AXIS APPEARS TO BE SLOWER THAN EARLIER ADVERTISED.
THIS WILL SIGNIFICANTLY APPLY THE BRAKES ON THE MAGNITUDE OF THE
WARMUP FOR THIS UPCOMING WEEKEND. IN FACT...THE LOWER TROPOSPHERE
NOW APPEARS IT WILL BE DOMINATED BY COOL EASTERLY DRAINAGE FLOW OFF
OF A STABLE ANTICYCLONE OVER PORTIONS OF QUEBEC. QUITE A LITTLE
DIFFERENCE HERE WITH THE FORECAST.

FRIDAY...A MIX OF MODEL DATA INCLUDING HIRES ECMWF AND IN-HOUSE
HIRES CONVECTION ALLOWING ENSEMBLE SUGGESTS MCS ACTIVITY WILL BE
SOUTH OF THE CWA BY 12Z. FOR NOW...DID NOT GET TOO AGGRESSIVE
LOWERING OR REMOVING POPS...BUT DID TAKE THE THUMB OUT OF THE
CHANCES. LARGE SCALE PURE DEFORMATION STRUCTURE SUGGESTS THE
THERMAL/EQUIVALENT POTENTIAL TEMPERATURE GRADIENT IN PLACE OVER THE
REGION WILL BE VERY STABLE...AND WILL NOT MOVE MUCH. WAVE
RESPONSIBLE AND LOW PRESSURE SYSTEM PARTIALLY DRIVEN BY THE MCS WILL
SETTLE TO THE SOUTHEASTWARD WHILE SHOWING SOME MARGINAL
STRENGTHENING. SO...ON THE NORTHERN EDGE OF THIS WAVE EXPECTING A
FAIRLY UNIFORM RESPONSE OF SURFACE WINDS TO AN EASTERLY DIRECTION.
HIGHS WILL ONLY RISE TO AROUND 80 DEGREES.

MODELS ARE SHOWING A VERY CLEAN SIGNAL IN EXPANDING AND
STRENGTHENING THE SURFACE HIGH OVER SEMICH FRIDAY NIGHT. THIS IS A
CLASSIC NOCTURNAL RESPONSE AND WENT DECIDEDLY COOLER WITH MINS.

SATURDAY...MODELS KEEP A VERY CLEAN SIGNAL FOR CONTINUED SURFACE
RIDGING OVER SOUTHEASTERN MICHIGAN ON SATURDAY. NOT A REAL LOT TO
SAY HERE...WITH A VERY DRY AND STABLE ATMOSPHERIC PROFILE IN THE
LOWEST 5000 FT AGL. REMOVED POPS ACROSS THE BOARD. ALSO PREFER THE
COOLER END OF THE SPECTRUM WHICH IS STILL LOW 80S FOR HIGHS...UPPER
70S LAKE HURON SHORELINE. BROKEN RECORD HERE...WENT COOL WITH LOWS
SATURDAY NIGHT.

SUNDAY...BY SUNDAY THE RIDGE IS EXPECTED TO BE FOLDING OVER INTO
SOUTHEASTERN MICHIGAN. STRONG AVA WITH SOLID WARM AIR ADVECTION
SUPPORTS A PATTERN OF STRONG SUBSIDENCE IN THE COLUMN. MODEL
SOUNDINGS FROM THIS VANTAGE POINT ARE SHOWING A DOMINANCE OF STABLE
LAYER THROUGH THE LOWEST 6 FT FOR ANOTHER DAY WITH A CAPPING
INVERSION. THE OFFERED GUIDANCE GAVE A LOW CHANCE POP AND THAT
APPEARS FINE GIVEN WARM AIR ADVECTION AND INTRODUCTION OF STEEPER
MIDLEVEL LAPSE RATES. THE FORECASTED HIGHS FOR SUNDAY ARE A COUPLE
OF DEGREES WARMER...LOW TO MID 80S.

OVERALL...WAS PRETTY AGGRESSIVE IN MAKING ADJUSTMENTS TO THIS
FORECAST PACKAGE. WHILE THERE WILL REMAIN NONZERO CHANCES FOR
SHOWERS AND THUNDERSTORMS DURING THE FRIDAY NIGHT THROUGH SATURDAY
NIGHT TIMEFRAME...FELT IT WAS NOT A GOOD CALL TO BLAST CHANCE POPS
DURING THAT TIMEFRAME.

&&

.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. THE BETTER POTENTIAL FOR THE STRONG TO SEVERE THUNDERSTORMS
WILL BE OVER SOUTHERN LOWER MICHIGAN AWAY FROM LAKE HURON. MODERATE
SOUTHWESTERLY FLOW WILL EVENTUALLY DEVELOP BY SUNDAY BUT WIND GUSTS
WILL REMAIN AT A MINIMUM.

&&

.AVIATION...ISSUED 1205 AM EDT THU AUG 21 2014

//DISCUSSION...

THE CLOUD PATTERN LEADING UP TO MIDNIGHT CONTINUES TO FAVOR MBS AND
FNT AS THE MOST LIKELY LOCATIONS FOR IFR FOG AND PERHAPS EVEN A LOW
END MVFR OR IFR CEILING BEFORE SUNRISE. EXPECT IFR CONDITIONS TO
RESULT IN SIMILAR RESTRICTION TO WEDNESDAY MORNING FOLLOWED BY A
TYPICAL TREND OF MORNING IMPROVEMENT. THE FOG SITUATION IN THE DTW
AREA WILL BE MITIGATED BY AN INCREASE IN MID CLOUDS ASSOCIATED WITH
THE WARM FRONT DEVELOPING UPSTREAM. A ROUND OF SHOWERS IS THEN
EXPECTED DURING THE LATE AFTERNOON INTO THURSDAY EVENING.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN CEILING BELOW 5000 FEET WITH SHOWERS BY LATE
AFTERNOON THROUGH THURSDAY EVENING.

&&

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

&&

$$

SHORT TERM...KURIMSKI
LONG TERM....CB
MARINE.......CB
AVIATION.....BT


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






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