textproduct: Juneau

SYNOPSIS

Key Messages:

-Suicide Basin glacier dammed lake continues to fill. At this time, it is expected to be full sometime August 11th or 12th. In the past, it has taken up to 6 days for the main flooding event to start after the basin is full. Visit weather.gov/ajk/suicidebasin for more information.

-No significant rain chances or rainfall amounts with a gradual warming trend expected through the week for the panhandle.

LONG TERM

/Wednesday through Saturday/ Wednesday, a closed low south of the Aleutian chain will reach full maturity, beginning to decay as it lifts north. Three primary features of interest as this system moves into the Gulf are: strength of the accompanying surface low, clear/warm over the Panhandle for the mid to end of the week, and moisture transport into the region by the weekend. Touching on the low first, ensembles show agreement that this system will make landfall along the AK Peninsula, with southerlies building in the central Gulf; winds remain below gale force. Our stubborn high over the eastern Gulf cedes territory, making a slight retreat into the Panhandle, with north-westerlies still impacting much of the coastal waters. Overall, little concern for major marine impacts with continued focus for northwest winds of moderate to fresh breezes along the Alexander Archipelago and sea breezes thru the inside.

As this high shifts into the Panhandle Thursday, warm and dry once again becomes the theme. Digging into the 850mb temps, the LREF shows a left-skewed distribution based around 7C to 15C, with the mode around 13C, translating to 75F to 85F surface temps, about 10F above normal for this time of year. The Extreme Forecast Index shines more light into this, with agreement in abnormal warmth increasing its footprint over the Panhandle into the end of this week. A note, its not just about the afternoon high temperatures, nightly low temperatures also likely remain about 10F above normal for most of the region.

Moving onto moisture, by the end of the weekend this pattern will begin to break down the dominant high, or at a minimum, push the ridge further east, with southwesterlies picking up on some equatorial moisture and funneling it into the Gulf. A few ensemble outliers want to bring a quick hit of moderate AR conditions; however, overall modest Integrated Vapor Transport values suggest just an increase in clouds, and perhaps some light rain, by the end of the weekend.

AVIATION

/through 12z Tuesday/ Upper level low situated over the southern panhandle in tandem with a west to east oriented surface high over the Gulf is keeping a variety of flight conditions across the area. Generally high level overcast ongoing across the northern panhandles keeping things mostly VFR, with brief periods of morning nuisance IFR/LIFR deck lying underneath. Southern panhandle saw more clearing overnight, as a result a nice morning marine IFR layer has worked its way in with CIGS 500 to 800ft over Prince of Wales, Ketchikan, and Annette. Expecting improvement through the early afternoon to predominate VFR across the panhandle with a general rinse and repeat forecast, albeit with slightly more sky clearing expected than previous days. Conditions improve during the afternoon to VFR with CIGS AoA 5000ft, however diminish routinely overnight has marine layer returns.

Similar to previous days, winds are expected to increase in the coming hours reaching sustained 10 to 15kts this afternoon, can't rule out a gust up to 20kts under any seabreeze influences, particularly near Taiya Inlet. No LLWS concerns through the TAF period.

MARINE

Outside: A 1023mb high pressure remains stationary over the central Gulf into early next week, keeping generally overcast skies with light and variable winds along in the outer waters. Wave heights remain largely benign through the early week, around 4ft or less along the coast with a persistent southerly swell of 2ft or less. Accompanying this high pressure is broad westerly to northwesterly winds in the NE gulf coast down to Dixon Entrance around 10 to 15 kts or less, with the strongest winds expected in the vicinity of Cape Spencer and Cape Decision, particularly by the afternoon hours. Main marine concern for outer and coastal waters will be nightly return of marine layer, dropping visibilities potentially as low as one quarter mile each morning. High pressure expands across the rest of the Gulf and panhandle and continues through the end of the week.

Inside: Conditions across the inside waters remain relatively benign this morning with only a few areas seeing winds above 10 kt, namely near ocean entrances near Cross Sound and into Icy Strait. Main hazard this morning is an area of dense fog near the entrance of Cross Sound, with visibilities 1nm or less as evident by FAA webcams near Cape Spencer. This pattern of relatively benign conditions with marine layer influence and patchy fog in the morning giving way to increasing winds and sea breezes by the afternoon will hold true through at least midweek. Wave heights remain 4 feet or less through early week as well with no significant systems to break down the influence of high pressure out in the gulf.

HYDROLOGY

Suicide basin continues to fill this Monday morning with no major changes overnight, rising to around 1343 ft as of 4am AKDT. The overall message remains the same, with the cloudy and cool weather in combination with the calving event over the weekend, the most likely date for a full basin is August 11th to 12th. The overflow channel remains around 1350ft. In the past, it has taken up to 6 days for the main flooding event to start after the basin is full and started to overtop into the overflow channel.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...None. MARINE...None.