Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 241322
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
522 AM AKDT MON OCT 24 2016
.ANALYSIS AND UPPER LEVELS...
A weakening area of low pressure over Siberia pushed a front
across the Bering Sea on Sunday. As of this morning, the front has
stalled out over the Alaska Peninsula and is rapidly falling apart
as it has moved far away from the parent low. As this front
dissipates this morning, all eyes will turn back to the western
Bering Sea where an area of low pressure is rapidly intensifying
just to the south and west of Shemya. Looking at model derived
pressure fields, this low pressure system formed near 47N 165E at
987 mb and will strengthen to 960 mb by late this morning. This
constitutes something known as rapid cyclogenesis (aka bombogenesis)
where a low deepens 24 mb within a 24 hour period. Scatterometer
data has shown winds increasing around the low pressure system as
the pressure gradient continues to compact. The eastern half of
the Bering Sea and the Alaskan mainland remains under high
pressure which has brought a period of calmer weather outside of
the Alaska Peninsula which is still seeing a little bit of rain
and gusty winds from the dissipating frontal boundary. Outflow
winds over Southcentral Alaska have also been weakening as the
pressure gradient between the Gulf of Alaska and the mainland
continues to gradually weaken.
Models are in really good agreement with a rapidly developing area
of low pressure currently just to the south and west of Shemya as
it evolves and moves into the Bering Sea. One decent change from
the numerical guidance 24 hours ago has been observed this morning
as they no longer suggest a frontal wave forming over the central
Aleutians this morning. This could impact the wind speeds (a tad
weaker than initially forecasted) across the western and central
Aleutian Islands where our current high wind warning products are
issued. Otherwise, there is great agreement with a strong storm
force front pushing through the heart of the Bering Sea over the
next couple of days. With the models in good agreement, a blend of
high-res data was used for forecast updates this morning.
PANC...VFR conditions and light winds will persist.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Persistent northerly flow and tight surface pressure gradients
will continue to produce localized gap winds along Prince William
Sound and the north Gulf Coast through Tuesday morning. Winds
will then quickly die down as the ridge moves overhead during the
day Tuesday. The ridge will continue to slide eastward Tuesday
Night, allowing a weakening front from the Bering Sea to approach
the Western Gulf. This will bring rain to Kodiak Island and
increasing mid to high clouds farther north and east. The shift
to southerly flow will also bring moderating temperatures for
most places, though mostly clear skies will keep the Copper River
Basin on the chilly side.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Low pressure across the Bering slowly erodes ridging across
Southwest through Tuesday. The surface front that pushed to the
coast overnight stalls today with southwesterly flow just off the
surface pushing a warmer Pacific air mass inland. Increased snow
and rain showers are possible, mainly along the coast, as a
strong shortwave slams into the western periphery of the mainland
ridge. The air mass is dry through the column, therefore, no
accumulations are expected today.
A pattern shift begins tonight as a strong organized storm system
swings a front to the southwest coast tonight. A warm front
pushes into the west coast by Tuesday morning bringing rain to the
coast and then spreads inland during the afternoon. Strong gusty
southerly winds develop this evening across coastal areas of the
Kuskokwim as the pressure gradient tightens between low pressure
approaching from the Bering and high pressure inland. Gusty
conditions continue through much of Tuesday then taper down behind
the front. The Coastal Flood Watch for the Kuskokwim Delta issued
on Sunday was continued with this morning`s package. Adjustments
were made to decrease the flood levels since winds are expected
to stay south versus southwest, which keep impacts lower at this
direction. Temperatures increase above freezing with the front
bringing precipitation mostly in the form of rain. However, light
snow accumulations are expected across the eastern areas of
Kuskokwim Valley and Aleutian Range Tuesday night as the front
moves faster off the surface, not mixing warmer temperatures down
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
An unsettled pattern is underway across the Bering as a parent
low center shifts across the western waters to Kamchatka. An
associated surface low rapidly occludes and deepens to 950 mb as
it tracks across the western Bering this afternoon. High winds are
expected to impact the Central and Western Aleutians this morning
through late evening, with only minor adjustments made on timing
and wind speeds for the warning products that were previously
issued. Hurricane force winds will develop around the marines
surrounding these islands and storm force winds with hurricane
force gusts are expected to be widespread today across the rest of
the Bering. Instability increases behind the fropa as colder air
advects in from the west. Isolated thunderstorms were added for
this evening through tonight for the western Bering and Aleutians
as a strong embedded wave is forced around by the parent low. A
cooler unstable pattern continues to bring showers on Tuesday
along with westerly flow behind the strong front.
.LONG TERM FORECAST (Days 3 through 7)...
A persistent and amplified trough over the Bering will continue
into late in the work week. This pattern will bring a series of
gale-storm force lows throughout the Bering and southwest
Mainland, bringing widespread rain and gusty southerly winds.
Depending on the exact track and strength of these lows and
associated fronts, there will also be the potential for coastal
erosion/high surf issues to south exposures of the Southwest coast
(such as Kuskokwim Bay). This will need to be monitored over the
coming days for more details regarding timing and strength, but it
certainly looks like an active week ahead for the Bering Sea
To the east of the Alaska Range, a blocking ridge will prevent
the active weather over the Bering from moving into Southcentral
or the northern Gulf. This will keep generally sunny and benign
weather over the region with daytime highs slightly above normal.
By late next week there is good agreement that this blocking
ridge will shift eastward, allowing for more active weather to
move into the Gulf and south Mainland. This trend will then
continue into early next week with no sign of a return to the ridging
and sunny weather that the south Mainland is currently enjoying.
PUBLIC...High wind warning...187 191.
Coastal flood watch...155.
MARINE...Storm...170 173 174 175 176 177 178 179 181 185.
Gale...127 165 171 172 180.
SYNOPSIS AND MODEL DISCUSSION...mc
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...kh