textproduct: Juneau

UPDATE.../to add the 18z aviation discussion/

SYNOPSIS

Key Messages:

- Outflow winds beginning to weaken and temperatures start a warming trend mid week.

- Increasing potential for a pattern change for the end of the week into the weekend.

- Potential for snow event for the central and northern panhandle; southern panhandle could see snow turning to rain.

LONG TERM

We continue to watch the upcoming shift in the weather pattern that would give the next round of significant snow to Southeast Alaska.

The next major system will begin to move into the Gulf of Alaska Friday, following behind the weak low clipping the panhandle Thursday. As the weaker low moves southeast, before the larger low approaches from the west Friday night, there will be another brief lull in the winds into Friday along the southern waters, while the northern offshore flow will remain stronger ahead of the next low moving in from the west. Winds begin to pick up across the entire panhandle Friday night into the weekend as the stronger low approaches, and a gale force front begins to move in from the southwest. These southerly winds moving into the panhandle will allow for some warming across the panhandle alongside bringing precipitation through from W to E into the start of the weekend.

As far as temperature relating to snow potential, the EURO and GFS ensembles and deterministic models have come into greater agreement over low tracks and 500mb flow. The Canadian remains the outlier. The 500 mb flow continues to have the deep trough further west, keeping a southwesterly flow into the panhandle and allowing for deep moisture and warmer air to be moved in from lower latitudes with the deep trough position, with the arctic trough and 500 mb cutoff low over the Pacific to the southwest connecting over the Kenai Peninsula down the west Gulf. Some of the deterministic models show the arctic trough separating from this lower latitude troughing as it becomes a cutoff again and moves southward, leaving a southwesterly flow into the southern panhandle but the arctic trough allowing for colder arctic air to move across the northern Gulf into the northern panhandle, bringing the potential for cooling the north much sooner than the southern panhandle into next week. This has not been shown on the ensembles as of yet, and is seen on the EC deterministic run and not the GFS one, so the certainty of the timing of the cold air coming back into the northern panhandle is still a bit uncertain for the period into early to mid next week.

Looking at the EFI tables, as well as looking at AR and IVT tools for this heavier precipitation coming up this weekend, QPF amounts have been adjusted to keep the southern panhandle at between 2.5 and 3.5 inches of liquid precipitation every 24 hours, coming down first as snow Saturday morning before quickly transitioning to rain from the SW coastline inwards as the warm front pushes through, with the switch to rain expected during the morning hours for PoW and Sitka into midday for areas like Ketchikan and Wrangell that are a bit further inland. This is from the extreme and AR tools showing a higher confidence of a shift of tails for QPF for the southern panhandle, particularly near the Ketchikan area, with an increased confidence from yesterday's model runs. Overall the heavy rain will begin for the southern panhandle Saturday, but the next wave of precipitation pushing through will bring another round of heavy rain Sunday that has been primed by the first warm front pushing through the day prior. The warm temperatures in the high 30s to low 40s will continue into the early week as onshore flow continues to bring in southerly warmer flow into the southern half of the panhandle.

For the rest of the panhandle, which includes everywhere north of Wrangell and Sitka, the snow will last into Saturday as that first front moves in, as the warmer temperatures will not bring temperatures up into the mid to high 30s until Sunday. This will allow for a switch to more of a mix potentially becoming rain by Sunday afternoon/evening up to Icy Strait corridor. These areas will see between 8 and 14 inches in 24 hours Saturday into Sunday morning before transitioning to rain/snow mix to potentially rain. Snow will start off lighter and fluffier Saturday as snow liquid ratios remain high, but as the area warms Saturday into Sunday, ratios will decrease to become a heavier and wetter snow. Areas to the north of Icy Strait corridor will remain snow the entire time through both fronts moving through, giving a significant amount of snowfall to the Skagway and Haines areas with between 10 and 18 inches in 24 hours both Saturday and Sunday with more expected along the Klondike Highway. However these amounts for all of the panhandle depend largely on how much of the precipitation actually reaches parts of the panhandle, particularly in these northern areas. Overall the northern half of the panhandle will see 1.5 to 3 inches of liquid precipitation during this system, but there remains uncertainty on how much snowfall there will be exactly during this system and the exact timing of a changeover to rain for the central parts of the panhandle. Overall this will remain more of a heavy rain event for the southern panhandle from Sitka and Wrangell southwards Saturday into Sunday, with only about 3 to 7 inches expected for Ketchikan Sitka and PoW Saturday morning before transitioning to rain, and 6 to 12 inches for Wrangell possible before they too transition to rain.

AVIATION.../Until 18Z Thursday/

VFR CIGs & VISs are anticipated through the 24-hour TAF period. The only exception is around the PAPG area for the next hour or 2, which could see a brief snow shower or 2 that may bring CIGs & VISs conditions down to within the MVFR flight category. Low-level turbulence & wind shear values up to around 35KT will also last through the afternoon for the PAJN & PAWG areas, which are areas that are prone to gap winds. The LLWS will start diminishing around the mid-afternoon through early evening timeframe. Strong northerly outflow winds of up to around 30G50KT continue for the PAGY area through this afternoon hours, diminishing to around 20G35KT starting this evening & lasting through the end of the TAF timeframe.

MARINE

Inside waters: Northerly outflow with freezing spray continues across the north. Lynn Canal and Taku Inlet are still showing gale force winds this morning while 25 kt winds extend down to Frederick Sound and Southern Chatham Strait. These winds are expected to slowly diminish through the next 24 hours with outflow nearly shutting off by late Wednesday night (winds down to 15 to 20 kt in Lynn Canal and Taku Inlet) as the Yukon high weakens. This low period will be somewhat short as the weak low moving SE across the gulf Thursday will strengthen the outflow again by Thursday afternoon with gales again in Lynn and Taku Inlet before diminishing again on Friday. Freezing spray is still ongoing, but with warmer temperatures across most marine areas, the heavy freezing spray is mainly limited to Northern Lynn for this morning. Otherwise expect the areas of freezing spray to diminish as the outflow wind diminish through early Thursday. Seas are still somewhat high in Lynn and Stephens passage this morning (reaching 13 ft in some areas) but those seas are expected to also subside as the winds do by early Thursday.

Gulf Waters: The gulf waters will be seeing a change from northerly winds to more westerly winds by Thursday as a weak low moves SE through the eastern gulf Wednesday night into Thursday. These W to NW winds will increase to 30 kt across the central gulf waters Thursday before diminishing and then switching to southerly on Friday ahead of the next front. Highest seas are still currently associated with what is left of the outflow that makes it into the gulf out of Cross Sound and Chatham Strait with up to 10 ft seas. These will subside as the winds do down to 4 to 6 ft by late Wed night. The seas will then start building again to 8 to 12 ft by Thursday afternoon due to the increased W winds at that time.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Extreme Cold Warning until noon AKST today for AKZ318-319. Strong Wind until 3 PM AKST this afternoon for AKZ318-325. Cold Weather Advisory until 6 PM AKST this evening for AKZ320- 321-323-326-327-329. Extreme Cold Warning until 7 PM AKST this evening for AKZ325. Cold Weather Advisory until 9 AM AKST this morning for AKZ328- 330-332. MARINE...Heavy Freezing Spray Warning for PKZ011. Heavy Freezing Spray Warning for PKZ012. Heavy Freezing Spray Warning for PKZ031. Gale Warning for PKZ012-013. Small Craft Advisory for PKZ021-031>034-036-641-642-661>663.