Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 230455
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1155 PM EST THU JAN 22 2015

.AVIATION...

A REDUCTION IN THE COVERAGE OF STRATUS FROM THE NORTH WILL PROVIDE
POINTS FROM AT LEAST PTK NORTHWARD WITH A PERIOD OF VFR/CLEAR SKY
DURING THE EARLY MORNING PERIOD.  A HIGHER DEGREE OF CLOUD COVER MAY
EXIST ACROSS THE DETROIT CORRIDOR AS SOUTHWEST FLOW PROVIDES SOME
RENEWED MOISTURE ADVECTION.  THIS PROCESS WILL WORK TOWARD EXPANDING
THE STRATUS BACK NORTHWARD INTO FRIDAY.  CONFIDENCE REMAINS ON THE
LOWER SIDE WITH BOTH THE OVERALL COVERAGE AND TIMING ON FRIDAY.

FOR DTW...METRO AIRSPACE CURRENTLY RESIDING ALONG THE FRINGE OF THE
EXISTING MVFR STRATUS DECK.  LOWER CONFIDENCE GOING FORWARD GIVEN
RECENT VARIABILITY IN POSITIONING OF THIS CLOUD COVER AS THE FLOW
DEEPENS OUT OF THE SOUTHWEST.  RECENT TRENDS WOULD SUGGEST THE
POTENTIAL IS HIGH ENOUGH TO INCLUDE A PERIOD OF VFR EARLY THIS
MORNING.

//DTW THRESHOLD PROBABILITIES...

* LOW FOR CEILING BELOW 5000 FEET TONIGHT AND FRIDAY.

&&

.PREV DISCUSSION...ISSUED 347 PM EST THU JAN 22 2015

SHORT TERM... THROUGH TONIGHT

MAIN FORECAST CHALLENGE IS WITH CLOUD COVER OVERNIGHT. SPLIT FLOW
PATTERN IN PLACE OVER NORTH AMERICA WITH SOUTHEAST MICHIGAN
POSITIONED IN THE POLEWARD ENTRANCE REGION OF A STRONG JET AXIS OVER
THE OHIO VALLEY. THIS WILL PROMOTE ACTIVE SUBSIDENCE THROUGH THE
PERIOD...AS EVIDENCED BY SPRAWLING SURFACE HIGH OVER THE WESTERN
GREAT LAKES. EXTENSIVE STRATUS DECK OVER THE UPPER MIDWEST HAS SHOWN
GOOD SIGNS OF CLEARING OVER WISCONSIN/UPPER MICHIGAN WITH BACK EDGE
OF THE STRATUS WORKING INTO NORTHERN MICHIGAN AND ACROSS LAKE
MICHIGAN. LINEAR EXTRAPOLATION OF THIS CLEARING WOULD WORK IT INTO
SOUTHEAST MICHIGAN AFTER 00Z. HOWEVER...CLIMATOLOGY IS A FACTOR
WORKING AGAINST CLEARING. NAM AND RAP RH PROGS ARE NOT MUCH HELP
HERE AS THEY DID NOT SHOW THE AREA OF CLEARING TO OUR WEST...HOWEVER
THEY DO SHOW POCKETS OF CLEARING OVER THE UPPER MIDWEST OVERNIGHT.
THE UPSHOT IS...TRENDED A BIT MORE OPTIMISTIC WITH CLOUD COVER THAN
PREVIOUS FORECAST...BUT KEPT PARTLY TO MOSTLY CLOUDY SKIES IN ORDER
THAT THE FORECAST NOT BOUNCE AROUND TOO MUCH AS CONFIDENCE IN
CLEARING SKIES IS STILL NOT HIGH.

CLOUD COVER WILL IMPACT LOW TEMPS AS WELL. SIDED WITH THE WARMER MET
MOS. SOME ROOM FOR TEMPS TO DROP BELOW FORECAST LOWS IF CLEARING IS
REALIZED...HOWEVER STILL THINK MAV MOS IS A BIT TOO LOW AS IT IS
UNDERDOING SURFACE DEWPOINTS. ALSO...INCREASING SW GRADIENT FLOW
TOWARD THE END OF THE FORECAST PERIOD SHOULD LIMIT POTENTIAL TEMP
DROP OVER NORTHERN PARTS OF THE FORECAST AREA. THE INCREASED
PRESSURE GRADIENT WILL OCCUR AS AN EXPANSIVE CYCLONE DEEPENS OVER
NORTHERN ONTARIO.

