Scientific Forecaster Discussion
fxak67 pajk 120001
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
301 PM akst Mon Dec 11 2017
Synopsis...a stalled front extending north south across the
central Panhandle will weaken Monday night as another front will
push north across the Panhandle early Tuesday morning. A third
front will track into the southern and central Panhandle late
Tuesday. A gale force front arrives in the eastern Gulf Wednesday.
Short term...the front ushering integrated vapor moisture values
of 6 Standard deviations above normal and precipitable water
values of 4 plus Standard deviations above normal has resulted in
persistent moderate rain rates across portions of the north-
central Panhandle and up to 10 inches of heavy wet snow at White
Pass this morning. Creeks and rivers across the Panhandle have
experienced some rises, and we are concerned enough to issue a
flood advisory for Jordan Creek (see hydrology below).
The other big story is the continuing warmth generated by the
deeply meridional southerly flow. Temperatures in the high 50s and
above have been reported from Wrangell south today with low 60s
on Annette Island to the far south. Forecast temperatures for
the next few days are still very mild for December, however, we
have not gone into the 50s, mainly because the southern Panhandle
should be much Rainier for next couple of days.
Another front will lift northward across the Panhandle late
tonight into Tuesday morning spreading more rain in the forecast
for the northern and central Inner Channels. By Tuesday
afternoon, the northern Panhandle should begin to dry out a little
with only scattered showers. However, another wave will lift
north Tuesday afternoon into Tuesday night spreading rain
northward from the southern Inner Channels.
By Wednesday, a stronger front, will deliver yet more round of
moderate to heavy rain across the Panhandle along with gale force
winds across the eastern Gulf. Likely winds across the Inner
Channels will increase as well. In line with a steady warming
trend through mid-week, we think it increasingly likely that White
Pass should see some rain mix in with snow, thus keeping snow
amounts below hazard criteria.
Confidence is high for warm, wet conditions, and has increased
somewhat on features. However, some details will need to be
sharpened in time.
Long term.../Wednesday through Sunday/ as of 10pm Sunday...long
range models have diverged on timing of lows/fronts moving into
the region through the extended forecast period. However the
overall idea of a very active pattern has not changed; warm/wet
to start with a slight cooling trend through the end of the week.
Wednesday will have start off wet with relatively light rain,
then a low and assoc gale force front will move north into the
central Gulf. This will likely pull the rain back from the far southeast
Panhandle for a period, then move back inland as the front shifts
east over the Panhandle Wednesday night. A wave moving north
along a front late Wed into thurs will infuse another shot of
moisture to the area with moderate to heavy rain. Will need to
watch this wave over the next couple days. Some models show a new
low center developing along the frontal trough near Cape Decision
while others only have a trough and still others have a stronger
low center out over the central Gulf. Have increased winds
slightly along the trough, but would need to adjust up more if the
low develops near Cape Decision. Will also see a wind shift to
the west-SW behind the frontal trough on Thursday.
There is lower forecast confidence for timing of fronts and rainy
vs. "Dry" breaks due to model spread through the end of the week,
but overall it looks to be more wet than dry. Due to
inconsistencies in models opted to make fewer changes to this
Hydrology...persistent rain rates of between 0.1 and 0.2 inches
per hour this morning coupled with high December freezing levels
have raised water levels in portions of the north-central
Panhandle, including Jordan and Montana creeks. Rain rates have
diminished as the front draped across the central Panhandle has
weakened. But with the trend in the river levels on Jordan not
falling, we elected to issue a flood advisory for Jordan Creek
effective through the next frontal passage Tuesday morning.
public...flood advisory for pkz025.
Marine...Small Craft Advisory for pkz036-041>043-051-052.
Small Craft Advisory due to seas for pkz022-053.