Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 220554

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1154 PM MDT Mon Aug 21 2017

.SHORT TERM...(Tonight through Tuesday night)
Issued at 325 PM MDT Mon Aug 21 2017

The sky cooperated relatively well late this morning and made for a
nice viewing of the total solar eclipse for much of the forecast
area under mostly to partly sunny skies. Further south in the Four
Corners and southwest Colorado scattered clouds persisted where
the better midlevel moisture remained. As expected, another round
of diurnal showers and thunderstorms developed over the higher
terrain and as has been the trend over the past several days, most
convection should end after sunset with the loss of daytime
heating. Overnight lows tonight will remain slightly above normal
for this time of year.

The axis of the upper level ridge attempts to build across the
length of the Rockies on Tuesday as the SoCal low remains planted
just off the California coast. A shortwave trough associated with
this low will be ejected through our southern forecast area Tuesday
afternoon which will enhance the coverage and intensity of showers
and thunderstorms over the southern and central mountains.
Elsewhere, expect typical pop-and-drop summer convection to fire
off over the rest of the higher terrain as a result of daytime
heating and residual moisture. Skies should clear pretty quickly
behind the aforementioned shortwave trough which will cool
overnight lows Tuesday night by several degrees across much of the

.LONG TERM...(Wednesday through Monday)
Issued at 325 PM MDT Mon Aug 21 2017

The deep upper level low dropping in from the Gulf of Alaska that
we`ve been watching over the past several days will migrate south on
Wednesday. As it digs into the Pacific Northwest throughout the day
the SoCal low will be ushered inland. Models had previously
projected the low to become an open wave and trek through the Great
Basin but latest guidance now suggests it will dive further south
into Baja. Even so, the monsoonal tap should still set up as the
ridge of high pressure shifts, allowing moisture to advect
northward. Additionally, another piece of energy from the SoCal
low will traverse across our region throughout the day, so
Thursday still looks to be the most active day in terms of
precipitation coverage for our CWA this week.

Northwesterly flow aloft will begin to set up late Friday and into
the weekend as high pressure rebuilds over the Great Basin. While
lingering moisture should allow for at least isolated orographic
storms to fire off each afternoon, generally drier and warmer
conditions will persist through the beginning of the new week under
the benign weather pattern.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1154 PM MDT Mon Aug 21 2017

Scattered showers will continue on the southwest flank of the San
Juan mountains through 09Z. During this time light showers will
continue off and on over KDRO. TAF sites across the remainder of
the area will see dry weather during the remainder of the night
with VFR conditions and CIGS above ILS breakpoints through 18Z,
even at KDRO.

Daytime heating and increased moisture will bring more widespread
showers and thunderstorms to the higher terrain during the
afternoon and evening. This activity poses some threat to TAF
sites, but those chances are pretty minimal except at KASE, KMTJ,
KTEX, KGUC and KDRO where there is a a 40 to 50 percent chance for
thunderstorm activity. Moisture levels are close to a point where
MVFR visibility is possible in heavy rain and ILS breakpoints
could be reached at KASE.






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