Small Craft Advisory 436, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKDT Fri Jun 2 2017

.ANALYSIS AND UPPER LEVELS...
A persistent elongated ridge over mainland Alaska and a broad
North Pacific low centered near 50N have formed a Rex block over
the region this morning. This is maintaining a dry offshore flow
pattern across most of the southern mainland. An easterly wave
rotating around the northern periphery of the low is starting to
spread some clouds and rain showers into the northeastern portion
of Prince William Sound, however the rest of the region remains in
a quiet and dry pattern beneath the dominant upper level ridge.
Meanwhile, another upper level trough is in place over the western
Bering, with a surface low near Kiska bringing rain to the
Western Aleutians. The rest of the Bering remains in a very benign
cloudy pattern within a col region between the dominant large
scale features.

&&

.MODEL DISCUSSION...
Guidance remains in generally good agreement through the short
term as models have converged on a solution for the next low
tracking along the Aleutian chain. The GFS/NAM have come more in
line with the EC/GEM over the past 24 hours in slowing the
progression of the low and keeping it south of the chain as it is
eventually shunted southeastward into the Pacific once it
encounters the mainland ridge. Given the better agreement, mainly
utilized Hi-Res NAM guidance to better capture local effects for
the morning forecast package.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through the TAF
period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Weak upper waves moving west across the Southcentral Mainland
combined with an active thermal trough will bring increased
chances of showers. Stability indices become favorable for
isolated wet thunderstorms along the Alaska Range, northern Copper
River Basin, and along the Talkeetna Mountains during the
afternoon and evening hours today and Saturday. Increased cloud
cover with waves and a marine stratus push up Cook Inlet tonight
will bring cooler temperatures to many areas. That said, max
temperatures could still climb to the lower 70s in the Copper
River Basin and Susitna Valley today with enough cloud breaks.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

The run of summer-like weather continues across Southwest Alaska
today. Plentiful morning sunshine, and temperatures in the lower
levels of the atmosphere continuing to warm will make 80 degree
readings in the Lower Kuskokwim Valley a distinct possibility.
This will be especially true in those areas that see sun the
longest before the usual daytime cumulus field develops. Isolated
thunderstorms will be possible in the mountains of the Alaska
Range today. Mountain snowmelt adding moisture to a very unstable
atmosphere will be the catalyst for those storms. Otherwise, the
lower atmosphere in the lower elevations remains very dry, with
dew point depressions in some areas exceeding 40 degrees during
peak afternoon heating. Thus, any storms that develop and move
over lower elevation areas will be dry as all the moisture from
any precipitation evaporates before reaching the ground.
Fortunately, very weak steering level winds mean any storms will
most likely sit in one location or only move a very small distance
during its life cycle. In addition to a moisture deficit, another
factor that will inhibit potential storms is a lack of any strong
upper level fronts or systems that will help lift the cumulus
clouds to grow into thunderheads.

A slightly better potential for storms will exist on Saturday
afternoon. Between marginal increases in moisture from Friday and
a slightly stronger steering level wind allowing any storms to
ingest new air into them as they drift along, it's possible that
any storms that form will be able to impact more people. However,
it's still likely that any storms would develop in the mountains
of the Alaska Range and move slowly westward with time, so the
area of potential storms is only modestly bigger. Outside of
thunderstorm potential, temperatures will once again be well above
normal, with relative humidity values in the 20s Saturday
afternoon.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A low moving through the central Aleutians today will move quickly
eastward with time, spreading rainfall through most of the chain
through Saturday. The center of the low will remain south of the
Aleutians, any nearly all the rainfall associated with the system
will be in the southeasterly flow out ahead of the low center. The
low will be tapping a long feed of moisture trailing across the
northern Pacific, so for a time, the potential for heavy rain
exists as the low sweeps eastward. Fortunately, once again it's
fast eastward movement will inhibit any one area from getting
large amounts of rain. The associated upper level low center will
keep a seasonably cool airmass in place over the Bering, so cloudy
conditions will persist for most areas away from the coast of
mainland Alaska.

The extra low level moisture will keep the chance of some patchy
fog over the Pribilofs and the southeastern Bering through this
morning, though any attempts by the fog to near the coast will be
thwarted by the very dry air mass in place across mainland Alaska.

&&

.SOUTHWEST FIRE WEATHER...

Fire weather conditions across Southwest Alaska will be very near
red flag criteria over the Middle Kuskokwim Valley the next couple
days. High temperatures peaking in the upper 70s to around 80,
coupled with relative humidity values between 15 and 25 percent
will effectively continue the dessication process of the flora
across the area. With the thermal trough axis expected to be
directly over the area this afternoon, there will only be a very
weak pressure gradient over the area, so winds will be light, 10
mph or less, though occasional gusts may exceed 15 mph. It will
certainly bear watching for the next couple days.

Isolated thunderstorms are possible through the Alaska Range both
Friday and Saturday afternoons. Mountain snowmelt adding moisture
to a very unstable air mass should be enough to get any cumulus
clouds growing during the afternoon, but very weak steering winds
will keep any storms that develop nearly stationary. A lack of
any organized fronts/forcing should result in any storms to be of
the pop-up variety, with very little helping organize them.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term will be dominated by a low that will sit south of
Kodiak Island and slowly meander east throughout next week. On
Friday it will be absorbed by another low that will approach from
the west. While the low stays south of Kodiak Island it will bring
constant, moist, east to southeast flow to the southern mainland.
Most of the rain from this setup will stay along the coast but
afternoon/evening showers should be expected for much of the week
for interior locations.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CB
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
LONG TERM...DK