FXUS63 KARX 090358
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
958 PM CST TUE DEC 8 2009
.UPDATE...
GOING FORECAST FOR THE WINTER STORM PRETTY MUCH ON TRACK...THOUGH
THE QUESTION IS IF MORE SNOW IS POSSIBLE THAN WHAT IS IN THE
FORECAST.
03Z WATER VAPOR LOOP ALONG WITH RUC 500MB HEIGHT ANALAYSIS SHOWED A
NEGATIVELY TROUGH STRETCHING FROM CENTRAL NEBRASKA INTO WESTERN
MISSOURI...WITH BUILDING RIDGING AHEAD OF IT OVER THE WESTERN GREAT
LAKES. THIS RIDGING IS ALSO BEING FORCED BY A LOW LEVEL JET AT
850MB...NOTED ON PROFILERS AND RADAR VAD WIND PROFILES...EXTENDING
FROM THE GULF OF MEXICO INTO INDIANA...THEN WRAPPING BACK TO THE
WEST INTO SOUTHEAST MINNESOTA. THIS LOW LEVEL JET IS TRANSPORTING
BOTH WARMTH AND MOISTURE NORTHWARD...AND AT A FAIRLY QUICK RATE
GIVEN WIND SPEEDS ON THE ORDER OF 40-50 KNOTS. HOWEVER...WITH A COLD
AIRMASS OVER THE UPPER MISSISSIPPI VALLEY REGION...THE NET RESULT OF
ALL THE MOISTURE ADVECTION HAS BEEN EXPANSION OF MODERATE TO HEAVY
SNOW THIS EVENING. REFLECTIVITIES CONTINUE TO INCREASE ON THE KARX
RADAR...AND HAVE HAD MANY REPORTS OF 1 TO 1.5 INCH PER HOUR RATES
UNDERNEATH RETURNS OF 28 DBZ OR GREATER. SEE THE LATEST MKEPNSARX
FOR TOTAL SNOWFALL REPORTS. AT THE SURFACE...991MB LOW PRESSURE WAS
LOCATED NEAR ST LOUIS MO. TIGHT PRESSURE GRADIENT EXISTS NORTHWEST
OF THE LOW...WHERE WINDS HAVE BEEN GUSTING 20-30 KNOTS FROM CENTRAL
NEBRASKA EASTWARD THROUGH CENTRAL IOWA.
OVERNIGHT...THE NEGATIVELY TILTED TROUGH WILL CONTINUE DIGGING TO
THE EAST-NORTHEAST...MOVING INTO NORTHWEST ILLINOIS BY 12Z WED. WITH
SUCH STRONG DIGGING...THE ATMOSPHERE IS GOING TO RESPOND BY RAPID
DEEPENING OF THE SURFACE LOW. MODELS ARE IN EXCELLENT AGREEMENT
SHOWING A 979MB LOW OVER CHICAGO. ALSO IN RESPONSE TO THE
DEEPENING...WOULD EXPECT THE DEFORMATION BAND SEEN DEVELOPING ON THE
KARX RADAR TO INTESIFY AS WELL. 18Z GFS/NAM AND 21Z SREF MODEL RUNS
ALL SHOW ABOUT 0.10 TO 0.20 OF AN INCH MORE OF QPF VERSUS THE GOING
FORECAST. NEW 00Z NAM ALSO SHOWS MORE QPF. GIVEN THE WIDE AGREEMENT
AND ONGOING PRECIPITATION TRENDS...RAISED BOTH QPF AND SNOWFALL
AMOUNTS OVERNIGHT. FURTHER INCREASES MAY BE NECESSARY. WIND FORECAST
ALSO ON TRACK...WITH WINDS INCREASING WEST TO EAST THROUGH THE NIGHT
AS THE LOW PASSES TO OUR SOUTHEAST. BEST CHANCE FOR BLIZZARD
CONDITIONS STILL EXISTS OVER SOUTHEAST MINNESOTA AND NORTHEAST IOWA
DURING THE OVERNIGHT HOURS...THEN EXPANDING INTO FAR SOUTHWEST
WISCONSIN WEDNESDAY MORNING.
