Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Junction Colorado
123 PM MST Monday Dec 22 2014
issued at 121 PM MST Monday Dec 22 2014
Canceled the Winter Storm Warning for Colorado zone 2 (craig Meeker Hayden
areas) and Colorado zone 7 (i-70 corridor through rifle). Temperatures warm
enough for mainly rain or rain/snow mix along this section of I-70
with mainly scattered snow showers in northwest Colorado. Radar indicating
that the precipitation is taking on more showery and banded
charactieristics as the strong jet core near the area. So while
heavier snow is possible underneath a band...no longer expecting
widespread signficant accumulations in these two zones.
Good vertical wind shear due to the upper jet along with modest
instability has resulted in a few lightning strikes north of the
Black Canyon of the Gunnison...with a stronger cell just north of
Grand Junction produced hail at the weather office. Updated the
forecast to include isolated thunderstorms across eastern Utah and much
of western Colorado for the remainder of the afternoon.
Update issued at 1041 am MST Monday Dec 22 2014
Radar indicated an area of precipitation working southward across
west-central and southwest Colorado at 10 am and appeared to be associated
with a difuse cold front at 700 mb underneath the nose of a
strong 300 mb upper level jet. Temperatures were warm enough for some
rain at Rifle... grand jct...Nucla..Delta and Cortez with snow
over the mountains colder air over Wyoming is expected to push south into
our forecast area this afternoon and to The Four Corners this
evening as the 170 kts upper jet core currently over the northern
rockies arrives by this evening. Despite the colder air having
less moisture content...believe this secondary cold push coupled
with the dynamics associated with the upper jet core should bring
another round of snow...so will continue the winter highlights
though not much snow apparent at the moment in the northwest Colorado valleys
and along the much of the I-70 west of Glenwood spgs.
Caic remote observations still showing wind gusts of 60-100
miles per hour above 11000 feet over the San Juans but sensors elsewhere in the
Blizzard Warning are much less. Visible satellite was showing
tight waveness in the midlvl clouds over eastern Utah into western Colorado and
often indicative of strong winds aloft. With that in mind...will
keep the Blizzard Warning intact though think areal coverage down
to 8000 feet may be a bit overdone.
Wind Advisory continues for the far southwest Colorado valleys as expect
wind and wind gusts to strengthen over the course of afternoon as
the gradient tightens with the approach of colder air and aided by
Short term...(today through tuesday)
issued at 405 am MST Monday Dec 22 2014
A complicated winter storm continues to evolve over the region.
There is strong confidence in the large scale details. Deep
moisture continues to stream over the region from the northwest with the
best forcing occurring over the eastern half of the forecast area
where strong cold advection occurred overnight.
The jet stream is oriented north-northwest-south-southeast in western Colorado but
enhances to an impressively strong 140kts along the Utah-Colorado border
this afternoon. Surface winds will likely be spatially complicated
with low cloud ceilings inhibiting mixing at times but showers
transporting momentum to the surface at times too. Already this
early morning down trees and powerlines have been reported along
Highway 550 between Ouray and Red Mountain Pass. These winds will only
strengthen through the day. Gusts of 80 to 100 miles per hour are expected in
much of the western mountains this afternoon and evening. Therefore
have issued a Blizzard Warning...above 8000 feet to capture
Douglas Pass also. Further North Highway 191 through the eastern
uintas will likely see very difficult conditions into this evening
under the jet. The far eastern mountains closer to the Continental
Divide will also have wind gusts but more in the 40 to 60 miles per hour
As for snow...the ongoing forecast looks generally on track. The
deepest accumulations continue to favor the eastern half of the
forecast area...east of a line from Vernal south-southeast to Durango. West
of that line will see only light accumulations. The gusty winds
will help to stir the lower levels and keep daytime temperatures
mild with a rain snow mix at times up to as high as 7000 feet. The
snow will wind down this evening as the trough continues to shift
east. Snow levels will drop into the valleys even as snow showers
shift east. One area of concern for heavy snow tonight into
Tuesday morning is the Uncompahgre Gorge that will be under due
North Mountain tops winds at 20kts with 700mb temperatures down to the
efficient -12c. Will let the day shift look at this in detail.
Long term...(tuesday night through sunday)
issued at 405 am MST Monday Dec 22 2014
Flat ridging builds in Tuesday night and shuffles east over the
forecast area on Wednesday as another system moves into the Great
Basin. This storm is expected to push across our forecast area on
Christmas day bringing another round of snow to the high country
and a chance of rain or snow to the valleys. Timing of the wave
would bring the best chance for precipitation during the late
morning and afternoon hours with activity lingering over the
mountains into Friday morning. Will continue to ramp probability of precipitation up but
will not be issuing any products for this potential Christmas day
event until we start wrapping up the current storm. Dry conditions
then expected Friday afternoon and Saturday...with another storm
dropping into the region Sunday...bringing more snow to the
northern and central mountains and high valleys. Temperatures will
run near normal through the period. Winter has definitely arrived
on the West Slope.
Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 939 am MST Monday Dec 22 2014
The jet stream will continue to stretch across the area from the
north-northwest through tonight...with the peak flow at over 140
kts from midday into early this evening. Therefore strong wind
shear below mountain top level will persist. Strong winds aloft will
mix down to the surface at times with gusts of 35-55kt possible
at area airports. If the wind is not gusting...low level wind
shear will likely occur within 020 feet above ground level.
Snow showers will continue over mountains impacting all airports east
of a line from kvel south-southeast to kdro. For khdn ksbs kege kase...
MVFR/IFR ceilings/visibility will occur at times in snow and blowing snow.
Other airports will have ceilings at or below 030 with scattered -snra at
times through this evening. Mountain obscurations will continue in
clouds and blowing snow. Conditions are expected to improve from
west to east after 06z tonight.
Colorado...Winter Storm Warning until 6 PM MST this evening for coz005-008-
Winter Weather Advisory until 6 PM MST this evening for coz003-
Blizzard Warning until midnight MST tonight for coz003-017>019.
Winter Storm Warning until midnight MST tonight for coz004-010-
Wind Advisory until 8 PM MST this evening for coz021>023.
Utah...Winter Weather Advisory until 6 PM MST this evening for utz023.
Blizzard Warning until midnight MST tonight for utz023.