Scientific Forecaster Discussion
fxak68 pafc 171345
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
445 am akst Wed Jan 17 2018
Analysis and upper levels...
The large low that churned across the Gulf of Alaska yesterday has
been steadily weakening and the center of the storm is basically
directly overhead Kodiak Island as of this writing. The main
weather front has weakened and pushed into interior AK, leaving
behind numerous residual bands of rain showers that are impacting
southcentral Alaska (primarily the coastlines). Southwest Alaska
is generally on the cold side of the storm, and is seeing periods
of wet snow falling along and west of a line from King Salmon to
Sleetmute. East of this line, precipitation is more intermittent
and is warm enough to fall as rain or patchy light freezing rain.
Meanwhile, way out west, a front has pushed through the western
Aleutians with rain and gale-force winds. The associated 981 mb low
pressure system is approaching Shemya Island, and this whole
system will be slowing down and weakening over the next 12-24
hours as high pressure begins to build in the Bering Sea.
All models are in good agreement on the evolution of the major
features over the next few days. As a result, forecast confidence
is above average. A pattern change is on the horizon for all of
southern Alaska, transitioning to a cold and dry airmass for all
panc...VFR conditions and light north winds will persist
throughout the period. Wind shear should increase by late this
morning as southeast winds aloft approach the area and continue
through early evening.
Short term forecast southcentral Alaska (days 1 and 2)...
The low is centered over Kodiak Island this morning with a slow
moving secondary front along the north Gulf Coast and stretching
into northern Cook Inlet. This continues to bring rain to the
coast and scattered rain showers inland. A few pockets of freezing
rain are possible this morning across southcentral Alaska in
areas where the temperature dropped just below freezing, but the
precipitation type is rain for the vast majority of the area as
temperatures have largely remained above freezing.
The rain should taper off today as the system weakens but
temperatures will remain warm over most of the area today before a
marked cooling begins tomorrow.
Patchy fog is likely to develop this morning in the Copper River
basin as that area has largely cleared out this morning. The fog
will likely be in-and-out throughout most of the day for lower
elevations and some areas of low stratus may persist into the day
The trend towards colder and drier conditions is still on track to
begin tomorrow as high pressure builds across the interior of the
state. This will shift winds to a northerly direction with outflow
winds developing along the north Gulf Coast tomorrow and
increasing Friday. Kodiak is the outlier for the region as the
remnants of the low currently there will take a little longer to
clear out continuing the threat for some rain and snow showers
there through Thursday before becoming all snow showers Thursday
Short term forecast southwest Alaska...
the low near Kodiak will continue to bring light snow to
southwest Alaska as it, and the snow, slowly diminishes into
Thursday. By Friday, most of the precip will be gone and cold
northerly flow will take its place bringing low temps below 0 f
Friday night. High pressure building in over the northern Bering
will help to keep the cold air and northerly winds coming.
Short term forecast Bering Sea/Aleutians...
the low near the western Aleutians will slowly track east as it
swings its front through the Aleutians. The front will make it to
the eastern Aleutians Thursday morning where it will stall and
fall apart. Behind this system, another system will move towards
the western Aleutians from the North Pacific with its front making
it to the islands Friday night. Both of these systems are warm
enough to bring some rain to mix in with the snow, with the second
system being even warmer than the first.
Long term forecast (days 3 through 7)...
as advertised in the past couple of long term forecast
discussions, a major pattern shift is expected over most of
Mainland Alaska this weekend and into next week. The upper level
pattern, which has been leading to warm and wet conditions over
southcentral, will migrate east this weekend with a high amplitude
upper level ridge setting up over the central Bering and an upper
level trough developing over central/eastern Alaska. This will
lead to strong northerly flow through the Bering straight and over
SW Alaska which will advect in bitterly cold air down from the
Arctic. The source of this cold air is currently bottled up over
northeastern Russia where temperatures in the yakutia region this
week were recorded as low as -80 f.
Models all show this cold airmass being pulled south into western
Alaska by the end of the weekend, though significantly modified
by the time it reaches the region. Long range ensemble guidance
shows marginal odds of minimum temperatures across western and
interior portions of Alaska being in the bottom 15th percentile of
climatology, or in layman's terms, temperatures are likely to be
well below normal next week, though not quite to record levels.
Temperatures could drop into the -30's to -40's along interior
sections of SW Alaska, with sub zero temperatures reaching the
Bristol Bay coast. This will be the coldest air of the season so
far and may be a shock to residents who have been getting used to
the near record warmth this winter. Luckily for residents of
southcentral, the coldest air will be blocked by the Alaska Range,
though temperatures will fall back to normal or slightly below
normal values by early next week.
Marine...Gale Warning 125 130 155 178
heavy freezing spray warning 180 181 185