Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 201718
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
118 PM EDT MON APR 20 2015

.AVIATION...

DISORGANIZED SHOWERS WORKING THROUGH SOUTHEAST MICHIGAN THIS
AFTERNOON AHEAD OF A COLD FRONT... WITH STILL LOW CHANCE OF ISOLATED
THUNDERSTORM DEVELOPING. WINDS WILL BE GUSTING BETWEEN 30 TO 40
KNOTS WITHIN ANY OF THE STRONGER SHOWERS. MVFR/LOW VFR CEILINGS
WILL HOLD INTO THE EARLY EVENING HOURS...AND STILL COULD BE
ISOLATED-SCATTERED LIGHT RAIN SHOWERS LEFT OVER...BUT WINDS
SHIFTING A BIT MORE SOUTHWEST-WEST BEHIND THE COLD FRONT WILL
ALLOW FOR A DRYING TREND. CLOUD COVER TONIGHT IS SOMEWHAT
UNCERTAIN AS COLD CYCLONIC FLOW OFF LAKE MICHIGAN MAY BE
SUFFICIENT TO MAINTAIN THE LOW VFR/BORDERLINE MVFR CEILINGS. IF
SKIES DO SCATTER OUT TONIGHT...HIGHER CONFIDENCE IN LOW VFR
CEILINGS REDEVELOPING TOMORROW MORNING...WITH POSSIBLY ENOUGH
INSTABILITY TO GENERATE SCATTERED SHOWERS DURING THE DAY. IT WILL
BE WINDY...ESPECIALLY UNDERNEATH ANY SHOWERS...AS WINDS COULD GUST
IN EXCESS OF 35 KNOTS.

FOR DTW...SHOWERS WILL BE CLEARING THE TERMINAL AT THE START OF THE
TAF PERIOD. THERE IS A CHANCE OF A COUPLE LIGHT RAIN SHOWERS EARLY
THIS EVENING...BUT AREA COVERAGE PRECLUDED THE MENTION.

//DTW THRESHOLD PROBABILITIES...

* HIGH CONFIDENCE IN CIGS AOB 5KFT THROUGH EARLY EARLY EVENING...THEN
  MEDIUM CONFIDENCE.

