929
FXUS66 KPDT 031019
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
319 AM PDT Fri May 3 2024

.SHORT TERM...Today through Sunday...A transitory ridge of high
pressure will be passing over the region today. This will provide a
mild Spring day with temperatures getting into the low 70s around
the Basin and 60s in the mountains. High clouds will begin to
increase and spread across the forecast area late today and
overnight as the next weather system approaches. This closed upper
level low pressure system is dropping SE out of the Gulf of Alaska
with the center of the low taking a path into SW Oregon Saturday
afternoon then continuing into the Great Basin on Sunday. This will
bring the leading edge of a cold front into the Cascades tonight but
its eastward progress overnight and into Saturday will be slowed as
the low center moves into SW Oregon. Eventually the cold front turns
into a deformation band of precipitation Saturday night into Sunday
as moisture wraps around the low back across northern Oregon and
southern Washington. 48 hour QPF amounts ending 12Z Monday continue
to show a very high probability that lower elevations could see .5 -
1.0 inches of precipitation while the eastern mountains and Cascade
crest could see 1 - 2 inches of precipitation. This amount of
precipitation is expected to cause streams and rivers to rise and
peak early next week but remain below flood stages.

Snow levels will initially be high Friday night and early Saturday
around 6000 to 7000 feet. They will begin to lower Saturday
afternoon and night as the low passes south of the forecast area.
Central Oregon will see snow levels down to 3500 to 4500 feet
Saturday night but remain 4500 to 6000 feet across the rest of the
forecast area. This could produce 4 to 10 inches of snow along the
Oregon Cascade crest impacting travel over the passes so a Winter
Weather Advisory has been issued Saturday morning through Sunday
morning.

Other concern will be some increasing S-SE winds overnight and
Saturday. This will produce some gusty winds over the higher terrain
of eastern Oregon and cause some downsloping off of the Blue
Mountains along the Foothills. A wind shift back to windy westerly
winds is expected to take place late Saturday and continue through
Sunday.



.LONG TERM...Monday through Thursday... Another, weaker weather
system will move across the Pacific Northwest on Monday and bring
another round of precipitation, mainly to the mountains.  However,
there will be chances even in the lower elevations Monday afternoon.
 QPF amounts will be fairly light in most areas. In the mountains
QPF will be a bit higher, ranging from 1/4 to 1/2 inch along the
crest of the Cascades to around 1/4 inch in the Blues and Wallowas.
Most other areas will see only a few hundredths.

Precipitation chances will end everywhere except over the mountains
by Tuesday morning.  Some additional shortwave energy could enhance
precipitation chances again Tuesday afternoon, mainly over the
eastern Oregon mountains, but overall QPF is expected to be very
light...only a few hundredths in most locations.

Snow levels start out at 4000 feet or higher on Monday, but drop to
between 2500 and 3000 feet by Tuesday morning.  So, certainly the
precipitation will mix with and change to snow in the higher
elevations of the Cascades and Blues, and a few inches are possible
along the crests with little elsewhere.  The ECMWF EFI focuses on
precipitation and snow over the Blue Mountains and nearby foothills
with and area of 0.6 to 0.8 on Monday.

Also on Monday, there is at least some chance of thunderstorms
mainly over the eastern Oregon mountains, as this next systems moves
through.  CAPE values are expected to be in the 100 to 300 J/KG
range, though the best CAPES look to be further southeast.  LI
values look to be between 0 and -2 degrees C.

By Tuesday evening into Wednesday and for the remainder of the
period, a ridge will build over the Pacific Northwest.  This should
bring drier weather and warmer temperatures.  A few shwoers over the
eastern mountains can`t be ruled out on Thursday, but confidence is
low (<30%) at this time.

Winds will start out quite gusty as a result of the pressure
gradient between the departing trough in the Great Basin and higher
pressure to the west.  WInds will gust 25 to 35 mph and possibly as
high as 40 mph in portions of the Columbia Basin, Blue Mountain
Foothills, Columbia Gorge.  Winds will decrease during the day but
remain gusty and become more widespread as the next system
approaches. Gusty winds look to continue into Tuesday, with speeds
25 to 35 mph, before decreasing into Wednesday.

The ECMWF EFI keys in on the Columbia Basin and Foothills of the
Blue Mountains for winds on Monday, with values ranging from 0.6 to
0.8, with a core of 0.8 to 0.9 over the Blue Mountains.

The NBM probabilities of wind gusts >= 39 mph on Monday are 70 to
90% across much of the Basin and Blue Mountain Foothills Simcoe
Highlands and Cascade Gaps.

On Tuesday, the NBM probabilities of wind gusts >=39 mph are 80%
plus across much of the Basin, Gorge, Blue Mountain Foothills ,
Simcoe Highlands, and Kittitas Valley.  The probabilities of wind
gusts >=47 mph are 50 to 70% across portions of the Columbia Basin,
Foothills of the Blue Mountains, Simcoe Highlands and 60-90% across
the Kittitas Valley.

High temperatures on Monday will start of 10 to 15 degrees below
normal and will mainly range from the 50s in central Oregon to the
60s across the Columbia Basin.   By Wednesday, high temperatures
will begin to rise and by Thursday, highs will be close to normal in
most areas and above normal in the Basin.

The ECMWF EFI shows this trend as well for high temperatures.  On
Monday, there is a large area of -0.7 to -0.8 across most of Oregon,
and -0.6 to -0.7 across much of southeastern Washington.  On
Tuesday, the area moves a bit eastward.  There is a large area of -
0.7 to -0.8 across much of the region and even an area of -0.8 to -
0.9 over the Oregon Blue Mountains.  By Wednesday, most of the
anomalous temperatures are gone in the EFI.


&&

.AVIATION...12Z TAFS...High confidence (100%) in VFR conditions
through the period with winds less than 10 kts.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  70  51  67  41 /   0  10  50 100
ALW  72  55  71  44 /   0  10  40 100
PSC  73  55  72  45 /   0  10  40  90
YKM  69  48  65  42 /   0  20  80  70
HRI  75  54  70  43 /   0  10  50  90
ELN  66  44  61  42 /   0  20  80  70
RDM  65  41  50  32 /   0  70  90  70
LGD  64  46  63  39 /   0   0  50 100
GCD  63  44  61  35 /   0  10  90 100
DLS  72  50  57  46 /   0  60  90  90

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 5 AM Saturday to 11 AM PDT Sunday
     for ORZ509.

WA...None.
&&

$$

SHORT TERM...91
LONG TERM....77
AVIATION...77