FXUS63 KDLH 081636 AAA
AFDDLH
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DULUTH MN
1036 AM CST TUE DEC 8 2009
.UPDATE...
RAPID CHANGES APPEAR TO HAVE FINALLY BEGUN OVER THE PAST HOUR WITH
APPROACH OF UPSTREAM INTENSIFYING WINTER STORM. LOW LEVEL FLOW
FIELD IS FINALLY RESPONDING TO STRONG PRESSURE FALLS ACROSS MOST
OF THE PLAINS AND UPPER MIDWEST..WITH SFC WINDS NOW COMING AROUND
TO EAST/NORTHEAST. LAKE-EFFECT SNOW BANDS THAT HAVE BEEN
PERSISTENT ALL NIGHT OVER WRN LK SUPERIOR HAVE SHOWN A TENDENCY
TO BEGIN ADVECTING WESTWARD IN THE LAST HOUR..ALONG WITH A
TRANSITION TO A MORE ENE/WSW ORIENTED BAND ON THE ECHOES EAST OF
ASHLAND. IN ADDITION..KMPX RADAR INDICATES THE LEADING EDGE OF
THE LARGE SHIELD OF SYNOPTIC-SCALE SNOW SPREADING RAPIDLY TO THE
NORTHEAST ACROSS SOUTHERN MINNESOTA.
IT WILL LIKELY TAKE SEVERAL MORE HOURS FOR THE LOWER LEVELS TO
SATURATE ACROSS THE SOUTHERN SECTIONS OF THE DLH CWA..WITH OUR
BEST ESTIMATE OF SNOW STARTING SOMETIME BETWEEN 1-4 PM ACROSS OUR
SOUTHERN TIER. THE LAKE EFFECT BANDS WILL TAKE A LITTLE WHILE
LONGER TO BEGIN AFFECTING LAND AREAS..BUT THIS IS EXPECTED SHORTLY
AFTER NOON.
AT THIS TIME WE ARE GOING TO HOLD CLOSE TO THE PREVIOUS
FORECAST WITH SNOW AMOUNTS. HOWEVER..THE WRN PERIPHERY OF THE
WARNING AREA WILL BE BORDERLINE AT BEST WITH SNOW AMOUNTS.
CONFIDENCE REMAINS HIGHEST OVER NW WI..WHERE AT LEAST 8-10 INCHES
OF SYNOPTIC SNOW IS ANTICIPATED..WITH LAKE EFFECT ZONES GETTING
POUNDED WITH 12-18 INCHES BY THE TIME THE STORM WINDS DOWN.
WE WILL LIKELY BE MAKING SOME SLIGHT ADJUSTMENTS TO THE HEADLINES
IN A COUPLE HOURS AFTER LOOKING AT THE 12Z GUIDANCE A LITTLE
MORE. UPDATES WILL BE OUT ASAP.
MILLER/MELDE
&&
.PREV DISCUSSION... /ISSUED 600 AM CST TUE DEC 8 2009/
UPDATE...FOR 18Z TAF DISCUSSION...
AVIATION...12 Z TAF ISSUANCE...MAINLY VFR ACROSS TAF SITES DURING THE EARLY
MORNING UNTIL ABOUT 16Z-18Z WHEN MVFR CIGS SPREAD INTO THE
SOUTHERN TERMINALS. SNOW APPEARS TO GET UNDER WAY AT KBRD/KHYR
FIRST AROUND 18Z...KDLH ABOUT 21Z...KHIB 00Z/09. KINL MAY NOT SEE
SNOW UNTIL AFTER 06Z. CIGS SHOULD BE MVFR INITIALLY...LOWERING
INTO THE IFR RANGE. CONSIDERABLE BLOWING AND DRIFTING OF SNOW WILL
REDUCE VISIBILITIES...AND CAN BE EXPECTED OVERNIGHT AS DEEPENING
LOW PRESSURE APPROACHES SOUTHERN LAKE MICHIGAN AND WINDS BECOME
NORTHERLY.
PREV DISCUSSION... /ISSUED 420 AM CST TUE DEC 8 2009/
DISCUSSION...FIRST MAJOR WINTER STORM IS THE MAIN FOCUS TODAY.
AT 4 AM...THE WEATHER WAS PRETTY QUIET THIS MORNING. SKIES HAD
CLEARED ACROSS THE NORTHERN AND WESTERN PORTIONS OF THE CWA...AND
TEMPERATURES HAVE RESPONDED ACCORDINGLY. SOME TEMPERATURES WERE IN
THE TEENS BELOW ZERO THIS MORNING WITH LIGHT WINDS AND CLEAR
SKIES. A NEARLY STATIONARY BUT SLIGHTLY MEANDERING BAND OF LOCALLY
HEAVY LAKE EFFECT SNOW WAS POISED JUST OFFSHORE FROM NORTH OF
CLOVERLAND TO SAND BAY. THIS BAND OCCASIONALLY MOVED ONSHORE BUT
THE TREND OVERALL HAS BEEN TO CONSOLIDATE OFFSHORE. THE EXPECTED
LAKE SWIRL ACTUALLY MAY BE STARTING TO TAKE SHAPE...AS THERE HAS
BEEN SOME EVIDENCE OF THE EVOLUTION OF A CYCLONIC TWIST IN THE
LAST SEVERAL RADAR FRAMES. OFFSHORE WINDS DRAINING INTO THE
WESTERN TIP OF THE LAKE WAS CREATING THE CONVERGENCE BAND...BUT
WITH CONTINUED DRAINAGE INTO THE WESTERN BOWL...WE COULD START TO
SEE THIS LINE ROTATE THROUGHOUT THE WESTERN TIP OF THE LAKE.
