Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 300931

Area Forecast Discussion
National Weather Service Grand Junction CO
331 AM MDT Thu May 30 2024


- Slightly cooler, more seasonable temperatures today and Friday
  in the wake of a cold front which continued to push southward
  across the area early this morning.

- Chances for isolated to scattered showers and thunderstorms
  remain along the higher terrain of the Continental Divide
  through early next week.

- Temperatures climb back above normal this weekend and a
  building ridge next week suggests temperatures are likely to
  climb even higher by midweek.


Issued at 331 AM MDT Thu May 30 2024

The cold front was just south of the I-70 corridor at 08Z this
morning according to latest surface observations. Aside from
scattered alto-cumulus clouds there was little else to mark its
presence. The mid-level trough that drove the front southward
had pushed east of the Continental Divide by this time so it`s
unlikely that the front will move much farther south. As a
result, cooler temperatures will impact the central and northern
zones of the forecast area today with little change across the

Dry zonal flow sets in behind the trough, though models
indicated that enough moisture remains to fuel some instability
driven showers/thunderstorms over the Divide with the southern
and central ranges favored. The subcloud layer remains dry so
this activity will continue to generate more wind than rain.

Diurnal cooling brings an early end to moist convection this
evening followed by decreasing clouds. Conditions will show
little change Friday, though models indicated less shower and
storm coverage during the afternoon. Temperatures are expected
to be a little warmer across the north with highs running near
persistence elsewhere.


Issued at 331 AM MDT Thu May 30 2024

Starting with the bottom line up front, the longwave pattern just
doesn`t want to let go of the spring weather with deep troughs
digging down into the western states and move on to a summer
pattern. The models keep building a strong ridge in over the
Intermountain West late in the period, but with each successive
run of the models, pushing the formation of the ridge further
into the future with guidance sending mixed signals. What this
spells for eastern Utah and western Colorado is continued warm
weather on the dry side with afternoon buildups of isolated to
scattered virga, showers and thunderstorms resulting from
diurnal heating and initiated by orographic lift. Some days
will see more activity and other days will see less. There is
general agreement on a warming trend over the weekend and into
next week with temperatures reaching 10-15 degrees above the
climatological mean for early June across the region and hitting
the century mark in the lower desert valleys by mid week. Heat
risks may become a concern in these areas and will be something
to watch.

Looking at the synoptic pattern, the longwave trough continues
across the northern CONUS and southern Canada keeping eastern Utah
and Western Colorado under a zonal flow with transient ridges and
shortwave troughs. With the last shortwave that passed to the north
of the region out on the Plains Friday evening, the next shortwave
trough will be just moving into the Pacific Northwest. Lacking jet
support, this next shortwave will move slowly east along the
Canadian Border, passing north of the region Sunday into Tuesday.
The models were in general agreement with this trough pulling a
significant surge of moisture off the Pacific inland over the
northern States and into the northern Utah and Colorado to feed
continued afternoon convective activity over the northern
mountains. Guidance hasn`t picked up on this moisture plume, low
balling probabilities of precipitation (PoPs) below 20%.
Afternoon PoPs closer to 50% seem more reasonable across the
higher terrain of the northern half of the region. In the latter
half of next week the European ensemble wants to build a ridge
in off the Pacific from the west while the GEFS builds the high
north out of Mexico over the Western States with a cutoff low
off Baja; two very different scenarios with significantly
different outcomes. Additionally, the upper level analysis of
the models, above 400 mb, indicates yet another deep trough
digging south over the eastern Pacific to erode a ridge over
the western CONUS. With all these discrepancies, there is low
confidence in this extended forecast beyond about Tuesday.


Issued at 1130 PM MDT Wed May 29 2024

Expect VFR conditions and generally light terrain driven winds
through the TAF period. The exception will be light afternoon
virga showers mostly through the central and southern Colorado
mountains producing gusty outflow winds.