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000
FXAK67 PAJK 221515 CCA
AFDAJK

Southeast Alaska Forecast Discussion...CORRECTED
National Weather Service Juneau AK
715 AM AKDT Sat Jul 22 2017

.SYNOPSIS...A 1000mb low in the SE gulf will gradually weaken
through Sunday as a high pressure ridge builds over the gulf. An
associated frontal band over the southern panhandle will spread
north eventually weakening over the northern panhandle Sat night.

&&

.SHORT TERM.../Saturday through Sunday night/ Somewhat wet front
moving through the panhandle right now. Ketchikan has seen
moderate rainfall since around midnight with hourly rainfall rates
of between 0.15 to 0.25 during that time. Other places in the
southern panhandle have not been raining that hard but some places
have seen around a half to 3/4 of an inch of rain in the last 24
hours. The heaver rain should start to diminish across the south
later this morning as the deformation band responsible moves into
the northern panhandle. Steadier rain should be starting up for
the north sometime this afternoon, but should start diminishing
Sat night as the deformation band weakens.

A little wind has been noted with the passage of this band but
nothing more then 25 kt for most marine areas and gusts to 30 kt
at Hydaburg overnight. Winds continue to diminish as the band
moves north and weakens.

For the south, rain will continue this afternoon and tonight but
it will be more convective in nature as onshore flow remains and
the upper level low will be starting to move through. The upper
low has a pocket of cooler air aloft associated with it which will
destabilized the atmosphere a little. Model convective parameters
suggest at least the possibility of some of the showers
producing some lighting this afternoon and evening over the SE
gulf and Panhandle so left the slight chance of thunderstorms in
the forecast.

The area starts to dry out late Sat night as the upper low moves
into Canada. The clouds do not depart however as lingering onshore
flow from a weak and flat ridge in the gulf keeps boundary layer
moisture rather high. Mostly cloudy skies and temps in the 50s
and low 60s remain the norm into early next week.

Short range models remain in rather good agreement through the
next 48 hours. Used mainly GFS and Nam for guidance.


.LONG TERM.../Monday through Saturday/ As of 1030pm Friday...An
upper level low traversing south of Haida Gwaii will assist in
providing offshore flow aloft over most of the panhandle during
the Monday to Tuesday timeframe. This pattern should allude to
cloudy skies with some showers possible, mainly over the southern
panhandle. By Wednesday, models seem to show the low lifting
north, but generally, it appears to deepen and remain over the
area through the rest of the time period. If this solution comes
to fruition, we could see bands of showers expand to include
portions of the northern panhandle. The forecast keeps a chance or
slight chance of showers over many areas through the rest of next
week. As has been the case all summer, our weather has been
influenced mainly by upper level features, rather than surface-
based, so this system warrants watching.

At the surface, anticyclonic flow dominates through much of the
week, as a weak ridge develops over the eastern gulf and persists
through the period of interest. Low level winds will be west-
northwesterly, but they will be relatively weak, due to a
generally stable airmass in the low levels. However, since the
ridge is somewhat flat, there may be plenty of opportunity for
clouds to move in with some isolated showers, as mentioned
previously.

Model differences pertaining to the upper level pattern increase
through as early as mid week, indicating that the surface pattern
may be even more different between models. The 12Z Canadian and
18Z GFS were in better agreement, with the 12Z ECMWF being the
outlier, but the 00Z GFS fell back in line with the ECMWF. This
indecisiveness of the models makes for even greater forecast
uncertainty through the next week.

&&

.AVIATION...Flight hazards this morning are patchy IFR in rain in
the south plus LLWS due to the approaching front. Also some brief
IFR in ground fog at Yakutat. Note mention of TSRA/CB in the
south TAFs this afternoon due to the cold air aloft moving over
Prince of Wales Island to Hyder with the upper low.

Most TAFs have MVFR CIGS/VSBY mentioned, progressing from the
south to north, but may have to tune to any IFR if it continues to
show up. Conditions improving tonight as front weakens and kicks
out, but may have to add fog for Sunday morning due to the
moisture gained today.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ042.
     Small Craft Advisory due to Seas for PKZ041-043.

&&

$$

EAL/Voveris

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