FXUS63 KBIS 151920
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
120 PM CST TUE DEC 15 2009
.UPDATE...
HIGH PRESSURE MOVING AWAY HAS ALLOWED FOR LIGHTER WINDS ACROSS
THE AREA EVEN WITH SUBZERO TEMPERATURES IN PARTS OF THE AREA.
WIND CHILLS HAVE DROPPED BELOW WARNING CRITERIA IN THE NORTH
AND SHOULD RANGE FROM 25 TO 35 BELOW ZERO. THUS IT WAS
DOWNGRADED TO A WIND CHILL ADVISORY UNTIL 4 PM. ELSEWHERE IN THE
SOUTH WHERE A WIND CHILL ADVISORY WAS IN EFFECT UNTIL NOON. LIGHTER
WINDS AND TEMPERATURES THAT WILL WARM FROM ZERO TO 5 ABOVE IN THE
CENTRAL TO 10 TO 20 ABOVE IN THE FAR SOUTHWEST...HAS RESULTED IN
CANCELLING THE ADVISORY.
MODELS THIS MORNING SHOW SLOW WARM ADVECTION BEGINNING IN THE
SOUTHWEST AND WILL SPREAD WITH TIME TONIGHT INTO WEDNESDAY. A
ZERO DEGREE H850 ISOTHERM WILL BE OVER THE AREA ON WEDNESDAY
REPLACING THE 20 TO 25 BELOW OVERNIGHT ACCORDING TO THE GFS.
WILL LOOK AT MODIFYING THE MAX AND MIN TEMPERATURES DOWN A
FEW DEGREES FOR TONIGHT AND WEDNESDAY AS THE COLD DENSE AIR WILL
BE SLOW TO MOVE OUT. PLUS THE WARM ADVECTION OVER THE TOP OF THE
COLD AIR AT THE SURFACE MAY RESULT IN A CHANCE FOR SOME LIGHT
FREEZING DRIZZLE OR FREEZING RAIN ON WEDNESDAY.
&&
.PREV DISCUSSION... /ISSUED 415 AM CST TUE DEC 15 2009/
SHORT TERM...TODAY THROUGH THURSDAY NIGHT
THE WIND CHILL ADVISORY AND WARNING ISSUED FOR THE FORECAST AREA
LOOKS GOOD AS WIND CHILLS HAVE BEEN IN THE 25 TO 40 BELOW RANGE. IN
THE WARNING AREA...THE WIND CHILLS HAVE BEEN SLIGHTLY BELOW
CRITERIA...BUT CONSIDERING THAT THE TEMPS SHOULD FALL SLOWLY
THROUGH SUNRISE AND THE WINDS HAVE BEEN RUNNING AROUND 10 MPH...WILL
LEAVE THE WARNING IN PLACE. A BAND OF MID CLOUD ON THE WEST SIDE
OF THE SURFACE HIGH HAS BEEN MOVING SLOWLY WEST AND SHOULD MOVE
INTO THE SOUTHWEST THIS MORNING. WILL ADD FLURRIES TO THE
FORECAST. AN UPPER LEVEL RIDGE NOW OVER THE ROCKIES WILL MOVE
INTO THE HIGH PLAINS BY WEDNESDAY PUSHING THE ARCTIC SURFACE HIGH
EAST AND BEGINNING A WARMING TREND. A WEAK SHORT WAVE WILL MOVE
ACROSS THE REGION TONIGHT AND THE INCREASED DYNAMICS WILL LEAD TO
A SLIGHT CHANCE OF LIGHT SNOW IN OUR NORTHERN COUNTIES. A SECOND
SHORT WAVE WEDNESDAY NIGHT WILL HAVE SIMILAR RESULTS. TEMPERATURES
WILL BE BELOW NORMAL TODAY...BUT SHOULD BE AT OR ABOVE NORMAL
WEDNESDAY AND THURSDAY.
LONG TERM...FRIDAY THROUGH MONDAY NIGHT...
THE MAIN FORECAST CONCERNS THIS PERIOD ARE TEMPERATURES AND CHANCES
OF PRECIPITATION. MODELS ARE NOT IN VERY GOOD AGREEMENT THROUGH THE
LONG TERM AND DIFFERENCES GET WORSE WITH TIME.
THE MODELS DO FAVOR A POSITIVE PNA (PACIFIC NORTH AMERICAN) PATTERN
OVER NORTH AMERICA THROUGH SATURDAY. DISTURBANCES MOVING OVER TOP OF
A WESTERN US RIDGE ARE FORECAST TO MOVE THROUGH THE NORTHERN PLAINS
INTO SATURDAY. THIS PATTERN WILL CONTINUE THE BRIEF RESPITE FROM THE
ARCTIC COLD WITH NORMAL TEMPERATURES FRIDAY AND SATURDAY. (HIGHS MID
20S/LOWS SINGLE DIGITS) UNCERTAINTIES IN THE MODELS BECOME MORE
PRONOUNCED BY THE END OF THE WEEKEND. GENERALLY...MODELS FORECAST A
CLOSED LOW OVER SOUTHEASTERN CANADA TO SLOWLY RETROGRADE WESTWARD.
THIS WILL BRING A COOLING TREND TO THE REGION EARLY NEXT WEEK WITH
HIGHS IN THE TEENS AND LOWS NEAR ZERO. THE ECMWF IS MUCH COOLER
DURING THIS TIME PERIOD OVER THE GFS.
THE MODEL DISAGREEMENT HAPPENS WHEN THE ECMWF CARVES A MUCH DEEPER
TROUGH OVER THE NORTHERN PLAINS...PULLING COLDER AIR INTO THE
REGION. THE GEM AND GFS HAVE WEAKER DISTURBANCES. THE GFS COOLS
TEMPERATURES SLIGHTLY THROUGH THIS PERIOD WHILE THE ECMWF KEEPS
COLDER AIR IN THE AREA. HAVE OPTED TO KEEP THE GENERAL COOLING
ACROSS THE REGION AND WILL NOT OPT FOR THE MUCH COOLER ECMWF.
AVIATION...EARLY TUESDAY MORNING...ARCTIC HIGH PRESSURE EXTENDS
ACROSS EASTERN MONTANA AND THE DAKOTAS. BY 00Z/6PM TUESDAY THE HIGH
WILL DRIFT EAST TO MINNESOTA WHILE A TROUGH OF LOW PRESSURE WITH AN
ASSOCIATED WARM FRONT MOVES INTO EASTERN MONTANA. MID TO HIGH CLOUDS
ASSOCIATED WITH THE WARM FRONT WILL MOVE INTO NORTH DAKOTA. HOWEVER
ALL TAF SITES WILL BE VFR THROUGH THIS FORECAST PERIOD.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY UNTIL 4 PM CST THIS AFTERNOON FOR NDZ001>005-
009>013-021>023-025-035>037.
&&
$$
VJ
