Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 230725 CCA
Southeast Alaska Forecast Discussion...CORRECTED
National Weather Service Juneau AK
1125 PM AKDT FRI JUL 22 2016
.SHORT TERM...A front has started to move into the panhandle this
afternoon and rain is becoming more persistent and widespread. The
assoc low pressure center will deepen over the north central gulf
overnight, causing rainfall rates to become heavy at times along
with increasing southerly winds. Expect most marine waters (inside
and out) to increase to small craft level this evening with a peak
early tomorrow morning. Have some places reaching 30kt at the peak
and Clarence Strait reaching a gale of 35kt. As the front passes
winds will shift to the SW. Some inside waters will start to ease
at this point, but the outside waters will continue to have SW
30kt winds and inside waters. Land areas should top out at
15-25mph and the wind direction shifting from E-SE to S-SW in the
afternoon will be quite noticeable. The low center over the
northern gulf will be a perfect set up for winds down the Chilkat
Valley in Haines, have increased winds there for this reason and
decreased them in Skagway some.
Rain will transition to showers behind the front as instability
increases with cooling aloft. Have left in a slight chance of
thunder near the low center tomorrow since model CAPE shows a
maximum there as well as favorable LIs.
Widespread rainfall and overcast skies will limit the diurnal
temperature range to about 5 degrees or less. Most places will be
in the mid to upper 50s. Adjusted these based on current
conditions, persistence and MOS.
Preferred the GFS22 and Canadian Regional models for updates to
pressure, Although all models had a similar solution and an
ensemble approach was used for what little changes were made.
Forecast confidence is above average for a very wet next 24hrs but
slightly lower on just how strong the wind speeds will get.
.LONG TERM...By Sat night the strong frontal system will be
exiting SE AK and the steady rain will have transitioned to
showers. The air mass cools aloft quickly behind the front which
results in noteworthy instability. So showers could be locally
heavy. I left the chance of thunderstorms in the forecast into Sat
evening for coastal sections between Cross Sound and Cape
Fairweather. Surface pressure rises behind the front likely to
keep N-S channels windy through the evening at least... maybe
later into the night in Lynn Canal. I did bump up Lynn Canal winds
a bit for Sat night.
The trend for Sun and Sun night is for gradually decreasing
showers under short wave ridging...albeit a flat ridge. The wind
flow aloft remains out of the SW so still plenty of cloud cover
for the first half of next week. Temps will gradually warm up a
few degrees Mon- Wed and be back to normal for late July. Another
weather front is forecast to move across the northern Gulf come
early Mon and will mainly affect the northern panhandle with
renewed chance of steady rain early next week but much lighter
than what will occur this weekend. Blended in EC model precip
forecasts which gave more temporal detail for Sun to Mon.
Forecaster confidence overall is average or above on these trends.
.HYDROLOGY...Heavy rain moving into the area with some locations
expected to receive in excess of 3 inches over the next two days
will cause smaller river systems to rise. Many rivers, especially
across the southern panhandle are low from the dry weather that`s
been occurring and will not reach bankfull. However some rivers
across the north that have seen rises lately due to warm
weather/snow melt at higher elevations may approach bankfull but
no flooding is expected.
The glacier dam release on the Salmon River near Hyder continues.
As of 2pm this afternoon the river level was 25.85 feet and rising
steadily (approx 1ft rise since 10pm last night). There is a lot
of uncertainty with this event since the gauge was out of service
when the event began. However, based on the past 5 years of data
the crest is typically between 26.5-28 feet. This would mean that
the peak should occur in the next 12 to 48hrs. Debris, including
trees and ice bergs, began flowing down the river last night and
is impacting travel into Portland Canal. Currently the river is
far enough from the road but may still be a factor if it crests at
the higher end of the predicted range.
MARINE...Gale Warning for PKZ036.
Small Craft Advisory for PKZ012-013-022-031>035-041>043-051-052.
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