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000 FXAK67 PAJK 221432 AFDAJK Southeast Alaska Forecast Discussion National Weather Service Juneau AK 532 AM AKST Wed Feb 22 2017 .SHORT TERM...
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As a weak system drops southeast, leaving the bulk of the Panhandle with mostly clear skies and chilly temperatures, another stronger one glides eastward across the Kodiak Island. This one will set up a very weak overrunning event prompted by warm air advection for coastal sections of Southeast Alaska, but potentially farther inland as well. Tonight its energy gets diverted to the southeast similar to the last, but weak lift will maintain a chance of snow across the Panhandle overnight. Visibility at Middleton Island is down to 3 miles at 13Z suggesting snow bands may have pushed east of Cape Suckling yet still lie well west of Yakutat. A surface low in the western gulf will track east today. Unlike the last feature and its negative tilt, this system`s structure comes in with hardly any tilt. And the 00Z and 06Z NAM both tempt us with both a more northerly track and more conducive southwesterlies in the low levels across the Northern Panhandle. This would perhaps mean light accumulations of snow over Pelican, Gustavus, Hoonah, Tenakee and Juneau. But both ECMWF and GFS (both 00Z and 06Z versions) maintain a more southerly track and quickly toss a few flurries across these same areas while offering moderate confidence for light snow with potential rain mixed in from Sitka south along the coast. This brings up the epic conundrum for the north central Panhandle of looking at each solution as a petal on a daisy: does the snow fall, does the snow not? Rather than fight we simply must present the forecast as is: we simply have little confidence which explains the unsatisfactory 50 percent pops. But should anything fall across this region, amounts will be light, and we would be shocked if anyone received a couple of inches out of this. An inch of snow, less, or nothing at all is more likely we think. Any snow along the coast, and potentially anything that makes it farther inland, will dissipate tonight as the deformation band stretches south away from our area and weakens. Clouds will generally persist most of the night. The southern Panhandle will see effects delayed with this system, as much of the area will experience sunny skies today. As the approaching shortwave crosses the gulf this evening, the energy split to the south will slow its progression, therefore, yielding a rapid increase of clouds with a chance of snow/rain for Prince of Wales Island and only a slight chance for the southern Inner Channels. As the surface low moves into the central gulf this evening, 30 kt easterlies will develop in the northern gulf with 25 to 30 kt northwesterlies appearing in the central gulf south of the center. Otherwise, seas will briefly rise to 8 feet across the northern gulf this afternoon and tonight. Winds across the Panhandle look to remain light but turn southerly ahead of the system this afternoon before flipping back to northerly tonight. EC/GFS offered the preferred track, but pops this afternoon and evening were adjusted minimally to preserve uncertainty. .LONG TERM...Somewhat quiet extended forecast today with an upper ridge situated just to our west providing mainly offshore flow over the panhandle. This pattern is broken once this weekend by a moderately strong short wave moving through the ridge, and again mid next week as a stronger trough suppresses the ridge to the south. Main forecast concern is the trough that will be moving through over the weekend (mainly Saturday) as forecast models are not quite on the same page with it at this time. The main sticking point appears to be on the strength of the system as the ECMWF and CanadianNH are both around 9 mb stronger with the surface low then the Nam and GFS. This is not the only difference between the two camps. The ECMWF and Canadian are also showcasing a stronger upper level jet on the western side of the trough and more cold air advection based on 1000-500mb thickness forecasts. The result at the surface is a noticeable difference in wind and precip forecasts between the two camps (stronger winds and more precip in the ECMWF and Canadian vs the Nam and GFS). Given the differences, decided to stay the course for the weekend forecast (which leans more toward the GFS at the moment) to see which way the models lean in subsequent runs. Expecting 20 to 30 kt winds out in the gulf, light snow for the northern panhandle with accumulations of around 1 to 2 inches, and rain and snow for the southern panhandle. These figures could ratchet up or down later depending on which way future runs trend. Otherwise, most of the extended forecast features mostly to partly cloudy skies with winds mostly 20 kt or less. Temperatures will likely range in the low 30 to low 40s for highs and 20s for lows. Pattern change is possible for mid next week as a trough suppresses the upper ridge to our west. This appears to bring in some cooler air and a more active westerly flow pattern. Still too early to get any details, but more precip and wind appears to be the going trend for mid next week.
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&& .AJK Watches/Warnings/Advisories...
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PUBLIC...None. MARINE...Small Craft Advisory for PKZ052. Small Craft Advisory due to Seas for PKZ051.
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&& $$ JWA/EAL Visit us at http://www.weather.gov/Juneau

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