Tornado and Hail in Oregon, May 6, 2022

Area Forecast Discussion
National Weather Service Pendleton OR
1004 AM PDT Fri May 6 2022

.MORNING UPDATE...A surface warm front continues to push a band of
light rain across southeast WA this morning, while behind the band
isolated light rain showers have started to develop. Today, rain
showers will continue to develop across most of the forecast area
ahead of an approaching potent shortwave trough and surface cold
front. Instability will be increasing across OR and the northeast
mountains in the afternoon today, allowing isolated to scattered
thunderstorms to develop as well. The best chance for
thunderstorms will likely be associated with the cold front
boundary passage and those areas that have cleared out this
morning. These storms are not expected to become severe, and with
seasonally weak instability and strong wind shear aloft, some of
these storms will struggle to develop. Otherwise, winds will also
increase across central and southern OR with the cold front
passage later this afternoon, with gusts 30mph to 40mph possible.
Lawhorn/82

&&

AVIATION...18z TAFs...Another round of showers will impact the
area today, with localized MVFR to IFR conditions possible under
heavier bands of rain. A chance for an isolated thunderstorm at or
near the vicinity of PDT and ALW cannot be ruled out this
afternoon. West winds will increase at most sites during the day
as well, especially for BDN/RDM where gusts could approach 30 kts
at points in the afternoon. Cigs generally bkn-ovc around 5 kft,
down to 2-3 kft under showers. Winds look to increase across all
sites overnight. 74/93

PREV DISCUSSION... /issued 248 AM PDT Fri May 6 2022/

SHORT TERM...Today through Sunday night...The weekend will be met
with wet and windy weather, and there are a few concerns that
should be noted. An upper level trough and surface cold front
will approach the coast today then traverse across the PacNW
tonight through Saturday morning. Currently, there is a band of
precipitation extending across the WA/OR border with weak warm air
advection, and the WSR-88D at PDT is showing embedded returns of
40-45dBZ with light to moderate rain reported along the Blue
Mountains and foothills. The warm front and precipitation will
lift north towards the Washington Palouse this morning with a
break break. However, numerous showers will increase from the
west as the day progresses. A few thunderstorms were observed
yesterday, and isolated to scattered thunderstorms are expected
this afternoon and evening. The biggest threat will be heavy rain
embedded within the convection. PWATs will be around 0.7-0.8
inches which are not high, and the storm motion will be somewhere
around 20-30 kts. Therefore, flash flood potential is minimal. The
main concern with the embedded heavy showers will be areas that
are already experiencing high waters along rivers and creeks that
could result in some sharp rises. The bulk shear is quite strong
with around 80 kts between 0-6km. This could limit some
thunderstorm development as the CAPEs will be too weak to overcome
the shear. However, CAMS are consistent with the high radar
reflectivity this afternoon and evening. Winds will increase this
afternoon and evening with the strongest winds in the southern
half of Oregon. Areas south of Redmond are forecast to receive
gusts 30-40 mph where the gradient is strongest.

After the cold frontal passage, snow levels will lower to around
4000-4500 feet Saturday morning and continue to lower to 3500-4000
feet early Saturday evening. Some of the mountain passes along the
Cascades and Blue Mountains will have snow accumulations up to one
inch. On Saturday, the forecast area will remain under the trough
and cyclonic flow aloft with a continued unstable atmosphere. The
main concern on Saturday will be the strong winds that may
require wind advisories. Since the strongest winds will occur late
in the afternoon and evening, will let the upcoming shifts
analyze further. The Kittitas Valley has me particularly concerned
with strong winds. A shortwave trough tracking across northern WA
will have a tight gradient behind it. MAV guidance shows 38 kts
of sustained wind at 00Z. NBM 4.1 shows 40 kt gusts in the 25th
percentile and 50 kt gusts in the 50th percentile. If this trend
continues in the models, this could be a high end advisory with
gusts 55 mph in the Kittitas Valley. Isentropic descent is quite
impressive on the 12km NAM for Saturday, so there could be other
areas across south central Washington and central and north
central Oregon that may need to be included. 850mb and 700mb winds
of 35-40 kts would indicate that high wind criteria will likely not
be met. Scattered showers and isolated thunderstorms on Saturday
may bring moderate rain, but the QPF will be less than today.

The showers and isolated thunderstorms will continue on Sunday
when another Pacific trough pushes across the region. On Sunday,
snow levels will be down to around 2500-3000 feet but the SLR is
low. In early May, there is around 15 hours of sun that aides in
keeping the SLR less than 5:1 for the lower elevations. QPF
amounts will also be low, but the instability may cause some areas
to experience brief heavy showers of graupel. The center of the
upper low will be along the OR Cascades Sunday afternoon with -32C
temps at 500mb. Winds will be breezy and locally windy on Sunday.
Wister/85

LONG TERM...Monday through Friday...Broad upper-level low centered
over the PacNW will continue to make for unseasonably colder weather
through much of the week next week, with high temperatures as much
as 20 degrees below average in some areas. Ensembles look to be in
good agreement on depicting this system stalling out over the
western CONUS through at least the midweek as an omega block pattern
sets up across North America. QPF ensembles also pointing toward
mostly dry conditions across our lower elevation zones, with precip
chances limited primarily to the mountains. This surge of colder air
will also increase chances for mountain snowfall, with snow levels
hovering around 2500-3500 ft on Monday, where models seem to have
the highest confidence in precip next week. Amounts look to be low,
however, so any precip-based impacts look to be minor in the
extended period. Deterministic guidance also shows weak signal for
instability over the eastern mountains on Monday and briefly during
the day Tuesday, so have opted to leave in a slight chance of
thunder for those areas as well.

Ensembles diverge substantially heading into late next week. While
most members agree on this broad low digging down into the
southwestern US, models split on either this low cutting off and
picked up by another oncoming shortwave, or the oncoming wave
replacing the current system altogether. Either way, better chances
for area-wide precip look to fall some time toward the end of the
work week next week, with cooler conditions continuing to prevail as
the predominately trough pattern allows colder, Canadian air to seep
in over the PacNW. Overnight lows during the period may also
approach freezing in the Basin as well, with current NBM guidance
suggesting mid 30s for the Yakima/Kittitas Valleys, as well as the
foothills of the Blues. 74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  65  44  55  37 /  90  90  50  10
ALW  64  46  57  39 /  90  90  60  20
PSC  66  50  63  42 /  80  60  30  10
YKM  64  43  60  34 /  80  50  30  10
HRI  68  47  60  40 /  90  70  30  10
ELN  58  39  54  35 /  80  60  30  10
RDM  67  38  52  29 /  80  80  50  30
LGD  66  40  51  32 /  90 100  70  20
GCD  66  40  51  31 /  80  90  70  30
DLS  65  47  57  41 /  90  90  50  40

&&

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

MORNING UPDATE...82
AVIATION...74/93