Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 040533
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1133 PM MDT Wed Jun 3 2020

.SHORT TERM...(Tonight through Thursday night)
Issued at 255 PM MDT Wed Jun 3 2020

Isolated showers and thunderstorms are forming over much of the
higher terrain across eastern Utah and western Colorado this
afternoon. The CWA generally falls under westerly flow aloft,
pushing any storm development that fires off to the east. A low
pressure system sliding across Canada has tightened the pressure
gradient across the Northern Rockies, which has slightly enhanced
winds over the northern tier of the forecast area. Minor
perturbations along the base of this shallow trough have aided in
convection this afternoon as well. Most convective activity will
quickly diminish as soon as we lose daytime heating, with skies
clearing after sunset.

Little change is expected with Thursday`s forecast, with the
blocking pattern in place over the Desert Southwest and zonal flow
across the northern CONUS. Diurnally driven showers and
thunderstorms will develop over higher terrain around noon
tomorrow, favoring the Uintas, Flat Tops, Tavaputs and along the
Divide. Surface conditions remain dry, increasing the likelihood
of virga showers and gusty outflow winds near or beneath
convection. As a result, spotty critical fire weather conditions
are possible tomorrow afternoon. Temperatures will continue to run
warm through the short term period, skirting with record high
temperatures each afternoon and well above normal overnight.

.LONG TERM...(Friday through Wednesday)
Issued at 255 PM MDT Wed Jun 3 2020

By Friday morning, a strong low pressure system off the PacNW will
ingest the cut off low, and kick the system over the Desert
Southwest. Simultaneously, ridging overhead shifts eastward and
strong southwest flow encompasses the forecast area. Though moisture
advection will be on the rise Friday, intensifying winds and dry
conditions preceding the system will lead to elevated critical fire
weather conditions...especially across the northwestern corridor of
the CWA. For that reason, we`ve included a Fire Weather Watch for
Friday afternoon/evening with this forecast package (see Fire
Weather section for more information below). Operational models
are beginning to align with the trough`s evolution across the
region...excluding the GFS, which tends to have a progressive
bias, pushing the system into our region much quicker than other
solutions. At this point, forecast and confidence is leaning
towards a slower progression for when the trough lifts over the
region.

Anticipate showers developing over higher terrain late Friday night
and increasing in coverage after midnight once the system evolves
into a negatively tilted trough. By Saturday morning, strong
southerly flow will tap into sub-tropical moisture and likely
enhance rainfall rates. The abnormally high temperatures have
accelerated the snow melt in the higher elevations and, as a
result, soils are more saturated. If moderate to heavy rainfall
can materialize from the system this weekend, then many waterways
may see a peak this weekend. Extra water, recent snowmelt and
reservoir releases may cause some rivers, creeks and tributaries
to respond fairly quickly and run near or slightly over bankfull
conditions, creating localized flooding. We will have to keep an
eye on this flooding potential and additional messaging, as
needed.

Dry air lifting in from the southwest will cut off moisture supply
Saturday evening, leaving the region back under a windy and dry
environment by Sunday. Thus, fire weather concerns may return
Sunday and into early next week due to a dry slot and a tight
pressure gradient persisting over the CWA as the strong PacNW
trough moves inland. A relief in warm temperatures will supplement
the trough passage, with highs dipping a few degrees below/near
normal through the weekend then dropping below normal as the
Pacific system moves across the intermountain west.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1129 PM MDT Wed Jun 3 2020

VFR conditions will continue to be the rule for the next 24 hours
though mid and high level ceilings are expected. Afternoon showers
and storms are possible in the afternoon with KTEX, KEGE, KASE,
and KHDN having the best chance for a quick shower or storm. Too
far out to include in any TAFs for now. TAF sites will also see
some afternoon gusts of 20 to 25 kts.

&&

.FIRE WEATHER...
Issued at 255 PM MDT Wed Jun 3 2020

Dry and hot conditions continue Thursday and Friday with
scattered thunderstorms possible over the mountains during the
afternoon and evening each day. Increased winds ahead of an
approaching Pacific storm combined with low relatively humidity
may lead to critical fire weather conditions for northwest
Colorado and east-central and northeast Utah on Friday. A Fire
Weather Watch is now in effect for affected areas from noon to 8
PM Friday. There is a high likelihood for wetting rain across the
region Friday night into Saturday as the Pacific storm passes
through. Significantly cooler temperatures are expected this
weekend into early next week.

&&

.HYDROLOGY...
Issued at 255 PM MDT Wed Jun 3 2020

Abnormally high temperatures have accelerated the high elevation
snow melt. Flows in area rivers, streams, and creeks will continue
to run at elevated levels due to the recent snowmelt and
reservoir releases. If moderate to heavy rainfall materializes
from the system this weekend, then some of the rivers, streams,
and creeks could react quickly and run near or slightly over
bankfull conditions causing localized lowland flooding. Anyone
planning to recreate on area waterways should maintain heightened
awareness and use an abundance of caution in or near the water.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Fire Weather Watch from Friday afternoon through Friday evening
     for COZ200-202.

UT...Fire Weather Watch from Friday afternoon through Friday evening
     for UTZ486-487-490.

&&

$$

SHORT TERM...ERW
LONG TERM...ERW
AVIATION...TGR
FIRE WEATHER...NL
HYDROLOGY...TGJT


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