&&
.SHORT TERM...TONIGHT THROUGH FRIDAY
FORECAST CONCERNS...AS THEY WERE THE PAST SEVERAL DAYS...CONTINUE TO
LASER IN ON THE ON GOING WINTER STORM AND ITS VARIETY OF IMPACTS ON
THE FORECAST AREA.
PREVIOUS FORECAST DISCUSSIONS COULD PROBABLY BE CUT AND PASTED INTO
THIS DISCUSSION...AS THE CONSISTENCY OF THE MODELS...WITHIN AND
COMPARED TO EACH OTHER...CONTINUES OUTSTANDING.
CURRENT SNOW ACROSS THE REGION...PER 88-D RADAR IMAGERY...BEING
MOSTLY DRIVEN BY ISENTROPIC UPGLIDE AND WARM AIR ADVECTION IN THE
LOW LAYERS. MEANWHILE...AN UPPER LEVEL SHORTWAVE TROUGH WAS SLIDING
INTO THE SOUTHERN PLAINS...WILL DRIVE NORTHEAST INTO THE GREAT LAKES
ON WED. THE SFC LOW WITH THIS EVOLVING STORM WILL TAKE THE SAME
TRACK...CENTERED AROUND THE SOUTHERN TIP OF LAKE MICHIGAN BY 12Z
WED. 08.12Z GFS AND NAM ARE IN GREAT AGREEMENT HERE...WITH ONLY A 2
MB DIFFERENCE. AGAIN...ITS A BROKEN RECORD...BUT ALL THE MODELS HAVE
BEEN PAINTING THIS STORM TRACK FOR AT LEAST THE PAST 4 DAYS...WITH
ONLY SMALL CHANGES THAT WOULD HAVE HAD LITTLE IMPACT ON THE SENSIBLE
WEATHER FOR THE LOCAL AREA. THIS SYSTEM BOMBS AS IT MOVES IN...WITH
SFC PRESSURES PROGGED TO DROP FROM 995 AT 00Z TONIGHT...TO 975 BY
12Z WED. THIS INCREASING PRESSURE GRADIENT WILL RESULT IN VERY
STRONG AND GUSTY WINDS DEVELOPING OVERNIGHT...CONTINUING THROUGH
MUCH OF WEDNESDAY. THIS TURNS THIS WINTER STORM FROM AN ALREADY
SIGNIFICANT STORM DUE TO THE HIGH AMOUNTS OF SNOW EXPECTED...TO A
HIGH IMPACT...VERY DANGEROUS STORM FROM THE BLOWING/DRIFTING/REDUCED
VISIBILITY ASPECT BY ADDING THE WIND WITH THE SNOW.
THIS IS THE KIND OF STORM WHERE FATALITIES OCCUR IF PRECAUTIONS ARE
NOT TAKEN.
LOOKING AT SOME OTHER FORCING MECHANISMS...THIS WINTER STORM WILL BE
PUSHED ALONG BY A 120+ KT 300 MB JET...WHICH WILL ENHANCE THE
AVAILABLE LIFT TONIGHT. QG CONVERGENCE IS STRONG THROUGH THE
LAYERS...MAXIMIZED FOR THE FORECAST AREA BETWEEN 00-12Z. PV
ADVECTION WITH THE STORM IS MAXED AT 06Z LOCALLY AND A NORTH-SOUTH
RUNNING TIME/HEIGHT X-SECTION SHOWS THE 2-D FRONTOGENETIC RESPONSE
STILL SLOPING ACROSS THE FORECAST AREA THROUGH 18Z WED. ALL ABOUT
THE SAME AS THE MODELS HAVE BEEN DEPICTED. THERE HAVE BEEN SOME
CHANGES THOUGH...WHICH COULD INDICATE EVEN HIGHER SNOW TOTALS. THE
12Z MODELS ARE SHOWING MORE THETA-E AIR...RICH IN
MOISTURE...WRAPPING AROUND THE SYSTEM...INTO THE DEFORMATION AREA.
