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fxus63 kbis 192052 
afdbis 


Area forecast discussion 
National Weather Service Bismarck ND 
325 PM CDT Tuesday Aug 19 2008 


Synopsis... 


Amplifying middle/upper level flow is forecast in the short range. A 
strong Rex block comprised of a cut off low over Oklahoma and a 
strong ridge extending north into northern Saskatchewan is slowing 
the progression of a negatively tilted middle/upper level trough 
pushing through the Pacific northwest. 


&& 


Short term...Tuesday through Friday night... 


Currently...height falls pushing slowly toward the northern plains 
is prompting Lee cyclogenesis in the northern High Plains...thereby 
leading to a stronger low-level pressure gradient and gusty 
southerly winds. Middle level capping is strong...and it should take 
several days to break down the aforementioned ridge. As is typical 
with southerly flow...temperatures are expected to continue rising 
over western and central North Dakota for tomorrow. By 
Thursday...there could be some clouds associated with convection in 
Montana that filter solar heating over the area...which should 
offset some of the warm air advection. 


Thereafter...expect to finally erode the cap and introduce a chance 
for precipitation on Thursday night and Friday. There are timing 
concerns...since the 06/12 UTC GFS runs are more progressive than 
the 06/12 UTC global ensemble forecast system means...12 UTC 
NAM...12 UTC Gem global...09 UTC sref mean. Conversations with 
NCEP/Hydrometeorological Prediction Center confirm that the latest 
European model (ecmwf) ensemble members are on board with the slower solutions. 
So..have decided to avoid the GFS and have kept probability of 
precipitation down below likely. 


Long term...Saturday through Wednesday... 


Definitely a cooler start to the long term on Saturday as the 
GFS run today is stronger in moving through a closed upper low 
to the north of the state. The European model (ecmwf) is weaker but shows a 
shortwave trough swinging through at that time. Both models 
move the precipitation east of the area then. From Sunday through 
Monday...upper level ridging builds over the northern plains once again 
so temperatures which will be near 80 on Saturday will warm 
back up to around 90 for Sunday and Monday. Large Pacific northwest 
states trough moves ashore on Monday and will impact our 
weather by Wednesday with a round of thunderstorms. 


Overall a roller coaster temperature pattern is expected in the 
long term. 




&& 


Aviation... 


No concerns other than a few 7,000 to 9,000 foot scattered 
cumulus into the early evening then clear overnight into 
Wednesday. Breezy winds will slowly subside during the evening 
to about 10 to 15 miles per hour overnight. 


On Wednesday...a scattered cumulus deck will develop in the 
afternoon as temperatures climb back into the 90s as the 
environment becomes a little more unstable. 


&& 


Fire weather... 


Developing low pressure in Montana has caused the strong gusty 
southerly winds of 20 to 30 miles per hour currently being observed across 
western North Dakota. These winds should continue this afternoon 
and evening. Very warm afternoon temperatures in the middle to upper 
90s have also resulted in relative humidities down to 10 to 15 
percent. The potential exists for rapid wildfire growth given the 
very dry vegetation that exists across portions of western North 
Dakota. The fire danger will lower as winds diminish and relative 
humidities rise later this evening as the sun sets. 


For Wednesday...expect temperatures to be similar to today...so 
relative humidities are forecast to drop into the upper teens by 
afternoon. They should not be quite as low as 
Tuesday...however...since there should be a bit more moisture in air 
that mixes down to the surface tomorrow afternoon. Southerly 
winds are forecast to gust into the middle 20s miles per hour...so there 
could be another red flag warning issued. 


&& 


Bis watches/warnings/advisories... 
red flag warning until 10 PM CDT /9 PM MDT/ this evening for 
ndz001-009-017-018-031>033-040-041-043-044. 


&& 


$$ 


Scheck/vj