FXUS66 KPDT 212353

AFDPDT



Area Forecast Discussion

National Weather Service Pendleton OR

452 PM PDT Sat Mar 21 2026





.UPDATED AVIATION DISCUSSION...





.KEY MESSAGES...



- Minor river flooding in south-central Washington through

  Monday



- Elevated river levels in south-central Washington continue

  through next week after flooding subsides Monday



- Areas of frost overnight in the Columbia Basin and along the

  Blue Mountain foothills



&&



.DISCUSSION...

Clear to partly cloudy skies are present across the majority of

the forecast area this afternoon. The air mass is quite dry,

PWATs of 0.2-0.3", and some of the dry air from aloft is mixing

to the surface. Dew points in the single digits to teens have 

surfaced in places, notably along the lee of the Washington 

Cascades as well as north-central Oregon. Elsewhere, dew points

have crashed relative to the early morning, but only in the 

20s. Anticipating these low dew points will become more 

widespread through the remainder of the afternoon and evening as

dry air continues to mix to the surface. 



Tonight, mostly clear skies coupled with the aforementioned dry

air mass will facilitate chilly temperatures. Areas of near- to

sub-freezing temperatures are forecast for the lowlands. While 

not atypical for late March, they come on the heels of an

anomalously warm stretch. Coupled with the fact that flowers 

and trees are blooming and budding several weeks early across 

parts of the forecast area, have opted to inject areas of frost 

into the gridded forecast where temperatures and relative 

humidity are supportive. Will note, the very dry air mass has

the potential to hinder frost formation if surface dew points

remain low enough, but thinking the recent precipitation will 

keep enough moisture near the surface to have at least patchy to

areas of frost in cold-prone locations.



Sunday, mostly dry conditions accompanied by near-seasonal 

temperatures are anticipated beneath quasi-zonal flow aloft. 

Very dry air aloft (single digit to teens dew points) is 

expected to mix to the surface in places, but the lack of 

significant wind should limit fire weather concerns.



Ensemble NWP guidance shows a plume of moisture from the Pacific 

moving into the Pacific Northwest by late Monday. Precipitation 

chances increase by Monday night as a strong offshore surface 

low tracks northeast towards British Columbia. Its attendant 

frontal system will move inland Tuesday into Wednesday, with 

perhaps another cold frontal boundary in its wake later 

Wednesday into Wednesday night as a 500-mb shortwave moves 

overhead.



The early-week system will also usher in breezy to windy

conditions across the forecast area.



Looking ahead, there is still significant uncertainty in details

of the 500-mb height pattern, but a building ridge is favored

(60-70 percent of ensemble members) and mostly dry weather is 

forecast later Thursday through Friday. 86



&&



.AVIATION /00Z TAFS THROUGH 00Z MONDAY...VFR conditions prevail 

for all sites. Winds will be gusting at 20-25 kts through 02Z this 

evening for KRDM/KBDN and 05-06Z tonight for KDLS/KYKM. Otherwise, 

the remaining sites will have winds less than 12 kts. Feaster/97



&&



.HYDROLOGY...

River flooding from snowmelt and previous rainfall is ongoing

for the Yakima and Naches rivers in south-central Washington.

These rivers have crested, or will crest this afternoon, for

most locations in the Yakima and Kittitas valleys. Locations

downstream towards the eastern end of the Yakima Valley and the

lower Columbia Basin have yet to crest, and the Yakima at Kiona

is forecast to crest between late Sunday afternoon and early 

Monday morning. 



Looking ahead, several forecast points along the Yakima and 

Naches rivers, including those at Easton, Cliffdell, Naches, and

perhaps Umtanum, are then anticipated to remain above action 

stage through the week according to the latest forecasts from 

the Northwest River Forecast Center in Portland.



&&



.Preliminary Point Temps/PoPs...

PDT  31  56  34  60 /   0   0   0   0 

ALW  35  56  38  60 /   0   0   0   0 

PSC  34  60  35  63 /   0   0   0   0 

YKM  29  56  34  59 /   0   0   0   0 

HRI  33  59  34  62 /   0   0   0   0 

ELN  29  52  31  55 /   0   0   0   0 

RDM  23  60  30  63 /   0   0   0   0 

LGD  28  58  35  64 /   0   0   0   0 

GCD  28  61  35  66 /   0   0   0   0 

DLS  34  60  38  62 /   0   0   0   0 



&&



.PDT WATCHES/WARNINGS/ADVISORIES...

WA...None.

OR...None.



&&



$$



DISCUSSION...86

AVIATION...97 

HYDROLOGY...86