Scientific Forecaster Discussion
Southeast Alaska forecast discussion...corrected
National Weather Service Juneau Alaska
600 am akst Thursday Feb 11 2016
Short term...should one count the number of fronts that have
crisscrossed the Gulf over the course of the last several days,
one may receive the same number of answers as the number of
meteorologists asked. As a parent low over the western Gulf
retreats to the west...an associated wave along a front lifts
north and west across the northern Gulf this morning. This
disturbance was characterized by A Reservoir of unstable air that
impacted winds at the surface much more efficiently overnight.
Gusty southeasterly sustained winds of 15 to 25 miles per hour were prevalent
across the Panhandle, none with strong wind gusts, but these winds
will fall during the morning. Another front will follow...lifting
northwestward this afternoon and tonight through the eastern Gulf.
In addition...its parent low will move into the central Gulf
tonight. This will present another round of gales spreading
northward tonight across the outside waters. But the energy for
this system will stay well offshore. In addition...the stable
nature of the warmer air mass advecting into the area tonight will
help keep winds generally lighter than the cooler system that
affected US during the last 12 hours...given comparable gradients.
Showers passing across the northern Panhandle with this system
will diminish from southeast to northwest through the day as
ridging helps entrain some drier air aloft over the Panhandle this
afternoon. Likewise...embedded thunderstorms offshore lifted
north with the front and may affect Cross Sound and Yakutat this
morning. But as the system lifts northwest, the threat ends by
afternoon. We are banking on points from Juneau south having a dry
afternoon. Rain with the next system spreads northward tonight but
amounts should be light except for the far southern Panhandle
where some areas may receive a half inch late tonight. Ridging
will hold stronger across the north limiting the rain's expanse.
Finally southerlies across the north will veer more towards the
northeast this afternoon and strengthen tonight in response to the
approaching front from the south. 500 mb winds indicate a strong
possibility of a good critical layer of parallel winds across the
Coast Mountains. This coupled with good cross-barrier flow should
provide the necessary ingredients for sustained gusts to 40 miles per hour
over downtown Juneau tonight.
Mainly used the NAM for tweaks. Temperatures again have been
difficult to establish trends given the complex passage of fronts
across our terrain. Confidence generally good to average.
Long term...extended range forecast begins with a large,
negatively tilted upper level trough over the Gulf, a weak ridge
upstream, and another large upper level trough and low extending
south of the western Aleutians. Several smaller circulations in
the lower levels and surface represent the active sensible weather
that will dominate the long range forecast period...namely wind
and precipitation from at least 4 fronts between Friday morning
and Sunday night.
Outrageously warm weather for this time of the year looks like it
may come to a gradual end during the upcoming week. Currently, temperatures
at around 5000 feet ranging from slightly above to slightly below
freezing will result in daytime highs in the upper 40s again on
Friday...with a slow cooling in the highs thereafter.
Used a blend of European model (ecmwf) and gfs22 for updates to pressure and wind
for Sunday and Sunday night to capture a weak low that will
develop from a wave south of the Gulf and track northeast towards
the central outer coast on Sunday. Pop and quantitative precipitation forecast updated for Friday
through Sunday night using gfs40, Canadian New Hampshire and European model (ecmwf). Temperatures
adjusted using GFS MOS as primary guidance. Overall forecast
confidence is average.
public...strong wind from this evening through late tonight for akz025.
Marine...Gale Warning for pkz041>043-051-052.
Small Craft Advisory for pkz012-013-021-022-031>036-053.
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