FXUS63 KDTX 271739
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1239 PM EST FRI NOV 27 2009
.UPDATE...
FORECAST WAS UPDATED TO EXTEND LIGHT SNOW SHOWERS THROUGH THE
AFTERNOON OVER MOST OF THE FORECAST AREA. THERMAL TROUGHING AT H850 HAS
COMBINED WITH MODEST DAYTIME HEATING TO GENERATE A FEW LIGHT SNOW
SHOWERS. RADAR IMAGERY AT 1220 PM WAS INDICATING SOME FAIRLY
ROBUST RETURNS WITH SOME OF THE SHOWERS...HOWEVER VISUAL
OBSERVATIONS FROM WHITE LAKE ACTUALLY SHOWED THEY WERE QUITE LIGHT
IN INTENSITY. LITTLE TO NO ACCUMULATION IS EXPECTED. THESE SHOWERS
WILL PRIMARILY AFFECT AREAS SOUTH OF CARO AND NORTH OF DETROIT AS
THE THEMAL TROUGH CONTINUES TO CLIP FAR EASTERN MICHIGAN THIS
AFTERNOON.
&&
.AVIATION...
A FEW LIGHT SNOW SHOWERS WILL AFFECT FNT...PTK...AND PERHAPS DET...
AS A THERMAL TROUGH NEAR 4000 FEET DROPS SOUTHEAST ACROSS THE AREA THIS
AFTERNOON. SNOW WILL BE VERY LIGHT AND IS NOT EXPECTED TO HAVE A
SIGNIFICANT IMPACT ON VISIBILITIES. OTHERWISE...MVFR CEILINGS
WILL CONTINUE THROUGH THE AFTERNOON AS NORTHWEST FLOW OVER LAKE
MICHIGAN REINFORCES MOISTURE ALREADY IN PLACE. MOISTURE WILL BEGIN
TO WANE ACROSS THE REGION THIS EVENING AS LOW PRESSURE MOVES
FURTHER AWAY FROM THE AREA AND WINDS ACROSS THE GREAT LAKES TURN
MORE WESTERLY. MODEL FORECAST SOUNDINGS INDICATE THIS SHOULD ALLOW
THE MVFR DECK TO SCATTER OUT...HOWEVER WILL KEEP AN EYE ON THIS AS
AN INVERSION IS EXPECTED TO STRENGTHEN AND LOWER OVERNIGHT WHILE HIGH
PRESSURE BUILDS IN OVERHEAD. IT DOES NOT LOOK LIKE ENOUGH MOISTURE
WILL REMAIN TRAPPED UNDER THE INVERSION TO FORECAST A LOW STRATUS
DECK AT THIS TIME...AND TAFS REFLECT LOW CLOUDS SCATTERING OUT INSTEAD.
&&
.PREV DISCUSSION...ISSUED 354 AM EST FRI NOV 27 2009
SHORT TERM...TODAY
MAIN SYNOPTIC FORCING LIFTING EAST EARLY THIS MORNING AS THE UPPER
LOW TRANSLATES NORTHEAST AND THE ATTENDANT COLD FRONT SWEEPS ACROSS
LAKE ERIE. GIVEN THE LACK OF STRONGER UPPER SUPPORT...SEEING
PRECIPITATION RAPIDLY DIMINISH IN COVERAGE. MODERATE POST-FRONTAL
COLD AIR ADVECTION CREATING SUFFICIENT OVERLAKE INSTABILITY /850 MB
TEMPS OF -8C/ TO GENERATE SOME LAKE EFFECT SNOW SHOWER ACTIVITY
ACROSS SOUTHWEST LOWER MI. LATEST RADAR IMAGERY/OBSERVATIONS
SUGGEST THIS ACTIVITY WILL SHIFT ACROSS AREAS SOUTH OF I-96 THIS
MORNING. MINIMAL ACCUMULATION GIVEN THE WARM GROUND AND LIMITED
SNOWFALL INTENSITY/COVERAGE...BUT ISOLATED LOCALES COULD SEE A
COUPLE HEAVIER BURSTS OVER THE NEXT SEVERAL HOURS.
FALLING EQUILIBRIUM LEVELS ACCOMPANYING A GENERAL SHIFT TOWARD THE
NORTHWEST IN THE LOW LEVEL WIND FIELD /925-700MB/ WILL CONFINE ANY
ADDITIONAL LAKE EFFECT ACTIVITY TO THE WEST BY MIDDAY. ANY
LINGERING ISOLATED LIGHT SNOW SHOWERS/FLURRIES GENERATED WITHIN THE
RESIDUAL CYCLONIC FLOW WILL END AT THIS POINT. ONLY EXCEPTION MAY
BE RIGHT ALONG THE THUMB AS SOME ENHANCED CONVERGENCE ACCOMPANYING
THE PASSAGE OF A SECONDARY SURFACE TROUGH MAY PROVE SUFFICIENT IN
SUSTAINING SOME SCATTERED SNOW SHOWERS THROUGH THE AFTERNOON.
