Area Forecast Discussion

KEY MESSAGES

- Scattered showers along the northern Washington mountains, and North Idaho Panhandle Tuesday. - 20 to 40 percent chance of showers and thunderstorms Thursday night into Friday over Southeast Washington and the Central Panhandle mountains.

- Warmer temperatures Wednesday through Sunday with afternoon highs in the mid 70s to low 80s.

SYNOPSIS

Cool temperatures will continue Tuesday with scattered showers over areas of higher terrain. Temperatures rebound into the 70s and 80s Wednesday through Sunday with mainly dry conditions. Southeast Washington and the Central Panhandle mountains will be the exceptions with a 20 to 40 percent chance of showers and thunderstorms Thursday night into Friday.

DISCUSSION

Today through Wednesday: An upper level trough developing over British Columbia will swing south through the area later this (Tuesday) morning through the afternoon. It will bring light rain showers to the Cascades, northern mountains, and northern Idaho Panhandle. Places such as Omak, Colville, Chelan, and Bonners Ferry have a 20 percent chance and above at seeing 0.10 inches of rainfall from Tuesday through Wednesday morning. Forcing associated with the incoming low combined with modest instability (a couple hundred J/kg of CAPE) will support a 10 to 15 percent chance of thunderstorms across areas receiving rain. Soundings show saturated mid and low levels (RH values greater than 80 percent), and PWATs near 0.7 inches. This indicates that main threats with any thunderstorms will be isolated heavy downpours. Elsewhere, expect dry conditions.

By Wednesday, the low will shift southward and retrograde slightly eastward. Rising heights downstream of a ridge off the Canadian coast will promote a warming and drying trend over the Inland Northwest. Temperatures on Wednesday will be in the mid 70s, which is right around normal for this time of year. No precipitation is expected.

Thursday through Monday: The aforementioned low will then begin weakening and moving northeastward. While much of the forecast area will continue seeing a drying trend, the low will brush far southeast Washington and the central Idaho mountains Thursday night into early Friday morning. Main areas impacted will be the Lewiston and Camas Prairie areas. A 10 to 20 percent chance of thunderstorms will accompany these light rain showers. While PWATs will still be high, mid and low level moisture will be lower than on Tuesday, and DCAPE values will be near 1000 J/kg. This suggests that the main threat with these thunderstorms will be gusty outflow winds.

After this low weakens and moves completely out of the forecast area, high heights will dominate the weather pattern, bringing a warming and drying trend through the weekend starting on Thursday. Temperatures will progressively rise through the weekend, with mid range guidance showing high temperatures reaching the 80s by Sunday. After the brief showers Thursday into Friday, the forecast area sees near zero chances of precipitation through the weekend. Cluster analysis unanimously supports this warming and drying trend through Sunday. Beyond Sunday, however, cluster analysis lowers slightly, though 75 percent of clusters broadly show a low pressure system approaching the coast. There is little agreement on track, strength, and placement, but this does hint at a potential return to unsettled weather next week. /AS

AVIATION

06Z TAFS: All terminals have improved to VFR and are expected to stay that way through the forecast period. A low dropping into the area tomorrow brings a small chance of rain (HREF shows around 10 to 20 percent) at GEG, SFF, and COE around 20Z. MWH and EAT see chances of rain earlier - around 16Z. EAT has the highest chances of seeing some rain showers, and these are included in the TAF. There is a small chance of patchy fog and lowered ceilings Tuesday morning. While HREF/RRFS probabilities don't support it, some BUFKIT soundings show a saturated enough surface to support fog. There is not enough confidence to include fog at specific terminals.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate to high confidence in widespread VFR conditions returning through the forecast period. Low confidence in patchy fog and lowered ceilings, which is the highest impact alternate scenario and would require amendments. /AS

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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 47 65 47 73 49 77 / 0 0 10 0 0 0 Coeur d'Alene 45 65 45 72 46 77 / 0 0 10 0 0 0 Pullman 43 66 44 73 45 73 / 0 0 10 0 0 0 Lewiston 48 72 51 77 53 78 / 0 0 10 0 0 0 Colville 46 66 43 77 42 81 / 10 30 10 0 0 0 Sandpoint 46 64 44 72 42 77 / 0 10 10 0 0 0 Kellogg 43 64 44 71 45 76 / 0 0 10 0 0 0 Moses Lake 46 67 47 75 47 79 / 0 10 10 0 0 0 Wenatchee 52 65 50 74 53 80 / 0 20 10 0 0 0 Omak 52 66 48 76 48 80 / 10 40 10 0 0 0

OTX WATCHES / WARNINGS / ADVISORIES

WA...None. ID...None.