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Area forecast discussion
National Weather Service Pocatello Idaho
354 am MDT sun Jul 21 2019

Short through Wednesday...dangerous heat is
expected, particularly Monday and Tuesday. High pressure will
continue to build in across Idaho today. With high pressure look
for continued dry conditions, much warmer temperatures, and
overall light winds. The upper level high pressure ridge axis then
moves east by Monday allowing monsoonal moisture to start to
enter the area in southwesterly flow by later Monday. There will
be a slight chance of showers and thunderstorms mainly for the
central mountains Monday afternoon into early evening. These
thunderstorms will be mostly dry setting up the potential for very
gusty outflow winds. There will be a better chance of
thunderstorms for the central mountains and the Montana Divide
Tuesday. But again the thunderstorms will be mostly dry with
little precipitation expected. Wednesday a weak and mostly dry
cold front will move through the area. Temperatures will rise to
above normal today and much above normal by Monday around 8 to 12
degrees above normal. Monday will likely be the hottest day of
the year so far. Some areas in the eastern Magic Valley, southern
Highlands, and lower Snake River Plain could hit 100 degrees
Monday afternoon, dependent on the amount of sun shine. For Monday
a heat advisory will likely be needed for the eastern Magic
Valley, southern Highlands and Snake River Plain. Tuesday will
again be very hot, maybe just a couple of degrees cooler. Again, a
heat advisory will likely be needed for the eastern Magic Valley,
southern Highlands, and the lower Snake River Plain. With the
passing weak cold front on Wednesday temperatures will not be as
hot but still around 5 degrees above normal. Wyatt

Long term...Thursday through next Sunday...Thursday look for dry
conditions with weak high pressure ridging starting to build back
in over Idaho. Monsoon moisture starts to move in mainly across
our southern areas by Friday bringing a slight chance of showers
and thunderstorms mainly for our most southern areas. Southwest
flow sets up for Saturday and Sunday with the high pressure ridge
axis moving east of our area. Models are indicating a slight
chance of showers and thunderstorms mainly across our southern
and eastern borders along the Utah and Wyoming state lines.
Temperatures look to be around 4 to 8 degrees above normal through
the period. Wyatt


Aviation...forecast confidence remains very high for no aviation
concerns and a continuation of hot, dry, mostly sunny wx for the
next 24-48 hours, with VFR cigs/vsbys at all terminals. Winds
generally look to remain under 10 knots. A slight push of
monsoonal moisture from the south may spark a few isolated
showers/T-storms Mon in the central mntns, but based on the latest
model data we continue to hold ksun dry.


Fire weather...dry and hot will be the theme today, with heat
building even further Mon/tues, but moisture slightly creeping up
as monsoonal moisture rotates northward around high pressure over
The Four Corners. This may allow for isolated T-storms across
zones 422/475/476 Mon, with a slick uptick in both potential and
coverage tues which may include zone 411, but it will take some
time for moisture to significantly modify the dry airmass at lower
levels. Thus, T-storms will be dry. Modest/poor overnight relative humidity
recovery will continue for the thermal belts/ridges. Slightly
cooler/drier wx is possible Wed/thurs.

With the above in mind, we have 2 primary fire weather concerns:

1) T-storms tues/Wed will be dry and carry the threat of lightning.
We had a long discussion in the office this morning about whether a
Fire Weather Watch is warranted for Mon in the central mntns despite
light winds/isolated storm coverage, considering ongoing/active
fires, how efficiently recent convective events have been at
sparking new fires, and the lightning threat. Decided confidence
just isn't there, especially with a few models still running dry and
the fact that some fuels still aren't critical across this region.

2) high temps rising into the mid-90s/low-100s across most valleys
and plains Mon/tues, coupled with ample sunshine and reduced
recovery at night (lows only dropping to 65-70 in the Magic Valley,
southern snake plain, and southern highlands), will pose significant
danger. Fire crews will need to take extra precautions to combat
heat-related illnesses and stay hydrated. Will again headline this
danger in the fwf product this morning.


Pih watches/warnings/advisories...

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