LONG TERM...FRIDAY THROUGH WEDNESDAY

UPPER LEVEL PATTERN BECOMES QUITE COMPLEX TO END THE WEEK. AMPLIFIED
RIDGING OVER THE WESTERN CONUS GET FOLDED OVER IN THE GREAT LAKES
FRIDAY WHICH TRIES TO PINCH OFF THE BASE OF THE TROUGH OVER THE FOUR
CORNERS. ENERGETIC SOUTHERN STREAM KEEPS IT FAIRLY PROGRESSIVE
PREVENTING A TRUE CUTOFF LOW FROM FORMING AS IT TRACKS ACROSS THE
SOUTHERN STATES. INCOMING NORTHERN STREAM ENERGY EVENTUALLY CARVES
OUT ANOTHER DOMINATE TROUGH BY THE END OF THE WEEKEND. AT THE
SFC...HIGH PRESSURE STRUNG OUT FROM THE CENTRAL PLAINS THROUGH THE
OHIO VALLEY AND TO THE EAST COAST ON FRIDAY WILL GET COMPRESSED
BETWEEN NORTHERN STREAM LOW TRACKING THROUGH NORTHERN ONTARIO AND
DEVELOPING SOUTHERN STREAM LOW UNDER THE AFOREMENTIONED PINCHED OFF
TROUGH. THE HIGH WILL MOVE OFF TO THE EAST BY SATURDAY AS THE
SYSTEMS DRAW NEARER EACH OTHER WITH THE ATTEMPTED PHASING OF THE
JETS. OVERALL THIS YIELDS A SOMEWHAT LOWER CONFIDENCE FORECAST AS
SLIGHT DIFFERENCES IN TIMING OF PHASING JETS OR LOCATION OF THE SFC
FEATURES USUALLY LEADS TO JUMPS IN THE FORECAST. LUCKILY IN THIS
CASE...THE PHASING IS ADVERTISED FAR ENOUGH DOWN STREAM TO NEGATE SOME
OF THE TYPICAL CONCERNS.

FOR FRIDAY...WITH HIGH PRESSURE LOCKED AT THE SFC...THE LOW PASSING
THROUGH ONTARIO WILL DROP A COLD FRONT/TROUGH THROUGH LOWER MI IN
THE AFTERNOON. WITH THE HIGH SLIDING TO OUR EAST...WINDS WILL BECOME
SOUTHWESTERLY IN THE MORNING AHEAD OF THE TROUGH AS THE RIDGE AND
TROUGH TIGHTEN THE PRESSURE GRADIENT OVER THE STATE. THESE SW WINDS
WILL BRING THE NOSE OF A THERMAL RIDGE INTO THE AREA THROUGH THE
AFTERNOON. THE WARM AIR WILL STEEPEN THE INVERSION BETWEEN 950-900MB
AS IT WARMS THE LAYER BETWEEN 700 AND 900MB. SO LOOK FOR ELEVATED
WINDS AROUND 15-20MPH WITH GUSTS TO AROUND 25MPH PEAKING IN THE
AFTERNOON. THE STOUT INVERSION WILL PREVENT BETTER MIXING FROM
BRINGING SOME OF THE HIGHER WINDS RIGHT ABOVE THE INVERSION DOWN TO
THE SFC.

