Area Forecast Discussion
Issued by NWS Juneau, AK
Issued by NWS Juneau, AK
417 FXAK67 PAJK 182325 AFDAJK Southeast Alaska Forecast Discussion National Weather Service Juneau AK 325 PM AKDT Wed Sep 18 2024 .SHORT TERM.../Through Thursday night/...Post frontal showers will prevail through this short term forecast period. As the remnants of the front cross into Canada, gusty winds over the northern inner channels will ease, but low level onshore flow will persist through the period before backing to the southeast in advance of the next front. Overnight lows through Thursday night will be getting down to the lower 40s, so no frost concerned yet. With the growing season behind us now, no frost or freeze warnings will be issued, so pay attention to overnight lows lest your late season outdoor plants get inadvertently damaged. Near White Pass, overnight lows tonight and tomorrow should be getting low enough that a mix of rain and snow is possible, though no accumulation is expected. Daytime highs in the mid to upper 50s forecast for tomorrow. .LONG TERM... Key Points: Multiple lows impact the Panhandle through next week bringing wind and rain. Most rainfall expected in the far southern region. Potential break in rain Sunday. For rainfall details see Hydrology section. Early Friday a long wave trough will be departing the Panhandle moving into western Canada, shutting off support to the surface low positioned in the Gulf. With the loss of reinforcing dynamics, expect the pressure gradient to weaken, allowing winds and rain to diminish into Friday afternoon. This break will be short lived as an extensive jet drops south of our region allowing multiple embedded shortwave troughs to rapidly move into the Panhandle. Current forecasts reflect a surface low associated with each of these features, bringing elevated wind Friday into Saturday and potentially Sunday. Snow levels are dropping but no impacts expected at this time. While the Panhandle is impacted by these lows this weekend, a broad open long wave trough will begin to move into the Gulf. Associated with this feature will be a 980 to 985mb surface low. While the low takes residence near Cook Inlet Sunday the pressure gradient will tighten over the Panhandle with winds increasing out of the south again. && .AVIATION...Flying conditions for the panhandle today have varied depending on location. Some places continue to report IFR conditions while other locations have improved to VFR while others are still experiencing MVFR CIGs. CIGs are expected to improve during the evening and overnight hours as showers continue to dissipate. There is the potential though that fog could develop during the overnight hours with the clearing skies. So that is something to be mindful of as we head into the overnight hours. && .HYDROLOGY...Multiple rounds of heavy rainfall through the next 7 days. SPS issued for Friday into Saturday in the south. First round, Friday into Saturday: Long range guidance is still flip-flopping on location, extent, and magnitude of an Atmospheric River (AR) that will be carried by the jet stream for this weekend. Current ensemble prognosis indicates a weak AR event with some outliers reaching moderate. With that said, guidance the ECMWF extreme forecast index continues to shift this first AR north a touch from Hecate Strait/Haida Gwaii; simply put, heavier rainfall is becoming more of a reality in the southern Panhandle, potentially breaking some record 24 hour values with rivers responding region wide. No flooding is anticipated at this time. Second round Monday into Tuesday: As a broad longwave trough positions itself in the western Gulf Monday and Tuesday, the jet axis will become positive, which will steer a more potent atmospheric river into the Panhandle. Guidance is showing some agreement that this could be a moderate to strong AR with most rainfall expected in the central and south. ECWMF EFIs are highlighting a significant shift from climate normal over most of the Panhandle with further trend analysis required over the next few days. Simply put we could see a more significant rainfall event Monday and Tuesday. && .AJK WATCHES/WARNINGS/ADVISORIES... PUBLIC...Strong Wind until 10 PM AKDT this evening for Akz018-319. MARINE...Small Craft Advisory for PCs-013-022-031-053-641>644-651-652- 661>664-671-672. && $$ SHORT TERM...Fritsch LONG TERM....AP AVIATION...SF HYDROLOGY...AP Visit us at http://www.weather.gov/Juneau