814 
FXUS65 KBOU 242055
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
155 PM MST Sat Feb 24 2018

.SHORT TERM...(This evening through Sunday)
Issued at 138 PM MST Sat Feb 24 2018

Very cold air is overhead today as the trough axis from an 
underperforming short wave trough departs the state. Another weak 
short wave digs south out of the northern Rockies tonight. 
Temperature advection at 700 and 500 mb is consistently neutral 
through Sunday, and it will remain cold aloft through Sunday 
evening when the second trough axis departs Colorado. Based on 
GOES-16 water vapor, the cores of both the first short wave 
trough currently across western Kansas and the second approaching 
trough across Idaho have 500 mb temps around -33 to -34 degC. 700
mb temps remain between -13 and -15 degC across our area. Unlike 
the past several events the jet stream or a jet streak will not 
play a role in vertical motion across our area, thus increasing 
overall confidence in where and how much snow may fall across the
mountains. The remaining challenge is the amount of convective 
available potential energy tonight and tomorrow morning. With the 
pool of cold air aloft, lapse rates are steep across the 
mountains, favorable for convection. Most of the synoptic scale 
lift will remain south and west of our area. The west upslope 
combined with instability should result in a decent snowfall 
across the Park Range, where isolated amounts to 6-8 inches are 
possible through Sunday evening. Most areas across the northern 
mountains should see a few inches. The I-70 corridor from 
Georgetown to Vail Pass could see a trace to 3 inches, with the 
highest around across the Eisenhower-Johnson Tunnel and Vail 
Pass. The short wave trough responsible for the snow chances 
tonight into midday Sunday departs quickly and PoPs drop to near 
0 area-wide by Sunday evening. Expect a cold and breezy day at the
ski areas and the rest of the high country with high temps near 
20 at and above 9000 feet and wind gusts 30-40 mph. Areas of 
blowing snow are likely tonight through much of Sunday across the 
high mountain passes and other wind prone areas. The high mountain
valleys will be less windy with high temps in the upper 20s.

Across the Plains, downslope flow will continue eliminating any
chance of precipitation through Sunday evening. The strong west
and northwest winds extend across all of our Eastern Plains, 
continuing through 5 PM or so. The currently strong bora winds 
will continue for a few more hours before the sun angle decreases 
and the boundary layer decouples. Until then areas of blowing snow
mainly west of I-25 (especially northern Larimer County and the 
CO-93 corridor from Boulder to Golden) will occur across roadways.
Late this evening and over night winds will be generally light 
and temperatures seasonably cold, with the coldest temps across 
the lowlands of Weld County where winds are lightest and there is 
still a good snowpack. In terms of high temperatures Sunday, 
despite second day of downslope the cold air aloft and continued 
snow cover (where it exists) will keep high temperatures in check 
on Sunday. Mid 30s to low 40s are expected.

.LONG TERM...(Sunday night through Saturday)
Issued at 138 PM MST Sat Feb 24 2018

WLY flow aloft will develop Sun night and then become more SWLY on 
Mon.  Cross-sections show limited moisture although there could be a 
few light snow showers in zn 31 Sun night.  Otherwise a mtn wave 
will develop Sun night and linger into Mon morning before weakening 
by midday.  Cross component flow is only in the 30-35 kt range so 
may see a few gusts in the 50-60 mph range in the foothills and 
higher mtns, however, high winds are not expected. Temps will be 
warmer on Mon with highs in the upper 40s to lower 50s over nern 
CO.

On Tue the flow aloft will remain SWLY as an upper level storm 
system develops over the swrn US.  Cross-sections don't show much 
moisture thru the day so will no mention any pcpn.  Across nern CO a 
weak cool fnt may affect the plains, however, highs will stay in 
the 45 to 50 degree range in most areas

For late Tue night thru Wed the upper level low over the swrn US 
will move eastward across New Mexico as a secondary weaker system 
affects nrn CO.  In addition a cold front will move across nern CO 
on Wed.  Overall best QG ascent will stay over srn CO into New 
Mexico so any pcpn over nrn CO will be on the light side.  As the 
weaker system in the nrn branch moves across there will be a period 
of light snow in the mtns late Tue night into Wed.  Across nern CO 
there could be a chc of light snow mainly south of a Denver to Akron 
line on Wed.  Highs on Wed will be in the upper 30s to mid 40s over 
the plains.

By Thu a flat upper level ridge will develop across the area with no 
pcpn expected.  As a sfc lee trough forms nr the foothills downslope 
low level flow should allow for warmer temps as highs rise into the 
upper 40s to lower 50s across nern CO.

For Thu night into Fri the flow aloft will become more WSW as the 
sfc lee trough strengthens over ern CO.  There is a weak disturbance 
along with some embedded moisture in the flow which affects the mtns 
Thu night thus will keep in a slight chc of snow.  Over the rest of 
the area it will be dry.  Highs on Fri will be in the 50s to around 
60 degrees across nern CO. 

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 138 PM MST Sat Feb 24 2018

VFR through Sunday. Strong west winds will continue for several
more hours. High-res models have consistently reduced the winds by
around 23Z at DEN and APA, a little later at BJC. With loss of sun
and weaker pressure gradient across the state, believe this will
play out and winds will indeed reduce to 10 kts or so later this
evening at the metro area terminals. Drainage winds should kick in
after 04/05Z tonight 8-12 kts. By late morning west winds will
pick up again but no where near as strong. Expecting up to 15 kts
out of the west through the late afternoon hours.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Schlatter
LONG TERM...RPK
AVIATION...Schlatter