Area Forecast Discussion
Issued by NWS Fairbanks, AK
Issued by NWS Fairbanks, AK
503 FXAK69 PAFG 212332 AFDAFG Northern Alaska Forecast Discussion National Weather Service Fairbanks AK 332 PM AKDT Fri Jun 21 2024 .SYNOPSIS... Upper-level ridging extending across northern Alaska will continue to bring warm temperatures and thunderstorm chances across portions of the Interior. High temperatures will hover in the 70s across the Interior through Saturday, with cooler temperatures along the coast. The Eastern Interior will see high temperatures closer to 80 on Sunday and Monday. Isolated to widely scattered thunderstorms across the Interior today become more limited to areas along the Alaska Range and in the Western and Central Interior this weekend. For the North Slope, expect winds to relax this weekend with a reprieve from fog and stratus through Saturday, though they make a return for Sunday and Monday. && .DISCUSSION... Upper Level Analysis... A ridge extends northwest from Western Canada, across Interior Alaska, into the Chukchi Sea, promoting fairly warm and dry conditions across much of northern Alaska this afternoon. There is a weakness in the ridge induced by a strong shortwave trough over the SE Interior and Yukon, providing upper-level support for isolated to widely scattered thunderstorms over the SE Interior. Out west, a second shortwave has stalled along the West Coast, contributing to cloudy conditions with isolated rain showers. Additionally, weak troughing continues to slowly sink southward across the Brooks Range, bringing drier air into the Eastern and Central Interior. Surface Analysis... A thermal trough extends west from Yukon through the far SE Interior into Southcentral Alaska, with a weak extension northward into the Western and Central Interior. Surface high pressure is centered in the Chukchi Sea with a ridge along the Arctic coast. Between these features, generally light northeasterly winds have developed across the forecast area. Some locations in the higher terrain east of Fort Yukon have observed 15 mph winds, while gap winds through the Brooks Range have gusted as high as 25 mph (and should continue to be generally lighter than yesterday). Light winds continue to allow smoke from the McDonald Fire to linger near the surface between Eielson AFB and Birch Lake. An elevated unstable air mass moving in off the Arctic Ocean has brought a reprieve from fog and stratus, instead providing patchy altostratus and even some light rain showers along the Arctic coast. Warm conditions with temperatures in the 70s with dew points in the 40s have allowed for the development of scattered to widespread rain showers and isolated to widely scattered thunderstorms across portions of the Interior. Central and Eastern Interior... Temperatures will peak broadly in the mid to upper 70s again this afternoon/evening across the Central and Eastern Interior. Widely scattered thunderstorms have developed along the high terrain of the White Mountains and Fortymile Country this afternoon and have drifted southwest over the Tanana Valley under the influence of an upper-level shortwave near the Alcan Border. Increased mid- level moisture brought by a series of shortwaves that lifted into the SE Interior yesterday will continue the threat of heavy rain in localized areas from showers and thunderstorms. Rainfall totals of a quarter to half an inch, or greater, will be possible in localized areas. A ridge forecast to build today over the Western Interior will influence the evolution of showers and thunderstorms this evening over the Eastern Interior, with some dependence on timing. Convective activity could be suppressed and storm motion over the Eastern Interior slowed if the ridge builds in quickly through the evening, otherwise, expect showers and thunderstorms to continue to drift southwest off high terrain into the valleys. Northeasterly winds continue to blow across the Yukon Flats and are anticipated to spread southward, with impacts to the direction of smoke dispersal from the McDonald Fire (namely, blowing it away from the Richardson Highway and out over the Tanana Flats). However, there is some uncertainty in how persistent the northeasterly winds will be, as there is some potential for winds to subside significantly overnight and allow dense smoke to once again lower visibility tonight and tomorrow morning along the Richardson Hwy. This weekend, northeasterly flow brings warmer and drier conditions as high pressure remains over the Western and Central Interior. Expecting convective potential to be more limited as a result, with thunderstorms confined primarily to the far SE Interior and Central Interior. High temperatures will approach 80 degrees on Sunday and Monday. Thunderstorms make a return to the Eastern Interior on Monday as a slow moving shortwave trough