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fxus65 kbou 251607 

Area forecast discussion
National Weather Service Denver/Boulder Colorado
1007 am MDT Sat Mar 25 2017

issued at 1005 am MDT Sat Mar 25 2017

Have delayed precipitation onset in the mountains this afternoon
after looking at satellite and radar observations. Do still
forecast scattered showers by late this afternoon over the
mountains, especially near the i70 corridor, with the rain/snow
line being quite high around 10kft. A thunderstorm or two
will be possible to bring heavier snow showers over the passes,
possibly affecting visibility.

After reviewing the latest models for the rain/snow line tonight
over the plains, have taken out mention of snow over the urban
corridor, from ft Collins to Centennial, with a mix elsewhere.


Short term...(today and tonight)
issued at 350 am MDT Sat Mar 25 2017

Positive tilt upper ridge aligned with The Crown of the Colorado-
New Mexico rockies early this morning is progged to migrate
eastward over the western Great Plains by this evening. Dry and
warmer air beneath this ridge will be in place over the forecast
area for most of the day. In the very short term...mesoscale
models still indicate patchy to areas of fog on the plains during
the next 2-4 hours. However, have yet to see any fog on infrared
satellite imagery or in sfc observations. Will reluctantly hold
on to the patchy fog east of the I-25 corridor for now. Otherwise
count on a dry day with a gradual increase in high clouds ahead
of an upper level trough now moving over western portions of the
Great Basin. Highs today will generally be 8-12 deg f warmer than
yesterday. Winds on the plains today should remain south-
southeasterly for the most part at speeds generally under 15 mph.
In the high country light southerly winds this morning are
projected to turn southwesterly and increase in speed this
afternoon in advance of the sfc cold front moving across nern
Utah/srn Wyoming by late this afternoon.

Models indicate a nearly solid band of light to moderate
precipitation along the frontal zone as it moves through western
Colorado this evening. Increasing qg ascent and mid-level
instability within the warm sector of this trough could support
pockets of upright convection over the higher terrain around
Summit and grand counties before midnight possibly resulting in
locally heavy snowfall. Snow level will start out high tonight...up
around 10000-10500 ft above sea level...then gradually fall to the mtn valley
floors after midnight with passage of the sfc cold front. Snow
totals overnight in the high country expected to range anywhere
from 1 to 4 inches. For the plains...could see isolated to
scattered showers forming around midnight as the boundary layer
moistens with a gradual shift to northerly direction late.
Precipitation should be light starting out as rain and then late
tonight possibly change to a rain/snow mix below 6000 feet...and
perhaps to all snow on the Cheyenne Ridge and Palmer Divide with
sfc temps lowering to around 0 deg c.

Long term...(sunday through friday)
issued at 350 am MDT Sat Mar 25 2017

Synoptic pattern change will help to bring increased chances of
moisture to the region through the period. For Sunday an upper
level trough will move across Colorado through the day with a surface
low spinning over the southeast. There is decent moisture associated with
this feature that will bring snow to the mountains and rain on
the plains given the 700mb temperatures of -2 to -5c. Models
trends have the better lift to the south with the track of the qg
fields. Current amounts still looking 3 to 6 inches for the
mountains with higher amounts along the eastern slopes with .01 to
half an inch of rain for the plains. Temperatures will continue
to be slightly cooler then what we have seen with highs in the
lower 50s.

Monday will see some warming under a fast moving ridge between
systems. Conditions with be dry with highs in the 60s. Monday
night into Tuesday moisture will increase over western Colorado
ahead of the next upper level feature that will be over the Great
Basin by 00z Tuesday. With the increased moisture and orographic
influence of the SW flow ahead of the trough snow will form at
higher elevations. Expect the heaviest to be over the central and
southern mountains given the northern mountains tend not to do as
well in this pattern. Current tracks of the closed low differ
between the GFS and ec with the Euro a bit faster and deeper by
midnight Tuesday. As the low progresses into the nm area there
will be enough moisture and cooler air provided by the front
Tuesday afternoon to bring snow to the mountains with definite
rain and possibly snow to the plains. Will keep higher pops with
this system given model agreement but still low confidence on
amounts and track without more runs to verify consistency.
Temperatures will drop once again on Tuesday with the onset of the
frontal boundary with highs in the 50s. This could also change
with possible intrusion of cooler air.

The latter half of the week will dry out under another
transitional upper level ridge for Wednesday and Thursday.
Temperatures will rebound back into the 60s both days. For Friday
the models are showing another possible good precipitation maker
for the region but this far out all I will say is stay tuned.


Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 1005 am MDT Sat Mar 25 2017

VFR conditions are expected at Denver area air terminals for
today. South-southeast winds of 5-15 kts will prevail. Should see
a gradual increase in high clouds through the day...with possibly
a few mtn top standing wave clouds forming this afternoon. Tonight
clouds will increase ahead of a surface cold front and upper
level trough moving over western Colorado. Could see cigs lowering
to around 6000-7000 ft agl after midnight and a 30-40 percent
chance of rain showers. Cigs could lower even more to around
3000-4000 ft above ground level after 09z, with rain mixing with snow towards
sunrise at apa as temperatures drop to near freezing. Little to no
snow accumulation is anticipated prior to 6 am MDT. Winds start
out south-southeast at 7-15kts early evening, then gradually shift
clockwise to west-northwest after midnight at speeds under 12


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