THE BIGGEST ISSUE THIS MORNING WAS RESOLVING MODEL DIFFERENCES
WITH RESPECT TO SURFACE LOW TRACK AND MODEL QPF. WILL CONTINUE TO
USE A BLEND OF THE GFS AND ECMWF. THE ECMWF CONTINUES TO BE PRETTY
LIGHT ON THE QPF COMPARED TO THE GFS...BUT HAS TRENDED HIGHER IN
THE 00Z MODEL RUN. IN TERMS OF QPF...WILL TREND CLOSER TO THE GFS.
AM A LITTLE NERVOUS ABOUT THE ECMWF QPF BEING LOWER...BUT WITH
ARCTIC AIR IN PLACE ACROSS THE CWA...WE SHOULD SEE FAIRLY HIGH
SNOW/WATER RATIOS OF CLOSE TO 20:1.
FOR TODAY...WILL HAVE TO WATCH THE POTENTIAL LAKE SWIRL TO SEE IF
IT EVOLVES INTO CIRCULATING TOWARD THE NORTH SHORE...FROM THE TWIN
PORTS AREA NORTHWARD. FOR THIS REASON...HAVE MAINTAINED CHANCE
POPS FOR THE MORNING HOURS. THE WINTER STORM WARNINGS AND THE
ADVISORIES GO INTO EFFECT AT 18Z. THIS MAY BE A BIT EARLY FOR SOME
OF THE NORTHERN AREAS...BUT WILL JUST TRY TO TREND THE
PRECIPITATION IN AS THE AFTERNOON WEARS ON. HAVE DECIDED TO ADD
THE BRAINERD AREA TO THE ADVISORY...AS ALL MODELS ARE HINTING AT
AN EXTENDED PERIOD OF LIFT WITH THE EVOLVING INVERTED TROUGH IN
THAT AREA. WILL GO WITH 3 TO 6 INCHES THERE. ELSEWHERE...WILL KEEP
SNOWFALL AMOUNTS FAIRLY SIMILAR TO THE PREVIOUS FORECAST. HAVE CUT
AMOUNTS DOWN IN A FEW AREAS...BUT ONLY BY AN INCH OR TWO. STILL
LOOKS GOOD FOR A RAPID NORTHWARD PROGRESSION OF SNOW AS THE
AFTERNOON WEARS ON.
FOR TONIGHT AND WEDNESDAY...RAPID CYCLOGENESIS AS THE LOW
PRESSURE SYSTEM MOVES INTO THE PLAINS AND EVOLVES INTO A WELL
DEVELOPED STORM AS IT APPROACHES THE SOUTHERN GREAT LAKES. MOST
MODELS TAKE THE LOW TO SOUTHERN LAKE MICHIGAN BY 12Z WEDNESDAY.
TONIGHT IS WHEN WE SHOULD SEE THE HEAVIEST SYNOPTIC SCALE
SNOW...WITH SNOW GRADUALLY DIMINISHING MOST AREAS AS THE DAY WEARS
ON. THE EXCEPTION WILL BE AREAS OF NW WI...AND ESPECIALLY THE
SOUTH SHORE. HAVE INCREASED AMOUNTS IN THE DOUGLAS COUNTY
AREA...AS THE 5 KM WRF EMS IS SHOWING A WELL DEFINED LAKE ENHANCED
BAND MOVING INTO THAT AREA ON WEDNESDAY. COULD BE SOME IMPRESSIVE
SNOWFALL RATES ALONG THE SOUTH SHORE...WITH MOST AREAS SEEING A
TOTAL OF 12 TO 18 INCHES NEAR LAKE SUPERIOR ON THE SOUTH SHORE.
THE WINDS WILL BE THE BIG PROBLEM TONIGHT AND WEDNESDAY...WITH
GALE FORCE WINDS ON LAKE SUPERIOR...AND STRONG WINDS OF UP TO 30
MPH OR SO ON LAND. THIS WILL CREATE SIGNIFICANT BLOWING AND
DRIFTING OF THE FLUFFY NEW SNOW.
TRAVEL IS EXPECTED TO BECOME DIFFICULT ACROSS THE CWA
TONIGHT...WITH SNOW STARTING TO ACCUMULATE BY THE EVENING COMMUTE.
