Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 202024
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
324 PM EST SAT DEC 20 2014

.SHORT TERM...THIS EVENING AND TONIGHT

A MID LEVEL SHORT WAVE IMPULSE SHOWN ROTATING ACROSS INDIANA ON
THE LATEST WATER VAPOR LOOP WILL TRACK INTO OHIO THIS EVENING...
SPREADING MID LEVEL HEIGHT FALLS ACROSS SE MI. DESPITE SOME WEAK
RADAR RETURNS OVER NW INDIANA/SW MI THIS AFTERNOON...A WEDGE OF
EXTREMELY DRY AIR IN THE 900-800MB LAYER OVER SE MI AND OVERALL
WEAK NATURE OF THE LARGE SCALE ASCENT WILL SUPPORT THE CURRENT DRY
FORECAST THIS EVENING. MID AND HIGH CLOUDS WILL HOWEVER CONTINUE
TO INCREASE DURING THE REMAINDER OF THE AFTERNOON AND EVENING.
THESE HIGHER BASED CLOUDS WILL DEPART TO THE NORTH AND EAST
OVERNIGHT AS THE SHORT WAVE SLIDES INTO PENNSYLVANIA.

THERE WILL BE SOME WEAK COLD AIR ADVECTION NEAR 850MB TONIGHT. THIS
IS NOT EXPECTED TO BE ENOUGH TO ERODE THE DEEP LOW LEVEL INVERSION
OVER THE AREA. WHILE THE LOSS OF A DIURNAL COMPONENT MAY LEAD TO
SOME DECREASE IN THE LOW CLOUD COVERAGE THIS EVENING...THE
DEVELOPMENT OF A LIGHT W-SW LOW LEVEL FLOW OVERNIGHT WILL CAUSE SOME
OF THE LOW CLOUDS ACROSS WRN LOW MI TO SLIDE INTO THE FORECAST AREA
UNDER THIS INVERSION. THE EXPECTED CLOUD COVERAGE AND NEAR NEUTRAL
SUB 925MB THERMAL ADVECTION TONIGHT WILL SUPPORT MIN TEMPS ON THE
WARM SIDE OF MOS /MID TO UPPER 20S/. THE POTENTIAL FOR A BRIEF
PERIOD OF CLEAR SKIES IN THE SAGINAW VALLEY AND THUMB WILL HOWEVER
SUPPORT FCST MIN TEMPS DOWN INTO THE UPPER TEENS/LOW 20S.

&&

.LONG TERM...SUNDAY THROUGH NEXT FRIDAY

THE EXTENDED PERIOD STARTS OFF QUIET BUT LATER IN THE WEEK A PAIR OF
LOW PRESSURE SYSTEMS LOOK TO TARGET THE REGION AS STRONG JET LEVEL
ENERGY WORKS ACROSS THE COUNTRY. A 160+ KNOT JET IS BEGINNING TO
MOVE ASHORE OVER THE FAR NW CONUS TODAY WHICH WILL DEVELOP A TROUGH
OVER THE CENTRAL CONUS SUNDAY AND THEN AMPLIFY IT THROUGH THE
BEGINNING OF THE WORK WEEK.

SFC RIDGE WILL BE HOLDING OVER THE AREA ON SUNDAY AS AN UPPER LEVEL
TROUGH EXITS THE AREA. THIS WILL USHER THE COLDEST AIR ALOFT TO THE
NE BUT 500MB TEMPS STILL REMAIN LESS THAN -20C WITH 850MB TEMPS
AROUND -3C. STILL EXPECT PLENTY OF CLOUDS AROUND AS SEVERAL UPPER
LEVEL LOWS DRIFT THROUGH THE NORTHERN PLAINS AND SOUTHERN GREAT
LAKES. WILL BE PESSIMISTIC WITH MOSTLY CLOUDY SKIES UNTIL
OBS/SATELLITE SUGGEST SOME THINNING/CLEARING. BY SUNDAY
AFTERNOON...THE SFC HIGH WILL DRIFT FAR ENOUGH EAST TO ALLOW
SOUTHERLY FLOW TO RETURN TO THE AREA. BEFORE THE UPPER LEVELS DEEPEN
TOO MUCH...CYCLOGENESIS WILL BEGIN OVER THE NORTHERN PLAINS
DEVELOPING AN AREA OF LOW PRESSURE AT THE SFC OVER THE NORTHERN
PLAINS LATE SUNDAY AND OVERNIGHT. UPPER LEVEL SHORTWAVE WILL SWING
THROUGH THE STILL LOW AMPLITUDE TROUGH AND LIFT NE THROUGH WI. THIS
WILL OPEN THE DOOR FOR SW FLOW TO COMMENCE THROUGHOUT THE COLUMN.
THE INITIAL BAND OF WEAK ISENTROPIC LIFT ON THE ELEVATED FRONT WAS
SUGGESTING SOME LIGHT PRECIP OVERNIGHT SUNDAY BUT MODELS CONTINUE TO
HOLD THIS RIBBON OF MOISTURE FURTHER WEST AND A DRIER BL OVER SE MI
THUS POPS WERE REMOVES SUNDAY NIGHT.

