Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 262030

Area Forecast Discussion
National Weather Service Pocatello ID
230 PM MDT Fri May 26 2017

.SHORT TERM...Today through Monday. Looking at current satellite
imagery, an upper level low continues to be centered over our
area. This system will bring scattered to widespread showers,
particularly over our Northern and Eastern areas this afternoon.
Also, look for 1 to 2 inches of mountain snow above 7500 to 8000
feet. Also, expect isolated thunderstorms across the area this
afternoon into early evening, particularly over our Southern and
Eastern areas. Precipitation tapers off early this evening and
gradually starts to clear out later this evening into tomorrow
morning as upper level high pressure ridging starts to build in.
Expect high pressure with overall clear skies and gradually
warming Saturday through Monday. Monday, models are indicating
that moisture may make its way into our Northern areas bringing a
slight chance of afternoon thunderstorms. Expect below normal
temperatures through Saturday and then becoming above normal by
Sunday and, particularly, on Monday. Wyatt

.LONG TERM...Monday night through next Friday. During the first half
of next week, a ridge of high pressure will be in place across our
region, bringing seasonably warm temperatures running around 10
degrees above climatological averages. This means high temperatures
well into the 80s across the Snake Plain. A couple of sneaky
disturbances will combine with daytime heating and topographic
effects to produce isolated showers and thunderstorms from mid-
afternoon through the evening hours across high terrain areas Tue and
Wed. By Thursday, the GFS and European forecast models both swing a
trough through the region, and as such indicate the potential for
more widespread shower and thunderstorm coverage. Given the late
afternoon timing of the trough passage, the trough will be swinging
through during peak heating when instability is maximized. Thus,
there may be an opportunity for some strong thunderstorms. After
Thursday, the GFS keeps conditions showery and unsettled while the
European, depending upon the model run, trends towards a return of
either a ridge or zonal (west-east) flow. So what is a forecaster to
do? Well, continue to prefer a blend of the two, and this idea has
support among ensemble (broad collection of models) means. So, this
favors a cooldown back to climatological average temperatures for
the end of the week into next weekend along with low-end
precipitation potential. AD/Wyatt


.AVIATION...Challenging TAF forecast through Saturday morning as an
area of low pressure currently centered just west of Pocatello is
forecast to slowly work eastward into WY through the morning. MVFR
to nearly IFR stratus in place from PIH to IDA. Ceilings have lifted
to VFR for BYI, but potential exists here for brief IFR conditions
in heavier showers and thundershowers. After 21Z, potential exists
for TS at all TAF sites, with the greatest potential at BYI...PIH
and DIJ. Am carrying an improvement to MVFR stratus at PIH and IDA
this afternoon, but confidence is low on this evolution. Tonight, an
abundance of low-level moisture is forecast to reside across the
area. Should cloud cover clear out after 06Z as forecast, fog and or
low stratus development is possible at all locations with the
exception of KSUN. Have thus hinted at this potential in TAF
forecast. Expect a return to VFR conditions at all taf sites by 18Z
Sat. Mainly light winds under 12KT expected at TAF sites except
in/near thunderstorms through this evening. AD/Wyatt


.HYDROLOGY...Expect light lingering valley rain and wet mountain
snow this afternoon which will help keep flows near current
levels. Expect gradually clearing and cooler temperatures tonight
into tomorrow which will slow down melt slightly through
tomorrow. A warming trend begins on Sunday and continues through
about Wednesday of next week. The lower valleys will warm into the
lower to mid 80s and the mountains the mid 60s to mid 70s. This
will be a warm enough to greatly accelerate snow melt in the
mountains bringing the next peak flow by mid to late next week.



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