Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 121521
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1121 AM EDT SAT JUL 12 2014

.UPDATE...

CLEANED UP THE GRIDS THIS MORNING TO ACCOUNT FOR LACK OF SKY
FRACTION EARLY. PUSHED A MORE OPTIMISTIC FORECAST INTO THE
AFTERNOON...ALTHOUGH HIGH CLOUD IS CLOSING IN FAST. OFF OF THE
WARM START...INCREASED MAXIMUM TEMPERATURES A DEGREE OR TWO.

RECENT HIRES..CONVECTION ALLOWING MODELS INCLUDING ITERATIONS OF
THE HRRR AND MEMBERS OF THE IN-HOUSE HI-RESOLUTION WRF ENSEMBLE
ARE PORTRAYING HIGH CERTAINTY THAT PRECIPITATION AND SHOWER/TSTORM
ACTIVITY WILL REMAIN WELL WEST OF THE CWA THROUGHOUT THE MAJORITY
OF THE AFTERNOON...THROUGH 6PM. BULLISH NAM IS REALLY ON AN ISLAND
WITH REGARDS TO BRINGING QPF INTO THE AREA BEFORE 00Z. FORECASTED
CAPE FROM PLAN VIEW IMAGES SHOW MODEST INSTABILITY BECOMING
BOTTLED UP THIS AFTERNOON ACROSS FAR WESTERN PORTIONS OF LOWER
PENINSULA CENTERED ALONG A WEAK LEE OF LAKE MICHIGAN SURFACE
TROUGH. CONTINUED ANTICYCLONIC CURVATURE SUPPORTS A SHORTWAVE
RIDGING FEATURE AMPLIFYING DOWNSTREAM OF THE INBOUND BULLDOZER
TROUGH WHICH WILL ACTUALLY SUPPORT SUBSIDENCE OR SYNOPTIC SCALE
DESCENT. SHORTWAVE ENERGY WILL ARRIVE AND PASS OVER THE AREA BETWEEN
6-8PM...WHICH WILL BE COLLOCATED WITH AN INCREASE IN TANGIBLE
LOWER TROPOSPHERIC HUMIDITY AND ENTRY LEVEL CAPE. IT IS ALONG THIS
LEAD EDGE AND THE RICH THETAE ADVECTION BURST THAT SHOWERS AND A
POSSIBLE THUNDERSTORM COULD ARRIVE FOR THE EARLY EVENING.
OTHERWISE...EXPECTING MUCH OF THIS TO STRUGGLE. NO STRONG OR
SEVERE WEATHER EXPECTED THROUGH THIS EVENING.

STILL EXPECTING THE CATEGORICAL PRECIPITATION CHANCES TO INCREASE
LATE TONIGHT...POSSIBLY AS LATE AS 8 OR 9Z. THIS WILL OCCUR IN
COMBINATION OF UPPER LEVEL FLOW BECOMING CYCLONIC IN TIME DUE TO
THE ARRIVAL OF THE INBOUND DIGGING CLOSED LOW AS WELL AS
UPSTREAM CONVECTION/FRESH LOW LEVEL JET RESPONSE SLIDING OVER FAR
SOUTHERN LOWER MICHIGAN. WILL INVESTIGATE THIS FOR THE AFTERNOON
PACKAGE.

&&

.AVIATION...ISSUED 658 AM EDT SAT JUL 12 2014

//DISCUSSION...

VFR CONDITIONS WILL PERSIST THROUGH TODAY WITH A SLIGHT UPTICK IN
WINDS THIS AFTERNOON OUT OF THE SOUTHWEST. CLOUDS WILL INCREASE IN
COVERAGE AS DIURNAL HEATING IGNITES A CU FIELD AND DEBRIS FROM
UPSTREAM CONVECTION STREAMS INTO THE AREA. THERE IS A POSSIBILITY
FOR A FEW THUNDERSTORMS TO DEVELOP LATE THIS AFTERNOON AND EVENING
BUT COVERAGE SHOULD BE QUITE SPARSE SO WILL KEEP OUT OF THE TAFS AT
THE MOMENT. BEST CHANCE FOR WIDESPREAD THUNDERSTORM ACTIVITY WILL
COME OVERNIGHT AS A COMPLEX WORKS EASTWARD ACROSS LOWER MI. AT THIS
POINT IT LOOKS LIKE THE BEST TIMING WILL BE BETWEEN 06-12Z.

//DTW THRESHOLD THREATS...

* THERE IS MEDIUM CONFIDENCE THAT THUNDERSTORMS WILL OCCUR OVERNIGHT.