&&

.PREV DISCUSSION...ISSUED 353 AM EDT MON APR 20 2015

SHORT TERM...TODAY AND TONIGHT

THE WELL ADVERTISED STRONG LOW PRESSURE SYSTEM HAS LIFTED INTO SW
LOWER MI AS OF 07Z THIS MORNING. IT WILL CONTINUE NORTHWARD REACHING
ONTARIO BY 00Z THIS EVENING. ALTHOUGH THE MAIN WING OF ISENTROPIC
ASCENT NORTH OF THE WARM FRONT AND COLOCATED RIBBON OF ENHANCED
MOISTURE IS NORTH OF SE MI...ELEVATED MOISTURE VALUES WILL LINGER
INTO THE EARLY AFTERNOON AS IT APPEARS THE EASTERN PORTION OF THE
CWA SHOULD RESIDE IN THE WARM SECTOR FOR SEVERAL HOURS. HOW THE
AFTERNOON WILL SHAPE UP WILL DEPEND ON A COMPACT SHORTWAVE ROTATING
AROUND THE BASE THE MID LEVEL TROUGH WHICH IS OVER THE UPPER
MISSISSIPPI VALLEY AND WILL SWING THROUGH THE OHIO VALLEY LATER
TODAY. THIS SHORTWAVE IS FORECAST TO LIFT SOMEWHERE THROUGH SE LOWER
MI OR WESTERN LAKE ERIE. THIS HAS BIG IMPLICATIONS ON THE FORECAST
DUE TO THE TIMING OF THE COLD FRONT THIS SECONDARY LOW WILL PULL
THROUGH THE AREA. CURRENTLY MODELS HAVE THE TIMING FAIRLY WELL
PEGGED DOWN TO THE 18-21Z TIMEFRAME. THIS WOULD ALLOW ENOUGH DIURNAL
HEATING TO POTENTIALLY BUILD UP A FEW HUNDRED J/KG OF CAPE AHEAD OF
THE APPROACHING COLD FRONT WITH VERY FAVORABLE LL LAPSE RATES AND
DEEP LAYER OF STRONG SW FLOW WITH SPEED SHEAR SETTING UP IN THE WARM
SECTOR. SPC HAS EXPANDED THE MARGINAL AREA TO INCLUDE A SLIVER OF
EXTREME EASTERN LOWER MI...EAST OF A LINE FROM ABOUT ADRIAN TO PORT
HURON. THERE IS CONCERN AS TO WHETHER THIS WILL ACTUALLY CONCERN AS
THE NAM/GEMREG/HRRR/ETC... SUGGEST THAT THE LL JET MAX WILL DRIFT
EASTWARD AND IGNITE THE COLD FRONT JUST SE OF MI LEAVING US WITH
ONLY RESIDUAL SHOWERS AND ISOLATED RUMBLES OF THUNDER AS THE FRONTAL
BOUNDARIES OCCLUDE AND SLIDE THROUGH THE AREA WITH THE TRIPLE POINT
STAYING SOUTH. AFTER SEVERAL MODEL RUNS TRENDING WESTWARD...THE
RECENT RUNS ARE STALLING IF NOT SHIFTING SLIGHTLY FURTHER EAST WHICH
LENDS CREDENCE THUNDERSTORM POTENTIAL DOUBTS. OVERALL THINK WE WILL
GET BRUSHED WITH SOME THUNDERSTORMS BUT THE BETTER ORGANIZED STORMS
WILL LIKELY STAY OUT OF THE AREA.

IN ADDITION TO COLD FRONTAL THUNDERSTORM POTENTIAL...WINDS WILL BE
QUITE GUSTY THROUGH THE DAY. THE DEEP MIXED LAYER WITH 900MB WINDS
MAKING A RUN AT 40 KNOTS WILL KEEP SW SFC FLOW AROUND 20KT WITH
GUSTS APPROACHING 35 KNOTS...ESPECIALLY EARLY THIS AFTERNOON EAST OF
THE FRONT.

AS THE FOR THE REST OF THE EVENING AND INTO THE OVERNIGHT...THE COLD
FRONT...OR OCCLUDED FRONT...WILL USHER IN MUCH COOLER AIR WHILE
KEEPING THE MIXED LAYER IN TACK THROUGH THE NIGHT WHICH WILL IN TURN
KEEP WINDS ELEVATED. THE ENHANCED MOISTURE PLUME WILL BE SHUNTED
EAST BUT SCATTERED SHOWERS WILL LINGER THROUGH THE OVERNIGHT AS CAA
RESULTS IN MORE FAVORABLE MID LEVEL LAPSE RATES. THE MIXING AND
CLOUD COVER WILL KEEP MIN TEMPS UP AROUND 40 FOR MOST LOCATIONS.

LONG TERM...

CLOSED UPPER LOW WILL REMAIN PARKED OVERHEAD THROUGH MIDWEEK.
EMBEDDED SHORTWAVES WILL BRING EPISODIC SHOWER ACTIVITY, THE TIMING
OF WHICH WILL REMAIN INHERENTLY ILL-DEFINED OUTSIDE OF 48 HOURS. A
COLD COLUMN AND CLOUD COVER WILL KEEP TEMPERATURES SOLIDLY BELOW
NORMAL.

