textproduct: Pendleton

DISCUSSION

Freezing fog across the central Oregon zone was evident with one half to three quarter mile visibility from three rivers to Bend. Additionally the I-84 corridor across dead and pass/cabbage hill was near zero visibility and up to three quarters across the local mesonet obs. These advisories remain intact until noon. Spatially , sky cover should linger all day in the lower Columbia and foothills of the Blues where a thinner near surface saturated layer should scatter out near the Cascades, (Bend/DLS/Yakima Valley) and some sun may be getting through, however confidence is low. The risk of freezing fog becomes reduced Tonight as the HRRR is showing a considerable decrease in low visibility spatially and more tied to the foothills of the northern Blue Mountains, and not across central and north central Oregon as of late. The more likely scenario would be for freezing fog headline to still be needed across the northern Blues foothills, if anywhere based on where the HRRR is continuing to place low visibility fields, and after 6 pm or as based on the development of the fog last evening. The mixing heights are lower by Monday however the stratus should break out as the top of the mixed layer warms up a few degrees to above zero. The stagnant pattern continues though at least Tuesday and the current Air Stagnation advisory is valid though then. This might need consideration of extending though Wednesday, as notable uptick in the NBMs mean transport winds and mixing heights is not really seen until Thursday afternoon. The next forecast pops return Thursday evening as both the GFS and ECMWF IVT forecast show weak (250-450 kg/ms) of moisture transport into the Columbia River region as weak AR rounds a surface high pressure near 38N/135W.

AVIATION...12Z TAFs

MVFR or lower conditions to prevail through the period. Upper level ridging will continue to sit over the PacNW through the TAF period, reinforcing the stratus layer from Central OR to the upper Columbia Basin. Numerical model guidance is handling this persistent stratus layer very poorly, though HREF mean sounding forecasts have overall matched closest to observations. Over the TAF period, have leaned towards a persistence forecast for most sites, with trends based off of HREF sounding forecasts.

CIGs will remain persistent at sites DLS/PSC through the period, with limited sinking/rising of the CIG height. Sites PDT/ALW/YKM will see persistent CIG heights through this evening, with IFR CIGs developing after 03Z. IFR vsby at site RDM and LIFR or lower vsby at site BDN will prevail through this morning, improving to MVFR or higher after 18Z, but then decreasing to IFR or lower after 01Z. CIGs at both sites will stay around 200ft through 18Z, then lifting as high as 500ft this afternoon before sinking to 200ft again after 01Z. Winds will be light at all sites through the period. Lawhorn/82

PRELIMINARY POINT TEMPS/POPS

PDT 34 23 36 23 / 0 0 0 0 ALW 34 25 36 26 / 0 0 0 0 PSC 36 25 38 24 / 0 0 0 0 YKM 38 23 39 23 / 0 0 0 0 HRI 35 25 37 24 / 0 0 0 0 ELN 37 22 36 22 / 0 0 0 0 RDM 42 17 43 20 / 0 0 0 0 LGD 47 25 48 26 / 0 0 0 0 GCD 52 26 53 27 / 0 0 0 0 DLS 40 27 41 26 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

OR...Air Stagnation Advisory until 4 PM PST Tuesday for ORZ041-044- 507-508-510-511.

Freezing Fog Advisory until noon PST today for ORZ502-507-510- 511.

WA...Air Stagnation Advisory until 4 PM PST Tuesday for WAZ024- 026>029-521.