THE DEGREE OF COLD AIR ADVECTION TODAY WILL KEEP THE DIURNAL
TEMPERATURE RECOVERY LIMITED. HIGHS WILL STRUGGLE INTO THE 35-40F
RANGE.
LONG TERM...
A MODEST WARMUP IS ON TAP FOR THE WEEKEND AS AN UPPER LEVEL RIDGE
BUILDS INTO THE CENTRAL GREAT LAKES. THE WARMUP WILL BE SHORT-LIVED
HOWEVER...AS UPPER WAVE OVER BRITISH COLUMBIA AND ENERGY OVER THE
GULF OF ALASKA COMBINE AND ARRIVE BY SUNDAY NIGHT WITH THE SURFACE
COLD FRONT MOVING THROUGH SOUTHEAST MICHIGAN SUNDAY
AFTERNOON/EVENING.
SATURDAY MORNING SHOULD START OUT RATHER COLD (MOSTLY UPPER 20S) AS
SURFACE RIDGE AXIS WILL BE IN PLACE WITH SKIES AT LEAST PARTLY
CLOUDY FOR A PERIOD. LOW LEVEL WARM ADVECTION ON SATURDAY...AS BOTH
NAM/GFS SHOWING 925 MB TEMPS WARMING TO AROUND +3 C (ON AVERAGE)...WHICH
SUPPORTS MAX TEMPS IN THE MID TO UPPER 40S...AS A DRY WARM FRONT
LIFTS NORTH INTO THE AREA.
THE COLD FRONT COMING THROUGH DURING SUNDAY IS WORTHY OF CHANCE POPS
WITH THE INCREASING LOW LEVEL CONVERGENCE/LIFT...BUT TOUGH CALL ON
WHETHER OR NOT THE DEEPER PACIFIC MOISTURE HANGING OUT OVER MEXICO
ARRIVES IN TIME. BETTER UPPER LEVEL SUPPORT COMES THROUGH SUNDAY
NIGHT...BUT LOW LEVEL MOISTURE AXIS IS PUSHING EAST BY THIS TIME.
NONE-THE-LESS...MID LEVEL FGEN COULD PROVE SUFFICIENT FOR PRECIPITATION
(RAIN TURNING TO SNOW).
POSITIVELY TILTED TROUGH AXIS SWINGING THROUGH THE CENTRAL GREAT
LAKES ON MONDAY...COUPLED WITH LAKE ENHANCEMENT AND DIURNAL
INSTABILITY (STEEPENING LOW LEVEL LAPSE RATES) WILL BRING WITH IT A
CHANCE OF SNOW SHOWERS...AS 850 MB TEMPS PROGGED TO DROP DOWN TO
AROUND -9 C (PER 00Z GFS). WITH THIS AMOUNT OF LOW LEVEL COLD
AIR...MAXES SHOULD BE STUCK IN THE MID TO UPPER 30S.
MARINE...
NORTHWEST WINDS WILL GUST UP TO 30 KNOTS AT TIMES TODAY AS COLDER
AIR MOVES ACROSS THE WARMER LAKE WATERS. GUSTS WILL DIMINISH
THROUGH THE EVENING AS A RIDGE OF HIGH PRESSURE BUILDS INTO THE
REGION. IN ADDITION TO THE GUSTY WINDS...A LONG FETCH OVER THE
WATER WILL ALLOW WAVES TO BUILD AS HIGH AS 7 FEET OVER THE NEARSHORE
WATERS OF LAKE HURON TODAY. WAVES WILL DECREASE INTO SATURDAY AS
WAVES SHIFT TOWARD THE WEST AND DECREASE. HIGH PRESSURE RIDGE
SLIDES EAST SATURDAY NIGHT AS A LOW PRESSURE SYSTEM LIFTS INTO THE
GREAT LAKES. A WEAKER WIND FIELD WILL EXIST IN ADVANCE OF THIS
SYSTEM...BUT MAY STRENGTHEN OUT OF THE NORTHWEST AS IT SHIFTS EAST
SUNDAY NIGHT INTO MONDAY.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...INNER SAGINAW BAY...UNTIL 6 PM FRIDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
HURON INCLUDING OUTER SAGINAW BAY...UNTIL 10 AM SATURDAY.
LAKE ST CLAIR...
SMALL CRAFT ADVISORY...UNTIL 6 PM FRIDAY.
MI WATERS OF LAKE ERIE...
SMALL CRAFT ADVISORY...UNTIL 6 PM FRIDAY.
&&
$$
UPDATE.......HLO
AVIATION.....HLO
SHORT TERM...MR
LONG TERM....SF
MARINE.......MR
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
