784
FXUS65 KGJT 171155
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
555 AM MDT Thu Jul 17 2025

.KEY MESSAGES...

- Scattered to widespread thunderstorms will be capable of
  producing wind gusts of 30-50 mph, frequent lightning, small
  hail and periods of heavy rain leading to localized flooding.

- Conditions dry out Sunday into early next week bringing a
  return of near critical fire weather conditions.

- Smoke will continue to be a problem until the large wildfires
  in the area receive some rain or higher relative humidity
  slows growth.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 544 AM MDT Thu Jul 17 2025

Models in good agreement with satellite imagery with the cutoff low
off Baja and high pressure over eastern Texas pulling deep monsoonal
moisture up into the Desert Southwest that will make its way into
the region today through Saturday. Clouds and light showers are
currently pushing up into southeastern Utah and southwestern
Colorado. These will continue to spread north to about I-70 through
the day leading to widespread showers and thunderstorms in the San
Juan Mountains this afternoon and evening with more scattered storms
through the central mountains and isolated along the I-70 corridor.
With pwats of 0.7 inches to over an inch and CAPES of 300-500 J/kg
today, some of these storms could produce periods of moderate to
heavy rain that can lead to localized flooding, especially in the
San Juans. Stay alert to the weather around you and watch for
weather advisories and warning issued for your location. These
storms will diminish through the late evening with some lingering
showers overnight.

Look for another round of scattered to widespread showers and
thunderstorms again tomorrow afternoon and evening, but with CAPES
of 500-1000 J/kg and available shear of 25-30 kts, the thunderstorms
will likely be much stronger than today with a slight chance of
producing large hail and damaging winds, but more likely periods of
torrential rain leading to possible localized flash flooding. Stay
tuned to the forecast today as we get updated model runs.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 144 PM MDT Wed Jul 16 2025

High pressure to our southeast will allow for moisture to advect into
our region with southwesterly flow. The main push of moisture moves
in Thursday evening and will linger through Saturday. On Friday the
greatest atmospheric moisture will be primarily north of I-70, but
PWATs will be above normal across the CWA. Ensemble guidance
suggests maximum PWAT anomalies around 150% of normal. On Friday
precipitation is expected be widespread, but the highest PoPs are
over the high terrain. This precipitation could raise some concerns
for rock slides and debris flow, particularly in the high terrain or
near the newly burned land from our wildfires. On Saturday moisture
begins to decrease, but enough lingers to bring another day of
widespread precipitation chances. Atmospheric moisture continues to
decrease on Sunday, making precipitation chances more constrained to
the higher terrain. The remainder of the long term looks similar, as
each day will have a chance of afternoon convection, primarily along
the Divide and in the southern mountains.

Critical fire weather conditions from low relative humidity and
gusty winds will be localized over the first few days of the long
term. Moisture advection keeps relative humidity values above
thresholds for most of the CWA on Friday and Saturday. Many of our
valleys are expected to drop below 15% relative humidity by the end
of the weekend, and this will persist through the long term.
Increasing wind speeds may raise critical fire weather concerns in
the northern half of our CWA early next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 544 AM MDT Thu Jul 17 2025

Isolated light showers continue in the Four Corners area as
moisture moves up from the Desert Southwest. Look for these
showers to become widespread in the San Juan Mountains and more
scattered farther north to the I-70 corridor with embedded
thunderstorms by 18Z. These storms will diminish after 03Z.
Primary threats from the thunderstorms is lightning and outflow
gusts to 45 kts. Expect generally light winds today becoming
southwest with gusts to 20 kts after 18Z and dropping off to
light drainage winds around sunset.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...DB
LONG TERM...GF
AVIATION...DB