Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211130
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
730 AM EDT TUE APR 21 2015


.AVIATION...

MAIN CONCERN FOR THE DAY WILL BE STRONG WINDS AS VFR CONDITIONS WILL
PREVAIL THROUGH MOST OF THE PERIOD AS DRY SFC LAYER AIR KEEPS CIGS
AOA 5KFT WITH LOW THREAT OF VSBY RESTRICTIONS. THERE IS POTENTIAL
FOR CONVECTIVE SHOWERS THIS AFTERNOON WHICH COULD BRIEFLY LOWER CIGS
AND VSBYS. DAYTIME MIXING COMBINED WITH STRENGTHENING COLD POOL
ALOFT WILL AID IN BRINGING DOWN STRONG WINDS THROUGH THE AFTERNOON.
SOUTHWESTERLY WIND GUSTS ACROSS THE REGION SHOULD BE NEAR 30 KNOTS
FOR MUCH OF THE DAYTIME WITH POTENTIAL TO REACH NEAR 40 KNOTS IN ANY
CONVECTIVE SHOWERS THAT DEVELOP.

FOR DTW...SOUTHWEST WINDS ALREADY GUSTING TO 20 KNOTS WILL QUICKLY
RAMP UP WITH THE ONSET OF DAYTIME HEATING...ROUGHLY AROUND 14Z. PEAK
GUSTS COULD REACH/EXCEED 40 KNOTS BRIEFLY WITH PASSING CONVECTIVE
SHOWERS BUT REACH 30-35 KNOTS FOR SEVERAL HOURS THIS AFTERNOON.
THERE ARE CHANCES OF RAIN SHOWERS THIS AFTERNOON AND AGAIN SHORTLY
AFTER DUSK BUT LOW CONFIDENCE IN COVERAGE RESULTS IN TEMPO GROUPS
FOR BOTH PERIODS.

//DTW THRESHOLD PROBABILITIES...

* LOW IN CEILINGS AT OR BELOW 5000 FT THROUGH THE PERIOD OUTSIDE OF
  SHOWER ACTIVITY THIS AFTERNOON AND AGAIN AFTER DUSK.

* LOW IN WIND GUSTS EXCEEDING CROSS WIND THRESHOLDS THIS AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 344 AM EDT TUE APR 21 2015

SHORT TERM...TODAY AND TONIGHT

A DEEP LOW PRESSURE SYSTEM STACKED FROM THE SFC INTO THE UPPER
LEVELS WILL CONTINUE TO SIT OVER THE NORTHERN GREAT LAKES REGION
MOVING VERY LITTLE THROUGH THE SHORT TERM. THE LOW WILL STEER THE
NORTHERN STREAM OF THE JET DOWN AROUND MI TAKING IT SE THROUGH THE
UPPER MS VALLEY AND DOWN THROUGH THE OHIO VALLEY. MEANWHILE OVER SE
MI...CAA AND INCREASINGLY DRIER AIRMASS IN THE BL WILL ENCOURAGE THE
DEVELOPMENT OF A DEEP DIURNAL MIXED LAYER...UP TO NEAR 750MB. STRONG
LL LAPSE RATES INTO THE MID LEVELS WILL PROMOTE A CONVECTIVE MODE TO
ANY SHOWERS THAT DEVELOP IN THE COLD CYCLONIC FLOW. AIDING IN THE
SHOWER POTENTIAL WILL BE SEVERAL PIECES OF ENERGY ROTATING ABOUT THE
LOW.

BIGGEST CONCERN WITH THE SETUP TODAY WILL BE THE WIND. MODEL
SOUNDINGS SHOW A FAIRLY UNIFORM WIND FIELD THROUGHOUT THE MIXED
LAYER...AVERAGING 35-40 KNOTS ACROSS THE CWA. SOME 50 KNOT WINDS ARE
SHOWING UP AS WELL IN THE 650-750MB LAYER...BUT MAINLY FOR POINTS
SOUTH OF ABOUT M59. NAM AND GEMREG BOTH SHOW THE STRONGEST
FLOW...WIDEST SWATH OF 50+ KNOT LL JET FLOW...JUST SOUTH OF THE
MI/OH BORDER ACROSS IN/OH. WE ARE LOOKING AT TWO POSSIBLE SCENARIOS
FOR POTENTIAL WIND ADVISORY STRENGTH WIND GUSTS OVER THE AREA. THE
FIRST...AS MENTIONED BY THE PREVIOUS FORECASTER...WILL BE THE
CONVECTIVE SHOWERS BRINGING DOWN SOME HIGHER WIND GUSTS. WITH
WIDESPREAD 30-35 KNOT GUSTS FROM SYNOPTIC FORCING...AND TAKING INTO
ACCOUNT A FEW GUSTS ON MONDAY TAPPED THE 40 KNOT RANGE...CANNOT RULE
OUT A FEW HIGHER GUSTS WITHIN THESE STRONGER SHOWERS. THE SECOND
SCENARIO IS THAT THE LL JET IS NOT HELD SOUTH OF THE BORDER AND
BLEEDS INTO OUR SOUTHERN TIER OF COUNTIES OR TWO. NOT REALLY SOLD ON
EITHER AT THIS POINT ENOUGH TO ISSUE A WIND ADVISORY...BUT THE GRIDS
ALREADY HAVE FAIRLY STRONG WORDING FOR GUSTS SO THINK THAT HANDLES
THE SITUATION WELL. IF GUSTS EARLY SEEM TO BE OVERACHIEVING...A
SHORT FUSED ADVISORY MAY BE WARRANTED.

