textproduct: Juneau

AVIATION.../Through Thursday morning/

The main aviation concern for today will be the effects of the marine layer on the outer coastal TAF sites lingering this morning and tomorrow morning. Some southern sites struggled to break out of LIFR/IFR conditions, though are now expected to persist in VFR through the TAF period. The exception being PAKW, which could likely see the return of low clouds tomorrow morning impacting both CIG/VIS. Northern/central coast sites and into Cross Sound (Elfin Cove) also seeing low clouds and MVFR/IFR conditions currently, with higher confidence in CIGs AoA 2000ft until the afternoon. VFR anticipated for these sites around 21Z to 00Z, breaking out from south to north.Everywhere else in the panhandle is seeing VFR conditions today with light winds to start, increasing through the afternoon due to sea breezes. Highest winds will likely reach 15 to possibly 20 kts at most. Late tonight, offshore flow will dominate the pattern so low clouds, possibly down to IFR or MVFR, will keep mostly to the outer coast with all other areas remaining generally VFR.

PREV DISCUSSION......ISSUED AT

805 AM AKDT Wed Aug 12 2026

SYNOPSIS...

Key Messages:

- Suicide Basin is releasing. Major flood stage on Mendenhall Lake and River expected to be reached Wednesday night.

- Warming trend for the week with highs in the 70s. Lower 80s will be possible, especially across interior locations across the south and far northern interior for mid to late week.

- The warm and dry conditions will bring elevated threat for fire starts across much of SE AK. A few small fires have been observed already over the past week.

SHORT TERM...Ridge of high pressure will build over the Gulf through today, lingering through the rest of the week to the west of the panhandle. Warm temperatures and dry weather is expected to continue across the panhandle today through the end of the week, with the warmest temperatures expected Thursday and Friday after the ridging strengthens over the Gulf as westerly flow transitions to a northwesterly offshore flow. Some marine layer clouds will still develop in the Gulf with this ridge placement, however any low stratus clouds are expected to stay just offshore and along the outer coast.

The majority of the panhandle will see clearing skies with the offshore flow, and by the end of the week most of the panhandle is expected to see warmer temperatures with highs reaching mid to high 70s Thursday and Friday. Inland areas along the Klondike and Haines Highways may see high temperatures in the high 70s to low 80s through the end of the week with these clear skies. The southern panhandle is also expected to see temperatures reach near 80 into the low 80s Thursday and Friday, with areas further from the water having potential to see daytime highs in the mid 80s.

There still is potential for some convective activity in the SE corner of the panhandle Thursday and Friday afternoon/evening, with the instability present and overall setup suggesting a very low chance for easterly thunderstorms moving into the area. The moisture still is not ideal however, and any development is likely to be isolated over the SE panhandle and along the coastal range. Some model guidance shows 60-70% RH at the low/mid levels with a bit of westerly component to lower level winds to bring moisture into the area, but confidence is still lacking as to if these ingredients align for thunderstorm development.

LONG TERM...CORRECTED the right long term section / Friday through Monday/...Ensemble models agreeing on an upper level ridge dissipating and being replaced by a weak trough over the southern panhandle by Friday, with the ridge rebuilding early next week. This shift will bring positive vorticity advection and some lifting, while moisture advection arrives via an easterly wave in the 700mb level. Additionally, a surface maritime ridge forming in the eastern gulf will generate northwesterly winds across the panhandle which could work in conjunction with diurnally driven sea breezes to promote weak onshore flow toward the end of the week.

Regarding severe weather potential for end of week/early weekend, guidance is keying in on seasonably high CAPE values in parts of the central and southern regions, though forecaster confidence remains low due to drier conditions in many of the atmospheric pressure levels and a lack of support for sustaining storms moving in from Canada. Cumulus fields are more likely than storms, as a lack of a cap and significant moisture inhibits potential convection. While westerly flow on Friday might drive some localized convection through upsloping, marine influences will likely stabilize the surface layer and choke off development. Meanwhile, light winds and clearing skies are expected to boost temperatures, with Friday and Saturday continuing this warm spell as temperatures reach the upper 70s to low 80s, before cooling returns Sunday into Monday as the surface high pressure weakens. There is still a lot of spread in the track of a low pressure center moving into the central gulf next week, and if lingering high pressure will block precipitation from moving in. We will continue to monitor this next system and associated rainfall accumulation.

MARINE... Outside: Marine forecast remains on track. High pressure over the Gulf will strengthen and shift eastward, tightening the gradient over the eastern Gulf. Gentle to moderate northwest breezes will become fresh for the outer coastal waters from near Cape Spencer down to Dixon Entrance. Wave heights of 3 to 4 ft will increase to 4 to 6 ft by midweek and remain through the end of the week. Winds will diminish by the weekend as the high weakens. Main marine concern for outer and coastal waters will be nightly return of marine layer, with fog and low stratus impacting visibility.

Inside: High pressure out in the Gulf is expected to linger through the week, with light to gentle W/NW-ly winds overnight shifting to a NW-ly moderate to fresh breeze for the inner channels by this afternoon. Localized wind shifts due to sea breezes are possible, alongside elevated gusts to 15-20 kt, but overall wind direction is expected to be from the NW. Strongest inner channel winds up to 15 to 20 kts are expected for the afternoon and evening hours. Winds across the inner channels will also diminish Thursday and Friday as the ridge begins weakening, however N-ly winds of 15 to 20 kt are expected for northern Lynn Canal from a tightened N-S gradient remaining across the northern panhandle the end of the week.

FIRE WEATHER...High pressure continues to sit over the area with no real signal of a pattern change likely until the upcoming weekend. With the persistent dry weather, we have started to see temperatures rise into the 70s with some pockets of 80s for the inland areas with warm temperatures expected to continue through the week. Looking at the past few days, relative humidities have fallen down to the 30s to 40s for some areas during the daytime hours with rebounding during the overnight hours into the 90s. With the continued lack of rain, fine fuels such as grasses will continue to dry. Models continue to suggest the potential for isolated thunderstorms along the Panhandle border with Canada as well as the SE panhandle on Thursday and Friday. However, due to the lack of low/mid level moisture the chance of thunderstorms is only around 15% or less.

Overall, expecting the dry and warm trend to continue through the week with fire weather conditions continuing to develop, the main variable to watch for will be daytime winds. As of now, expecting the worst fire weather conditions to be Thursday and Friday afternoon, however given the persistent pattern can't rule out this extending further into the weekend.

HYDROLOGY.../Flood Warning in Effect/

Mendenhall Lake gauge levels, along with USGS imagery from Suicide Basin and water levels within the basin, indicate that a glacial lake outburst flood is ongoing into Mendenhall Lake and River.

As of 10am AKDT, the Mendenhall River is at 5.85 ft and rising. It usually takes around 2 days from when the basin release starts to when you see the highest water levels. Water levels on the Mendenhall Lake and River will rise through today as the release continues, with a forecast crest between 16.1 to 16.6 feet expected early Thursday morning. Compared to previous years this is slightly below last year's high water mark, and above the high water marks of 2023 and 2024.

Visit weather.gov/ajk/SuicideBasin for the latest updates on the Glacial Lake Outburst Flood for Mendenhall Lake and River. The weather.gov/ajk/SuicideBasin web page is currently updated every two hours by the NWS Juneau office and as we move further into the event, this cadence will increase to hourly updates.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Heat Advisory until 7 PM AKDT Thursday for AKZ318-319. Heat Advisory from noon Thursday to 7 PM AKDT Friday for AKZ328- 330>332. MARINE...None.