Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 270044
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
444 PM AKDT SUN JUN 26 2016
.ANALYSIS AND UPPER LEVELS...
The upper level trough encompassing much of the Alaska mainland
has drifted further south across the Gulf of Alaska. An easterly
wave that moved across the Mat-Su Valleys has weakened as it
drifted to the southwest. As such the rain has tapered off to
showers across much of the Anchorage bowl with a little light rain
holding over the Matanuska valley. A weak wave along the north
Gulf coast will continue to provide showers this evening. A
secondary wave in the eastern Gulf is rotating through the flow
and will eventually move north and west. A weak southeasterly wave
across far western Alaska has dropped into the Kuskokwim Valley
and western Bristol Bay regions. This wave, combined with
instability from daytime heating will spark some showers and
thunderstorms across the Kuskokwim Valley and interior Bristol
Bay. Cooler air at the low levels moving across the Kuskokwim
Delta should hinder afternoon/evening convection.
Across the Bering Sea, high pressure has made some progress moving
eastward through the day. Marine stratus remains extensive across
the eastern and central Bering Sea as evident from visible
satellite. The low that developed off the Kamchatka Peninsula has
strengthened and moved eastward towards the far western Aleutians.
An associated frontal boundary is just south and west of Shemya
and Attu Island and is traversing north and east.
Model QPF initializations were not all that impressive with the
broad band of rain extending Northeast to Southwest across the
Matanuska Valley and Anchorage Bowl. However, the high resolution
ARW did a fair job of capturing the areal extent of rain. Models
overall are handling the broad synoptic pattern over the next
couple of days. The higher resolution NAM will be used in this
afternoon`s forecast packages.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The Anchorage Bowl will have a brief window of sunny skies this
evening before increased cloud cover as an upper level shortwave
moves through the region by Monday afternoon. The bulk of the
precipitation through Monday will remain along the northern gulf
coastline except for a few showers spilling over the Chugach and
Kenai Mountains. The Turnagain Arm gap winds will continue through
the the upcoming weak as a ridge of high pressure builds along
the southeast Panhandle towards the northern Gulf. We have a
northeast storm motion which will result in some isolated
thunderstorms tracking over the alaska range from the north before
dissipating this evening.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Mon and Tue)...
The start of the week will be much like the weekend has been. The
thermal trough will remain the key feature. It will bring
widespread showers and the potential for scattered thunderstorms
each afternoon and evening. There is a weak trough approaching the
YK-Delta from the northwest. This feature should help to further
intensify convection this evening. It will also serve to induce a
low-level jet over the Kuskokwim Valley during the overnight hours
tonight. So there could be some gusty southerly winds for the
higher elevations from Sleetmute East.
Ridging over the Bering will also continue to approach the Delta
over the next 24 hours. Underneath this ridge is a nearly
continuous blanket of fog and low marine stratus. As the ridge
nudges closer, this fog and stratus will start to encroach upon
the Coast. Nunivak island and Bristol Bay are already seeing some
of it. By Tue morning it should be able to make it far enough
inland to affect Bethel.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Mon and
The pattern over the Bering could be divided in two, but the
impacts would be much the same. From the Central to Eastern
Bering, strong high pressure remains dominant. It continues to
plague those areas with fog and marine stratus. While some of the
fog has lifted into just low stratus this evening, we expect it to
reduced visibility at the surface for many locations as
subsidence increases overnight. Over the Western Bering, it is a
slightly trickier scenario. Weak warm occlusions keep trying to
push into that area. However, they are mostly falling apart before
they can reach Shemya, Atka, or Adak. This has kept precipitation
to a minimum and allowed fog to linger. A stronger front will push
from west to east through Shemya tonight. This will bring rain to
the far Western Aleutians and should provide enough mixing to
improve visibilities out there. But the front gets hung up over
the Central Aleutians and just weakens in place through Tue. This
could make for a very warm and moist air mass just sitting across
that area. Thus, we have increased the coverage of the fog and
lowered the visibilities over those locales.
.LONG TERM FORECAST (Days 3 through 7)...
A mountain rain shower pattern with breaks of sun will begin the
forecast on Tuesday afternoon and continue through Wednesday
afternoon. Conditions look to begin to go downhill on Thursday.
Several disturbances in the flow will affect the forecast there
after. Thursday`s mountain showers/thunderstorms will be enhanced
by one of these disturbances, but a stronger one comes through
Southcentral overnight Thursday into Friday. The disturbance should
bring widespread wetting rain from east to west Friday. The
details get a little fuzzy over the weekend, but the gulf system
responsible for the active weather will still be in the area
promoting cloudiness and at least mountain showers. Expect mostly
cloudy conditions with generally light winds and seasonable
temperatures. Cloud cover will increase and temperatures will
moderate through the remainder of the week.
Technically...the upper level low pressure spinning in the Gulf
will control the weather through the remainder of the week. Early
on, Southcentral Alaska is on the periphery of this system leaving
any diurnal convective activity over the mountains on
Tuesday/Wednesday, enhanced by any embedded easterly shortwaves.
A stronger shortwave (not embedded, actually a limb of the upper
low), looks to amplify on the baroclinic zone between the Yukon
ridge and Gulf trough late week, bringing widespread moderate
rain. However, model guidance is notoriously bad at resolving
these type features, and some spread among guidance still exists
as far as where to track this wave.
SYNOPSIS AND MODEL DISCUSSION...LIW/BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO