Area Forecast Discussion

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today through Monday evening)...

A deep, upper-level trough is digging south from the western coast of Alaska to the North Pacific. A potent upper-level low and 978mb storm-force low sit at the base of this trough, its front beginning to occlude and push into the southwest Gulf of Alaska south of Kodiak Island. Downstream, a rapidly weakening upper- level shortwave and surface low have moved inland over the Copper River Basin this morning, with rain over parts of the Basin and lingering showers from Middleton Island into Prince William Sound (PWS). A surface trough to the west of the these features is draped over the Anchorage Bowl, with a few scattered, slow moving, and locally heavy rain showers across East Anchorage north and east to the Matanuska Valley. These showers are expected to taper off by mid morning.

The front associated with the North Pacific low will continue to lift north over the western Gulf today and over the northern Gulf by late tonight. The upper-level and surface lows will trail the front as its occludes, pushing into the southern Gulf by Saturday night. By Sunday morning, the upstream trough is reinforced by an arctic shortwave digging south over the eastern Bering and AKPen, resulting in further amplification of the long wave pattern. This amplification will allow the occluded front to stall along the immediate Southcentral coast and Kodiak Island while the parent low lifts north toward Middleton Island, eventually making landfall around the Copper River Delta Sunday afternoon. There is plenty of moisture along and out ahead of the front, allowing for persistent rain along the coast (1 to 3" around PWS) and periods of rain showers father islands through the weekend.

Models also continue to suggest that the atmosphere looks conducive for marine lightning (70-80% chance) during this low's journey across the Gulf (Saturday afternoon through Sunday afternoon), mainly due to the upper low component of the surface low steepening lapse rates, and that the Gulf will be under the influence of being below the left exit region of a 300 mb jet streak, which will further enhance instability. Aside from that, widespread westerly to southwesterly small crafts and gales are also to be expected in the wake of this system across the Gulf as the cold air advection associated with the arctic trough spills southward starting Sunday afternoon.

-TM/AM

.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS (Days 1 through 3/ Today through Monday Evening)...

Key Messages: - Strong northerly to northwesterly winds develop across the eastern Aleutians and AKPEN Saturday afternoon and evening, with the strongest winds through favored gaps, including Cold Bay, King Cove, False Pass and Sand Point.

- Colder air continues to spread south across Southwest Alaska and the Bering through the weekend, with falling snow levels and snow possible across higher elevations.

- Winds gradually diminish Sunday into Monday as high pressure builds across the Bering, though cool and showery conditions persist.

- A colder and increasingly windy pattern remains on track across Southwest Alaska, the Bering and Aleutians this weekend. On saturday, a strengthening low moves southeast of the Alaska Peninsula and into the Gulf while high pressure builds across the western and central Bering. The tightening pressure gradient between these features will strengthen northerly to northwesterly flow across much of the Bering, eastern Aleutians and AKPEN. The latest guidance remains in good agreement with the overall evolution of this system, though some differences remain with the exact strength and position of the low.

The strongest winds Saturday afternoon into Saturday evening will focus across the eastern Aleutians and AKPEN where terrain enhancement will result in locally stronger winds through favored gaps. Cold Bay, King Cove, False Pass and Sand Point will be among the locations most susceptible to stronger gusts. Meanwhile, colder air moving south across the Bering will maintain scattered showers across the Aleutians and portions of Southwest Alaska. There are gale-force winds developing along portions of the AKPEN Saturday night as the pressure gradient tightens.

By Sunday, the low continues eastward into the Gulf while high pressure remains over the Bering. Persistent northwesterly flow will continue across the eastern Bering, eastern Aleutians and AKPEN, though winds will gradually diminish through the day as the pressure gradient relaxes. Cold air advection will keep temperatures below recent values, with snow levels falling to around 2000 ft or lower. This may allow showers to fall as snow across higher elevations of Southwest Alaska and the AKPEN, with a rain/snow mix still possible at times near portions of the Kuskokwim Delta coast.

