Marine Weather and Tide Forecast for Ponderay, ID

SYNOPSIS
Showers with isolated thunderstorms will dissipate late this evening with clearing skies. This will set up an additional night of frost for the northern valley locations. A wetter storm system widespread rain moves in across the region Monday evening into Tuesday morning.
Breezy with showers Tuesday afternoon with the threat for isolated thunderstorms. The rest of the week will be drier with warming temperatures. Widespread 80s to low 90s for highs by the weekend.

DISCUSSION

Rest of this afternoon through Monday morning: The Inland Northwest is on the back edge of an upper level low pressure system with a cold pool of -25 Celsius extending across the eastern half of the forecast area. Diurnally forced showers will continue into the early evening hours. These showers are expected to die off quicker that yesterday as warmer air moving in ahead of a warm front will erode the cold pool over the region and have a stabilizing effect on the atmosphere. Before this happens however, I do expect isolated thunderstorms to pop up where we have roughly 100-300 J/kg of skinny CAPE across the Northeast Mountains into North Idaho and along the Panhandle/Montana border. Thunderstorms will be relatively weak and pulse type growing just enough to spit out a lightning strike or two before collapsing. Convection will wane between 8-10pm with skies clearing out rather effectively and this will set up the potential for another chilly night across the northern mountain valleys. Dew points will be in the lower 30s and may drop below 30 for some colder pockets with as moisture frosts out of the atmosphere. I see a better potential for frost for the Methow Valley, around Republic, Deer Park, Springdale, Chewelah, Colville, Priest River, Metalline Falls and other cold pockets in this part of the region and have issued a frost advisory that is in effect for tonight through early Monday morning. Make sure to cover sensitive vegetation or bring them indoors to protect from frost damage.

Monday through Wednesday night: The next weather maker is already walking up to the doorstep. An upper level low pressure system spinning in the Gulf of Alaska will direct a robust P-Wat plume of 1.0-1.5 inches into the west coast. This moisture plume is taking shape across the North Pacific between 40-50N latitude riding a 140 mph jet streak at 250 mb. Moist isentropic ascent with the warm front will increase across the region from late afternoon on Monday into Monday evening. All areas will see the potential for wetting rains as our typical rain shadow areas in the lee of the Cascades will be absent with southerly to southeasterly flow will actually result in favorable upslope across the east slopes of the Cascades. There is an 80% chance for wetting rains (at least a tenth of an inch) over the Columbia Basin into the Wenatchee Area, and near 100% chance everywhere else. There is pretty good agreement among the ECMWF Ensemble and GEFS members for a surface low to track into southwest Washington Monday evening and then into north-central Washington around midnight. The low fills in pretty quickly as it tracks inland, but this track is favorable for southerly flow across the Columbia Basin with the northern mountains across eastern Washington likely to do well with ringing out moisture, and then than trend continue across extreme eastern Washington into the Idaho Panhandle as the trailing cold front tracks across during the overnight into early morning hours on Tuesday.
The Northeast Mountains and Idaho Panhandle will see a 90% and higher chance for receiving over a quarter of an inch of precipitation. Those probabilities are a little less into the Spokane Area and Palouse at 70-90% chance; for over a half of an inch of precipitation, there's a 60-75% chance and 30-40% chance respectively, and the North Idaho has a 10% chance for seeing at least an inch of precipitation. Snow levels do drop down to around 6,000 feet by early Tuesday morning over the Cascades with light wet snow expected at the highest peaks; otherwise, it will be rain everywhere else. There will be some pockets of more moderate rainfall especially as the cold front pushes through and creeks and small streams will see rises, but rain will overall be a beneficial sight for an area experiencing drought conditions. This storm system will be the last significant rain that many areas will experience for some time and we could use it as our climatologically driest time of the year, a.k.a summer is coming up.

We transition to showery precipitation in the afternoon on Tuesday and the morning rainfall will prime the pumps for convection with just a little bit of diurnal heating. The atmosphere will become conditionally unstable with a modest cold pool of -21 degrees Celsius at 500 mb. Thunderstorms are expected to begin developing pretty early in the day across much of the region, but higher probabilities in the 20-30 percent chance being across the Palouse, Spokane Area, Okanogan Highlands, Northeast Mountains, and the Idaho Panhandle. Thunderstorms will be pulse type storms featuring occasional lightning, heavy downpours, and brief small hail.
Pressure gradients will tighten as well with breezy westerly winds for the afternoon. Winds will be strongest across central Washington in the lee of the Cascades from Wenatchee/Chelan into the western Columbia Basin with gusts up to 30-40 mph expected. Locally stronger wind gusts with a 20-40% chance of seeing gusts up to 45-50 mph will be possible in the lee of the Cascades around Chelan, Wenatchee, and the Waterville Plateau.

Cloud cover remains over extreme eastern Washington into the Idaho Panhandle on Wednesday with just some lingering showers and winds remaining a little breezy. Temperatures will be below normal through Wednesday, but that will quickly change heading through the latter half of the week.

Thursday through Sunday: There is good consensus from the model ensembles for a ridge of high pressure to be pumped up over the eastern Pacific Ocean. This means high confidence in the far extended portion of the forecast for temperatures warming above normal. Some uncertainty remains with where the ridge axis will set up and this will play a part in how warm we get. There is a 30% chance for moderate HeatRisk to be a factor by next weekend though with a 30-50% chance for widespread 90 degree temperatures by next Sunday into the beginning of the following week for the Columbia Basin, in the Lewiston- Clarkston Valley, at Wenatchee, and in the Okanogan Valley. /SVH

AVIATION
18Z TAFs: The Inland Northwest will be on the back edge of a cold upper level trough of lower pressure today. There will be enough instability across far northeast WA and north Idaho to support a 15-20% chance of lightning. Showers with towering cumulus will be spotty around KGEG, KSFF, KCOE with the better chances and a 30% probability of a passing showers impacting KCOE this afternoon. Lightning activity is expected to remain north and east of the Spokane/Coeur d'Alene corridor. Breezy west-southwest winds into the afternoon with gusts 20 to 25 kts, then decline after 02-04Z.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence VFR conditions at all TAF sites. Low confidence in shower or thunderstorm developing over a given TAF site. /SVH

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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 41 71 47 64 43 65 / 0 0 90 90 40 0 Coeur d'Alene 41 70 49 59 44 62 / 0 0 80 100 70 10 Pullman 39 69 45 59 41 60 / 0 0 90 100 50 10 Lewiston 45 76 53 68 48 69 / 0 0 80 90 40 0 Colville 35 71 41 64 36 68 / 0 0 80 100 80 20 Sandpoint 39 68 46 57 42 61 / 0 0 70 100 90 30 Kellogg 39 71 48 57 43 58 / 0 0 60 100 90 50 Moses Lake 41 72 45 71 41 73 / 0 20 90 40 0 0 Wenatchee 48 69 52 68 49 71 / 0 30 90 20 0 0 Omak 40 72 48 70 42 73 / 0 0 90 80 10 0

OTX WATCHES/WARNINGS/ADVISORIES
WA...Frost Advisory from midnight tonight to 8 AM PDT Monday for Northeast Mountains-Okanogan Highlands-Western Okanogan County.
ID...Frost Advisory from midnight tonight to 8 AM PDT Monday for Northern Panhandle.