FXUS63 KMQT 061147 AAA
AFDMQT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MARQUETTE MI
647 AM EST SUN DEC 6 2009
...MAJOR WINTER STORM POSSIBLE BY MID WEEK...
.SYNOPSIS...
COLD TROUGHING CONTINUES ACROSS UPR GREAT LAKES WITH MAINLY WNW
FLOW LK EFFECT THE END RESULT. DOMINANT LK EFFECT SNOW SHOWERS
BROUGHT SEVERAL INCHES OF SNOW TO THE KEWEENAW PENINSULA THE LAST
24-48 HRS...BUT LOW-LEVEL WINDS OVR WESTERN LK SUPERIOR INTO NW UPR
MI ARE NOW BECOMING LESS FAVORABLE FOR VERY STRONG SNOW SHOWERS.
IN THE LARGER VIEW...EXTENSION OF THE TROUGHING HEADS BACK INTO WRN
CONUS WITH A UPR LOW OVR NRN UT. SHORTWAVE TROUGH ALONG THE BRITISH
COLUMBIA/WASHINGTON BORDER WILL MERGE INTO THIS UPR LOW...KICKING A
LEAD SHORTWAVE TROUGH INTO THE CENTRAL GREAT LAKES ON MONDAY. NEWLY
FORMED UPR TROUGH OVR THE WRN CONUS EJECTS OUT INTO THE SOUTHERN
PLAINS ON TUE. MODELS ARE QUITE PERSISTENT IN SHOWING A STRONG SFC
LOW LIFTING INTO THE CNTRL GREAT LAKES WED. IF THIS LOW TRACK DOES
VERIFY...A WIDESPREAD HEAVY SNOWFALL WITH BLSN WOULD OCCUR OVER ALL
THE CWA TUE NIGHT/WED/WED NIGHT WITH HEAVY LK EFFECT SNOWS ALONG LK
SUPERIOR TO END THE WEEK FOR W/NW FLOW AREAS.
&&
.DISCUSSION...
LINGERING LK EFFECT LOSING ITS PUNCH AS LOW-LEVEL CONVERGENCE HAS
FINALLY WEAKENED AND LARGE SCALE ENVIRONMENT BECOMES LESS FAVORABLE
AS SHORTWAVE TROUGH MOVES INTO QUEBEC. RESULT IS SUBSIDENCE AND
LOWERING INVERSION HEIGHTS. LAST AREA OF HEAVIER SNOW SHOWERS
CURRENTLY PUSHING ONSHORE OVR EASTERN ALGER TOWARD NORTHERN LUCE
COUNTY. RADAR INDICATES SNOW BANDS ARE REMAINING TRANSIENT WITH A
GENERAL NW STEERING FLOW FAVORING MULTIPLE BANDED SNOW VERSUS A
SINGLE DOMINANT BAND OF SNOW. DESPITE NW FLOW...STILL WILL SEE
ENHANCED CONVERGENCE OVR NE CWA AND THIS IS WHERE HIGHEST POPS
WILL BE LOCATED TODAY. LOCAL SNOW AMOUNTS UP TO 5 INCHES POSSIBLE IN
THE MORE PERSISTENT SNOW SHOWERS...BUT WIDESPREAD ADVY LEVEL SNOWS
NOT ANTICIPATED. POSSIBLY UP TO A FEW INCHES IN THE WEST...ALTHOUGH
DRY AIR AND LOWERING INVERSION MAKES EVEN MORE OF AN IMPACT THERE.
925MB TEMPS SIMILAR TO SAT...SO HAVE KEPT TEMPS WITHIN A FEW DEGREES
OF MAX TEMPS ON SAT.
