Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 212247
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
645 PM EDT TUE APR 21 2015

.AVIATION...

LOSS OF DAYTIME HEATING WILL PROVIDE A NOTABLE DECREASE IN BOTH WIND
GUST SPEED AND FREQUENCY THROUGH THE LATTER HALF OF THE EVENING.
THIS PROCESS WILL ALSO RESULT IN A STEADY REDUCTION IN THE COVERAGE
OF SHOWERS THROUGH THIS TIME.  EXPANSIVE LOW PRESSURE SYSTEM WILL
TAKE A PROGRESSIVE HOLD OF CONDITIONS LOCALLY THROUGH THE REMAINDER
OF THE TAF PERIOD.  THE RESULTING SEASONABLY COLD MOIST CYCLONIC
FLOW WILL ENSURE A HIGH DEGREE OF CLOUD COVER REMAINS IN PLACE
THROUGH WEDNESDAY.  CEILINGS LARGELY EXPECTED TO REMAIN AT
VFR...LOWEST HEIGHTS EMERGING WITH DAYTIME HEATING BY LATE MORNING
WEDNESDAY.  THIS WILL AGAIN PROMOTE GUSTY CONDITIONS...WITH A WEST-
NORTHWEST WIND GUSTING 25 TO 30 KNOTS BY AFTERNOON. ANOTHER ROUND OF
SCATTERED RA/SN SHOWERS FOR THE LATTER HALF OF THE DAY.

FOR DTW...SOUTHWEST GUSTS WILL EASE WITH TIME MIDNIGHT AS MIXING
CEASES.  LOWER CONFIDENCE ON CEILING HEIGHTS THROUGH LATE
EVENING...STILL SOME POTENTIAL FOR HEIGHTS TO INTERMITTENTLY DROP
BELOW 5000 FT PARTICULARLY WITHIN ANY LINGERING SHOWERS.  A MORE
DEFINITIVE DROP IN CEILINGS TO LOWER VFR EXPECTED ON WEDNESDAY.

//DTW THRESHOLD PROBABILITIES...

* LOW CONFIDENCE IN CEILINGS BELOW 5000 FT THIS EVENING.  HIGH
  CONFIDENCE ON WEDNESDAY.

&&

.PREV DISCUSSION...ISSUED 338 PM EDT TUE APR 21 2015

SHORT TERM...TONIGHT

GUSTY WINDS AND SCATTERED SHOWERS WILL CONTINUE THROUGH THE
REMAINDER OF THE AFTERNOON. WINDS HAVE BEEN GUSTING ALL DAY WITH
SOME LOCATIONS REPORTING GUSTS UP TO 45 MPH...HOWEVER...CURRENT
MODEL SOUNDINGS INDICATE A DECREASE IN THE LOW LEVEL JET TOWARDS
EARLY EVENING WHICH WILL RESULT IN SURFACE WINDS TO BEGIN TO
DIMINISH AFTER 7PM. THIS WILL ALLOW THE WIND ADVISORY TO EXPIRE AT
THIS THAT TIME. WITH STRONG LOW LEVEL LAPSE RATES AND PLENTY OF LOW
LEVEL MOISTURE OVER SOUTHEAST MICHIGAN...SCATTERED RAIN SHOWERS WILL
CONTINUE THROUGH THE EVENING HOURS...BEFORE TAPERING OFF AROUND
MIDNIGHT. RAIN SHOWERS ARE EXPECTED TO RETURN TOWARDS DAYBREAK
/AFTER 6AM/ AS THE LOW PRESSURE SYSTEM REMAINS SITUATED TO OUR NORTH
OVER CANADA AND AREAS OF ENERGY AND LOW LEVEL MOISTURE CONTINUE TO
PIVOT ACROSS LOWER MICHIGAN. COLD AIR ADVECTION WILL CONTINUE TO
FILTER IN MUCH COLDER AIR INTO THE GREAT LAKES TONIGHT...RESULTING
IN LOW TEMPERATURES TO DROP INTO THE LOW 30S FOR MOST LOCATIONS.

LONG TERM...

LARGE AND DEEP UPPER LEVEL LOW/CIRCULATION CENTERED OVER
NORTHEASTERN ONTARIO WILL MAINTAIN NORTHWEST FLOW AND RENEWED SURGE
OF COLD AIR IS EXPECTED TOMORROW...AS 850 MB TEMPS DROP TO -7 TO -9
C OVER LOWER MICHIGAN...WITH COLD CORE OF -19 C AT 700 MB SLIDING
THROUGH NORTHERN LOWER MICHIGAN. WITH SOME SEMBLANCE OF SURFACE
TROUGH/CONVERGENCE WORKING INTO SOUTHEAST MICHIGAN...COUPLED WITH
LAKE MICHIGAN ENHANCEMENT/INSTABILITY AND THERMAL TROUGH AXIS
WORKING THROUGH...AT LEAST HIGH SCATTERED COVERAGE IS EXPECTED...AS
DECENT CAPE (75 J/KG) RESIDES IN THE DGZ. WITH GRAUPEL OCCURRING
TODAY...SEEMS LIKE A NO BRAIN-ER WE WILL SEE SNOW SHOWERS TOMORROW
WITH THE COLDER AIRMASS...AND QUICK DUSTING OF ACCUMULATION...MAINLY
ON GRASSY SURFACES IS EXPECTED WITH HEAVIER ACTIVITY...BUT ONCE CELL
MOVES ON...SNOW WOULD LIKELY MELT WITH SURFACE TEMPS IN THE UPPER
30S TO LOWER 40S. 700 MB JET (50-60 KNOTS) ALONG AND SOUTH OF THE
MICHIGAN BORDER TODAY WILL BE DROPPING SOUTH AND EAST...AND THUS
WINDS SHOULD BE CONSIDERABLY WEAKER TOMORROW...BUT 45 KNOTS DOES
APPEAR TO HANG AROUND TOWARD THE OHIO BORDER...ENOUGH TO SUPPORT
GUSTS IN THE 30S MPH. CARRYING HIGHS IN THE LOW TO MID 40S...TO
ACCOUNT FOR SUPERADIABATIC NEAR SURFACE LAPSE RATES...BUT
PRECIPITATION WILL TEND TO KNOCK THE TEMPERATURE BACK DOWN.

