FXUS63 KEAX 092139
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
340 PM CST WED DEC 9 2009
.DISCUSSION...
INTENSE CYCLONE OVER THE GREAT LAKES NOW PROGRESSING THROUGH ITS
OCCLUSION PHASE...HOWEVER DEEP SFC PRESSURES (NEAR 974 MB) HAVE
MAINTAINED A SIGNIFICANT GRADIENT SUCH THAT WIND GUSTS AOA 30 MPH
ARE STILL BEING OBSERVED ACROSS THE CWA. OUTSIDE OF THE OBVIOUS
IMPACTS AND LEGITIMATE BLIZZARD CONDITIONS ACROSS NRN MISSOURI AND
IOWA...THE CLIMATOLOGICAL RARITY OF THIS STORM SYSTEM SHOULD NOT BE
OVERLOOKED. IN THE BRIEF HISTORY OF THIS FORECAST OFFICE...IT IS
BELIEVED THAT THIS WAS POSSIBLY THE FIRST BLIZZARD WARNING EVER
ISSUED...WITH ONLY A FEW INSTANCES IN THE PAST 20 PLUS YEARS OF
WEATHER CONDITIONS BRIEFLY TOUCHING BLIZZARD CRITERIA (YET NOT
REALIZING THE 3 CONSECUTIVE HOURS TO QUALIFY AS A TRUE BLIZZARD).
REGARDLESS...THE SFC CYCLOGENESIS EXPERIENCED YESTERDAY FROM SRN
MISSOURI THROUGH THE WRN GREAT LAKES NEARLY REACHED BOMB STATUS (1
MB/HR FOR 24 HOURS)...WHICH IS QUITE AMAZING FOR A MIDCONTINENT
EXTRATROPICAL CYCLONE. EVEN MORE SPECTACULAR WAS THE 24 HOUR SEA
LEVEL PRESSURE FALLS AT NUMEROUS CNTRL CONUS OBSERVATION
POINTS...WHERE 34 MB PRESSURE FALLS WERE EXPERIENCED AT BOTH KDSM
AND KSTL...AND AN ASTOUNDING 46MB/24 HR SLP FALL AT CHICAGO (KORD).
SFC HIGH PRESSURE HAS SETTLED INTO NRN OKLAHOMA THIS
AFTERNOON...WHICH WILL KEEP SOME PRESSURE GRADIENT OVER THE CWA
TONIGHT (ALBEIT NOT NEARLY AS TIGHT AS THIS AFTERNOON). SINGLE DIGIT
TEMPERATURES HAVE ALREADY FILTERED INTO FAR NWRN MISSOURI...AND
DESPITE A CONTINUED MEASURE OF SUSTAINED WINDS OVERNIGHT...EXPECTING
BOTH DEWPOINTS AND AMBIENT TEMPERATURES TO FALL
SIGNIFICANTLY...ESPECIALLY CONSIDERING THE EXPANSIVE SNOW PACK
ACROSS NRN MISSOURI AND FAR UPSTREAM. AS SUCH...HAVE UNDERCUT
VIRTUALLY ALL NUMERICAL GUIDANCE FOR LOW TEMPERATURES WHERE
MEASURABLE SNOW HAS BEEN REPORTED. WITH WIND SPEEDS GRADUALLY
DECREASING AFTER SUNSET...THINKING IMPACTS FROM BLOWING SNOW ACROSS
NRN MISSOURI WILL BE SIGNIFICANTLY MUTED...AND WILL STILL PLAN ON
EXPIRING WINTER WEATHER ADVISORY FOR BLOWING SNOW AT 00Z (EVENING
SHIFT CAN REEVALUATE ANY NECESSITY TO LOCALLY EXTEND SAID ADVISORY).
INSTEAD...WILL HIGHLIGHT THE BRUTALLY COLD WIND CHILL READINGS
EXPECTED TO PREVAIL THROUGH THE MAJORITY OF THE EVENING AND
OVERNIGHT...WITH APPARENT TEMPERATURES RAPIDLY FALLING BELOW THE
-15F THRESHOLD OVER MAINLY THE DEEPER SNOW PACK.
