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fxus65 kpih 260856 

Area forecast discussion
National Weather Service Pocatello Idaho
256 am MDT Tue Sep 26 2017

Short and tonight. A weak system is working across
the state from the north this morning. The main impact will be
cloud cover, although a light shower is still possible closer to
The Divide on higher peaks and ridgetops. Fog will be minimal due
to the cloud cover, but we wouldn't be surprised to a few patches
pop up where clear spots remain this morning. Otherwise, this
begins a "warming trend" through the end of the week. Warm in this
case is relative, as in getting closer to normal for this time of
year. Keyes

Long term...Wednesday through next Tuesday. As the low dropping
over US today scoots southeast, it will split and form a closed
low across the Desert Southwest. The high builds over US to
the north, developing what is called a temporary Rex block (high
to north and low to the south). This allows temperatures to warm
back up, but like we said only where we should be at the end of
September. This will allow for some good temperature spreads
between daytime and nighttime for many locations. We will be
monitoring daily to see if we have major fog and frost/freeze
issues. However, that won't last too long. By Friday, the big
storm moving toward the West Coast helps "kick" the low northeast.
At the moment, all of the models bring the low close enough to
the southeast corner for increasing clouds over far eastern Idaho.
Will there by any showers with that? The answer at the moment is
not likely. For now, any threat of rain is closer to 10%. Although
there is still some measurable disagreement between the models,
the trend is quickly heading toward wetter and colder by the
weekend. Everything points toward the potential of a
splitting/deepening storm over the west. We really ramped up the
chance of rain and mountain snow showers starting Saturday
morning, spreading east during the day. The chance GOES down on
Sunday but remains overall higher over the central mountains and
eastern Highlands. It also looks quite breezy. Snow levels during
the day Saturday are in the 9000-10000ft range. They lower Sunday
morning to 7000-7500ft in the central mountains and 7500-8500ft
across the rest of eastern Idaho, rising about 500ft or so in the
afternoon. Beyond that, model and ensemble data looks like chaos.
It seems split between the cold/wet pattern remaining or it
shifting back to north & west. Since we couldn't find anything too
specific to hang our hat on, we kept it cool with some showers in
the forecast. Keyes


Aviation...minimal aviation concerns through the period. Broad area
of mid-level cloud deck covers the northern half of the forecast
area, mainly along and north of a ksun to kpih line. This cloud deck
is forecast to gradually diminish/move east out of the area by this
evening. Sfc winds expected to remain below 12kt at terminals
through the period. Ad/Keyes


Fire weather...gradual warming trend forecast to continue through
the end of the week, with temperatures climbing to near to slightly
above seasonal normals by Thursday across the area. Significant
changes are now reflected in the forecast as confidence continues
to increase in the idea of a Gulf of Alaska low dropping down into
the Pacific northwest this weekend, bringing a significant cooldown
beginning Saturday and lasting through the weekend. Strong winds and
a good chance of wetting rains are expected to accompany this low
pressure system for the weekend. Currently, the best chance of
wetting rains is forecast to occur over the Salmon-Challis nf
eastward along The Divide into the targhee nf. For early next week,
a considerable amount of uncertainty exists with regards to details
in the forecast, with forecast models offering a wide range of ideas
on how to handle the evolution of the above-mentioned low. One trend
that stands out among the uncertainty is that temperatures will
begin to moderate, but remain below seasonal normals for the first
couple of days next week. Ad/Keyes


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