Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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094
FXUS63 KDTX 302334
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
734 PM EDT SAT APR 30 2016


.AVIATION...

COMPROMISED AVIATION CONDITIONS BOTH IN CEILINGS AND SURFACE
VISIBILITIES ARE EXPECTED THROUGHOUT THE NIGHT AND WELL INTO SUNDAY
MORNING AS A MOISTURE LADEN FRONTAL ZONE LIFTS INTO THE STATE.
SURFACE OBSERVATIONS TO THE SOUTH OF DTW...OVER NORTHERN
OHIO/INDIANA HAVE BEEN SOLID IFR IN CEILING HEIGHTS. WITH YIP
REPORTING A CIG AT LESS THAN 1000 FT AGL AN HOUR AGO...DECIDED TO
DUMP ALL THE DETROIT TAF SITES INTO IFR TO START THE PERIOD. IT IS
APPEARING THAT AT LEAST FOR A NUMBER OF HOURS TO START THE
EVENT...VISIBILITIES WILL HOLD MVFR. ADDED SOME TIMING TO THE
DURATION OF THE RAIN TONIGHT FOR THE SOUTHERN TAF SITES...BUT THEN
SWITCHED TO DRIZZLE FOR LATE TONIGHT...POST 09Z WITH MIDLEVEL
MOISTURE STRIPPING OUT. WILL NEED TO WATCH FOR THE POTENTIAL OF
FOG DEVELOPMENT AFTER THE WIDESPREAD PRECIPITATION ENDS. THERE IS
SOME LOW POTENTIAL FOR VSBYS TO FALL BELOW 1 MILE...BUT WINDS WILL
LIKELY STAY UP ENOUGH TO DISCOURAGE IT. MAIN FRONTAL FORCING WILL
LIFT INTO THE SAGINAW BAY REGION BY THE MID MORNING HOURS...WITH
PRECIPITATION FREE CONDITIONS FOR MANY OF THE TAF SITES FOR A
GOOD CHUNK OF SUNDAY. MVFR CIGS TO PERSIST.

FOR DTW...THE COMBINATION OF FORECAST DATA AND AN IFR CIG HEIGHT
AT YIP SUPPORTS GOING WITH IFR CIG HEIGHTS AT METRO TO START THE
PERIOD. PER SFC OBSERVATION TRENDS THE PREDOMINATE SURFACE
VISIBILITY APPEARS TO BE IN THE 3-5SM MILE RANGE. WILL WATCH
TRENDS LATER TONIGHT FOR POSSIBILITY OF THICKER FOG ONCE MIDLEVEL
MOISTURE STRIPS OUT...POST 9Z. ATTM...CONFIDENCE IN THIS
DEVELOPMENT IS VERY LOW. OTHERWISE...MVFR CIG HEIGHTS EXPECTED TO
PERSIST RIGHT THROUGH THE MID TO LATE MORNING HOURS SUNDAY.
THUNDERSTORM POTENTIAL REMAINS VERY LOW.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CIGS BELOW 5000 FT AGL THROUGHOUT THE ENTIRE TAF
  FORECAST PERIOD.

* VERY LOW FOR A THUNDERSTORM TO IMPACT DTW TONIGHT.

&&

.PREV DISCUSSION...ISSUED 323 PM EDT SAT APR 30 2016

DISCUSSION...

