Severe Thunderstorm Warning 2, NWS Pendleton, OR

Area Forecast Discussion
National Weather Service Pendleton OR
427 PM PDT Thu May 28 2020

Updated aviation discussion

.SHORT TERM...Tonight to Saturday night.

Latest day cloud phase RGB imagery shows a modest increase in
shallow to deep cumulus across central OR and Strawberry
mountains, elsewhere mid/high thick clouds across mainly Columbia
Basin on north. Latest water vapor imagery shows the cutoff low
offshore Baja California with upper ridge over the Northern
Intermountain West. Current thinking is isolated showers and
thunderstorms cannot be ruled out across central OR and parts of
the Strawberry mountains, specifically where we are starting to
see the deeper cumulus develop on satellite. No glaciation of any
towering cu evident yet on RGB imagery. Modest elevated
instability and so-so mid-level lapse rates in place across
central OR this afternoon extending from south central OR,
however, low and mid-level flow aloft is pretty low. Current
thinking is orographic forcing could be sufficient across the
higher terrain and west/south facing slopes in lieu of better
synoptic scale forcing for ascent. Thus some isolated shower and
thunderstorm development possible and in the forecast. A few of
the hi-res guidance depict some convection in the aforementioned
areas as well. While isolated activity may develop and continue
over the higher terrain and northeast across the Blue Mountains
into the small hours tonight, confidence in this occurring is
low-moderate.

Conditions will be 5-10 degrees warmer tomorrow compared to today
as the surface trough sharpens Friday. Somewhat better
instability in place tomorrow with surface dew points in the mid
40s to mid 50s in the afternoon. While forcing for ascent remains
largely weak, convergence and orographic forcing will promote
chances for showers and some thunderstorms across the eastern
slopes of the OR Cascades, parts of central OR, and portions of
northeast mountains. Meanwhile, the mid-level closed low offshore
weakens into an open wave Saturday and moves across northern CA
into the Pacific Northwest. Greater coverage of showers with
better chances of thunderstorms Saturday with better moisture in
soundings and surface dew points in the 50s to low 60s in the
Columbia Basin. Some uncertainty with regard to destabilization
and forcing but looks like Columbia Basin WA/OR border north will
hold the greatest likelihood for risk of isolated strong-severe
storms. Large hail and damaging winds cannot be ruled out there
with any severe storms that develop. Activity is expected to then
start tapering off late Saturday night. Meanwhile, moderate winds
are expected Saturday as the surface low evolves north across
eastern OR to WA Saturday. Decent mixing and winds in the low
levels should promote gusts as high as around 45 mph via momentum
transfer based on BUFKIT soundings across parts of the Columbia
Basin northward to east central WA. Some blowing dust is possible
as well thus patchy blowing dust included across parts of the
Columbia Basin late Saturday/Saturday evening. 80

.LONG TERM...Sunday through Thursday.

On Sunday, a few showers will linger over the mountains from
central Oregon through northeast Oregon. A low pressure area will
move into central California by late Monday and this will allow
moisture to spread from California north across southern and
eastern Oregon. This pattern will persist through much of the
week. The moisture along with daily heating will keep a chance of
showers and and some thunderstorms each afternoon and evening over
the higher terrain from central Oregon through the Blue Mountains
and Wallowa County. Temperatures will be near to slightly above
normal. 93

&&

.AVIATION...00Z TAFs...VFR conditions with light winds will prevail
over the next 24 hours.  Some cumulus build ups this
afternoon/evening over central Oregon with a slight chance of a
thunderstorm for that area possibly impacting BDN. Some clearing
overnight and a return of buildups Friday afternoon.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  91  62  91 /  10   0  10  30
ALW  61  92  64  94 /  10   0   0  20
PSC  60  96  66  96 /   0   0  10  30
YKM  58  93  64  91 /   0   0  10  50
HRI  59  95  64  92 /   0   0  10  30
ELN  55  91  61  87 /   0   0   0  40
RDM  53  91  58  76 /  10   0  30  70
LGD  58  87  60  88 /  20  10  10  20
GCD  58  91  62  86 /  20  10  10  40
DLS  61  94  66  79 /   0   0  30  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

80/93/93