Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 160853
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
353 AM EST TUE DEC 16 2014

.SHORT TERM... TODAY AND TONIGHT

LOW PRESSURE SLIDING THROUGH LOWER MICHIGAN WILL MAINTAIN DAMP BUT
MILD CONDITIONS ACROSS THE AREA TODAY. AFTER THE FIRST WAVE OF RAIN
EARLIER IN THE NIGHT...DRIZZLE AND FOG WILL BE ONGOING UNTIL THE
NEXT ROUND OF SHOWERS ARRIVES DURING THE DAYLIGHT HOURS OF THE
MORNING. RAIN WILL THEN CONTINUE OFF AND ON THROUGHOUT THE DAY AS
TEMPERATURES REMAIN STEADY OR RISE SLIGHTLY FROM THE MID 40S TO
AROUND 50 DURING THE AFTERNOON. THE LOW WILL THEN MOVE INTO ONTARIO
TONIGHT AND PULL COLDER AIR INTO THE REGION ON INCREASING WESTERLY
WIND. GUSTS INCREASING TO NEAR 30 MPH LATE IN THE NIGHT WILL HELP
CARRY MIN TEMPERATURES BELOW THE FREEZING MARK BY SUNRISE WEDNESDAY.
A MIX OF RAIN AND SNOW CHANGING TO SNOW WILL BE POSSIBLE ON THE
TRAILING EDGE OF THE PRECIPITATION PATTERN OVER THE SAGINAW VALLEY
AND NORTHERN THUMB BUT WITH LITTLE TO NO ACCUMULATION EXPECTED.

EARLY MORNING SATELLITE IMAGERY SHOWS THE MID LEVEL DRY SLOT
ASSOCIATED WITH THE UPPER LOW SLIDING OVER LOWER MICHIGAN AT PRESS
TIME. THE MID LEVEL DRY AIR WILL LIMIT PRECIPITATION TO DRIZZLE IN
DEEP BOUNDARY LAYER MOISTURE AHEAD OF AND WITHIN THE SURFACE
OCCLUDED FRONT. DRIZZLE AND FOG WILL CONTINUE WITHIN THE OCCLUSION
AS IT LEADS THE SURFACE LOW THROUGH LOWER MICHIGAN WHILE COVERAGE OF
SHOWERS INCREASES AGAIN FROM ABOUT MID MORNING THROUGH THE REST OF
THE DAY. EARLY MORNING RADAR COMPOSITE AND MODEL FIELDS INDICATE
SHOWERS RELOADING OVER INDIANA AS A NEW ROUND OF ISENTROPIC ASCENT
INTERACTS WITH DYNAMIC FORCING OF THE UPPER LOW. THE ASSOCIATED COLD
POOL ALOFT...NEAR -25C AT 500 MB...WILL ALSO CONTRIBUTE ELEVATED
INSTABILITY TO AID IN EXPANSION OF THE RAIN PATTERN. COVERAGE MAY
NOT BE SOLID THROUGHOUT THE DAY BUT ENTRY LEVEL CATEGORICAL POPS ARE
A GOOD FIT AS THE UPPER LOW OPENS OVER LOWER MICHIGAN AND SETS UP A
WELL ORGANIZED BAND OF DEFORMATION TO ENHANCE THE OCCLUSION.

