Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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591
FXUS63 KDTX 020440
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1240 AM EDT MON MAY 2 2016

.AVIATION...

A WELL ORGANIZED ARC OF CONVECTIVE SHOWERS HAS DEVELOPED WITHIN THE
WARM ADVECTION WING OF THE INBOUND UPPER LEVEL LOW PRESSURE CENTER.
THIS DEVELOPMENT IS IN AGREEMENT WITH THE RECENT PROGS SUPPORTING A
PERIOD OF WIDESPREAD RAINFALL ACROSS SOUTHEASTERN MICHIGAN GENERALLY
ALONG AND SOUTH OF THE I 69 CORRIDOR. BASED ON LATEST TRENDS REMOVED
RAINFALL MENTION FOR KMBS...OTHERWISE HAVE KEPT LARGELY TO THE
PREVIOUS TAF NARRATIVES. A RUMBLE OF THUNDER/BRIEF VCTS WILL BE
POSSIBLE AT KDTW...BUT HAVE NOT ADDED IT TO THE TAF YET. FEEL THERE
IS JUST TOO LOW OF A CHANCE AS ACTIVITY CONTINUES TO WORK UP THE
COLUMN...UP THE FRONTAL SLOPE. A PERIOD OF HEAVY RAINFALL WILL BE
POSSIBLE ESPECIALLY UNDER THE LONGEST STRETCH/DURATION OF THE
COMPACT RADIUS DEFORMATION FORCING. WIDESPREAD IFR CIGS ARE IN PLACE
OVER SW AND SOUTH CENTRAL LOWER MICHIGAN...JUST A MATTER OF TIME
BEFORE THIS SLIDES INTO DETROIT. REFRAINED FROM LIFR IN THE TAFS
ATTM...WITH A LACK OF OBSERVATIONAL SUPPORT UPSTREAM. PERSISTENT
OVERCAST IS FORECASTED FOR MONDAY BUT THERE CONTINUES TO BE A BETTER
SIGNAL FOR CIG TREND TO MVFR BY THE EARLY AFTERNOON.

FOR DTW...CIGS WILL LOWER BACK INTO IFR MOMENTARILY WITH GREATEST
WARM AIR ADVECTION SUPPORT WASHING ACROSS SOTUHEASTERN MICHIGAN.
STILL CANNOT RULE OUT THE POSSIBILITY FOR LIFR BUT NO UPSTREAM
OBSERVATIONS SUPPORT THIS ATTM. A THUNDERSTORM IS ALSO POSSIBLE BUT
ACTIVITY CONTINUES TO WORK UP THE FRONTAL SLOPE WHICH SEVERLY
COMPROMISES ANY CONVECTIVE INSTABILITY HERE. THERE IS A RELATIVELY
STRONGER SIGNAL IN SUPPORT FOR MVFR CIGS BY LATE MORNING/EARLY
AFTERNOON.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CIG AOB 5KFT

* LOW FOR CIG AOB 200 FT 6-12Z.

&&

.PREV DISCUSSION...ISSUED 929 PM EDT SUN MAY 1 2016

UPDATE...

THE IMPENDING WEATHER EPISODE FOR TONIGHT WILL BE DRIVEN BY THE
STRONG UPPER LEVEL LOW PRESSURE (STILL A CLOSED CIRCULATION
ACCORDING TO WATER VAPOR IMAGERY) THAT WILL OPEN AND TRACK ACROSS
SOUTHERN LOWER MICHIGAN BETWEEN 03-12Z TONIGHT.

