100 
fxus65 kbou 072058 
afdbou 


Area forecast discussion 
National Weather Service Denver Colorado 
259 PM MDT sun Sep 7 2008 


Short term...laps surface analysis showing high over central 
Nebraska with low pressure across central Colorado. Southeasterly 
surface gradient across plains beginning to tighten...though current 
winds still fairly light. Surface low expected to move into eastern 
Colorado this evening as upper disturbance slides across Wyoming. 
The airmass across plains should become unstable during the evening 
as qg ascent begins to increase. Some storms possible...though best 
chance near the northern border and northeast corner closest to the 
greatest lift. Forecast soundings show cape values nearing 1000 j/kg 
in the northeast corner. Could see some small hail with the storms 
there. No storms across mountains tonight as airmass stable and area 
will be away from any ascent. As disturbance moves into Nebraska 
tonight...associated surface front to slide southeast across the 
Colorado plains. Models still show this front reach dia around 06z. 
Upslope flow develops behind front and will be enhanced by flow from 
surface high. Precipitation chances to increase after midnight as qg ascent 
continues to increase. Again...highest probability of precipitation far eastern zones. With 
deepening moisture...should also see some fog. Again...mountain 
araeas void of any precipitation. On Monday...forecast soundings Show Low 
level moisture around 5000 feet deep during the early morning. As 
previous forecaster had stated...soundings look more like a drizzle 
producer. Current grids have areas of fog and drizzle for the plains 
and foothills during the morning...this is still looking on track. 
By afternoon...models begin to dry atmosphere as upslope starts to 
weaken and low level moisture decreases. Current grids show this 
trend...will continue. Mountains continue to miss out on this precipitation 
event. As for highs...the cooler met guidance looking more 
reasonable that FWC guidance given the clouds and moisture. Current 
temperature grids more in line with the met guidance...no changes at 
this point. 


Long term...westerly flow aloft is prognosticated Monday night into 
Tuesday. By Tuesday afternoon continuing into Wednesday evening 
..west-southwesterly flow aloft is prognosticated. The qg vertical 
velocity fields show benign synoptic scale energy Monday night 
through Tuesday night. There is weak upward motion prognosticated on 
Wednesday. The boundary layer flow looks to be dominated by regular 
diurnal trends through the periods. The GFS has a surge and upslope 
moving into the forecast area Wednesday night/Thursday morning. For 
moisture...it looks pretty dry Monday night into Tuesday. Tuesday 
afternoon into Wednesday morning...models show moisture increasing 
and deepening from west to east over the forecast area. Both models 
show the mountains with pretty deep moisture for much of Wednesday. 
The GFS keeps ample moisture over the forecast area Wednesday night 
and much of Thursday. Precipitable water values are in the 0.35 to 
0.55 inch range Monday night and Tuesday. By late Tuesday through 
Wednesday...values climb into the 0.60 to 0.85 inch range. Models 
are now showing fairly decent cape over the foothills and adjacent 
plains late day Tuesday. Yesterday's runs had none. By late day 
Wednesday...there is decent cape over the northeastern corner...less 
over the rest of the plains. Lapse rate fields show a strong low 
level cap over the eastern 2/3rds of the plains for Tuesday...but 
by Wednesday there is only a bit of middle level cap in place for most 
areas. The quantitative precipitation forecast fields show limited measurable precipitation for 
late day Wednesday...none for the other times. Will put some minor 
probability of precipitation in the mountains and near-by plains late Tuesday. Moisture is 
pretty good on Wednesday well into the extended period...will have 
10-20% probability of precipitation for Wednesday. For temperatures...tuesday's highs are 
5-8 c warmer than monday's. Wednesday's highs are 0-1.5 c cooler 
than tuesday's. For the later days...Thursday through Sunday... 
models have upper troughiness for the forecast area well into 
Saturday. They also show more moisture than yesterday's runs 
indicated. Will put some minor probability of precipitation in through Friday anyway. 
Temperatures look close to seasonal normals. Will lower current gfe 
temperature grids a bit. 


&& 


Aviation...slight chance of thunderstorms through 06z across area 
airports with gusty winds to 30kts the main concern. Surface winds 
to become northeast during the evening. Cold front to move across 
area after 06z with low level upslope increasing. Areas light rain 
and fog expectd...with MVFR/IFR ceilings and visibilities from 06z 
to 16z. Conditions to slowly improve by 18z as upslope weakens. 




&& 


Bou watches/warnings/advisories...none. 


$$ 
D_l/rjk