Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 181947
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
347 PM EDT SAT OCT 18 2014

.SHORT TERM... AFTERNOON THROUGH TONIGHT

GUSTY NORTHWEST WIND CONTINUES TO CARRY COOLER AIR INTO SE MICHIGAN
DURING THE MID AND LATE AFTERNOON. THIS WILL SET THE STAGE FOR A
FROSTY NIGHT AS THE WIND DROPS OFF AND MIN TEMPS DROP BELOW
FREEZING. READINGS AS LOW AS THE UPPER 20S WILL BE POSSIBLE THROUGH
INTERIOR LOWER DEPENDING ON CLOUD COVER.

MODEL FORECAST SOUNDINGS CAPTURE THE AFTERNOON BOUNDARY LAYER
BECOMING INCREASINGLY SHALLOW AND MORE STABLE TOWARD EVENING...A
TREND ILLUSTRATED IN THE 12Z OBSERVED SOUNDINGS BETWEEN APX AND
DTX...AND REFLECTED IN RADAR TREND DURING THE AFTERNOON. FROM
THERE...IT IS MORE DIFFICULT TO GAGE THE MODEL SOUNDING QUALITY
THROUGH THE REST OF THE NIGHT. THE MAIN STICKING POINT LIES WITH THE
AMOUNT OF MOISTURE AT THE BASE OF THE STRENGTHENING SUBSIDENCE
INVERSION THAT DROPS AS LOW AS 900 MB BY 12Z SUNDAY. THERE IS ABOUT
AN EVEN SPLIT BETWEEN THE CLOUDIER NAM AND RAP MODELS VS THE MORE
OPTIMISTIC GFS AND SREF MEAN. OBSERVATIONAL EVIDENCE SUPPORTS THE
LATTER AS DRIER AIR MAKES INROADS THROUGH THE NORTHERN GREAT LAKES.
SATELLITE IMAGERY INDICATES UPSTREAM CLOUDS TAKING ON A CONVINCING
LAKE INFLUENCE AND DIURNAL DEPENDENCY OVER LAND WHICH WILL RESULT IN
NOCTURNAL STRATOCU REMAINING CLOSER TO THE SHORELINES. NEUTRAL
NORTH-NORTHWEST LOW LEVEL FLOW ALSO FAVORS LESS CLOUDS IN OUR AREA
WITH A DRY DOWNSLOPE TRAJECTORY FROM NORTHERN LOWER INTO THE SAGINAW
VALLEY AND OVER THE REST OF SE MICHIGAN DURING THE NIGHT. THE
EXCEPTION COULD BE OVER THE NORTHERN/EASTERN THUMB WHERE A LONGER
OVER WATER FETCH WILL BE POSSIBLE FROM ABOUT STURGEON POINT
SOUTHWARD WHICH COULD MAINTAIN GREATER STRATOCU COVERAGE THERE
THROUGH SUNRISE SUNDAY.

&&

.LONG TERM...

MODEST HEIGHT RISES TOMORROW WITH SOME SEMBLANCE OF WARM FRONT
LIFTING NORTH THROUGH LOWER MICHIGAN. UNCERTAINTY IS WITH THE AMOUNT
OF LOW LEVEL WARMING AND SCOURING OUT OF REMNANT LOW LEVEL
MOISTURE...AS NAM SOUNDINGS/925 MB RH FIELD STILL PAINTS A POTENTIAL
CLOUD HINDRANCE...AND A SOMEWHAT CONSERVATIVE APPROACH IN MAXES WILL
BE TAKEN OFF THE COLD START AND WITH 925 MB TEMPS FORECASTED TO ONLY
RISE TO 4 C DURING PEAK HEATING...WORTHY OF MAXES AROUND 50/LOWER
50S DE AS HIGH CLOUDS ALSO EXPECTED TO RAMP UP DURING THE AFTERNOON
HOURS.

UPPER LEVEL ENERGY OVER WESTERN CANADA WILL BE CARVING OUT ANOTHER
UPPER LEVEL LOW/TROUGH OVER THE GREAT LAKES/OHIO VALLEY AS WE HEAD
INTO MONDAY. THE RATE OF AMPLIFICATION IS A BIT UNCERTAIN...BUT
850-700 MB THETA-E RIDGE/MOISTURE AXIS LOOKS PRETTY GOOD...ARRIVING
DURING THE FIRST HALF OF MONDAY...WITH HIGH CHANCE/LOW LIKELY POPS
SEEMING APPROPRIATE. 500 MB COLD CORE (-23 TO-25 C) TO TRAVERSE
ACROSS THE NORTHERN GREAT LAKES...AND LI`S ARE FORECASTED TO DROP
TOWARD ZERO...WITH AROUND 500 J/KG OF CAPE (PER NAM)...AND AN
ISOLATED THUNDERSTORM CAN NOT BE RULED OUT. UPPER LEVEL TROUGH AXIS
WILL BE SLOW TO CLEAR SOUTHEAST MICHIGAN TUESDAY EVENING/NIGHT AND
CONTINUED LOW CHANCE POPS IN CASE AMPLIFICATION IS FASTER...YIELDING
SLIGHTLY SLOWER FRONTAL PASSAGE/DRYING OUT PROCESS.

