textproduct: Juneau

UPDATE

Update to the Aviation Section with the issuance of the 06z TAFs and for the addition to the end of the long term discussion.

PREV DISCUSSION......ISSUED AT 245 PM AKDT Mon Apr 6

SYNOPSIS...

Key Messages:

- A westerly surge of winds is on our doorstep, bringing a shift in winds and relatively cooler temperatures.

- Some clearing is expected on Tuesday, bringing warmer temperatures and drier weather.

- Rain returns to the northern half of the panhandle Wednesday and spreading south by Thursday

- Drier weather looks to lead SE AK into the weekend.

SHORT TERM.../Monday through Tuesday Night/... A weakening low moving inland near Ketchikan at time of writing, with a building ridge in the eastern gulf being left in its place upstream. The result is a westerly surge of winds in communities from Angoon southward, along with relatively colder temperatures and localizing any remaining precipitation to west facing mountains.

Tuesday is significantly more uncertain, relying on cloud cover and solar heating. What could have been a high magnitude ridge is interrupted by a weakening shortwave trough racing along the ridge. The result is a somewhat flat ridge, and with it moisture, cloud cover, and additional shower potential for the Icy Strait area on Tuesday, particularly in the afternoon and overnight into Wednesday. The big question is how much this shortwave will moderate out the ridge, how much will this impact clearing and warming in British Columbia and the Yukon, and the resulting strength of the thermal gradient between inland and the coastline. Naturally, a temperature update may be necessary tomorrow depending on where moisture and cloud cover set up, but what can be said is that SE AK is in for more normal temperatures for this time of year, instead of the below normal temperatures we have dealt with all March.

LONG TERM.../Wednesday through Monday/... Hints of spring will continue to grace the panhandle over the coming week as multiple mid and upper level troughs and ridges bring slightly warmer temperatures interspersed with light to moderate precipitation. A short wave that brought showers to the northern gulf coast beginning Tuesday will be reinforced late Wednesday and bring more widespread precipitation to the panhandle through Thursday and the end of the week. While this is expected to be primarily rain, some snow could mix in in the overnight hours, with highest likelihood north of Icy Strait. However, little to no accumulation at sea level is expected at this time. Some minimal accumulations are possible for higher elevations of the Klondike and Haines Highways. Overall these features are expected to have minimal surface reflections and thus keep seas to at or below 6 ft in the gulf by Thursday. Winds also look to not be that impressive as of this forecast issuance, with some locations potentially reaching strong breeze (22 to 27 kt) at most. Onshore flow with the aforementioned short waves impacting the panhandle will be replaced by offshore and/or parallel flow by the end of the week and into the weekend as another ridge builds into the gulf.

With clearer skies expected to develop over the weekend, modest sea breezes will be on tap for communities along the inner channels. Some weak offshore flow could develop over the northern inner channels briefly Friday night into Saturday as the latest feature exits the region, however this should then be offset by sea breeze development during the day Saturday and overall relaxing of the pressure gradient over the inner channels. Overall it looks to be a relatively quiet and benign pattern ahead for the weekend.

Some ensemble guidance and the NBM hint at the ridge breaking down late weekend and bringing a low out into the Gulf and trying to swing a front with rain into the panhandle later Sunday into Monday. However, confidence in this occurring is low due to high model uncertainty and capped the probability of precip to chance. Moderate to high confidence for milder, more seasonable spring time temps and generally light winds to continue.

AVIATION.../through 06z Wednesday/ VFR to MVFR flight conditions continue this evening with ceilings being the biggest challenge. With high pressure moving in, precipitation has mostly come to an end across the panhandle. With the low cloud decks though, some light rain or drizzle might be possible though during the overnight hours. Cloud cover is expected to remain the same going through the overnight hours but some improvements might be noticed across the southern panhandle. Elsewhere, clouds should stick around at least through midday tomorrow before a more significant break in the clouds is expected. With the high pressure over the Gulf and clearing skies during the day, onshore flow and some sea breezes will be possible especially from the middle of the day onward. As for icing and turbulence concerns, the folks at AAWU are highlighting most of the panhandle for some potential isolated moderate turbulence and isolated moderate icing towards the Coast Mountains during the overnight hours.

MARINE... Outside Waters: A building ridge with a low passing into British Columbia will keep strong breezes to near gales in the forecast with much of the outer coastal waters, diminishing by the early morning hours of Tuesday. Similarly, seas will be on the downward trend, with the localized area of swell passing into Dixon Entrance early this evening. Wave heights 10 - 17 ft at 10 seconds will diminish down to 5 - 7 ft at 8 seconds by the morning hours of Tuesday.

Inside Waters: Highest area of concern for the immediate short term is the southern half of the panhandle, specifically Clarence Strait. A westerly surge of winds to 20 knots will move through the channel shortly at time of writing, associated with the SW quadrant of a low pressure moving inland currently near Ketchikan. Southeasterly winds will rapidly shift to westerly to northwesterly winds up to 20 knots in Clarence, Chatham, Frederick, and Sumner with this surge. For Tuesday, somewhat more uncertain forecast particularly in the Icy Strait and Chatham Strait forecast. Daytime heating in SE AK, Yukon, and British Columbia will result in a thermal and tighter pressure gradient in the Lynn Canal area, with winds up to a fresh breeze. It is currently uncertain how far this will extend down into Icy Strait and Chatham Strait, with winds being anywhere between 10 and 20 knots around Sisters Island, Point Couverden, and Point Cravens.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...None. MARINE...Gale Warning for PKZ641-642-644. Small Craft Advisory for PKZ022-643-651-661>664-671-672.