FastCast—Thursday, June 2 to Sunday, June 5:
Wednesday was an odd day…with total cloud cover accompanying highs in the low 70s. Some showers were added to the mix as a weak system moved through this afternoon. That will be the same story for Thursday, except temperatures will be slightly warmer, in the low to mid 70s. Expect full cloud cover like Wednesday, and expect muggy conditions, with dewpoints in the upper 50s to low 60s. These conditions are due to another weak system moving through the region. This system will capitalize on the warmth and mugginess to produce instability across the area, with the most in the foothills and over the Cascades. The NWS has introduced a 30-50% chance of thunderstorms across most of the lowlands from Thursday afternoon, through the night, and into early Friday morning. With any showers that develop, be prepared for heavy rain and potential lighting & hail. More showers (with a lesser chance of thunderstorms) are possible on Friday. Highs on Friday will be much cooler, in the low to mid 60s. Showers on Thursday and Friday will bring 0.1-0.4 inches of rain around the region, with the highest amounts only where stronger showers develop. Expect a break in the weather on part of Saturday, before rain arrives in the afternoon. A stronger system will impact the area from Saturday afternoon to Sunday evening, bringing widespread rain and another slight chance of thunderstorms. Expect weekend precipitation to be around 1-1.5 inches for the lowlands. Temperatures will be cool, with highs in the low to mid 60s and lows in the upper 40s to mid 50s. Stay tuned for more information about the weekend weather.
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The combination of warm temperatures, high dewpoints, and generally muggy conditions will fuel a chance of thunderstorms around Western Washington from Thursday afternoon to Friday morning. The UW model below shows CAPE (instability) levels at 6 PM Thursday.
CAPE values will reach 600-800 over the Cascades and parts of E. WA/OR, and will be in the 200-500 range in the foothills. Both these numbers are quite respectable for the Pacific Northwest. There is even a chance of severe thunderstorms in NE Oregon on Thursday, including in the Pendleton area.
One aspect of instability is the temperature, as instability can’t develop when the temperature is too chilly. That won’t be a problem on Thursday, as seen in the HRRR high-resolution temperature forecast for Thursday afternoon.
Thursday’s highs will likely reach the low to mid 70s across the lowlands. There is a slight chance of temperatures reaching the upper 70s in the lowlands, but this will likely be hindered by cloud cover. The coast won’t even get near the mid 60s, but Eastern Washington will soar into the low-mid 80s!
An interesting aspect of this thunderstorm setup is that instability-inducing conditions will remain overnight Thursday into Friday. This is seen in the HRRR high-resolution forecast for dewpoints at 9 PM Thursday.
Around dusk, dewpoints will still be in the upper 50s to low 60s across the Puget Sound area.
The UW forecast below shows instability (CAPE) at 10 PM Thursday. Around this time, instability has actually moved further into the lowlands than earlier in the evening.
Values of 200-400 are observed over the lowlands. This is definitely enough for thunderstorms in Western Washington.
From Thursday afternoon to Friday afternoon, there is a chance of thunderstorms around Western Washington. The highest chance is in the foothills and mountains, but be prepared all around the region for lighting, heavy rain, and potential hail and gusty winds.
Additionally, areas shaded in dark green on the NWS Spokane map below are under a Flash Flood Watch through late Thursday night.
This alert has been issued due to burn scars in North Central Washington. Anytime thunderstorms or heavy rain falls on a burn scar, there is a chance for debris flows and flash floods because burn scars can’t absorb rain.
Stay tuned for more information about the active (and quite wet) weekend that is coming up!
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