Area Forecast Discussion
Issued by NWS Juneau, AK

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000 FXAK67 PAJK 202243 AFDAJK Southeast Alaska Forecast Discussion National Weather Service Juneau AK 243 PM AKDT Tue Apr 20 2021 .SHORT TERM.../Through Wednesday night/...An extensive marine layer present along the outer coast early today largely diminished by late morning. Farther inland, broken to overcast conditions gave way to sunny skies by this afternoon. Clouds over the eastern Gulf continue to flow west towards the outer coast, but have the appearance of a more convective environment rather than a stratiform marine layer. Higher up in the atmosphere, mostly cloudy conditions at the start of the day gave way to partly cloudy or even sunny skies. Current forecast calls for mostly cloudy skies north of Frederick Sound tonight, but satellite imagery shows the present cloud deck to be somewhat thin. This could result in another night with a large diurnal spread and overnight lows in the low to mid 30s. Complicating this, models are indicating a short wave dropping southeast out of the interior and the Yukon later tonight. Models are in good agreement that this feature will contain some measurable precipitation. This feature can be seen easily on IR satellite imagery, but current visible channel imagery shows the corresponding colder clouds to be rather thin and not very representative of precipitation bearing clouds. The afternoon forecast issuance reflects the idea that models are correct, but no precipitation being reported where those clouds currently are does not instill a sense of confidence. If, in fact, the precipitation does happen as modeled, the outcome could likely be snow for White Pass. Other locations are not expected to get cold enough for snow before the short wave passes into British Columbia. In the wake of this short wave, strong high pressure over the interior will build southeast in the Yukon and create a stiff northerly pressure gradient over the far northern inner channels. Have included small craft advisories for Lynn Canal, Stephens Passage, and southern Chatham Strait for tomorrow as a result. Clearing skies early tomorrow should provide for slightly warmer daytime highs in spite of the weak cold air advection that will accompany the short wave tonight. .LONG TERM.../Thursday through Tuesday as of 10 pm Monday evening/...A large blocking ridge over the eastern Pacific extending into the Northwest portion of Alaska continues Thursday. Part of an upper level (500 mb) low, south of the central Aleutians, slides southeast. As it does, the low continues to move southeast of the CONUS into Saturday. The upper level ridge repositions to extend from the north central pacific, through the gulf to Alaskan interior for Sunday and Monday. The pattern Monday starts to look more chaotic as another low from the Bering moves into the western gulf. With the blocking pattern in place aloft, the forecast for SEAK is expected to be dry. There may be a possibility of rain around Friday night/early Saturday from a low in the gulf, or maybe some drizzle along the coast from the marine layer on Wednesday. Although conditions remain dry, sky cover may not remain as clear. A marine layer is expected to push into Southeast Alaska Tuesday night into early Wednesday. With this, temperatures are expected to be cooler. Seasonal normals include Highs in the 50s to 60s. The marine layer is expected to move offshore or be eroded by Thursday and late Thursday into weekend as the potential for sunshine returns. This being said don`t think the temps will push back to the warmth of the last couple days for SEAK. Did not need to make many changes to the forecast package. Forecast confidence is average to above average as a more stable forecast pattern develops. && .AJK WATCHES/WARNINGS/ADVISORIES... PUBLIC...None. MARINE...Small Craft Advisory for PKZ012-013-031-033-041>043-051-052. && $$ FCF/CDC/Bezenek Visit us at http://www.weather.gov/Juneau

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