Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 291954
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
254 PM EST THU JAN 29 2015

.SHORT TERM...LATE THIS AFTERNOON AND TONIGHT

THE BACK EDGE OF THE PRECIPITATION SHIELD WILL CONTINUE ON AN
EASTWARD TRACK LATE THIS AFTERNOON...ADVANCING ACROSS SE MI OVER THE
NEXT TWO TO THREE HOURS. SOME LINGERING MID LEVEL DEFORMATION
ASSOCIATED WITH THE SHORT WAVE NOW OVER OHIO AND BRIEF MID LEVEL
FGEN PRECEDING A MID LEVEL TROUGH NOW WORKING INTO LAKE MI HAVE BEEN
THE PRIMARY FORCING MECHANISMS DRIVING THIS PRECIP. THERE HAS BEEN
JUST ENOUGH LOW LEVEL COOLING TO SUPPORT A COMPLETE CHANGE OVER TO
SNOW IN MOST LOCALS. STEEP MID LEVEL LAPSE RATES WILL CONTINUE TO
SUPPORT SOME BRIEF BURSTS OF HEAVY SNOW. GIVEN THE SHORT DURATION
AND WITH SFC TEMPS IN THE 30S OVER MOST OF THE FORECAST
AREA...ADDITIONAL SNOW ACCUMS PRIOR TO THE END OF THE PRECIP SHOULD
REMAIN A HALF INCH OR LESS.

LARGE SCALE SUBSIDENCE WITHIN THE DESCENDING BRANCH OF THE MID LEVEL
FRONTAL CIRCULATION WILL OVERSPREAD SE MI EARLY THIS EVENING. THIS
WILL SUSTAIN A DEEP LOW LEVEL INVERSION...HOLDING AMPLE LOW CLOUDS
OVER THE REGION. A POTENT NORTHERN STREAM MID LEVEL TROUGH HAS BEEN
TRACKING ACROSS NRN ONTARIO THIS AFTERNOON. THIS WAVE WILL CONTINUE
TO ADVANCE TO THE SOUTHEAST TONIGHT...MOVING ACROSS SE MI DURING THE
FIRST HALF OF THE OVERNIGHT PERIOD. THIS WILL DRIVE AN ARCTIC COLD
FRONT ACROSS THE FORECAST AREA DURING THE 03Z TO 06Z TIME FRAME.
PRIOR TO THE ARRIVAL OF THIS FRONT...LIMITED COLD AIR ADVECTION WILL
HOLD TEMPS IN THE LOW 30S EARLY THIS EVENING. 925MB TEMPS ARE THEN
FORECAST TO PLUNGE TO -18C BY DAYBREAK FRI IN THE WAKE OF THE COLD
FRONT. THIS WILL CAUSE SFC TEMPS TO DROP TOWARD THE LOW TEENS/UPPER
SINGLE DIGITS. THE COLD AIR WILL BE DRIVEN INTO THE AREA VIA STRONG
W-NW WINDS. WHILE THE SFC ISSALOBARIC COMPONENT WILL BE RATHER
WEAK...A PUSH OF GOOD SYSTEM RELATIVE ISENTROPIC DESCENT TRAILING
THE MID LEVEL WAVE AND STEEPENING LOW LEVEL LAPSE RATES WILL BRING
SOME STRONGER WIND GUSTS TO THE SFC. RECENT MODEL SOUNDINGS WOULD
SUPPORT A FEW GUSTS TOPPING 30 MPH OVERNIGHT. WIND CHILLS WILL IN
TURN BE DRIVEN DOWN TO THE SINGLE DIGITS AND SUB ZERO READINGS BY
EARLY FRI MORNING.

ALTHOUGH THERE WILL BE GOOD LARGE SCALE ASCENT LATE THIS EVENING
PRECEDING THE MID LEVEL WAVE...THE LACK OF MOISTURE ABOVE THE
INVERSION WILL LIMIT SNOWFALL POTENTIAL. LAKE CONTRIBUTION INTO SE
MI WILL ALSO BE LIMITED BY THE MEAN NW WIND TRAJECTORIES. THUS JUST
SOME FLURRIES OR LIGHT SNOW SHOWERS LOOK POSSIBLE /MAINLY ALONG THE
LEAD PUSH OF LOW LEVEL ASCENT ALONG THE ARCTIC FRONT/.

&&

.LONG TERM...

