A ridge of high pressure continues to dominate weather conditions across the Pacific Northwest, with many locations above 100° Saturday afternoon and a few places around the Tri-Cities getting around 110°.
For several days, weather models had shown significant cooling Monday and beyond, but as we’ve gotten closer it now appears that the weather may not improve until Tuesday. This has prompted the National Weather Service to extend the excessive heat warning to last through Monday.
The culprit behind this change is how models handled a shortwave trough on its way here from Kamchatka. As it dips south through British Columbia, earlier forecasts had it moving far enough south to bring a cutoff low in the Pacific toward the region to bring cooler weather to the Columbia Basin.
Now it appears that this will not be the case, leaving the low well offshore and the Tri-Cities plenty hot heading into the start of the week. The trough in British Columbia may still help to moderate temperatures some, but look for a high around 105° for Monday and near 100° Tuesday.
Beyond Tuesday, models have significant disagreement on what the low offshore will do making it hard to determine how good the midweek cool down will be. Regardless, the ridge is likely to weaken somewhat allowing for more westerly flow and bringing cooler temperatures across the Cascades.
Breezy conditions are likely during the afternoons to start the week, increasing fire risk. Temperatures are expected to modestly cool, but not enough to bring relative humidity values above fire danger thresholds. In and to the south of the Blue Mountains fire danger from possible dry thunderstorms exists.
The National Weather Service has highs in the mid 80s Wednesday and Thursday. This is certainly the current best guess for the time period, but there is very little model agreement and it is possible that highs stay closer to average (93° at the Tri-Cities).
Any relief that comes isn’t expected to last long. Confidence is increasing for another heatwave beginning as early as next weekend and into the beginning of next week.
