Area Forecast Discussion

FXUS65 KPUB 172253
Area Forecast Discussion
National Weather Service Pueblo CO
353 PM MST Sat Feb 17 2018
.SHORT TERM...(This evening through Sunday)
Issued at 353 PM MST Sat Feb 17 2018
...High Winds to return for the southeast mountains and adjacent 
eastern slopes mainly west of I-25...
...Critical Fire Weather Conditions expected for the southeast 
plains and lower slopes of the southeast mountains on Sunday...
Challenge in short term is how far down the slopes high winds will 
progress again overnight.  With upper low digging southward into the 
Pacific NW tonight, flow aloft shifts to a more west southwesterly 
component.  This is a more favorable cross barrier flow for much of 
the southeastern mountains.  However various high res models have 
differing solutions on the development of a mountain wave and how 
far down the slopes it progresses.  The local 4 km WRF and 3km NAM 
Nest suggests strong downslope winds will spread from the higher 
peaks into portions of the I-25 corridor from late tonight through 
Sunday morning...while HRRR is more conservative and keeps winds 
confined to the higher peaks.  Model cross-sections look best across 
northern areas (El Paso county) with a good amount of reverse shear 
developing towards morning though there isn't much of a mountain top 
inversion. However there doesn't necessarily have to be as we saw 
last night and models are not good at handling these details anyway. 
 Leaning on various high res models have upgraded the high wind 
watch to a warning, though wasn't getting enough coverage in the 
west central portions of Las Animas county to warrant an upgrade 
there.  In the El Paso county area...think focus will shift to the 
southwest side of Colorado Springs and Fort Carson area towards dawn 
given the more southwesterly component aloft.  Another area to watch 
will be the I-25 corridor south of Colorado City.  The west side of 
Custer county into the wet mountain valley could also see a period 
of damaging winds overnight according to WRF and NamNest.  Will keep 
overnight lows on the warm side to account for downslope winds which 
are likely to continue overnight to at least some degree along/west 
of I-25.  
For Sunday looks like mountain wave parameters should break down by 
late morning...though winds will remain strong as upper jet 
translates in aloft.  Should start to see moisture increase along 
the Continental Divide during the afternoon with snow developing 
during the late afternoon.  Main brunt of the accumulations holds 
off until later Sunday night.  Meanwhile...gusty winds will spread 
into the plains during the afternoon.  Temperatures across the 
plains will warm into the 70s...well above normal for this time of 
year, and combined with dry surface dew points will lead to 
widespread critical fire weather conditions.  Have upgraded the Fire 
Weather Watches to Red Flag Warnings.  Have added zone 225 to 
account for the lower eastern slopes along the I-25 interface as 
winds will be particularly strong in this area.  -KT
.LONG TERM...(Sunday night through Saturday)
Issued at 353 PM MST Sat Feb 17 2018
...Windy with Snow and Blowing Snow across the ContDvd Monday... 
Sunday night-Tuesday...Current models continue to dig the Pac 
Northwest system into the Great Basin and lift it out across Rockies 
in the late Sunday night through Tuesday timeframe, with only slight 
differences in timing. The ECMWF still is a tad slower with this 
system, which allows for shallow cool airmass to filter across the 
Eastern Plains through the day Monday, where as the GFS and the NAM 
solutions keep the cooler air north of the the area with strong west 
to southwest flow in place across the Southeast Plains. 
All solutions point to increasing snow along and west of the ContDvd 
Sunday night, with snow likely across the ContDvd Monday and Monday 
night. With strong orographic southwest winds of 25 to 50 mph, have 
upgraded winter storm watch for the Eastern San Juan Mountains to a 
warning from 06z Monday through 12z Tuesday. Snow amount of 8 to 14 
inches are expected, with localized amounts up to 20 inches possible 
on favored southwest peaks. We have also issued winter weather 
advisories for lower Rio Grande Valley (3 to 6 inches) and for the 
Sawatch and Mosquito Ranges (4 to 8 inches, locally up to a foot) 
for the same timeframe. Strong and gusty southwest winds through the 
day Monday becomes more westerly Monday night and Tuesday, with 
difficult travel expected across the higher mountain passes in snow 
and blowing snow.  
Further east, the increasing southwest flow aloft will again lead to 
potential for strong downslope winds across the Southern Mountains 
and lower eastern slopes Sunday night into early Monday morning, 
with model cross-sections indicating a mean critical layer mainly 
across the Southern Sangre de Cristo Mountains. Current grids 
indicating gusts in the 60 to 70 mph range across this area, and 
later shifts may need to go with wind hightlights. Monday 
temperatures and winds across the plains are tricky at this time, 
with another big bust potential with a shallow cold airmass moving 
across the Plains. As mentioned earlier, the faster GFS and NAM have 
an induced surface low across the Southeast Plains Monday, keeping 
strong and gusty west to southwest winds across the I-25 corridor 
and gusty southerly winds across the far Eastern Plains, where as 
the slower EC solution has a weaker low near TAD Monday morning, 
which allows for shallow cold airmass to filter across the Plains 
through the day. Have tried to blend towards this cooler solution, 
with temps in the 40s and 50s along and north of the Highway 50 
Corridor Monday morning, with temps then cooling into the afternoon. 
If the GFS and NAM solutions are more correct, there will be 
possible critical fire weather conditions across most of the plains 
on Monday, with current grids indicating possible fire weather 
highlights for Las Animas County and possibly southern portions of 
Baca County.  
By Monday night, snow spreads across the high mountain valley and 
into the Eastern Mountains, with generally light accumulations 
expected. Shallow cold airmass spreads across all of the southeast 
plains with stratus banked up across the lower eastern slopes, 
leading to chances of light snow across the I-25 Corridor and the 
eastern plains through the day Tuesday, with the overrunning 
pattern. Cool upslope flow across the plains on Tuesday will keep 
highs in the 20s and 30s areawide.  
Wednesday-Saturday...Continued west to southwest flow aloft will 
lead to a slow warming trend across the area through the end of the 
work week. Dry conditions look to return to Eastern Colorado, with 
light snow possible across the ContDvd through the period.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 353 PM MST Sat Feb 17 2018
Mountain wave activity brings gusty and variable wind conditions and 
low level wind shear to the forecast points. See discussion below 
for details.
VFR conditions are expected throughout the forecast period. Expect 
gusty winds during the daytime hours.
High resolution models are resolving a mountain rotor forming over 
KCOS during the overnight hours. During this time period, expect low 
level wind shear. Gusty winds are expected during the afternoon 
hours tomorrow. VFR conditions are expected throughout the forecast 
Pueblo should be far enough west from any mountain rotor activities, 
but expect strong winds for the majority tomorrow, gusting in the 
afternoon hours. VFR conditions are expected throughout the forecast 
Red Flag Warning from 10 AM to 6 PM MST Sunday for COZ222-
High Wind Warning from 10 PM this evening to noon MST Sunday for 
Winter Weather Advisory from 11 PM Sunday to 5 AM MST Tuesday 
for COZ058-060-061-065>067.
Winter Storm Warning from 11 PM Sunday to 5 AM MST Tuesday for