Weather

922 
fxus63 kbis 060904 
afdbis 


Area forecast discussion 
National Weather Service Bismarck ND 
305 am CST Tuesday Jan 6 2009 


Short term...today through Thursday night 
forecast concerns/highlights in the short term period will be 
chances for snow each day...possibly significant Thursday into 
Thursday night. Will utilize an overall blend today...then lean more 
towards a compromise of the latest European model (ecmwf)/UKMET/sref/GFS guidance 
tonight through Thursday night. 


Currently...relatively weak clipper system sliding across the North 
Dakota/Canadian border this early morning. This system has mainly 
produced increased sky cover across the local region...with some scattered 
light snow across north central ND closer to the middle level shortwave 
impulse and thermal lift ahead of the surface low. Much warmer 
temperatures across the state as well compared to the past couple of 
nights with warming west/southwesterly winds ahead of the low. 


The clipper pushes southeast this morning...followed by additional 
embedded shortwave impulses which will act to keep cyclonic flow aloft 
across the northern plains into tonight. Resultant weather will be 
cold air advection and cloudy skies...along with continued chances for light snow 
or flurries today through tonight. Despite the cold air advection...daytime 
temperatures will actually be similar to slightly warmer in some 
places compared to monday's highs...as our morning temperatures will 
be much warmer than the past couple of days. 


Attention shifts to Wednesday where we will have another embedded 
middle level wave riding over the western Continental U.S. Ridge and into the 
local region. Models have trended closer to a similar solution 
here...with decent agreeability now depicted between the latest 
GFS/ECMWF/and sref guidance...particularly in regards to the 
strength of the middle level energy resulting in a stronger surface 
boundary and hence better overrunning precipitation potential across 
my western counties. Have increased probability of precipitation accordingly Wednesday daytime. 
Forcing diminishes Wednesday evening into the overnight so trended 
downwards 00z-12z Thursday. In addition...enough warm air advection will raise the 
potential for freezing rain mixing with any lingering snow showers Wednesday night 
far west. 


A stronger middle level shortwave trough and surface low move across the 
northern plains Thursday and Thursday night. This has potential for 
significant snow amounts as quite a bit of warm air and hence 
moisture look to feed into this system. Much uncertainty still but 
latest guidance indicates the best potential for heavy snow will be 
across northern ND. In addition...enough warm air advection ahead of the low for 
rain across the south Thursday afternoon. Will continue to 
monitor. 




Long term...Friday through Monday... 
main forecast problem in the day 4-5 period will be temperatures... 
precipitation chances and winds with the system moving across the 
local area on Friday. As mentioned in the short term 
discussion...the best potential for accumulating snow will remain 
across the north. GFS is farthest north with the placement of quantitative precipitation forecast 
during the day on Friday...keeping accumulating snow north of the 
border with the surface low moving across northern North Dakota. The 
European model (ecmwf) places the surface low much farther south...over the Central 
Plains...with an inverted trough into western North Dakota at 12z 
Friday. This trough gets squashed quickly during the day as strong 
northwest flow moves across the County Warning Area with the passage of the upper 
level trough. The placement of the inverted trough and the track of 
the upper trough do allow for more significant precipitation across 
the north during the day Friday than the GFS indicates. The global 
Gem is in between the two...but also shows more quantitative precipitation forecast along our 
northern tier counties on Friday than the GFS. Have updated probability of precipitation on 
Friday to place chance probability of precipitation across the north in addition to the 
east. Kept slight chance probability of precipitation in the southwest. 


Models indicate a period of strong northwest winds moving west to 
east across the County Warning Area with the passage of the shortwave trough on 
Friday. Any problems with blowing and drifting snow will depend on 
the amount of snow Thursday night into Friday...in addition to the 
amount of warming we see in the short term. With lightest snow 
amounts expected south...and warmer temperatures in the short 
term...we may not see much blowing snow here. Northern zones will 
likely be more of a problem. For now...will not mention blowing 
snow...and will let later shifts evaluate as we get closer to Friday. 


With the discrepancy in the placement of the surface low between the 
GFS and European model (ecmwf)...we also see a wide range of temperatures on Friday 
with the GFS much warmer. For now will side with persistence and the 
cooler European model (ecmwf). 


Beyond Friday...upper ridging pushes into the area...and have raised 
temperatures a bit from previous guidance through the rest of the 
day 4-5 period. With the upper ridging...the next clipper system 
stays north of the region...and have kept the remainder of the 
day 4-5 period dry. 


&& 


Aviation... 
frontal boundary draped northwest to southeast across the forecast 
area this morning with mainly middle level cloudiness. A weak upper 
level impulse slides southeast across the area today bringing 
increasing low level moisture...followed by cold air advection. Current satellite 
image does not indicate the amount of low level moisture depicted by 
the GFS. Will start tafs out more optimistic than current guidance. 
Later today and tonight will likely bring in some MVFR ceilings with 
increasing boundary level moisture. NAM MOS guidance is indicating 
extensive low ceilings and fog across much of western North Dakota 
tonight. With increasing low level moisture and light winds...can 
not rule this out but will not be as bullish as this guidance. 


&& 


Bis watches/warnings/advisories... 
none. 


&& 


$$ 
New Hampshire/twh