over Western Alaska ejects eastward. West Coast and Western Interior... Upper-level high pressure builds over the Western Interior today, leading to another day with high temperatures in the 70s for the interior valleys of Western Alaska. Warm temperatures and increased instability will support isolated to widely scattered thunderstorms today and Saturday across the Western Interior as a shortwave trough lingers across Western Alaska. An upper-level low dropping south from the high Arctic will entrain the shortwave, pulling it northeast. This will begin to shift the upper-level high and the warmest temperatures to the east beginning Sunday. Temperatures will therefore cool somewhat along the West Coast for Sunday and Monday, while highs remain in the 70s in the Western Interior. At the surface, a ridge builds into the northern Bering Sea this weekend, promoting stronger westerly flow along the coast. This will increase the potential for stratus/fog along the West Coast heading into next week. North Slope and Brooks Range... An elevated unstable air mass moving in off the Arctic Ocean will continue to bring a reprieve from fog and stratus for the North Slope through Sunday. At the same time, a weakening surface high along the Arctic coast will mean northeasterly onshore flow relaxes somewhat this weekend. Then, an upper-level low drops south from the high Arctic and arrives along the Arctic coast by Monday, leading to a return of fog and stratus, with increased chances for rain/snow showers as well. Along the Brooks Range, isolated thunderstorms are likely to develop each day. Extended Forecast Days 4-7... Expect a warming and drying trend for the Eastern Interior as an upper-level high looks to establish over Southcentral Alaska and Yukon, leading to continued fire weather concerns. A series of upper-level lows near the Arctic coast, over Far Eastern Russia, and in the Bering Sea will help to build and maintain ridging in place through the week. High temperatures next week will likely hover in the 70s and 80s in the Eastern and Central Interior. Out west, there are indications that a low in the Bering lifts north mid- to late-week, bringing southerly to southeasterly winds and elevated chances of precipitation to the West Coast and Western Interior. Southerly gale force winds may also produce elevated surf along south-facing coasts. Thunderstorm potential will extend across much of the Interior initially, before more stable air moves up with the Bering low for the latter half of the week. This will push the bulk of thunderstorm activity into the Eastern Interior. Coastal Hazard Potential Days 3 and 4...None. && .FIRE WEATHER... Temperatures will peak broadly in the 70s across the lower elevations of the Interior today, with RHs generally remaining above 25 percent. Isolated to widely scattered thunderstorms continue this evening as they push slowly southwest off the higher terrain over Interior valleys. Increased mid-level moisture brought by a series of troughs lifting into the SE Interior will lead to the potential of heavy rain from showers and thunderstorms, particularly from Delta Junction south and east, leading to increased chances for wetting rains in the area. Further north and west, storms will be drier with lower probability for wetting rain. A shortwave trough dipping south of the Brooks Range combined with high pressure along the Arctic coast will continue to bring northeasterly winds with drier air spreading southward across the Interior. Gusty winds will continue to be possible each afternoon in and around the Yukon Flats, especially over the higher terrain east of Chalkyitsik, where sustained winds could exceed 15 mph through Sunday, though winds diminish heading into the weekend. Some areas will approach red flag conditions, however there is increased confidence that hot, dry, and windy conditions will not coincide, with temperatures peaking in the low 70s in the area. This weekend, drier air causes RHs across the Eastern Interior to dip well into the 20s. Isolated to widely scattered thunderstorms largely focus over the Western and Central Interior for the weekend, before pushing back eastward for Monday as an upper-level shortwave sitting over Western Alaska becomes caught in the flow of an upper low off the Arctic coast. RHs make a modest recovery on Monday with a shift to westerly flow through the Interior. && .HYDROLOGY... Showers and thunderstorms in the SE Interior may produce heavy rainfall rates of half an inch or greater per hour in localized areas. This could contribute to rapid rises on creeks in steep terrain along the Alaska Range and in the Upper Charlie and Upper Fortymile River Basins this evening. && .AFG WATCHES/WARNINGS/ADVISORIES... AK...None. PK...Small Craft Advisory for PKZ812. Small Craft Advisory for PKZ858. && $$ Quesada