textproduct: Juneau

UPDATE

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.

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.

AVIATION

MVFR/VFR conditions are and will likely remain the predominant situation over the next 24 hours. When the front makes its final exit out of the panhandle, winds will be rather calm for most of SE AK. In addition, rain will become less consistent in its coverage with some weak ridging toward the southern panhandle. Throughout the day on Monday, clouds will generally lift above 3kft, hopefully providing for improved flight conditions to start the week.

The northern panhandle may remain rainier for longer, as well as retain lower cigs as there will be some continued onshore flow. By Monday afternoon/evening rain chances are low enough for central and southern panhandle sites that rain has largely been removed as the prevailing weather condition.

PREV DISCUSSION......ISSUED AT

305 PM AKDT OCT 11

SYNOPSIS...

Key Messages:

- A front swinging through the region will bring gusty winds and moderate rain to the panhandle through tonight, especially across the northern half of the panhandle.

- Quieter weather for the first part of the work week with lighter rain showers possible.

- A larger, impactful system to move into the Gulf midweek and impact SEAK by late week.

SHORT TERM... Sunday into mid-week will feature some rounds of rain and some wind but nothing we cant handle. Touching on rain, 850mb temps remain too warm to see snow at sea level. Folks heading up the passes into Canada will likely see a mix of rain and snow falling at times but no impacts expected. Widespread rain of 1 to 2 inches tonight becomes showery Monday afternoon. While the central and north see drier conditions Tuesday morning, another slug of rain moves into the south.

For winds, a gale force front moving into the coast of the Alexander Archipelago Sunday will increase the north-south pressure gradient through Sunday night, freshening up southerly winds to 20 to 30 knots, more in the marine discussion below. For folks nestled safely on terra firma, gusty winds of 20 to 35 mph likely in the north tonight, highest in Skagway. Winds begin to come down Monday. These smaller systems will warm us up for a much bigger system Thursday into Friday, more info in the long term.

LONG TERM.../Tuesday through Friday/...A weaker wave will move north from Haida Gwaii Tuesday and Wednesday, providing enough disturbance to generate scattered showers, mostly in the southern panhandle. The larger impacts may come as early as Thursday from a much deeper low. The latter low will intensify in the western Gulf, and will have ample to mature as it looks to be held out over the open waters of the Gulf by some Fujiwara Effect related to a smaller orbiting low which most guidance has combining together.

By Friday the extent of its influence will likely reach us here in SEAK. Exact timing still differs between deterministic guidance runs. One of the larger variables being how long the two lows orbit one another before joining and allowing the resultant low to track east. A later arrival will most likely result in a stronger system, but there is good confidence in strong gusty winds, especially over coastal waters, and widespread rainfall Friday heading into the weekend.&&

AVIATION...VFR to MVFR conditions continue for most of the panhandle this afternoon with the exception of the Yakutat area which has seen conditions down to IFR. With the front pushing through, there should still be some decreasing conditions across the panhandle. The main concern will be ceilings decreasing with the rain but some visibility reductions are also possible, especially during the heavier periods of rain. Another concern will be after the front passes. Current satellite imagery shows clearing behind the front which could allow for some fog development this evening and overnight. Confidence for the TAFs for this evening is moderate with some reduced conditions being noted but not as significant as what some forecast guidance is hinting at.

MARINE... Outer Waters: A front in the Gulf of Alaska has brought gale force winds from Cape Suckling to Cape Fairweather, and elevated seas across the Gulf. As the low pressure system pushes into the Panhandle, expect the front to dissipate and marine conditions to improve through Monday morning. Behind the front, a low in the Bering Sea will continue onshore flow for Southeast Alaska. Tuesday, a low pressure system is expected to form near Kodiak Island and another low will form in the North Pacific. As the northerly low moves toward Prince William Sound Tuesday morning, expect a easterly barrier jet with winds up to 20 kts near Cape Suckling. The next more organized system arrives Wednesday night into Thursday.

Inside Waters: A front is pushing into the Alaska Panhandle and leading to winds up to 25 kts and seas up to 5 feet. As the front dissipates, expect the marine conditions to generally improve for the inner channels. With the low in the Bering Sea, expect generally onshore flow to continue for Southeast Alaska. Monitoring the potential for two lows to develop Tuesday: one near Kodiak Island and in the North Pacific. Guidance still disagrees on the exact track, but generally bring it toward Haida Gwaii. If the low tracks further north, this may increase winds in the southern inner channels. However, the main impactful system for Southeast Alaska looks to arrive Wednesday night into Thursday.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...None. MARINE...Small Craft Advisory for PKZ012-013-031-034-641>643-661-662-672.