Heading into Monday, the initial low continues to pull farther away while broad upper-level troughing remains across southern Alaska. Winds continue to weaken across the eastern Bering and AKPEN, with gradually quieter conditions compared with this weekend. However, the lingering cold air mass and cyclonic flow will maintain scattered showers across portions of SOuthwest Alaska and the Aleutians through Monday evening. Attention then turns farther west as the next disturbance begins approaching the wester Bering/ Aleutians beyond the short-term period.

LM

.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...

The longterm period beginning Tuesday morning will start out with a longwave trough extending across much of Mainland Alaska down into the Alaska Gulf. A Gale Force low will likely be maturing and reaching maximum intensity somewhere over the central to eastern Gulf. Current model consensus suggests this system will stall out over open waters as it slowly weakens through the middle of next week, resulting in limited impacts to Southcentral. Out to the west, a longwave ridge is anticipated to be moving across much of the Bering Sea in between the Gulf low and a shortwave trough and attendant low evolving near the Kamchatka Peninsula on Tuesday.

Much of the remainder of the long term beyond Tuesday will hinge heavily on the degree of interaction between the trough/low moving off of Kamchatka into the western Bering and the remnants of what is currently Typhoon Dujuan out in the West Pacific. Dujuan will recurve north and east after making a close pass with Japan this weekend, eventually approaching the western parts of the Aleutian Chain after transitioning to an extratropical low around Tuesday to Wednesday next week. Models are still struggling quite a bit to determine how the remnants of Dujuan will behave as the center gets closer to the separate low pressure system progressing across the Bering. Some earlier deterministic solutions and current EPS/GEFS ensemble members suggest that a strong phasing interaction could occur between the two lows, perhaps resulting in a much stronger low that deepens rapidly somewhere across the southern Bering Sea and Aleutians/AKPen as the two systems essentially merge. If this comes to fruition (about a 20-30% chance), high winds and waves could become a substantial hazard across a large portion of the Bering Sea, Aleutians and possibly Southwest towards the middle to latter part of next week.

In contrast to the scenario above, much of the 12z deterministic guidance coming in today is depicting Dujuan's remnants taking a little more time to move northeast across the North Pacific, effectively causing it to miss the stronger interaction with the other low progressing across the Bering Sea. This version of events (more likely scenario, around 70% chance) would keep Dujuan tracking off to the south of the entire Aleutian Chain, with an overall lower threat for strong winds and large waves across the Bering Sea near the secondary low to the north. Even so, the low moving off of Kamchatka could still pull a significant amount of moisture north from Dujuan's remnants as they pass to the south, enough to support a heavy rain threat across parts of the Pribilofs, Aleutians and Southwest sometime between Wednesday and Friday as the system tracks northeast towards the western coastline. The influx of warm, moist air could also help deepen the Kamchatka system to a Gale Force low as it tracks across the Bering, so the wind and wave potential across the Aleutians and Southwest would certainly not be zero in this case. Bottom line, anticipate a strong low to affect parts of the Aleutians, Bering and Southwest next week, regardless of exactly how the remnants of Dujuan play a role.

Meanwhile, much quieter conditions are expected for the most part across Southcentral by the middle of next week. A seasonably cool air mass will be in place across the region initially, but some warming is likely towards Wednesday and Thursday as the Bering ridge moves overhead. There could be a threat for strong southerly gap winds to develop late in the week along with increasing rain chances, but this will be highly dependent on the complex and uncertain interaction between multiple systems out west as described above.

-AS

AVIATION

PANC...Light and variable winds combined with lingering low-level moisture could result in patchy fog near or over the terminal Saturday morning, otherwise mainly MVFR to low VFR ceilings are expected through the morning hours. VFR Ceilings are likely to prevail by this afternoon, although periods of MVFR ceilings remain possible with any shower activity that is able to develop this afternoon through this evening.