CAA WILL INCREASE OVERNIGHT AS THE TROUGH OF COLD AIR SHIFTS
EASTWARD. 850MB TEMPS WILL DROP FROM -2C TO AROUND -7C BY 12Z
WEDNESDAY. DRY AIR IN THE LOW LEVELS WILL AID IN EFFICIENT COOLING
SETUP WITH LOWS DIPPING INTO THE LOW 30S.

LONG TERM...

DEEP LAYER MOIST CYCLONIC FLOW WITHIN THE CYCLONE CENTERED NEAR THE
STRAITS WILL PERSIST THROUGH THURSDAY. EMBEDDED PV ANOMALY WILL
ROTATE ACROSS LOWER MICHIGAN LATE TUESDAY NIGHT/EARLY WEDNESDAY
FORCING A COLD FRONT THROUGH THE AREA PRIOR TO SUNRISE. COLD
ADVECTION WILL ENSURE ANOTHER DAY CHARACTERIZED BY DEEP BOUNDARY
LAYER MIXING PRODUCING PLENTY OF WIND AS H85 TEMPERATURES FALL TO -
8C BY WED AFTERNOON. STRATOCU DEVELOPMENT WILL BE PLENTIFUL AND, AS
A RESULT, FELT IT PRUDENT TO LEAN TOWARD THE COLDER GUIDANCE AS
INSOLATION WILL BE GREATLY LIMITED THROUGH THE DAY. HIGHS WILL
STRUGGLE TO 40F ALONG THE GLACIAL RIDGE WITH LOW TO MID 40S IN
DOWNSLOPE AREAS. WIDESPREAD WIND GUSTS THROUGH THE DAY WILL CONFINE
WIND CHILLS TO AROUND 30 DEGREES. THOUGH THE NAM REMAINS DRY, IT
WOULD CERTAINLY SEEM THAT DIURNAL SHOWERS WILL ONCE AGAIN BE
POSSIBLE. IT DOES APPEAR THAT THERE WILL BE A LACK OF FOCUSED
FORCING, BUT STILL HAVE TO RESPECT POTENTIAL GIVEN SYNOPTIC SCALE
ENVIRONMENT AND MODEST SBCAPE. MAINTAINED THE INHERITED CHC POP. IF
ANY MORE VIGOROUS SHOWERS DO DEVELOP WEDNESDAY, THE CORES WILL BE
CAPABLE OF PRODUCING SNOW GIVEN FREEZING LEVELS OF 1KFT AND SUB-
FREEZING SURFACE WET BULB TEMPS.

850MB TEMPERATURES ARE PROGGED TO BOTTOM OUT AT AN IMPRESSIVE -10C
DURING THE MORNING ON THURSDAY BEFORE UNDERGOING MODEST WARMING
THROUGH THE AFTERNOON AS AN EMBEDDED SHORTWAVE RIDGE PIVOTS THROUGH.
MINOR MID-LEVEL WARMING WILL MOST LIKELY BE RENDERED MOOT BY THE
VERY COLD THERMAL PROFILE THAT WILL BE IN PLACE FOR THE FIRST HALF
OF THE DAY, PARTICULARLY WITH EXPANSIVE DIURNAL STRATOCU EXPECTED
ONCE AGAIN. CURRENT FORECAST OF UPPER 40S MAY ULTIMATELY BE
OPTIMISTIC. MOISTURE QUALITY WILL DIMINISH AS THE LOW PULLS AWAY AND
THE GRADIENT WILL FINALLY EASE THURSDAY NIGHT SUPPORTING LOW
TEMPERATURES FALLING INTO AT LEAST THE UPPER 20S BY FRIDAY MORNING.

MARINE...

FRESH SOUTHWESTERLY WIND GUSTING AS HIGH AS 30 KNOTS WILL DEVELOP
TODAY AND PERSIST INTO THIS EVENING WITHIN ALL NEARSHORE ZONES.
SMALL CRAFT ADVISORIES THEREFORE REMAIN IN EFFECT. LIGHT TO MODERATE
WINDS WILL DOMINATE THE BULK OF THE OVERNIGHT HOURS BEFORE PICKING
UP AGAIN WEDNESDAY THROUGH THURSDAY NIGHT. ADDITIONAL SMALL CRAFT
ADVISORIES FOR THE NEARSHORE ZONES WILL BE LIKELY DURING THIS TIME.
IN ADDITION...COLD NORTHWEST FLOW WILL RESULT IN GUSTS TO NEAR GALES
THURSDAY INTO THURSDAY NIGHT. PERSISTENT OFFSHORE FETCH THROUGHOUT
THIS TIME WILL LIMIT SIGNIFICANT WAVE HEIGHTS TO 3 FEET OR LESS FOR
NEARSHORE AREAS.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR LHZ421-422-
     441>443.

LAKE ST CLAIR...SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR LEZ444.

&&

$$

AVIATION.....DRK
SHORT TERM...DRK
LONG TERM....JVC
MARINE.......JVC


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



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