THERE ARE A COUPLE OF ITEMS WORTH DISCUSSION. THE FIRST IS THE
AMOUNT/VIGOR OF THUNDERSTORM/SHOWER ACTIVITY THAT IS OVER PORTIONS
OF CENTRAL INDIANA AND NORTHERN ILLINOIS. SIFTING THROUGH MODEL
DATA...IT APPEARS THAT MODELS ARE UNDERESTIMATING THE AMOUNT OF
ELEVATED INSTABILITY THAT EXISTS TO THE NORTH AND WEST OF THE
SURFACE WARM FRONT LOCATED NEAR INDIANAPOLIS EASTWARD INTO
SOUTHERN OHIO. ITS PROBABLY NOT A LOT...BUT THE SHEAR/INSTABILITY
BALANCE HAS BEEN FAVORABLE. NWP SUGGESTS THAT SYSTEM RELATIVE
ISENTROPIC ASCENT AND ELEVATED WARM AIR ADVECTION WILL INCREASE
SUBSTANTIALLY OVER FAR SOUTHEASTERN MICHIGAN FROM 00-06Z IN
ADVANCE OF THE UPPER LEVEL LOW. THIS WILL RESULT IN VERY LOW
STATIC STABILITY IN THE MIDLEVELS...WITH 850-500MB LAPSE RATES
INCREASING TO OR IN EXCESS OF 7.0 C/KM SHORTLY BEFORE 06Z. NOT
OVERLY TRUSTWORTHY OF THE 18Z NAM...AS IT IS SHOWING SOME PECULIAR
REDISTRIBUTION IN THE MASS FIELDS IN THE 3 HOURLY OUTPUT. THE NET
RESULT BASED ON UPSTREAM TRENDS AND THE FORECASTED MIDLEVEL LAPSE
RATES...INTRODUCED A MENTION OF THUNDER FOR FOR THE DETROIT METRO
AREA SOUTHWARD. THERE IS HIGH CONFIDENCE IN ANY ACTIVITY
REMAINING ELEVATED WITH NO SURFACE BASED INSTABILITY. AS A RESULT
NO SEVERE WEATHER IS EXPECTED. THE 2ND ITEM TO DISCUSS IS THE
POTENTIAL FOR HEAVY RAINFALL. THIS IDEA IS ASCERTAINED WITH THE
LOOK OF AND AMOUNT OF SHOWERS OVER NORTHERN ILLINOIS...VERY SMALL
CURVATURE/RADIUS TO THE DEFORMATION ON THE NORTHERN PERIPHERY OF
THE CLOSED LOW. THIS WILL LIKELY STREAK DIRECTLY ACROSS IN SOME
CONFIGURATION DIRECTLY OVER THE SOUTHERN DTX CWA. SO...WITH THE
VERY STEEP LAPSE RATES AND A REASONABLE DURATION OF LENGTH...COULD
SEE VERY QUICK PRECIPITATION AMOUNTS IN EXCESS OF 1.0 INCH
POSSIBLE. PWATS ARE FORECASTED TO EXCEED 1.0 INCH LATE THIS
EVENING. LATEST RAP AND HRRR...SUGGESTS THE HEAVIEST RAINFALL
AXIS MAY OCCUR DIRECTLY SOUTH OF MICHIGAN BORDER OVER OHIO.
HOWEVER...CONFIDENCE IS NOT HIGH THAT IT WILL REMAIN THAT FAR
SOUTH. THERE IS TYPICALLY ERROR IN WHAT PORTION OF THE ELEVATED
FRONTAL BOUNDARY WILL FIRE. PREFER SLIGHTLY NORTH IN THIS
INSTANCE...DIRECTLY IN LINE WITH THE STRONGEST/SHARPEST OF DIRECT
DCVA.

PREV DISCUSSION...ISSUED 334 PM EDT SUN MAY 1 2016

DISCUSSION...

MOISTURE/CLOUDS TRAPPED BENEATH AN INVERSION AND NORTHEAST FLOW OFF
THE LAKES HAVE KEPT TEMPERATURES COOL TODAY...GENERALLY IN THE UPPER
40S TO LOW 50S THIS AFTERNOON. MAY SEE ONLY A FEW BREAKS IN CLOUDS
THIS EVENING BEFORE CLOUD SHIELD ASSOCIATED WITH THE NEXT AREA OF
LOW PRESSURE BEGINS TO SPILL OVER THE AREA.

UPPER LOW OVER NE/IA WILL TRACK EAST TONIGHT...OPENING AS IT BEGINS
TO PHASE WITH THE BAGGY TROUGH OVER THE GREAT LAKES AND EASTERN
CANADA. UPPER ENERGY IS EXPECTED TO PASS THROUGH SOUTHERN MICHIGAN
AND THE NORTHERN OHIO VALLEY TONIGHT...WITH THE SURFACE LOW CENTER
LOOKING TO PASS TO OUR SOUTH OVER OHIO. SYSTEM WILL TRACK ALONG A
FRONTAL BOUNDARY DRAPED OVER THE REGION...ELEVATED PORTIONS OF WHICH
WILL REMAIN OVER SOUTHERN LOWER MICHIGAN. CONVERGENCE/ASCENT ALONG
THE FRONT LOOKS TO INCREASE AS THE SYSTEM RIDES ALONG THE BOUNDARY
TONIGHT...WITH FORCING ALSO GETTING A BOOST FROM LEFT EXIT REGION
FORCING FROM A JET STREAK TO OUR SOUTH. THIS SHOULD PROMPT A NICE
RESPONSE IN THE FORM OF RAIN TONIGHT...WITH EMBEDDED CONVECTION AS
MID-LEVEL LAPSE RATES STEEPEN TO 7-8 C/KM. HIGHEST RAIN TOTALS WILL
BE SITUATED ALONG/SOUTH OF THE M-59 CORRIDOR...CLOSER TO WHERE A
WEAK LOW-LEVEL JET WILL BE FEEDING ADDITIONAL MOISTURE INTO THE
AREA. DEFORMATION AREA AND ASSOCIATED RAIN LOOK TO PASS EAST OF THE
AREA BY SUNRISE AS THE LOW QUICKLY SCOOTS TOWARDS THE EAST COAST.