THE NORTHERN STREAM UPPER WAVE OVER CENTRAL CANADA TODAY WILL MOVE
INTO THE UPPER MIDWEST TONIGHT AND KICK THE GREAT LAKES SYSTEM OUT
OF THE AREA. DRY AIR BETWEEN THE TWO SYSTEMS WILL BRING AN END TO
PRECIPITATION FROM SW TO NE OVER LOWER MICHIGAN DURING THE OVERNIGHT
HOURS. THE EXCEPTION WILL BE THE SAGINAW VALLEY AND NORTHERN THUMB
NEAR THE SOUTH FLANK OF MID LEVEL DEFORMATION STRUNG OUT BETWEEN THE
TWO UPPER WAVES. A LIGHT MIX OF RAIN AND SNOW IS LIKELY THERE AS
COLDER AIR INVADES THE LOW LEVELS. MODEL PROJECTIONS OF LOW LEVEL
THICKNESS AND FORECAST SOUNDINGS SUGGEST ALL RAIN TO START THE NIGHT
THEN BECOMING MIXED WITH AND CHANGING TO SNOW AROUND AND AFTER
MIDNIGHT. AT THIS POINT...THE SLIGHTLY LATER TIMING ON THIS
TRANSITION COMBINED WITH A SLOW BUT STEADY DOWNWARD DRIFT IN SURFACE
TEMPERATURES WILL LIMIT ANY ACCUMULATION TO POSSIBLY A SLUSHY
COATING BY SUNRISE WEDNESDAY. WIND GUSTS WILL BE DRIVEN BY THE LOW
LEVEL COLD ADVECTION AND MIXED LAYER DEEPENING TO ABOUT 900 MB AFTER
MIDNIGHT. PEAK WIND GUSTS NEAR 30 MPH SUGGESTED BY MODEL SOUNDINGS
APPEARS REASONABLE GIVEN THE SURFACE LOW IS FILLING WITH TIME AS IT
EXITS INTO ONTARIO.

&&

.LONG TERM...WEDNESDAY THROUGH MONDAY

A CLOSED 500 MB LOW WILL TRACK EAST SOUTHEAST THROUGH THE NORTHERN
GREAT LAKES ON WEDNESDAY WITH A STRONG PV ANOMALY MAKING ITS WAY
THROUGH SOUTHERN LOWER MICHIGAN.  THIS WILL BE OCCURRING AS THE
STRONGEST 850 MB COLD AIR ADVECTION TAKES PLACE WITH TEMPERATURES
PLUNGING TO -10 TO -12 CELSIUS.  THE STRONG LOW AND COLD AIR
ADVECTION WILL CAUSE WESTERLY WINDS TO INCREASE TO 20 TO 30 MPH ON
WEDNESDAY. IN ADDITION SOME LIGHT SNOW AND FLURRIES WILL BE POSSIBLE
WITH THE LIFT AND COLD AIR IN PLACE.  MOISTURE WILL BE THE LIMITING
FACTOR ON WEDNESDAY AS MODEL SOUNDINGS SHOW A FAIRLY SHALLOW LAYER
OF MOISTURE IN PLACE ACROSS MOST OF THE CWA. THE DEEPEST MOISTURE
WILL BE ACROSS THE SAGINAW VALLEY AND THUMB REGION...WHERE SNOWFALL
AMOUNTS ARE EXPECTED TO BE HALF OF AN INCH OR LESS. ACROSS THE
SOUTHERN CWA JUST SOME LAKE MICHIGAN FLURRIES OR LIGHT SNOW IS
EXPECTED AS THE FLOW BACKS TO THE WEST NORTHWEST.

RIDGING THEN SLOWLY WORKS ITS WAY ACROSS THE WESTERN GREAT LAKES
WEDNESDAY NIGHT AND THURSDAY...PUSHING ANY CHANCE OF SNOW OFF TO
EAST AS WINDS TURN TO A MORE NORTHWESTERLY DIRECTION.  UNDER THIS
SETUP THE EXTREME EASTERN THUMB MAY GET BRUSHED WITH SOME FLURRY
ACTIVITY...HOWEVER WINDS APPEAR TO BE TOO WEST TO MAKE MUCH OF AN
IMPACT ACROSS THIS AREA. THE PATTERN THEN GOES FAIRLY DRY FOR THE
REMAINDER OF THE FORECAST AS THIS RIDGE BUILDS IN ACROSS THE GREAT
LAKES REGION THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.  THE MAIN
SYSTEM OF CONCERN DURING THIS WEEKEND IS A SYSTEM EMERGING OUT OF
THE SOUTHERN PLAINS AND TRACKING THROUGH THE SOUTHEASTERN CONUS AND
EVENTUALLY OFF THE COAST OF NEW ENGLAND. HOWEVER THE AFOREMENTIONED
HIGH PRESSURE IN PLACE IS EXPECTED TO KEEP THIS SYSTEM WELL TO OUR
SOUTH AS IT FEEDS DRY AIR IN FROM CANADA. ALTHOUGH THE PATTERN WILL
BE DECIDEDLY COLDER THAN THE LAST FEW DAYS...TEMPERATURES WILL
ACTUALLY BE FAIRLY CLOSE TO NORMAL DURING THIS PERIOD AS THE COLDEST
AIR STAYS LOCKED IN ACROSS THE ARCTIC.

