Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
602 am akst Sat Nov 28 2015
Short term...at 5 am the stationary front is estimated to be from
Juneau to Sitka and extends well to the south offshore.
Precipitation varied in location and intensity overnight.
Satellite derived rainfall rates suggest a band of heavier rain
south of Sitka will push onshore into the central Panhandle through
the morning hours. Precipitation is more widespread northwest of the frontal
boundary but light rain was occurring in zones 27 and 28
Strongest winds are along the front in areas favoring southeast wind
direction such as Stephens Passage... Icy Strait... and coastal
gaps. Models show pressure gradients relaxing during the day
today before strengthening again tonight. The hi res NAM model
indicated a surge of southerly wind through southern and central Inner
Channels late afternoon and Sat evening.
Forecast confidence in the general trend through Sun morning is
average. The ec model pressure and precipitation solutions matched well
with observations last night and was used to nudge existing
forecasts. Wind forecast grids were then blended with the hi res
NAM solution. The result was to spread another round of
precipitation inland from south to north during the day. Precipitation
edges west-northwest tonight as the stationary front begins to slowly pull
that way. The Winter Storm Warning continues for the higher
reaches of Klondike Highway. A lull in the snow there this fades
as snow picks up later this afternoon and overnight.
Long term...a 30+ knots south-southeasterly low level jet will persist into the beginning of
the long term /sun/ over the central/southern Panhandle as a frontal
boundary weakens over the eastern Gulf. This will favor strong
moisture flux resulting in locally heavy rain. Heaviest rainfall
will occur near a deep-layer moisture plume...which models have
begun to shunt northwest /compared to previous solutions/ toward the northern
half of the County Warning Area...and replacing it with much drier air over the
southern Panhandle. Given this trend...pop values have been reduced
from Ketchikan to Hyder. Elsewhere...model guidance indicates
precipitation rates will continue to be robust near White Pass on
sun...and with low-level temperatures remaining near
freezing...snow is expected /possibly heavy/.
Otherwise...previously mentioned low level jet and tight surface
pressure gradient /augmented by a weak wave moving north along the
front/ will yield small craft to gale force winds over the Inner
Channels...while locations such as Juneau...Ketchikan...and
Hydaburg experience gusts to 40 miles per hour. In fact...quick/late glance
at latest hi-res nmm/arw output suggests winds depicted in
outgoing long term grids could be under-done for sun/Mon.
Beyond sun...the entire region remains in a favorable pattern for
rain. However...there is large spread in shortwave details...which
results in low confidence regarding location/timing of heaviest
precipitation and enhanced wind speeds. For this reason...few
changes were made to the inherited forecast.
public...strong wind through late tonight for akz026-027.
Strong wind until 9 am akst this morning for akz019-025.
Strong wind from noon akst today through this evening for akz023.
Strong wind from 9 am akst this morning through late tonight for
Winter Storm Warning until noon akst Sunday for akz018.
Marine...Gale Warning for pkz033-035-036-041-042.
Small Craft Advisory for pkz012-013-021-022-031-032-034-043-051-
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