LOW CENTER WILL MEANDER FROM INTERNATIONAL FALLS THIS AFTN TO THE
STRAITS BY MIDDAY TUESDAY. APRIL INSOLATION AND VERY COLD H5 TEMPS
WITHIN THE MID-LEVEL COLD POOL OF -30C WILL RESULT IN A DEEP MIXED
LAYER PERHAPS APPROACHING 600MB. ROBUST WSW WIND FIELD WITHIN THIS
VERY WELL-MIXED ENVIRONMENT WILL SET THE STAGE FOR WIDESPREAD WIND
GUSTS IN EXCESS OF 30 KNOTS FOR THE BALANCE OF TUESDAY AFTERNOON.
THE TRADE-OFF OF THE DEEP MIXING WILL BE TEMPERATURES REACHING THE
LOW 50S IN SPITE OF SUB-ZERO 850MB TEMPERATURES. SUFFICIENT MID-
LEVEL MOISTURE RESIDING IN THE 800-600MB LAYER WILL RESULT IN, AT
MINIMUM, WIDESPREAD AFTERNOON CLOUDS. MODELS ALSO POINT TO MID-
MORNING SHOWER GENERATION AS WELL, GIVEN A FEW HUNDRED J/KG CAPE
AVAILABLE FOR SURFACE BASED PARCELS. PASSING ELONGATED H4 PV ANOMALY
WILL PROVIDE BROAD SCALE ASCENT WHILE INLAND TROUGHING HELPS IS
NOTED TO HELP FOCUS ACTIVITY ALONG/NORTH OF M59. CLASSIC INVERTED V
THERMODYNAMIC PROFILE WILL ALLOW SHOWERS TO POTENTIALLY PRODUCE WIND
GUSTS OF 45 KTS.

LOSS OF DIURNAL HEATING WILL MEAN AN END TO SHOWERS TUESDAY EVENING.
THE GRADIENT WILL REMAIN ELEVATED AS BROAD LOW PRESSURE REMAINS
CENTERED OVER THE GREAT LAKES. COMBINED WITH CLOUDS, LOW
TEMPERATURES WILL BE COLD - BUT NOT AS COLD AS THEY COULD BE GIVEN
THE AIRMASS. PREFER NAM12 DEPICTION OF 34-38F TUESDAY NIGHT.

LITTLE CHANGE IN SYNOPTIC SCALE REGIME FOR WEDNESDAY, MEANING
CONTINUED DIURNALLY DRIVEN BOUNDARY LAYER CLOUD COVER AND AFTERNOON
WIND GUSTS IN THE 25-30 KT RANGE FROM THE WEST. BETTER LOW-LEVEL
MOISTURE QUALITY WILL BE OFFSET BY LACK OF FOCUSED FORCING, BUT HAVE
TO RESPECT POTENTIAL WITH A LOW END CHC POP. THE MOST NOTEWORTHY
CHANGE BY WED WILL BE POSITION OF THE THERMAL TROUGH OVERHEAD AS H85
TEMPERATURES FALL TO -6 TO -7C SUPPORTING HIGHS IN THE MID 40S AND
WIND CHILLS IN THE MID 30S.

MARINE...

FRESH TO LOCALLY STRONG SOUTHEAST WINDS WILL VEER TO THE SOUTHWEST
THROUGH TODAY. A FEW GUSTS TO NEAR GALES WILL BE POSSIBLE...MAINLY
IN NEARSHORE ZONES INCLUDING LAKE SAINT CLAIR AND ERIE. SMALL CRAFT
ADVISORIES THEREFORE REMAIN IN EFFECT FOR ALL NEARSHORE ZONES.
BREEZY WESTERLY WINDS WILL PERSIST THROUGH MIDWEEK AS CONDITIONS
REMAIN RELATIVELY STATIC WITH LOW PRESSURE PARKED OVER THE GREAT
LAKES. ADDITIONAL SMALL CRAFT ADVISORIES FOR WIND WILL LIKELY BE
NEEDED ON TUESDAY AND POSSIBLY ONCE MORE ON WEDNESDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR LHZ421-422-
     441>443.

LAKE ST CLAIR...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR LEZ444.

&&

$$

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


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