Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
356 PM akst Thursday Feb 11 2016
Short term...the latest satellite imagery shows a gale force low
over the North Pacific and its associated weather front over the
southeast Gulf. There are some showers over the northeast Gulf
that are rotating to the northwest late this afternoon. The rest
of the forecast area is mostly dry with winds relatively on the
light side. As the front moves north through tonight precipitation will
slowly spread northward with Cat rain over the the southern two
thirds of the area by late tonight. The far northern areas will
not see that much precipitation tonight with a north gradient but they
will get into the precipitation by Friday morning. Most of the precipitation
will be in the liquid form with temperatures very mild. There will be
some cold air advection over the area tonight so the temperatures will slowly fall from
the Upper/Middle 40s to the upper 30s/lower 40s. The highways may see
some snow as dew points will cool with offshore flow to the lower
30s. The front will push through the forecast area by Friday
afternoon with showers over the north and scattered over the south
with less positive vorticity advection. There is a chance that there will be some isolated
thunderstorms over the Gulf with a strong upper level vort, steep
lapse rates from above normal SST. At this time the isolated ts is
confined to the Gulf but later shifts may need to bring them into
the coastal areas due land base convergence zones.
Wind wise...the front will produce solid 40 knots gales tonight with
continued large sea heights. The winds will persist into Friday
as the low tracks over the central Gulf but the southeast Gulf will see
the wind speeds relax by the afternoon. The north half of the Inner
Channels are seeing the winds switch around to the north and they
will increase as the front approaches the Panhandle. Speeds will
range from 20 to 30 knots. The main pressure gradient is from the east/west
so those channels will increase to 20 to 25 knots with lighter winds
in north/S channels. The winds will Switch Back to the south through
Friday as a weak surface ridge builds over the Inner Channels. The
strongest winds will be northern Lynn with 20 knots.
Overall there is about average forecaster confidence in the short
term period. Used a mix of the 18z NAM and GFS.
Long term...active pattern will continue into early next week as
upper trough over the Aleutians persists. Minor perturbations
ejecting out of the parent low will result in quick moving frontal
systems moving across the forecast area with at least 3 systems
between this weekend into next week. These impulses will also
slightly weaken the upper ridge over west noam resulting in slightly
cooler temperatures. Model solutions diverge towards the middle of next
week with both ec and GFS showing an upper low/open wave
undercutting the ridge and impacting the West Coast. As this feature
moves S...another low will become established over the central
Gulf maintaining active pattern through the extended. Since
sensible weather will depend greatly on the timing/track of each
impulse...mainly maintained inherited forecast. Biggest change was
to temperatures early next week...used GFS MOS to nudge temperatures slightly
down and increase diurnal spread. Overall forecast confidence
remain about average.
Marine...Gale Warning for pkz041>043-051-052.
Small Craft Advisory for pkz012-013-022-031-035-036.
Small Craft Advisory due to seas for pkz033-053.
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