A GOOD AMOUNT OF MOISTURE POOLED UP OVER WESTERN OHIO VALLEY (12Z
KILX SOUNDING INDICATED 9 C DEW PT AT 850 MB) WILL CONTINUE TO
PROGRESS OFF TO THE NORTHEAST INTO SOUTHERN LOWER MICHIGAN EARLY
THIS EVENING. SOLID UPPER LEVEL DIVERGENCE/PV ADVECTION/HEIGHT FALLS
AND LOW LEVEL MOISTURE TRANSPORT/ISENTROPIC ASCENT TO SUPPORT
WIDESPREAD RAINFALL...WITH PW VALUES REACHING 1 INCH ALONG/SOUTH OF
I-69 CORRIDOR...SUPPORTIVE OF AMOUNTS REACHING AND LIKELY ECLIPSING
HALF AN INCH TONIGHT...ESPECIALLY WITH ANY CONVECTIVE ELEMENTS...AS
SHOWALTER INDEX PROGGED TO DROP BELOW ZERO JUST PAST THE SOUTHERN
MICHIGAN BORDER...BUT LITTLE IN THE WAY OF ACTUAL CAPE...SHOULD BE
HARD PRESSED TO SEE ANY THUNDERSTORMS. MID LEVEL LAPSE RATE DO
BECOME STEEP ON SUNDAY (7+ C/KM)...BUT MAINLY DUE TO THE DRYING
OCCURRING IN THE MID LEVELS...AND DON`T EXPECT MUCH SHOWER ACTIVITY
DURING THE DAY. VERY TIGHT LOW LEVEL BAROCLINIC ZONES IN PLACE (850
MB TEMPS OF 1 C OVER SAGINAW TO 10 C NEAR OHIO BORDER PER 12Z
EURO)...AND EVEN WOULD NORTHEAST SURFACE WINDS...COULD SEE FAR SOUTH
REACH AND EXCEED 60 DEGREES WITH PREVIOUSLY MENTIONED DRYING/LULL IN
ACTIVITY.

THE 00Z MODEL SUITE INDICATED A FARTHER NORTH SURFACE/LOW LEVEL
FRONTAL BOUNDARY PLACEMENT TOMORROW...WHICH LOOKS TO SET US UP FOR
ANOTHER ROUND OF RAINFALL SUNDAY EVENING....AS SECOND WAVE AND
LEFTOVER UPPER LEVEL CIRCULATION FROM THE CENTRAL PLAINS SLIDES
EAST...PROVIDING GOOD UPPER LEVEL DIVERGENCE/DEFORMATION AXIS WHICH
LOOKS TO CLIP AREAS SOUTH OF I-69 CORRIDOR. THE 12Z MODEL
NAM/GFS/CANADIAN HAVE SHIFTED BACK TO THE SOUTH A BIT...BUT 12Z EURO
REMAINS MOST AGRESSIVE/ADAMANT...AND FEEL CONFIDENT TO GO LIKELY
POPS SOUTH OF I-69 TO CATEGORICAL NEAR THE OHIO BORDER. SUBSTANTIAL
COLD ADVECTION TO TAKE PLACE BEHIND THE MERGING NORTHERN STREAM
TROUGH AXIS PASSAGE MONDAY MORNING...WITH 850 MB TEMPS STILL PROGGED
TO FALL TO ZERO...OR EVEN SLIGHTLY COLDER. NORTHEAST FLOW OFF LAKE
HURON AND EXPECTED CLOUD COVER ON MONDAY COULD PROVE SUFFICIENT TO
KEEP MAXES UNDER 60 DEGREES. IF LOW CLOUDS DISSIPATE MONDAY
NIGHT...FROST CONCERNS WILL RETURN AS TEMPERATURES POTENTIALLY
FALL BACK INTO THE 30S WITH CALM/NEARLY CALM WINDS.

WEAK AND FRAGILE HIGH PRESSURE WILL LINGER OVER LOWER MICHIGAN
TUESDAY BETWEEN LOW PRESSURE OVER THE OHIO VALLEY AND THE NEXT COLD
FRONT PUSHING THROUGH NORTHERN ONTARIO. EXPECT THERE WILL AT LEAST
BE CLOUDS AROUND WITH A PORTION OF THE UPPER TROUGH SUPPORTING THE
OHIO VALLEY SURFACE TROUGH. THIS WILL PRODUCE TEMPERATURES RIGHT
AROUND NORMAL FOR EARLY MAY FOR ONE MORE DAY BEFORE THE ONTARIO
FRONT MOVES THROUGH THE GREAT LAKES WEDNESDAY. THERE IS INCREASING
EVIDENCE IN GLOBAL MODEL SOLUTIONS THAT SUPPORT CLOSING OFF THE
ASSOCIATED UPPER WAVE BY THURSDAY WHICH WILL KEEP SHOWERS AND COOLER
TEMPERATURES OVER THE REGION POSSIBLY EVEN INTO FRIDAY. THIS IS AN
UNPLEASANT WEATHER SCENARIO FOR THE SECOND HALF OF NEXT WEEK
HIGHLIGHTED BY TEMPERATURES THAT WILL STRUGGLE TO REACH GUIDANCE
VALUES IN THE LOWER TO MID 50S...ESPECIALLY FOR THURSDAY. THESE
TYPES OF CLOSED SYSTEMS OFTEN END UP BEING SLOWER TO EVOLVE THAN
MODEL FORECASTS WHICH ALSO POINTS TO A SHAKY START TO NEXT WEEKEND
AS WELL.

