Scientific Forecaster Discussion
Northern Alaska forecast discussion
National Weather Service Fairbanks Alaska
100 PM akst Wednesday Dec 17 2014
Deterministic guidance are generally in good agreement through
the first 60 hours...with differences becoming more apparent
thereafter. Specifically...differences in how the 500 hpa ridge
evolves that noses into northern Alaska...Yukon...and northwest
territories and the handling of the broad low pressure area over
the Bering and southwest Alaska beginning late Friday and Sat. Guidance
otherwise is still on course for much of the short-term and
medium range up to Friday...outside of mesoscale details and local
effects. As such...the spirit of the going forecast overall is OK
and no drastic changes are anticipated.
WV satellite shows a well defined low in the central Bering with
another low in the northern Pacific south of the Aleutian Islands
and the Alaska Peninsula. The latter...is a strong cyclone that will
be influencing areas more so outside of our area of
responsibility. A short-wave trough is currently moving north over
the lower Yukon valley that\s apparent from WV as well. NASA sport
nighttime microphysics shows middle-level stratus with bases around
6-9 kft over most of the North Slope coast. A mix of stratus and
high- level clouds are elsewhere in northern Alaska
The surface low associated with the low over the Bering has a central
pressure of around 983 hpa at 9 am...while the cyclone in the
northern Pacific has a pressure of about 967 hpa. Surface observation show
flurries over portions of the North Slope. Light snow is seen over
the upper Koyukuk valley and in the Seward Peninsula north to the
western Brooks range. This weather is associated with the
approaching short wave trough and topographic lift. Otherwise...the rest
of the active weather is south of the Alaska Range in terms of
Long wave trough firmly in place aloft over the Bering Sea and
the western half of Alaska with a ridge building on the West
Coast/western Canada Thursday. Jet stream is located in the northern
Pacific with it staying well south of northern Alaska through the
forecast period. The middle-level low in the Bering will continue to
move west and weaken then dissipate by Thursday...as a strong middle-
level low moves eastward south of the Kamchatka peninsula. 500
hpa low in the northern Pacific will move into the southern half
of the Gulf of Alaska Thursday while weakening...and then be drawn into the
broad area of low pressure that\s developing over the Bering late
Thursday/early Friday. The broad low is generally centered over Southeast
Alaska and the eastern Aleutian Islands by Sat. Otherwise...ridge
builds into northern Alaska and the MacKenzie river basin Thursday and
stays in place Friday over northern Alaska.
The surface low in the Bering will continue to weaken and drift
west. A weak frontal boundary extends from the low east into the
Kotzebue Sound currently. The front will continue to weaken and
dissipate tonight. Otherwise...the surface low south of the Aleutian
Islands will move east into the southern half of the Gulf of Alaska
while weakening. Complex surface pattern develops thereafter with
a broad surface low coming from the west that moves east into the
western Aleutian Islands Thursday with multiple low pressure centers.
A strong surface low pressure system then develops and organizes south
of the Alaska Peninsula/eastern Aleutian Islands Friday with guidance
generally suggesting two main low centers Friday/early Sat.
Main concern is winds for this forecast period. Precipitation
in on the quiet side in our aor. Local winds...Tanana Valley
jet...will become active as the pressure gradient increases with
high pressure in the Yukon and the surface low moving into the
southern half of the Gulf of Alaska late Thursday and Friday. Increasing gusts
and winds in the passes of the Alaska Range are also expected
beginning tomorrow into Friday. Winds will continue to be moderate
over the Bering Strait and over our marine areas near St Lawrence
Island. Winds will become more elevated in those areas Friday into
Sat as the pressure gradient increases in magnitude that is
associated with the developing low in the Gulf of Alaska Fri-Sat.
Tonight and tomorrow...isolated to scattered snow showers over the
North Slope...near the Brooks range...and on the extreme end of
West Coast/over the northeastern Bering Sea. Dry conditions are
generally anticipated tomorrow night into Friday night over the West
Coast and interior.
Coastal hazard potential days 3 and 4...none
heavy freezing spray warning for pkz210.
Small Craft Advisory for pkz210.
Gale Warning for pkz210.
Brisk Wind Advisory for pkz225-pkz230.
Et Dec 14