FXUS63 KDTX 281728
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1228 PM EST SAT NOV 28 2009
.AVIATION...
VFR CONDITIONS WILL PREVAIL THROUGH THE AFTERNOON AND EVENING
BEFORE CONDITIONS DETERIORATE OVERNIGHT. CONCERN IS BECOMING HIGH
THAT LOW STRATUS WILL FILL THE SKIES OVER SOUTHEAST MICHIGAN AFTER
MIDNIGHT...DROPPING TO IFR OR LOWER BY 10Z. LOW-LEVEL MOISTURE
PRECEDING A LOW PRESSURE SYSTEM IS EXPECTED TO RIDE DOWN AN
EXISTING LOW-LEVEL THERMAL BOUNDARY THIS EVENING. THIS BOUNDARY
IS CURRENTLY IN PLACE FROM SOUTH CENTRAL MINNESOTA ARCING DOWN
THROUGH SOUTHEAST MICHIGAN. UPSTREAM OBSERVATIONS ALONG THE EDGE
OF THIS BOUNDARY FROM WISCONSIN AND MINNESOTA ALREADY SUPPORT LOW
STRATUS IDEA...WITH SEVERAL SITES NOW REPORTING CEILINGS LESS THAN
700 FEET. MODEL FORECAST SOUNDINGS SUPPORT IFR TO LIFR CONDITIONS DEVELOPING
OVERNIGHT...SHOWING ABUNDANT MOISTURE BECOMING TRAPPED BENEATH
THE INVERSION BY 6Z. GIVEN MODEL DATA...AND TAKING INTO ACCOUNT
UPSTREAM OBSERVATIONS AND ADDITIONAL MOISTURE THAT MAY BE PICKED
UP OVER LAKE MICHIGAN...HAVE ADDED PREVAILING MVFR GROUPS AFTER
5/6Z AND IFR GROUPS AFTER 10Z TO ALL SITES FOR THE 18Z PACKAGE. THERE IS
SOME POTENTIAL THAT LIGHTER WINDS COULD CAUSE GROUND FOG TO FORM
INSTEAD OF THE LOW STRATUS AT MBS AND POSSIBLY FNT...AND THERE IS
POTENTIAL FOR CEILINGS TO DROP TO LIFR AT ALL SITES. WILL
CONTINUE TO MONITOR TRENDS AND INCOMING MODEL DATA TO SEE IF
ADDITIONAL CHANGES ARE NEEDED.
&&
.PREV DISCUSSION...ISSUED 401 AM EST SAT NOV 28 2009
SHORT TERM...TODAY
SURFACE RIDGE AXIS CURRENTLY DRAPED OVERHEAD WILL SHIFT EAST TODAY
WHILE THE UPPER LEVEL FLOW BECOMES INCREASINGLY ANTICYCLONIC. THIS
WILL ESTABLISH MORE PRONOUNCED WARM AIR ADVECTION IN THE LOWER
LEVELS AND ALLOW ANY RESIDUAL MORNING STRATUS TO SCATTER WITHIN THE
DEVELOPING SOUTHWESTERLY FLOW. BACK EDGE OF THE CLEARING LINE
CONTINUING TO GRADUALLY SHIFT EAST-NORTHEAST PER LATEST SATELLITE
TRENDS AND EXTRAPOLATING THIS MOVEMENT SHOWS THE LINE ROUGHLY IN
THE VICINITY OF THE I-75 CORRIDOR BY SUNRISE. THIS POINTS TOWARD
MOST AREAS SEEING MOSTLY SUNNY SKIES FOR THE AFTERNOON...OUTSIDE
OF SOME THICKER CIRRUS ACROSS NORTHERN AREAS.
THE THERMAL PROFILE WILL RESPOND WELL TO THE WARM AIR ADVECTION...
WITH A 925/850 MB TEMPERATURES CLIMBING 6-8 DEGREES FROM 24 HOURS
AGO. GIVEN ADDED INSOLATION TODAY...ALBEIT OF SMALLER IMPACT GIVEN
THE LOWER SUN ANGLE...THIS WILL TRANSLATE INTO HIGHS GENERALLY IN
THE MID-UPPER 40S OR SEVERAL DEGREES ABOVE NORMAL FOR LATE
NOVEMBER.
LONG TERM...