LEAD SHORTWAVE EMERGING OUT OF THE SW CONUS BRINGS SWATH OF LGT TO
MODERATE SNOW TO WESTERN AND CNTRL GREAT LAKES FOR MONDAY. SYNOPTIC
PCPN STAYS TO THE SOUTH OF UPR MI AS WEAK SFC-H85 LOWS TRACK ACROSS
CNTRL LWR MI. ISSUE TO CONTEND WITH OVR OUR CWA WILL BE PERSISTENT
LK EFFECT SNOW SHOWERS CLOSE TO LAKE SUPERIOR. BLYR WINDS LIGHT AND
DIRECTION WILL BE COMPLETELY DEPENDANT ON HOW FAR NORTH SFC WAVE
TRACKS. RIGHT NOW...EXPECT LL WINDS MAINLY FM NW DIRECTION...BUT
WINDS ARE SO LIGHT...MESOSCALE EFFECTS MAY DISRUPT ANY GENERAL WIND
DIRECTION. ALTHOUGH INVERSIONS ARE LOWER THAN 5KFT AND LARGE SCALE
SUBSIDENCE IS IN PLACE...MAJORITY OF MOIST LAYER IS WITHIN BETTER
SNOW GROWTH ZONE...WITH TEMPS BTWN -10C AND -15C. LOCAL LK EFFECT
GUIDANCE AND HIGH END QPF FM HIGHER RESOLUTION NAM/LOCAL WRF-ARW
MODELS SUGGEST SNOWFALL WILL TOP OUT AT ONLY A FEW INCHES. IF A
PERSISTENT CONVERGENCE BAND COULD DEVELOP...MAY SEE LOCALIZED
HIGHER AMTS. FOR NOW...WENT WITH UP TO 3 INCHES IN NW FLOW AREAS
OF HOUGHTON COUNTY AND OVR NE CWA.
FOCUS THEN TURNS TO DEVELOPING POTENTIAL FOR HIGH IMPACT WINTER
STORM EVENT TUE/TUE NIGHT/WED/WED NIGHT OVER MUCH OF THE CWA. AS
ALLUDED TO EARLIER THE PRIMARY SHORTWAVE TROUGH DRIVING THE
FORMATION OF THE SYSTEM IS STILL JUST ALONG THE NW CONUS ATTM.
EVENTUALLY...THIS TROUGH HELPS SPIN UP A STRONG SFC LOW OVR THE
SOUTHERN PLAINS ON TUE. MODEL GUIDANCE SEEMS TO BE LATCHING ONTO A
COMMON IDEA FOR THE STRENGTH AND TRACK OF THE SFC LOW LATER TUE INTO
WED AND THU. LAST FEW RUNS OF BOTH THE GFS/ECMWF ARE PROJECTING A
SUB 980MB LOW HEADING TOWARD CHICAGO BY DAYBREAK WED AND TO GEORGIAN
BAY BY WED EVENING. UPR TROUGH BECOMING NEGATIVELY TILTED...AN OPEN
GULF OF MEXICO ALLOWING FOR PWATS 150-200 PCT OF NORMAL...AND A
COUPLED JET STRUCTURE RESULT IN A DEEPENING SFC LOW ON WED WITH A
LARGE AREA OF DEEP MOISTURE/STRONG Q-VECTOR CONVERGENCE/LARGE SCALE
LIFT CONTRIBUTING TO A SWATH OF MODERATE TO HEAVY SNOW OVR MUCH OF
THE WESTERN GREAT LAKES TUE NIGHT INTO WEDNESDAY. A GENERAL QPF
CONSENSUS SUGGEST TOTAL AMOUNTS TUE NIGHT AND WED ON AVERAGE OF
0.40-0.60 WITH HIGHER AMOUNTS WHERE ONSHORE ENE WINDS LEAD TO LAKE
ENHANCEMENT AS H85 TEMPS ARE -8C TO -10C WITH LK TEMPS AROUND 6C.
