Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
413 PM akst sun Jan 25 2015
Short term...gradients, wind, precipitation are all largely decreasing this
afternoon as weakening eastward-propagating low lets go of US on
its back side and moves off to the east. Skagway winds as well as
northern Lynn are hanging on to strong southerlies for the
moment...these should weaken and eventually the Lynn winds should
flip tomorrow morning. Haines also still has easterly gusts to
30 miles per hour but these should drop off in the next few hours. Small Craft Advisory there
in the northern portion lasts well into tonight though. Drying
trend is already starting this afternoon with just remnant showers
in much of Panhandle and model runs are largely consistent. Put
patchy fog in the southern 2/3 of Panhandle for 09z into tomorrow
as drying trend and breaks in clouds are already being
observed...not enough to begin the fog earlier although that is in
the realm of possibilities. Dynamic fields in grids did not need
updating other than minor wind tweaks in the channels (lynn,
clarence) and over higher terrain to the north. The latter was to
bump up winds tomorrow as the new low brushes the south end.
Impacts from this system still appear likely to be minor although
still the NAM is at odds with ec/Gem output on this system (18z
NAM still weaker and further south). Thermodynamic fields updated
using NAM/ec output and depended mostly on MOS temperature updates.
Long term...look for a brief drying trend to continue past the
short term period and last at least into early next week. As is
typical in these cases, temperatures will be a bit cooler as well
during this time frame.
At the start of the extended range, a low will be approaching the
extreme southeast Gulf from the southwest. Fairly strong frontal
signature will clip the far southern zones with potentially heavy
precipitation...mainly in the Misty Fjords area. A brief period of
surface ridging over the central Gulf will follow the passage of
this low and will be primarily responsible for the dry break. The
ridge then get shifted to the east by the next advancing frontal
system which should arrive along the central outer coast early
Wednesday. A pair of developing waves on this frontal boundary
will roll up the front late on Wednesday and then again early on
Thursday, reinforcing the precipitation already in place over
Southeast Alaska. Model agreement currently very good on yet
another front that will sweep south to north across the Gulf and
Southeast Alaska Friday through at least Saturday night. There is
some snow in the long range forecast through middle week, but
southwesterly synoptic flow during the second half of the week will
likely result in rising temperatures and a Switch Back to rain for
all but the highest elevations.
Used a blend of GFS and European model (ecmwf) for updates to pressure and wind
through Thursday night. Pop and quantitative precipitation forecast updated primarily with GFS
with some help from both Gem and European model (ecmwf). Temperatures per MOS and gfs40.
Overall forecast confidence is average.
Marine...Small Craft Advisory for pkz011>013-022-041-052.
Small Craft Advisory due to seas for pkz042-043-051.
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