UPPER RIDGE WILL BUILD INTO THE UPPER MIDWEST IN THE WAKE OF THE
SLOWLY-DEPARTING UPPER TROUGH WHICH WILL CUT OFF OVER THE
MID-ATLANTIC/NORTHEAST WEDNESDAY AND BEYOND. THIS WILL LEAD TO
MAINLY DRY CONDITIONS AND GRADUALLY MODERATING TEMPERATURES...WITH A
RETURN TO HIGHS IN THE 60S POSSIBLE BY FRIDAY INTO NEXT WEEKEND.

&&

.MARINE...

OBSERVATIONS LATE THIS AFTERNOON SHOW WIND GUSTS BELOW GALE FORCE
AND WILL DROP THE GALE WARNINGS WITH THIS FORECAST PACKAGE...AS
PRESSURE GRADIENT SLACKENS AND THE COLD ADVECTION DIMINISHES INTO
TONIGHT. MUCH LIGHTER WINDS ARE EXPECTED TOMORROW AS SURFACE RIDGE
AXIS SLIDES THROUGH THE CENTRAL GREAT LAKES...LEADING TO A SHIFT IN
THE WINDS OUT OF THE SOUTHWEST...AHEAD OF A COLD FRONT...WHICH WILL
PASS THROUGH LATE MONDAY. SUSTAINED WINDS ARE EXPECTED TO PEAK OUT
AROUND 20 KNOTS SUNDAY NIGHT AHEAD OF THE FRONT...WITH SCATTERED TO
NUMEROUS SHOWERS DEVELOPING. A STRONG HIGH BUILDING OVER ONTARIO
MONDAY NIGHT INTO TUESDAY WILL TRANSLATE TO STRONG NORTHEAST WINDS
OVER LAKE HURON...WITH GUSTS TO 30 KNOTS POSSIBLE OVER THE CENTRAL
PORTION OF THE LAKE...WHERE THE FETCH WILL BE GREATEST. HIGHER WAVES
WILL IMPACT NEARSHORE WATERS WITH THE ONSHORE FLOW...AND SMALL CRAFT
ADVISORIES WILL LIKELY BE NEEDED.

&&

.AVIATION...ISSUED 103 PM EDT SAT OCT 18 2014

//DISCUSSION...

NORTHWEST FLOW CARRYING IN COLDER AIR WILL CONTINUE TO SUPPLY CLOUD
COVER OVER SE MICHIGAN DURING THE AFTERNOON INTO THE EVENING.
STUBBORN MVFR CEILING REMAINS EXPECTED TO MIX INTO THE LOWER END OF
VFR BELOW 5000 FT AND THEN LINGER A LITTLE LONGER INTO THE
EVENING...ESPECIALLY THROUGH THE DTW TERMINAL CORRIDOR. UPSTREAM
OBSERVATIONS INDICATE SOME DRYING AND MIXING OCCURRING OVER THE
NORTHERN GREAT LAKES WHICH STILL SUPPORTS A CLEARING TREND OVER SE
MICHIGAN FROM LATE EVENING THROUGH THE OVERNIGHT. ONE THING TO
MONITOR WILL BE COVERAGE OF LAKE INDUCED STRATOCU AND/OR TRAPPING OF
STRATOCU BUT LOW LEVEL WIND FROM ABOUT 320 IS TYPICALLY A DRY
TRAJECTORY INTO OUR AREA FROM NORTHERN LOWER. CLOUDS INDUCED BY LAKE
MICHIGAN MAY BECOME MORE RELEVANT DURING SUNDAY MORNING AS THE LOW
LEVEL WIND BACKS TOWARD THE WEST.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET THROUGH EVENING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
     HURON INCLUDING SAGINAW BAY...UNTIL 4 AM SUNDAY.

LAKE ST CLAIR...NONE.

MI WATERS OF LAKE ERIE...NONE.

&&

$$

SHORT TERM...BT
LONG TERM....SF/DT
MARINE.......SF
AVIATION.....BT


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






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