FXUS63 KDTX 300446
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1146 PM EST SUN NOV 29 2009
.AVIATION...
LOW PRESSURE ACROSS THE EASTERN GREAT LAKES CONTINUES TO MOVE OUT OF
THE GREAT LAKES EARLY THIS MORNING. THE PRECIPITATION ASSOCIATED
WITH THE SYSTEM HAS ALL BUT ENDED...WITH AN HOUR OR TWO OF
ADDITIONAL PRECIPITATION POSSIBLE AT KPTK AND THE METRO AIRPORTS.
SOME SNOW MAY MIX IN ACROSS KPTK BEFORE THE RAIN ENDS...HOWEVER IT
WILL NOT BE ENOUGH TO CAUSE ANY ISSUES. MVFR CONDITIONS WILL IMPROVE
TO VFR AS A RIDGE OF HIGH PRESSURE BUILDS INTO THE CENTRAL GREAT
LAKES LATER THIS MORNING WITH NORTHWEST WINDS AROUND 10 KNOTS.
NORTHWEST WINDS WILL BACK TO THE SOUTHWEST AHEAD OF ANOTHER
APPROACHING LOW PRESSURE SYSTEM THIS AFTERNOON. THIS LOW WILL BRING
THE CHANCE FOR SNOW TO THE TAF SITES TONIGHT AS IT PASSES THROUGH
THE NORTHERN GREAT LAKES. HOWEVER CHANCES ARE LOW ENOUGH TO LEAVE
OUT OF THE AIRPORTS ALONG AND SOUTH OF M-59. SINCE KMBS/KFNT ARE
CLOSER TO THE LOW WITH HIGHER SNOW CHANCES WILL INCLUDE SNOW
STARTING AROUND 00Z AS CONDITIONS DETERIORATE TO MVFR.
&&
.PREV DISCUSSION...ISSUED 355 PM EST SUN NOV 29 2009
SHORT TERM...TONIGHT
AREA OF LOW PRESSURE OVER LAKE HURON WILL LIFT NORTHEAST ACROSS
ONTARIO TONIGHT AS AN UPPER TROUGH PUSHES ACROSS THE WESTERN GREAT
LAKES. ATTENDANT COLD FRONT WAS DROPPING INTO CENTRAL LOWER MICHIGAN
AT 20Z THIS AFTERNOON...WHILE AN EXPANSIVE AREA OF RAIN WAS LOCATED
AHEAD OF THE SURFACE FRONT OVER SOUTHEAST MICHIGAN...IN AN AREA OF
GOOD FRONTOGENETICAL FORCING...GOOD MID-LEVEL INSTABILITY...AND LEFT
EXIT REGION DYNAMICS. RAIN WILL PRESENT OVER THE AREA INTO THE
EVENING AS THESE SAME DYNAMICS REMAIN FAVORABLE. MAIN AREA OF
PRECIPITATION SHOULD THEN CLEAR THE AREA BY 03Z...WITH JUST A FEW
SHOWERS LINGERING ON THE BACKSIDE OF THE SYSTEM THROUGH THE NIGHT.
THERMAL PROFILES REMAIN FAVORABLE TO SEE MOST OF THIS PRECIPITATION
FALL AS RAIN...HOWEVER STILL EXPECT A FEW SNOWFLAKES TO START MIXING
IN AS PRECIPITATION STARTS TO TAPER OFF. CHANCES FOR LIGHT SNOW
SHOWERS AFTER MIDNIGHT REMAIN LOW AS GFS/NAM FORECAST SOUNDINGS SHOW
INSUFFICIENT MOISTURE REMAINING IN THE SNOW GROWTH REGION.
TEMPERATURES TONIGHT ARE EXPECTED TO FALL WITHIN A FEW DEGREES OF
THE FREEZING MARK.
LONG TERM...MONDAY THROUGH NEXT SUNDAY
SNOW SHOWERS ON LAKE HURON WILL BE OFFSHORE AND WANING DURING MONDAY
MORNING FOSTERED BY BACKING LOW LEVEL FLOW AS SURFACE HIGH PRESSURE
BUILDS INTO THE REGION. WE ARE CAUTIOUSLY OPTIMISTIC THAT THIS HIGH
PRESSURE WILL ALSO BRING A FEW BREAKS IN THE CLOUDS BY LATE MORNING
THROUGH ABOUT MID AFTERNOON. USUALLY THE STRONG ANTICYCLONIC FLOW
HELPS WITH A RELIABLE CLEARING TREND BUT THERE IS QUITE A BIT OF LOW
LEVEL MOISTURE INDICATED OVER MINNESOTA AND IOWA TODAY. THIS
SUGGESTS A CONSERVATIVE APPROACH TO ANY CLEARING TREND EXPRESSED IN
THE FORECAST FOR MONDAY BUT WITH ENOUGH BREAKS OF SUNSHINE TO HELP
TEMPERATURES TOUCH THE 40 MARK FOR HIGHS.
