247
FXUS63 KBIS 202046
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
246 PM CST FRI NOV 20 2009
SYNOPSIS
PERSISTENT NEGATIVE HEIGHT ANOMALIES CENTERED OVER SIBERIA AND
ALASKA SHOULD RESULT IN A MORE PROGRESSIVE WEATHER PATTERN ACROSS
NORTH AMERICA AS WESTERLIES CRASH INTO WESTERN NORTH AMERICA.
SOME COOLER...BUT STILL ABOVE CLIMATOLOGICAL...TEMPERATURES ARE
EXPECTED THIS WEEKEND INTO EARLY NEXT WEEK.
SHORT TERM...FRIDAY THROUGH MONDAY NIGHT
CURRENTLY...THERE IS UPPER LEVEL RIDGING ALONG THE FRONT
RANGE/HIGH PLAINS WITH A POTENT TROUGH MOVING INTO THE PACIFIC
NORTHWEST. AT THE SURFACE...CENTRAL PLAINS HIGH PRESSURE IS SLOWLY
SLIDING SOUTHEAST. EXPECT SOUTHERLY WINDS TO CONTINUE OVERNIGHT
AND STRENGTHEN DURING THE DAY TOMORROW AS THE PRESSURE GRADIENT
TIGHTENS OVER THE REGION AHEAD OF A DEVELOPING SURFACE LOW IN
CENTRAL ALBERTA.
THE PREVIOUSLY MENTIONED UPPER LEVEL TROUGH MOVES INTO
CENTRAL MONTANA ON SATURDAY PUSHING A COLD FRONT THROUGH THE
NORTHERN PLAINS. TIMING THIS FEATURE IS THE FORECAST PROBLEM OF
THE DAY. THE 12 UTC NAM SLOWED DOWN THE PASSAGE OF THIS COLD
FRONT FAR MORE THAN THE SLIGHTLY SLOWER TREND OBSERVED IN THE 12
UTC GFS. BASED ON HPC MODEL DIAGNOSTICS DISCUSSION...GRIDDED
FORECASTS FAVORED CONTINUITY BLENDED WITH THE MORE CONSISTENT GFS.
LIMITED MOISTURE AVAILABILITY WILL ELIMINATE PRECIPITATION CHANGES
WITH THIS SYSTEM.
IN THE WAKE OF THE EXITING COLD FRONT A SHORT WAVE RIDGE BUILDS
INTO NORTH DAKOTA FOR SUNDAY. TEMPERATES SHOULD BE 10 TO 15F
COOLER ON SUNDAY BUT STILL WELL ABOVE AVERAGE.
ANOTHER TROUGH APPROACHES WITH ANOTHER...STRONGER...COLD
FRONT PASSING THROUGH THE REGION SUNDAY NIGHT INTO MONDAY. MODELS
SUPPORT BETTER MOISTURE TRANSPORT...THUS THE CHANCE FOR PRECIPITATION.
THE 12 UTC ECMWF/GFS CONTINUE TO DISAGREE ON THE TRACK OF THIS
FEATURE. THE GFS IS FARTHER NORTH ALLOWING PRECIPITATION ACROSS
WESTERN AND CENTRAL NORTH DAKOTA WHILE THE ECMWF TRACKS THE SYSTEM
THROUGH KANSAS AND NEBRASKA WITH LIMITED PRECIPITATION FOR NORTH
DAKOTA.
LONG TERM...TUESDAY THROUGH FRIDAY NIGHT
MODELS DEVELOP A STORM CENTER THAT MOVES EAST ACROSS THE ROCKIES IN
THE SHORT TERM...AND BY TUESDAY MORNING THE LONG TERM MODELS HANDLE
THE PLACEMENT/TIMING OF THE SYSTEM AS IT MOVES EAST/NORTHEAST ACROSS
THE CENTRAL PART OF THE COUNTRY. THE GFS IS MORE PROGRESSIVE WITH
THE SYSTEM...WHICH PUTS THE LOW CENTER OVER IOWA/WISCONSIN TUESDAY
MORNING AND MOVES IT OVER THE GREAT LAKES BY WEDNESDAY MORNING AND
INTO HUDSON BAY AREA BY THURSDAY. MEANWHILE THE ECMWF IS
SLOWER...WITH THE LOW CENTER OVER NEBRASKA/KANSAS TUESDAY MORNING
AND INTO IOWAS BY WEDNESDAY...AND OVER THE GREAT LAKES BY THURSDAY.
THE NATIONAL GUIDANCE FAVORS THE CONSISTENCY OF THE ECMWF. BASICALLY
KEPT ONLY A SLIGHT CHANCE OF PRECIP ON TUESDAY NIGHT FROM THE
PREVIOUS FORECAST PACKAGE.
THEN KEPT THE REST OF THE LONG TERM DRY. AFTER THE LOW MOVES TOWARDS
HUDSON BAY...RIDGING OVER THE ROCKIES AND PLAINS WILL KEEP A
WEST/NORTHWEST FLOW OVER THE NORTHERN PLAINS.
TEMPERATURES AT OR ABOVE AVERAGE WITH HIGHS 35 TO 45 AND LOWS IN THE
TEENS AND 20S.
AVIATION
HIGH PRESSURE OVER MINNESOTA AND LOW PRESSURE IN THE LEE OF THE
ROCKIES WILL KEEP A SOUTHERLY WIND FLOW ACROSS TAF SITES. A SURFACE
TROUGH IS FORECAST TO ENTER WESTERN NORTH DAKOTA AROUND 15Z SATURDAY
AND MOVE EAST ACROSS THE STATE. SOUTH WINDS AHEAD AND WEST WINDS
BEHIND THE TROUGH. VFR CONDITIONS WITH HIGH CIRRUS CLOUDS THROUGH
12Z SATURDAY...WITH MID CLOUDS AFTER 18Z SATURDAY.
BIS WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS/SHORT TERM...DC/SCHECK
LONG TERM/AVIATION...JV
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