textproduct: Pendleton

DISCUSSION

Current night time satellite shows some split flow occurring across the PacNW with southeast flow to the southwestern portion of the region and southwest flow along the east and north eastern portion of the region. Much of the cloud cover is currently over central OR with radar showing some light returns in that area as well. Ground observations show that there rain is not currently affecting central OR at this time but is expected to move over the area after 10 AM.

Models show the low that is causing the southeast flow will continue to move to the east and bringing increased chances of rainfall to the region. Much of the rainfall will begin along the southern and eastern portion of the region Tuesday before becoming widespread after 5 PM. 24 hour QPF totals between 5 AM Tuesday to 5 AM Wednesday is 0.08-0.10 through central and north central OR as well as the Kittitas Valley with 10-25% of the NBM raw ensembles in agreement. Along the foothills of the southern and northern Blues, Yakima Valley and the Columbia Basin, QPF amounts between 0.20-0.30 inches are likely with 30-50% of the NBM raw ensembles in agreement. Highest rainfall totals will be along the eastern mountains ans along the higher crests of the Blues with 0.70-0.99 inches with 30- 40% of the NBM raw ensembles in agreement. Not only will there be an increase in precipitation, but models show an increase in instability as the moisture moves into the region.

Models show the low to usher in even more precipitation on Wednesday as it advects more moisture into the region. NBM QPF 24 hour totals show central and north central OR, portions of the Gorge, Yakima and Kittitas Valley seeing only 0.02-0.05 inches with 30-50% raw ensemble agreement. Rain amounts will increase as you move est with the southern Blues, Columbia Basin of OR and WA and portions of the eastern mountains will see QPF amounts between 0.10-0.50 with 35-65% of the raw ensembles in agreement. Foothills of the northern Blues and the eastern Basin could see between 0.60-0.80 inches with 50-70% agreement. Lastly, the ridges of the norther Blues could see between 0.80-1.90 inches with 50-70% agreement. However, snow levels will begin to decrease across the eastern portion of the region to below 5000 feet Wednesday so above this the precipitation will fall as snow with 50% ensemble agreement of 6+ inches of snowfall is possible between 5 AM Wednesday and 5 AM Thursday.

Forecast soundings show sfcCAPE values between 150-300 J/kg, 7.1 C/km lapse rates and 30 kt bulk shear all add up to the probabilities of thunderstorms along the eastern mountains and portions of central OR and WA Cascades. In house calculations show a 20-30% probability of thunderstorms along those areas as well as HREF paintball showing high concentrations of the members in agreement on location of the thunderstorms. SPC also has the region in a general thunderstorm outlook for Tuesday. Moving into Wednesday CAMs model NAM shows sfcCAPE values of 150-250 J/kg appearing again with lapse rates around 7 C/km and bulk shear around 30 kts again with paintball members showing the highest concentration being over Grant and Cook counties then moving off towards Wallowa later in the evening.

Wednesday, deterministic models show a very tight surface pressure gradient building along the Cascades and spilling over into the Basin. Many areas will see breezy to windy conditions Wednesday through Wednesday night. In house model guidance shows a very tight pressure gradient forming across the region bring 30 mph sustained winds Kittitas Valley, foothills of the southern and northern Blues of WA and OR, the Gorge, Simcoe Highlands, lower Columbia Basin of OR and north central OR with 40-70% of the HREF raw ensembles in agreement. The aforementioned areas will also see 30-70% probabilities of 45-50 mph gusts.

In the long term after Wednesday, models begin to fall out of agreement with the next incoming system. Some models, GFS and EURO do show a weak Rex block wanting to set up off the coast with a bit of a hint of the upper level low retrograding back into the area. Models are in agreement that the region will primarily be dominated by northerly flow aloft which will keep the region mostly dry and cool over the weekend. 90

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

VFR conditions will persist through much of the forecast period before all site minus RDM/BDN see MVFR conditions due to low CIGs after 07Z. Showers will begin to approach TAF sites between 17Z-22Z with mostly light showers. RDM/BDN will continue to see winds below 10 kts while the remaining TAF sites will see breezy winds between 13-18 kts with gusts nearing 30 kts after 16Z. 90

HYDROLOGY

With the amount of rainfall and snowfall expected through Wednesday, some river forecasts show a few rivers to exceed action stage by Thursday. These rivers are as follows: Grande Ronde at Troy, Naches near Cliffdell and Naches, Walla Walla near Touchet. 90

Preliminary Point Temps/PoPs

PDT 72 44 53 39 / 40 90 90 40 ALW 73 45 52 41 / 20 90 100 50 PSC 78 49 63 43 / 10 70 80 20 YKM 76 50 65 43 / 20 50 40 10 HRI 74 46 58 41 / 20 80 80 20 ELN 70 45 56 40 / 30 50 40 10 RDM 61 36 53 28 / 50 50 40 0 LGD 74 41 47 39 / 40 100 100 70 GCD 69 39 47 34 / 70 100 90 50 DLS 66 49 59 43 / 30 40 60 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.