MARINE...

WINDS WILL INCREASE FROM THE NORTHEAST TONIGHT AS LOW PRESSURE
PASSES THROUGH THE OHIO VALLEY...AND REMAIN GUSTY OVER LAKE HURON
TOMORROW AS THE LOW MOVES INTO THE EASTERN GREAT LAKES. SMALL CRAFT
ADVISORIES REMAIN IN EFFECT LATE TONIGHT THROUGH SUNDAY FOR THE LAKE
HURON NEARSHORE WATERS...INCLUDING SAGINAW BAY...AS PERSISTENT AND
STRONG FLOW ACROSS THE LAKE ALLOWS WAVE HEIGHTS TO BUILD BETWEEN 4
AND 8 FEET. GUSTS AROUND 25 KNOTS WILL ALSO DEVELOP TONIGHT AND
CONTINUE INTO SUNDAY BEFORE LOW PRESSURE MOVES EAST AND SPEEDS
DECREASE. THIS WILL ALSO ALLOW LARGE WAVES TO SUBSIDE DURING THE
LATE EVENING. A VERY LARGE DOME OF HIGH PRESSURE CENTERED OVER THE
CENTRAL PLAINS WILL THEN KEEP WINDS FAIRLY LIGHT MONDAY INTO TUESDAY.

A BRIEF PERIOD OF GUSTY EAST-NORTHEAST WINDS IS ALSO EXPECTED THIS
EVENING...BETWEEN 6 PM AND 11 PM...OVER WESTERN LAKE ERIE AS THE
CENTER OF LOW PRESSURE DRAWS CLOSER. GUSTS MAY APPROACH 25 KNOTS FOR
SEVERAL HOURS BEFORE WINDS WEAKEN AND FINALLY TURN LIGHT FROM THE
NORTH BEFORE SUNRISE.

HYDROLOGY...

LOW PRESSURE PASSING THROUGH THE OHIO VALLEY WILL SPREAD WIDESPREAD
AND STEADY RAINFALL INTO SOUTHEAST MICHIGAN LATE THIS AFTERNOON
THROUGH TONIGHT...WITH SHOWERS THEN LINGERING THROUGH SUNDAY. THE
HEAVIEST RAIN LOOKS TO FALL BETWEEN 9 PM AND 4 AM TONIGHT. TOTAL
RAINFALL THROUGH 2 PM SUNDAY LOOKS TO EXCEED 0.25 INCHES ACROSS ALL
OF SOUTHEAST MICHIGAN...WITH TOTALS BETWEEN 0.75 AND 1.00 INCH SOUTH
OF THE M-59 CORRIDOR. THIS RAINFALL WILL PROMPT RISES ON AREA
RIVERS...CREEKS...AND STREAMS...BUT FLOODING IS NOT EXPECTED.

ANOTHER QUICK ROUND OF RAINFALL IS EXPECTED SUNDAY NIGHT ACROSS FAR
SOUTHERN MICHIGAN. LOCATIONS ALONG AND SOUTH OF I-94 MAY PICK UP AN
ADDITIONAL 0.25 INCHES OF RAIN.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY FROM 5 AM TO 8 PM EDT SUNDAY FOR LHZ421-422-
     441>443.

LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

AVIATION.....CB
DISCUSSION...SF/BT
MARINE.......HLO
HYDROLOGY....HLO


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



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