HIGH PRESSURE CENTERED OVER THE NORTHERN GREAT LAKES WILL EXPAND
BACK INTO THE AREA MONDAY AS THE LOW DEPARTS. COOLER AIR SPILLING IN
ALOFT BEHIND THE LOW...ENHANCED BY ANOTHER UPPER WAVE PASSING FROM
ONTARIO INTO QUEBEC...WILL PROMOTE STEEP LAPSE RATES UP THROUGH
ABOUT 750MB AS SURFACE HEATING COMMENCES. MODEL SOLUTIONS ARE
INCONSISTENT WITH HOW MUCH MOISTURE WILL BE PRESENT UP THROUGH AN
INVERSION POSITIONED JUST ABOVE THIS LEVEL...WITH NAM MUCH MORE
MOIST THAN GFS. NAM WOULD SUPPORT DEVELOPMENT OF SCATTERED SHALLOW
CONVECTION AND PERHAPS SOME MORNING DRIZZLE AS SOME DRYING OCCURS IN
THE MID LEVELS. WILL HOLD OFF ON ADDING RAIN MENTION AND STICK WITH
JUST CLOUDS BASED ON GFS/EURO...AS NAM SOMETIMES CARRIES A BIAS WITH
TOO MUCH LOW-LEVEL MOISTURE. WARMING WILL BE TEMPERED BY SOME CLOUD
COVER (ESPECIALLY SOUTH) AND NORTH FLOW...BUT HIGHS SHOULD BE ABLE
TO REACH THE MID 50S TO NEAR 60.

SOUTHWEST FLOW AND MIXING ON TUESDAY AHEAD OF TROUGH APPROACHING
FROM THE NORTH SHOULD BRING NOTICEABLY WARMER TEMPERATURES...WITH
MAX TEMPS EXPECTED TO REACH INTO THE MID OR PERHAPS EVEN UPPER 60S.
SURFACE TROUGH AXIS AND COLD FRONT LOOK TO WORK DOWN THROUGH
SOUTHEAST MICHIGAN LATE TUESDAY NIGHT PER LATEST MODEL CONSENSUS.
THIS WILL BRING ANOTHER CHANCE FOR RAIN SHOWERS.

CUTOFF UPPER LOW PROGGED BY GLOBAL MODELS TO DRIFT OVER SOUTHEAST
MICHIGAN WEDNESDAY WITH LOWER HEIGHTS LINGERING INTO EARLY THURSDAY.
RESULT WILL BE COOL AND SHOWERY WEATHER. CURRENT INDICATIONS ARE
THAT THE LARGE RIDGE OVER THE CENTRAL US WILL EXPAND EASTWARD INTO
THE GREAT LAKES FRIDAY AND SATURDAY...LEADING TO A SOLID WARMING AND
DRYING TREND.

MARINE...

NORTHEAST WINDS CONTINUE ACROSS THE CENTRAL GREAT LAKES INTO
TONIGHT...GENERALLY LIGHT...BUT SOME CHANNELING ACROSS SAGINAW BAY
TO SUPPORT GUSTS ABOVE 20 KNOTS INTO THE EVENING. A WEAK PRESSURE
GRADIENT TOMORROW WILL SUPPORT LIGHT AND VARIABLE WINDS...CONTINUING
INTO TUESDAY. A COLD FRONT IS FORECASTED TO SWING THROUGH THE
CENTRAL GREAT LAKES...CAUSING WINDS TO SHIFT TO THE NORTHWEST BY
WEDNESDAY EVENING...BUT STILL 20 KNOTS OR LESS.

HYDROLOGY...

A COMPACT AND FAST-MOVING SYSTEM WILL MOVE THROUGH THE AREA
TONIGHT...WITH AROUND HALF AN INCH OF RAIN EXPECTED ALONG AND SOUTH
OF M59 CORRIDOR. THE BULK OF RAINFALL IS FORECAST TO OCCUR
BETWEEN MIDNIGHT AND 6 AM LOCAL TIME. NO FLOODING IS EXPECTED...WITH
JUST MODEST RISE IN STREAMS AND RIVERS...ALONG WITH PONDING/STANDING
WATER IN NORMALLY PRONE LOW LYING AREAS.

&&

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

$$

AVIATION.....MR
UPDATE.......CB
DISCUSSION...HLO/DT
MARINE.......SF
HYDROLOGY....SF

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



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