FXUS65 KGJT 111727

Area Forecast Discussion
National Weather Service Grand Junction CO
1027 AM MST Mon Dec 11 2023


- Times of snow for the northern mountains of Colorado through
  Monday afternoon. Several inches of snow possible for the
  Elkhead and Park Ranges.

- Warm temps move back in Tuesday onwards.


Issued at 235 AM MST Mon Dec 11 2023

Light to occasionally moderate snow has been falling for much
of the night over the northern mountains as well as in the town
of Steamboat Springs westward into Hayden. Wouldn't be surprised
to see a couple of inches for those valley locales. Elsewhere,
plenty of high clouds continue to stream across the area. Those
spots with more cloud cover have seen much milder temps than 24
hours ago. IR satellite does show more variable cloudiness up
north moving into the area so we'll see how this affects our
temps over the next few hours for the northern valleys, if at

For the rest of today, a trough will start dropping down from
the PacNW as a weak shortwave pushes out ahead of said trough.
This shortwave, and westerly flow, will keep some light precip
in the forecast for the northern mountains where a few more
inches of snow may fall. However, as the trough amplifies and
continues to drop southward, flow becomes more westerly through
southwesterly for the entire CWA and will essentially shut off
the orographics for the northern mountains. Thus, the lowering
PoPs for that area from mid-afternoon onwards. Some very
isolated snow showers can't be ruled out but any appreciable
accumulation looks to end. More clouds for the northern
valleys/mountains today while variable cloudiness will be the
rule elsewhere. Of course, said that yesterday and plenty of
clouds moved across the whole CWA so we'll see how we land
today. Highs should be warmer than yesterday though cloud and
snow cover will directly impact how much warmer it gets.

By Tuesday, the jet will be rounding the base of the trough
which will be located over Nevada. As it does so, it will carve
out an area of low pressure as it approaches Las Vegas from the
north. Southerly flow will be the rule across the CWA as will an
increase in mid to high level clouds bringing mostly cloud
skies to just about the entire CWA. Despite the clouds, highs
will remain above seasonal norms thanks to warm advection from
the south. Alas, the northern valleys will continue to see more
seasonal values thanks to the continued cloud and snow cover. As
far as any precip is concerned, very low PoPs (20 to 30%) for
some light precip over the San Juans and along the Continental
Divide, as per the NBM, seems reasonable for now. Dry elsewhere.


Issued at 235 AM MST Mon Dec 11 2023

A cold surface high over the the Western Plains is pulling Gulf
moisture north into the Panhandle of Texas, northeastern New
Mexico and southeastern Colorado. A cold core low descending
down through the Great Basin and cutting off from the arctic jet
will keep southwestern Colorado under a southwesterly flow and
holding the Gulf moisture off to the east. The low continues to
drop into Arizona overnight Tuesday before a weak subtropical
jet leaf across Baja turns the low track east across the
southern half of Arizona Wednesday and southern New Mexico
Thursday before picking up steam crossing the southern States to
Florida Friday to Sunday. As the low drops into southern
Arizona Wednesday, it will be able to tap into the Gulf
moisture, pulling it west across the Divide into the San Juan
Mountains. The more resent guidance is slowing the track of the
low, allowing deeper moisture to move up into the southern
mountains over a longer time period extending through Thursday
before shutting off the tap into the southern mountains Thursday
night as the low ejects east into West Texas. This has doubled
the QPF guidance over the southern mountains from yesterday's
model run. This will be a storm to watch since cutoff lows tend
to slow way down, and this could keep the low over Arizona for
and extended period allowing significant moisture in over the
southern slopes of the San Juans. The deterministic GFS looks to
eject the low much quicker than the operational European and
Canadian models, and faster than the GFS ensemble that agrees
well with the European. This would support the low slowing its
track, but confidence is low at this point. Stay tuned to see
how this plays out in the next day or so.

Behind the low, models move a ridge into the Great Basin and
slowly shift it east over the weekend as another strong cold low
drops south out of the Gulf of Alaska and cutting off over the
Pacific off the California Coast. This looks like the long wave
pattern is setting up a pseudo omega block with the ridge
centered on the Rockies, but with the eastern low still tracking
slowly east, the block shifts east with it. This would bring a
return of extended warm temperatures to eastern Utah and Western
Colorado through next weekend. Confidence is very low as there
is wide variation on the model solutions run to run. Again, stay


Issued at 1027 AM MST Mon Dec 11 2023

VFR conditions will prevail for the next 24 hours with light,
terrain driven winds. Mid and high level clouds will pass
overhead through the day and night, though ceilings should
mostly stay above ILS breakpoints. The lowest ceilings will be
confined to KHDN where a snow shower or two can't be ruled out.