HEALTHY SHOT OF ARCTIC AIR IN PLACE TO START THE DAY ON
FRIDAY...WITH 925 MB TEMPS ADVERTISED TO BE IN THE NEGATIVE UPPER
TEENS. THE LOW LEVEL COLD ADVECTION WILL BE EXHAUSTED DURING THE
DAY...AS FLOW WEAKENS AND UPPER LEVEL RIDGE BUILDS OVER THE WESTERN
GREAT LAKES LATE IN THE DAY. NAM SOUNDINGS INDICATING
SUPERSATURATION WITH RESPECT TO ICE BETWEEN 1000-2000 FOOT
LAYER...ENOUGH FOR MENTION OF A FLURRY OR TWO.
HOWEVER...FLOW WILL BE NORTHWEST-NORTH...UNFAVORABLE FOR ANY LAKE
FEED (EXCEPT FOR EASTERN THUMB SHORELINE WHERE MAIN LAKE BAND WILL
HAVE TO BE WATCHED)...WITH DOWN SLOPING COMPONENT INTO MUCH OF
SOUTHEAST MICHIGAN. WILL THUS ALLOW FOR GOOD SHARE OF
SUNSHINE...ALLOWING MAXES TO REACH INTO THE MID TEENS TO AROUND 20
DEGREES...WHICH IS STILL OVER 10 DEGREES BELOW
NORMAL.

SEVERAL KEY FEATURES TO FOCUS ON FOR THE WEEKEND FORECAST.
THE FIRST ONE BEING THE INTENSE CYCLONE OFF THE NEW ENGLAND COAST
FRIDAY NIGHT. THIS SYSTEM IS SLOW TO EXIT...AND THUS BECOMES MERGED
WITH NEXT STRONG UPPER LEVEL TROUGH SWINGING THROUGH ONTARIO ON
SATURDAY. THE FAILURE OF THIS SYSTEM TO CLEAR EASTERN CANADA IN
TIMELY MANNER LIKELY CONTRIBUTING TO SUPPRESSING/DELAYING THE
AMPLIFICATION OF THE SYSTEM COMING OUT OF THE CENTRAL/SOUTHERN
PLAINS FOR THE SECOND HALF OF THE WEEKEND. THAT SYSTEM IS RELYING ON
THE INTERACTION OF AT LEAST TWO UPPER WAVES...ONE ZIPPING OUT OUT OF
THE GULF OF ALASKA AND THE OTHER BEING THE UPPER LEVEL LOW OFF THE
COAST OF BAJA CALIFORNIA. THAT SOUTHERN SYSTEM IS AWFUL FAR TO THE
SOUTH AND OFFSHORE...WITH ONLY A PIECE OF ENERGY EXPECTED TO BREAK
OFF AND INTERACT WITH NORTHERN STREAM WAVE. AS SUCH...MODEL
CONSENSUS (GFS/NAM) IS FOR UPPER LEVEL WESTERN CONFLUENT FLOW AND
HIGH PRESSURE BUILDING UNDERNEATH TO WIN OUT OVER MUCH OF GREAT
LAKES REGION ON SUNDAY...AS EVEN 12Z CANADIAN HAS ABANDONED SHIP
FROM ITS 00Z RUN. STILL...UNTIL THE WAVE OVER THE GULF OF ALASKA
FULLY COMES ONSHORE AND MAGNITUDE IS RESOLVED...WILL NOT RULE OUT
LIGHT ACCUMULATING SNOW ALL TOGETHER FOR SUNDAY JUST YET...SEE 12Z
EURO/NAVGEM...BUT CHANCES ARE CERTAINLY HIGHEST TOWARD THE OHIO
BORDER WHERE WILL CARRY A 50 POP. A NORTHEAST COMPONENT OFF LAKE
HURON MAY ALSO BE SUFFICIENT TO GENERATE SOME LAKE EFFECT SNOW
SHOWERS...BUT OVERALL DRY AIRMASS (SURFACE DEW PTS OF -20 TO -30 F
NEAR GEORGIAN BAY) AND LOW INVERSION HEIGHTS WILL BE TOUGH TO
OVERCOME.

THE LOW WILL BE IN THE PROCESS OF LIFTING OFF TO THE NORTHEAST
TOWARDS THE EAST COAST OVERNIGHT SUNDAY INTO EARLY MONDAY.  THINGS
SETTLE DOWN ON MONDAY AS HIGH PRESSURE BUILDS IN...HOWEVER LOOKING
AT TEMPS ONLY TOPPING OFF IN THE TEENS FOR HIGHS ON MONDAY.  THE
NEXT ACTIVE PERIOD RETURNS TO THE AREA IN THE TUESDAY/WEDNESDAY
TIMEFRAME AS ANOTHER POTENTIAL CLIPPER MOVES IN.

