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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska
340 PM akdt Monday Aug 3 2015

Short term...afternoon water vapor satellite image shows an
upper level low over the western British Columbia. Upper dynamics
wrap around the low and pull cooler air aloft over the south
central and southern Panhandle areas. At the surface...northerly
pressure gradient became tight between the high pressure across
the Yukon and a trough of low pressure over the north central
Panhandle. Small craft level northerly winds over the northern
Inner Channels persist. A plenty of sunshine over the northern
half of the Panhandle with downsloping winds...brings afternoon
temperatures soaring up to the lower to middle 70s...while gloomy
skies with scattered to numerous showers continue across the
southern areas with their temperatures in the lower to middle 60s.

Models remain in fair agreement for the upper low continues drifts
southeast across British Columbia through Tuesday and an upper
ridge builds behind over the southeastern Gulf. The trough of low
pressure will weaken and a ridge of high pressure build across the
central and eastern Gulf. Refreshed the inherited forecast with
the nam12 for its good initialization.

The embedded cooler air aloft around the upper low will continue
to increase instability over the southeastern Panhandle this
evening and expect slight chance of thunderstorms from Petersburg
south to Ketchikan and Hyder areas. As the ridge builds over the
eastern Gulf...northwesterly winds will increase to become small
craft level over the outside waters on Tuesday...while the small
craft level winds across the northern Inner Channels continue.
Underneath the building ridge...marine stratus will remain over
the outer waters...slowly drift southeast through Tuesday.
Northern half of the Panhandle will continue to be dry and Tuesday
highs will be warm again to the lower to middle 70s. Showers will
become scattered across the southern zones later tonight as the
upper low drifts farther east over British Columbia.

Long term...slow-moving closed low will be exiting the southern
Panhandle to the east on Wednesday PM...chance of showers persist for
the southern zones into the evening. New moderate closed low is
prognosticated to be just south of Aleutians centered at about 56n/156w
at 06z Wednesday. Thus aside from increasing winds over the western
marine areas in the afternoon looks like a quiet Wednesday. Enhanced
surface pressure gradient will enter the eastern Gulf around 00z
Thursday. Somewhat enhanced local gradient will likely lead to
marginal/brief Small Craft Advisory conditions with southerly winds in northern
Lynn by 21-00z Wednesday...and with 25kt over marine waters (mostly southeast
flow) by 06z Thursday or so. Ongoing software problems here do not increase
confidence in these wind solutions though. Leading edge of
frontally- forced rainbands should reach the coast in the 06z- 09z
Thursday period and spread throughout Panhandle shortly afterwards. At
this point models point towards 25-30kt maximum for the offshore
zones but this will need to be monitored as models are updated.
Primary update to grids was to go with a somewhat stronger Gulf
low with increased marine gradients and winds from 18z Wednesday Onward
as advertised by the new NAM/ec models. Chose also to update the
inherited thermodynamic grids with a combo of NAM/ec/GFS solutions
through day 4.

By 00z Friday the 12z ec model is a bit stronger with the
southeastern Gulf closed low...at that time the low is phased with
a deep trough extending up into the eastern Alaska Mainland similar to
the GFS 18z solution. The 12z Gem model is somewhat of an outlier
at that time with the main closed low to the west out over the
southern Gulf. On Sunday the ec is showing more progression than
the GFS...with a double-barrel upper low poised upstream over
western Alaska and the Aleutians and shortwave ridging over most of the
Panhandle. This also paints a gloomier/wetter picture for early
next week than the GFS forecasts for the Panhandle and is the more
likely scenario at this point. It is in agreement with wpc
guidance which went mostly with the ec model throughout and seems
to be the preferred solution...days 5-8 in the grid update
followed wpc guidance with mostly ec quantitative precipitation forecast udpates. Result in all of
this is a chance of rain area-wide on Sat...too early to go with
"likely" or "none" at this point. Odds are sun will see a break if
the ec solution pans out. Model confidence is only average
considering the model spread from the weekend Onward.

&&

Ajk watches/warnings/advisories...
public...none.
Marine...Small Craft Advisory for pkz012-013-041>043.

&&

$$

Ahn/Wesley

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