COOLING OF BOUNDARY LAYER WEDNESDAY NIGHT...ALLOWING 850 MB TEMPS TO
BOTTOM OUT AROUND 11 BELOW ZERO THURSDAY MORNING...ALTHOUGH SHARP
TEMP GRADIENT WILL RISE TOWARD THE OHIO BORDER...AS SHEAR/JET AXIS
RETREATS NORTHWARD THROUGH THE DAY...SUPPORTING MODERATING
AIRMASS...850 MB TEMPS OF -5 C SOUTH TO -8 C NORTH TOWARD 00Z
THURSDAY...SUPPORTING HIGHS SOLIDLY INTO THE 40S. DRY AIRMASS IN
PLACE COUPLED WITH SURFACE HIGH OVERHEAD THURSDAY NIGHT WILL SET THE
STAGE FOR GOOD RADIATING NIGHT...AND NORMALLY COLDER LOCATIONS
EXPECTED TO FALL INTO THE MID TO UPPER 20S...APPROACHING RECORD
VALUES FOR APRIL 24TH:

FLINT...    25 (1996)
SAGINAW...  25 (1918)
DETROIT...  27 (1892)

RESIDUAL COLD AIRMASS OF MID NEGATIVE SINGLE NUMBERS AT 850 MB TO
START THE DAY WILL LIKELY SUPPORT SOME CU UP...BUT ENOUGH INSOLATION
EXPECTED TO BOOST TEMPS INTO THE UPPER 40S TO LOWER 50S...STILL 10
DEGREES BELOW NORMAL.

A QUICK LOOK AT THE 12Z EURO SHOWS UPPER LEVEL NORTHWEST CONFLUENT
FLOW/DRY AIRMASS HOLDING OVER THE CENTRAL GREAT LAKES...WITH
DAMPENING UPPER LEVEL WAVE COMING OUT OF THE SOUTHERN PLAINS...AND
THE FORECAST IS FOR DRY CONDITIONS TO HOLD THROUGH THE
WEEKEND...ALTHOUGH CANADIAN/GFS/EURO HAVE SIGNIFICANT DEVIATIONS AT
500 MB FOR THE SECOND HALF OF THE WEEKEND OVER EASTERN CANADA
EXTENDING SOUTH TO THE GREAT LAKES REGION/NEW ENGLAND.

MARINE...

COLD ADVECTION AND DEEP MIXING TODAY HAS ALLOWED FOR SOUTHWEST WIND
GUSTS OF 25 TO 40 KNOTS ACROSS THE CENTRAL GREAT LAKES...WITH
CONVECTIVE SHOWERS ENHANCING THE WINDS. GALE WARNINGS WILL CONTINUE
FOR SAGINAW BAY...LAKE ST CLAIR AND WESTERN LAKE ERIE INTO EARLY
EVENING. LOSS OF THE DAYTIME HEATING AND MID LEVEL JET SINKING SOUTH
TONIGHT WILL ALLOW WINDS TO DIMINISH. THERE WILL BE A PICK UP AGAIN
TOMORROW...BUT HIGHER CONFIDENCE IN WINDS REMAINING BELOW GALES WITH
THE MID LEVEL JET DISPLACED SOUTH. ADDITIONAL SMALL CRAFT ADVISORIES
WILL LIKELY BE NEEDED HOWEVER. ONE MORE ROUND OF UNUSUALLY COLD AIR
WILL ROTATE THROUGH LAKE HURON WEDNESDAY NIGHT INTO THURSDAY...AND
SOLID GUSTS TO AT LEAST 30 KNOTS ARE EXPECTED OVER NORTHERN LAKE
HURON...WITH LOW CHANCE OF GALES. HIGH PRESSURE BUILDING IN ON
FRIDAY SHOULD PROVIDE FAVORABLE BOATING CONDITIONS...EXTENDING INTO
THE WEEKEND.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR MIZ068>070-075-076-
     082-083.

LAKE HURON...GALE WARNING UNTIL 8 PM EDT THIS EVENING FOR LHZ421-422.

     SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR LHZ441>443.

LAKE ST CLAIR...GALE WARNING UNTIL 8 PM EDT THIS EVENING FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...GALE WARNING UNTIL 8 PM EDT THIS EVENING
     FOR LEZ444.

&&

$$

AVIATION.....MR
SHORT TERM...RK
LONG TERM....SF
MARINE.......SF


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



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