Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
606 am akst Sat Feb 6 2016
Short term...a weakening trough along the Panhandle is being
moved inland by a ridge of high pressure over the Gulf of Alaska
through Saturday. The trough has a collection of showers along
the coast from Prince William Sound to haida gwaii. The showers
this morning are a mixture of rain and snow showers. Accumulation
of snow for the central to northern Panhandle looks to have been
around 1 to 2 inches. A few snow showers may continue into midday
however am not expecting much accumulations through the morning
The developing low moving north out the Pacific headed towards
Kodiak Island is right on the track we had been watching. The low
which was the deepest Saturday morning in the upper 950 mb range
will weaken to the upper 960 mb Saturday night. The weather front
arches east across the Gulf of Alaska to a triple point near haida
gwaii late Saturday night. Rain and areas of heavy rain will start
to move back into the Prince of Wales Island and southern
Panhandle late Saturday night. The northeast outflow from Portland
Canal will keep some cooler temperatures in the Hyder area so
precipitation likely to start as snow there late Saturday night.
Winds along the front are maximum gales... although areas of min
storms may be found as well. Have kept the forecast to 45 knots.
Southern Inner Channels and have increased up to gale force. Also
looks like Cross Sound will also reach gale force late Saturday
The frontal band will start to spread gusty winds to the
coastal areas form the southern Panhandle to the Baranof Island.
Have gone with strong wind headlines for late tonight for those
Long term...cyclone centered over 45 north and 155 west at the base of a
longwave trough will continue on a northward trajectory and
weaken as it at first lunges toward Kodiak through Sunday...and
then tip-toes towards Kodiak Sunday night. An associated gale-
force front will enter the far northern Gulf on Sunday morning and
begin weakening. Farther southwest...strong winds spawned by the
front will weaken even faster as most of the frontal energy pulls
to the northwest. Thus gusty winds across the southern and coastal
Panhandle should relatively quickly subside.
The big story continues to profile the long fetch of warm, moist
air aimed mainly towards the southern Panhandle Sunday into early
Tuesday. Two big issues with this event are one, the heavy rains
and resulting rises in rivers and streams over this region, and
two, the interaction of the heavy precipitation with the strong
possibility of cold air dammed into Hyder resulting in heavy snow.
Confidence continues to build on the progression of the deepest
moisture plume and strongest lift setting up over the far
southern Panhandle...mainly zones 28 and 29 for Sunday and Sunday
night before potentially migrating slowly westward. European model (ecmwf)
potentially wants to turn the plume west, as far north to Juneau
by Monday, but uncertainty is highest on Monday with the European model (ecmwf)
pushing a wave much farther north than both the GFS and the NAM.
At this point our best guess is for zones 28/29 to receive 3 to 6
inches of rainfall with 2 to 4 inches over 26 and 27 during this
event. But a miscalculation of just thirty/forty miles to the
west and Klawock and Craig should receive much more than forecast.
Rainfall rate satellite products suggest bands of 0.1 to 0.2
inches/hour. Given topographic lift, this should be magnified at
landfall...thus heavy rain bands should not be a stretch.
The other issue is whether Hyder warms up at the surface given the
warm conveyor belt aloft. It has to...yes. But when? There is no
evidence that warm southerlies will travel up Portland Canal...but
the surface will more likely warm by heat Transfer from the whole
column above. The heavy precipitation rates may just succeed at
this. The deeply saturated column should have no room for
evaporative cooling. But given a topography that stubbornly locks
cold air in place, we must respect its ability to surprise. For
this reason we issue a watch for the possibility of a borderline
warning or advisory event. Heaviest snow will likely occur on
Monday with an increasing possibility of a switchover to rain
Sunday night. Possible accumulations in Hyder range from 8 to 14
inches and purposefully also reflected a lighter end given
temperatures near the melting point. Other than Hyder...
precipitation will also begin as snow over much of the northern
Panhandle as the edge advances on Sunday before changing to rain
across this region by Sunday night.
A ridge finally buckles northward over the Panhandle by
Tuesday...thus ending the rain train into southeast. However
another wave restarts things by Wednesday for a continued wet and
warm pattern through the end of the forecast period.
Used ecwmf/GFS for minor changes Sunday/Sunday night. Model
disagreement discouraged changes on Monday. Forecast confidence
Dicey on precipitation type and snow amounts for Hyder...especially
Sunday night. Confidence greater for other issues.
public...strong wind from late tonight through Sunday morning for akz027.
Strong wind late tonight for akz022-028.
Strong wind late tonight for akz023.
Winter Storm Watch from Sunday morning through late Sunday night
Marine...Gale Warning for pkz022-033-036-041>043-051-052.
Small Craft Advisory for pkz011>013-021-031-032-034-035-053.
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