Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
401 PM akst Sat Feb 28 2015
Analysis and upper levels...
there is an upper level short-wave trough situated along about 155
degrees west longitude which is rapidly moving east. There is a
large upper ridge that this short-wave is essentially "barreling"
through. Further west there is a deep low centered just east of
the Kamchatka peninsula with a strong weather front over the
western Aleutians. There is also a low well south of the central
Aleutians that is moving northward.
the numerical models are in good agreement through the short term.
They differ somewhat on the timing and location of surface lows
moving into the Bering and to near Kodiak on Monday. The GFS and
European model (ecmwf) are fairly close and are the preferred models at this
Short term forecast southcentral Alaska (days 1 and 2)...
snow will taper off this evening throughout southcentral as the
upper trough continues its rapid track eastward. Ridging will
build in behind the trough clearing out skies overnight. These
stable conditions should lead to fog development around much of
southcentral. However...there is some uncertainty with fog
development based on how quickly the skies will clear and thus how
far temperatures will drop before tomorrow morning. On Sunday
evening a front will make its way to Kodiak from the south and to
the Kenai Peninsula on Monday.
Short term forecast southwest Alaska...
High pressure builds into the southwest Alaska through Sunday and
will bring drier conditions through the region. A low pressure
system pushing north from the Pacific will bring moisture along
the southwest coastline and will spread inland by Monday
afternoon. This will bring warmer temperatures and result in a
wintry mix with a slight chance of light freezing rain for
Bristol Bay by Monday morning...then Monday afternoon for the
Kuskokwim Delta area. The precipitation will change to a rain and
snow mixture except for all rain along the coastlines as the
warmer temperatures continue to move farther inland through
Short term forecast Bering Sea/Aleutians...
the gale force low near the Kamchatka peninsula will continue to
track to the north before merging with a weak North Pacific low
tracking across the central Aleutians by Monday morning. This will
form a broad area of low pressure through the central Bering Sea
through Monday evening. This low then tracks into the Bering
Strait by Tuesday. This low pressure will bring a large swath of
moisture and stratus with patchy fog through the Bering Sea and
the Aleutians. The eastern Bering Sea and Aleutians will have a
shortwave trough push through by Monday resulting in southeasterly
winds. This will bring a swath of moisture with warmer temperatures
resulting in a mixture of rain of snow before transitioning to all
rain along the eastern Aleutians. The warmer air will push into
the eastern Bering Sea by Monday night and spread northward. By
Tuesday a weak ridge of high pressure will work its way into the
central Aleutians and the Bering Sea. The western Aleutians will
have a weather front entering the area by late Monday night and
push past Shemya by Tuesday. This will bring gusty winds and
widespread wintry mix of precipitation through Tuesday.
Long term forecast (tuesday through saturday)...
Tuesday is shaping out to be an active weather day across much of
southern Alaska as an upper level low pushes across southwest
Alaska and a potent shortwave moves across southcentral Alaska.
Across southwest Alaska...a weak surface reflection associated
with an upper level low will drive a front across the region on
Tuesday bringing an increased chance of rain. Precipitation in
the vicinity of Bristol Bay will be predominately rain while the
Kuskokwim Delta and lower Kuskokwim valley should see mostly snow
with some locations mixing with rain. Precipitation chances then
begin to taper off into Wednesday as the upper low phases with a
second upper low in the Gulf of Alaska and weak longwave ridging
builds shifts eastward over southwest Alaska. A series of
Kamchatka lows will skirt across the western half of the Bering
Sea Wednesday and again on Friday bringing near gale force winds
and increased chances for rain (possibly mixed with snow during
the overnight hours).
Back to southcentral Alaska...models continue to be in good
agreement bringing a shortwave into southcentral Alaska from the
favorable southwest direction. This will bring likely precipitation
chances as far north as Talkeetna by Tuesday morning. The temperature
trend on Tuesday will be a determining factor for precipitation
type across southcentral Alaska. It looks as if precipitation for
most places early Tuesday morning to begin off as snow and
gradually transition to rain through the course of the day. There
is a slight chance for some light freezing rain at the onset of
precipitation along the Kenai Peninsula but would quickly change
to rain as temperatures warm. Precipitation chances will then
taper off from west to east late Wednesday into Thursday and bring
another round of above normal temperatures heading into the next
Marine...gale 177 185. Storm 178. Heavy freezing spray 180.