Scientific Forecaster Discussion
fxak67 pajk 281258
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
458 am akdt Wed Jun 28 2017
Short term...a ridge of high pressure over the far eastern Gulf
will move onshore over southeast AK, further upstream there is a
developing low over the NE Pacific moving north into the SW Gulf
by tonight. The associated weather front will move northeast to
the eastern Gulf by Thursday night.
Used a nudge to the GFS to tighten up the gradient and increase
the winds for the western side of marine zone 310 and 52. A brief
period of 20 kt winds late this afternoon in northern Lynn Canal
is expected, otherwise most areas across the Panhandle will have
winds of 15 kt or less. Late overnight and early morning will see
light winds over much of the area, as well.
The big question about precipitation is where and how much. The
timing is tricky with the showers moving quickly across the
Panhandle depositing amounts from trace to just a few hundredths
Wednesday, drying out east of Yakutat by late Wednesday night.
Yakutat area is the exception to all of this where stable rain
with higher amounts will fall. With the approach of the weather
front precipitation returns to the entire Panhandle by early
Thursday morning. East of Clarence Strait has potential for being
drier through Thursday, a few sprinkles will still be possible.
Long term...Friday through Tuesday...as of 1030 PM tues...we
continue to see an upper level ridge with an associated high
pressure at the surface progress east out of the area during the
Friday timeframe. Precipitation chances will increase as we move
into the weekend, which is in line with the approach of a surface
front, the increasing onshore flow, and plentiful moisture
available. A strengthening front associated with a shortwave
moving east out of the Gulf will begin to impact the area Friday
into Saturday, bringing significant chances for rain and
increasing quantitative precipitation forecast. We also increased the winds with the frontal
progression across the eastern Gulf and into Cross Sound.
Likewise, winds were increased for the Post-frontal time period
for northern Lynn Canal late Sunday. Additional shortwaves moving
out of the parent upper level low situated over the Gulf will
impact the area Sunday through the rest of the time period of
interest and will continue the likely pops trend, with a possible
drier period beginning Tuesday. We'll continue to monitor
developments for next week.
We strengthened friday's front by nudging to the NAM/GFS and made
minor adjustments to the period beyond with wpc guidance. But
overall, few changes were needed. Overall confidence is average.
Marine...Small Craft Advisory for pkz052.
Small Craft Advisory due to seas for pkz043-051.