&&

.MARINE...

LOW PRESSURE EXITING THE CENTRAL GREAT LAKES THIS AFTERNOON...WITH
QUICK RAMP UP TO NORTHWEST GALES EXPECTED BY EARLY THIS EVENING AS
AIRTIC AIRMASS STREAMS INTO THE AREA. CONFIDENCE IS HIGH IN GALES
FOR MAJORITY OF LAKE HURON WITH LAKE INDUCED TROUGHING ENHANCING THE
FLOW...ALONG WITH WINDS BECOMING NORTHWEST-NORTH INCREASING THE
FETCH. LARGE AREA OF HIGH PRESSURE WILL SLOWLY BUILD EAST INTO THE
ENTIRE GREAT LAKES REGION ON FRIDAY...ALLOWING WINDS TO BECOME LIGHT
LATE IN THE DAY INTO FRIDAY NIGHT. A WEAK LOW WILL TRACK ACROSS THE
NORTHERN GREAT LAKES ON SATURDAY...LEADING TO MODERATE SOUTHWEST
FLOW OVER CENTRAL LAKE HURON AHEAD OF IT. WINDS WILL THEN SWING
AROUND TO THE NORTHWEST AND VEER AROUND TO THE NORTHEAST AS WE HEAD
INTO SUNDAY.

&&

.AVIATION...ISSUED 1203 PM EST THU JAN 29 2015

THE REGION OF PRECIP NOW MOVING ACROSS SW MI WILL ADVANCE ACROSS THE
TERMINALS EARLY THIS AFTERNOON. THE BULK OF THIS WILL FALL AS SNOW
FROM PTK NORTH AND RAIN/SNOW SOUTH. THERE IS A DEFINITE BACK EDGE TO
THIS PRECIP /MARKED BY THE END OF LARGER SCALE FORCING/. THIS BACK
EDGE WILL MOVE THROUGH SE MI BETWEEN 20Z AND 22Z. THE ASSOCIATED SFC
LOW WILL PASS EAST OF METRO DETROIT AFTER 19Z CAUSING A VEERING OF
THE WIND TOWARD THE W-NW WITH A MODEST INCREASE IN WIND SPEED.
SHALLOW COLD AIR ADVECTION UNDER A DEEP LOW LEVEL INVERSION WILL
SUSTAIN MVFR CIGS THROUGH WELL INTO THE OVERNIGHT. A SECONDARY COLD
FRONT...MARKED BY A PUSH OF ARCTIC AIR WILL ARRIVE LATE THIS EVENING
AND WILL CAUSE A DRAMATIC INCREASE IN THE WINDS /POSSIBLY GUSTING UP
TO 30 KNOTS AT TIMES/.

FOR DTW...ENOUGH WARM AIR IS IN PLACE OVER METRO DETROIT TO SUPPORT
RAIN MIXED WITH SOME SNOW AS THIS SECOND BATCH OF PRECIP ARRIVES
WITHIN THE NEXT HOUR. SFC TEMPS WILL REMAIN ABOVE FREEZING...SO NO
ACCUMULATIONS WITH ANY SNOW IS EXPECTED.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CIGS BELOW 5000 FT THIS AFTERNOON AND TONIGHT.

* MEDIUM IN PRECIPITATION BEING MOSTLY RAIN THIS AFTERNOON.

* MEDIUM IN WIND GUSTS EXCEEDING CROSS WIND THRESHOLDS TONIGHT.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...HEAVY FREEZING SPRAY WARNING FROM 7 PM THIS EVENING TO 7 PM EST
     FRIDAY FOR LHZ362-363-441-462.

     GALE WARNING FROM 7 PM THIS EVENING TO 10 AM EST FRIDAY FOR LHZ362-
     363-421-441-462.

     HEAVY FREEZING SPRAY WARNING FROM 10 PM THIS EVENING TO 7 PM EST
     FRIDAY FOR LHZ463-464.

     GALE WARNING FROM 10 PM THIS EVENING TO 10 AM EST FRIDAY FOR LHZ442-
     443-463-464.

     HEAVY FREEZING SPRAY WARNING FROM 7 PM THIS EVENING TO 4 AM EST
     FRIDAY FOR LHZ361.

     GALE WARNING FROM 7 PM THIS EVENING TO 4 AM EST FRIDAY FOR LHZ361.

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

$$

SHORT TERM...SC
LONG TERM....SF/SS
MARINE.......SF
AVIATION.....SC


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



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