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Area forecast discussion 
National Weather Service Grand Junction Colorado
227 PM MDT sun Apr 19 2015

Short term...(tonight through Monday night)
issued at 227 PM MDT sun Apr 19 2015

Models continue to depict impulses of energy moving over the County Warning Area
through the short term period. This is being borne out with observation
showing some light precipitation across the area while the radar mosaic
shows some convective development under the impulses. Bumped up
probability of precipitation to account for this and also expanded storm coverage. No
lightning strikes yet but steep lapse rates...cape...and available
moisture may lend themselves yet to some thunder. Nam12 and GFS
keep precipitation in the picture picking up after midnight. Hard to see
if one impulse or two...leaning towards two impulses but if
so...there's hardly a break between them. Whether it's one or two
the end result is the same...spotty showers with possible thunder
this afternoon/evening becoming more isolated/scattered in nature overnight.

A perturbed northwest flow will continue over the area through
Monday night...between high pressure over the West Coast and low
pressure across the eastern half of the Continental U.S.. lingering moisture
and warmer daytime temperatures will allow some afternoon
convection confined mainly to the higher terrain. Moisture and
generally weak northwest orographics will favor the
expect better coverage from the mountains near Aspen and
northward. The flow weakens overnight and high pressure shifts
over the area. The warming trend will continue.

Long term...(tuesday through sunday)
issued at 227 PM MDT sun Apr 19 2015

The big picture across North America will be dominated by strong low
pressure over the Great Lakes to Quebec...and a less stable mean
trough along the West Coast. For US an unsettled Spring pattern will
persist through next weekend. Pacific moisture and a series of
disturbances originating from the western trough will move across
the region. For now the details remain elusive. However models
agree that a split pattern will persist along the Pacific
coast...with a couple of southern lows set to impact the Desert
Southwest to the south and central rockies.

It appears that the first and weaker of the two lows will begin to
lift out Tuesday. A second trough develops along the West Coast and
closes off a low west of the so California/no Baja California coast by Wednesday. Ahead of
the first low...moisture will continue to stream into our
area...which will be dominated by a southeast to northwest leaning
ridge of high pressure. In spite of the ridge overhead...some
diurnal showers will be possible as the remnants of the first low
provides a little energy as it moves into the southern Great

The stronger low then moves inland and opens up pumping moisture
into the region. Models still show differences in its handling
and timing. But it seems this storm system has a the potential to
bring widespread precipitation to our forecast area. For now it
appears that the best chance of precipitation will be late Thursday and
Friday. Snow levels will be very high as models keep 700mb temperatures
mostly above zero c degrees into Sat.

With less confidence the European model (ecmwf) shows another Pacific trough moving
across the Pacific northwest and into our region Sat and sun.
However the 12z solution is much farther north as compared to the
previous run...and keeps the best action well to our north. The
later run is also a little faster. On the flip side the GFS shows


Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1116 am MDT sun Apr 19 2015

The first series of disturbances is currently moving across the
County Warning Area bringing some snow at high elevations and a broken to overcast deck
for the northestern portion of the County Warning Area. Ceilings will vary between 5k to 10k
feet though some lower ceilings may form. Some isolated showers also
possible under this wave through this afternoon and evening. A
slight chance also exists for an isolated storm or two to fire over
eastern Utah...western Colorado and over portions of the San Juans. Any convection
that forms will die down quickly after sunset. Biggest flight
concerns will be kase and kege with low ceilings and possibly a shower
or two. Conditions will begin improving after 18z tomorrow.


Gjt watches/warnings/advisories...


Short term...tgr/eh

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