Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/02/20

Southeast Alaska Forecast Discussion...UPDATED

National Weather Service Juneau AK

 723 PM AKDT Wed Jul 1 2020

.UPDATE...After mid-afternoon temperatures did more than inch
higher than forecast for today, in line with still strong offshore
winds Thursday, we went ahead and pushed highs tomorrow up to the
low 80s for Juneau and Upper Lynn Canal. Considering we are
squarely under the influence of a very warm air mass, despite any
potential channel breezes developing Thursday afternoon, we feel
like these temperatures will not be difficult to reach. Mid 80s
are not out of the question away from the water in Upper Lynn
Canal. AMDAR Soundings out of Juneau Airport around 0230Z Thursday
(around one hour ago) reveal that 850 mb temperatures are merely
up to 8.9 C. Coupled with the strong offshore winds, we rose to
78 F this afternoon. Given some models are going up to 13 C at 850
tomorrow, albeit with slight weakening of offshore flow in the
afternoon, we feel strongly that the northern Panhandle will be
even warmer Thursday. Other than this, we went more optimistic on
sky cover this evening for Wrangell, Petersburg, and Sitka before
allowing clouds to re-enter from the east.


&&

.PREV DISCUSSION......ISSUED AT ...314 PM AKDT Wed Jul 1 2020

SHORT TERM...Afternoon satellite imagery shows continued clearing
across the bulk of the panhandle which has contributed to the
balmy temperatures much of SE Alaska is enjoying. The main weather
story continues to be the impacts of the developing inverted
trough over the Panhandle. A more northerly wind regime has taken
hold, and has helped scour the cloud cover from much of SE, as
well as contributed to downsloping winds in locations like Haines
and Skagway, helping to drive temperatures back into the 70s in
these locations. Another consequence of this inverted trough will
be generally dry weather for the panhandle through the short term
forecast period. Exceptions do exist, particularly for the
southern inner channels including places like Misty Fjords,
Ketchikan, Klawock, and possibly Petersburg and Wrangell. These
areas will see easterly wave shower activity increase through the
next 48 hours, though do not expect any substantial precipitation
accumulation at this time. The clear skies throughout the rest of
SE will allow daytime high temperatures to warm well into the 70s
at the surface across much of the central and northern panhandle
on Thursday, with 850mb temperatures approaching 13 C. Low 80s
cannot be ruled out yet, but would be dependent on local effects.

Apart from the dry weather, relative humidity values are falling,
particularly over the far northern inner channels. We are not in
a situation that warrants a Red Flag Warning, but conditions will
definitely becoming more conducive for fire weather. Fortunately,
any lightning associated with thunderstorm activity is expected to
remain on the Canadian side of the Coast mountains.

Winds have reached SCA in Lynn Canal, and look set to remain
blustery through Thursday night as a pressure gradient builds over
the northern Panhandle. Winds will also reach between 15 and 20
kt throughout most of the other inner channels, though it does
look like winds will begin to calm down on Friday.

Models remain in fairly good agreement. Overall forecast
confidence is average.

LONG TERM.../Friday through Wednesday/An omega block consisting
of two lows--one over the Bering Sea and the other the west coast
of North America--and a ridge sandwiched over the western Gulf of
Alaska will keep Southeast Alaska in more or less a static
weather pattern this weekend into next week.

The pattern favors drier northwesterly flow aloft and potential
lower pressure over Southeast and the eastern gulf. Thus, we can
also expect warmer than normal temperatures given weaker flow
through the Inner Channels and a tendency towards mean offshore
flow. Forecast challenges will periodically arise from poorly
discernible waves that support convection in Canada. While models
are bullish for showers across northern BC in largely upslope
flow, they continue to tone down threat of any reaching the Inner
Channels. We lowered rain chances for most of the weekend and
warmed temperatures slightly for the north where highs should
fall mainly in the mid to upper 60s. With thermal troughing
induced across the northern and central Inner Channels, the south
looks likely to find itself in a slightly cooler regime with
largely southerly flow opening up the marine atmosphere of Dixon
Entrance/Hecate Strait. Thus we limited temperatures across the
south to the lower to mid 60s with presumed cooler temperatures
along the immediate coast like Sitka.

As ensembles continue to indicate an overall upper atmospheric
pattern of northwest flow, we kept slightly above normal
temperatures into next week. This is in line with the CPC`s
expectation of above normal temperatures next week, which is quite
a change from June as we draw deeper into July. Those with
outdoor plans on the Fourth of July should be in luck, as only a
slight chance of showers exist for the southern and central
Panhandle.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ012-013-022-041>043-053.

&&

$$

JWA/GFS/JWA

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