THIS COULD LEAD TO THE ACCUMULATING SNOWS LINGERING LONGER ON
WED...WITH HIGHER AMOUNTS AFTER 12Z. THE FAVORABLE DENDRITIC GROWTH
ZONE HAS INCREASED IN DEPTH...WHICH WOULD SUPPORT HIGHER SNOW
RATIOS. COBB OUTPUT VIA THE GFS AND NAM HAVE INCREASED FROM AN
AVERAGE OF 14:1 FOR THE PAST FEW DAYS...TO CLOSER TO 18:1 TONIGHT
THROUGH WED. BELIEVE THIS LOOKS REASONABLE...AND WILL BE INCREASING
SNOW TOTALS A BIT.
AS MENTIONED...THE ADDITION OF THE STRONG/GUSTY WINDS IS WHAT WILL
SEPERATE THIS STORM FROM BEING A SIGNIFICANT SNOW PRODUCER...TO ONE
WHERE WHITE-OUT CONDITIONS ARE COMMON AND THE POTENTIAL FOR WEATHER
RELATED FATALITIES ARE HEIGHTEN. THIS IS A VERY DANGEROUS
STORM...AND THAT CANNOT BE OVERSTATED.
SHIFTING THE FOCUS TO THE WIND...AGAIN...PRESSURE GRADIENT TIGHTENS
AS THE BOMBING SYSTEM APPROACHES. NORTHWEST WINDS WILL INCREASE TO
20 TO 30 MPH OVERNIGHT TONIGHT...WITH GUSTS UP TO 40 MPH. WOULDN/T
BE SURPRISED IF THE OPEN/UNSHELTERED AREAS OF SOUTHEAST MN/NORTHEAST
IA EXPERIENCE WINDS OF 25 TO 35 MPH...GUSTS TO 45 MPH...ON WED
MORNING. WITH ABOUT 8 INCHES OF FRESH...POWDERY SNOW BY THE TIME THE
STRONGEST WINDS KICK IN...WITH AN ADDITIONAL SEVERAL INCHES OF SNOW
FALLING...THERE WILL BE SIGNIFICANT BLOWING AND DRIFTING.
VISIBILITIES WILL BE REDUCED TO UNDER 1/4 MILE AT TIMES...AND
WHITE-OUT CONDITIONS APPEAR VERY LIKELY IN THE WINDIER AREAS...IF
NOT ALL OF THE FORECAST AREA...FROM LATE TONIGHT INTO EARLY WED
AFTERNOON.
WILL ALL THIS IN MIND...HAVE UPGRADED THE WINTER STORM WARNING TO A
BLIZZARD WARNING...WHICH WILL ALSO BE IN EFFECT UNTIL 06Z THU.
SO...THE ENTIRE FORECAST AREA IS NOW UNDER A BLIZZARD WARNING.
LASTLY...HAVEN/T TOUCHED ON THE DANGEROUS WIND CHILLS THAT ARE
EXPECTED ON THE BACKSIDE OF THIS SYSTEM. LOTS OF COLD AIR MOVES IN
ON WED AS THE STORM SYSTEM PULLS NORTHEAST. COUPLE THIS WITH WINDS
OF 15 TO 20 MPH...AND WIND CHILLS OF 20 TO 25 BELOW ZERO ARE
ANTICIPATED BY 12Z THU. A PARTING SLAP FROM THIS
DANGEROUS...POTENTIALLY DEADLY WINTER STORM. AFTER THE WARNING
EXPIRES...A WIND CHILL ADVISORY MIGHT BE NEEDED FOR THU MORNING.