TEMPERATURE FORECASTS REMAIN THE PRIMARY CHALLENGE HEADING INTO THE
WEEKEND...AS UNCERTAINTIES REGARDING THE EXTENT AND SPEED OF
MELTING/SUBLIMATION TO THE EDGE OF THE SNOW COVER...AS MODIFIED
RETURN FLOW DEVELOPS OVER THE CWA. DEPENDING ON THE POSITION OF THE
DEEPER SNOW PACK...QUITE AN IMPRESSIVE TEMPERATURE GRADIENT MAY BE
REALIZED ACROSS THE FORECAST AREA (BOTH FOR LOW AND HIGH
TEMPERATURES). HAVE PUSHED FORECAST TEMPERATURES AT OR BELOW THE
LOWEST GUIDANCE MEMBERS WHERE SNOW COVER WAS THE DEEPEST...AND KEPT
AROUND THE LOWER GUIDANCE MEMBERS ELSEWHERE. KEPT A DRY FORECAST
HEADING INTO THE WEEKEND...THROUGH PATCHY DRIZZLE OR A STRAY SHOWER
MAY BE POSSIBLE AS MOISTURE IN THE H8-H9 LAYER ATTEMPTS TO WORK
NORTH FROM THE WRN GULF COAST.
21
DAYS 5-7 (SUNDAY-TUESDAY)
AN AREA OF LOW PRESSURE WILL ENTER THE EASTERN ROCKIES AND GREAT
PLAINS REGIONS ON SUNDAY. A SHORTWAVE ASSOCIATED WITH THIS LOW
PRESSURE WILL CLIP THE CWA SUNDAY EVENING...BRINGING WITH IT A
CHANCE FOR SNOW SHOWERS. HOWEVER...GFS/ECMWF/GEM MODELS
STILL DO NOT HAVE A GOOD GRASP ON THIS WAVE PATTERN YET OR THE TRACK
IT WILL TAKE. THUS...KEEPING POPS AT SLIGHT CHANCE FOR SUNDAY NIGHT
THROUGH MONDAY UNTIL A BETTER CONSENSUS IS SEEN AMONGST THE MODELS.
AS THIS SHORTWAVE PASSES TO THE EAST...A DEEP UPPER LEVEL TROUGH
WILL BEGIN TO DIP DOWN INTO THE NORTHERN PLAINS ON TUESDAY. UNLESS
THIS UPPER LEVEL TROUGH DEEPENS FURTHER SOUTH ACROSS THE
PLAINS...CONDITIONS ARE LOOKING TO REMAIN DRY ACROSS THE CWA THROUGH
MID WEEK. HOWEVER...THIS WAVE PATTERN WILL ALSO HELP TO KEEP
TEMPERATURES UNSEASONABLY COOL OVER THE REGION.
ACH
&&
.AVIATION...
FOR THE 18Z TAFS MVFR CIGS WILL PERSIST THROUGH LATE
THIS AFTERNOON WITH ENOUGH RESIDUAL MOISTURE IN THE ATMOSPHERE KEEP
CLOUDS FROM COMPLETELY MOVING OUT. BELIEVE CLOUDS WILL BEGIN TO
DISSIPATE THIS EVENING WITH CLEAR SKIES FOR THE REMAINDER OF THE
VALID PERIOD. WINDS WILL ALSO BEGIN TO DIMINISH THIS AFTERNOON AS THE
PRESSURE GRADIENT RELAXES FROM WEST TO EAST. WINDS SHOULD STAY
NORTHWESTERLY THROUGH TH REMAINDER OF THE DAY BECOMING LIGHT AND
WESTERLY OVERNIGHT.
CDB
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...WIND CHILL ADVISORY UNTIL 9 AM CST THURSDAY FOR MOZ001>008-
011>017-020>024.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR
MOZ001>008-011>017-020.
KS...WIND CHILL ADVISORY UNTIL 9 AM CST THURSDAY FOR KSZ025-102.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR KSZ102.
&&
$$
