Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus65 kpih 230907 
afdpih

Area forecast discussion
National Weather Service Pocatello Idaho
307 am MDT Wed Oct 23 2019

Short term...through Friday. Broad northwest flow will remain in
place across the region through Thursday, as the northern rockies
region remains on the eastern fringes of a strong high pressure
ridge located just off of the California coast. This ridge will
nudge in our direction Friday. The net effect of this evolution on
our weather is that winds will gradually subside through the day
today, and light snow shower chances along the Wyoming border will
diminish through the day, as the drying effects of the approaching
ridge take over. Any snow accumulations today should be relegated
to less than an inch. Another effect of the approaching ridge will
be an increase in temperatures. They'll remain on the cool side
through Thursday, but will take a 10 degree leap on Friday, when a
rare (for this month) above-average temperature day is expected.
Meanwhile, a strong cold front (with origins across the northwest
Canadian provinces) will begin to intrude into Montana, with its
sights set southward. This will cause an increase in the pressure
gradient, with a corresponding increase in winds first felt
across the central Idaho mountains and Continental Divide region
by afternoon, and have thus raised inherited wind forecasts here
as a result.

Long term...through next Tuesday. The above-mentioned cold front
will sustain its southward March on Saturday, crossing southeast Idaho
from north to south. Ahead of the front, the belt of increasing
winds will sag southward, reaching the snake plain, where SW/west
winds in the 15-25 mph range will develop Saturday, along with
higher gusts. Strong northerly winds will surge into the state
through The Divide and pashimeroi valleys by afternoon, creating
a surface convergence zone. This zone, along with a boost from jet
dynamics and cyclonic flow aloft will act to promote snow shower
(possibly mixed with rain over the southern snake plain) activity
by afternoon. Before this occurs, showers are expected to develop
over the central Idaho mountains and then sag southward across southeast
Idaho through the remainder of the afternoon and evening hours,
generally following the front's southward progression. There
remains some uncertainty with regards to the extent and amounts
that may occur as a result of this activity, but will continue to
monitor forecast trends as the weekend approaches.

In the wake of the front, breezy, cold conditions will envelope
southeast Idaho. In fact, near record low temperatures may be in the
offing Sunday and especially Monday morning. In terms of daytime
highs, they're expected to struggle to around 10 degrees below
climatological averages for late October. With October 2019
already ranking in the top-five coldest across southeast Idaho, this
incoming cold surge may nudge October 2019 even closer towards the
record books for the coldest October in southeast Idaho's climate
history.

By next Tuesday, guidance indicates yet another strong cold front
surging southward from the northwest Canadian provinces, with this front
crossing southeast Idaho Tuesday into Wednesday, potentially ushering
another surge of Arctic air. There are still some lingering
uncertainties with this second cold front, but until then forecast
confidence is high. Ad



&&

Aviation...mainly VFR conditions are expected through the period
along with gradually slackening winds. Winds this afternoon should
peak in the 10-20 kt range at pih, Ida and byi, some 10-15 kts
lighter than Tuesday. Some guidance (the NAM in particular)
continue to advertise the potential for fog/low cloud development
across the snake plain in generally the 10-15z time period this
morning. At this time, think this scenario has a low probability
of occurrence, so will leave out of the tafs at this time but
continue to monitor trends. Outside of this low-end threat, VFR
conditions are expected at the taf sites through the period. Ad



&&

National Weather Service Glossary of Abbreviations