FXUS63 KDDC 090951
AFDDDC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DODGE CITY KS
345 AM CST WED DEC 9 2009
.DISCUSSION...
DAYS 1-2...
THE MOST EXCITING METEOROLOGICAL PHENOMENON TODAY IS THE FRIGID
ARCTIC AIR THAT INVADED KANSAS TUESDAY AFTERNOON. TEMPERATURES POSE
THE GREATEST FORECAST CHALLENGE.
THE NORTHERN PORTION OF THE SHARP UPPER LEVEL RIDGE EXTENDING FROM
THE EASTERN PACIFIC TO NEAR THE NORTH POLE HAS CLOSED OFF AND IS
RETROGRADING SLOWLY TOWARD SIBERIA. MID LATITUDE WESTERLIES 30N TO
40N ARE UNDERCUTTING THE RIDGE, AND THE STRONGLY MERIDIONAL FLOW
OVER WESTERN CANADA GRADUALLY IS SHIFTING WESTWARD. INCREASINGLY
ZONAL FLOW WILL DEVELOP ACROSS THE UNITED STATES LATER THIS WEEK,
AND AN EXTENDED PERIOD OF RATHER QUIET WEATHER WILL PREVAIL IN THE
CENTRAL PART OF THE COUNTRY.
THE DEEP UPPER LEVEL LOW PRESSURE SYSTEM THAT WAS IN NORTHERN
ARIZONA 24 HOURS AGO PROGRESSED RAPIDLY EASTWARD ACROSS THE CENTRAL
UNITED STATES AND WAS CENTERED OVER NORTHERN MISSOURI EARLY THIS
MORNING. SNOW FELL ACROSS MUCH OF WESTERN KANSAS TUESDAY. THE
HEAVIEST SNOW WAS IN NORTHERN KANSAS, WHERE SIX TO NINE INCHES
ACCUMULATED GENERALLY NORTH OF A LINE FROM LARNED TO SCOTT CITY.
FRIGID ARCTIC AIR SPILLED SOUTHWARD TUESDAY AFTERNOON AND WILL BE
SLOW TO MODIFY. PRESSURE TENDENCIES AT 09Z SUGGEST THAT THE GRADIENT
IS WEAKENING IN WESTERN KANSAS, AND NORTHWEST WINDS WILL DIMINISH
FAIRLY QUICKLY BY EARLY MORNING. WIND CHILL VALUES IN THE ADVISORY
RANGE HAVE BEEN COMMON AT REPORTING STATIONS OVERNIGHT. ALTHOUGH
WINDS WILL DIMINISH TOWARD SUNRISE, TEMPERATURES WILL BE COLD ENOUGH
THAT WIND CHILLS WILL REMAIN NEAR ADVISORY LEVELS. THE EXISTING WIND
CHILL ADVISORY EXPIRATION OF 15Z SHOULD BE LATE ENOUGH WIND CHILLS
WILL BE WELL BELOW ADVISORY CRITERIA.
ARCTIC HIGH PRESSURE WILL BUILD OVER WESTERN KANSAS TODAY, AND VERY
COLD TEMPERATURES WILL REMAIN EVEN WITH NEARLY FULL INSOLATION. H8
TEMPERATURES IN THE -10 TO -16 RANGE AND INCREASED ALBEDO FROM SNOW
COVER WILL KEEP HIGHS IN THE SINGLE DIGITS IN NORTHERN KANSAS, WHILE
SOMEWHAT WARMER TEMPERATURES CAN BE EXPECTED NEAR THE OKLAHOMA
BORDER WHERE SNOW COVER IS MUCH MORE LIMITED. THE NAM LOW LEVEL
TEMPERATURES WERE CLOSER TO OBSERVED CONDITIONS, AND THE NAM LARGELY
WAS USED FOR MINOR GRID ADJUSTMENTS THIS MORNING.
THE ARCTIC HIGH WILL BE CENTERED OVER CENTRAL KANSAS THIS EVENING.
AN UPPER LEVEL TROUGH EVIDENT ON SATELLITE IMAGERY IN THE NORTHERN
ROCKIES WILL RIPPLE ACROSS THE NORTHERN PLAINS TONIGHT, AND
PRESSURES WILL LOWER IN THE NORTHERN PLAINS AS A RESULT. EVEN THOUGH
DOWNSLOPE GRADIENT FLOW WILL DEVELOP ACROSS NORTHERN KANSAS TONIGHT,
LIGHT WINDS EARLY IN THE NIGHT LIKELY WILL ALLOW FOR DEVELOPMENT OF
A SHARP INVERSION OVER THE SNOW PACK THAT WILL PRECLUDE MIXING AS
THE GRADIENT FLOW INCREASES. TEMPERATURES WILL DROP WELL BELOW ZERO
OVER THE SNOW PACK AND MAY APPROACH RECORD LEVELS.
