textproduct: Juneau

SYNOPSIS

Key Messages:

- Quieter weather for the first part of the work week with light rain showers possible and potential for overnight fog.

- A fast moving low moving just south of the panhandle will bring a period of moderate rainfall Tuesday for the southern panhandle.

- A larger, impactful system to move into the Gulf midweek and impact SEAK by late week, bringing moderate to heavy rain and elevated winds.

LONG TERM

Thursday morning sees the beginning of a stronger atmospheric river move into the area. Some rather impressive dynamics look to be associated with this storm, with strong initial warm air advection, and relatively cold air advecting eastward. These ingredients coupled with sea surface temperatures still around the mid 50s means that the environment leans more towards the convective. Furthermore, a strong jet aloft with plenty of divergence behind the warm front sets the stage for meso vertices forming along the front. These cause a number of issues: timing, location, and intensity of rainfall and highest winds can shift drastically. Individual model runs tend to struggle with these environments, with run to run consistency of both the GFS and EC inconclusive on individual features. Ensemble guidance provides a clue on the location of highest wind speeds and rainfall however. At this point, the southern half of the panhandle has the highest likelihood of longer duration, heavier rainfall. The specifics regarding the hydrology portion of this storm are noted in the hydrology section.

Looking towards the weekend, there is roughly a 60-40 split of active weather continuing and a stronger low passing south respectively. If active weather continues, then generally southerly winds will accompany mostly rain for the panhandle. For the low passing south, this would invite stronger, downsloping northerlies, which would dry out the panhandle and bring cooler temperatures overnight.

AVIATION

Behind a front this morning, there is onshore flow and showers across Southeast Alaska. Within heavier showers, there is potential for IFR ceilings and visibilities. A round of showers currently bringing IFR visibility to Yakutat is expected to push perhaps as far east as Sitka and Gustavus. An occasional lightning strike has also been along the NE Gulf Coast, and occasional lightning strikes remain possible near Yakutat. Outside of showers, expect ceilings to generally be high MVFR/low-end VFR.

Depending on clearing tonight, fog is anticipated to develop across the Panhandle. The highest confidence in fog occurring, and potential LIFR conditions, is for the Central Panhandle (Petersburg and Wrangell). However, where fog develops will ultimately depend on where enough clearing can occur and allow for radiational cooling. After 18Z Tuesday, a low pressure system in the North Pacific will move Northeastward toward Haida Gwaii. As the system moves northeastward, expect it to increase chances along and south of Fredrick Sound. The highest chances look to be for Ketchikan and points to the east.

MARINE

Outside: As of Monday morning, ASCAT passes across the Gulf show diminishing southwesterly flow, with winds at or below moderate breezes. Seas are southwest and also diminishing, with coastal buoys reporting 6 to 8 ft near 6 to 9 seconds. Monday night southwest flow continues to feed smaller systems into the Gulf bringing periods of fresh to strong breezes, mainly to Cape St. Elias and Dixon. However, southwesterly seas continue to remain at or below 8 ft through Wednesday morning.

Wednesday afternoon east to southeast winds build in the eastern Gulf, reaching near gale force over much of the coast by early Wednesday evening and fresh seas building to 10 to 12 ft. Thursday morning conditions continue to deteriorate as a front moves into the coast, with gales to strong gales impacting many areas and seas reaching 20 to 25 ft in the northern Gulf, seas near 15 ft south of Edgecumbe. Southwesterly winds of fresh to strong breezes persist Friday with thunderstorms possible along much of the coast.

Inside: Across the inside, for the most part winds remain at or below moderate breezes with areas of fog remaining the primary threat Tuesday and Wednesday mornings. Mariners navigating southern Clarence Strait and Revilla might see the higher end of moderate breezes, perhaps fresh breezes, as a low moves into Dixon Tuesday into Wednesday. Thursday a large system moves into the Gulf freshening up the winds across much of the inner channels to 20 to 30 knots, with localized areas of gales possible, and bringing heavy rainfall. Thunderstorms are likely to impact the Panhandle Friday bringing gusty winds. Active weather persists through the weekend.

HYDROLOGY

Impressive plume of moisture looks to be associated with the incoming atmospheric river Thursday morning. Strong WWA ahead of the moisture looks to raise freezing levels to above 5000 ft, with an atmosphere relatively saturated. Associated PWAT via ensemble mean looks to exceed the 95th percentile for this time of year for the southern panhandle. This coupled with the strong flow aloft means that IVT will likely exceed 500 kg/ms at around 80%. The big question here is timing of this moisture, and if any mesoscale features will keep this flow of moisture directed at the southern panhandle for longer. Dynamics continue to favor higher rain rates, with divergence aloft and stronger 850-700 mb southerly flow. Rain rates could exceed 0.3 in/hr for longer periods of time, and exceed 0.5 in/hr at elevation. Flooding is certainly possible with this rainfall intensity, but uncertainty in duration (see long term) has cast some doubt on overall impact level. Stay tuned for updates as the event approaches.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...None. MARINE...Small Craft Advisory for PKZ652.