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fxus65 kbou 271027 

Area forecast discussion
National Weather Service Denver/Boulder Colorado
427 am MDT Mon Mar 27 2017

Short term...(today and tonight)
issued at 420 am MDT Mon Mar 27 2017

SW flow aloft will be over the area today in advance of an upper
level trough that will move into the Great Basin by this evening. At
the sfc low pres will gradually dvlp over ern co with increasing sly
low lvl flow by late aftn.

Cross-sections show some increase in moisture across the mtns during
the aftn along with minor mid lvl ascent so will see sct showers
dvlp. Across nern Colorado it will be dry although I can't completely
rule out some widely sct -shra nr the foothills by late aftn. As
for highs readings will be in the lower to mid 60s across the

For tonight an upper level low will eventually dvlp over sern Utah
with the flow becoming rather diffluent across the area. In
addition, with increasing moisture and favorable mid lvl acent fcst
over the area, along with improving lapse rates should see a better
chc for showers across most of the area. Buffer soundings show snow
levels will be mainly abv 8500 feet overnight.

Long term...(tuesday through sunday)
issued at 420 am MDT Mon Mar 27 2017 storm track promises wet and snowy weather for the region
this week...

The first of two Pacific storm systems just off the West Coast is
forecast to deepen as it propagates eastward across the Great Basin
today. 00z models have clustered around the idea that this trough
and the deepening upper low will pass over The Four Corners region
tonight. Some of the models also indicate a lead shortwave
disturbance that moves newrd over the eastern Colorado late tonight.
Strengthening sely low-level flow and swly upper-level flow in
advance of this feature will further saturate the Front Range
airmass and by Tuesday morning precipitation should be well under
across the high country of N-central Colorado and up along the Wyoming-
Nebraska borders in nern Colorado. Whereas in the Lee of the Front
Range models show the formation of a pronounced dry slot with the
700-500 mb flow becoming sly with upper low moving over nwrn New
Mexico. This should delay any significant precip along the foothills
from Douglas County northward to around the Longmont-Loveland area
until the afternoon. Mild temperatures will keep the snow level up
around 9000-9500 ft above sea level during the day. So to start out, any snow
accumulation will be confined to the mtns and higher foothills where
we could see anywhere from 1-4 inches of snow by evening. Precip
will remain all rain at lower elevations and with increasing
instability through the day and boundary layer convective available potential energy now projected
in the 200-500 j/kg range, there is also a slight chance of T-storms
mainly east of the Front Range, but would not rule them out in the
high country. By Tuesday evening as the upper low tracks along the
Colorado-New Mexico border, should see E-sely upslope flow deepening
as qg Omega steadily increases with greater cyclonic shear and
cooling aloft. Models indicate widespread precip acrs N-cntrl/
northeast Colorado Tuesday night into Wednesday morning as the upper
tracks over ern New Mexico. GFS is most ambitious with rain/
snowfall rates over and near the Front Range overnight. It indicates
anywhere from 0.60 inch to 1.40 inches of liquid by 12z/Wednesday
and another quarter to half inch by midday Wednesday. The European model (ecmwf)
indicates about half of this amount and it is faster to move precip
out Wednesday morning. As for snowfall...the sref is most optimistic
regarding snow amounts with totals by midday Wednesday anywhere from
8-15 inches on the East Face of the Front Range, to 4-11 inches
within the I-25 corridor. Other models are no where as wet/snowy as
the sref, however the GFS does indicate 3-7 inches of snow on the
Palmer dvd by midday Wednesday. European amounts generally in the 1-
4 inch range with a small area of 6 inches south of Denver. How cold
it becomes overnight will largely dictate how much snow we'll see at
lower elevations. For now will hold off issuing any winter weather
highlights and allow for US to examine later model guidance before
doing any hoisting.

Models show this system slowly moving out over the Great Plains late
on Wednesday as a shortwave upper ridge builds in from the Great
Basin. Thursday looks dry and warmer as the ridge passes overhead.

Going into Friday...GFS/ECMWF and their ensemble means cluster
around the next storm system dropping down from the Pacific
northwest. This system appears to be dynamically more potent and
colder. By Friday morning, these same models show a deep low forming
near Las Vegas and through day tracking east over the 4-corners
area. The Canadian model also shows this system winding up in the
same area but it takes the upper low southward over southern Arizona
by Saturday morning. The other models show an west-east elongated
trough/closed low wrapping a deep layer of moisture and cold air
back into eastern Colorado Friday night into Saturday. Should this
verify, the Front Range and eastern plains of Colorado end up with
significant rainfall and snowfall when all said and done with. This
one bears watching. Models eventually move this system out by Sunday
night and shortwave ridge moving in from the west.


Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 420 am MDT Mon Mar 27 2017

Some stratus has developed to the northwest of dia however as long as winds
stay sly early this morning I believe it will not affect the Airport
unless winds switch to a more nwly direction. For the rest of the
day should have VFR conditions with winds generally SSE thru the

For this evening with increasing instability and mid lvl ascent will
see a chc of showers especially between 00z-06z with ceilings of
6000-8000 ft developing. In addition winds may become more Ely as a
Denver cyclone becomes more defined. Late tonight into Tue morning
may see low clouds and some fog depending on where cyclone is


Bou watches/warnings/advisories...


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