Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KDTX 041636
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1236 PM EDT WED MAY 4 2016

.UPDATE...
WATER VAPOR IMAGERY INDICATES UPPER ENERGY IS STARTING TO CLOSE
OFF OVER SOUTHWEST MICHIGAN AS PREDICTED BY NWP SUITE. THIS SHOULD
PIVOT THE NORTH-SOUTH ORIENTATED BAND OF PRECIPITATION THAT WAS
OVER WESTERN MICHIGAN THIS MORNING MORE INTO SOUTHEAST LOWER
MICHIGAN AS CYCLONIC FLOW INCREASES AROUND THE SYSTEM AND THE
DEFORMATION BAND TAKES ON A MORE NORTHWEST TO SOUTHEAST
ORIENTATION. THIS IS ALREADY STARTING TO TAKE SHAPE PER LATEST
RADAR IMAGERY. BAND OF HEAVIEST RAIN IS EXPECTED TO STRETCH
ROUGHLY FROM THE SAGINAW VALLEY DOWN THROUGH THE DETROIT AREA THIS
AFTERNOON BEFORE DROPPING SOUTH EARLY TONIGHT AS THE LOW CENTER
WORKS SOUTHWARD. SOME MINOR ADJUSTMENTS WERE MADE TO PRECIPITATION
PLACEMENT BASED ON RADAR TRENDS AND LATEST RUNS OF HIGHER-RES
MODELS (HRRR...NAM12...NMM)...WITH HIGHEST POPS AND QPF SHIFTED
VERY SLIGHTLY TO THE WEST AND SOUTH. BIGGEST CHANGES WERE IN THE
FORM OF HIGHER POPS OVER LENAWEE COUNTY...LOWER POPS OVER THE
THUMB...AND A MORE PRONOUNCED DRYING TREND OVER THE NORTHERN HALF
OF THE FORECAST AREA EARLY TONIGHT.

STRONGER SHOWERS AND THUNDERSTORMS HAVE ALSO STARTED TO DEVELOP
EARLY THIS AFTERNOON AS WARMING OCCURS WITH DIURNAL HEATING IN THE
LOW LEVELS AND THE UPPER LEVELS COOL IN THE PROXIMITY OF THE
DEVELOPING UPPER LOW. THIS HAS RESULTED IN A FEW HUNDRED J/KG OF
MU CAPE PER LATEST SPC ANALYSIS. STILL NOT EXPECTING SEVERE
WEATHER...BUT LOCALLY HEAVY RAINFALL IS EXPECTED.

&&

.AVIATION...ISSUED 709 AM EDT WED MAY 4 2016

STEADY STREAM OF MID LEVEL MOISTURE WILL SUSTAIN POCKETS OF SHOWERS
WITHIN A HIGH BASED CLOUD THIS MORNING.  SE MICHIGAN EXPECTED RESIDE
ALONG THE EASTERN EXTENT OF THE DEEPER MOISTURE AND FORCING
ASSOCIATED WITH LOW PRESSURE TRACKING THROUGH LOWER MICHIGAN.
MBS/FNT REMAIN MORE FAVORABLY POSITIONED TO SEE A PERIOD OF
WIDESPREAD PRECIPITATION THIS AFTERNOON WITH AN ACCOMPANYING
REDUCTION IN CONDITIONS INTO MVFR...PERHAPS BRIEFLY IFR AT MBS.
OVERALL TIMING A TOUCH SLOWER NOW...BUT WILL HOLD WITH THIS GENERAL
TIMING. LESS CERTAINTY FROM PTK SOUTHWARD...BUT WITH GROWING
CONFIDENCE THAT PREVAILING CONDITIONS WILL REMAIN IN VFR AS SHOWERS
FILL IN.  A WEAKLY UNSTABLE ENVIRONMENT MAY SUPPORT EMBEDDED
THUNDER...UNCERTAINTY IN BOTH TIMING AND COVERAGE PRECLUDING A
DEFINED MENTION.

FOR DTW...MINIMALLY IMPACTFUL LIGHT SHOWERS IN CEILINGS ABOVE 5000
FT FOR THE MORNING PERIOD.  METRO WILL THEN RESIDE AT THE EASTERN
EDGE OF MORE ORGANIZED PRECIPITATION /AND POSSIBLE THUNDER/ EXPECTED
TO DEVELOP BY MID-LATE AFTERNOON. EXISTING DRY LOW LEVEL
ENVIRONMENT MAY PROVE A FORMIDABLE LIMITING FACTOR IN GREATER
DEVELOPMENT LOCALLY. THIS CONTINUES TO LEND SUPPORT TOWARD A MORE
OPTIMISTIC OUTLOOK ON CEILING/VISIBILITY TRENDS DURING THIS TIME.

