textproduct: Juneau

UPDATE

Updated 18z Aviation Section.

LONG TERM

Through the rest of the week and into the weekend, systems will continue to bring rain across the panhandle with little to no breaks between systems. The precipitation amounts are looking to be impactful due to the longer duration of moderate to heavy rainfall. EFIs are showing an increasing trend of confidence of extreme precipitation as the systems move through.

This is also something to keep an eye on moving forward due to indications of it being a potential AR event from Thursday night through Sunday. GEFS and EC AR guidance shows potential for a moderate AR event that will be long duration with a lower peak in IVT. Models still are showing a bit of spread in the precipitation amounts across the panhandle, and are not fully aligned on where the higher IVT values will impact, with the GEFS bringing it more southward to the coast of British Columbia while the EC has it approaching closer to the southern panhandle.

Overall expecting 2 to 3 inches across the northern Gulf coast in 24 hours Thursday, and around 1 inch for the rest of the panhandle. As it moves to impact the rest of the panhandle, Friday into Saturday, the 24 hour totals for the central and southern panhandle will be between 2 and 3 inches as well. The highest rates are expected to be Friday into Saturday afternoon, with areas in the central panhandle (Juneau, Sitka, and Petersburg) having a 40 to 50% chance of exceeding 3 inches by midday Saturday when using the NBM 5.0 and 4.3 probabilities. The southern panhandle, particularly around Ketchikan, may be somewhere to watch closely as guidance begins to narrow down on precipitation values for this time frame, as NBM probabilities show a 60% chance of exceeding 3 inches in 24 hours, a 30 to 40% chance of exceeding 4 inches, and a 15% chance of exceeding 5 inches in 24 hours. The most 24 hour accumulation Friday afternoon through Saturday afternoon is expected to be between 2.5 and 3 inches, though higher amounts may be expected if the IVT values are directed more along the southern panhandle on the 20th.

Winds in these upcoming systems are expected to be at most high end gales, with the majority of the increased winds to be along the outer Gulf coastline, particularly the northern Gulf coast on Thursday night.

AVIATION

Deteriorating conditions expected as a gale force front approaches the coast in the following hours. Mostly VFR conditions enjoyed by most TAF sites look to diminish to MVFR from west to east early this afternoon, followed by IFR conditions in the evening to overnight timeframe. As deep moisture and heavy rain rates are associated with the incoming rain, expecting the low level atmosphere to saturate quickly, bring down both CIGs and VIS to the aforementioned IFR conditions overnight.

LLWS continues to be a concern in the immediate 6 hours and is expected to bump up as the gale force system moves over the panhandle. Winds aloft look to shift from SEerlies to southerly as the front moves through as well. Went slightly pessimistic with wind shear early in the period, but expecting winds to pick up shortly.

MARINE

Outside(Gulf and Coastal Waters): Multiple systems will track across the Gulf through Thursday night. First up will be a Gale force low pushing into the eastern Gulf of Alaska through Thursday mid morning, with sustained winds up to 35kts with gusts up to 40kts. Seas will build to 9 to 12 feet off the coast of Baranof Island westward towards Cape Suckling through late Thursday afternoon. Reinforcing front follows quickly behind through Thursday night, keeping Gale force sustained winds along the coast from Port Alexander westward to Cape Suckling up to 35kts with gusts up to 40kts, with wave heights increasing to 10 to 15ft into early Friday morning. Along the coast, expecting light southerly to southeasterly swell through today, increasing along the Gulf up to 6 to 8 ft, outside of Yakutat Bay up to 8 to 10 ft. Offshore areas, swell turns southwesterly up to 5 to 7ft through late Thursday night into Friday morning ahead of long pattern on-shore flow.

Inside (Inner Channels): As aforementioned systems push into the panhandle, anticipating sustained winds to increase up to 25kts across majority of inner channels with gusts up to 40kts possible through Thursday afternoon,. Winds within Clarence Strait will hold out the longest through Thursday night, up to 30kts. Wave heights should remain around 3 to 5 ft across inner channels, higher near ocean entrances up to 6 to 8 ft.

HYDROLOGY

Light rain continues this morning across the panhandle with most surface observations reporting minor accumulations. Some occasional periods of moderate rain have been reported as heavier periods of rain move over. But the trend of light rain is expected to continue as radar, satellite, and surface observations continue to show the lighter rain trend. Heavier periods of rain are expected to move in later today bringing 1-2" of rain to the NE Gulf coast down the Central Panhandle. The exception to this is the N Lynn Canal area which will likely remain below an 1" of accumulation for today. For the southern panhandle, rainfall amounts for today were reduced to match timing with the guidance and showing most places seeing less than 1" through today. Rainfall amounts were increased for tomorrow for the Southern Panhandle which lines up more with thinking from yesterday in that the heavier solution is more likely. NBM probabilities of exceedance continue to show a growing likelihood of 2 year recurrence intervals being met as well as a growing probability for 5 year recurrence intervals. Left the flood watch in place that was inherited and will let day shift decide in any expansion or modifications will be needed going into today and tomorrow.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Flood Watch from this evening through Saturday evening for AKZ326-328>332. MARINE...Gale Warning for PKZ642>644-651-652-662>664-671-672. Small Craft Advisory for PKZ012-013-021-031>036-053-641-661.