Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Grand Junction Colorado
1042 am MST Thu Nov 21 2019
Short term...(today through friday)
issued at 356 am MST Thu Nov 21 2019
Southwest flow continues to produce steady orographics to the
southern and central mountains this early morning with some sites
in the southern mountains already picking up over an inch of swe
(snow water equivalent) since yesterday evening. A steady band of
moderate showers is currently moving through the central and
southern portions of western Colorado this early morning, having
come from The Four Corners and southeast Utah around midnight.
A few lightning strikes even showed up north of Durango in the
foothills of the southwest San Juan Mountains as a little bit of
instability is present. Deterministic and hi resolution model
guidance is in excellent agreement on showing the progress of this
band of showers, tracking through northwest Colorado and central
Colorado through the morning, arriving to The Divide and Front
Range by noon. Used the namnest as a good proxy for depicting the
timing of this precipitation band in the pop and weather grids.
Temperatures remain mild ahead of this low pressure system
centered around Las Vegas this morning. This is resulting in
higher snow levels around 8500 feet with a good soaking rain below
this level in most valleys and mid slopes.
This closed low will open up as it tracks across northern Arizona
this afternoon with the flow shifting from southwest to westerly.
The main circulation weakens and gets absorbed by the upper level
trough over the region. Expect the heaviest snow rates to occur
this morning through about noon, before a bit of a break occurs
with loss of dynamics. This mainly will result in a scattered
convective regime with periods of sun and some scattered showers
while the west-facing slopes continue to see orographics
generating snowfall, although the rates will lessen. Expect steady
rain through noon with scattered showers in the valleys this
afternoon. Isolated thunderstorms cannot be ruled out as a little
bit of instability is present this afternoon. Another period of
moderate snow will occur this evening along the central Colorado
Divide as the back edge of this trough axis and jet push through.
This low will arrive to eastern Colorado and western Kansas by
Friday morning with some light orographic snowfall continuing in
northwest flow through Friday afternoon as the system pulls out of
the region. The northwest Colorado valleys will see some light
snowfall periodically but this looks to mainly transition to
orographics Thursday afternoon into Friday morning. Not
anticipating any need for winter highlites for the valleys. The
winter storm warnings for the southern mountains, Grand Mesa and
west elks and sawatch remain on track as they will see the best
dynamics and prolonged period of favorable orographics in
combination with the moisture. Winter weather advisories still
look good for the northern mountains and Elk Mountains with less
dynamical forcing this afternoon through Friday morning under a
more favorable west to northwest flow for them. 5 am Friday still
looks like a good time for the winter highlites to end but may
need to re-evaluate this Friday morning.
Long term...(friday night through wednesday)
issued at 356 am MST Thu Nov 21 2019
Dry northwest flow sets up Friday night into the weekend with
temperatures holding steady in that normal range. Clouds will be
present from time to time across northwest Colorado as some
embedded waves move through. The next chance for precipitation
looks to be Monday morning through Tuesday as a strong cold front
and 140 kt west to east oriented jet drop southward from Wyoming.
The GFS is more robust than the European model (ecmwf) with 700 mb temps dropping to
between -10c and -14c behind this front mainly across the northern
and central areas by Monday night. The GFS is further south with
this cold air plunge while the ec is further north and the
Canadian is on vacation, not even showing this system.
Southwest flow develops on Wednesday as the previous system
departs and another low pressure system drops into the Pacific
northwest and Great Basin. This system has potential to bring
another round of prevalent moisture as well as colder air
Wednesday afternoon into Thanksgiving. The jet is overly strong
at this time with a 180 kt jet streak. Something Worth noting.
This is still a ways out and details are a bit fuzzy, but
potential does exist for the Thanksgiving Holiday to be quite
eventful with this unsettled, cooler and progressive pattern
staying firmly in place.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1032 am MST Thu Nov 21 2019
Light to moderate showers continue to move north across the
region today. Expect isolated to scattered showers to develop this
afternoon near taf sites mainly along and south of the I-70
corridor, while the band of showers exits to the north. Conditions
will improve for most sites this afternoon behind the band of
precipitation, with ceilings and visible dropping briefly in scattered
Showers. Mountain sites will remain obscured though this evening
with additional snow showers possible overnight.
Colorado...Winter Weather Advisory until 5 am MST Friday for coz004-010-013.
Winter Storm Warning until 5 am MST Friday for coz009-012-018-
Utah...Winter Weather Advisory until 5 am MST Friday for utz023.
Winter Storm Warning until 5 am MST Friday for utz028.