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FXAK67 PAJK 231337
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
537 AM AKDT Sat Sep 23 2017

.SYNOPSIS...A weak low pressure system is currently passing over
the southern panhandle with shower activity ongoing across most
of the panhandle. Shower activity continues but diminishes across
the panhandle through Saturday afternoon. Then another weather
front will track northeast across the gulf and panhandle through
Saturday bringing another round of rain to SE Alaska. Between
Sunday night and Monday a low pressure system will pass south of
southern panhandle. A brief dry period is expected Monday as a
ridge builds over the panhandle before another front arrives on
Tuesday.

&&

.SHORT TERM.../Saturday through Sunday as of 500am Saturday/ An
active, wet weather pattern continues through the short term.
Currently, a weak low pressure passing over the southern
panhandle, has increased shower activity within its vicinity.
Satellite derived rain rates are between 0.10" to 0.20" per hour
within the heavier showers. As this system passes shower activity
will diminish through the afternoon. Largest decreases in shower
activity are likely over the far northern and western portions of
the panhandle. This afternoon another front will track northeast
over the gulf and panhandle bringing rain back to the panhandle.
It is expected to reach the southern panhandle during the
afternoon hours spread into the northern panhandle through this
evening. Rain associated with this front is expected to be heavy
at times.

Sunday will follow a decreasing shower trend once again across the
panhandle. The northern panhandle is expected to have more
numerous shower activity especially early in the day compared with
the southern panhandle. However, late Sunday afternoon a low
pressure system will pass over Haida Gwaii, which will keep the
southern panhandle wet into early Monday.

Fog is possible and/or present in many this morning associated
with the very moist surface conditions. Late Sunday night into
early Monday it will be possible once again as conditions clear
and the surface remains saturated.

A few changes were made to the short term forecast. Fog was added
near Yakutat this morning as well as some marine areas. In addition,
fog was added between Sunday night and early Monday due to the
very moist surface conditions. PoP values were increased along
the front today and around the low pressure system that passes
just south of the southern panhandle Sunday night. Models are
still carrying discrepancies with how much the shower activity
diminishes ahead of the front that arrives later today. Primary
model guidance was a blend of the NAM, NAMNest, and Canadian
Regional.


.LONG TERM...Monday through Saturday...An upper level shortwave,
developing from a parent circulation with its center positioned
near the Aleutians, will propagate across the northeastern gulf
and lift across the panhandle Sunday night into early Monday
morning. A subtropical jet feature will assist with advecting
additional moisture with this system, but most of the
precipitation increases will primarily be confined to the more
southern portions of the panhandle. A ridge of high pressure will
then begin to build over the eastern gulf Monday. We should start
to see most locations across the panhandle dry out for the day.
Fog development may be a possibility, especially during the
morning commute on Monday, so we`ll continue to monitor this
trend for subsequent forecasts. The ridge should then begin to
weaken and retreat east before another shortwave develops and
progresses northeast across the gulf, impacting the panhandle on
Tuesday. Models continue to show additional subtropical jet setups
to assist with pushing additional moisture over the panhandle.
This type of pattern appears poised to continue through the
remainder of next week, with additional shortwaves that develop
out of the parent trough over the gulf. Due to this tropical
moisture push over the area, we expect chances of precipitation to
remain high through the week and temperatures to maybe be
slightly above average, especially in southern areas.

For adjustments to the forecast, we updated PoPs with a blend of
the ECMWF and Canadian, relying more on the EC, to continue to
show the increasing precipitation trend through the week. We also
increased winds throughout the eastern gulf waters to account for
the tighter pressure gradient that develops with the subsequent
shortwaves that progress out of the parent circulation. A lot of
uncertainty will then remain regarding the synoptic pattern after
about Day 8.

&&

.AVIATION...Conditions that begin between IFR and MVFR this
morning are expected to improve during the day. Fog that is
currently present will diminish during the morning hours, while
ceilings are expected to lift through the afternoon hours. The
improvement that is seen will vary from location to location;
however, the best conditions are likely over the northwestern
panhandle. Whether or not conditions are able to increase to VFR
conditions today remains a difficult portion of forecast. These
improved conditions will diminish once again between this
afternoon and evening from south to north as a front tracks
northeast across the panhandle. Low level wind shear is another
concern over the southern panhandle later this morning into the
afternoon hours as the front approaches.

&&

.MARINE...Small craft level winds are expected over much of
eastern gulf Saturday along the front. Clarence Strait is
expected to reach small craft levels this evening as the front
passes. While not in the current forecast, winds near Cape
Decision and Cross Sound may also reach small craft levels today.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ036-041-043-052.
     Small Craft Advisory due to Seas for PKZ042-051.

&&

$$

Byrd/Voveris

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