QUICK LOOK AT SOUNDINGS AND GUIDANCE FM HPC INDICATES SNOW RATIOS IN
THE 15-20:1 RANGE SO SNOW AMOUNTS OVR 10 INCHES WOULD BE LIKELY IN
MANY AREAS. TIGHT PRESSURE GRADIENT WITH THE SFC LOW ALSO LEADS TO
STRONG BLYR WINDS AND THE POTENTIAL OF BLSN AT THE PEAK OF THE EVENT.
SYSTEM SNOW ENDS FM SW TO NE WED NIGHT...BUT AS H85 TEMPS DROP TO
-12C TO -14C BY THU MORNING SIGNIFICANT LAKE ENHANCED/EFFECT SNOW
AND BLSN WOULD OCCUR IN N/NW FLOW AREAS NEAR LK SUPERIOR.
925MB-850MB TEMPS (-15C TO -20C) EASILY COLD ENOUGH FOR LK EFFECT
SNOWS TO PERSIST ALL THE WAY INTO FRIDAY FOR MAINLY W FLOW AREAS
NEAR LK SUPERIOR. ADJUSTED POPS UP TO ACCOUNT FOR THIS AND ALSO
LOWERED HIGH TEMPS THU AND FRI AS GUIDANCE IS TRENDED LOWER WITH
TEMPS SPILLING INTO THE AREA IN WAKE OF THE MID WEEK STORM. FURTHER
ADJUSTMENTS MAY BE NECESSARY.
THOUGHT ABOUT ISSUING A WATCH FOR THE STORM...BUT SINCE THIS IS A
SOLID 2-3 DAYS AWAY...DECIDED TO GO WITH A SPECIAL WEATHER STATEMENT
INSTEAD. DOES SEEM LIKE IF THE TRACK HOLDS UP WE WILL NEED TO ISSUE
WINTER STORM WATCHES IN THE NEXT DAY.
&&
.AVIATION /FOR THE 12Z TAF ISSUANCE/...
MVFR CONDITIONS WILL CONTINUE THROUGH THE PERIOD AS LAKE EFFECT SNOW
IN NW FLOW REGIME AFFECT KCMX. THERE COULD BE A FEW TIMES WHEN VIS
OR CIGS GET DOWN TO IFR FOR BRIEF TIMES WHEN HEAVIER BANDS COME
THROUGH. ALSO THIS MORNING...VFR CONDITIONS WILL PREDOMINATE WITH
MVFR BANDS GOING THROUGH KCMX AT TIMES.
AT KSAW...CONDITIONS WILL PROBABLY REMAIN VFR THRU THIS FCST PERIOD.
WITH A NW WIND DURING THE DAY...EXPECT STRATOCU AND MAYBE SOME
FLURRIES OFF LAKE SUPERIOR...BUT THERE SHOULD STILL BE SUFFICIENT
DOWNSLOPE COMPONENT TO KEEP CIGS VFR.
&&
.MARINE... /FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE/
THE MAIN STORY FOR THIS FORECAST PERIOD WILL BE THE STRONG WINTER
STORM FOR MID WEEK AND LIKELY GALES ASSOCIATED WITH IT. THE QUESTION
OF THE STRENGTH OF THE LOW AND TRACK. FOLLOWED A COMBO OF GFS/ECMWF
FOR THIS FORECAST AND WOULD NOT BE SURPRISED TO SEE SOME STORM FORCE
WIND GUSTS ACROSS LAKE SUPERIOR THEN FOR WED THROUGH THU. ONE MAJOR
CHANGE I MADE WAS TO KEEP WINDS GOING INTO FRIDAY. PRESSURE GRADIENT
GETS AWFULLY TIGHT THROUGH THEN AND THIS HIGH WIND EVENT WILL BE
LONG LASTING. UNTIL MID WEEK...WINDS WILL BE LIGHT AS HIGH PRESSURE
COMES ACROSS.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...NONE.
LAKE SUPERIOR...NONE.
LAKE MICHIGAN...NONE.
&&
$$
SYNOPSIS...JLA
DISCUSSION...JLA
AVIATION...07
MARINE...07
