Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Grand Junction Colorado
528 am MDT Fri Oct 18 2019
Short term...(today through saturday)
issued at 321 am MDT Fri Oct 18 2019
Water vapor imagery shows the main trough extended over the Great
Basin as it continues to progress eastward. Warm advection ahead of
the front finally has the moisture needed to produce rain showers
across portions of northwest Colorado and the central mountains.
Large-scale lift is not overly impressive, but it along with the
front and orographics is supporting a more organized band of valley
rain and mountain snow. The front is moving through far northeast
Utah currently and should reach the northern mountains around
sunrise, central mountains by late morning and southern mountains by
mid day. The latest short-term guidance is hinting at an increase in
the warm advection convection over the San Juans in the next few
hours, but it quickly falls apart over The Divide. The Elkhead,
park, Gore, Flat Top and Elk ranges will be favored as the flow
becomes westerly with 2 to 5 inches expected there and 1 to 3 in
the uintas, Grand Mesa and San Juans.
Snow ratios will likely average 6-12:1 this morning with 700 mb
temperatures only reaching -5 c and a dendritic growth zone around
50 mb deep. It still appears that Rabbit Ears, Vail and McClure
passes could have minor accumulations by late morning, but by the
higher sun angle at mid day will likely improve any snow covered
roads. Snow levels drop to 6500 to 7500 feet behind the front, but
most of the accumulations are above 9000 feet. Soundings show
some shallow instability along the front this afternoon which may
favor more convective showers or bands. There will be some gusty
winds accompanying this system so perhaps brief drops in
visibility may be possible in these high elevation snow showers.
Not much is expected for the valleys given the speed of the front
and the meager snow rates that should limit saturation to the
surface. By late afternoon dry air quickly filters southward
causing an end to the precipitation and lingering clouds. Highs
will be a good 10 to 15 degrees cooler today than yesterday
setting the stage for a chilly night. Tomorrow we are in between
systems and slightly moderating temperatures so highs rebound. The
next shortwave trough approaches from the northwest later in the
day, but most locations stay dry through at least sunset. A lack
of midlevel ridging allows the pressure gradient to persist and
support gusty surface winds into the day Saturday. Low-level
moisture is also non-existent so critical fire weather conditions
return for portions of eastern Utah and southwest Colorado.
Long term...(saturday night through thursday)
issued at 321 am MDT Fri Oct 18 2019
The next shortwave trough and its associated cold front will dive
southward across the County Warning Area Saturday night. Precipitation entering the
northwest portion of the region will spread south and eastward over
night, favoring higher terrain along The Divide. Much colder
temperatures are associated with this trough passing, with 700 mb
temperatures dropping to -8 to -10 degrees c by Sunday morning
across the north. The best push within the dendritic growth zone and
higher snowfall rates appear over the Elkhead, park, Gore and
Flat Top Mountain ranges after midnight. Snowfall totals reaching
advisory criteria are possible for these ranges by Sunday morning,
as well as the elks, west elks, and sawatch ranges. Northern
valleys could also see up to 5 inches in Steamboat and 2 inches of
snow over Craig and Meeker by Sunday morning. Moving south, snow
levels rise and totals lessen, however, up to 1-2 inches of snow
isn't out of the question along the I-70 corridor between Glenwood
and Eagle, which may cause some travel impacts Sunday morning.
Although most of the action will favor the central and northern
mountain ranges, snow showers will reach the northern San Juans
and higher terrain along the Uncompahgre Plateau.
The mid-level shortwave will move east of The Divide Sunday, however
lingering moisture and west-to-northwesterly flow will allow snow
showers to persist over the northern and central Colorado mountains
through Monday. Otherwise, showers will generally taper off Sunday
with a Post-frontal, cold air mass sinking into the region. High
temperatures will bottom out Sunday before gradually warm back up
through the beginning of the workweek.
By mid week, the mid-to-upper level trough will be ingested into a
broader Canadian low, turning winds back to the northwest aloft.
Wiggles of energy with this broad system could spin up some mountain
showers Wednesday night into Thursday, although these appear to be
confined to the northern and central Colorado mountains.
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 523 am MDT Fri Oct 18 2019
Scattered to widespread rain and snow showers have move into
northern Colorado and northeast Utah. A front will continue to
push this area of precipitation southward through out the day.
Brief MVFR conditions and ils breakpoints will be possible at
times mainly at the northern and higher sites. Gusty winds could
reduce visibility within the snow showers mainly above 6500 feet
and cause mountain top turbulence. Showers will exit east of The
Divide late this afternoon allowing skies to clear out.