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Southcentral and southwest Alaska forecast discussion 
National Weather Service Anchorage Alaska
534 am akdt Tuesday Jun 2 2015

Analysis and upper levels...
water vapor satellite imagery shows a low spinning south of the
Alaska Peninsula and another south of Shemya. These systems are
bringing wide spread low and middle level clouds back into the
southern Mainland and surrounding waters. At the surface...a broad
area of low pressure is centered across southcentral with a weak
boundary spread from the Copper River basin to the Kuskokwim
Delta. Rain across the Kuskokwim Delta continued this morning from
the front that pushed in from the north on Monday. A rain band
formed overnight as a short wave moved a front up from the Alaska
Peninsula low with rain stretching across Bristol Bay...to the
Kenai and the Prince William Sound. This rain band is slowly
making its way inland this morning. To the west over the Bering
and Aleutians...a front is stretched across Shemya to Adak
bringing light rain with general low clouds and fog across the
eastern Bering. Another weak front is approaching the Alaska
Peninsula.

&&

Model discussion...

Models were in good agreement with the general synoptic pattern. A
blend of models were used to update the current forecast with only
minor changes made overall. The biggest challenge today is where
thunderstorms develop as a marine moisture boundary pushes north.
Isolated thunderstorms are expected mainly across mountainous
areas of southcentral with instability limited by clouds and
cooler conditions.

&&

Short term forecast southcentral Alaska (days 1 and 2)...
showery weather will continue to spread across Southeast Alaska
with cooler more seasonable temperatures and higher relative
humidities through midweek. While the thermal trough in place
over southcentral has weakened and drifted further north it will
continue to provide enough instability for scattered to numerous
showers while low level onshore flow from the Gulf brings in a
good moisture supply. Further to the north over the Talkeetna
Mountains and the northern half of the Copper River basin isolated
thunderstorm will likely fire off again this afternoon and evening
as well as on Wednesday afternoon.

A weak frontal system currently over the southern Gulf will lift
north across the central and northern Gulf tonight and into
southcentral Alaska on Wednesday. In addition to bringing rain to
the coast and showers inland...this front will strengthen the
surface ridge along the north Gulf Coast significantly increasing
southeasterly onshore gap wind through Turnagain Arm...the Knik
River Valley and into the Copper River basin Wednesday afternoon
and evening.

A substantially stronger frontal system will swing through the
southern and central Gulf on Wednesday...reaching the northern
Gulf Wednesday night. In addition to bringing a swath of solid
gales to the outer waters...north to northeasterly gales are likely
in Shelikof Strait and southern Cook Inlet as well as east to
northeasterly gales through the Barren Islands. Further north
along the northern Gulf Coast...conditions look rather favorable
for the formation of a barrier jet with easterly winds in the 40
to 45 knots range which may push into the entrance of Prince William
Sound late Wednesday night and early Thursday morning.

&&

Short term forecast southwest Alaska (days 1 and 2)...
the wet pattern is expected to continue over the southwest
Mainland through the short term. Today...the deformation zone
aloft that aided with convection the last two days will continue
to weaken...thus limiting support of thunderstorm development
today although providing ample support for widespread showers.
Models are less enthusiastic about thunderstorm development today
than in previous days with with the 06z NAM being the most
aggressive with development....and even that is marginal. The
Bethel sounding this morning is still fairly unstable with a Li
value just below zero and numerous showers are present on the
Bethel and King Salmon radars. That being said...thunderstorm
development is expected mainly along the interior regions of
Bristol Bay and into the middle Kuskokwim valley this afternoon as
this area seems to have the best chance for some breaks for sun to
aid diurnal heating which the main trigger for the isolated
thunderstorms.

Rainfall will continue tomorrow as the low moving to near Kodiak
Island begins to impact the region. Winds will begin to increase
through the kamishak gap tomorrow as the front moves inland over
south-central Alaska.

&&

Short term forecast Bering Sea/Aleutians (days 1 and 2)...
winds will remain fairly light over much of the Bering Sea and
Aleutians as the low south of Shemya moves south of the region and
weakens today. Near gale force winds over the western Aleutians
will continue today before decreasing tonight. As the low re-
develops near Kodiak Wednesday much of the western 2/3rds of the
Bering will come under dry northerly flow...which should produce
rare partly cloudy to mostly clear conditions over much of the
region. Areas of fog and marine stratus can be expected to
continue over the eastern 1/3rd of the region...keeping the
pribilofs and the Bering side of the Alaska Peninsula in lower
clouds and fog.

&&

Long term forecast (days 3 through 7)...
the impending shift to a cooler and wetter pattern will be well
underway by Tuesday as high amplitude ridging over the Mainland is
replaced by a sprawling longwave trough extending from the
Canadian Arctic into the North Pacific south of the Alaska
Peninsula. This will yield a more showery regime as temperatures
moderate to around seasonal normal values through the end of the
week. A front approaching the Gulf in the Thursday/Friday
time frame along with continued onshore flow will keep abundant
rainfall focused along the coast into the weekend. Farther to the
west...a persistent weak upper level flow pattern will keep
relatively benign conditions over much of the Bering through the
next week as the most active weather remains south of the Aleutian
chain.

&&



Afc watches/warnings/advisories...
public...none.
Marine...gales 352.
Fire weather...none.

&&

$$

Synopsis and model discussion...kh
southcentral Alaska...jer
southwest Alaska/Bering Sea/Aleutians...rf
long term...ml

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