FXUS63 KMQT 231133 AAA
AFDMQT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MARQUETTE MI
633 AM EST WED DEC 23 2009
.UPDATED FOR TAF.
&&
.SYNOPSIS...
WV IMAGERY AND RUC ANALYSIS INDICATED A BLOCKY PATTERN WITH
MID/UPPER LEVEL LOWS OVER NRN NEW ENGLAND...THE SW CONUS AND ALBERTA
RESULTING IN CONFLUENT NW FLOW FROM NRN ONTARIO THROUGH THE
GREAT LAKES. AT THE SFC...A RIDGE FROM NRN ONTARIO INTO THE CNTRL
GREAT LAKES CONTINUED TO BRING DRY AIR INTO THE REGION WITH ACYC
NORTHEASTERLY FLOW. RADAR SHOWED THAT SOME -SHSN/FLURRIES WAS
TRANSITIONING TO MORE MULTIPLE WIND PARALLEL BANDS ALIGNED WITH NE
FLOW. IR LOOP INDICATED THAT LOWER CLOUDS HAD SPREAD BACK ACROSS THE
N AND E CWA LEAVING A SMALL CLEAR AREA OVER THE S AND W PORTION OF
UPPER MI.
&&
.DISCUSSION...
TODAY AND TONIGHT...ENE FLOW OFF OF LAKE SUPERIOR MAY BRING SOME
LIGHT SNOW SHOWERS INTO NORTH CNTRL UPPER MI AND THE KEWEENAW THIS
MORNING. HOWEVER...WITH 900-850 MB TEMPS ONLY TO AROUND -11C AND
INVERSION HEIGHTS NEAR 3K FT...NO MORE THAN FLURRIES ARE EXPECTED.
OTHERWISE...LOWER CLOUDS SHOULD CONTINUE TO SPREAD ACROSS UPPER
MI...PER SATELLITE TRENDS AND NAM 925-900 MB RH FCST. PCPN WITH WAA/
280K-290K ISENTROPIC LIFT AHEAD OF THE STORM SYSTEM MOVING INTO THE
SRN PLAINS MAY APPROACH SW UPPER MI LATE TONIGHT BUT WITH LITTLE
ACCUMULATIONS BY 12Z/THU AS DRY LOW LEVEL EASTERLY FLOW LIMITS THE
ADVANCE OF THE PCPN INTO UPPER MI.
THURSDAY INTO FRIDAY...THE MODELS WERE IN DECENT AGREEMENT WITH THE
OVERALL PATTERN WITH PHASING OF THE ALBERTA AND SW CONUS MID LEVEL
LOWS AND CONSOLIDATION OF A STACKED LOW OVER IA FRI. A LARGE AREA OF
ISENTROPIC LIFT AND ABUNDANT LOW LEVEL MOISTURE LIFT TOWARD THE
REGION WITH AT LEAST 4 G/KG AVAILABLE IN THE 280K-290K LAYER.
SIGNIFICANT DIFFERENCES REMAIN THOUGH WITH THE QPF PATTERN AND LOW
LEVEL THERMAL FIELDS. THE NAM IS SLOWEST IN BRINGING THE PCPN INTO
UPPER MI WITH MUCH LIGHTER AMOUNTS INTO WEST UPPER MI WITH TOTAL
AMOUNTS ONLY TO A QUARTER INCH NEAR IWD BY 18Z/FRI. THE GFS
DISPLAYED GOOD CONTINUITY WITH ITS PREVIOUS FCSTS WITH AMOUNTS UP TO
1.25 INCH. SO...KEPT THE FCST TRENDED TOWARD A COMPROMISE VALUE NEAR
THE 00Z/23 ECMWF TO ABOUT 0.75 INCH. WITH SNOW/WATER RATIO VALUES
NEAR 12/1...SNOWFALL AMOUNTS WILL MARGINAL FOR WARNING CRITERIA.
GIVEN THE AMOUNT OF MODEL UNCERTAINTY...WILL JUST LEAVE THE WATCH IN
PLACE. GIVEN THE INFLOW OF DRY AIR FROM THE RETREATING NRN ONTARIO
HIGH...CANNOT DISCOUNT THE SLOWER/DRIER NAM SCENARIO. QPF AMOUNTS
INTO THE REST OF UPPER MI WOULD BE LIGHT ENOUGH SO THAT MAINLY ADVY
LEVEL SNOW WOULD BE EXPECTED...IN THE 2 TO 6 INCH RANGE FROM LATE
THU NIGHT THROUGH FRI.