//DTW THRESHOLD PROBABILITIES...

* LOW IN CEILINGS AT OR BELOW 5000 FT PRIOR TO 20Z...MEDIUM FROM
  MID AFTERNOON INTO THE EVENING.

* LOW IN THUNDERSTORMS IMPACTING THE AREA TODAY.

&&

.PREV DISCUSSION...ISSUED 337 AM EDT WED MAY 4 2016

DISCUSSION...

IMPRESSIVE SPREAD STILL EXISTS AMONG THE GUIDANCE THIS MORNING AS
FORECAST LEAD TIME DIMINISHES TO ZERO. WATER VAPOR IMAGERY SHOWS A
POWERFUL LEAD WAVE DIGGING INTO THE MIDWEST WITH A NEARLY
EQUIVALENTLY STRONG TRAILING WAVE OVER WEST-CENTRAL WISCONSIN AT
07Z. THE TRAILING WAVE HAS BEEN POORLY RESOLVED BY MANY MEMBERS OF
THE GUIDANCE...THE RAP APPEARING TO HANDLE IT THE BEST. EVEN SO, THE
RAPID REFRESH IS STRUGGLING TO KEEP UP WITH 3-HOUR PRESSURE FALLS OF
3-5MB THIS MORNING.

EXPANDING SHOWER COVERAGE IN ADVANCE OF THE WAVE IS OCCURRING WITHIN
THE CORRIDOR OF MOISTURE TRANSPORT THAT HAS EMERGED OVER SOUTHWEST
MICHIGAN DURING THE LAST COUPLE OF HOURS. FOR NOW, THIS ACTIVITY IS
STRUGGLING TO PENETRATE THE CWA DUE TO ANTECEDENT DRY AIR EVIDENT ON
THE 00Z DTX SOUNDING. COVERAGE IS EXPECTED TO INCREASE IN SE
MICHIGAN OVER THE NEXT SEVERAL HOURS AS THE COLUMN SATURATES, LARGE
SCALE FORCING INCREASES, AND DIURNAL DESTABILIZATION GETS UNDERWAY.

THE PRIMARY FEATURE OF INTEREST, THE BAND OF RAIN WITH EMBEDDED
HEAVY SHOWERS, IS SO FAR BEHAVING AS ANTICIPATED. ITS NARROW
STRUCTURE IS ATTRIBUTABLE TO DEEP LAYER LINEAR/CONVERGENT FORCING
ALONG THE STRONG TROUGH AXIS. THE UPPER TROUGH WILL BEGIN THE
PROCESS OF CLOSING OFF LATE THIS MORNING OR EARLY THIS AFTERNOON AS
ENERGY CONTINUES TO FLOOD SOUTH INTO THE WESTERN GREAT LAKES. AS
THIS OCCURS, THE BAND WILL STALL AND PIVOT IN CYCLONIC FASHION WITH
PRECIPITATION RATES INTENSIFYING AS DEFORMATION FORCING RAMPS UP
WEST OF US-23. IN ADDITION, DIURNAL HEATING AND STEEP LAPSE RATES
WILL CONTRIBUTE TO A LOW DENSITY CAPE PROFILE CHARACTERIZED BY A FEW
HUNDRED J/KG OF POTENTIAL ENERGY. SKINNY CAPE WITHIN PERSISTENT
STRONG DEFORMATION WILL BE SUFFICIENT TO PRODUCE A SOLID HALF INCH
TO THREE QUARTERS OF RAIN OVER WESTERN AREAS. A LOCALIZED AREA -
PERHAPS JUST THE FOOTPRINT OF A COUNTY OR TWO -COULD EASILY SEE OVER
AN INCH IN THIS SETUP. MOST LIKELY AREA FOR HEAVIEST RAIN WILL BE
BETWEEN LIVINGSTON AND BAY COUNTIES WEST OF US-23/I-75. THE LACK OF
SIGNIFICANT MOISTURE (PWAT < 0.80") AND A VERY SHALLOW (< 5KFT) WARM
CLOUD LAYER WILL PUT A DEFINITE CEILING ON POTENTIAL RAINFALL
AMOUNTS SO THINGS WILL NOT GET OUT OF CONTROL.

