Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 231627
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1227 PM EDT THU APR 23 2015


.AVIATION...

MOISTURE ROTATING AROUND A LOW PRESSURE SYSTEM OVER CANADA AND FLOW
OFF LAKE MICHIGAN WILL KEEP A LOW VFR STRATUS DECK IN PLACE OVER
SOUTHEAST MICHIGAN THROUGH MUCH OF TODAY. THIS DECK IS EXPECTED TO
GRADUALLY THIN THROUGH THE DAY BEFORE CLEARING FROM WEST TO EAST
BETWEEN 00Z TO 05Z. WINDS WILL REMAIN GUSTY INTO THE EARLY EVENING
FROM ABOUT 300-310 DEGREES...WITH GUSTS TO ABOUT 25 KNOTS.

FOR DTW...STRATUS DECK WILL GRADUALLY THIN THROUGH THE AFTERNOON AND
EVENING. CEILING HEIGHTS COULD POTENTIALLY LIFT ABOVE 5000 FEET
DURING THE LATE AFTERNOON/EARLY EVENING BUT CONFIDENCE IS NOT HIGH
ENOUGH TO TIME INTO 18Z TAFS. WILL AMEND IF TRENDS START TO SUPPORT
THIS IDEA. SKIES ARE EXPECTED TO CLEAR OVERNIGHT IN THE EVENING.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM CONFIDENCE IN CEILINGS AT OR BELOW 5000 FT THROUGH THIS
  AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 337 AM EDT THU APR 23 2015

SHORT TERM...TODAY AND TONIGHT

WELL THE DOMINATING BROAD UPPER LOW THATS BEEN THE WEATHER STORY FOR
A WEEK NOW WILL FINALLY BEGIN TO MOVE OFF TO THE EAST TODAY AS
RIDGING BUILDS ACROSS THE PLAINS. WE WILL NOT SEE MUCH RELIEF TODAY
AND TONIGHT FROM THIS SHIFT IN THE PATTERN AS WE WILL REMAIN IN NW
FLOW WITH A GOOD GRADIENT BETWEEN THE SLOWLY EXITING LOW AND
APPROACHING RIDGE. THE 500MB COLD POOL WILL SHIFT THE THE NE OVER
QUEBEC WITH JUST ONE ADDITIONAL NARROW FILAMENT OF COLD AIR SLIDING
THROUGH THIS AFTERNOON. MEANWHILE 850MB WILL HOLD FAIRLY STEADY
THROUGH THE DAY BUT WILL SHOW IMPROVEMENT OVERNIGHT FROM -10C TO -
5C. SO THERMALLY SPEAKING WE WILL HAVE YET ANOTHER DAY OF STEEP LL
LAPSE RATES BUT MIXING DEPTHS SHOULD BE LIMITED TO 5-6KFT. LOOKS
LIKE WE SHOULD HAVE A GOOD INVERSION SET UP EARLY IN THE DAY LEADING
TO PLENTY OF CLOUD COVER BUT A SHORTWAVE SLIDING THOUGH IN THE
EVENING WILL PUSH THE MOISTURE OUT OF THE AREA AND ALLOW SKIES TO
CLEAR OUT SOME. THIS WILL ALSO MARK THE BEGINNING OF THE WARM
ADVECTION ALOFT AS HEIGHTS SLOWLY START INCHING UPWARD. IN TERMS OF
PRECIPITATION...WE SHOULD STAY DRY TODAY...NOTING THE NARROW LAYER
OF MOISTURE PRESENT IN MODEL SOUNDINGS. CANNOT COMPLETELY RULE OUT
SOME FLURRIES FROM OVERACHIEVING CLOUDS DURING PEAK HEATING BUT
COVERAGE LOOKS TO BE SO MINIMAL WILL LEAVE OUT OF THE FORECAST. WITH
THE COLD AIR STILL LOCKED IN THE LOW LEVELS AND CLOUDS CLEARING OUT
TONIGHT...LOOKS LIKE A FAVORABLE RADIATIONAL COOLING SETUP. THIS
WILL DROP US TO NEAR RECORD LOWS IN THE MID 20S OUTSIDE OF THE
DETROIT METRO...WHICH ITSELF WILL FALL TO AROUND 30.

