Heavy Rain in Idaho, May 4 to 5, 2024

Area Forecast Discussion
National Weather Service Boise ID
227 PM MDT Sat May 4 2024

.SHORT TERM...Tonight through Monday night...Major north Pacific
storm now inland in OR and CA, preceded in our CWA by gusty
southeast to southerly winds. Current Wind Advisory in the
Upper Treasure Valley, Western Magic Valley, and Harney County
is set to expire at 3 PM MDT /2 PM PDT/.  Latest MOS guidance
supports that expiration time with winds forecast to diminish.
The Pacific storm's cold front will then move into our CWA with
moderate to heavy rain late today through tonight, with the
front reaching central Idaho early Sunday morning. Latest
forecast rain amounts through Sunday remain consistent with
previous forecast: .15 to .50 inch in the Oregon valleys, .50
to 1.00 inch in the Oregon mountains, .40 to 1.00 inch in the
Idaho valleys, and .80 to 1.75 inch in the Idaho mountains.
Pcpn should decrease to lighter rain and mountain snow showers
Sunday and Sunday night, then increase again Monday night as a
weaker Pacific trough comes inland. The extra pcpn will add
another .15 to 25 inch to the amounts stated above. Latest
models now show little chance (less than 10%) of thunderstorms
through Monday morning, but a 20 percent chance Monday afternoon
and evening throughout our CWA. High temperatures Sunday will
only be in the 40s to lower 50s. For Idaho that means about a 20
degree drop from today. Monday will be also be cold with the
main upper trough still nearby (but east of our CWA).

.LONG TERM...Tuesday through Saturday...After Monday's system,
we will be left with moist NW flow aloft and steadily decreasing
chances of showers going from Tuesday through Tuesday night.
The big story Tuesday will be strong winds, with gusts 30-50
mph possible. The strongest gusts are expected to develop from
around Mountain Home south and east into the western Magic
Valley. Wednesday, the only chance of precipitation worth
mentioning (15-30%) will be in eastern Valley County as
relatively dry northerly flow aloft builds in. Winds will
still be breezy, but much weaker than Tuesday. Ridging aloft
to our north, combined with a low to our south, will result in
(relatively rare) easterly flow Thursday and Friday. Models
begin to differ significantly late Friday and Saturday, but
odds are we will be dry with temperatures near or a little
above normal.

&&

.AVIATION...Mainly VFR this afternoon into the evening, then
areas of MVFR as precipitation becomes widespread. Mountains
obscured at times this afternoon, then consistently tonight.
There's a 10% chance of thunderstorms from 22-04Z. Snow levels
7-9kft MSL, lowering to 3- 4kft SE OR and 4-6kft SW ID Sunday
morning. Surface winds: S-E 10-25 kt, with gusts 25-40 kt
becoming W-NW 10-20 kt tonight. Winds aloft at 10kft MSL:
S 20-40 kt today, becoming W through S tonight.

KBOI...VFR today with gusty SE surface winds. Rain will begin
22-24Z this afternoon and increase this evening. Wind will
shift to NW between 01-03Z and there will be periods of MVFR.
After 03Z probability of ceilings below 2kft increases to
40-60% with a 20-30% chance of IFR conditions developing.

Sunday Outlook...Rain changing to snow in the mountains will
produce widespread IFR and obscure terrain across w-central
Idaho and e- central Oregon. Snow levels 3500-5500 feet,
lowest in SE Oregon Sunday morning. Elsewhere low VFR-MVFR
with showers continuing through the day. Surface winds:
W 10-20 kt with gusts 20-30 kt.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory until 6 PM MDT this evening IDZ014-016.
OR...Wind Advisory until 5 PM PDT this afternoon ORZ061.

&&

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SHORT TERM...LC
LONG TERM....SP
AVIATION.....SP