THE MORNING COMMUTE ON WEDNESDAY WILL BE EVEN WORSE...WITH FALLING
AND BLOWING SNOW CONTRIBUTING TO LOW VISIBILITIES AND SNOW COVERED
ROADWAYS. IF YOU HAVE TRAVEL PLANS OVER THE NEXT FEW DAYS...BE
SURE TO KEEP A CLOSE EYE ON THE LATEST FORECAST AND ROAD CONDITIONS.
WEDNESDAY NIGHT THROUGH SUNDAY NIGHT...HAVE LEANED TOWARD THE GFS
WHICH HAS HAD GOOD RUN TO RUN CONTINUITY WITH ITSELF...AND HAS
COME NICELY IN LINE WITH ITS ENSEMBLE MEMBERS. ADDED A BLEND OF
THE ECMWF DURING THIS PERIOD AW WELL. THE LATEST ECMWF HAS SLOWED
DOWN A TOUCH AND COME A BIT FURTHER NORTH...SO THAT THE DEEPENING
LOW WILL HAVE REACHED ITS LOWEST PRESSURE OVER LAKE HURON ON
WEDNESDAY NIGHT BEFORE ITS PULLS OUT NE AND FILLS. SOME BLOWING
AND DRIFTING OF THE NEW SNOW WILL DURING THE EARLY PART OF THE
OVERNIGHT WILL WANE FROM WEST TO EAST. COLD NW FLOW ENSUES ON THE
BACK SIDE OF THE LOW WHICH WILL KEEP FLUFFY LAKE EFFECT SNOW
SHOWERS POSSIBLE ALONG THE SOUTH SHORE WED/NIGHT...AND THEN WINDS
BECOME MORE BACKED TO THE WEST BY THURSDAY AFTERNOON. THIS WILL
SHIFT THE BEST CONVERGENCE ZONE OVER THE BAYFIELD PENINSULA. A FEW
ADDITIONAL INCHES ARE POSSIBLE ALONG THE SOUTH SHORE.
ADDITIONAL PIECES OF ENERGY ON THE SOUTHERN END OF THE POLAR VORTEX
WILL MOVE THROUGH THE NORTHERN TIER ON THURSDAY. THERE IS LITTLE IN
THE WAY OF ANY SURFACE REFLECTION AND MOST LIFT WILL BE IN SOUTHERN
CANADA...BUT WE LEFT SLIGHT CHANCE POPS ALONE FOR NOW...MAYBE MORE
LIKE FLURRIES.
FOR THE REMAINDER OF THE WEEK...THE POLAR VORTEX WILL THEN ROTATE
SOUTH TOWARDS THE INTERNATIONAL BORDER FRIDAY NIGHT INTO SATURDAY.
THE MAIN ENERGY WILL AGAIN BE NORTH WITH THE SURFACE LOW ALONG THE
BORDERLAND..BUT THE VORTEX WILL BE ACCOMPANIED BY A POTENT COLD
FRONT THAT WILL PUSH THROUGH THE REGION. WE HAVE ADDED/INCREASED
POPS A TOUCH FRIDAY NIGHT IN KOOCH COUNTY...AND THEN SPREAD SLIGHT
CHC POPS FOR LIGHT SNOW EAST IN NW WISC SATURDAY AFTERNOON. AND
WHILE IT HAS BEEN QUITE COLD FOR A FEW DAYS...THIS FRONT WILL
PROVIDE A REINFORCING SLAM IN THE FACE SATURDAY AFTERNOON AND
ESPECIALLY SATURDAY NIGHT...WITH THE COLDEST OVERNIGHT LOWS OF THE
SEASON EXPECTED. HIGH PRESSURE BUILDS IN BEHIND THE FRONT TO PROVIDE
FOR DRY CONDITIONS SAT PM THROUGH SUNDAY...AND THOUGH WE'LL SEE SOME
SUNSHINE AND A SLOW WARMUP SUNDAY INTO MONDAY...TEMPS WILL REMAIN
BELOW NORMAL.
&&
.POINT TEMPS/POPS...
DLH 10 15 -1 7 / 100 100 20 10
INL -2 9 -8 2 / 50 60 10 20
BRD 5 10 -9 6 / 90 70 10 10
HYR 15 19 -4 5 / 100 100 30 10
ASX 20 22 3 9 / 100 100 70 20
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR
MNZ012-019>021-037-038.
WINTER WEATHER ADVISORY UNTIL 6 PM CST WEDNESDAY FOR MNZ034>036.
WI...WINTER STORM WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR
WIZ001-006>009.
WINTER STORM WARNING UNTIL 6 AM CST THURSDAY FOR WIZ002>004.
LS...SMALL CRAFT ADVISORY FROM 6 PM WEDNESDAY TO 6 PM CST THURSDAY
FOR LSZ121-140>148.
GALE WARNING FROM 6 PM THIS EVENING TO 6 PM CST WEDNESDAY FOR
LSZ121-140>148.
&&
$$
