Area Forecast Discussion
Issued by NWS Juneau, AK
Issued by NWS Juneau, AK
209 FXAK67 PAJK 191314 AFDAJK Southeast Alaska Forecast Discussion National Weather Service Juneau AK 514 AM AKDT Thu Sep 19 2024 .SHORT TERM...Post frontal showers will continue through mainly Thursday morning before clearing north to south through the day. Looking at satellite, the low responsible for generating much of yesterday`s showers has largely disintegrated. While numerous to widespread showers are still present, expect these to diminish quite rapidly over the course of the day. The deepening trough upstream from the incoming low on Friday, discussed in the long term section, will promote upper level ridging near the NE gulf coast. From this ridging, mid level drying and clearing will spread from north to south down the panhandle as the ridge strengthens. Therefore, main changes to the forecast included decreasing PoP across the CWA. Furthermore, due to lack of forcing, reduced winds across the inner channels tonight to 10 knots or less. Finally, introduced widespread fog across the panhandle. .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...Showers are the rule of the morning for just about the entire panhandle this morning. So far VFR or MVFR conditions prevail though some brief periods of IFR in heavier showers are being observed. The lowest conditions are along the outer coast and up against the coast mountain range. Winds have quieted down overnight with the Skagway area still seeing some gusts to 30 kt. Improving conditions expected today as showers diminish and exit the area from NW to SE. Expect mostly VFR conditions by this evening and into tonight though some areas could see fog develop late with the accompanying IFR vis and ceilings. Conditions expected to deteriorate again Friday as the next system begins to move into the area. && .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...None. MARINE...Small Craft Advisory for PKZ012-022-053-641>644-651-652-661>664- 671-672. && $$ SHORT TERM...NC LONG TERM....AP AVIATION...EAL HYDROLOGY...AP Visit us at http://www.weather.gov/Juneau