Scientific Forecaster Discussion
fxak68 pafc 211841 cca
Southcentral and southwest Alaska forecast discussion...corrected grammatical in southwest
National Weather Service Anchorage Alaska
941 am akst Thu Nov 21 2019
Analysis and upper levels...
on satellite imagery, there are a series of lows along the
Aleutians and a well-defined cold front extending towards Japan.
In ascat (advanced scatterometer) data, storm forces winds have
been detected south of Adak. Driving this storm is a jet with a
core with a magnitude of 180 knots. Light precipitation, mostly
rain showers, has been detected on the radars at Middleton Island,
Kenai and King Salmon this morning as a warm front pushes inland
across southern Alaska. Looking north at the Kuskokwim Delta and
valley, cold temperatures are keeping snow showers as the dominant
precipitation type. Areas along the central Aleutians have seen
rain and gusty conditions associated with a complex low situated
south of the chain.
there is consensus with the synoptic features amongst the
GFS/ECMWF/Canadian through the weekend. The Pacific, the Bering
and the Gulf of Alaska look very progressive.
panc...low level wind shear will develop by 20z today. Cigs are
already under 5,000 feet with the possibility of dropping to 3,000
Short term forecast southcentral Alaska (days 1 and 2/today
through Friday night)...
Fast upper level flow will drive two surface fronts across the
Gulf today and onshore along southcentral tonight. The second,
stronger front will actually catch up with the first front along
the north Gulf Coast and Prince William Sound this evening.
Expect a barrier jet to develop this afternoon and intensify
this evening, peaking at around 60 kts along the north Gulf
Coast. Would expect some of the channeled areas near Hinchinbrook
Entrance will see hurricane force wind gusts. The front will be
slow to actually push onshore. Thus, as it moves through the
Cordova area it should be in a weakening state. Have strengthened
winds there, but kept them below warning levels (75 mph).
Another interesting feature is the triple Point of the second
frontal system. Some models now show an actual low forming south
of Seward and tracking into western Prince William Sound. This
should be just enough to disrupt the strongest winds ahead of the
front and back winds in western Prince William Sound a bit toward
the northeast. Believe this will spare Passage Canal, Whittier,
and Portage of the strongest winds.
Conditions ahead of the second front (and triple point) look
more favorable for west Turnagain Arm and higher elevations of
Anchorage, with lot of gradient stacked up along Turnagain Arm
and a strong low level jet crossing the mountains. The 12z
Anchorage sounding is weakly unstable all the way up to 11,000
feet or so. However, warm advection out ahead of the first front
as well as warming from subsidence in the Lee of the mountains
should lead to development of a stable layer to help trap winds
(and perhaps force them downward). The namnest seems to be
overdone with its depictions of high winds coming down the
chugach and across much of the Anchorage bowl (perhaps a mountain
wave signal?). with good vertical mixing as winds ramp up, do
think will see some strong winds gusts move down the hillside and
into areas near the Chugach Mountains. However, this does not
seem like a scenario to produce high winds in these areas. Have
maxed the winds gusts near the mountains at 35 to 50 mph.
Expect another round of heavy precipitation along the south side
of mountain ranges through Friday morning with lighter precipitation
elsewhere. Temperatures will remain quite balmy across the region
thanks in part to the gusty winds. This will lead to rain for
most areas. The exceptions will be Thompson Pass and the northern
Susitna Valley and northern Copper River basin, which will be cold
enough for snow. A series of upper level waves will continue to
traverse southcentral through Friday night, producing periods of
Short term forecast southwest Alaska (days 1 and 2)...
Southwest Alaska will remain under a showery pattern today as a
front associated with a surface low in the eastern Bering moves
inland through the afternoon. Precipitation will start off as snow
for areas north of Dillingham, but will switch over to rain or a
rain/snow mix to areas just south of Bethel as this warm front
lifts northward. There is still some uncertainty in how far north
the warm temperatures and rain will move in. By Friday morning,
most areas will see snow showers as the precipitation begins to
diminish across the area.
High temperatures across the region should remain at or above
freezing today, with the exception being the Kuskokwim Delta coast,
which will see highs in the mid-20s with the Arctic front positioned
over this area. A cooling trend will drop the temperatures a few
degrees across the southwest over the next few days, with many areas
not reaching above the freezing mark on Saturday as an upper level
trough moves over the area.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
A series of complex lows remain across much of the central
Aleutians and into the eastern Bering this morning, keeping an
area of gale force winds in the northern Bering and also south of
the eastern Aleutians and Bering. Northerly flow and Small Craft
Advisory winds will continue through Friday over much of the
Bering as the complex low moves inland. Freezing spray could be a
concern for areas in the northern Bering. Snow showers are likely
over much of the western and northern Bering, while areas south
will see rain or a mix of rain/snow.
Marine (days 3 through 5)...
The period begins with a vertically stacked low moving ashore
somewhere between 60n and Bristol Bay Saturday afternoon in the
neighborhood of 990 mb with a surface front moving into the
northwest Gulf and coastal southcentral Alaska. Northerly winds on
the backside of the low appear to be just below the gale mark in
the coastal waters of southwest Alaska and the Alaska Peninsula.
Coastal locations of the northern Gulf appear to remain below gale
in the 30kt range. However, some gales will appear in the
southern Gulf on Sunday afternoon, along with the waters of Kodiak
Island. With winds hovering in the near gale range, will want to
watch the next couple of model runs for changes. Localized gales
are also possible near the Standard favored offshore flow terrain
gaps along the Gulf Coast Sunday night through Monday. High
pressure in the central Bering follows the system on Sunday as it
moves towards the Alaska Panhandle. The next gale force frontal
boundary enters the western Bering and Aleutians Sunday night and
will strengthen to storm force by Monday afternoon in the central
Bering. Again, model discrepancies will need to be addressed, but
with a potential parent 960 mb low, strong winds will be on the
menu as this system comes ashore Tuesday morning.
Long term forecast (days 3 through 7)...
By Saturday morning an upper level low will be centered over the
southern Bering and Bristol Bay with an associated surface low
offshore over the Kuskokwim Delta. The upper level low will move
inland over the greater Bristol Bay area through Saturday afternoon
and evening while the surface low rotates southeastward along the
coast and moves into Bristol Bay. In the Gulf, a frontal system
stretching across the western and northern Gulf will swing onshore
across the Prince William Sound area and northern Gulf Coast on
The upper level low will continue to the east northeast, pushing
into southcentral Alaska Saturday night through Sunday bringing
significantly colder air aloft and some snow showers with it.
Upper level ridging will move across the Bering from west to east
Saturday night through Sunday. As the ridging amplifies over the
eastern Bering Sunday night and southwest Alaska on Monday,
offshore flow will strengthen rapidly over southcentral Alaska
with snow showers tapering off and skies clearing.
A Kamchatka low will spin up to a rather strong frontal system in
the western Bering Sunday and Monday. The front will reach the
central Bering Monday afternoon and evening and eastern Bering
and Kuskokwim Delta Monday night. A trailing portion of the front
will reach the eastern Aleutians Tuesday morning where it will
merge with a North Pacific frontal wave and then continue east
over the Alaska Peninsula through Tuesday afternoon. The front
will move further inland across southwest Alaska Tuesday night and
into southcentral Wednesday. The southern frontal wave will spin
up into surface low over the southwest Gulf on Tuesday night and
track into central Gulf Wednesday through Wednesday night.
public...High Wind Warning 101.
Marine...Storm Warning 119 125.
Gale Warning 120 130 131 132 138 139
150 155 172 185 412.