Marine Weather and Tide Forecast for Wenatchee, WA

SYNOPSIS
Warm and dry conditions today with an increasing risk for showers and thunderstorms over the mountains. Warm and windy Thursday leading to elevated to critical fire weather concerns.
The pattern shifts toward the end of the week and into the weekend as a weather system delivers much cooler temperatures, gusty winds, and rain showers for much of the region.

DISCUSSION
Wednesday: It will be another very warm day across the Inland NW with forecast high temperatures topping out in the upper 80s to lower 90s, around 1-2 degrees warmer than Tuesday. One shortwave passed through the region Tuesday night mainly delivering mid and high clouds and a few sprinkles. A slightly deeper wave is approaching from the west and will track through late this afternoon and evening. Cumulus build-ups will be more pronounced across the mountains of the Cascades and Okanogan Highlands this afternoon with a 20-40% chance for cells to develop into showers and thunderstorms. The latest HRRR has a bit more convection developing across Central WA vs previous runs and is supported by several HRRR members. Surfaced CAPE ranges from 300-700 J/kg with a ribbon of 1000 K/kg along the spine of the Cascades. Consequently, we anticipate a few stronger, slow moving thunderstorms to develop over the higher terrain. These slow moving cells will be capable of pockets of 0.1-0.3 inches of rainfall with a 10-15% chance for amounts up to 0.50". This will need to be monitored near sensitive burn scars. The boundary layer over the lower elevations will remain warm and dry so any rain cooled air will bring the potential for gusty outflow winds of 30-45 mph. This is captured in the output from the hi-res models showing small outflow winds of this nature. As these outflow winds expand into the lowlands of Central WA, this may provide enough lift to create new cells around Wenatchee, Moses Lake, Coulee City, and Davenport. The CAPE in these areas does not as robust but enough to have some concern for isolated lightning strikes and additional outflow winds. Any lightning strikes will also remain a concern for new fire starts. Confidence is moderate that lightning activity will be isolated. As the aforementioned shortwave drifts east in the evening and overnight hours, the focus will shift into Northeastern WA and North Idaho with a threat for showers and storms lingering over North Idaho through much of the night.
Southeastern WA and the lower Idaho Panhandle carry the lowest risk (5-10%) for convection today.

Thursday-Sunday: A significant pattern change will arrive through this period. Thursday will be the start of the pattern change with the focus mainly on fire weather as breezy to gusty south to southwest winds develop ahead of a incoming cold front.
Temperatures will cool a few degrees but remain warm with highs still in the mid to upper 80s. Humidity values will continue to dip into the 14-23% range. Sustained winds of 10-20 mph will be accompanied by gusts of 25-30 mph though winds to look very persistent with a well mixed profile to 9-10k ft AGL and steady 15-20kts winds throughout the layer. This will result in elevated to critical fire weather conditions and fire weather watches have been issued given the potential for new or ongoing fires to spread rapidly within our dry fuels.

Fire weather concerns will lower Friday into the weekend as the cold front comes onshore bringing increasing chances for rain, much cooler temperatures, and higher humidity values. Nearly the entire Inland NW has a 60% chance for at least a hundredth of rain. When viewing the chances for a wetting rain (0.10" or more), probabilities drop toward 20% or less for across the lower Columbia Basin but the Cascades, Okanogan Highlands, Northeastern WA, and North Idaho increase to 50-80%. As the low settles over the region Saturday-Sunday, shower chances continue to retreat into the mountain districts and rising terrain of the Columbia Basin around the Palouse and Spokane Area.
Nonetheless, fire indices will be on the downward trend as temperatures cool into the 60s and 70s with afternoon humidity values of 30-50%. The only caveat will be continued windy conditions, especially in the lee of the Cascades, Columbia Basin, and into the foothills of the Blue Mountains and Palouse.
European ensemble means suggest Wenatchee winds will increase each day from Friday through Sunday.

Monday-Wednesday: There is moderate confidence for the heat to remain subdued heading into next week with some degree of weak troughing over the Northwest. The details are still being sorted out in the models to the depth of the trough and reinforcing shot of cooler air coming from the Gulf of AK but general consensus amongst the ensembles support below normal temperatures and continued chances for mountain showers. This will come with periodically breezy conditions as well. /sb

AVIATION
18Z TAFs: As of 1730z isolated showers and thunderstorms were already developing along the East Slopes of the Cascades. A shortwave will move into the region Wednesday afternoon/evening supporting expanding convection into the northern mountains as well. As the cells travel off the higher terrain, gusty outflow winds will be possible within the lower elevations of Central WA. Greatest concern will be in proximity of KEAT, KMWH, KOMK, and KCQV 21-03z. These sites come with a 10-20% chance for new cells to develop along the outflow winds.
Some hi-res models hint at lesser impacts at KGEG-KSFF 03-06z but still some impacts from decaying outflow winds and a small threat (~15%) for showers. A bulk of the shower and t-storm threat will retreat into North Idaho 6-12z.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in VFR conditions at all terminals through the forecast period.
Greatest uncertainty is coverage of showers and t-storms over Central and Northern WA and how outflow winds will spread into the Basin. Some hi-res models showing brief gusts of 35kts with this activity and high-based cells developing between KEAT-KGEG.
JW

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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 90 57 86 53 68 48 / 0 20 10 10 80 80 Coeur d'Alene 89 59 85 55 66 49 / 0 20 10 10 90 80 Pullman 86 54 82 50 66 45 / 0 0 10 10 80 50 Lewiston 94 62 91 60 73 53 / 0 0 10 20 90 60 Colville 90 54 87 50 69 42 / 10 20 20 20 80 90 Sandpoint 87 56 84 52 64 46 / 0 20 20 10 90 90 Kellogg 86 57 82 54 64 48 / 0 20 10 10 90 80 Moses Lake 95 60 89 55 76 48 / 0 20 0 10 30 40 Wenatchee 92 65 86 60 73 54 / 20 20 0 20 50 30 Omak 94 60 89 58 74 49 / 20 20 10 10 60 80

OTX WATCHES/WARNINGS/ADVISORIES
WA...Fire Weather Watch from Thursday afternoon through Thursday evening for Colville Reservation (Zone 702)-Eastern Columbia Basin -Palouse -Spokane Area (Zone 708)- Foothills of Central Washington Cascades (Zone 705)-Lower Palouse -Snake River (Zone 709)-Okanogan Valley (Zone 703)-Waterville Plateau (Zone 706)-Western Columbia Basin (Zone 707).
ID...None.