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797
FXUS65 KGJT 180919
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
319 AM MDT Tue Jun 18 2024

.KEY MESSAGES...

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- Due to a cold front highs today will be 15-20 degrees cooler
  than yesterday.

- Unsettled conditions return Thursday with afternoon showers
  and thunderstorms expected into the weekend. Modest moisture
  could support the potential for heavy rain during this period.
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&&

.SHORT TERM /THROUGH WEDNESDAY/...
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Issued at 251 AM MDT Tue Jun 18 2024

A cold front is currently pushing through the region due to a strong
low pressure tracking over the Northern Rockies. A band of high-
based showers has developed behind the front north of I-70. Rain is
most likely not reaching the ground at most locations and these
showers will remain close to the Wyoming state line as they move
eastward. Winds are still gusty along the front, but are gradually
diminishing in its wake. High temperatures will be 15 to 20 degrees
cooler than yesterday thanks to the cold front. Conditions will be
mostly dry today as well. Wind gusts generally around 25 mph are
expected south of I-70 this afternoon. Tomorrow that system
progresses into southern Canada allowing temperatures to modify by
about 10 degrees. Meanwhile a ridge begins to build into the
Southern Plains causing southerly flow and moisture return for our
region. As of now this is only the beginning of the moisture so
there may only be enough for some terrain-driven showers tomorrow
afternoon. Most of the activity will be east of the Divide.
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.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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Issued at 251 AM MDT Tue Jun 18 2024

An active weather pattern sets up for the latter part of the week as
a broad area of surface high pressure sets up over the southeastern
CONUS. This helps advect Gulf moisture across Mexico into the base
of an upper-level trough before southwest flow advects the moisture
into the forecast area on Thursday-Friday. Models continue to
produce precipitable water values in the 90 to 99th percentile for
mid-June area wide with the highest values extending from the Four
Corners into the San Juans. This signal has proven very consistent
over the last couple of days. Dry near-surface air is leading to
some uncertainty in how precipitation will evolve early Thursday, but
the ingredients (CAPE, 7-9+ g/kg mixing ratios, lapse rates >6 C/km)
look to be in place for coverage of showers and storms to increase
by early Thursday afternoon. Convection continues into Friday when
the brunt of the moisture will be overhead. Higher elevation areas
in the southern part of the forecast area have the potential for
heavy rain during this period. Confidence in the heavy rain
potential decreases for lower elevation locations and the northern
two thirds of the forecast area, but a wetting rain is expected (70-
90% chance) area wide.

The passage of a shortwave trough late Friday into Saturday helps
dry things out on Saturday, but there are differences between models
for the timing and strength of the localized ridging on the backside
of the shortwave so we will have to continue to monitor this period
for the potential for additional precipitation. Temperatures remain
near-normal on Saturday before gradually building to 5-10 degrees
above normal by early next week.
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&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1115 PM MDT Mon Jun 17 2024

A front is moving through the forecast area and causing winds to
shift to the north-northwest. It is producing gusts around 40
mph, and should clear the area over the next few hours. It may
disrupt the typical drainage winds especially the northern
sites. VFR conditions are expected through the taf period.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...KJS
LONG TERM...KAA
AVIATION...TGJT