PCPN TYPE FCST WILL ALSO BE TRICKY. THE GFS THERMAL PROFILES SUPPORT
MAINLY SNOW OVER MOST OF UPPER MI EXCEPT THE SOUTHEAST WITH
EVAPORATIVE COOLING AND LIFT ELIMINATING THE 900-800 MB WARM LAYER.
HOWEVER...THE NAM OFTEN PERFORMS BETTER WITH LOW LEVEL TEMP DETAILS
THAN THE GFS IN SUCH WAA EVENTS. SO...THE FCST CONTINUES TO MENTION
POTENTIAL FOR RAIN OR FZRA OVER THE CNTRL AND EAST. MAINLY JUST
RAIN/SNOW IS EXPECTED NEAR THE WARMING INFLUENCE OF LAKE MICHIGAN.
OVER CNTRL UPPER MI...EXPECT TEMPS TO ONLY SLOWLY CLIMB TO AROUND
FREEZING FROM LATE THU NIGHT INTO FRI MORNING. IF A MORE PRONOUNCED
WARM LAYER DEVELOPS WITH STRONG SE 40-50 KT 900-800 MB INFLOW...SOME
FZRA/SLEET WOULD BE POSSIBLE. HIGH UNCERTAINTY ON ANY
AMOUNTS...LIKELY BLO 0.10 INCH. A WARM ENOUGH BNDRY LAYER WOULD BE
MORE LIKELY OVER LOWER ELEVATIONS IN THE EAST HALF...PER MDL FCST
SOUNDINGS AND WET-BULB ZERO EEIGHTS... WHERE RAIN MAY MIX WITH THE
SNOW TIL LATE IN THE DAY WHEN COLDER AIR MOVES IN FROM THE SOUTH IN
THE WRAPPED UP SYSTEM.
FRIDAY NIGHT AND SATURDAY...LITTLE CHANGE WAS MADE TO THE PREVIOUS
FCST AS PERIODS OF LIGHT SNOW SHOULD CONTINUE AS THE MID LEVEL LOW
ONLY SLOWLY EDGES INTO SRN WI...THE DRY SLOW PIVOTS THROUGH THE
AREA...AND THE HEAVIER TROWAL REGION PCPN REMAINS WEST OF UPPER MI.
&&
.AVIATION.../FOR THE 12Z TAF ISSUANCE/...
SOME MVFR CLOUDS OVER LAKE SUPERIOR AND FAR WESTERN UPPER MICHIGAN
CONTINUES TO WRAP BACK ACROSS CMX AND SAW EARLY THIS MORNING.
OTHERWISE...WINDS WILL BECOME MORE EAST NORTHEAST LESS THAN OR EQUAL
TO 10 KNOTS THROUGH THE PERIOD. AT CMX THE RESULT WILL BE UPSLOPE
CONDITIONS...WITH A BETTER CHANCE OF THOSE MVFR CEILINGS COMING BACK
INTO PLAY. IT SHOULD TAKE A FEW HOURS LONGER AT SAW...WITH HIGH
CLOUDS BEGINNING TO STREAM ACROSS DURING THE LATE AFTERNOON AND
EARLY EVENING HOURS AT BOTH SITES...WITH THE LOWER LEVELS DRYING OUT
A BIT AFTER 00Z AS WINDS BECOME MORE OFFSHORE.
&&
.MARINE /FOR THE 4 AM LAKE SUPERIOR ISSUANCE/...
WINDS WILL REMAIN LIGHT UNDER 25 KNOTS UNTIL GALES ARRIVE FOR THU
WITH APPROACH OF THE STRONG LOW PRESSURE SYSTEM FROM THE SOUTH.
FOLLOWED THE GFS/ECMWF SOLUTION WHICH BRINGS THE LOW UP NORTH AND
THEN SLOWS IT DOWN OVER OUR AREA AND WEAKENS IT WITH TIME...SO
STRONGEST WINDS LOOK TO BE THROUGH FRI BEFORE THE LOW AND PRESSURE
GRADIENT WEAKEN ENOUGH FOR WINDS TO GO BELOW GALES.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
EVENING FOR MIZ002-009-010.
LAKE SUPERIOR...
NONE.
LAKE MICHIGAN...
NONE.
&&
$$
DISCUSSION...JLB
AVIATION...DLG
MARINE...DLG
