Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 180527
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
1027 PM MST Sat Feb 17 2018

.UPDATE...
Issued at 840 PM MST Sat Feb 17 2018

Winds a little slow to increase this evening, though high mountain
pass obs were finally beginning to trend upward at 03z. Latest few
runs of the HRRR suggest strongest winds may not occur until after
sunrise on Sun, with a peak in mid to late morning. Won`t change
any highlights at this point, though may need to decrease wind
speeds somewhat overnight in the next update if downslope flow
continues to be slow to develop.

&&

.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 06Z TAFS through 06Z Sunday night)
Issued at 1021 PM MST Sat Feb 17 2018

VFR at all taf sites the next 24 hrs. KCOS will see a risk of llws
overnight as winds aloft increase, before surface winds increase
and become gusty by mid-morning. All terminals will see strong
w-sw winds during the day Sun, with gusts over 30 kts likely.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 10 AM to 6 PM MST Sunday for COZ222-
225>237.

High Wind Warning until noon MST Sunday for COZ072>075-078>082-
084-085-087.

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
COZ068.

&&

$$

UPDATE...EP
SHORT TERM...KT
LONG TERM...MW
AVIATION...PETERSEN


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