Area Forecast Discussion

UPDATE

Updated aviation section for 6z taf issuance and long term section.

SYNOPSIS... Key Messages:

- Inner channel marine winds remain light through Monday night up to 10 kts expected except locally gusty near eastern Icy Strait.

- Pattern change on the horizon as a weather system approaches late Tuesday, bringing a return of rain and elevated winds across the panhandle by mid week.

SHORT TERM...

Surface high pressure continues to exist in the northern gulf today and tonight, resulting in relatively benign conditions. The most impactful portion of the forecast is the incoming clouds from both a lower level marine layer and a mid to upper level disturbance moving eastward along the ridge aloft, generating some clouds. Apologies in advance to all Aurora hunters out there looking for clear skies.

Going into Tuesday, we have the beginnings of a stream of moisture coming up from far south in the Pacific. This plume looks to wrap around the ridge tomorrow evening, pushing the high pressure southeastward, and bringing rain back to the panhandle. Not expecting much impact from this round of rain, as the anticyclonic flow the moisture is following does not lend itself to strong lift dynamics, but could see some moderate rain for the Yakutat area mainly in part to orographic lift. Could see some river rises, particularly on west facing slopes (Montana Creek, Jordan Creek, Indian River in Sitka); however, the shortwave moving eastward looks somewhat progressive, shifting moisture to the south by Wednesday morning and diminishing. Therefore, no flood is expected at this time around, but rivers are expected to rise.

Going into the late week, a round of heavier rain looks increasingly likely. More in the long term discussion.

LONG TERM.../Thursday through Tuesday/ Upper level features continue to show a rather active pattern through the long range period. We start out with overall zonal W to E flow over much of the region that will gradually transition to a broad upper trough stretching from the Russian Far East to NW Canada by the weekend. The transition is set in motion by an upper low moving out of Russia late week that eventually anchors itself over SW mainland Alaska. The broad trough stays in place into early next week, but several short waves are evident rotating around the southern edge of it.

The active weather pattern is still apparent at the surface with a series of fronts expected to move through the region late week, through the weekend, and into early next week. First the low and front that is approaching on Friday that was a new feature in the guidance yesterday is still there, but details are still being worked out. Guidance has been somewhat split on whether this system will track S to N farther west and stronger or farther east and weaker. The trend so far looks to be toward the latter, but it will still be a wet (up to 1 to 2 inches of rain Fri morning to Sat morning) and breezy (winds of 15 to 25 kt for the SE gulf and inside waters) Friday regardless.

The weekend is looking interesting as well with a strong broad area of low pressure moving into the gulf from the SW and heading toward the northern gulf coast. In addition to the stronger onshore SW flow it will bring, it its wake is a shot of cooler air that will be coming in from the west. Forecast convective indices are already indicating that Sunday into Monday may be rather convective/showery in nature as the cooler air moves in and the potential is there for some thunderstorms across a large area of the gulf and outer coast at that time. I have added a broad area of slight chance of thunder at that time with the potential that areas along the outer coast could see more frequent thunderstorms from the interaction with the terrain. We will keep monitoring these systems as more details emerge.

AVIATION... A ridge of high pressure in the Gulf of Alaska has led to generally VFR conditions this afternoon, with the exception of Sitka. The main concern for aviation tonight will be the potential for marine layer fog. In terms of fog, the coverage is looking fairly similar to what was around the area tonight, but Ketchikan may also see some lower ceilings. There is highest confidence in fog occurring for Yakutat and Petersburg. However, it cannot be completely ruled out for Juneau.

Conditions are not expected to clear out as much Tuesday as this they did today. This is thanks to a warm front approaching from the west. This is expected to bring ceilings AoA 1500 feet and rain chances after 03Z Wednesday to the Northern Panhandle. This front looks to impact east of Sitka after 06Z Wednesday. Based on the orientation of the front, this may lead to some low level wind shear concerns for Yakutat. However, the strongest winds look to occur with the front after 06Z Wednesday.

MARINE... Outside Waters: High pressure gradually weakens through this week as several surface features make their way east across the northern Gulf. Winds predominantly NW'rly at 10 to 20 kt in the eastern Gulf Monday afternoon, trending toward a more W'rly component in the central and northern Gulf through tonight. Winds start picking up Tuesday morning and shifting to a more southerly direction with the upcoming system. Generally expecting an increase to 25 to 30 kt winds, gusts to 40 kt, for the central and northern Gulf Tuesday afternoon through Wednesday morning. Also noting a high likelihood of increased winds near prominent capes. Wave heights of 3 to 6 ft expected Tuesday morning, building to 8 to 11 ft in the central and northern Gulf by early Wednesday morning, before diminishing through midweek, all with a SW-ly swell. Anticipating less marine layer influence tomorrow morning, however visibilities could still be impacted along the NE Gulf coastline south toward Cross Sound.

Inside Channels: The retreating morning marine layer and clearing skies have generated light sea breezes around 10 to 15 kt over the northern panhandle this afternoon, specifically within Icy Strait around the Sisters Island to Rocky Island region. Elsewhere, seeing light to gentle breezes prevailing through this afternoon and overnight. Winds are expected to start picking up Tuesday morning across the panhandle as the pressure gradient tightens with the incoming system. Predominately southerly winds will continue to increase Tuesday afternoon through Wednesday across the northern and central inner channels. The highest of these winds will be in Lynn Canal with S winds 25 to 35 kt, gusts to 40 kt, with brief gales in Northern Lynn mainly overnight into Wednesday morning. As this systems exits the region, winds are expected to decrease some, but remain elevated ahead of another Gulf system moving in late week.

AJK WATCHES / WARNINGS / ADVISORIES

PUBLIC...None. MARINE...Gale Warning for PKZ012. Small Craft Advisory for PKZ013-022-643-644-651-652-662>664-671- 672.