THE NEXT SYSTEM WILL MAKE ITS APPROACH TOWARD MONDAY EVENING DRIVEN
BY A STRONG UPPER JET MOVING IN FROM CENTRAL CANADA. MODEL FIELDS
SHOW THE EXIT REGION OF THIS JET SUPPORTING A MID LEVEL WAVE SHOWN
BEST BY 850 TO 700 MB THETA-E AND WINDS RATHER THAN MUCH OF WAVE IN
THE 500 MB HEIGHT FIELD, ALTHOUGH THE SHEARED VORTICITY FIELD DOES
GIVE AWAY THE UPPER JET. THERE IS ALSO A REFLECTION OF THE WAVE IN
THE MSL PRESSURE THAT SUGGESTS AN ENVIRONMENT OF LOW STABILITY BELOW
500 MB THAT WILL MAKE THE FORCING MORE EFFECTIVE AT GENERATING
VERTICAL MOTION. THAT, ALONG WITH SPECIFIC HUMIDITY IN THE 2 TO 3
G/KG RANGE IN THE 850 TO 700 MB LAYER SUGGESTS THIS SYSTEM WILL BE
CAPABLE OF GENERATING SOME LIGHT SNOW ACCUMULATION AS IT MOVES
THROUGH LOWER MICHIGAN MONDAY NIGHT. THE POINT IS THAT THE WAVE IS
PLENTY CAPABLE OF GENERATING SNOW ON ITS OWN BUT WILL ALSO GET A
BOOST FROM LAKE MICHIGAN. EXPECTING AT LEAST LOW STABILITY, MODEL
CROSS SECTIONS IN FACT SHOW THE LOW LEVELS BECOMING CONVECTIVELY
UNSTABLE AS THE UPPER LEVEL WAVE APPROACHES WITH THE UNSTABLE LAYER
GROWING TO NEAR 700 MB DURING THE EVENING. LAKE SURFACE TO 850 MB
DELTA-T IS ALSO SHOWN TO BE IN THE RANGE OF 12 TO 15C WITH AN 850 MB
TEMP AROUND -8C. DURATION IS THE ONLY CONCERN AS A LIMITING FACTOR
AS THE SYSTEM MOVES QUICKLY THROUGH THE REGION BEFORE SUNRISE
TUESDAY. FOR NOW, WE BROADENED THE AREA OF 1 INCH ACCUMULATION BASED
ON THE STRENGTH OF THE WAVE RATHER THAN RAISE IT ANY HIGHER BASED ON
FOCUSED LAKE EFFECT.
A SHORT WAVE RIDGE WILL MOVE IN BRIEFLY ON TUESDAY AND HELP ENSURE
DRY CONDITIONS, FOLLOWED BY WARM ADVECTION LATER IN THE DAY AND
DURING TUESDAY NIGHT. THE WARM ADVECTION WILL BE IN ADVANCE OF THE
NEXT LOW PRESSURE SYSTEM MOVING INTO NORTHERN MINNESOTA. MODEL
AGREEMENT IS QUITE GOOD ON THE TIMING AND INTENSITY OF THIS FEATURE
AS IT TRACKS THROUGH THE NORTHERN GREAT LAKES AND LAYS A DRY COLD
FRONT DOWN THROUGH SE MICHIGAN ON WEDNESDAY.
