FXUS63 KBIS 291021
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
420 AM CST SUN NOV 29 2009
.SHORT TERM...TODAY THROUGH TUESDAY NIGHT...
CURRENTLY...UPPER LEVEL SHORTWAVE WAS EXITING THE STATE INTO
MINNESOTA...WITH AN AREA OF LOW CLOUDS OVER THE EASTERN HALF OF THE
STATE DISSIPATING FROM WEST TO EAST. SURFACE HIGH PRESSURE WAS
MOVING INTO THE STATE FROM THE WEST. SURFACE TEMPERATURES WERE
COOLING INTO THE TEENS OVER WESTERN NORTH DAKOTA WHERE LIGHTER WINDS
AND CLEAR SKIES WERE ALLOWING PLENTY OF RADIATIONAL COOLING TO TAKE
EFFECT. AREAS OF FOG HAD DEVELOPED OVER EASTERN MONTANA AND SOUTHERN
SASKATCHEWAN NEAR THE SURFACE HIGH CENTER...AND SATELLITE PICS SHOW
A TREND OF THE FOG MOVING EAST AND/OR EXPANDING TOWARDS WESTERN
NORTH DAKOTA. EXPECT THIS TO CONTINUE UNTIL JUST AFTER SUNRISE...SO
ADDED A MENTION OF FOG TO WESTERN COUNTIES UNTIL AROUND 9 AM CST
THIS MORNING.
A RIDGE BUILDS OVER THE ROCKIES AT UPPER LEVELS FOLLOWING THE
EXITING SHORTWAVE AND TODAY AND MONDAY NORTH DAKOTA IS UNDER THE
INFLUENCE OF MILD PACIFIC HIGH PRESSURE. EXPECTING ABOVE AVERAGE
TEMPERATURES TO CONTINUE WITH HIGHS FROM THE MID 30S TO LOWER 40S
TODAY...AND LOWER 40S TO LOWER 50S ON MONDAY.
TUESDAY WILL BE A DIFFERENT STORY ALTOGETHER AS A CLIPPER-TYPE
SYSTEM SETS UP OVER ALBERTA MONDAY AFTERNOON. THE MODELS ARE COMING
CLOSER TO A CONSENSUS WITH THE TIMING AND PLACEMENT OF THIS
SYSTEM...AND THE GFS AND ECMWF ARE IN CLOSER AGREEMENT THAN THE NAM.
THUS FOLLOWED THE GFS FOR DETAILS. THE SURFACE LOW MOVES INTO
WESTERN MANITOBA BY TUESDAY MORNING...OVER LAKE WINNIPEG BY
NOON...AND INTO SOUTHWESTERN ONTARIO BY TUESDAY EVENING. THE SURFACE
COLD FRONT EXTENDING SOUTHWARD FROM THE LOW IS EXPECTED TO ENTER
NORTHWESTERN NORTH DAKOTA AFTER MIDNIGHT MONDAY NIGHT AND REACH THE
SOUTHEAST CORNER OF THE STATE BY NOON TUESDAY. STRONG COLD ADVECTION
AND H850 WINDS OF 40 TO 50 KNOTS WITH A TIGHT SURFACE PRESSURE
GRADIENT WILL LIKELY TRANSLATE TO STRONG SURFACE NORTHWESTERLY WINDS
OF 30 TO 40 MPH WITH HIGHER GUSTS. A WIND ADVISORY MAY BE NECESSARY
FOR TUESDAY IF THE MODELS ARE CONSISTENT WITH THE STRENGTH OF THIS
SYSTEM AS WELL AS THE TIMING/PLACEMENT OF THIS LOW IN THEIR NEXT FEW
RUNS. THE COLD ADVECTION WITH THIS FEATURE WILL KEEP HIGH
TEMPERATURES ON TUESDAY IN THE LOWER 30S NORTH TO LOWER 40S
SOUTHEAST. LOW TEMPERATURES TUESDAY NIGHT ARE EXPECTED TO BE IN THE
TEENS (NEAR AVERAGE FOR LOW TEMPERATURES) WITH 10 TO 20 MPH WINDS.
.LONG TERM...WEDNESDAY THROUGH SATURDAY NIGHT...
AMPLIFICATION OF THE NORTHEAST PACIFIC RIDGE DUE TO A SUBTLE
POSITION SHIFT OF THE EASTERN RUSSIA/BERING SEA POLAR VORTEX SHOULD
RESULT IN A MORE ACTIVE PATTERN THAN THAT IN PLACE FOR MUCH OF
NOVEMBER. AS IS COMMON...THIS PATTERN SHIFT IS CAUSING SERIOUS
DIFFICULTIES FOR MODELS/ENSEMBLES...RESULTING IN HUGE MODEL SPREAD
AND LARGE UNCERTAINTY BY LATE IN THE PERIOD. THE GREATEST FORECAST
CONCERN CENTERS AROUND A POSSIBLE LATE WEEK STORM LEADING TO A
PATTERN SHIFT.
THERE SHOULD BE NORTHWEST FLOW ALOFT IN PLACE OVER THE NORTHERN
PLAINS FOR THE START OF THE LONG TERM. COLDER AIR IS IN PLACE ACROSS
THE NORTHERN PLAINS BRINGING TEMPERATURES CLOSER TO MORE SEASONAL
AVERAGES FOR THIS TIME OF YEAR. MULTIPLE DISTURBANCES MOVING THROUGH
THE NORTHWEST FLOW ALOFT JUSTIFY A SLIGHT CHANCE OF SNOW SHOWERS ON
WEDNESDAY/WEDNESDAY NIGHT. ALONG WITH THE CHANCE FOR
PRECIPITATION...THE NORTH-NORTHWESTERLY FLOW ALOFT SHOULD DIRECT
SOME VERY COLD AIR INTO THE NORTH CENTRAL PLAINS. THAT SAID...THERE
IS SOME UNCERTAINTY REGARDING LINGERING OF CLOUDS ACROSS EASTERN AND
CENTRAL NORTH DAKOTA. THE WESTERN THIRD SHOULD HAVE NO PROBLEM
CLEARING OUT...BUT WITH UNCERTAINTY THE GRIDDED FORECASTS INDICATE A
FORECAST AROUND 0.5-SIGMA BELOW AVERAGE.
THE 00 UTC GFS/ECMWF ARE DRASTICALLY DIFFERENT BY FRIDAY. ENSEMBLES
DO LITTLE TO FAVOR ANY ONE SOLUTION OVER ANOTHER. IT DOES APPEAR
THAT AT LEAST A FEW OF THE ENSEMBLE MEMBERS CALL FOR ADVECTION OF A
VERY STRONG ARCTIC AIRMASS INTO THE NORTHERN PLAINS.
&&
.AVIATION...
VFR CONDITIONS EXPECTED AT THE WESTERN TAF SITES THIS MORNING WITH
MVFR CEILINGS AT KMOT...KBIS...AND KJMS. EXPECT MVFR CEILINGS TO
LIFT TO VFR BY 18 UTC SUNDAY AT THE EASTERN TAF SITES. AREAS OF FOG
ARE A POSSIBILITY FOR THE WESTERN TAF SITES THIS MORNING WITH CLEAR
SKIES AND LIGHT WINDS THANKS TO SURFACE HIGH PRESSURE OVER THE
NORTHERN HIGH PLAINS. VISIBILITIES SHOULD GENERALLY BE MVFR WITH
VISIBILITIES DOWN TO LIFR AT TIMES.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...JV
LONG TERM...SCHECK/DC
AVIATION...DC/SCHECK
