323
FXUS65 KGJT 161102
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
502 AM MDT Fri Aug 16 2024

.KEY MESSAGES...

- Drier and warmer weather is expected today. Some breezy winds
  near the Colorado / Wyoming state line will bring localized
  near critical fire weather conditions this afternoon.

- Weak monsoon moisture will bring isolated to scattered showers
  and storms on Saturday, favoring the mountains and eastern
  Utah.

- More robust monsoonal moisture will impact the region Sunday
  and beyond. Showers and thunderstorms will bring back the
  threat of localized flooding Sunday and into the new work
  week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 215 AM MDT Fri Aug 16 2024

A departing shortwave has allowed some pesky light showers to
continue early this morning north of I-70. Elsewhere has been
nice and dry and this trend will continue throughout the day.
Behind this morning`s wave westerly flow will set up aloft
across eastern Utah and western Colorado, while the Subtropical
Ridge flattens and elongates to our south. Some weak moisture
entrenched in the westerly flow will lead to some passing clouds
and maybe fire off a high-based storm along the Divide this
afternoon. Elsewhere, a 65-75 kt jet will drape across north-
east northeast Utah and northwest Colorado, resulting in some
occasionally breezy conditions later today. For the most part,
gusts will be in the 20 to 25 mph range, though some slightly
stronger gusts to near 30 mph will be possible near the Wyoming
border. Coverage is not widespread enough, but we can still
expect to see localized near-critical fire weather conditions
this afternoon. The jet migrates north tonight as the ridge re-
amplifies over Arizona. This will be in response to a trough of
low pressure elongating off the West Coast through the end of
the short term. Flow aloft will be shifted to the southwest as
the high`s center drifts over far northwest Arizona. This will
allow monsoon moisture to advect back into the region, with
PWATs increasing from 80 to 90 percent of normal by daybreak
Saturday to at least 120 to 140 percent of the norm later that
evening. As a result, look for the return of showers and storms
throughout the day. There are some discrepancies in the CAM
guidance regarding overall coverage in convection on Saturday
with the HRRR being much more bullish than the NAMNest. One
thing favoring the HRRR solution attm is a shortwave which is
projected to track around the periphery of the high on Saturday,
lifting across eastern Utah and portions of western Colorado
into the evening hours. This would aid in the development of
showers and storms, so we`ll see how future model runs track
this feature. Storms will be capable of producing gusty outflow
winds as the profile gradually saturates, but brief moderate to
heavy rain will still be possible. Regardless, after a brief
break in monsoonal activity, we can expect a return to cooler
and more unsettled conditions beginning Saturday and continuing
through the weekend. More on that in the long term below.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 215 AM MDT Fri Aug 16 2024

Showers and thunderstorms will linger into the evening hours on
Saturday night as deep monsoonal moisture continues to advect in on
southwesterly flow aloft. This is thanks to a deep trough off the
Pacific Northwest that nudged the Subtropical high eastward into the
Southern Plains. This pattern, known as an Omega Block, will remain
in place through the weekend into early next week, with that
favorable monsoonal flow surging into the Four Corners region. Model
guidance indicates PWAT values climbing back above normal, running
120-160% of normal by Sunday, and 140-180% of normal by Monday.
Current guidance does place the best of the moisture plume, with
PWATs of nearly 200% of normal, over western Utah rather than over
eastern Utah and western Colorado. Regardless, Sunday and Monday are
shaping up to have the greatest shower and thunderstorm coverage, as
well as the greatest threat of heavy rain and flash flooding.
Current guidance tries to wobble the high back to the west a bit by
Wednesday, shifting the moisture plume away slightly and limiting
the amount of moisture advecting in. However, without a strong
system to sweep out pooled surface moisture, there will be more than
enough recyclable moisture to work with. So expect showers and
thunderstorms once again each afternoon through the end of the week,
although with gradually diminishing coverage. Higher terrain will be
most favored to see activity through the entire long term period.
Lower elevations will see their best chances of storms and heavy
rain on Sunday and Monday. Main threats will be gusty winds, heavy
rain, frequent lightning, and small hail.

Temperatures will start out near to slightly below normal for the
end of the weekend and early next week, thanks to increased clouds
and showers. Temperatures will gradually warm to around 5 degrees
above normal by midweek as the high pressure slides back overhead
and storm coverage slowly diminishes. Overnight lows remain
mild.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 502 AM MDT Fri Aug 16 2024

VFR conditions will prevail area-wide through the TAF period
under dry westerly flow. Skies will remain mostly sunny apart
from some passing clouds. Gusts of 20 to 25 kts are expected,
mainly north of I-70, between 18Z and 02Z. Otherwise, winds will
remain light and terrain-driven.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...None.
UT...None.

&&

$$

SHORT TERM...MMS
LONG TERM...BGB
AVIATION...TGJT