340 
FXUS65 KBOU 190510
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1110 PM MDT Mon Oct 18 2021

.UPDATE...
Issued at 853 PM MDT Mon Oct 18 2021

Evident on water vapor imagery, an upper level low gradually pushes 
eastward into Utah which will eventually enter Colorado tomorrow 
morning. Radar is starting to show echoes for showers over the 
northern mountains with little reaching the ground currently. Snow 
showers will further develop over the mountains after midnight into 
tomorrow morning followed by another round of showers in the 
afternoon. Forecast remains on track for light accumulations in
the mountains. Breezy W to NW flow expected across NE Colorado 
Tuesday. With gusts to 25 mph combined with low relative 
humidities, southern Lincoln County continues to look favorable 
for near-critical fire weather conditions for a portion of the 
afternoon.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 242 PM MDT Mon Oct 18 2021

The upper low over the Great Basin this afternoon will move 
across Utah tonight and should be near the tri-state border of 
Utah, Wyoming and Colorado early tomorrow morning. QG fields show 
light synoptic subsidence turning to moderate ascent across 
northeast Colorado after midnight. Continue to expect a band of 
precipitation to bring showers to the northern mountains after 
midnight with the colder mid level air. Forecast accumulations 
haven't really changed much, most of the mountains should see a 
trace to 2 inches mainly during the late night hours. The Park 
Range may see greater accumulations due to better moisture and 
orographic forcing, generally 2 to 4 inches but 6 to 8 inches 
possible for the higher peaks. 

There will be strong southwesterly flow aloft tomorrow as the 
upper low moves across the central Rocky Mountains near the 
Wyoming-Colorado border with 100 knot jet winds embedded on its 
southern side. Temperatures will be much cooler, a few degrees 
below normal for most of the area. Highs should be in the upper 
50s to mid 60s across the lower elevations and 30s and 40s in the 
high country. There will be a breezy northwesterly to westerly 
flow across northeast Colorado through the afternoon, with peak 
gusts reaching 30 to 35 mph in many areas. Showers should increase
again Tuesday afternoon, though synoptic scale ascent will start 
to gradually turn to subsidence as the low moves away to the 
northeast. Warm downsloping winds should keep the lower elevations
mostly dry, except for some isolated rain showers along the 
Wyoming border. Snowfall will again favor the northern Front Range
Mountains and the Park Range, elsewhere accumulations should 
again be fairly light. 

.LONG TERM...(Tuesday night through Monday)
Issued at 242 PM MDT Mon Oct 18 2021

A cut off trough will be departing our forecast area Tuesday 
evening. There will be just enough low level moisture left over 
for a few snow showers to continue across the western slopes of 
the mountains. Across the northeastern plains, there will be good 
lapse rates and decent QG ascent which may allow for a couple rain
showers to form mainly north of a line from Greeley to Akron. By 
midnight, the trough will have moved far enough east to 
essentially end the chance of precipitation in our CWA. There will
be some gusty winds across the mountains and northern plains
overnight as gusts could reach 30-35 mph. 

Ridging will develop over the Intermountain West on Wednesday that 
will last through the beginning of the weekend. There will be a 
stretch of dry weather with temperatures warming from near normal 
Wednesday to 5 to 10 degrees above normal Thursday through Saturday. 
Winds will not be very strong during this period but the dry air 
will create a few pockets of elevated fire danger across the 
plains. 

The upper level flow will become more zonal Saturday night into 
Sunday as a very weak shortwave trough moves across. There will be 
very limited moisture with this system and almost no QG ascent so 
very little, if any, precipitation is expected. 

By next Monday, a strong trough will move ashore on the 
California coast and make its way into the Great Basin. Meanwhile,
a strong and broad ridge will develop over the eastern two-thirds
of the US. For being so far out, there is decent agreement 
amongst the global ensembles that our forecast area will see 
strong southwesterly flow in-between these features. This is a 
classic pattern for high fire danger to develop in our CWA. This 
period will also see well above normal temperatures. Eventually, 
the trough will move across our forecast area during the middle of
next week bringing a chance of precipitation and lower
temperatures. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1101 PM MDT Mon Oct 18 2021

All TAF sites will continue in VFR conditions through the TAF
period. Southwesterly winds will shift west through the early
morning hours. Wind gusts will begin to increase significantly up
to 25-30kts at all sites starting 15Z through Tuesday evening.
There is a possibility of anticyclone development near all sites
Tuesday afternoon which may lead to northerly winds staying
dominate through the forecast period. Short term guidance suggests
an isolated shower is possible for all terminals but forecast
confidence decreases for any chance of precipitation due to the
low pressure system pushing too far north. 

&&

.FIRE WEATHER...
Issued at 242 PM MDT Mon Oct 18 2021

Fire danger will decrease this evening as temperatures fall and 
humidity improves, though breezy winds are expected to persist 
through the evening. Tomorrow, there will be elevated fire danger 
on the plains southeast of the Palmer Divide in the afternoon 
again as low humidity in the 15 to 20 percent range for a few 
hours is coincident with persistent breezy winds gusting near 30 
mph. Critical fire weather conditions are likely for localized 
areas and possible for the wider zone if humidity falls lower than
forecast. We have maintained the Fire Weather Watch in effect for
southern Lincoln County Tuesday from noon through 6 pm. Fire 
danger will decrease through the evening as humidity improves and 
winds relax.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch Tuesday afternoon for COZ247.

&&

$$

UPDATE...Mensch
SHORT TERM...EJD
LONG TERM...Danielson
AVIATION...AD
FIRE WEATHER...EJD