.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY
MODELS IN GENERAL AGREEMENT WITH THE OVERALL UPPER LEVEL FLOW
BECOMING ZONAL FOR THE WEEKEND INTO EARLY NEXT WEEK. SOME
DIFFERENCES IN HOW THEY HANDLE VARIOUS PERTURBATIONS TO MOVE ALONG
THE FLOW THOUGH...LOWERING FORECAST CONFIDENCE A BIT. THE GFS AND
ECMWF BOTH WANT TO BRING A WEAK SHORTWAVE TROUGH TOWARD THE REGION
BETWEEN 00-12Z MON...THEN DROP A STRONGER SHORTWAVE TROUGH OUT OF
CANADA AND ACROSS THE UPPER MISSISSIPPI RIVER VALLEY BY 12Z TUE. THE
MODELS PRODUCE MORE QPF WITH THE SUN NIGHT SYSTEM...HAVING MORE
SATURATION...COMPARED TO THE POTENTIAL SHORTWAVE FOR TUE. WILL
LIKELY SIDE TOWARD HPC GUIDANCE FOR PCPN CHANCES IN THESE PERIODS.
WHILE THERE IS SOME INDECISION ON THE PCPN POSSIBILITIES...WHAT DOES
LOOK CERTAIN IS THAT IT WILL BE COLD. TEMPERATURES WILL TUMBLE
BEHIND THE WINTER STORM...AND COLD CONDITIONS WILL PERSIST THROUGH
THE WEEKEND. SOME SLIGHTLY WARMER AIR LOOKS LIKE IT MAY MOVE BACK
INTO THE REGION FOR THE START OF THE NEW WORK WEEK.
&&
.AVIATION...
AIRPORT OPERATIONS AND AIR TRAFFIC TO SEE MAJOR IMPACTS THE NEXT
24-36 HOURS AS MAJOR WINTER STORM/BLIZZARD TRAVERSES THE REGION.
BROAD AREA OF SNOW ALREADY UNDERWAY WELL AHEAD OF THE MAIN SYSTEM AS
ADVECTION OF MOIST AIR LIFTED OVER THE COLD AIR ALREADY IN PLACE.
MAY HAVE A FEW HOURS THIS EVENING BEFORE WE DETERIORATE TO IFR/LIFR
CONDITIONS.
MODELS REMAIN IN EXCELLENT AGREEMENT...AND ALL SHOW FRONTOGENETIC
BANDING WITHIN THE MAIN LIFT AREA. SIGNIFICANT SNOWFALL OF UP TO
10-14 INCHES ANTICIPATED FOR BOTH TAF LOCATIONS BY MID-DAY
WEDNESDAY. BUT ADDING TO THE TURMOIL WILL BE THE STRONG WINDS AS THE
SYSTEM CONTINUES TO RAPIDLY DEEPEN AS IT TRACKS FROM WESTERN KANSAS
UP TOWARD CHICAGO. INCREASED EXPECTED WIND SPEEDS IN THE 18Z TAFS
WITH G45KT AT KRST IN THE OPEN AREA. MAY NOT BE QUITE AS GUSTY AT
THE KLSE TAF LOCATION...BUT WITHIN THE VICINITY FOR SURE.
SNOW WILL TAPER OFF WEDNESDAY AFTERNOON/EVENING...BUT WINDS WILL
HOWL THROUGH THE DAY. NOT ONLY WILL AIRCRAFT OPERATION BE
DIFFICULT...BUT OVERALL AIRPORT OPERATIONS WILL BE SEVERELY AFFECTED
AS WELL. BLOWING AND SEVERE DRIFTING WILL BE DIFFICULT TO CONTEND
WITH.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...BLIZZARD WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR WIZ017-
WIZ029-WIZ032-WIZ033-WIZ034-WIZ041-WIZ042-WIZ043-WIZ044-
WIZ053-WIZ054-WIZ055-WIZ061.
MN...BLIZZARD WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR MNZ079-
MNZ086-MNZ087-MNZ088-MNZ094-MNZ095-MNZ096.
IA...BLIZZARD WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR IAZ008-
IAZ009-IAZ010-IAZ011-IAZ018-IAZ019-IAZ029-IAZ030.
&&
$$
UPDATE... AJ
SHORT/LONG TERM... RIECK
AVIATION.......... MW
