Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 222246
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
246 PM AKDT Sat Apr 22 2017
.SYNOPSIS...Low pressure over the southwest gulf moves west
tonight. A weather front well south of Haida Gwaii will move north
into the southeast gulf and near Dixon Entrance by late Sunday.
High pressure across northwest Canada will weaken through Sunday.
.SHORT TERM...Higher clouds across the southern Panhandle were not
enough to hold down surface temperatures in the 50s today given
850 mb temps of 4 to 5 C. In locations of downsloping winds, they
have soared into the middle and upper 60s with Annette (68 F) already
breaking a daily high maximum temperature. While 850 temperatures
across the north were not as warm, adiabatic warming combined
with sunnier conditions threaten some records in the north as well,
notably Juneau Airport at 62 and Skagway as of 2 PM. Not to be
outdone, higher elevation observations last night suggest an
inversion likely held White Pass in the mid 30s this morning. As a
result, we have raised low temperatures Sunday morning across those
same higher elevations.
As an upper low well to our south progresses eastward into
Vancouver Island tonight, upper level winds will increasingly veer
onshore through Monday over Southeast Alaska. This will translate
into a chance of rain spreading northward starting early Sunday
morning for the far southern Panhandle and expanding into the
Juneau area by Sunday night. Any rain that does fall however is
expected to be light with better lifting farther south across the
Pacific and the BC Coast. Confidence is still not high enough to
even raise chances to likely. Due to these increasing rain
chances and thicker cloud cover, high temperatures will fall
around 5 to 10 degrees Sunday/Monday. Gradients will steadily
ease through Monday, thus winds will be increasingly light with
some diurnal channels breezes developing during the afternoons.
NAM/ECMWF were used for small changes. Forecast confidence good.
.LONG TERM.../Monday night through Fri/as of 11 PM Friday
night/ Ridging begins to weaken and shift further inland as a
series of southerly waves tracking up the western periphery of the
ridge track over the southern portions of SEAK through Mid-week.
This will bring increasing chances of precipitation and cloud
cover to the southern and central portions of SEAK as we approach
Wind flow over the Gulf of AK becomes more SW in time next week.
Generally speaking more of SE AK will have gradually wetter
weather as the week moves on. Model guidance for the latter part
of the week continues to suggest fairly widespread rain in the
Wed-Fri time frame. However, discrepancies still exist pertaining
to the finer details of timing and placement of the approaching
waves and the precipitation they bring.
Extended forecast grids were nudged toward NAM/EC from Mon morning
into Tue morning, then WPC was mainly used from Tue morning
through the end of the week. Confidence is fair during the early
part of the week, but drops off during the later part of the
week. The seasonally weak weather pattern without major weather
leaves confidence in details falling by mid week.
.AVIATION...Widespread VMC conditions will continue through 00Z
Monday. Due to a drying boundary layer, no fog and low visibility
are anticipated tonight. Significant easterlies of 15 kt and
higher gusts due to mixing late this afternoon will fall quickly
.MARINE...Activity across the western and outer gulf has spread
high seas into the eastern gulf; therefore, small craft high seas
persist in the gulf through much of Sunday before beginning to
diminish. While northerly gradients begin to re-tighten across
the northern Panhandle tonight, a weakening front over the western
gulf and subsiding high pressure across northwest Canada will
keep winds below 25 kt through the Inner Channels into Sunday.
MARINE...Small Craft Advisory due to Seas for
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