UNCERTAINTY IN PRECIP POTENTIAL INCREASES FOR EASTERN AREAS,
INCLUDING DETROIT METRO, AS THE CONVERGENT RAINFALL BAND STALLS UPON
THE MID-LEVEL LOW CLOSING OFF. HOWEVER, LATEST RAP SIMULATIONS SHOW
RESPECTABLE CAPE OF A FEW HUNDRED J/KG ACROSS THE EAST. WILL LIKELY
SEE SOME SUBTLE RIDGING FORCED OVER THE EASTERN CWA DURING PEAK
HEATING, BUT LOW/MID-LEVEL THETA MAY BE JUST ENOUGH IN THE STEEP
LAPSE RATE ENVIRONMENT TO SERVE AS A TRIGGER FOR DISORGANIZED SHOWER
ACTIVITY DURING THE AFTERNOON. THUS, LIKELY POPS REMAIN IN PLACE IN
SPITE OF THE WESTWARD ADJUSTMENT FROM YESTERDAY MORNING`S FORECAST.

WARMING TREND INTO THE 60S THURSDAY AND LOW 70S FRIDAY AS RIDGING IS
FORCED THROUGH THE CWA DURING THE LATE WEEK PERIOD. LINGERING
CYCLONIC FLOW AND MOISTURE WILL KEEP A PARTIAL COVERAGE OF DIURNAL
CU AND POSSIBLY JUST AN ISOLATED SHOWER IN THE FORECAST THROUGH
THURSDAY. DEEP LAYER SUBSIDENCE WILL SUPPORT FULL SUN AND MUCH
WARMER TEMPS ON FRIDAY AS THE BOUNDARY LAYER TAPS INTO 850MB TEMPS
IN THE HIGH SINGLE DIGITS BY AFTERNOON.

MARINE...

MODEST NORTHERLY WINDS WILL BEGIN TO TAKE HOLD ACROSS THE CENTRAL
GREAT LAKES TODAY AS LOW PRESSURE PIVOTS THROUGH LOWER MICHIGAN.
SLIGHT INCREASE IN NORTHERLY FLOW TONIGHT INTO EARLY THURSDAY MAY
LEAD TO A BRIEF PERIOD OF GUSTS NEAR 20 KNOTS ACROSS SOUTHERN
SECTIONS OF LAKE HURON DURING THIS TIME.  THE ONSHORE FLOW WILL ALSO
BRING A PERIOD OF ELEVATED WAVE CONDITIONS ALONG THE THUMB DURING
THIS TIME.  HOWEVER SMALL CRAFT ADVISORY LEVEL CONDITIONS ARE
CURRENTLY NOT ANTICIPATED.  HIGH PRESSURE WILL THEN BRING TRANQUIL
MARINE CONDITIONS FOR THE LATE WEEK PERIOD.

HYDROLOGY...

STRENGTHENING LOW PRESSURE WILL DROP SOUTHEAST ACROSS THE STATE
THROUGH THIS EVENING.  A PERIOD OF STRONG FORCING ASSOCIATED WITH
THIS SYSTEM WILL SLIDE INTO WESTERN PORTIONS SE MICHIGAN LATE TODAY.
THIS WILL FOCUS AN AXIS OF HEAVIER RAINFALL ALONG HIGHWAY 23
CORRIDOR...WHERE RAINFALL AMOUNTS FROM ONE HALF TO THREE QUARTERS OF
AN INCH ARE EXPECTED.  DECREASING RAINFALL AMOUNTS WITH EASTWARD
EXTENT...LEAVING EASTERN PORTIONS OF METRO DETROIT NORTHWARD INTO
THE THUMB WITH LESS THAN A QUARTER OF AN INCH.  THE BULK OF THIS
RAINFALL WILL OCCUR DURING THE AFTERNOON AND EARLY EVENING HOURS.
RAINFALL WILL TAPER OFF QUICKLY EARLY TONIGHT WITH GENERALLY DRY
WEATHER THURSDAY AND FRIDAY.

&&

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

$$

UPDATE.......HLO
AVIATION.....MR
DISCUSSION...JVC
MARINE.......MR
HYDROLOGY....MR


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


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.