Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 290709
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
109 AM MDT Sat Apr 29 2017

.UPDATE...
Issued at 107 AM MDT Sat Apr 29 2017

Bumped up beginning time of the winter storm warnings to the
current time for the remainder of the southeast plains as web cams
and surface obs are showing most areas have already switched over
to snow. Nice presentation on satellite and radar of intensifying
upper low/deformation band. Only some minor tweaks needed to POP
and Temperature grids for now. -KT

&&

.SHORT TERM...(This evening through Saturday)
Issued at 324 PM MDT Fri Apr 28 2017

...Strong late Spring storm on track for southern CO with a
prolonged period of heavy wet snow...

Upper low taking shape near the 4 corners this afternoon, with
clouds and precip rapidly increasing across the area as dynamic lift
ramps up. Still a pocket of drier surface air over the plains/I-25
corridor at mid-afternoon which was limiting limiting shower chances
across the lower Arkansas Valley, though moister air has begun to
push westward as of 21z as deep layer of upslope flow intensifies.
In general, 12z models all came in with fairly good agreement on
position and movement of the upper low, as system will take a very
favorable track E-SE across NM overnight and through the day Sat,
producing a prolonged period of deep upslope and strong dynamic lift
across the region.

Over the mountains, snow already increasing this afternoon along the
Continental Divide, and expect most mountains and high valleys will
see steady snowfall near/shortly after sunset as lift increases.
Periods of heavy snowfall are then likely overnight into Sat
morning, before snow gradually ends from west to east during the
day. Forecast N-NE low/mid level winds suggest eastern slopes of the
Sangres/Wets will see big snowfall totals, along with nrn slopes of
the Spanish Peaks. Some 2 foot plus storm totals not out of the
question, especially above 9000 feet. Interior valleys will see
modest amounts of snow, with perhaps a sliver of heavier snow over
the wrn edge of the San Luis Valley as easterly flow becomes deep
enough to push over the Sangres and through the valley by Sat
morning.

Across the I-25 corridor and plains, snow will develop early this
evening along the Palmer Divide, with rain showers filling in
farther south as air mass moistens. Snow line will drop south
through the evening and overnight, with a change-over along I-25 by
midnight and across most of the ern plains around 3 am. All areas
should then see a burst of heavier snow early Sat morning, before
strongest lift shifts south of the Arkansas River and eastward
across the plains early Sat afternoon. Main problem areas with the
forecast would appear to be the usual suspects in srn El Paso and
nrn Pueblo counties (including COS and PUB), as strong downsloping
north winds developing Sat morning may limit snowfall, leaving a
rather tight gradient in amounts over the north side of COS and
between PUB and Colorado City. On the other end of the spectrum, srn
I-25 corridor and plains south of Highway 50 may see some fairly
impressive snowfalls, with some nearly 2 foot storm totals possible
in a few terrain favored locations near the NM border.

Given warm ground, the spread between snow depth and snowfall will
be fairly large, with some fairly quick melting once snowfall rates
begin to diminish.

Regarding temps, most areas will fall to at or below freezing levels
by early Sat morning, with perhaps some slight warming to the
mid/upper 30s at lower elevations late Sat, especially in
locations where snowfall rates diminish.

.LONG TERM...(Saturday night through Friday)
Issued at 324 PM MDT Fri Apr 28 2017

Saturday night through Sunday...Models have fluctuated the past 48
to 72 hrs, but agree on placing the upper low over northeastern New
Mexico Sat night, then tracks it across the Panhandles and Kansas on
Sunday. This solution is a bit slower than previous thinking just 24
hrs ago, allowing for a longer window of accumulating snow for the
eastern CO plains through Sat night. Snow will gradually taper off
from west to east as the system pulls away, with snow lingering over
the far eastern plains through Sunday morning. Current highlights
persist until 9 am Sun morning for the east, and expected snowfall
amounts can be found in the various winter weather highlight
products. Expect brisk n-nw flow for the forecast area as the low
moves east, with isolated showers continuing over the central mts
but ending across the east by mid-afternoon. Expect min temps below
freezing for all areas Sat night, then highs on Sun in the 40s for
most locations.

Monday through Wednesday...Northwest flow aloft settles in across
the state in the wake of the departing system. There will be a
continued threat of isolated to low end scattered showers across the
central mts and spilling over to Pikes Peak on Mon. A stronger
shortwave crosses the Rockies on Tue, producing a better shot of
convection for all of the forecast area including the plains for Tue
afternoon through Wed afternoon. Expect max temps all three days to
top out in the 50s to right around 60F.

Thursday and Friday...A ridge of high pressure over the desert SW
will produce dry north to northwest flow across the forecast area to
finish out the work week. Look for temps to warm into 60s to around
70F for Thu, then 60s to lower 70s for the high valleys and 70s to
near 80F for the plains on Fri. Moore

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1124 PM MDT Fri Apr 28 2017

Forecast remains on track with IFR to LIFR tonight for KCOS and
KPUB terminals and across most of southern Colorado as strong
storm system develops and moves across the region. KALS will also
see a period of IFR to LIFR develop but for a smaller window late
tonight and early Saturday.

At KCOS...periods of moderate snow overnight into Saturday
morning, before gusty northerly winds of 25-35kts begin to
decrease snowfall by midday Saturday. Conditions will improve to
MVFR during the afternoon as snowfall begins to decrease.

At KPUB....snow tonight. Gusty northerly winds and snow will
persist into Saturday morning with MVFR conditions gradually
developing Saturday afternoon as snowfall rates diminish and CIGS
begin to rise.

KCOS and KPUB terminals will have the potential for snow
accumulations in the 4 to 8 inch range by Saturday afternoon,
although warm pavement surfaces will help melt snow at times.

At KALS...best window for snow and IFR to LIFR conditions will
come in 08z-14z timeframe with the potential for a couple inches
at the terminal by midday Saturday.


&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 9 AM MDT Sunday for COZ089-093>099.

Winter Storm Warning until 6 AM MDT Sunday for COZ072>075-079-
080-087-088.

Winter Storm Warning until 6 PM MDT this evening for COZ078-081-
082-084>086.

Winter Weather Advisory until 6 PM MDT this evening for COZ058-
060-061-063-065>068-076-077-083.

&&

$$

UPDATE...KT
SHORT TERM...PETERSEN
LONG TERM...MOORE
AVIATION...LW


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