Weather

555 
fxus65 kbou 070912 
afdbou 


Area forecast discussion 
National Weather Service Denver Colorado 
305 am MDT sun Sep 7 2008 


Short term...surface high pressure sliding into the Central Plains 
while surface pressures are starting to fall along the Front Range. Low 
level flow has shifted southeast so stratus not making many in-roads 
across snr/western portions of Denver and southward over the Palmer Divide. 
Stratus more widespread to the north but ceilings likely to remain VFR. 
Surface winds will shift southerly on the plains which will likely 
develop a Denver cyclone in the afternoon. Expect a bit cooler with weak 
northerly flow west and north of Denver and undercut MOS guidance 
again. Will keep the County Warning Area dry through today as airmass initially dry and 
capped. The moderate northwest flow pattern will continue with next 
disturbance and cold front to slide into northeast Colorado tonight. Surface 
low pressure will deepen across southeastern Colorado with a cold front will move 
southward into northestern Colorado this evening. Nerly upslope flow will deepen 
along the Front Range overnight with status and some light precipitation 
developing. The best ascent with the jet and moisture with this trough 
will be over the far northestern plains later tonight and will raise probability of precipitation to 
likely there. Further west...moisture depth will be more shallow but 
deep enough for very light rain/drizzle. 


Long term...changes to the forecast package this time around 
included tweaking temperatures down a few degrees for each day and 
then making adjustments to weather types and cloud cover on Monday. 
Concerning temperatures...MOS guidance values...almost across the 
board...have been running too warm over the past couple weeks. And 
this appears to be the case again this morning. The model upper air 
patterns show a progression of flow patterns over Colorado through 
the week. Early on...light-moderate northwesterly flow will prevail 
followed by westerly and then southwesterly by the end of the week 
as a weak upper ridge early in the week breaks down to be replaced 
by a digging upper trough over the Great Basin. The pattern early 
in the week can be a good one for generating banded precipitation 
due to jet stream enhancement. But just like late last week...it 
looks like most of the dynamics will stay to our north and 
northeast...leaving the northeast corner of the state as the only 
ones to receive any appreciable rain. Temperature fields at 850 and 
700 mb show some warming through the middle of the week... but 
nothing too extraordinary and probably not warm enough to justify 
the lower 80s that the mav is showing. Temperatures after Monday 
should be close to seasonal normals as we ease into autumn. Monday 
looks like it will have the most weather for the week as a cold 
front moves into northeast Colorado late Sunday night. This should 
bring a good shot of stratus into the area by Monday morning... 
making the day a lot like what we saw this past Friday. Model 
soundings show a 5000 foot deep layer of cool and saturated air 
across the plains with much warmer air aloft. It looks more like a 
drizzly sounding than light rain...so changed the weather for the 
daytime period to areas of drizzle along with patchy fog. Models 
show rapid drying by Monday afternoon which is what was already in 
the grids. Drier conditions should prevail the rest of the week 
unless a surge of subtropical moisture develops over Arizona and New 
Mexico on Wednesday which would then move over Colorado on 
Thursday. A slight chance of precipitation is included on Thursday 
morning to account for this. Temperatures are also a little cooler 
because of the possibility of more clouds at that time. 


&& 


Aviation...high stratus deck covers much of northestern Colorado but not much 
west/south of Denver due to srly flow. VFR through 03z. Denver cyclone 
expected to develop as winds shift north-northwest from fnl to bjc by afternoon 
while south winds continue east of Denver. Surface cold front to move 
into area this evening 03-06z as surface winds shift northerly with 
light precipitation developing and MVFR/IFR ceilings/visibilities developing 06-12z. 


&& 


Bou watches/warnings/advisories...none. 


$$ 


Swe/kdrby