Area Forecast Discussion
Issued by NWS Juneau, AK
Issued by NWS Juneau, AK
976 FXAK67 PAJK 201212 AFDAJK Southeast Alaska Forecast Discussion National Weather Service Juneau AK 412 AM AKDT Thu Jun 20 2024 .SHORT TERM...Our period of overall warm and dry weather is slowly starting to come to an end. High pressure continues to shift to the east and weaken while a low remains in the gulf. Marine cloud cover this morning is nowhere near what it was in coverage earlier this week. Along the outer coast, a marine layer still exists up to Cape Fairweather but farther offshore, mid and high level clouds are obscuring satellite imagery of clouds near the surface. These clouds are expected to continue to move closer to the panhandle and then inland throughout the day. As the low moves closer to the coast, winds across the area will start to become more influenced by this instead of the sea breezes we have been seeing during the day. Winds are still expected to remain light across the panhandle with the strongest winds remaining offshore during this time. .LONG TERM.../Friday into next week/...The next round of rain and wind arrive in the panhandle Friday with the rain chances lasting into the weekend. We`ll be watching a low tracking east through the gulf towards Haida Gwaii. The associated front will swing north into the panhandle. This front will likely (greater than 80% chance) bring rain to the area, especially in the southern half. Farther north, confidence is a little lower, so stuck with PoPS around 50 to 70%. This is due to low confidence in how far north the front, and organized precip, will go. In addition to the incoming rain, wind speeds will be elevated along the front as well. For now, went with marine wind speeds up to 25 knots along the front in the gulf. Euro ENS and GFS ENS give greater than 60% chance for wind speeds greater than 20 knots along the front during this time. As the front tracks through the inner channels, went with wind speeds around 15 to 20 knots. This was supported by the latest NBM, EURO ENS, GFS ENS, and EURO AIFS. Increased winds in Clarence Strait to up to 20 to 25 knots due to EFI tables highlighting the wind speeds in the southern inner channels. Precip will slowly diminish through the weekend and early next week as the front slowly falls apart, though elevated winds remain possible. The forecast for the 25th of June and beyond will prove to be more optimistic, with frequent breaks between systems, and periods of clearer skies across the panhandle. Aloft, the previous low which was ejected E into the Canadian Interior will be swiftly replaced by another broad area of low pressure diving into Gulf of AK. The newest low itself isn`t all that impressive, showing a closed circulation reaching 557 decameters in depth at 500 mb as per operational guidance. The operational model runs are in broadly good agreement - at least given how far out they are past initialization - on the bulk of the associated energy with this system passing S into southern BC and the Pacific Northwest. However, chances of showers will still linger across much of the panhandle - associated with the remnants of an old occluded frontal band from the previous system which the new low dragged back across the Coast Mountains and into Alaska, and which will bring some moisture with it despite the impact of synoptic scale E flow over the Coast Mountains. Anticipate some breaks in the clouds between these showers, which could result in fog formation for some areas during the early morning hours of the 25th and the 26th. As ridging builds over the Gulf in the wake of the (now) departing low on the 26th, expect those breaks to become the predominant weather pattern, though some showers may linger. The synoptic scale pattern on the 26th - a ridge over the Gulf bringing NW flow across the panhandle, could encourage the development of a marine layer across the outer coastal waters overnight. This brings with it the potential for cooler temperatures for outer coastal communities during the daytime on the 26th and the 27th should the marine layer be able to advance though at this time forecasting the extent of low level stratus coverage remains a challenge. For the remainder of the panhandle, widespread warm weather will return in force the 26th, the 27th, and potentially the 28th as diurnal heating thanks to the midnight sun takes hold. While some showers could form with the heat of the day, am not anticipating anything significant and think that current guidance is overestimating chances of precip during this time frame. There are some indications that another system will approach the panhandle the 28th or the 29th, but this far out, operational and ensemble guidance alike trend towards being too aggressive in breaking down ridging, and so anticipate that this system will likely be delayed beyond what current guidance is indicating; if it reaches SE AK at all. && .AVIATION... Marine layer is working its way up the southern panhandle once again this morning with IFR CIGS between 600-900ft near PAKT and PAKW. Will see gradually improving CIGS across the southern panhandle to general VFR flight conditions by the afternoon as high level clouds move in overhead. For the northern panhandle, expect predominate VFR flight conditions through today. A weak front in the northern Gulf of Alaska will spread BKN to OVC skies across the area with CIGS AoA 5000 ft. A stronger reinforcing low moves into the eastern Gulf by Friday early morning, increasing shower potential after 09z for the northern panhandle. Winds should remain 10kts or less expect for PAGY, where sustained winds up to 15kts will be possible after 23z. && .MARINE...As high pressure moves to the east, a low will continue to take control of the gulf. This will bring small craft conditions to the offshore areas as winds and seas are expected to increase. Headed into the weekend, a second low is expected to move up from the south and west bringing more elevated winds and seas to the area. && .HYDROLOGY...Minor flooding continues along the Chilkat as warm daytime and overnight temperatures have continued to allow for more snow and ice melt. These conditions are expected to continue into the start of the weekend before more clouds and cooler temperatures will help to reduce how warm we have been getting. Elsewhere, other river and stream basins have been responding to the warmer temperatures by showing increased flows. && .AJK WATCHES/WARNINGS/ADVISORIES... PUBLIC...None. MARINE...Small Craft Advisory for PKZ663-664-671-672. && $$ SHORT TERM...SF LONG TERM....GJS/GFS AVIATION...NM Visit us at http://www.weather.gov/Juneau