* THERE IS HIGH CONFIDENCE THAT CEILINGS WILL FALL BELOW 5000 FT
OVERNIGHT...BUT LOW CONFIDENCE ON EXACT TIMING.

&&

.PREV DISCUSSION...ISSUED 351 AM EDT SAT JUL 12 2014

SHORT TERM...TODAY AND TONIGHT

THE INTERACTION OF A STRONG MID/UPPER LEVEL TROUGH DIGGING INTO THE
GREAT LAKES AND A RESIDUAL STATIONARY BOUNDARY OVER THE OHIO VALLEY
EXTENDING WESTWARD TO THE MISSISSIPPI WILL MAKE FOR AN ACTIVE
STRETCH OF WEATHER THIS WEEKEND. ADDING TO THE COMPLEXITY WILL BE
SEVERAL SHORTWAVES EMBEDDED WITHIN BOTH FEATURES. AS THE SYSTEM GETS
DEEPER INTO THE HIRES RUNS WE CONTINUE TO GET A BETTER FEEL FOR
HOW THE EVENT LOOKS TO PLAY OUT. TODAY WILL BE A PERIOD OF
TRANSITION FROM THE DRY AND STABLE AIRMASS BROUGHT TO US BY THE
EXITING HIGH PRESSURE SYSTEM. THE INITIAL SURGE OF JET ENERGY
EXITING THE TROUGH WILL STAY TO THE NORTH OVER LAKE SUPERIOR AS IT
ROUNDS THE RIDGE STILL IN PLACE AS WE START THE DAY OFF. SEMBLANCE
OF A LOW AMPLITUDE SHORTWAVE RIDGE IN THE NEARLY ZONAL FLOW OVER THE
MIDWEST SHOULD ADD TO THE ALREADY STABLE/WARM MID LEVELS HELPING TO
KEEP THE AREA DRY. THE LEAD EDGE OF THE THETA E PLUME IS ENTERING
THE AREA AT PRESS TIME ON THE HEALS OF A SHORTWAVE SEEN ON WATER
VAPOR EXITING LAKE HURON. THIS WILL MERELY START THE SATURATION
PROCESS IN THE COLUMN WHICH HAD A PWAT OF ONLY 0.73 INCHES IN THE
00Z DTX SOUNDING FROM FRIDAY EVENING. MODEL SOUNDINGS SHOW THIS
JUMPING TO ABOVE 1.3 INCHES BY 12Z THIS MORNING AND CLOSE TO 1.8
INCHES BY THIS EVENING.

A STRONGER SHORTWAVE EMBEDDED IN THE SOUTHERN STREAM OF THE JET WILL
UNDERGO CYCLOGENESIS AS IT TRACKS ALONG THE AFOREMENTIONED
STATIONARY BOUNDARY TARGETING SE MI AROUND 00Z THIS EVENING. THIS
WILL REALLY ENHANCE THE MOISTURE FLUX INTO SOUTHERN MI WITH DEEP
LAYER OF SW FLOW DEVELOPING AHEAD OF THIS LOW. THE LOW WILL REACH US
CO-LOCATED WITH UPPER LEVEL DIFFLUENCE ALOFT...RIGHT ENTRANCE REGION
OF THE JET STREAK...NOCTURNAL LL JET AND THE STRONGEST INSTABILITY
GRADIENT. THIS SHOULD YIELD THUNDERSTORMS OVER MOST OF THE AREA
OVERNIGHT. BEST TIME FOR STORMS LOOKS TO BE AROUND 06-12Z TONIGHT. A
FEW SHOWERS/THUNDERSTORMS MAY POP UP AS EARLY AS 21Z MAINLY ACROSS
THE WESTERN COUNTIES AS INSTABILITY AND MOISTURE BEGIN TO SPILL INTO
THE AREA ON THE LEADING EDGE OF THE WEAKER THETA E GRADIENT. WE
COULD ALSO SEE SOME ACTION ACROSS THE FAR SOUTH AS THE COMPLEX SET
TO DEVELOP ON TONIGHTS LL JET WORKS ALONG THE STATIONARY FRONT. THE
TREND FOR THESE STORMS SHOULD BE TO WEAKEN AND FADE OUT AS THEY LOSE
THE BATTLE TO STABLE AIR BUT COULD CLIP THE AREA.

SPC HAS THE SLIGHT RISK AREA TO OUR WEST BUT DOES COVER A PORTION OF
SW LOWER MI. THIS SEEMS FAIR WITH THE TREND IN THE MODELS TO KEEP
THE LL JET FROM ENTERING SE MI TIL POTENTIALLY 09Z. WILL MONITOR
TRENDS IN TIMING THE MAIN FEATURE AND HOW WELL DEVELOPED THE SYSTEM
GETS TONIGHT. CURRENTLY THINKING IS THAT FEW STRONG STORMS COULD
DEVELOP WITH A WIND AND HAIL THREAT OVERNIGHT...BUT HEAVY RAIN WILL
BE A BIGGER THREAT WITH SUCH A MOIST AIRMASS ADVECTING IN.

