849
FXUS65 KBOI 020223
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
823 PM MDT Sat Jun 1 2024

.DISCUSSION...Showers continue this evening, but they are very
light, and there appears to be more virga than precipitation
reaching the ground. This will change drastically over the next
24 hours as the previously described atmospheric river brings
moderate to heavy rain to the region. See the previous
discussion below for details. The forecast is in good shape this
evening and no update it planned at this time.

&&

.AVIATION...VFR with mid and high level clouds. A slight chance
of showers until about 02/06Z, but low confidence (less than 20
percent) in any of the showers reaching terminals. Gusts up to
30 kt near showers and virga. Surface winds: SW-NW 5-15 kt. 10k
ft MSL winds: W 10-20 kt, becoming SW-W 15-25 kt by 02/18Z.

KBOI...VFR. W to NW winds 10 kt or less. Continued nearby virga
with occasional gusts to 15 kt through 02/04Z.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Monday night...A weak trough is
approaching today, bringing some mild unsettled conditions.
Upper level clouds today are limiting shower development, but
isolated showers and scattered virga is evident over the higher
terrain this afternoon. There is still a 10-20% chance of
thunder over the West Central Mountains this evening. The trough
brings a weak cold front though this evening that will cause
keep winds a little breezy overnight with gusts to 25 mph. The
front will also bring cooler/drier air for early Sunday.

An atmospheric river in the Pacific will transport up to 1" of
PWat Sunday evening through Monday night. The enhanced moisture
flow is supporting precipitation chances of 70-90% for most of
the area, with chances of 90-100% over mountains. Rainfall
totals in the West Central Mountains and Boise Mountains are
around 1" in Valleys to 2" on ridges, with a few summits
forecast to receive even more. The significant mountain rain,
lows on Monday morning above freezing, and lingering snowpack
are creating some concern for small stream flooding in the
mountains. There is also some convective potential Monday
afternoon that could see some terrain driven storms forming.
This raises concern for rapid onset flooding, but convective
potential may be limited in the cloud cover and steady rain.
Even a little concern for convection on saturated soil and
snowpack was enough to warrant an increase to slight risk in the
WPC ERO. Overall, confidence in flood potential is a little too
low for a Flood Watch at this time as river, but a Hydrologic
Outlook has been issued. Elsewhere this event still looks like a
soaker, with portions of eastern Oregon in a marginal risk for
excessive rain. Storm total QPFs in the Snake Plain range from
0.2" along the southwestern edges and 0.5" along the
northeastern edges and foothills. Winds will gust to 20-30 mph
Sunday afternoon/evening ahead of the moisture.

LONG TERM...Tuesday through Saturday...Zonal flow is forecast over
the area Tuesday with dry conditions. Ensemble forecasts continue to
show a strong upper level ridge developing over the region the
second half of next week resulting in hot/mostly dry conditions.
Temperatures will warm from around normal on Tuesday to 15-20
degrees above normal Thursday through Saturday. Models are showing
increasing moisture in southerly flow aloft late next week resulting
in a slight chance of showers (generally less than 20 percent) near
the Nevada border Thursday afternoon. The chance of showers
increases to 15-30 percent Friday and Saturday generally across
the entire forecast area.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.

&&

$$

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DISCUSSION...SP
AVIATION.....SP
SHORT TERM...JM
LONG TERM....TL