Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Junction Colorado
1105 PM MDT Wednesday Aug 20 2014

Update...
issued at 846 PM MDT Wednesday Aug 20 2014

Some showers and storms continuing this evening as a weak wave
moves overhead especially for northern areas. Plenty of convection
also continues south of Salt Lake City and is moving to the
east-northeast. If the convection holds together...we can expect
to see a bit more precipitation for the next couple of hours so
bumped up probability of precipitation to account for this possibility north of I-70. The
rest of the County Warning Area may see a passing shower but not expecting much
quantitative precipitation forecast.

&&

Short term...(tonight through Thursday night)
issued at 308 PM MDT Wednesday Aug 20 2014

Drier air is entraining into the area from the southwest and this
appears to be helping hold down vertical development over central
and SW Colorado and southeast Utah. A weak upper trough is dragging across northwest Colorado
and this will continue to provide the extra lift needed for single
cell thunderstorms to form...mainly over higher terrain. Still...
with a few more hours of sun available the rest of the
afternoon...scattered showers and thunderstorms should develop over the
mountains of central Colorado after about 22z and continue until
sunset...with isolated development elsewhere.

Continued drying is expected late tonight through Thursday night with
lower probability of precipitation and cloud cover expected. The interesting thing to
watch will be the interaction of moisture from Tropical Storm
Lowell in the eastern Pacific with the approach trough from the northwest.
Some moisture is being drawn north over Baja California California and is
drawing a bead on The Four Corners. By Thursday night the nam12
combines this moisture with the next monsoonal surge coming up
from northwest Mexico.

Long term...(friday through wednesday)
issued at 308 PM MDT Wednesday Aug 20 2014

Ts Lowell is forecast to remain nearly stationary off of the
coast of Baja California California and continue to feed some middle to high
level moisture into The Four Corners region. Another closed low
is forecast to drop into the Pacific northwest as an offshoot of
the high amplitude western US trough in place. As this closed low
dives into the intermountain west this weekend...ts Lowell will
slowly shift to the west and have less of an influence on moisture
in the region. Friday night...the approaching longwave trough will
bring the coupling of a baroclinic zone and upper level jet which
should bring nocturnal activity to the northern part of the gjt
County Warning Area. Qg forcing is moderate with this boundary. Expecting rain
and storms Friday night through Saturday morning across northern
Utah and Colorado...with scattered precipitation over the
mountains elsewhere.

This troughy pattern will continue through early next week...with
Monday night/Tuesday looking like the next somewhat active
weather day after Friday night/Saturday. There is considerably
good agreement between the GFS and ec in the long term...and the
current models suggest high pressure may arrive by the end of next
week.

&&

Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1058 PM MDT Wednesday Aug 20 2014

Precipitation has just about ended across the County Warning Area with VFR conditions
becoming predominant. More storms and showers expected again
tomorrow but still thinking coverage will be less with only
kase...kege and ktex maybe seeing some precipitation. Vcsh for kase and
kege with thunderstorms in the vicinity for ktex in the afternoon looks a safe bet for now
with low to medium confidence. Remaining taf sites should remain
VFR with some high ceilings moving in during the afternoon.

&&

Gjt watches/warnings/advisories...
Colorado...none.
Utah...none.
&&

$$

Update...tgr
short term...cirrocumulus
long term...jam
aviation...tgr

National Weather Service Glossary of Abbreviations