ONLY GRADUAL MODIFICATION OF THE COLD AIR WILL OCCUR THURSDAY. SOME
INCREASE IN CIRRIFORM CLOUDINESS IS LIKELY AS THE UPPER LEVEL TROUGH
NEAR 130W APPROACHES KANSAS, BUT MOST OF THE CLOUDINESS PROBABLY
WILL BE THIN. TEMPERATURES THURSDAY WILL BE A FEW DEGREES WARMER
THAN TODAY BUT STILL WILL BE WELL BELOW SEASONAL AVERAGES. LOWS
THURSDAY NIGHT SHOULD DROP TO ZERO OR BELOW ONCE AGAIN OVER THE
DEEPEST SNOW.
DAYS 3-7...
MEDIUM RANGE MODELS START OUT IN PRETTY GOOD AGREEMENT, WITH RIDGING
OVER THE GULF OF ALASKA, A STRONG UPPER LOW OVER CANADA, AND NEAR
ZONAL FLOW OVER THE CENTRAL PLAINS. A WEAK LEE SFC TROUGH WILL BE
IN PLACE FOR FRIDAY, BUT TEMPS WILL STILL BE STRUGGLING TO RECOVER
FROM THE CURRENT ARCTIC BLAST, SO KEPT HIGHS MAINLY IN THE 20S AND
30S. THE ECMWF AND GFS BOTH BRING A VERY WEAK SOUTHERN BRANCH
SHORTWAVE THROUGH ON SATURDAY, BUT IT DOES NOT LOOK TO HAVE MUCH OF
AN IMPACT WITH MINIMAL MOISTURE TO WORK WITH. TEMPS SHOULD RECOVER A
FEW DEGREES MORE. BY SUNDAY, THE MODELS DIFFER ON HOW THEY HANDLE
THE UPPER LOW OVER SOUTHERN CANADA, WHICH WOULD IN TURN AFFECT COLD
AIR COMING DOWN. THE ECMWF HAS THE UPPER LOW UNIFIED AND
PROGRESSING TOWARDS THE MANITOBA/ONTARIO BORDER, WHICH WOULD HELP
PUSH COLD AIR SOUTH QUICKER. THE GFS BREAKS THE UPPER LOW UP, WITH
ONE WEAKER SHORTWAVE MOVING RAPIDLY INTO EASTERN CANADA WHILE THE
STRONG LOW STAYS OVER ALBERTA. THE GFS IS ALSO LESS AGGRESSIVE ON
ANY COLD AIR COMING DOWN INTO THE CENTRAL PLAINS. THERE IS A LOT OF
UNCERTAINTY, AND THE 00Z ECMWF THAT HAS BEEN TRICKLING IN IS ALSO
NOT AS FAST WITH THE COLD AIR SURGE. THUS, WILL KEEP TEMPS CLOSE TO
WHAT WE HAVE GOING WITH MINOR TWEAKS TO IMPROVE INTERSITE
CONSISTENCY. MODELS ALSO HAVE POOR CONSENSUS ON SOUTHERN BRANCH
SHORTWAVES COMING THROUGH EARLY NEXT WEEK. THE GFS BRINGS ONE
THROUGH ON MONDAY, WHILE THE ECMWF IS MORE MONDAY NIGHT INTO
TUESDAY. SUCH FEATURES ARE PRETTY MUCH NOISE AT THIS POINT IN THE
FORECAST, BUT EVEN THE SLOWER ECMWF HAS THE SYSTEM PAST US BY
TUESDAY AFTERNOON. ENSEMBLE PROBABILITIES FOR PRECIP ARE ALSO LESS
IMPRESSIVE FOR TUESDAY. THEREFORE, WILL KEEP THE LOW POPS WE HAVE
GOING FOR MONDAY AND MONDAY NIGHT BUT PULL TUESDAY FOR NOW.
&&
AVIATION...
BLSN STILL RESTRICTING VIS AT KHYS DOWN TO MVFR, BUT CLEARING SKIES
HAVE ALLOWED THE OTHER TWO TAF SITES TO GO VFR. VIS AT KHYS WILL
IMPROVE AROUND 12Z AS WINDS DECREASE DOWN TO 15 KTS OR LESS. WINDS
WILL CONTINUE TO DIMINISH THROUGH THE REST OF THE PERIOD AS SURFACE
HIGH PRESSURE BUILDS INTO THE AREA, BECOMING WESTERLY AT 10 KTS OR
LESS. VFR CONDITIONS WILL PREVAIL THROUGH 12Z THURSDAY WITH ONLY A
FEW HIGH CLOUDS PASSING THROUGH.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 13 -6 24 10 / 0 0 0 0
GCK 12 -7 25 10 / 0 0 0 0
EHA 21 6 31 19 / 0 0 0 0
LBL 19 -1 31 13 / 0 0 0 0
HYS 8 -10 18 -4 / 0 0 0 0
P28 18 4 31 16 / 0 0 0 0
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY UNTIL 9 AM CST /8 AM MST/ WEDNESDAY FOR
KSZ030-031-043>046-061>066-074>081-084>090.
&&
$$
FN01/26/26
