Scientific Forecaster Discussion
fxus65 kgjt 212315
Area forecast discussion
National Weather Service Grand Junction Colorado
415 PM MST Thu Nov 21 2019
Short term...(tonight through Friday night)
issued at 208 PM MST Thu Nov 21 2019
Latest satellite and radar imagery shows precipitation continuing
to spread northward across the forecast area today. In areas that
experienced a little more sun this morning (southeast Utah and
southwestern colorado), a few convective cells are occurring this
afternoon...even a couple thunderstorms. The morning runs from
the NAM nest did a pretty decent job highlighting precipitation
trends so far today. The latest run (in addition to other short-
term and long-term models) shows another swath of precipitation
moving in from northern New Mexico around 00z. Latest water vapor
imagery supports those model solutions.
Thus, current thinking is that this band of precipitation will
move through southern portions of the forecast area this evening
and hang up in the central Colorado mountains. This will signal a
shift to more to orographic precipitation versus dynamic forcing
as the low progresses further east. This precipitation is
anticipated to linger into Friday morning before shutting off by
mid-afternoon. With additional snowfall (1-6 inches across upper
elevations across the cwa) expected, decided to continue
highlights as planned through 12z. Temperatures cool slightly on
the back side of the low as flow turns northwesterly with dry
conditions expected to start the weekend.
Long term...(saturday through thursday)
issued at 208 PM MST Thu Nov 21 2019
Dry northwest flow settles over the forecast area on Saturday as our
winter-like storm retreats farther eastward over the Central Plains.
This pattern holds on Sunday with temperatures hovering right around
normal. A fast moving mid-level shortwave is expected to begin
impacting the forecast area Sunday night, driving a cold front north
to south across the region by late afternoon/early evening on
Monday. Colder air behind the front should bring snow levels down to
valley floors as the trough axis passes overhead.
Snow is likely across the mountains and high valleys and model
consensus suggests this fast moving system could bring 6 to 12
inches of new snow to the northern and central Colorado mountains
with lesser amounts in the eastern Uinta and San Juan Mountains by
Tuesday morning. Scattered showers linger on Tuesday, mainly over
the Colorado mountains. Along with snow, temperatures will be
falling below seasonal norms on Tuesday with highs running about 5
to 10 degrees below normal.
Models all agree with a deepening trough over the West Coast
impacting the region for the end of the week including Thanksgiving.
However, both GFS and Canadian were much more aggressive in bringing
moisture into the area ahead of this system Tuesday night and
Wednesday. The European model (ecmwf) was slower in deepening the trough over the
west and as a result generates very little moisture over the area
during the same timeframe. All models indicated best chances for
showers come on Thanksgiving day as a strong southwest to northeast
oriented jet settles over the area. This system threatens to bring
significant snowfall along with wind driven snow. However, given
model differences, far to early to speculate on amounts and
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 410 PM MST Thu Nov 21 2019
Scattered showers and a few thunderstorms are ongoing near the
Colorado/Utah state line and that area will gradually move towards the
central mountains tonight. This rain and snow will continue
through late tomorrow morning Manly in the central mountains of
Colorado. MVFR and IFR conditions will be likely at sites like
khdn, kase, kege, kguc.
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.