Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 231006
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
406 AM MDT Wed Aug 23 2017

.SHORT TERM...(Today through Thursday)
Issued at 406 AM MDT Wed Aug 23 2017

A shortwave trough moving through the ridge of high pressure over
eastern Utah and western Colorado was responsible for clouds north
of the I-70 Corridor and lingering showers over the western Uinta
Basin early this morning. Meanwhile, to the south isolated
thunderstorms southwest of Pagosa Springs had developed on the
nose of a southwest to northeast oriented 50 KT jet streak
directed at the Four Corners region. Dewpoints were reflective of
the passage of the shortwave with sites from the western end of
the I-70 Corridor northward up by around 8 degrees over the last
24 hours bringing them in line with those in the south. In fact,
valley dew point values across the forecast area were in the mid-
40s with the exception of KGJT which recorded dew points in the
low 50s early this morning.

The shortwave will continue to impact the north throughout the day
as it slowly shifts east-northeastward. Lift associated with this
feature is expected to yield some light showers this morning then
provide a focus for increased showers and thunderstorms this
afternoon. Meanwhile, instability resulting from diurnal warming
working on residual moisture is all that is needed for another
round of showers and thunderstorms across the south. As is often
the case in this part of the world, this activity will favor the
mountains, though some cells should move over adjacent valleys
during the latter part of the afternoon and into the evening.

Moist convection will largely diminish later tonight, but a weak
secondary shortwave may sustain some light showers into the early
morning hours, mainly north of the I-70 Corridor. In the wake of
the disturbances discussed previously, flow becomes west to
northwest across the forecast area on Thursday heralding the
beginning of a drying trend. However, lingering low level residual
moisture will be more than sufficient to fuel diurnal showers and
thunderstorms from late morning through the afternoon.

High temperatures should rebound a bit across the south as early
sunshine and fewer clouds favor warming today. The opposite is
true across the north where clouds and showers will be more
prevalent. Thursday`s highs are expected to be pretty close to
those forecast for today.

.LONG TERM...(Thursday night through Tuesday)
Issued at 406 AM MDT Wed Aug 23 2017

Three things going on at the start of the long term period. First,
a possible tropical depression or storm will be just about coming
ashore over Texas while a weak area of low pressure will continue
to spin over SoCal. This low has been in the same general area
for several days now but finally looks to start filling in by the
weekend. Finally, a trough and associated front will be moving
over British Columbia to our northwest. So where does that leave
us? Still under the influence of increased moisture from the south
though winds will become more westerly which will allow moisture
content to slowly drop.

By Friday, the trough over Canada will force the plume of moisture
to shift to the high plains and this is borne out in PWAT values
that will drop to the .6 to .75 inch range where .65 inches is just
about right for this time of year. Friday looks considerably drier
with not much precip showing up in models but find it hard to
believe that moisture will dry out that quickly. Expect another
round of showers and storms with coverage a bit less than seen
recently.

Saturday, a very broad area of high pressure will start to build
in over the Great Basin and persist through much of next week.
Usually, we`d expect a downturn in convection but both the GFS and
EC want to keep some convection going along the Continental
Divide Monday and Tuesday overspreading into adjacent terrain to
the west and south. However, with high pressure remaining
overhead, couldn`t imagine any convection would be too strong
since it would have to overcome some mid to high level stability.
Time will tell.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 406 AM MDT Wed Aug 23 2017

A disturbance aloft will push across northeast Utah and northwest
Colorado throughout the day. This feature could bring some light
showers and a few isolated showers to areas north of the I-70
Corridor before noon. However, daytime warming will become the
main driver for showers and thunderstorms from late morning
through the afternoon and into the evening. Activity will begin
over higher terrain with some storms moving over adjacent lower
elevations during the latter part of the afternoon and into the
evening. TAF sites may be impacted during the period, however
expect showers/thunderstorms will be brief and unlikely to cause
conditions to fall below VFR. However, CIGS may briefly fall below
ILS breakpoints for KEGE and KASE. Outflow winds to 40 MPH are
possible.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...NL
LONG TERM...TGR
AVIATION...NL


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