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fxak68 pafc 111355 
afdafc

Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
455 am akst Mon Dec 11 2017

Analysis and upper levels...
the persistent and deja vu-like pattern continues in the Gulf as
yet another storm force low is making landfall early this morning
with another developing system quickly approaching on it heels.
Overnight observations confirmed that the departing low as one of
the strongest that has quickly moved through the Gulf over the
last week, as widespread storm force winds with hurricane force
gusts were apparent from the Barren Islands eastward along the
coast to Cordova. While the front and associated winds/rain are
beginning to diminish, the pressure gradient along Prince William
Sound and pressure rises behind the front are increasing, which
should allow for increasing gap winds from Turnagain Arm eastward
to the Copper River this morning. Along the western side of this
low, areas of rain/snow moved through Bristol Bay overnight which
are now spreading northward into the kuskowim River Valley/Delta
as the low crosses the Aleutian Range. Over the Bering Sea, a
broad area of cold air advection and gale force northerly winds
are evident on satellite imagery from the persistent northerly
flow that has developed over the Bering over the last 2-3 days.

&&

Model discussion...
little change has occurred in the overall model agreement, as
they all remain in great synoptic acquirement through about 48
hours, then begin to break down with the placement of a Gulf low
beyond that. The main challenge comes from what appears to be the
last low that will quickly move through the Gulf from this pattern
on Wednesday. Model runs yesterday varied widely as it whether
this system would track towards Kodiak (as many of the lows have
as of late) or much further east into the eastern Gulf. Overnight
runs have all began to trend further west, towards the GFS and ec
solutions that have been the most consistent with the more
westward track and was the preferred track for this mornings
forecast updates.

&&

Aviation...
panc...the primary concern today will be with the timing of southeast
winds that are expected to develop early this morning as pressure
rises setup through Turnagain Arm. As these winds begin to
increase is a possibility of some low level wind shear as winds aloft also
increase, but should end as the strongest of the southeast winds develop
by mid morning. At this point it still appears that wind gusts
should generally be around 35 kt, though there may be some peak
gusts in the 40-45 kt range, especially between 18-00z today. Southeast
winds should then diminish early this evening. Otherwise
conditions will remain VFR with persistent downsloping today.

&&

Short term forecast southcentral Alaska (days 1 and 2)...
the active pattern continues across southcentral Alaska. A storm
force low near Kodiak Island moves to over Bristol Bay and weakens
this morning. Its associated front will move rapidly north across
southcentral today. Warning level winds will linger on across
Turnagain Arm and Portage Valley until pressure gradients
sufficiently weaken by mid to late this morning. Although warning
level winds will diminish in these areas, strong isallobaric
pressure rises behind the front will give rise to gusty and
locally strong winds (mostly southerly) today. In particular,
along the Copper River, Cook Inlet, Kenai Peninsula, and the
Anchorage bowl and Matanuska Valley. Except for gusty winds along
Turnagain Arm and Portage Valley, winds will diminish over most
Mainland areas this evening/overnight. The next low to affect the
area on Tuesday will be much further to the west near the Alaska pen
as it tracks north. The front however will move north across the
Gulf. These systems will be weaker than the last, but will bring
increased winds, increased precipitation changes (mainly coastal),
and continued mild temperatures.

&&

Short term forecast southwest Alaska (days 1 and 2: Monday and
tuesday)...
a strong area of low pressure has crossed the Alaska Peninsula
this morning and is now centered near King Salmon. Associated
showers continue over much of the Bristol Bay area this morning. A
few isolated locations are still mixing with snow, but most areas
by now have turned to rain. The low center will continue tracking
northwestward across southwest Alaska today, rapidly weakening as
it does so. Thus, the coverage of showers should continue to
diminish through the day. South to southeast winds will also
develop behind the low, which will continue warming the atmosphere
via downsloping and advection. Thus, the chances for frozen
precipitation will continue dropping as well. In fact, many areas
near the Alaska Range where the downsloping will be strongest
could see temperatures topping out into the 40s today.

Precipitation associated with the next low in the set develops
across portions of southwest Alaska as early as this evening. Much
of the heaviest precipitation will be from Dillingham north and
west as the Kuskokwim Mountains help to upslope out more moisture.
Due to there being no opportunity for the atmosphere to cool
between now and then, rain will be by far the dominant
precipitation type in the lower elevations, with communities from
King Salmon north and east hardly seeing any precipitation at all
due to continued downsloping on strong southeast winds. This
second low will track a bit further west than the first one,
crossing the Alaska Peninsula Tuesday morning where there is less
terrain interaction, then staying over the eastern Bering after
that, tracking along the coast. On this track, nearly all of
southwest Alaska will get into the warming southerly flow, with
the exception of the immediate coast. Thus, assuming the flow is
southerly enough, even Bethel may mix with or change over to rain
for a time Tuesday afternoon and evening.

&&

Short term forecast Bering Sea/Aleutians (days 1 and 2: Monday
and tuesday)...
strong northerly gale-force winds with embedded snow showers will
continue to be the rule for much of the Bering. The northerly
winds will split the Bering between lows tracking through
southwest Alaska from the occasional fronts that invade the
western Aleutians and Bering, causing them to weaken, fall apart,
and retreat back into the North Pacific. Such has been the
pattern for much of the past week. However, by Tuesday, the next
front moving into the western Bering will have more Success
tracking eastward. This is because the last low tracking up the
coast will cause the winds to turn more westerly behind it by
Wednesday, helping aid the progressing front to push eastward.
This will finally help to bring some changes to the weather,
involving colder air mass moving into the eastern Bering and a
warmer air mass moving into the western Bering by midweek.

&&

Long term forecast (days 3 through 7)...
an active pattern remains through the long range forecast as
multiple low pressure systems track to the southern Mainland from
the Gulf and Bering. Tuesday night the persistent pattern
continues with amplified ridging over the southeast, however a
pattern shift begins to take place across the Bering and
Aleutians. A zonal subtropical jet begins to nose closer to the
Aleutian chain sending a storm system northward which pushes a
front across the central Aleutians and western Bering on
Wednesday. A jet streak puts this storm into eastward motion along
the chain which works to break down the high amplitude ridge by
the end of the work week. There is high confidence for the
anticipated pattern change as all the models are showing these
trends. Only minor changes were made for the extended range
forecast Wednesday through Saturday night with an equally
weighted trend of the operational models and ensembles.

&&



Afc watches/warnings/advisories...
public...High Wind Warning 101 125.
Marine...gale 119 120 121 125 129 130 131 132 136 137 138 139 150
173 174 175 176 178 179 181 185.

&&

$$

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