Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 301703
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1103 AM MDT Thu Mar 30 2017

.UPDATE...
Issued at 1044 AM MDT Thu Mar 30 2017

Much of this morning has been devoted to the storm that will
start impacting Colorado tomorrow, starting with the mountains
and then spreading across the Plains Friday evening into Saturday
midday. A winter storm watch has been issued above 6000 feet for
the Palmer Divide and the Front Range mountains. Confidence is
increasing in accumulating snow for those areas. Still a lot of
uncertainty in accumulating snow across I-25 corridor from Denver
north to Wyoming given poor agreement among available model
guidance. Much more to come in the afternoon package.

For today, adjusted temps down a few degrees to account for the
thick wave clouds. GOES-16 trends shows the wave clouds loosening
their grip during the day so we still feel low 60s are possible
later this afternoon across most of the Plains. Also adjusted sky
cover to mostly cloudy because of those wave clouds.

&&

.SHORT TERM...(Today and tonight)
Issued at 415 AM MDT Thu Mar 30 2017

Upper high pressure ridge over Colorado early this morning but
will be shifting east into the central plains tonight. This
movement in response to next Pacific storm system which will be
dropping into the Great Basin through the short term period.
Despite the ridge, moisture is already advecting into the the
mountains and western colorado while stratus deck looms just east
of the Colorado/Kansas border. May see some of this stratus slip a
bit westward into the far ne corner after sunrise. Warmer across
the plains today with readings back up into the 60s.

As the upper low moves closer to Colorado late today expect
increasing ascent as noted in layered QG fields for later this
afternoon and tonight. Given some weak instability expect showers
to develop in the mountains this afternoon and maybe even some
spilling out over the far northern plains tonight. Low level flow
will increase over the eastern plains from the southeast which
will import low level moisture and stratus later tonight. With
this flow expect a denver cyclone to also develop after midnight
tonight with possible stratus/fog over the Denver area and points
north to the Wyoming border. Expect higher coverage of showers
near the Wyoming border as the southeast flow will create a better
chance of showers. Better chance of precip will develop during
the day on Friday.

.LONG TERM...(Friday through Wednesday)
Issued at 415 AM MDT Thu Mar 30 2017

Some differences remain in the long term with the initial system
Friday and Saturday, however they are coming to a slightly better
solution of the upper low position. As thought, the GFS and NAM
where the too fast and north outliers, and the 00z and now 06z
runs have been trending back toward the GFS ensemble mean, EC and
GEM. The upper low will be over northern Arizona Friday morning
with southeasterly low level flow transporting moisture into the
plains. Showers are expected to increase over the northern plains
as well as the mountains as a jet moves north into the area and
upward QG motion increases. Low level clouds are expected over
most of the plains, however some clearing further south may allow
for some thunderstorm development which may be transported into
our area in the afternoon with strong forcing and shear. Upslope
flow will be increasing with PWs around half an inch. Rain and
snow showers will be increasing across the plains, especially
along the foothills and up onto the eastern slopes of the Front
Range Mountains. Snow levels should start around 7500 feet that
morning, but then lowering through the day, to be down around 5500
by the evening. As the upper and surface low move into New Mexico,
winds will turn northerly through the night. A wet and slushy snow
is expected over the urban corridor and out over some of the
eastern plains, with some good potential snowfall rates overnight.
Have increased the forecasted snowfall for most of the area with
slightly better agreement, however differences in the position and
temperatures are still keeping the forecast confidence lower than
average. Best dynamics remain to the south of the forecast area as
well. Also, northerly winds play with the snowfall amounts over
the northern urban corridor with higher density if not all rain at
times. Forecasted low temps Friday night will be in the upper 20s
to lower 30s.

Rain and snow, potentially heavy at times over the Palmer Divide
and southern Foothills, will continue into Saturday morning, with
the system pulling away in the afternoon. HIghs will likely peak
into the low 40s for the plains. Skies should clear that night
briefly but another shortwave trough will bring more cloud cover
and a slight chance of snow over the northern mountains Sunday.

A system from the Pacific Northwest will push in quickly for
another round of precipitation Monday night into Tuesday, with
strong northerly winds expected Tuesday. It will be another tricky
rain/snow line forecast for the plains.

Upper ridging is then forecast to build over the region for warmer
and drier weather Wednesday and Thursday with temperatures getting
back to near average for this time of year.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1044 AM MDT Thu Mar 30 2017

VFR conditions will continue today at all three TAF sites through
Friday morning. Watching closely the potential for stratus/fog
pre-dawn, with DEN having the strongest potential for ceiling/vis
issues. This is because of the formation and sustainment of the
Denver Cyclone this afternoon. This could lead to NW flow at DEN
and APA early Friday morning and advect in stratus and possibly
fog. Confidence is moderate at this point as high res models have
been showing the a strong potential for stratus, but fog less
likely but a good enough signal to include 3/4M at DEN, 2M at BJC,
and VCFG at APA. Will continue to monitor the high res model
trends for any changes in the Fog potential Friday morning. Winds
will remain on the light side all three terminals under the
influence of the Denver Cyclone through 18Z Friday, then flow
should turn more easterly and increase to 15 kts or so as the
surface low strengthens across S. CO/N. NM.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Friday evening through Saturday
afternoon for COZ041.

Winter Storm Watch from Friday afternoon through Saturday
morning for COZ033>036.

&&

$$

UPDATE...Schlatter
SHORT TERM...Entrekin
LONG TERM...Kriederman
AVIATION...Schlatter



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