textproduct: Juneau

UPDATE

Update includes aviation discussion for 6Z TAF issuance.

AVIATION.../Through 6Z Saturday/

VFR conditions across the board this evening with clear skies going into the tonight period. The forecast remains on track with TAFs being mainly a persistance forecast. The main concern for the overnight hours is fog at coastal locations, with the confidence for low VIS higher at PAYA and PAKW and lower at PASI and PAGS. This lack of confidence comes from the drier conditions that we have been seeing across the panhandle that will prohibit the formation of fog. Any fog that develops, though, is likely to burn off by morning because we are expecting another clear, warm day on Friday. Sea breezes are going to be the main driver for winds through the period, with variable to no wind overnight. Winds on Friday are not expected to exceed 10kts.

PREV DISCUSSION......ISSUED AT

SYNOPSIS...

Key Messages:

- Suicide Basin has released. Major flood stage on Mendenhall Lake and River was reached Thursday morning with a crest of 14.7 ft around 2:15pm Thursday afternoon.

- Very warm temperatures to end the work week with highs in the mid 70s to lower 80s. - 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.../through Saturday night/...Warm temperatures, mainly clear skies and mostly dry weather will dominate the short term period. High pressure out of the Gulf has weakened slightly, with weak surface troughing and offshore northerly and easterly low-level flow, allowing for drier and warmer interior airmass to build into the panhandle. High temperatures will max out on Friday as 850mb temps up to 15C and full sun will allow for very warm interior temps away from the coast to climb into the upper 70s to possibly as high as the mid 80s. Heat Advisories are in effect through Friday. Locations near the coast will likely climb into the mid and possibly upper 70s before any sea breezes kick in by the afternoon and bring cooler marine air back inland. Still warm but slightly cooler for Saturday as ridging begins to builds back towards the coast and 850mb temps drop a couple of degrees as cooler marine air starts to build back inland. High temps are still expected to reach the 70s to possibly low 80s with mostly sunny skies. Additional Head Advisories may be needed. Each afternoon/evening, convection will fire up east of the coastal mountains in western BC and Yukon and drift west towards the border. This afternoon, a few showers have fire near and east of Hyder and could drift west through the evening towards Ketchikan, but the threat is limited. No thunder expected we are lacking significant moisture and lifting mechanism. Friday and Saturday will see a slightly better potential for showers and thunderstorms to drift into the southern panhandle, mainly for Hyder, Ketchikan and Misty Fjords. Any rain amounts will be light as the warm and drier low levels will bring high cloud bases and limit the potential for a wetting rain. Dangerous cloud to ground lightning and gusty winds are possible with any thunderstorms. Any marine layer stratus development will likely be limited along and just off the outer coast.

LONG TERM.../Sunday through Wednesday/...The upper level ridge is expected to begin to dissipate Sunday as a weak trough builds over the gulf, shifting the region toward zonal flow that will bring cooler, more saturated air onshore. Temperatures are expected to follow a cooling trend, due to 850mb level temps dropping, and leading to daily highs in the mid 60s by next week, though inland and southern areas may remain warmer in the low 70s due to the residual influence of a weakening surface ridge. As surface high pressure also weakens, a series of weak frontal bands originating from a surface trough dropping into the gulf from the Alaska Peninsula will move across the panhandle, resulting in widespread overcast skies and moisture advection in the low to mid levels. The northeast gulf coast, particularly near Yakutat, will be the primary focus for precipitation, with the most significant activity expected between Monday and Tuesday. While deterministic models show some spread still, the highest forecaster confidence results in 24 hour rainfall accumulations of 0.75 to 1.25 with this disturbance. The remainder of the week is expected to stay showery with lighter, intermittent rain and cooler temperatures across the panhandle, offering relief from the recent dry spell.

AVIATION.../ Through Friday afternoon/...

VFR conditions dominate SEAK for the next 24 hour TAF valid period. Offshore flow will keep most marine layer clouds out to sea, leaving cigs either non-existent or very high, in the case that clouds form during peak heating Friday afternoon. A dry atmosphere should also serve to limit cloud formation. Winds are generally light and should remain under 10kts.

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MARINE... Outside: High pressure over the Gulf keeps a tighter gradient over the eastern waters. Moderate to fresh breezes for the outer coastal waters through tonight. Winds will gradually diminish on Friday, becoming a gentle to moderate breeze that will remain into the weekend as the high weakens and gradient relaxes. Wave heights of 4 to 6 ft will diminish slightly through the weekend. Seas will diminish about a foot by Friday and continue into the weekend. Main marine concern for outer and coastal waters will be nightly return of marine layer, with fog and low stratus offshore. Winds and seas look to trend back upward by early next week as a change in weather pattern brings a low and front into the Gulf.

Inside: Weakening high pressure out in the Gulf will allow for moderate to fresh N to NWly to trend downward as the gradient weakens across the panhandle. Winds will become light to gentle and more N to NEly by Friday low pressure sitting south of the panhandle and troughing drifting west. Lynn Canal will likely see moderate to fresh northernly with the tightened N-S gradient remaining. Light to gentle winds should continue into the weekend with occasional moderate winds for Lynn Canal. Winds will become more onshore through the weekend as the high pressure builds east towards the panhandle. Slight chances remain for isolated thunderstorm development from Canada moving into the southern panhandle this evening, but especially on Friday and Saturday Friday afternoon/evening, primarily near Misty Fjords and Clarence Strait. Gusty winds and lightning would be possible if any thunderstorms make it into the area.

FIRE WEATHER...High pressure out the the Gulf continues to bring mostly dry and warm weather across the panhandle. Warm temperatures with daytime highs reaching the 70s to mid 80s and dry weather are expected to continue through the end of the week and into the weekend. More inland areas are expected to continue reaching relative humidities down to the 30s to 40s during the daytime hours with rebounding during the overnight hours into the 80s to 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 Friday and Saturday during the afternoon/evening.However, due to the lack of low level moisture each day the chance of thunderstorms is still only around 15% or less.

Overall, expecting the dry and warm trend to continue through the end of the week with fire weather conditions looking to last into the weekend as well, however 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. The dry conditions are looking to last through the weekend, with the next chance of rain not being until Monday.

HYDROLOGY...The Mendenhall River crested around 2:15pm this afternoon with a height of 14.7 ft. The river will continue to drop through the afternoon and evening tonight before exiting flood stage during the overnight. Levels in Suicide Basin could still continue to fall somewhat even though the release has stopped but should come to a steady here eventually. The water in the Mendenhall river basin will continue to drain out but will take some time to move from the lake down to below Brotherhood bridge.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Heat Advisory until 7 PM AKDT Friday for AKZ318-319-321-325-328- 330>332. MARINE...None.