Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 040737
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
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.

&&

.AVIATION...ISSUED 1154 PM EDT TUE MAY 3 2016

A REGION OF RAIN WILL SLOWLY PUSH TOWARD THE EAST DURING THE EARLY
MORNING. MID LEVEL MOISTURE ADVECTION IN ADVANCE OF THE MAIN REGION
OF RAIN MAY TRIGGER SOME BRIEF HIGH BASED LIGHT SHOWERS PRIOR TO
DAYBREAK. RECENT MODEL GUIDANCE SUGGESTS THE MAIN REGION OF RAIN
WILL WORK INTO MBS AND FNT JUST PRIOR TO DAYBREAK. WITH THE UPPER
WAVE FORECAST TO DEVELOP INTO A CLOSED MID LEVEL LOW OVER NRN
INDIANA ON WEDNESDAY...THE AXIS OF STRONGER FORCING WILL STRUGGLE
TO PUSH MUCH FARTHER EAST THAN FNT AND PERHAPS PTK. INITIAL DRY
AIR IN THE LOW LEVELS WILL LEAD TO A RATHER GRADUAL LOWERING OF
CEILING HEIGHTS DURING THE COURSE OF THE MORNING. SOME DEGREE OF
MVFR TYPE CIGS ARE EXPECTED AT FNT AND MBS BY AFTERNOON.
DEVELOPING SFC LOW PRESSURE FORECAST TO TRACK SOUTH OF THE REGION
WED AFTERNOON WILL DRAW A LITTLE COOLER LOW LEVEL AIR INTO FNT AND
MBS...OFFERING A GOOD CHANCE OF LOW END MVFR AND/OR IFR CIGS LATE
WED AFTERNOON/EVENING. A PERSISTENT INFLUX OF LOW LEVEL DRY AIR
FARTHER EAST MAY IN FACT LEAD TO A RATHER NARROW REGION BETWEEN
IFR/MVFR CONDITIONS AND VFR CONDITIONS.

FOR DTW...RECENT RADAR IMAGERY IS SUGGESTING THE SCATTERED HIGH
BASED SHOWERS WILL IMPACT METRO DETROIT DURING AT LEAST THE FIRST
TWO TO FOUR HOURS OF THE TAF PERIOD. OTHERWISE...RECENT MODEL TRENDS
SUGGEST DRIER LOW LEVEL AIR GETTING ADVECTED INTO METRO DETROIT FROM
THE EAST ON WEDNESDAY AS THE SFC LOW DEVELOPS TO THE SOUTHWEST. THIS
MAY HOLD THE MORE WIDESPREAD RAIN AND LOWER CEILINGS WEST OF METRO
AIRPORT.

//DTW THRESHOLD PROBABILITIES...

* LOW IN CEILINGS AT OR BELOW 5000 FT THIS MORNING. MEDIUM THIS
  AFTERNOON.

* LOW IN THUNDERSTORMS IMPACTING THE AREA TODAY.

&&

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

$$

DISCUSSION...JVC
MARINE.......MR
HYDROLOGY....MR
AVIATION.....SC


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


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