141
FXUS65 KGJT 131128
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
528 AM MDT Sat Jul 13 2024

.KEY MESSAGES...

- Near-record daytime temperatures are expected today and
  Sunday, particularly in the valleys of eastern Utah and the
  Grand Valley in Colorado.

- Afternoon showers and thunderstorms will develop over higher
  terrain each day throughout the seven-day forecast with an
  increase in coverage expected early next week.

- Temperatures remain elevated beyond the weekend, but some
  relief is expected from cloud cover and shower activity as
  monsoonal moisture is forecast to return early next week.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 417 AM MDT Sat Jul 13 2024

Early morning radar imagery showed an area of virga/sprinkles
over east-central Utah west of the Green River. Notably, looped
reflectivity suggested the center of the dome of high pressure
was roughly west of Hanksville which matched the positioning of
the high according to latest operational models. Otherwise,
aside from scattered areas of lingering altocumulus, skies were
mostly clear across the forecast area.

In the absence of cloud cover, temperatures will rapidly rise
through the morning with afternoon highs expected to be near
record levels again today. Highest impacts from heat continued
to be in the valleys of eastern Utah and the Grand Valley of
western Colorado where Heat Advisories remained in effect. The
high pressure center drifts over southwest Colorado where it
will remain today. With the high over Colorado it`s unlikely
that there will be any appreciable increase in moisture over the
forecast area. This seemed to be borne out by the HREF
precipitable water (PW) field. Consequently, expect modest
moisture over the San Juan Mountains and central Colorado
portion of the Continental Divide will fuel another round of
isolated to scattered afternoon/early evening showers and
thunderstorms. Storm characteristics will be similar to
yesterday`s with lightning, gusty winds and small hail the main
threats.

Diurnal cooling will bring an end to moist convection early this
evening with all but a few lingering showers remaining after
sunset. Models indicated an uptick in moisture tonight as the
high center drifts east of the Continental Divide by 12Z/Sun.
Increased moisture should yield unusually mild overnight lows.

The HREF suggested a PW increase close to 0.30" from 00Z/Sun to
00Z/Mon. Operational runs were a bit less aggressive coming in
closer to a 0.20" increase in PW. Am inclined to favor the
operational runs as moisture flux doesn`t look all that
impressive. In any event, increased shower/thunderstorm coverage
appeared reasonable with the central and southern Colorado
mountains favored. Despite the expected increase in clouds and
shower/thunderstorm activity, models continued to indicate
unusually hot conditions will persist for the areas in today`s
Heat Advisory. Since the morning is likely to have few clouds
over those areas and showers/thunderstorms are likely to be
more distant, decided to extend the Heat Advisories through
Sunday evening.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 417 AM MDT Sat Jul 13 2024

High pressure continues to drive the forecast through the coming
week. The biggest change heading into Monday and Tuesday is
increased subtropical mositure wrapping around the high and into
the forecast area. Ensemble guidance continues to be very
consistent with its projection of PWAT values 100-150% of normal
during this period so while the coverage of afternoon showers
and storms will increase with the additional moisture present,
it is not looking like this system will pose an organized heavy
rain threat. A shortwave trough passes through the Northern
Plains on Wednesday and could nudge the surface high slightly
westward. A brief drop in the moisture advection may occur as a
result, but it picks right back up for the latter half of the
week. Increase cloud coverage throughout the week will work to
lower our high temperatures by a few degrees. However,
temperatures remain well above normal through the forecast
period.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 528 AM MDT Sat Jul 13 2024

VFR conditions with no ceilings below ILS breakpoints expected
at all TAF sites across eastern Utah and western Colorado during
the next 24 hours. Winds will generally be light and terrain
driven. However, outflow winds from showers and thunderstorms
over the San Juan Mountains and portions of Colorado`s central
mountains could generate strong and unpredictable wind gusts at
KDRO, KTEX, KMTJ, KGUC and KASE during the afternoon and early
evening.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Heat Advisory until 9 PM MDT Sunday for COZ006.
UT...Heat Advisory until 9 PM MDT Sunday for UTZ024-027-029.

&&

$$

SHORT TERM...NL
LONG TERM...KAA
AVIATION...NL