RECORD LOWS FOR APRIL 24TH:

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

LONG TERM...

RIDGE AMPLIFICATION IN ADVANCE OF THE TROUGH EJECTING OUT OF THE 4-
CORNERS REGION WILL SUPPORT DEEP LAYER SUBSIDENCE ACROSS ALL OF
SOUTHEAST MICHIGAN FOR THE BALANCE OF THE DAY FRIDAY. DEWPOINT
DEPRESSIONS BETWEEN 5-10KFT WILL BE 30C OR GREATER AND 15C OR SO AT
THE SURFACE DURING PEAK HEATING. NOTHING MORE THAN A PARTIAL
COVERAGE OF HIGH CLOUD IS EXPECTED AS UPPER MOISTURE CIRCULATING
OVER THE SIERRAS SPILLS ACROSS THE RIDGE AXIS LATE IN THE DAY. DEEP
MIXING AND WARMING THERMAL PROFILE WILL SUPPORT HIGHS REACHING 50 TO
55. DOMINANCE OF THE LAKE AGGREGATE DOWN LOW WILL MAINTAIN A WEAK
GRADIENT AND LIGHT WINDS. CLOUD FRACTION WILL BE KEY FOR FRIDAY
NIGHT`S LOW TEMPERATURES, BUT EVEN MODERATE RADIATING WILL SUPPORT
MID 20S ACROSS THE NORTH/LOW 30S SOUTH.

SATURDAY WILL FEATURE THE ONLY REASONABLY WELL-DEFINED CHANCE FOR
PRECIPITATION FOR THE NEXT SEVERAL DAYS. 00Z PROGS CONTINUE TO
CONFINE THE BULK OF FORCING ASSOCIATED WITH THE PASSING 4-CORNERS
WAVE TO THE SOUTH OF THE CWA. ONLY WEAK ISENTROPIC ASCENT IS SHOWN
TO REACH UP TO AROUND 8 MILE. SEVERAL HOURS OF WEAK FORCING WILL
REALLY STRUGGLE TO OVERCOME THE ENTRENCHED DRY AIRMASS. THE GFS
PRODUCES AN ABUNDANCE OF QPF OVER THE AREA WHICH NOT ONLY SEEMS
UNREALISTIC, BUT THE MODEL`S OWN SOUNDINGS ARE REALLY NOT CONVINCING
AND WOULD BE MUCH MORE SUPPORTIVE OF VIRGA. THE NAM/ECMWF APPEAR
MUCH MORE REASONABLE IN TERMS OF QPF PLACEMENT. NUDGED POPS UP TO 30
PERCENT FOR THE SOUTHERN TIER OF COUNTIES BUT STILL FAVOR
PREDOMINANTLY DRY FORECAST ELSEWHERE. INCREASING FLOW OUT OF THE
EASTERLY QUADRANT WILL LIMIT HIGH TEMPERATURE POTENTIAL ON
SATURDAY...PARTICULARLY BENEATH EXTENSIVE CLOUD COVER. ALTHOUGH MOST
LOCALES SHOULD REACH THE LOW 50S...ANY DURATION OF PRECIP REACHING
THE GROUND WOULD POTENTIALLY COOL SOUTHERN AREAS BY 5 TO 10 DEGREES.

MARINE...

FRESH NORTHWEST WINDS WILL PERSIST ACROSS THE WATERS TODAY WITH NEAR
GALES EXPECTED OVER NORTH-CENTRAL LAKE HURON. PERSISTENT NORTHWEST
FETCH WILL MAINTAIN ELEVATED SIGNIFICANT WAVE HEIGHTS OVER THE
EXPOSED NEARSHORE WATERS OF THE THUMB WHERE SMALL CRAFT ADVISORIES
REMAIN IN EFFECT. WINDS WILL GRADUALLY EASE THROUGH FRIDAY AND WILL
REMAIN LIGHT TO MODERATE THROUGH SATURDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR LHZ441-442.

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

$$

AVIATION.....HLO
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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