What the forecast actually says — NWS Area Forecast Discussions, decoded into plain English.
Area Forecast Discussion · National Weather Service Fairbanks (AFG) · issued Thursday, September 10 at 2:49 PM AKDT.
Revised in 31 passages since the 5:35 AM discussion. See every revision.
Synopsis
A strong coastal storm pushing into the Chukchi Sea will be the primary driver of inclement weather conditions for the next few days. Strong winds and onshore flow along the Bering and Chukchi coastlines will continue to produce high surf and coastal erosion through Friday afternoon. Meanwhile very heavy rainfall associated with an atmospheric river will take aim on the West Coast and western Brooks Range tonight and early Friday with the heavy rain threat slowly shifting east towards the Interior by the weekend.
Messages
Central and Eastern Interior. Continued cool and damp conditions are expected across much of the Interior for the next few days. Highs will be a tad bit warmer Friday (generally 50's and lower 60's) before dropping back into the 50's over the weekend.
A warm front associated with a storm in the Chukchi will continue to bring widespread precipitation to the Interior through this evening with rain tapering off by Friday morning.
A second wave of precipitation will push into the region later Friday and continue into parts of Saturday as a cold front associated with the Chukchi low moves eastwards. This feature will also tap into an atmospheric river, so rainfall may be heavier in some locations. Additional rainfall amounts through the weekend could range from 0.50" to 1.50".
By early next week, another low is expected to move into the Bering Sea and bring additional chances for rain and gusty winds across the Central/Southern Interior, especially for the Alaska Range.
West Coast and Western Interior. High Surf Advisories remain in effect through late Friday night along the coast from the Yukon Delta to Kivalina for water level rises around 2 to 5 feet above the normal highest high tide line.
High Wind Warnings remain in effect through Friday afternoon for St. Lawrence Island and the Bering Strait for wind gusts up to 65 mph.
Short Term
A potent coastal storm continues to unfold along the west coast of ALaska as well as along the Northwest Arctic Coastline as a strengthening surface low slowly emerges from Russia's Chukchi Peninsula into the Chukchi Sea proper near Wrangel Island tonight. The upper atmospheric pattern remains unchanged with an associated upper trough over the Chukchi region while an anomalously strong Pacific ridge extends into the northern Gulf of Alaska. This setup lends high confidence to the eventual path of the surface low as models all agree on an eastward progression across the southern Beaufort over the next several days.
Sensible weather highlights for the rest of today and into tonight will still focus on strengthening southwest flow through the Bering Strait and into the southern Chukchi. This wind direction represents mostly onshore flow for west coast communities leading to much higher than normal water levels through tonight and into parts of Friday. Several High Surf advisories along with High wind Advisories and Warnings will remain in effect through Friday as a result.
Aside from the short term wind concerns, there is also a threat for very heavy rainfall. A warm frontal boundary that has advanced from the west coast through the Interior the past 24 hours has continued to prime the area with widespread moderate rainfall. Southwest flow aloft will tap into an atmospheric river which will focus a band of heavy rainfall from the Seward Peninsula through the western Brooks Range and up onto the western North Slope tonight and Friday. Storm total rainfall amounts will range from 0.50" to 1.00" regionwide with the highest rainfall amounts expected in the Southern Seward Peninsula, south slopes of the Western Brooks Range, and the Kobuk/Noatak/Wulik River Valleys. In these areas, rainfall amounts will range from 1.50" to 2.50" with locally higher amounts nearing 2.75" to 3.50" possible across the higher terrain due to strong upslope flow. Hydrologic concerns across this area will continue through the early weekend as runoff and saturated soils could play a role inn some localized flooding. Additional information on this is found below in the Hydrologic section.
This atmospheric river will shift eastwards towards the Central and Eastern Brooks Range as well as much of the Interior for Friday evening into Saturday. Additional moderate will fall in these areas as well as the weekend gets underway. In general, additional rainfall amounts of 0.10 to 0.50" can be expected in these areas as the cool damp conditions of the past several days continues. However, some drying could set in, especially for the Interior by late in the weekend.
Meanwhile the tail end of the weekend will not be as pleasant along the eastern Arctic coastline as the remnants of the original surface low over the Chukchi advances eastwards. While models are all in agreement that this system will result in additional precipitation across portions of the North Slope, there are disagreements on the intensity of the surface winds, especially near the coastline. While it is too early for any headlines, the potential for high winds from Utqiagvik to Kaktovik will exist Sunday into early Monday as a potential coastal low-level jet sets up near the coastline.
Long Term
Our extended period begins on Monday with an arctic low north over Alaska, and low pressure system moving north into the Bering Sea. As the Bering Sea low progresses north it will force a ridge east over Alaska by Tuesday morning. Tuesday evening through Wednesday morning, the Bering Sea low will strengthen as it begins to approach the West Coast. Wednesday morning the arctic low's flow will get wrapped into the Bering Sea low, which will deepen the cyclone, and strengthen it before it moves through Alaska on Wednesday afternoon. As the storm travels across Alaska throughout Wednesday it will travel northeast up the ridge leaving our area Thursday morning.
Model guidance has shown a greater confidence and alignment in the Bering Sea low's track, as well as the atmospheric river associated with these systems. Guidance shows the Bering Sea low progressing north through the Bering Sea, and then moving east towards Alaska. During this time, guidance has suggested that the atmospheric river, that previously was directly headed for our area, will now instead trend east and be caught within the pacific highs flow. Which as a result, directs the heaviest amounts of atmospheric moisture east away from our area. Although there is enough evidence to see a diminish in the moisture supply with this storm, the Bering Sea low still will likely hold a substantial amount of atmospheric moisture within its core as it tracks towards Alaska.
Due to the previous moisture that was supplied by the atmospheric river, this storm has the potential to produce a substantial amount of rainfall for majority of the Western Interior, and YK-Delta. There is a chance for the South/Central Western Interior receiving rainfall accumulations up to a total of 2 inches Wednesday through Thursday, with the West Coast seeing amounts anywhere between 0.5 to 1 inch. As this storm rides up the ridge over the eastern portion of Alaska, the cyclones circulation can shift to a more southerly trend. If this occurs, the remaining amount of moisture will likely be downsloped, and light to moderate rainfall accumulations would impact the Eastern Interior Wednesday through Thursday. However, there is general uncertainty in all of these rainfall totals, and will continue to be monitored through the week until higher model confidence is demonstrated.
Throughout the extended, wind gusts are expected with this upcoming storm. When the low approaches the Bering Sea Monday through Wednesday it will form a pressure gradient with the sustained ridge over Alaska. This pattern supports development of a 925 mb Jet, and as the northern low's arctic air gets wrapped into the Bering Sea low, chances for these winds to mix down to the surface increase. If this pattern persists, the YK-Delta, Southwestern Interior, West Coast, and Alaska range may experience another round of gusty winds Wednesday morning. Exact wind gust speeds still need to be monitored but at this current solution, models are suggesting the Yk-Delta, West Coast, and Southwestern Interior seeing gusts between 30 to 40 mph Tuesday through Thursday. If the Bering Sea low supports southerly flow on its approach to Alaska Tuesday through Wednesday, gusts could potentially reach warning criteria along the Alaska Range, specifically within Isabel and Windy pass. However, there is discrepancy on the low track through the Interior.
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