Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 171140
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
740 AM EDT FRI APR 17 2015


.AVIATION...

VFR THROUGH THE PERIOD WITH A WEAK PRESSURE GRADIENT SUPPORTING
LIGHT TO VARIABLE WINDS OUT OF THE WESTERLY QUADRANT. LOW COVERAGE
OF HIGH-BASED CU AROUND 7KFT MAY DEVELOP BY MID-AFTN.

//DTW THRESHOLD PROBABILITIES...

* NONE

&&

.PREV DISCUSSION...ISSUED 338 AM EDT FRI APR 17 2015

SHORT TERM...TODAY AND TONIGHT

DRY UPSTREAM AIRMASS NOTED ON 00Z DVN/GRB SOUNDINGS ADVECTING INTO
THE AREA THIS MORNING WITHIN WEAKLY CONFLUENT MID-LEVEL FLOW REGIME.
MSLP PATTERN IS MODELED TO BE RATHER NONDESCRIPT FOR MOST OF THE DAY
AND LARGELY DOMINATED BY LAKE INFLUENCES. AS SUCH, THE GRADIENT
SHOULD BE SUFFICIENTLY WEAK FOR LAKE HURON HIGH PRESSURE TO PUSH
INLAND OVER THE THUMB AND CAP HIGH TEMPERATURES IN THE LOW TO MID
60S. ELSEWHERE, POTENTIAL FOR SIGNIFICANT BOUNDARY LAYER GROWTH TO
800MB OR HIGHER AND A RELATIVELY LOW CLOUD FRACTION WILL SET THE
STAGE FOR HIGHS EASILY REACHING 70 DEGREES. MAIN CONCERN WITH REGARD
TO THE TEMPERATURE FORECAST WILL BE THE DEGREE OF CONVECTIVE DEBRIS
OVER THE PLAINS THAT ADVECTS ACROSS SE MICHIGAN SKIES 18-00Z. HIGH
CIRRUS IS LIKELY DURING THIS TIME BUT NOT OVERLY CONCERNED ABOUT
IMPACTS ON TEMPS GIVEN THE LACK OF ORGANIZED STEERING FLOW DIRECTED
FROM THE SOURCE REGION TO LOWER MICHIGAN. ATTM, EXPECTING A
RELATIVELY LOW COVERAGE OF DEBRIS. IN ADDITION, A LOW COVERAGE OF
HIGH-BASED CU WILL BE POSSIBLE BY MID/LATE AFTN AS MID-LEVEL
MOISTURE NOTED ON 00Z MPX SOUNDING IS DRAWN EAST WITHIN DEVELOPING
WESTERLY FLOW. AS NOTED ON PROGGED AREA SOUNDINGS FROM THE NAM, MOST
MOISTURE CAN BE EXPECTED TO MIX OUT, LEAVING LITTLE TO WORK WITH IN
TERMS OF SURFACE BASED CU.

BACKDOOR COLD FRONT WILL BEGIN TO MAKE INROADS INTO THE NW PORTION
OF THE CWA DURING THE PREDAWN HOURS SATURDAY MORNING. WEAK FORCING
AND DRY COLUMN WILL LIMIT NOTEWORTHY SENSIBLE WX, THOUGH ELEVATED
PRESSURE GRADIENT WILL LIMIT COOLING POTENTIAL. OVERNIGHT LOWS WILL
STRUGGLE TO FALL MUCH BELOW 50 DEGREES.

