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401
FXUS65 KPUB 211122
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
422 AM MST Thu Feb 21 2019

.SHORT TERM...(Today and tonight)
Issued at 407 AM MST Thu Feb 21 2019

Western U.S. upper trough continues to deepen over the Great
Basin early this morning, with moist s-sw mid level flow spreading
across the wrn half of CO. Snowfall overnight has been heaviest over
the eastern San Juan Mountains, while lighter snows have spread
north over most of the Central Mountains and upper Arkansas Valley.
For today, western upper trough moves very little, with closed low
over NV this morning drifting south to near Las Vegas tonight. Deep
s-sw flow will persist over the area today, with orographic lift and
plentiful moisture continuing to produce heavy snowfall over the
eastern San Juan mountains. Weaker orographic lift will keep snow
lighter farther north over the Central Mountains, with some
spillover snow showers reaching the crests of the Sangres by late
afternoon as well. Upper wave ejects from the main wrn trough later
today, lifting northward through UT tonight. Upward motion ahead of
this feature expands across the western half of CO, which should
help increase snowfall coverage and intensity over the mountains
from the Sangres westward, though again heaviest snow will remain
anchored over the San Juans, where at least another foot of snow is
likely during the next 24 hrs. Current set of highlights, with
warnings for the San Juans/La Garitas and advisories for the nrn
Sangres/Central Mountains look fine for now. East slopes/I-25
corridor and southeast plains will miss out on snowfall today and
tonight, with just a thickening high level cloud shield over the
area through the period. Did lower max temps several degf over the
eastern plains, where clouds and lack of much wly wind component
will hold back readings, especially along and north of the Arkansas
River.

.LONG TERM...(Friday through Wednesday)
Issued at 407 AM MST Thu Feb 21 2019

Friday - Saturday...

The previously discussed upper trough will strengthen as it
accelerates east across Arizona and into New Mexico on Friday, and
lifts northeast into Kansas Saturday morning. Deterministic model
runs have been consistent over the last couple of days with the
track and strength of the trough as it impacts Colorado, with only
minor differences in its speed remaining. Ensembles show low
spread through Saturday as well. Guidance consistently strengthens
the trough into a closed upper low over northeast New Mexico early
Saturday morning. Associated surface low pressure deepens over
the CO/KS/OK border early Saturday morning, which quickly lifts
northeast during the morning and drives a cold front down the
eastern Colorado plains. Given consistency among guidance over the
last couple of days, forecast confidence is high.

Snowfall associated with the trough and attendant southwesterly
100 kt 300 mb jet will continue across the mountains Friday,
coming to an end during the morning on Saturday. All mountain
areas should see an additional 4-8 inches of snow accumulation
through the period, with the high valleys receiving another 1-3
inches. The winter weather warnings and advisories currently in
place look on track to expire Friday evening when the heaviest
snow is expected to end. Snowfall is not expected to really get
going over the far southern Sangre`s until Friday afternoon. An
advisory may be needed there in a future forecast package.

The plains will remain dry most of Friday, with
south/southwesterly winds aloft keeping the area dry and mixing
to the surface causing breezy conditions, especially over far
southern and eastern locations. It should be noted that while most
guidance develop a well-mixed boundary layer during the day
Friday, the NAM does not, maintaining weak easterly flow and
cooler temperatures. Went ahead with the majority of guidance and
what seems like the most likely scenario. That being the case,
highs across the plains on Friday should be in the mid 40s to low
50s, with temperatures around 40 expected in Colorado Springs.

As the trough and associated upper forcing move east, precip will
spread across the I-25 corridor and eastern Colorado plains late
Friday, increasing in coverage and intensity early Saturday
morning behind the front on the backside of the low. Precip will
likely start as rain across much of the eastern plains, switching
over to snow from west to east as the cold air pushes south during
the evening. Given the fast motion of the storm and low snow-
liquid ratios, it does not appear that snow totals will be too
great. Further, deep and strong northwesterly (downsloping) flow
across the plains on the backside of the low should counteract
some degree of the large scale forcing. Anticipate anywhere from
1-4 inches of snow falling across the plains, with the high end of
the range being most likely east of the I-25 corridor, and
Colorado Springs to Pueblo likely only seeing up to an inch of
accumulation during the evening. Given gusty winds behind the cold
front, reduced visibilities will be possible due to blowing snow,
particularly over the far eastern plains, Saturday morning. Snow
should be over across the forecast area by early afternoon. The
rest of the day will be dry, and temperatures slightly cooler,
with highs in the low to mid 40s across the plains, and low 30s in
the high valleys. Gusty north winds across the plains will become
light during the early evening.

Sunday - Wednesday...

Primarily zonal flow will dominate the weather over Colorado for
at least the first half of next week, with the upper jet and
disturbed flow staying just north of the state. This will lead to
dry conditions for most of southern Colorado. The exception may
be along teh Continental Divide, particularly in the central
mountains, where periodic isolated light snow showers may develop
due to disturbances passing through the northern Rockies.
Temperatures across the forecast area will be near normal, with
highs around 50 forecast across the plains, and 30s to mid 40s in
the high valleys.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 407 AM MST Thu Feb 21 2019

Expect VFR conditions at all taf sites today and tonight, with
slowly lowering VFR cigs tonight. Will see snow over most mountains
surrounding the San Luis Valley today and tonight, and with few shsn
drifting across the valley close to KALS after 00z, will include a
vcsh mention overnight.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 2 PM this afternoon to 11 PM MST
Friday for COZ058-060-061-063-072-073.

Winter Storm Warning until 5 PM MST Friday for COZ066-068.

&&

$$

SHORT TERM...PETERSEN
LONG TERM...LINE
AVIATION...PETERSEN