THIS FRONT WILL LIKELY MAKE IT TO OUR SOUTH AND EAST BEFORE THE GULF
COAST SYSTEM MAKES IT NORTHWARD MOVE IN RESPONSE TO YET ANOTHER
ROUND OF HEIGHT FALLS OVER THE PLAINS AND CENTRAL CANADA. THIS NEXT
SHORT WAVE WILL MAINTAIN THE LONG WAVE TROUGH TO OUR NORTH AND WEST
AND KICK THE GULF SYSTEM TOWARD US. AS LONG AS THE CENTRAL CANADIAN
UPPER TROUGH REMAINS TO OUR WEST, WE HAVE TO GIVE THE GULF SHORT
WAVE A CHANCE TO MOVE WEST OF THE APPALACHIANS. THE EVENTUAL TRACK
OF THIS SYSTEM WILL BE MOST STRONGLY INFLUENCED BY THE CHARACTER OF
HEIGHT FALLS OVER THE NORTHERN PLAINS AND HOW PROGRESSIVE/POSITIVELY
TILTED THE TROUGH BECOMES. UNCERTAINTY IS ADDED BY QUESTIONS
REGARDING THE AMOUNT OF SHORT WAVE ENERGY BREAKING INTO THE LONG
WAVE RIDGE ALONG THE WEST COAST. SHOULD THIS NOT BE AS STRONG, THEN
THE LONG WAVE RIDGE WILL MORE EFFECTIVELY REMAIN FARTHER WEST AND
ALLOW A FARTHER WEST POSITION ON THE LONG WAVE TROUGH OVER THE
PLAINS, AND A FARTHER WEST TRACK OF THE GULF SYSTEM. OTHER SOURCES
OF CONCERN INCLUDE CONVECTIVE INFLUENCE ON THE EVOLUTION OF SURFACE
LOW PRESSURE ALONG THE GULF COAST AND SOUTHEAST STATES WHICH COULD
IN FACT PLAY A STRONG ROLE IN THE EVOLUTION OF THE SYSTEM, OR IT MAY
NOT, WHICH WOULD ALSO FAVOR A WESTWARD TREND TO THE TRACK OF THE
SURFACE SYSTEM IN THE MODEL SOLUTIONS. AS IT STANDS NOW, THERE
REMAINS CONSIDERABLE SPREAD IN THE INDIVIDUAL GLOBAL MODELS IN TERMS
OF BOTH THE TIMING AND TRACK OF THE SYSTEM. PREFER THE SLOWER AND
WESTWARD ADJUSTMENTS SHOWN IN THE 12Z ECMWF AS OPPOSED TO THE FASTER
GFS WITH A TRACK ALONG THE SPINE OF THE APPALACHIANS. THE PARALLEL
GFS IS WEST OF THE APPALACHIANS BUT STILL TOO FAST. TOGETHER THIS
OFFERS ENOUGH EVIDENCE COMBINED WITH THE LAST PANEL OF THE NAM TO
INDICATE WE WILL AT LEAST GET BRUSHED BY THE WESTERN FRINGES OF THE
SYSTEM WEDNESDAY NIGHT AND THURSDAY. THIS IS IN SUPPORT OF OUR GOING
FORECAST BUT WITH CONTINUED VIGILANCE FOR A WESTWARD TREND.
ONCE THE LEAD WAVE EXITS TO OUR NORTH/EAST ON THURSDAY, THE DOOR
WILL BE OPEN FOR COLD AIR TO ESTABLISH RESIDENCE IN SE MICHIGAN
THROUGH THE WEEKEND. THE PRESENCE OF THE UPPER LEVEL TROUGH/LOW AND
ASSOCIATED COLD POOL WILL COMBINE WITH THE COLD NORTHWEST FLOW IN
THE LOW LEVELS AND KEEP UNSETTLED CONDITIONS OVER THE REGION. SNOW
SHOWERS WILL BE COMMON IN THIS SCENARIO, ESPECIALLY FRIDAY AND
SATURDAY, WITH HIGHS LIMITED TO THE 30S.
MARINE...
WINDS WILL INCREASE THIS EVENING FROM THE NORTHWEST BEHIND THE
PASSAGE OF A COLD FRONT. COLD AIR STREAMING ACROSS THE WARMER LAKE
WATERS WILL HELP GENERATE WIND GUSTS TO 25 KNOTS ACROSS THE
NEARSHORE WATERS OF LAKE HURON AND SAGINAW BAY. THE GUSTY WINDS AND
LONG FETCH ACROSS LAKE HURON WILL ALLOW WAVES TO BUILD AS HIGH AS 7
FEET. WINDS AND WAVES WILL DECREASE TOMORROW AS WEAK HIGH PRESSURE
BUILDS INTO THE REGION AND THE WIND DIRECTION TURNS TO THE WEST.
WINDS OVER LAKE ST CLAIR AND WESTERN LAKE ERIE WILL BE A LITTLE
LIGHTER...HOWEVER A BRIEF PERIOD WITH NORTHWESTERLY GUSTS TO 22
KNOTS CAN BE EXPECTED FROM 1000 PM THROUGH 200 AM.
WINDS WILL BEGIN TO INCREASE AGAIN FROM THE SOUTHWEST MONDAY
EVENING. THIS WILL ALLOW WAVE HEIGHTS TO BEGIN BUILDING ONCE
AGAIN...POSSIBLY REACHING THE 3 TO 5 FOOT CRITERIA NEEDED FOR A
SMALL CRAFT ADVISORY.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...SAGINAW BAY...UNTIL 10 AM MONDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
HURON...UNTIL 4 PM MONDAY.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
AVIATION.....KURIMSKI
SHORT TERM...HLO
LONG TERM....BT
MARINE.......HLO
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