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FXAK67 PAJK 031409

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
609 AM AKDT Fri Apr 3 2020

.SHORT TERM...Light snow has already begun in Yakutat early this
morning, and high clouds are streaming across the northern
Panhandle as a ridge axis shifts eastward. Meanwhile, satellite
still reveals clear skies across the southern half of the
Panhandle. Earlier skies were clear across the entire Panhandle
and allowed temperatures to drop quickly yesterday evening. At
this 5 AM hour, temperatures largely sit between 18 and 32
degrees. This is important as a low in the western gulf slowly
drives eastward and supports light precipitation ahead of it (like
what is occurring in Yakutat). Dynamics are weak and moisture
supply poor. But a cold air dome across the Panhandle is in place
and perhaps a little more robust than expected. One, this will
ensure that most of the precipitation that falls across the
northern Panhandle will be snow. But two, the very dry air mass
will take awhile to moisten up sufficiently for snow to fall. Our
light accumulations today seem very reasonable. And we feel the
steps taken yesterday to lower QPF should hold. All told, we still
only anticipate a couple of inches at Yakutat and one inch or
less for the rest of the northern and central Panhandle. Despite
low 1000-850 mb thicknesses, daytime snow accumulations with a
weak system like this one are difficult to impress. Add in the
time of year, and we feel very confident in our low amounts for
this Friday.

The low is a quick mover, and as sure as snow begins this this
morning to around midday, we expect snow to end this evening.
Meanwhile, the southern Panhandle looks to also have a chance of
snow, as cold temperatures are even entrenched here, for instance
21 degrees in Kake and 28 degrees in Ketchikan. But warming
through the afternoon and the threat of southerly flow ahead of
the low should undoubtedly force preciptiation into rain.

The low exits our region to the south Friday night, allowing the
longwave ridge to re-strengthen. This should ensure a very nice,
and dry day on Saturday. In fact, slight warming should send most
Southeast communities into the low to mid 40s. The sun looks to
make a return as well.

Winds in general will be a non-factor, although there could be
some small craft winds in the general vicinity of the low, but
these should not be so widespread as to mention. We did raise
northerly wind speeds through Lynn Canal on the back side of the
low early Saturday morning.

Forecast confidence is good.

.LONG TERM.../Sunday to Friday as of 10 pm Thursday/...The ridging
which has contributed to SE Alaska`s string of sunny days will
begin to slide E out of the panhandle. More zonal flow behind it
will enable quick moving shortwaves to move across the Northern
Gulf, interacting with the panhandle and bringing a renewed chance
of precipitation next week.

In regards to surface features, the first system to impact the
panhandle will be a shortwave trough which will interact with the
area Sunday night into Monday. Sunday night in particular looks
like it could see an inch or two of accumulating snow from this
trough for Juneau and some other locations in the central
panhandle. The key limiting factors in any accumulating snow will
likely be the speed of the system combined with quickly rising
daytime temperatures. Following the passage of this system,
westerly flow will help continue to encourage the propagation of
showers throughout the panhandle, and there is a chance of some
follow-up snow showers Monday night in areas where the cloud deck
proves insufficient for keeping temperatures above freezing.

The long range models solutions have continued to indicate the
probable development of a low in the North Pacific which will
enter the Gulf of Alaska and impact the panhandle sometime between
Tuesday and Wednesday. There is still significant disagreement on
what exact track it will take though some of the most recent
model runs and ensembles have trended further to the west. As it
stands currently, it looks like the majority of the panhandle will see
precipitation out of this event-most likely with rain being
predominant given the presence of the system`s warm sector-but
the timing and quantity of the precipitation will ultimately
depend on what track the low takes, and the system will need to be
monitored closely as additional data is received.


.AJK Watches/Warnings/Advisories...




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