LONG TERM...SATURDAY THROUGH THURSDAY

THE LONGWAVE PATTERN BREAKS DOWN THIS WEEKEND LEADING TO A FAIRLY
ACTIVE WEATHER PERIOD SUNDAY INTO MIDWEEK WITH A COOL DOWN ON THE
WAY AS WELL. THE LONGWAVE PATTERN BEGINS SATURDAY WITH A SPLIT FLOW
REGIME. THE NORTHERN STREAM FEATURING LOW AMPLITUDE NORTHWESTERLY
FLOW WITH THE SOUTHERN STREAM OVER MEXICO AND THE GULF COAST
STATES...BLOCKED FROM ANY NORTHERN PROGRESS BY A LARGE CUTOFF LOW
OVER THE FOUR CORNERS. THIS CHANGES SATURDAY NIGHT AND INTO SUNDAY
AS A FAIRLY POTENT SHORTWAVE IN THE NORTHERN STREAM DIGS INTO THE
NORTHERN CONUS AND PHASES WITH THE CUTOFF LOW. THERE WILL ALSO BE
FAIRLY COMPLEX INTERACTION AT THE SFC OF LOW PRESSURE FROM THE
NORTHERN STREAM WAVE ABSORBING A FEW SHORTWAVES LIFTING NORTH AROUND
THE CUTOFF LOW. THE OVERALL SFC LOW LOOKS TO DEEPEN AS IT TRACKS
THROUGH THE NORTHERN GREAT LAKES. A WARM FRONT WILL LIFT NORTH
THROUGH SOUTHERN MI ON SUNDAY BRINGING WIDESPREAD SHOWERS TO THE
AREA BY EVENING. MODEL SOUNDINGS SUGGESTS THE LAPSE RATES WILL BE
VERY WEAK AS DEEP SOUTHERLY FLOW KEEPS THE MID LEVELS MILD...AND
MODELS HAVE ELIMINATED ANY MENTION OF INSTABILITY AS THE WARM FRONT
LIFTS THROUGH THUS PULLED MENTION OF THUNDER SUNDAY AND SUNDAY
NIGHT. PWATS WILL BE DECENT...NEAR 1.5 INCHES...THUS WE SHOULD GET
SOME GOOD SOAKING RAINS FROM THIS.

A COLD FRONT WILL THEN RACE THROUGH ON MONDAY KEEPING THE LIKELY
POPS IN THE FORECAST WITH A MENTION OF THUNDER. SHOWALTER INDICES GO
NEGATIVE WITH SEVERAL HUNDRED J/KG OF CAPE AND DECENT MID LEVEL
LAPSE RATES AHEAD OF THE FRONT. THE FRONT LOOKS TO MOVE THROUGH IN
THE AFTERNOON ALLOWING ONE MORE DAY WITH TEMPS IN THE 60S BEFORE THE
MID LEVEL COLD POOL...500MB TEMPS AROUND -30C AND 850MB TEMPS DOWN
TO -8C...BEGINS TO ADVECT IN WITH THE DEVELOPING WESTERLIES. THE
COLD POOL AND SEVERAL LOBES OF VORTICITY ROTATING AROUND THE
MID/UPPER LEVEL LOW STALLING OVER THE GREAT LAKES WILL KEEP A CHANCE
POP MENTION THROUGH MID WEEK. HIGHS WILL THEN REMAIN IN THE LOW 50S
WITH LOWS DIPPING INTO THE LOW 30S AT TIME THROUGH THE END OF THE
WEEK. THERE WILL BE SOME OPPORTUNITIES FOR LIGHT NOCTURNAL SNOW
SHOWERS...BUT LOW MOISTURE LEVELS WILL PREVENT ANYTHING SUBSTANTIAL
FROM FALLING.

MARINE...

MARINE CONDITIONS WILL BE FAIRLY CALM TODAY AS WINDS ARE LIGHT WITH
HIGH PRESSURE OVERHEAD. WINDS BECOME SLIGHTLY AGITATED TONIGHT AS A
CLIPPER DIVING ACROSS THE NORTHERN LAKES DROPS A COLD FRONT THROUGH
LAKE HURON. WINDS LOOK TO BRIEFLY GUST TO AROUND 20 KNOTS FROM THE
NORTHWEST BEHIND THE FRONT SATURDAY MORNING BUT HIGH PRESSURE
FILLING IN BEHIND THE FRONT WITH THE LOSS OF DAYTIME HEATING SHOULD
ALLOW WINDS TO DROP BACK OFF SATURDAY NIGHT. THE COLD FRONT WILL
RETURN NORTHWARD AS A WARM FRONT SUNDAY ASSOCIATED WITH A LARGE LOW
PRESSURE SYSTEM DEVELOPING OVER THE NORTHERN PLAINS. THIS WILL CAUSE
WINDS TO RAMP UP AGAIN AS THEY BECOME SOUTHEASTERLY BEHIND THE
FRONT.

&&

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

$$

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


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


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