textproduct: Pendleton

DISCUSSION

Key Messages:

1. One more day of strong high pressure and air stagnation.

2. Precipitation returns Thursday, with freezing rain chances Thursday night into Friday and precipitation chances continuing at least over the mountains into the weekend.

The area of high pressure that has been over the western states will begin to move eastward today. As it does, a more southerly flow will develop. Conditions are expected to remain dry again today.

However, moisture will move northward from California on Thursday and will bring mainly low elevation rain and light mountain snow during the day on Thursday.

Late Thursday into Thursday night and continuing into early Friday is the period that we continue to watch. Guidance continues to disagree as to the amount of QPF moving across the region... especially the Columbia Basin/Yakima Valley/Kittitas Valley Thursday night. But QPF is negligible in some models and a bit more in others.

Additionally, the latest deterministic guidance has come in warmer as well. While guidance often tends to be too warm when there is cold air trapped in the Basin and nearby valleys, so will have to see it the warmer temperatures both at the surface and aloft continue with runs.

So, the bottom line up front is there is at least the potential for some light freezing rain mainly Thursday night into early Friday across portions of the Columbia Basin, Yakima and Kittitas Valleys before temperatures warm up on Friday.

NBM probabilities currently are highest for >= 0.01 inches of ice over portions of the Simcoe Highlands, north-central Oregon and areas of the Yakima and Kittitas Valleys. Probabilities in these areas are about 30 percent. It is all going to come down to what the temperatures are and how much QPF there ultimate is.

By later Friday, temperatures should rise enough in most areas and any precipitation should end that any freezing rain threat would be over.

An area of low pressure will move northward later Friday into Saturday and will bring the next round of precipitation, mainly to the mountains. Snow levels will be 3500-4000 feet in the Washington Cascades and 4000-4500 feet elsewhere with this system and accumulations up to 4 inches are possible, with some locally higher amounts along the crests.

AVIATION

12Z TAFS...VFR conditions and light winds are expected for the most part, through the TAF period. There are a few possible exceptions...Both PDT and ALW could see some reduced CIGS/VSBYS this morning though confidence is less than average on occurrence. Otherwise, ALW could see some reduced CIGS/VSBYS again Thursday morning.

PRELIMINARY POINT TEMPS/POPS

PDT 36 22 35 29 / 0 0 30 70 ALW 34 25 34 30 / 0 0 30 70 PSC 38 22 34 28 / 0 0 20 60 YKM 39 22 36 28 / 0 0 10 40 HRI 37 23 34 29 / 0 0 20 70 ELN 34 19 34 28 / 0 0 10 40 RDM 44 24 44 33 / 0 10 40 40 LGD 44 29 42 36 / 0 0 40 70 GCD 48 29 44 38 / 0 10 70 80 DLS 40 27 37 33 / 0 10 30 80

PDT WATCHES/WARNINGS/ADVISORIES

OR...Air Stagnation Advisory until noon PST Thursday for ORZ044-507- 508-510-511.

Wind Advisory until 3 PM PST this afternoon for ORZ049.

WA...Air Stagnation Advisory until noon PST Thursday for WAZ026>029.