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284
FXUS65 KGJT 191754
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1154 AM MDT Wed Jun 19 2024

.KEY MESSAGES...

- Localized critical fire weather conditions are possible for
  portions of west-central and southwest Colorado this afternoon.

- Scattered to widespread showers and storms are expected
  tomorrow and Friday. Significant moisture supports the
  potential for heavy rain during this period.

- Conditions dry out for this weekend, but there is still a
  slight chance for afternoon storms.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 251 AM MDT Wed Jun 19 2024

A general trough remains anchored over western Canada keeping
our region under southwest flow aloft. High clouds have spread over
the northwest half of the area, which are keeping temps on the mild
side compared to last night. There is still a significant amount of
dry air in place, but that begins to change today. As high pressure
builds westward across the central US the pressure gradient
increases. This increased flow out of the south and southeast is
pumping rich moisture into the Front Range now. This moisture will
gradually advect into our forecast area today, with the big surge
taking place tonight and tomorrow. There appears to be enough
moisture and instability for scattered showers and storms in the
mountains this afternoon. Gusty winds will be the main threat with
these showers. Highs today will be warmer than yesterday due to the
southerly flow. Wind gusts this afternoon could reach 30 mph where
RH drops into the teens and single digits. This may cause localized
critical fire weather this afternoon mainly focused in west central
Colorado. Wind speeds did decrease with this forecast package and
the moisture advection adds some uncertainty therefore decided to
cancel the Fire Weather Watch.

Tonight the central US high pressure continues to build westward
allowing it to tap into the Gulf. This Gulf moisture is expected to
advect into our region early tomorrow and combine with steep lapse
rates aloft. The result will be scattered to widespread showers and
storms with peak heating. The PWAT is expected to be 200-300 percent
of normal, mixing ratios reaching 7-10 g/kg and surface dew points
above 45F. This is moisture more typical in late July. Instability
is also expected to reach 500-1000 j/kg, which is sufficient for
heavy rainfall and small hail. The potential for heavy rain is
better in the higher elevations mainly along and south of I-70.
Lower valleys will still be relatively dry in the lower levels
therefore gusty outflow winds remain a concern. Models show that
convection continues into the overnight hours. Instability should
decrease after sunset, but the environment might remain unstable
enough to support weak convection through the night. The moisture
advection does not let up during this time frame either, which is
another contributing factor.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 251 AM MDT Wed Jun 19 2024

Wet conditions continue on Friday with an additional pulse of
moisture arriving mid-day. Scattered showers may be ongoing Thursday
night into Friday morning, but coverage will likely increasing by
Friday afternoon/evening. The main difference in the synoptic setup
between Thursday and Friday is the passage of a shortwave trough
Friday evening. Enhanced upward vertical motion downstream of the
trough axis could work to amplify the lift already present due to
orographic effects and moisture advection leading to convective
activity across much of the forecast area. Storms that form could
produce gusty outflows of 40-60 mph and a heavy rain threat,
especially in areas that receive showers and storms on Thursday. The
biggest unknown at this point is how morning showers and cloud cover
will impact the amount of CAPE available later in the day. Current
guidance shows a 50-70% chance for CAPE greater than 500 J/kg along
and west of the Colorado/Utah border.

With the shortwave trough moving out to the east Friday night, direr
conditions are expected on Saturday. Some lingering moisture could
lead to diurnal showers and storms in high terrain areas, but much
lower mixing rations and lapse rates with a near-zonal upper-level
flow pattern does not support the coverage and amount of
precipitation we are anticipating on Thursday afternoon-Friday.
Warmer and drier conditions return later this weekend into early
next week with a broad ridge setting up over the western and central
US.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
-- Changed Discussion --
Issued at 1154 AM MDT Wed Jun 19 2024

VFR conditions will prevail over the next 24 hours. Should see
mostly sunny skies today, with exception of the higher terrain
where SCT to BKN cumulus are forming. Expect some gusty winds of
20 to 30 mph at times this afternoon. Isolated storms are
possible in the high country along the Divide this afternoon,
namely KASE where confidence was high enough to include VCTS in
TAF. Clouds increase overnight into Thursday, especially across
southwest Colorado, where some showers look to develop overnight
over the San Juans and potentially southern valleys, including
KDRO.
-- End Changed Discussion --

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...KJS
LONG TERM...KAA
AVIATION...MDA