Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 142149

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
349 PM MDT Thu Sep 14 2017

.SHORT TERM...(Tonight through Friday night)
Issued at 348 PM MDT Thu Sep 14 2017

Very aggressive system lifting out of S.Nevada is spreading
significant large scale ascent over the 4 Corners region this
afternoon. Steep lapse rates in place in helping ascent along
with a decent speed max aloft which in real life means efficient
thunderstorm development through this evening. These storms are
moving in excess of 40 mph which will bring a widespread wind
threat to much of SE.Utah and W.Colorado along with some of the
storms producing moderate sized hail and heavy rainfall. The speed
at which these storms are moving still leave low confidence in a
widespread flash flood threat though localized heavy runoff is
still very probable in any training storms. This storm is looking
more like a fall mid latitude cyclone with the strong dynamics and
wind. It also will be carving out a decent dry slot behind this
lead wave which cuts off the dendritic layer moisture over all but
the tri-state area in the north (UT/CO/WY). This lead wave gets
absorbed by the colder and much stronger northern stream system
that will be organizing over the northern Rockies overnight. The
base of this system will be sweeping across Utah and Western
Colorado tomorrow through tomorrow night. Most of the forcing for
precipitation will be will right along and behind the surface
front that arrives to NE.Utah around noon tomorrow and slowly
drops into our southern CWA by sunrise on Saturday. There is a
really good chance that some of the precipitation will be falling
as snow across the northern mountains above 10000 feet Friday
night with a dusting to a few inches above timberline. Friday
actually looks to be a rather cool day ending up slightly below
normal...definitely a change.

.LONG TERM...(Saturday through Thursday)
Issued at 348 PM MDT Thu Sep 14 2017

The weekend is shaping up for a sunny start as this system drives
out the moisture as it lifts back north toward the higher
latitudes. Again Saturday will be cooler than normal behind the
front with a feel of fall in the air. Sunday will prove warmer and
be back toward normal thanks to WAA ahead of the next Pacific
trough moving into the Intermountain West. There is limited
moisture and instability but a few light showers could pop over
the central and northern mountains in the late afternoon heating.
All eyes turn upstream as an anomalously strong system drops out
of the Gulf of Alaska and spreads lower heights over W.NOAM
through the first half of next week. This system will have a good
tap to cooler air which jives with the 6-10 day outlook suggesting
chances are better than normal for a blob of cold air over much of
the West. Much of the precipitation with this system look to be
located with the surface front which models are not handling very
well as far as timing. The slower Euro probably the way to go
which is later in the week. For now expect seasonable temperatures
and mainly dry weather until this fropa.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1142 AM MDT Thu Sep 14 2017

A Pacific storm will impact the region through early Friday.
Ongoing scattered showers and thunderstorms will become numerous
late this afternoon and evening as the storm passes overhead. All
TAF sites are likely to experience light to moderate rainfall
with localized heavy rain possible. Heavier showers may result in
MVFR visibility, though CIGS are likely to remain in the VFR
range. However, CIGS below ILS breakpoints from KRIL, KEGE and
KASE are probable. In addition, outflow winds to 45 MPH are
possible with stronger cells. Conditions improve from north to
south after midnight with nocturnal showers lingering north of
I-70 through early Friday.

Scattered showers and thunderstorms will redevelop after 15Z
Friday as a cold front approaches the region with areas north of
I-70 once again favored for activity.




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