PREDOMINATELY WESTERLY FLOW OVER THE NORTHERN CONUS DURING THE
NEXT SEVERAL DAYS...ALLOWING FOR PROGRESSIVE STORM SYSTEMS...WITH
THE TREND ON SUNDAY'S SYSTEM A BIT FASTER AS MAIN UPPER WAVE RESIDES
OVER CENTRAL CALIFORNIA...DROPPING SOUTH-SOUTHEAST. THIS WAVE WILL
HAVE TO BE WATCHED CLOSELY LATER IN THE WEEK FOR POSSIBLE PHASING
WITH THE NORTHERN STREAM.
FASTER FROPA ON SUNDAY WOULD TEND TO LIMIT OUR PRECIPITATION
CHANCES...AS FLOW FAILS TO BACK TO THE SOUTHWEST-SOUTH...PREVENTING
DEEPER PACIFIC MOISTURE FROM ADVECTING NORTH INTO LOWER MICHIGAN.
MID LEVEL DRY SLOT THEN ARRIVES FOR SUNDAY EVENING/NIGHT. WILL BE
KEEPING POPS JUST IN THE CHANCE CATEGORY...AS 00Z NAM/CANADIAN ARE
BASICALLY DRY...BUT 00Z GFS/UKMET BOTH INDICATING SUFFICIENT
CYCLOGENESIS/FGEN TO SUPPORT SOME RAIN DURING SUNDAY AS CPD'S ON THE
290 K SURFACE QUICKLY COME CRASHING DOWN.
THE POSITIVELY TILTED 500 MB TROUGH AXIS WILL SLIDE THROUGH THE
CENTRAL GREAT LAKES DURING MONDAY...WITH THE AVERAGE OF
UKMET/NAM/GFS INDICATING 850 MB TEMPS HOVERING AROUND -9 C...WHICH
SUPPORTS MAXES IN THE UPPER 30S AT BEST. WESTERLY FLOW OFF LAKE
MICHIGAN COUPLED WITH STEEP LOW LEVEL LAPSE RATES SHOULD BE
SUFFICIENT FOR FLURRIES OR SCATTERED LIGHT SNOW SHOWERS. THERE COULD
EVEN BE A QUICK RAMP UP TO THE LAKE EFFECT ACTIVITY EARLY MONDAY
EVENING AS SHORTWAVE/LEFT EXIT REGION OF JET IMPINGE ON THE AREA.
WITH INVERSION HEIGHTS RISING TO 10000 FEET (PER GFS
SOUNDINGS)...POSSIBLE WE COULD HAVE A LAKE BAND LEAD TO LOCALIZED
LIGHT ACCUMULATIONS BEFORE THE GOOD LOW LEVEL WARM ADVECTION
TRANSLATES TO THE EAST AND SHUTS OFF THE LAKE EFFECT.
TIMING OF THE NEXT NORTHERN STREAM UPPER WAVE/TROUGH AND THE
POSSIBLE PHASING OF THE 500 MB LOW WHICH IS EXPECTED TO BE OVER/NEAR
THE WESTERN GULF COAST STATES DURING THE MID WEEK PERIOD ARE
THE MAIN QUESTION MARKS. THE OVERWHELMING EVIDENCE BASED ON THE 00Z
MEDIUM RANGE MODELS (EUROPEAN/CANADIAN/WRF-HEMI/GFS) IS FOR A
FASTER TIMING AND PHASING...THUS THE COLD AIR (-10 C OR COLDER AT
850 MB) ARRIVES BY THURSDAY. WHETHER SIGNIFICANT PRECIPITATION
(RAIN>SNOW) PRECEDES THIS COLD BLAST REMAINS TO BE SEEN...BUT WILL
MAKE DOWNWARD ADJUSTMENTS IN TEMPERATURES FOR LATE IN THE WORK
WEEK.
MARINE...
A RIDGE OF HIGH PRESSURE SLIDING ACROSS THE AREA WILL LEAD TO WEAKER
WINDS AND LOWER WAVES TODAY AND TONIGHT. THE PASSAGE OF ANOTHER
COLD FRONT SUNDAY NIGHT AND MONDAY WILL ALLOW NORTHWEST WINDS TO
INCREASE ONCE AGAIN. SMALL CRAFT CONDITIONS MAY DEVELOP DURING THIS
TIME ACROSS THE NEARSHORE WATERS AIDED BY COLDER AIR MOVING ACROSS
THE RELATIVELY WARMER LAKE WATERS.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
AVIATION.....HLO
SHORT TERM...MR
LONG TERM....SF
MARINE.......MR
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