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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
558 am akst Wed Jan 17 2018 


Short term...transition period for Southeast Alaska continues through the 
day as one system exits the NE Gulf to the west and a second moves 
into the far southeast Gulf from the North Pacific. Infrared satellite imagery 
this morning shows the gale force frontal band associated with a 
parent low over Kodiak tracking westward. Overnight rain showers 
have been diminishing from south the north. 24 hour precip amounts 
showed rather large range from around 0.10 to upwards of 1.00 
inches. The drying/clearing trend for the central and northern 
Panhandle will last into Thursday night, however southern regions 
will be back into rain through the day with the next advancing 
low. At this time this system just enters the southeast Gulf where it 
will linger off the coast of haida gwaii through Thursday before 
it begins to progress eastward. Offshore flow for the central and 
northern areas expected to keep and potential precip bands 
rotating around the low center not making it much farther north 
than Frederick Sound. The slow March back to winter conditions now 
begins in earnest. As with previous days getting some of the 
warmest temps in the early morning followed by a slow downward 
path through the day. A more typical diurnal trend expected 
tonight. Still slightly above normal with 850 mb temps around 0 c 
and Max surface temps in the low to mid 40s. With clearing 
tonight central and northern locations min temps will finally dip 
below freezing. But any snow potential is very low since if the 
precip bands around the southern low do get further north, so will 
warmer temps. Along with the incoming se Gulf low and high 
pressure building over the British Columbia the increasing 
pressure gradient will flip winds to the east/north through the 
day and increasing speeds by this afternoon. Winds at 925 mb 
showing llj around the low. Highest jet steak magnitudes are 
mainly to the south of west of the Panhandle. Indication for 
mountain wave setting up over Juneau this afternoon with good 
cross barrier flow (see 925 mb llj) and critical level, but 
inversion may be over done with models dropping surface temps down 
too much. For now expecting 40 to 45 mph gusts for Douglas and 
downtown Juneau. Other outflow areas and east-west channeled terrain 
likely to see some similar higher gusts. 


Models were in fair agreement at mid levels and also with surface 
pressure. In addition little difference between new model runs 
and previous forecast for these fields. Bit more spread comparing 
pop to winds with overall lower amounts compared to previous day. 
NAM/namnest were picking up the outflow winds the best. Challenge 
today was once again tracking temperature trend this morning then 
determining fog development for tonight. Clearing, radiational 
cooling and moist air mass prime for fog but increased winds 
should limit this. Forecast confidence is only average, even with 
the good model agreement for mid level pattern, mainly due to this 
transition timing. 




Long term.../Friday through Wednesday as of 10 PM Tuesday/ 
models coming into better agreement on the larger scale flow 
pattern over the high latitudes. Upper ridge will build over the 
Bering Sea Fri-sun. This will cause an upper trof to dig S into 
the west Gulf during this time. Still some model differences on what 
the upper trof does after sun, with main issue whether it shifts east 
or more to the SW. Still some model differences on what 
interactions the upper trof will have with southern stream systems 
moving east across the npac. This interaction will be the big driver 
of weather for early to middle of next week over the area. 


Still looking like a cool down is in store for the area during the 
first half of the long range, but the stream interaction issue for 
latter half of the period will determine how much area might warm 
back up. If more southern stream energy is lifted north into the area, 
it would allow for a stronger warm up. The initial cool down will 
likely take temps to near or slightly below normal. The cool down 
should be accompanied by increasing outflow winds as well, but 
given lack of a strong sfc high to the north of the area, probably 
will not see more than gales with the outflow. 


Looking like a generally drier period for the first half of the 
long range, although this will depend on where a low near haida 
gwaii moves during this time. Models have been all over the place 
on it, from kicking it east toward SW British Columbia or lifting remnant of system 
more to the north and northwest as another system tries to undercut it. For 
now, staying with drier idea until a better signal on what that 
low will do shows up. Later on, upper trof over the Gulf will 
likely send some showers across the Gulf, and southern stream 
systems will have their own precip field moving across the npac. 
If upper trof shifts E, area will see increasing threat for 
showers (with mostly snow showers as airmass would be fairly 
cool in this scenario). If trof stays further W, this would likely 
allow southern stream system to move NE into the area, with a more 
stratiform precip shield. Ptype would be tricky as warmer air 
would likely move in as well, although the north half could stay cold 
enough for snow depending on track of any sfc low that moves into 
the East Gulf. Overall, do have an increasing threat for precip from 
sun Onward as both scenarios would give some precip to the area. 


&& 


Aviation...low level wind shear over the NE Gulf Coast subsides 
as the current low pulls east. In addition diminishing precip, 
improving visibilities and increasing ceilings through the day for 
central and northern areas. Potential for fog development tonight 
but should be limited to locally wind sheltered areas. Opposite 
situation for the southern Panhandle with the next advancing low, 
increasing wind shear, increasing precip, lowing, decreasing 
visibility and lowering ceilings. Expect only to be MVFR 
conditions. 


&& 


Marine...southeast gale force winds over the northeast Gulf diminish 
this morning as the current front/low pulls to the west. East gale 
force winds over the southeast Gulf Coast increase this afternoon 
as the next low moves up from the NE Pacific. Similar trend with 
wave heights from wind wave/swell: diminished over the NE Gulf 
Coast and increase over the southeast. Southerly inner channel winds 
diminished this morning and will flip to the north then increase 
through the afternoon. North Lynn Canal nearing Max small craft to 
possible gales with tightening pressure gradient. Highest gusts 
will develop this afternoon out of interior passes as gradient 
between the southeast Gulf low and high pressure over British Columbia 
increases. 




&& 


Ajk watches/warnings/advisories... 
public...strong wind from noon akst today through this evening for akz025. 
Marine...Gale Warning for pkz041-042. 
Small Craft Advisory for pkz012-013-022-031-033-036-043-051-052. 
Small Craft Advisory due to seas for pkz053. 


&& 


$$ 



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