Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Junction Colorado
1117 PM MDT Thursday Sep 18 2014

issued at 904 PM MDT Thursday Sep 18 2014

The line of thunderstorms over northwest Utah have been sliding
northeast. Latest rap13/hrrr indicate that some convective
activity will be approaching Daggett County after
the forecast trend appears to on track. The remainder of the
forecast area is clear except for some convective debris over the
high terrain near the Sawatch and San Juans. Minor adjustment to
the sky grids to reflect more clear conditions instead of partly


Short term...(tonight through Friday night)
issued at 305 PM MDT Thursday Sep 18 2014

The large scale pattern featured a deep trough off the West Coast
with high pressure centered over central Colorado. This has kept
the remnants of Odile well to the south of the area. As a result
..the forecast area remained relatively dry. Clouds were building
over the higher terrain but none have broken the cap as of 20z.
Expect the eastern Uinta and San Juan Mountains may have just
enough juice to spark a storm or two...otherwise anticipate quiet
weather late this afternoon and evening.

The eastern Pacific trough splits tonight with a shortwave in the
northern stream ejecting eastward across the northern rockies
while the closed low in the southern stream stalls off the central
California coast. In response...subtropical moisture begins to
stream northward across Utah. Lift and moisture may be sufficient
for a few showers or thunderstorms over the eastern Uinta
Mountains late tonight through Friday morning. As flow becomes
more zonal the moisture from Utah translates eastward over western
Colorado. Though not especially deep...this moisture will fuel
afternoon/evening showers and thunderstorms...mainly over the
mountains. Drying and subsidence indicated late Friday night so
expect clearing skies and quiet weather during the remainder of
the night.

Overnight lows will stay near persistence both tonight and Friday
night. However...boosted afternoon highs on Friday as latest model
guidance indicated less shower/storm coverage than earlier runs.
However...shaved a couple of degrees of persistence to account
for clouds.

Long term...(saturday through thursday)
issued at 305 PM MDT Thursday Sep 18 2014

Saturday high pressure rebounds over the region. Moisture
diminishes somewhat and middle-level subsidence diminishes
instability. So isolated afternoon storms will be limited mainly
to the Colorado mountains.

The California closed low works into the Great Basin on Sunday and
lifts into Wyoming on Monday. Precipitable water values increase
to near one inch in The Four Corners region on Sunday but
generally stay below that critical value. Storm motion will be
fairly brisk to the NE then east those days but model quantitative precipitation forecast still
produces orographic bullseyes up to 0.25 inch.

Drier air works over the region beginning Tuesday. Warmer than
normal temperatures return. The next moisture surge is currently
forecast for the final weekend of September.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1114 PM MDT Thursday Sep 18 2014

Dry conditions expected across the region through 18z. After
18z...isolated showers and thunderstorms will develop over the
higher terrain...with northeast Utah and northwest Colorado
favored. Gusty outflow winds to 40 kts...small hail and brief
heavy rain can be expected. A few storms will develop in the vicinity
of ktex...kase and kege after 21z. Storms dissipate after 03z
Friday evening.


Gjt watches/warnings/advisories...

short layers
long term...Joe

National Weather Service Glossary of Abbreviations