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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KPDT 050535
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
935 PM PST Thu Mar 4 2021

Updated aviation discussion

.SHORT TERM...Tonight and Friday...A deep upper level ,trough off
the coast is keeping a cold front nearly stationary along the west
coast. Most of the precipitation will stay west of the Cascades
overnight. The front will slowly start moving eastward Friday
afternoon increasing the chance of precipitation along the Cascades
but stay dry across the rest of the forecast area until Friday
night. Even then it looks like the precipitation will be light and
spotty. Will begin seeing some increasing southerly winds overnight
mainly across the higher terrain of eastern Oregon. A wind advisory
has been issued for the southern Grande Ronde Valley but this looks
like a low end advisory event. Increasing winds and a little bit of
high clouds will help hold temperatures up in some areas overnight
so adjusted temperatures up in the evening forecast update.

.AVIATION...06Z TAFs...VFR conditions currently across all sites,
and will continue through the period but expect some lowering
ceilings Friday afternoon and evening as a cold front begins to move
over the Cascades. Breezy winds are expected for central Oregon
sites as wind gusts 20-30 kts out of the South. Locally breezy S/SE
winds are likely at PDT and ALW, as sustained winds hover around 10-
15 kts and occasionally higher gusts.

&&

.PREV DISCUSSION... /issued 246 PM PST Thu Mar 4 2021/

Updated Aviation Discussion.

SHORT TERM...Tonight through Saturday night. Low pressure offshore
with a cold front along the coast this afternoon. Ahead of this
system a southwest flow aloft spreading mid and high level clouds
over Washington and Oregon. This will continue through the evening
and overnight. Temperatures will be milder than the past few
nights with lows in the 30s to lower 40s. As the front moves
onshore surface gradients will tighten with increasing southerly
winds developing overnight across central and northeast Oregon. On
Friday the frontal boundary will move to near the Cascades with
rain in the afternoon. Elsewhere across the forecast area partly
to mostly cloudy and warm with highs in the 50s and 60s. Breezy to
windy over central and northeast Oregon. The upper trough and
weakening front move through the region Fri night and Sat with a
period of rain and higher elevation snow. Southerly winds will
become westerly with locally breezy conditions. Cooler with highs
only in the 40s to mid 50s. The next upper trough and front moving
into the Pacific northwest Sat night with increasing clouds and
precipitation reaching the Cascades by morning. 94

LONG TERM...SUNDAY THROUGH THURSDAY...The long term pattern is
dominated by a deep trough slowly traveling south along the PacNW
coast before moving onshore in CA midweek. This feature is coupled
with persistent southwest flow aloft, allowing for moisture to spin
up and around the system and develop upslope precipitation along the
Cascades and northern Blues. The trough will also keep partly to
mostly cloudy skies overhead as mild temperatures are expected with
highs in the upper 40s to low 50s for lower elevations and low to
mid-40s in the mountains, and lows near freezing for the Basin. As
the system near the WA/OR coasts late Monday into Tuesday,
precipitation chances will be heightened to allow for the best
chance for low elevation rain, primarily during the afternoon hours
on both days. As the system drops along the northern CA coast, drier
air should infiltrate into our area late Tuesday into Wednesday to
provide a slight dry period before the next system approaches from
the northwest. Upper level flow will also be shifting from southwest
to northwest by Wednesday afternoon/early evening to bring a return
to upslope rain/mountain snow along the Cascades and northern Blues.

A weak system looks to be forced south through central and eastern
BC early Thursday, and will pick up some Pacific moisture on its way
through the interior PacNW, allowing for mountain snow chances to
increase - especially for the WA Cascades. The system will be
dissipating as it near the CAN/USA border, so precipitation chances
are mainly expected at elevation and primarily along the western
slopes of the Cascades and Blues, with little making it to lower
elevations.

Snow levels should stay relatively consistent through the workweek,
mainly staying between 2000-3000 feet. During frontal passages,
Tuesday and late Wednesday into Thursday, snow levels will hover
between 1000-2000 feet. No hydrologic concerns are currently
expected due to low variability in snow levels and cloud cover
through the long term. Models are in fairly good agreement on the
offshore system until late Tuesday/Wednesday, where the GFS slows
down the system as it moves onshore just south of the Bay Area, and
the ECMWF keeps its earlier speed and because of that, pushes
farther south and moves onshore along the USA/MEX border before
continuing east. Observing ensemble cluster and phase space data,
confidence is leaning slightly toward the ECMWF outcome. This would
lead to a quicker and more southerly track of the system, resulting
in faster drying behind the system and a more substantial influence
from the offshore ridge FRI/SAT. 75



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  68  37  49 /   0   0  20  40
ALW  43  68  40  51 /   0   0  20  40
PSC  36  66  41  56 /   0   0  20  30
YKM  35  56  36  54 /   0  10  40  10
HRI  39  67  40  54 /   0   0  30  30
ELN  33  51  34  49 /   0  10  50  10
RDM  33  62  34  46 /   0  10  50  30
LGD  36  53  33  42 /   0   0  10  50
GCD  34  59  32  43 /   0   0  10  40
DLS  36  55  38  53 /   0  20  60  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 7 PM PST Friday for ORZ049.

WA...None.
&&

$$

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