Area Forecast Discussion

KEY MESSAGES

- Warming trend through midweek with temperatures pushing upper 90s to near 100 through Thursday. Widespread moderate and major HeatRisk.

- Elevated to Critical fire weather conditions likely Thursday through Saturday due to isolated thunderstorms followed by dry and breezy winds

SYNOPSIS

Dry weather with occasionally breezy winds will prevail through at least midweek. Temperatures will trend warmer in this timeframe with high confidence for widespread moderate and major HeatRisk through Thursday. Increasing moisture in the mid to late week timeframe may bring an elevated threat of thunderstorms. Dry and breezy winds Friday and Saturday will result in elevated to critical fire weather conditions.

DISCUSSION

Tonight through Thursday: A strong upper ridge centered over the south central US combined with a low off the California coast is providing a broad south to southwest flow across the western US. The south to southwest flow will bring continued warming of temperatures on Wednesday, with hot weather persisting into Thursday. Continued light north to northeast winds into Wednesday morning will allow for continued haze and smoke to linger with the highest amounts across Central and Northeast Washington given closer proximity to active wildfires. There is not much in the way of wind given the influence of high pressure through Thursday morning so not expecting any major improvements to the smoke and haze situation through then.

The main weather feature of interest is the low off the California coast which will send an increase in monsoonal moisture up into the region along with a mid level short wave passage on Thursday. Precipitable water values increase to 150-180 percent of normal while 700-500mb most unstable CAPE, as well as surface based CAPE Thursday afternoon increase to as much as 300-700 J/KG. The one missing ingredient is strong mid level forcing. With the low still well off the coast and the best upper level diffluence to the south across Oregon, the forecast is leaning towards isolated coverage of thunderstorms, with the best chances along the East Slopes of the Cascades into the northern mountains, as well as over SE Washington into the Central Panhandle where models indicate the two areas of best instability. Yet would not rule out thunderstorms for any areas. And even isolated thunderstorms are a concern given the hot and dry weather preceding Thursday and dry fuels. Despite the high moisture content in the atmosphere, the quick movement of storms is expected to produce only light rain with storms, further raising concerns for new fire starts.

Friday and Saturday: On Friday a large low from Alaska begins to swing into British Columbia, which will act as a kicker to bring the offshore low into the region as an open wave on Saturday. This transition will bring dry and breezy winds on Friday, followed by an additional wind increase for Saturday as a cold front moves through. This will result in elevated to critical fire weather conditions as west to southwest winds increase to 15 to 25 mph with gusts of 30-40 MPH. A cooling trend will begin to help increase the relative humidity, but yet the increasing winds will be a concern for any new or going fires. No precipitation is expected as this system moves in, except for the Cascade crest with most members from the ECMWF generating at least light precipitation for Stevens Pass.

Sunday through Tuesday: Another low associated with the upper level trough over British Columbia intensifies off the central BC coast on Sunday, potentially sending another weak front across the region on Monday. This will help keep our temperatures in check with highs down in the 80s, which is near to slightly cooler than normal. This should help bring some moderation to the fire weather conditions for early next week. Yet little to no precipitation is expected with this system except for a chance of light showers along the Cascade crest. JW

AVIATION

00Z TAFS: High pressure and light winds will allow smoke and haze to continue across the Inland NW. MVFR conditions will be prevalent across Central and Northeast Washington. Otherwise mid and high clouds will continue to stream into the region from the southwest.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate confidence in the visibility forecast at the TAF sites. JW

----------------------- Confidence descriptors:

Low - Less than a 30 percent chance Moderate - 30 to 70 percent chance High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,

please refer to the Aviation Dashboard on our webpage: https:/www.weather.gov/otx/avndashboard

Preliminary Point Temps/PoPs

Spokane 64 97 65 97 66 94 / 0 0 0 20 10 0 Coeur d'Alene 66 95 67 95 65 93 / 0 0 0 20 10 0 Pullman 59 91 59 91 57 90 / 0 0 0 10 20 0 Lewiston 69 98 69 99 68 99 / 0 0 0 20 20 0 Colville 59 97 62 96 61 94 / 0 0 0 20 20 0 Sandpoint 62 94 63 95 63 91 / 0 0 0 20 10 0 Kellogg 62 91 63 92 61 89 / 0 0 0 20 10 0 Moses Lake 65 99 68 98 64 97 / 0 0 0 20 0 0 Wenatchee 74 100 77 98 69 96 / 0 0 20 20 0 0 Omak 69 101 71 99 68 98 / 0 0 0 20 20 0

OTX WATCHES / WARNINGS / ADVISORIES

WA...Heat Advisory until 9 PM PDT Thursday for Central Chelan County-Lower Garfield and Asotin Counties-Moses Lake Area- Northeast Blue Mountains-Northeast Mountains-Okanogan Highlands-Okanogan Valley-Spokane Area-Upper Columbia Basin-Washington Palouse-Waterville Plateau-Wenatchee Area-Western Chelan County-Western Okanogan County.

Air Quality Alert until 9 AM PDT Wednesday for Moses Lake Area- Northeast Mountains-Okanogan Highlands-Okanogan Valley- Spokane Area-Upper Columbia Basin-Washington Palouse- Waterville Plateau-Western Okanogan County.

ID...Heat Advisory until 9 PM PDT Thursday for Coeur d'Alene Area- Lewis and Southern Nez Perce Counties-Lewiston Area- Northern Panhandle.