277 
FXUS65 KBOU 191800
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1200 PM MDT Tue Oct 19 2021

.UPDATE...
Issued at 1013 AM MDT Tue Oct 19 2021

Water vapor shows a cut off trough over western Colorado this
morning with subtle shortwave troughs embedded within the larger
trough. One of these subtle shortwaves is setting up over north-central
Colorado which is helping to provide strong QG ascent in southern
Wyoming where widespread rain and snow is occurring. On the 
eastern side of this feature (over the northern foothills and I-25
corridor), there is good 700 mb frontogenesis setting up along 
with warm air advection. Radar is starting to show a band of 
precipitation from Elk Mountain to Laramie to Cheyenne in 
Wyoming. As the day progresses, this band will develop 
southeastward into Laramie, Weld, and Logan counties in Colorado.
High resolution models are showing decent rainfall totals up to a
third of an inch just south of the CO/WY border. Therefore, PoPs 
and QPF were raised to account for the higher confidence that 
precipitation will fall in those three counties. 

A couple of the models in the HREF show showers developing this 
afternoon across the Denver metro. There is some skepticism that
these will be anything more than virga especially since the dew 
points are rather dry. However, PoPs were increased slightly to 
bring the mention of rain showers into the northwestern Denver 
suburbs. This chance of rain in the Denver metro will need to be
watched since the model trend is certainly towards a higher
likelihood that they do happen. 

&&

.SHORT TERM...(Today and tonight)
Issued at 420 AM MDT Tue Oct 19 2021

An upper level low will arrive in area bringing light snow showers 
to our mountains zones Tuesday morning. Overall, snowfall 
accumulations have decreased due to this system becoming weaker and 
placement of this system does not favor much snowfall due to a 
northeastward track. Therefore, areas north of I-70 in the mountains 
will experience slick travel conditions and snowfall totals up to 
1.5 inches on the highest peaks. A isolated rain shower cannot be 
ruled out for the north eastern plains but overall areas outside of 
the mountains should be fairly dry. Strong subsidence will bring 
strong low level winds across the CWA with the highest wind gusts of 
45 MPH. Most areas will range from 25-30 MPH through Tuesday 
afternoon. Areas such as the urban corridor, plains, and parts of 
the foothills will experience partly cloudy skies and cooler 
afternoon highs in the upper 50s to lower 60s. 

.LONG TERM...(Wednesday through Monday)
Issued at 420 AM MDT Tue Oct 19 2021

WNW flow aloft will develop over the area on Wed and continue into 
Thu.  There will be some mid and high level moisture embedded in the 
flow, however outside of some clouds, no precip is expected either 
day. Highs will be near seasonal levels on Wed and then rise to 
above normal by Thu.

For Fri into Sat the flow aloft will become more WSW.  Once again 
there will be some mid and higher level moisture in the flow, 
however, no precip is expected either day. Meanwhile, with downslope 
WSW low level flow, highs across nern CO will rise into the lower to 
mid 70s by Sat. 

By Sun into Mon the flow aloft will become more southwesterly.  The 
GFS wants to bring in deeper lower level moisture, into portions of 
the mtns Sun night into Mon, while the ECMWF holds off this moisture 
until late Mon into Tue. Overall will just mention a chc of precip 
due to timing differences. As for highs, will trend towards ECMWF 
Guidance with readings staying well above normal, over nern CO.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1138 AM MDT Tue Oct 19 2021

A few virga showers may create periods where ILS is needed this
afternoon. Ceilings should stay at or above 6 kft but the rain 
below the cloud deck may reduce slantwise visibility. Some of the
showers could create brief sporadic winds but overall, winds will
be out of the north. This evening, the low pressure system will
move out of the area and VFR conditions will return for the rest
of the TAF period. Wind speeds will decrease this evening and will
be light overnight and tomorrow. 

&&

.FIRE WEATHER...
Issued at 420 AM MDT Tue Oct 19 2021

A Red Flag Warning is in effect
starting 12 PM to 6 PM Tuesday for southern Lincoln county due to
low humidity ranging from 14-18 percent and strong low level 
winds. Areas near the Palmer Divide will trend with the lowest
humidity percentages across the region. Gusty winds are expected
throughout Tuesday afternoon into early evening. Fire weather
concerns will subside by early evening and dry conditions will
prevail Tuesday night.  

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 6 PM MDT this evening for COZ247.

&&

$$

UPDATE...Danielson
SHORT TERM...AD
LONG TERM...RPK
AVIATION...Danielson
FIRE WEATHER...AD