Sunrise 6:01 AM   Sunset 7:58 PM Moonrise 2:44 PM   Moonset 3:49 AM

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FXUS66 KOTX 191106 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 406 AM PDT Fri Apr 19 2024

SYNOPSIS
Dry weather conditions will be in place through Saturday. Winds will be breezy from the northeast. A strong cold front arrives early Sunday morning ushering gusty westerly winds and chance for showers. Mild and dry weather returns for the start of work week.

DISCUSSION
Today through Saturday: The remnants of an expansive low pressure system that stretches from Ontario to the Pacific NW will begin to moderate today as high pressure inches closer to the WA Coast.
500mb temperatures warm nearly 10C today basically eliminating any threat for afternoon showers. The main weather impact for the next 24 hours will be breezy northeasterly winds. Offshore pressure gradients between Kalispell, MT and Portland, OR are already near 11 mb and expected to range between 11-15 mb through tonight. This is in response to cooler Canadian air sliding down the Continental Divide creating surface high pressure and warmer air nosing along the CA/OR coastline creating thermally induced lower pressure. Strongest winds will be found through the Purcell Trench and across the Columbia Basin with speeds up to 20 mph and gusts to 35 mph. Exposed ridgetops of Northeastern WA and North Idaho can expect similar speeds. Winds will weaken going into Saturday with a slow shift back to the southeast and then south as the next cold front approaches. Saturday will deliver another day of dry conditions with plenty of sunshine as the ridge axis passes through the Inland Northwest promoting stable weather conditions. Temperatures today (FRI) will be several degrees warmer, especially for NE WA and N ID which experienced quite a bit of shower activity on Thursday. Afternoon highs will be in the upper 50s to mid 60s. On Saturday, widespread 60s return with areas along the Snake River Valley creeping into the lower 70s.

Saturday night - Sunday: A robust shortwave and associated cold front will swing through the region ushering windy conditions and chance for showers. This is well agreed upon amongst the forecast models with subtle differences with the speed/timing of the front.
General timing brings the cold front toward the Cascades around midnight and to the ID/WA border around 3AM. This is likely to bring a sharp increase in winds overnight with sustained speeds of 20-30 mph and gusts 30-40 mph. I am more confident with the sustained winds given the strength of the front and strong cold air advection. Would not rule out gusts 40-50 mph for some wind prone areas and exposed benches and ridgetops but right now, a bulk of the winds aloft are closer to 30-35kts which good news and a limiting factor for gusts over 40 mph. In the past, these type of fronts can be impactful due to the sharp increase in winds.
Typically, the strongest speeds only last 1-2 hours with these nocturnal events but this is not to say it will not remain windy through the day Sunday as wind speeds persist in the 15-25 mph range with gusts around 30 mph. Added patchy blowing dust to the Western Basin for early Sunday morning yet this comes with low confidence. Would not rule out minor tree damage (small branches)
and a few power outages. Potentially the biggest impact will be light weight objects blowing around like garbage cans, lawn furniture, and trampolines. Be sure to secure those patio umbrellas before heading to bed on Saturday!

The front will not bring much in the way of precipitation with amounts ranging between a trace and tenth from the lee of the Cascades to the Palouse and Camas Prairie. The Bitteroots and Selkirks carry a greater chance for a tenth or more with probabilities around 40% for at least 0.10". Numerous showers will also be intercepted along the immediate Cascade Crest where amounts could vary from 0.25-0.60". Snow levels will come crashing down as well falling to 3000 feet before sunrise Sunday morning with slushy accumulations possible over Stevens Pass. The best chance for precipitation over the Basin-Palouse will come with the frontal passage early Sunday morning. Showers will continue for the Cascades Crest, Northeastern WA, and North Idaho into Sunday afternoon.

Monday through Thursday: High pressure returns to the region early in the work-week bringing another period of warming and drying.
Temperatures for Monday morning will likely start off cool with temperatures in the lower 30s and potential for freezing temperatures. Temperatures rebound into the 60s by the afternoon and continue to warm into Tuesday with many more locations across the lower Columbia Basin showing increasing odds for 70s. Winds will be lighter. The next Pacific trough arrives middle to late week with yet another change in the weather pattern toward cooler and unsettled. There are considerable differences with the evolution of the next trough. Leaning toward an arrival closer to Thursday-Friday but this will fine tuned over the coming days. As we transition air masses, winds are likely to become breezy conditions and precipitation chances will return. /sb

AVIATION
12z TAFS: A tight northeast pressure gradient will result in gusty northeast winds down the Purcell Trench and over the Columbia Basin. Expect gusts of 20-30 kts for KSZT-KDEW-KCOE-KGEG- KMWH on Friday. Shortwave ridging into region for Friday will result in less cloud cover and VFR conditions.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high confidence in VFR conditions through the TAF period.

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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 56 34 64 39 57 33 / 0 0 0 30 10 0 Coeur d'Alene 54 33 63 38 54 32 / 0 0 0 50 20 0 Pullman 56 33 64 37 52 33 / 0 0 0 30 10 0 Lewiston 64 36 71 43 60 38 / 0 0 0 20 0 0 Colville 56 26 63 35 57 30 / 0 0 0 50 20 0 Sandpoint 51 34 59 38 52 32 / 0 0 0 70 40 10 Kellogg 51 32 62 39 50 34 / 0 0 0 60 30 10 Moses Lake 63 37 69 40 62 34 / 0 0 0 20 0 0 Wenatchee 60 37 63 41 59 37 / 0 0 0 20 0 0 Omak 61 34 65 40 62 35 / 0 0 0 30 10 0

OTX WATCHES/WARNINGS/ADVISORIES
ID...None.
WA...None.

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