THIS INITIAL SFC LOW REMAINS FAIRLY UNORGANIZED THROUGH MONDAY AS
THE UPPER LEVEL TROUGH STILL DIGS DEEPER INTO THE GULF COAST STATES
AND SEVERAL SHORT WAVES TRAVERSING THROUGH IT. INSTEAD OF SHOWING
SIGNS OF STRENGTHENING...THE CENTER OF THE LOW MEANDERS SOME AS IT
SEARCHES OUT THE STRONGER PRESSURE FALLS. DURING THE OVERNIGHT THE
UPPER LEVEL TROUGH REALLY COMES TOGETHER SPARKING STRONGER
CYCLOGENESIS FURTHER SOUTH ALONG THE BAROCLINIC ZONE. THIS ALLOWS
THE DEEPER RIBBON OF MOISTURE TO DRIFT EAST OVER CENTRAL LOWER MI
BEHIND THE ELEVATED OCCLUDED FRONT. WITH WAA THROUGHOUT THE DAY
MONDAY...THERMAL PROFILE WILL BE ABOVE 0C FROM THE SFC TO 700MB
WHICH WOULD RESULT IN PURE RAIN SHOWERS WITH LOW TEMPS IN THE
MID/UPPER 30S.

STORY FOR THE EXTENDED WILL BE THE DYNAMICALLY EVOLVING LOW PRESSURE
SYSTEM SET TO IMPACT THE EASTERN THIRD OF THE CONUS TUESDAY THROUGH
CHRISTMAS. WITH TEMPERATURES ABOVE FREEZING FOR MOST OF THE
EVENT...SNOW WILL BE A SECONDARY OR TERTIARY IMPACT OF THE EVENT.
FOR SOUTHEAST MICHIGAN...HIGH WINDS WILL BE THE MAIN IMPACT. A TIGHT
SURFACE PRESSURE GRADIENT WILL BRING SWIFT WARM ADVECTION PROCESSES
TO THE AREA AS PRESSURE RAPIDLY DROPS 12 MB PER 12 HOURS. 850 MB
TEMPS ALSO MAKE STRONG SWINGS AS THEY INCREASE TO 8-10C WED
AFTERNOON...THEN QUICKLY DROP TO -5C THU MORNING. THE STRONG COLD
ADVECTION WILL HELP INCREASE WIND SPEEDS TO GUST NEAR 30 MPH ON
CHRISTMAS. CAA WILL ALSO SWITCH PRECIP TYPE TO ALL SNOW WED EVENING.
FROM THAT POINT ON...QPF DROPS TO A TENTH OF AN INCH OR SO...WITH
STRONG WINDS AND MARINE INTERESTS TAKING THE FORECAST ATTENTION.
MODEL SOLUTIONS ARE NOT IN AGREEMENT WITH STRENGTH OR PLACEMENT OF
THE LOW...SO LOOK FOR FUTURE UPDATES ON STORM TRACK.

&&

.MARINE...

LIGHT WINDS WILL CONTINUE ACROSS THE MARINE AREAS THROUGH THE
REMAINDER OF THE WEEKEND. LOW PRESSURE WILL DEVELOP AND DEEPEN OVER
THE CENTRAL US SUNDAY NIGHT INTO MONDAY. THIS WILL LEAD TO THE
DEVELOPMENT AND SLIGHT INCREASE IN SOUTH-SOUTHEAST WINDS THROUGH
THIS PERIOD. SECONDARY SURFACE LOW DEVELOPMENT IS FORECAST ACROSS
THE GULF COAST ON TUESDAY...WITH THE LOW FORECAST TO RAPIDLY
INTENSIFY AS IT LIFTS NORTH ACROSS THE GREAT LAKES REGION WEDNESDAY.
THIS SYSTEM HAS THE POTENTIAL TO PRODUCE GALES WEDNESDAY NIGHT AND
THURSDAY.

&&

.AVIATION...ISSUED 1203 PM EST SAT DEC 20 2014

//DISCUSSION...

A THIN LAYER OF MOISTURE TRAPPED UNDER A DEEP LOW LEVEL INVERSION
WITH VERY LITTLE FLOW IN THE BOUNDARY LAYER WILL SUPPORT A
PERSISTENCE FORECAST THROUGH THE REMAINDER OF THE AFTERNOON. SO THE
MVFR STRATUS DECK THAT HAS BEEN COVERING THE METRO DETROIT AND PTK
TAFS SHOULD LAST WELL INTO THE EVENING. FNT WILL REMAIN ON THE EDGE
OF THIS CLOUD DECK LEADING TO THE POTENTIAL FOR MORE VARIABILITY IN
CLOUD COVERAGE. THE EXPECTATION FOR SOME CONTINUED DIURNAL
ENHANCEMENT WILL SUPPORT A PREDOMINATE BKN COVERAGE AT FNT.

FOR DTW...THERE HAS BEEN A REGION OF CLEARING ACROSS SOUTH CENTRAL
LOWER MI AS SOME DRIER AIR HAS FUNNELED THROUGH THE INVERSION. A
WEAK LOW LEVEL W-SW FLOW WILL DEVELOP LATER TODAY...WHICH MAY BRING
SOME DEGREE OF THIS CLEARING INTO METRO LATE THIS EVENING OR
OVERNIGHT. THE EXPECTATION FOR AT LEAST SOME DIURNAL ENHANCEMENT
THIS AFTERNOON AND THE PERSISTENCE OF THE LOW LEVEL INVERSION
TONIGHT WILL SUPPORT MAINTAINING CONTINUITY WITH THE PREVIOUS
FORECAST IN HOLDING AN MVFR CIG THROUGH THE TAF PERIOD.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET THIS AFTERNOON AND
  EVENING. MEDIUM CONFIDENCE OVERNIGHT AND SUNDAY MORNING.

&&

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

$$

SHORT TERM...SC
LONG TERM....DRK/MM
MARINE.......SC
AVIATION.....SC


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


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