Area Forecast Discussion - Southeastern
FXAK67 PAJK 010229 CCA
Southeast Alaska Forecast Discussion...CORRECTED
National Weather Service Juneau AK
629 PM AKDT THU JUN 30 2016
.SHORT TERM...Leftover showers over the panhandle continue to
weaken through this afternoon. A low is approaching the southern
outer coast, bringing rain and small craft winds with it. The
transition from showers to rain will be hard to discern for more
southerly locations, but a brief break in precip farther north
will mark the end of one event and the beginning of the next.
Models have slowly been increasing the strength of this next low
and walking the forecast track further and further north. Morning
model update was sufficiently different to warrant a change to
pressures and winds for late tonight and tomorrow. Used the
Canadian NH model for these changes. Used a blend of official and
Canadian NH for updates to POP grids with little change to the
forecast. QPF increased via a blend of the RFC and Canadian REG.
3-hourly rainfall totals 0.22 inches or less, so no flooding
concerns from rainfall. The glacially dammed lake release near
Juneau is another issue, discussed below.
Updates to pressure increased winds over the coastal marine zones
and ocean entrances late tonight through tomorrow afternoon and
affect the area between Cape Decision to Kruzof Island mostly. Of
note, the easterly winds to 30 kt over coastal marine zone 41 were
Overall forecast confidence is average.
.LONG TERM...The low discussed in the short term section will be
west of Sitka in the southern portion of marine zone 43 Friday
evening. As mentioned, latest models this morning deepened the
low quite a bit and shifted it north a bit faster. There will be a
band of 25kt winds near the low center and could have some gusts
of 35-40kt near ocean entrances. Some of the rainfall assoc with
this system will likely be moderate to heavy at times.
Another low looks to approach from the SW Saturday, but looks to
pass south of the area or through Dixon Entrance. This should in
turn cause a lower chance of precip across the northern panhandle,
but keep the far southern areas wet. Adjusted POPs down slightly
across the north as things become more isolated/scattered Sat
night. These may need to be lowered further if models continue
trending dryer, think that models are smoothing things out too
much and that precip will be intermittent/scattered and more dry
than wet...however mostly cloudy. Being 4-5 days out there is
still quite a bit of uncertainty with this portion of the forecast
and will be fine tuned with subsequent updates.
Used an ensemble approach to the forecast with an emphasis on the
Canadian NH model in the shorter term. Few adjustments were made
beyond this time frame due to uncertainty.
.AVIATION...MVMC occasionally IMC conditions will prevail over the
southern half of the panhandle through the next 24 hours due to
both low CIGS and reduced VSBY in heavier bands of rain.
Conditions better to the north. Light chop below ridge tops
increasing from south to north due to low level 30-45kt jet
associated with the approaching low.
.HYDROLOGY...Suicide Basin has released and a flood warning is in
effect for Mendenhall River and Lake. The current forecast crest
of 11.6 feet is close to the previous record value of 11.85 feet
set in 2014. As of early this afternoon, Mendenhall Lake had risen
to a stage of 6.5 feet and is rising very nearly as predicted. The
level in Suicide Basin has fallen 6 feet since early this morning
and continues to fall at around 1 foot per hour. Residents near
the lake or the river should remain alert and keep track of
updates to this event as they are issued by NWS Juneau.
MARINE...Small Craft Advisory for PKZ012-036-041-042.
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