THE WEAKENING COLD FRONT WILL ENTER CENTRAL MI AROUND MIDNIGHT WHICH
WILL BRING A CHANCE OF SNOW SHOWERS TO THE SAGINAW VALLEY AND
NORTHERN THUMB. MOISTURE POOLING AHEAD OF THE TROUGH IS DECENT WITH
PWATS INCREASING FROM UNDER 0.2 TO AROUND 0.5 INCHES. THE RIBBON OF
THETA E ALONG THE FRONT IS VERY NARROW WITH A GOOD GRADIENT ON THE
LEAD EDGE INITIALLY...BUT WEAKENING AS IT TRACKS THROUGH SOUTHERN
MI. SEE NO REASON TO DEVIATE FROM THE CHANCE/SLIGHT CHANCE POPS
RIGHT NOW FOR FRIDAY NIGHT. SEVERAL OTHER SMALL WAVES ARE ADVERTISED
TO SHOOT THROUGH THE DEVELOPING NW FLOW KEEPING LOW CHANCE POPS
THROUGH THE DAY SATURDAY. A SECOND...STRONGER COLD FRONT WILL DROP
INTO LOWER MI SATURDAY NIGHT STALLING ACROSS THE AREA AS THE
TRANSITION TO NW FLOW CONTINUES. WITH BL MOISTURE STILL PREVALENT
AND THE FRONT DRAPED ACROSS THE REGION WITH DECENT LAPSE RATES
THROUGH 800MB...WILL HOLD ONTO SOME LOW POP SNOW SHOWER MENTION
THROUGH SAT NIGHT.

CLIPPER DROPS OUT OF MANITOBA AND BEGINS INFLUENCING CONDITIONS
LATE SATURDAY NIGHT THROUGH SUNDAY. THIS SYSTEM COULD BRING IN
ANOTHER SHOT AT ACCUMULATING SNOW SUNDAY INTO EARLY MONDAY MORNING.
COLD AIR ADVECTION BEHIND THE FRONT ON MONDAY IS EXPECTED TO DROP
DAYTIME HIGH`S INTO THE TEENS AND LOW 20`S WITH SINGLE DIGIT
OVERNIGHT LOWS RETURNING FOR BOTH TUESDAY AND WEDNESDAY MORNING.
SCATTERED LIGHT SNOW SHOWERS WILL BE POSSIBLE ON THURSDAY AS ANOTHER
CLIPPER SWINGS THROUGH. TEMPS WARMING INTO THE LOW 30`S DURING THE
DAYLIGHT HOURS FOR THURSDAY AND FRIDAY.

MARINE...

A LOW PRESSURE SYSTEM TRACKING THROUGH CENTRAL CANADA WILL REACH
NORTHERN QUEBEC FRIDAY AFTERNOON. THIS SYSTEM WILL DROP A WEAKENING
COLD FRONT INTO THE REGION FRIDAY. THIS WILL TIGHTEN THE PRESSURE
GRADIENT BETWEEN IT AND THE EXITING SURFACE HIGH ALLOWING WINDS TO
AMPLIFY SOMEWHAT OVER CENTRAL AND NORTHERN LAKE HURON. THOUGH
SUSTAINED WINDS APPEAR TO REACH INTO THE MID 20 KNOT RANGE...WARM
AIR ALOFT AND A STEEP LOW LEVEL INVERSION APPEAR PREVENT STRONGER
GUSTS FROM REACHING THE SURFACE. FEEL FAIRLY CONFIDENT THAT WINDS
WILL GUST AT OR JUST ABOVE 30 KNOTS ACROSS NORTHERN AND CENTRAL LAKE
HURON. THOUGH GALE FORCE GUSTS CANNOT BE RULES OUT
ENTIRELY...CURRENT MODELS AND ANALYSIS SUGGEST WINDS TO THIS
STRENGTH WOULD BE QUITE SPORADIC...AND NOT WIDE SPREAD ENOUGH TO
WARRANT A GALE WARNING OR CONTINUING THE WATCH AT THIS TIME SO THE
WATCH HAS BEEN CANCELLED. EXTENSIVE ICE COVER IN THE LAKE HURON
NEARSHORE ZONES WILL PREVENT ANY WAVES DEVELOPING WITH THE OFFSHORE
FLOW TO AROUND 25 KNOTS...SO SMALL CRAFT ADVISORIES WILL NOT BE
NEEDED AT THIS TIME. COLD NORTHWEST FLOW THIS WEEKEND WILL KEEP
WINDS ELEVATED THROUGH THAT PERIOD...BUT WILL REMAIN BELOW GALE
FORCE.

&&

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

$$

AVIATION.....MR
SHORT TERM...DT
LONG TERM....DRK/DE
MARINE.......DRK


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