LONG TERM...

SUNDAY GETS A BIT TRICKY AS THERE ARE VARYING MODEL SOLUTIONS WITH A
FAIRLY DRY GFS/ECMWF/GEM SOLUTION WHILE THE NAM HOLDS ON TO ABUNDANT
QPF. WHILE MODEL CONSENSUS BY ITSELF IS NOT ENOUGH TO THROW OUT THE
NAM...UPPER LEVEL FEATURES LEND CREDENCE TO THIS SOLUTION AS A
PRONOUNCED 700 MB DRY SLOT ADVECTS IN FROM THE WEST WHILE THE UPPER
LEVEL JET SINKS SOUTH...GIVING THE BEST MOISTURE AND DYNAMICS TO
AREAS ACROSS THE SOUTH AND EAST. THIS IS ALSO IN LINE WITH THE MOST
RECENT SPC DAY 2 OUTLOOK WHICH HAS PUSHED THE SLIGHT RISK JUST SOUTH
OF OUR CWA WHICH SEEMS REASONABLE GIVEN THE AFOREMENTIONED FACTORS.
THE DRY SLOT AND SOME SUNSHINE WILL ALLOW TEMPERATURES TO GET INTO
THE LOWER 80S ACROSS SOUTHEAST MICHIGAN SUNDAY AFTERNOON.

THIS DRY AIR BECOMES VERY PRONOUNCED SUNDAY NIGHT WITH THE LOSS OF
DAYTIME HEATING TAKING AWAY ANY BOOST FROM INCOMING SOLAR RADIATION.
POPS SUNDAY NIGHT WILL MAINLY BE CONFINED TO THE EVENING HOURS WITH
MAINLY DRY WEATHER EXPECTED LATER IN THE EVENING INTO THE OVERNIGHT
HOURS. THE DRIER COOLER AIR WILL ALLOW SOME RADIATIONAL
COOLING...PUSHING NIGHTTIME LOWS DOWN INTO THE UPPER 50S TO LOWER
60S.

AN UNSEASONABLY COLD AIRMASS WILL THEN INVADE THE GREAT LAKES REGION
FROM CANADA DURING THE UPCOMING WORK WEEK AS A DEEP TROUGH TAKES
CONTROL OF THE WEATHER. AS 850 MB TEMPERATURES TUMBLE WELL INTO THE
SINGLE DIGITS ABOVE ZERO...HIGH TEMPERATURES WILL BE LIMITED TO THE
MIDDLE TO UPPER 60S ON TUESDAY AS LOWS TUESDAY NIGHT FALL INTO THE
LOWER TO MIDDLE 50S TUESDAY NIGHT. THIS COLD AIR MASS COULD
CHALLENGE SOME RECORDS...ESPECIALLY WEDNESDAY WHEN THE RECORDS ARE
FAIRLY HIGH. WITHIN THE TROUGH PRECIPITATION CHANCES WILL
REMAIN...ALTHOUGH THE BEST CHANCES WILL BE DURING THE DAYTIME WHEN
DIURNAL HEATING PROVIDES A BOOST TO RAIN CHANCES. MODEST RIDGING
WILL PUSH DAYTIME HIGHS BACK INTO THE UPPER 70S BY FRIDAY...WHICH IS
STILL A GOOD 5 DEGREES BELOW NORMAL FOR THIS TIME OF YEAR.

MARINE...

LIGHT SOUTHERLY WINDS TODAY WILL BRING WARMER AND MORE HUMID
AIR INTO THE REGION BY LATE IN THE DAY. THE CHANCE FOR SHOWERS AND
THUNDERSTORMS WILL INCREASE OVER THE CENTRAL GREAT LAKES BY LATE
TODAY AND TONIGHT...CONTINUING INTO SUNDAY. AN UNSEASONABLY COOL
AIRMASS WILL TRACK INTO THE REGION DURING THE EARLY PART OF THE
WEEK...WITH GUSTY WEST WINDS EXPECTED ON TUESDAY. HOWEVER WINDS AND
WAVES ARE EXPECTED TO REMAIN BELOW HEADLINE CRITERIA.

&&

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

&&

$$

UPDATE.......CB
AVIATION.....DRK
SHORT TERM...DRK
LONG TERM....KURIMSKI
MARINE.......KURIMSKI


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






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