Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 250324

Area Forecast Discussion
National Weather Service Boise ID
924 PM MDT Thu May 24 2018

.DISCUSSION...Area of showers and thunderstorms crossing the Snake
River Plain this evening will bring brief heavy rain and gusty
winds up to 40 MPH. It will continue to slowly propagate
northward, but is expected to diminish by 11 PM. Areas east of
Boise are most likely to see precipitation, with the Boise metro
area and points west just getting the outflow winds. The next
area of showers and thunderstorms is already approaching the OR/NV
border and will push into southern Harney and Malhuer counties by
midnight MDT. Because of the accompanying upper dynamics expect
these showers and storms to hold together overnight as they move
northward. Activity is expected to remain over southeast Oregon
reaching northern Harney and Malheur counties toward sunrise.
Showers and thunderstorms will be accompanied by brief heavy rain.
Have updated the forecast for conditions this evening, otherwise
forecast is on track.


.AVIATION...Mostly VFR with mountains obscured at times. Showers
and  thunderstorms diminishing after sunset. Another round
arrives after 25/09Z in SE OR, spreading from south to north.
Then, widespread showers and thunderstorms across the entire area
after 25/20Z, some severe. Expect hail, frequent lightning, and
gusty winds to 40 kts with stronger storms. Otherwise, surface
winds will be variable and less than 8 kts. Winds aloft near 10
KFT MSL: Becoming ESE 10-20 kts.


SHORT TERM...Tonight through Saturday...An upper level ridge will
move across the area overnight, as our next upper level low moves
onshore over northern CA. This low is expected to help create
strong to possibly severe convection across the area late tonight
and tomorrow. SPC has placed most of our forecast area in a
"marginal" risk for severe thunderstorms. This category means that
isolated severe storms are possible. A convective complex is
expected to develop across northeast CA and northwest NV this
evening, and move north into southeast Oregon overnight as it
weakens. After a break Friday morning, new storms will develop
Friday afternoon across southeast Oregon and southwest Idaho, and
these storms will last into the evening. It is this round of
storms that has the best chance to be severe. Threats include
large hail (up to 1.5 inches), strong winds (up to 70 mph), and
heavy rain (total amounts could be over 1 inch in isolated cases).
A dry slot will move into the southeast part of our forecast
area, reducing the chance of convection south and east of
Mountain Home. Tomorrow will also be the warmest day of the
period, with highs in the upper 80s in the valleys. As the upper
low moves into northwest NV Saturday, cooler air will be drawn
southward over the region. Highs Saturday will be around 10
degrees cooler than Friday. Moisture is high through the period,
with PW values between 0.6 and 0.8 inches.

LONG TERM...Saturday night through Thursday...An upper level low
moving through southern NV through the weekend will bring showers
across the area with afternoon thunderstorms. SE Oregon will begin
to dry out Monday and remain dry through Tuesday. Showers linger in
SW Idaho through the end of the period, but do remain confined to
mostly the higher elevations. A short wave ridge does build over the
region Tuesday afternoon, but yet another upper level trough begins
to impact our CWA by Wednesday increasing shower activity.
Temperatures will hover right around normal for this time of year.





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