Area Forecast Discussion
Issued by NWS Grand Junction, CO

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
FXUS65 KGJT 251950

Area Forecast Discussion
National Weather Service Grand Junction CO
150 PM MDT Mon Sep 25 2023

.SHORT TERM...(Tonight through Tuesday night)
Issued at 150 PM MDT Mon Sep 25 2023

Winds remain light underneath a building ridge of high pressure
that remains parked over the western slope, stretching into the
Northern Rockies. This is resulting in mostly sunny skies, drier
conditions as evidenced by 0.25 inches of precipitable water on
the 12Z GJT sounding and a very stable layer. The hi res CAMs are
showing a little bit of instability over the San Juans but thus
far, this really is only amounting to a few fair weather cumulus
clouds popping over the peaks. Outside of the clouds over the San
Juans, that is about it. Meanwhile, a large upper low is entering
the Pacific Northwest and will be somewhat blocked by this
downstream ridge which remains overhead. This low looks to be a
potential player late in the week towards next weekend, but until
then dry conditions and above normal temperatures remain. This low
will ever so slightly nudge the high pressure ridge to the east,
allowing for increasing southwest flow to kick in for Tuesday.
This will result in some breezy conditions and better mixing,
allowing high temperatures to climb a bit to 5 to 10 degrees above
normal. Overnight lows, however, will continue to be cool and
crisp as efficient radiational cooling takes place. Therefore,
bumped the highs up a bit closer to the 75th percentile NBM and
lowered the overnight lows this week a bit closer to the 25th
percentile NBM, which kept lows on the cooler end of guidance
like we have been seeing the last few nights.

.LONG TERM...(Wednesday through Monday)
Issued at 150 PM MDT Mon Sep 25 2023

By midweek, the overall synoptic pattern will be a bit stalled out
thanks to a Rex Block over the Great Lakes region. This will keep a
ridge of high pressure in control over eastern Utah and western
Colorado, and a deep trough of low pressure in place over the
Pacific Northwest. A lobe of energy will drop through the base of
this trough on Wednesday, dragging along a potent cold front. This
cold front will remain well to the north of Utah and Colorado, thus
not bringing any precipitation or even much change in the
temperatures. What it will do is nudge the ridge to the east and
allow the trough to expand south and east ahead of the next lobe of
energy. This in turn will increase the pressure gradient aloft,
leading to increasing southwesterly winds each afternoon from
Thursday onward. The southwesterly flow will also advect dry air
into the region, leading to increasing concerns for critical fire
weather conditions through the end of the work week.

As the next lobe of energy drops into the base of the Pacific
Northwest trough, it will begin to elongate and split, eventually
forming a cutoff low pressure over the western Great Basin by late
Saturday or early Sunday. In comparison to previous model runs,
current guidance is slower but in better agreement overall regarding
the development and timing of this low. Strengthening southerly flow
over eastern Utah and western Colorado associated with the
development of this low will likely leave Saturday as the windiest
day of the period. By Sunday morning, model guidance begins to show
increasing disagreement over the speed that this low fills and
eventually ejects to the northeast, and what that means for eastern
Utah and western Colorado. Hopefully, subsequent forecasts over the
next few days will show better agreement. As it stands, the sunshine
and above normal temperatures that are expected through the end of
the work-week will, by late in the weekend, give way to cooler and
unsettled conditions that will linger into early next week.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1113 AM MDT Mon Sep 25 2023

VFR conditions will prevail for the next 24 hours, with generally
clear skies and light, terrain driven winds.




AVIATION...TGJT is the U.S. government's official web portal to all federal, state and local government web resources and services.