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000
FXUS66 KPDT 140329
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
829 PM PDT Sat Apr 13 2024

.UPDATE...
Latest radar imagery showed showers and decaying convection mainly
across central Oregon. Have updated pops to account for latest
radar trends. Precipitation is further north than precious model
guidance was showing. Otherwise, only made minor changes to the
rest of the overnight period as any thunderstorms should continue
to dissipate over the next few hours and will just be left with
areas of showers through daybreak.




&&

.PREV DISCUSSION... /issued 442 PM PDT Sat Apr 13 2024/

AVIATION...00Z TAFS...Most sites will be at VFR with cloudy skies
(FEW to OVC, 040-250 kft). Though, KRDM and KBDN could be at MVFR at
around 00-03Z due to low VSBY, if not improved later tonight.
Thunderstorms are the primary concern this evening for KRDM and
KBDN, but might diminish tonight (>70% confidence). KRDM and KBDN
are also expected to have a 30%-40% chance of rain Sunday morning.
Winds will be light for all sites except KDLS being breezy for
Sunday morning and KRDM/KBDN for tonight and again Sunday afternoon
with wind gusts between 20-30 kts. Feaster/97

SHORT TERM...This afternoon through Monday...Focus is on
convection this afternoon, primarily across central and north-
central OR where a Marginal risk of severe thunderstorms is being
highlighted by the Storm Prediction Center. The main hazards will
be a low-end chance (5%) of severe hail (1" or greater in
diameter) and severe wind (58 mph or greater) with any organized
convection that develops in an environment characterized by steep
mid-level lapse rates (7-8 C/km) and ample effective shear (35-45
kts). 12Z HREF members continue to advertise neighborhood 30%
neighborhood probabilities of exceeding 3-hr precipitation of 1"
for the Bend-Redmond-Prineville metro region so an isolated flash
flood threat with any training thunderstorms remains a
possibility. Additionally, low-level hodographs are supportive of
a very low (2%) chance of a tornado.

While some showers are ongoing across central OR early this
afternoon, additional convective initiation is expected in Lake,
Klamath, and Deschutes counties on the northwest side of a
developing surface low beneath diffluent flow aloft in the exit
region of an upper-level jet associated with the deep offshore low
centered just west of the SF Bay area in CA. The threat of severe
storms tapers off later this evening, though some lingering
showers and isolated thunderstorms may continue (20% chance) into
the overnight hours.

Looking east across the Blue Mountains, while 12Z HREF
mean and 50th percentile surface-based CAPE increases to around
500-1000 J/kg, locally higher than 1000 J/kg, and becomes
uncapped, there is a lower chance of thunderstorms due to a lack
of synoptic forcing. Isolated air-mass type cells may develop,
but confidence is low (<30% chance), and given weak effective
shear (<25 kts), chances of severe storms are very low (<5%
chance).

Sunday through Monday: Sunday, will likely see another round of
afternoon convection focused on a line oriented southwest to
northeast from eastern Deschutes County through the Blue Mountains
to the Washington border. Effective shear of less than 25-30 kts
(except for the southern end of the line) appears less supportive
of severe storms compared to the past couple days, though the most
aggressive CAMs suggest significant SFC and MLCAPE (1500-2500
J/kg) coupled with steep low- and mid-level lapse rates, so cannot
completely rule out an isolated strong to severe storm (<5%
chance).

The upper-level low will move inland through the day on Sunday,
paving the way for an incoming shortwave trough from British
Columbia. This will usher in strong west to northwest winds
through the Cascade gaps and across the Columbia Plateau Sunday
afternoon through Monday. Advisory-level winds appear likely --
though forecast 700 mb winds are unimpressive, forecast 850 mb
winds are more robust at 35-50 kts, forecast PDX-GEG pressure
differences peak at 10-15 mb, and NBM probabilities of exceeding
45 mph gusts are a widespread 50-80% with locally higher values
for our most wind-prone locations such as portions of the lower
Columbia Basin of OR and the foothills of the southern Blue
Mountains. Additionally, have retained mention of patchy blowing
dust in the forecast. Have held off on issuing any wind
highlights this afternoon as the focus remains on today`s severe
weather threat. Plunkett/86

LONG TERM...Tuesday through Saturday...While ensembles are a bit
divisive on depicting the synoptic pattern in the long term, the
general picture they paint is that of benign and seasonable
conditions, with the only real sensible weather threat being a
slight chance (15-30%) of high mountain precip above 4000 ft,
mainly Tuesday and Wednesday. Even if anything materializes,
moisture is severely lacking across guidance, so not much to speak
of weather-wise in the long term.

While the forecast area will be under amplified NW flow due to a
broad low centered over BC and Alberta, much of this flow will be
dry in nature as it taps primarily into the continental Canadian
airmass. PWATs crater to around a quarter of an inch by midweek,
so outside of a few scant orographic showers across primarily
the Washington Cascades and Blues, the atmosphere just isn`t
properly primed to produce any meaningful precip under an
otherwise supportive flow pattern. Ensembles are then divided on
what follows this Canadian low, split between weak ridging and
zonal flow, but either pattern results in dry, seasonable weather
for the forecast area. Expect temps typical of late spring, with
highs in the 70s across our population centers Wednesday onward,
with lows sinking down into the mid 30s to low 40s thanks to clear
skies and light winds. Evans/74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  46  73  43  61 /  10  10   0   0
ALW  49  76  47  64 /  10  10  10   0
PSC  47  81  48  69 /  10   0   0   0
YKM  46  79  42  64 /   0   0   0   0
HRI  48  79  45  66 /  10   0   0   0
ELN  46  73  42  56 /   0   0   0   0
RDM  43  66  35  56 /  90  30  10   0
LGD  46  72  41  58 /  10  40  50   0
GCD  45  70  38  58 /  40  60  30   0
DLS  53  72  47  60 /  20   0   0   0

&&

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

$$

SHORT TERM...77
LONG TERM....74
AVIATION...97