&&

.MARINE...

AS AN OCCLUDED SURFACE LOW MOVES INTO THE GREAT LAKES REGION...A
WARM FRONT WILL LIFT NORTH THROUGH LAKE HURON AND USHER IN WARM AND
MOIST AIR. THE SURFACE LOW IS EXPECTED TO WEAKEN AS IT TRACKS ACROSS
THE REGION...BUT THERE WILL STILL BE A DECENT AREA OF COLD AIR
ADVECTION ON THE SOUTHWEST FLANK OF THE LOW. THE TIMING OF THIS
FEATURE WILL HELP INCREASE WIND SPEEDS TONIGHT AND WEDNESDAY. MODEL
SOUNDINGS SUGGEST THE PEAK WINDS WILL BE AT THE 925 MB/2000 FT
LEVEL. AT THESE HEIGHTS...WINDS COULD REACH UP TO 35 KT. PEAK MIXING
WEDNESDAY AFTERNOON MAY ALLOW FOR BRIEF GUSTS TO GALES...BUT
WIDESPREAD AND PERSISTENT GUSTS AT THAT SPEED ARE NOT LIKELY. COMMON
WIND VECTORS WILL BE 25-30KT FROM THE WEST ON WEDNESDAY. WINDS AND
WAVES WILL DROP OFF NOTICEABLY ON THURSDAY AS HIGH PRESSURE BUILDS
IN ACROSS THE GREAT LAKES. WAVES DO NOT LOOK TO REACH SMALL CRAFT
CRITERIA ACROSS PORTIONS OF THE LAKE HURON NEARSHORE AND OUTER
SAGINAW BAY UNTIL WEDNESDAY...THEREFORE WILL HOLD OFF ON ISSUING
ANY HEADLINES UNTIL LATER FORECASTS.

&&

.AVIATION...ISSUED 1155 PM EST MON DEC 15 2014

//DISCUSSION...

SHOWERS WILL CONTINUE TO PIVOT NORTH THROUGH AREA AS THETA-E RIDGE
OVERSPREADS LOWER MICHIGAN. ADDITIONAL -SHRA ACTIVITY APPEARS TO BE
EXPANDING OVER IL/IN...SO EXPECT DRY SLOT NOW APPROACHING THE CWA TO
FILL BACK IN FOR THE OVERNIGHT HOURS. AS LOW PRESSURE REACHES THE
AREA TUESDAY MORNING...DO NOT EXPECT ANY APPRECIABLE BREAK IN THE
SCATTERED SHOWERS AND EXPANDING FOG AS LOWER CIGS SURGE NORTH INTO
AREA WITHIN FLOW OF INCREASINGLY MOIST LOW LEVEL AIR. WESTERLY WINDS
WILL REPLACE THE SOUTHEAST FLOW BY MIDDAY TUESDAY AS THE LOW PASSES
GRADUALLY TO THE EAST. WHILE SOME IMPROVEMENT IN CIGS/VSBYS WILL BE
POSSIBLE...THIS REMAIN HIGHLY IN QUESTION GIVEN LACK OF SUPPORT FROM
GUIDANCE ATTM.

FOR DTW...IFR CONDITIONS WILL EXPAND BACK INTO AREA AT OR SHORTLY
AFTER THE BEGINNING OF THE FORECAST PERIOD...AND PERSIST INTO MIDDAY
TUESDAY...DROPPING TO LIFR AT TIMES IN BEST POOLING OF MOISTURE
ALONG LOW PRESSURE TUESDAY MORNING. A GENERAL TREND BACK TO MVFR
SHOULD BE ONGOING IN THE 18Z-00Z TIME FRAME AS WEST/SOUTHWEST FLOW
ENSUES IN THE WAKE OF THE PASSING LOW PRESSURE.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET MUCH OF THE FORECAST
  PERIOD.

* HIGH CONFIDENCE IN PRECIPITATION TYPE FALLING AS RAIN.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.

&&

$$

SHORT TERM...BT
LONG TERM....KURIMSKI
MARINE.......KURIMSKI
AVIATION.....DG


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



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