Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 031738
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1138 AM MDT Mon Aug 3 2020

.SHORT TERM...(Today through Tuesday)
Issued at 430 AM MDT Mon Aug 3 2020

Hot weather will once again dominate the forecast headlines to
start the week as a ridge of high pressure remains in place over
central Arizona and southern Utah. Eastern Utah and western
Colorado will remain on the northern periphery of this ridge,
resulting in general westerly flow aloft. This light westerly
flow will help push our lingering monsoon moisture east of the
Divide for today and tomorrow, resulting in a lower chance for
afternoon showers and thunderstorms in the higher terrain. Still,
a few isolated areas of convection are possible over the higher
terrain of the Sawatch and San Juan ranges this afternoon. High
temperatures will run near 10 degrees above normal across valley
locations...and a few isolated record highs are not out of the
question in places such as Grand Junction, Canyonlands and
Montrose.

The overall weather pattern will remain largely the same over the
western slope for Tuesday. The southwestern ridge will break down
slightly, resulting in a northwest component to upper-level
winds...however no change to the overall dry and hot forecast is
expected. In fact, forecast guidance supports even lower moisture
content through the column as well as lower surface dewpoints on
Tuesday, resulting in even lower shower coverage even in the San
Juans. Afternoon highs will once again run nearly 10 degrees above
average area-wide with near record heat along the US-50/I-70
corridors. Forecast confidence remains extremely high through the
short-term and only minimal adjustments were done in this
forecast package.

.LONG TERM...(Tuesday night through Sunday)
Issued at 430 AM MDT Mon Aug 3 2020

Some subtle changes in the synoptic pattern arrive by Wednesday. A
weak trough will drift inland along the northern California coast
on Wednesday morning and slowly inch eastward. This will force
what is left of the southwestern ridge farther south and eastward.
Subtle southwesterly flow will increase over Utah and western
Colorado. This will allow a small amount of moisture to drift in
from the southwest, potentially resulting in better chances for
afternoon showers and thunderstorms in the higher terrain.
Forecast guidance (namely the GFS) does not respond to this
change in flow with much rain at all in the 0z model runs. The
ECMWF is a bit more optimistic...however a dry subcloud layer will
still likely limit any chances for wetting rains on Wednesday.
Precipitation chances increase on Thursday as a better push of
monsoon moisture arrives by the early afternoon. Thursday
afternoon and evening appear to be the wettest timeframe in the
long- term...however guidance has continued to back off on the
more bullish outlook for heavy monsoon rains seen in prior
forecasts a few days ago.

The upper-level pattern becomes muddled by Friday into next
weekend. Both the ECMWF and GFS cut off the weak trough over the
west coast and send it back west into the Pacific. A weak ridge
will likely redevelop somewhere over the southern plains, although
forecast guidance is mixed on the extent and strength of this
feature. Regardless, these events will place the Four Corners in
a `no-mans-land` region between a very weak Pacific cutoff low
and the weak plains ridge. The net result will be a mainly dry
forecast with isolated afternoon showers in the higher terrain -
but no major monsoonal surges through the weekend. Any change to
the location/strength of either the Pacific cutoff low or plains
high will greatly impact the forecast...so expect changes before
next weekend arrives. Needless to say, forecast confidence
decreases dramatically from Friday onward through next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1138 AM MDT Mon Aug 3 2020

Midlevel clouds will continue across much of the region this
afternoon, though CIGS will remain above ILS breakpoints. Isolated
to scattered showers and thunderstorms will redevelop over the
next couple of hours over the San Juan and west-central Colorado
mountains. VCTS is expected at KTEX and KDRO with no impacts
likely at any other TAF sites. Storms will diminish by 03Z with
widespread VFR conditions returning through Tuesday morning.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&

$$

SHORT TERM...MAC
LONG TERM...MAC
AVIATION...MMS


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