Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 252312
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
312 PM AKDT THU AUG 25 2016
.SHORT TERM...A short wave aloft will move across the northern
panhandle tonight and then will move southeast across the
panhandle on Friday. The precipitation band stays over the
northern half of the panhandle through late tonight and then
shifts southward into the southern panhandle Friday morning and
afternoon. A band of vorticity moving south during the day Friday
may be strong enough to develop stronger showers over the
northern third of the panhandle along the higher terrain of the
Chilkat Range and the Coastal Range north of Juneau. Have not put
a mention of thunder in the forecast but will need to watch if it
continues to persist.
Gusty southerly winds will develop over the Lynn Canal to Skagway
late this afternoon to evening hours. Wind are expected to reach
Small Craft Advisory in the northern canal and gusts to near 35
mph are possible around Skagway. Once the trough moves through
this evening expect the winds to lessen as the gradient weakens.
Meanwhile the winds over the central inner channels of Southeast
Alaska will increase in advance of the trough.
Patchy fog across the north central inner channel marine waters
again is a solid possibility. Not sure if it will be lowering
visibilities to less than a mile however mariners should be aware
that it may into early Friday.
.LONG TERM...The short wave described in the section above will
continue a southward track exiting the region Friday evening.
Precip will diminish over the region from north to south as upper
level vorticity and energy pushed into southern British Columbia.
Inverted surface trough extends over the panhandle Saturday then
begins to shift into the eastern gulf Sunday. Dry, sunny and very
warm day expected for Saturday with highs nearing the daily
records for the 27th. As broad upper low moves in from the
northeast Sunday into Monday as the surface low shifts to the
gulf. Upper level vorticity once again moves over the panhandle
precip will begin starting later in the day Sunday. At this time
flow should shift onshore for the southern regions with precip
starting there first. Pops increase by Monday across the
panhandle. Due to interaction with a low over the Bering Sea,
ridge over the western gulf and the low moving in from the Yukon
models are showing large spread with higher uncertainty for the
rest of the week.
Winds will shift to the north as the trough moves south.
Increasing pressure gradient brings winds to near gales for the
northern inner channels Friday night into Saturday. Weakening
gradient as the inverted surface trough extends over the panhandle
with decreasing winds and more offshore flow with possible
increases in channeled terrain.
Similar model trend compared to the past few days with good model
agreement early on then increased differences. There is a bit
more spread between GFS/NAM and ECMWF/GEM on the Friday night trough
but liked the consistency of the GFS/NAM so overall left forecast
through early Sunday as is. Began to blend in operational
GFS/ECMWF which were showing similar position of the low in the
gulf late Sunday into Monday then used WPC as an ensemble
approach. Forecast confidence is good initially then drops by the
start of next week.
.HYDROLOGY...Rainfall up to 1 inch across the Northern Lynn Canal
through Friday is expected to be sufficient to bring the Taiya
River above action stage /16.0 ft/ but below minor flood stage of
16.5 ft Friday afternoon. A special weather statement has been
issued about the situation and we continue to monitor and adjust
if the situation changes.
Warm temperatures in the Misty Fjords area has increased snowmelt
flowing into the Salmon River near Hyder. With warm temperatures
persisting expect that the Salmon River may continue to slowly
rise into Friday or Saturday. We will continue to monitor the
river levels. At this time there is no published flood stage for
the Salmon River.
MARINE...Small Craft Advisory for PKZ012-022-041>043-051.
Small Craft Advisory due to Seas for PKZ052.
Visit us at http://www.weather.gov/Juneau