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FXAK67 PAJK 262211

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
211 PM AKDT TUE JUL 26 2016

.SHORT TERM...An upper trough extended southward from SRN interior
AK to the NCNTRL PAC Tuesday afternoon, which places SERN AK
beneath an expansive zone of southwesterly flow aloft. WV imagery
also showed a shortwave impulse rounding the base of the larger-
scale trough, and is forecast to cause the upper trough to eject
northeastward across the gulf during Wednesday.

As this occurs, surface low pressure will move north over the
central/western gulf, resulting in strengthening deep-layer
southerly flow, which will aid in transporting PW values from 1 to
1.4 inches northward to the panhandle. This moisture combined
with increasing large-scale and orographic ascent will favor a
large area of moderate rainfall developing over the central and
northern panhandle during Wednesday afternoon. Locally heavy rain
will also be possible, particularly over AKZ017/Yakutat area,
where mesoscale forcing for ascent will be augmented due to an
easterly barrier jet and terrain enhanced lift upwind from the
Saint Elias Mountains.

Small craft wind speeds are probable over much of the coastal
marine zones with the previously mentioned barrier jet, which
will develop late this evening and persist through Wednesday
afternoon. In addition, gale force winds are expected to develop
late Wednesday afternoon over marine zone 52.

Inherited pressure grids were nudged to the 12Z NAM and GFS. POP
and QPF were based on an ensemble of hi-res and coarse-res
guidance, as well as support from RFC. Temperatures during Tuesday
afternoon did not warm significantly, and expect Wednesday will be
similar due to widespread rain and clouds.

.LONG TERM...A low will move north into the western gulf Wed
evening, then weaken and drift east across the gulf for late
week. Models differ on how strong the low will get
initially, then diverge on how much of it will be left as it
tracks across the gulf. Current forecast looked like a good
compromise amongst the models for the latter part of the week so
little change was made to it for then. Bigger differences develop
by the weekend with another upper trof that moves toward the gulf
from the northwest, with the ECMWF model the most aggressive
digging the trof into the gulf, while other models split the
energy more upstream and show little in the way of the trof
getting into the gulf. Kept current forecast going for now as it
was good middle ground compromise for the weekend and beyond at
this point.

Watching for locally heavy rainfall for Wed night into Thu morning
with occluded front then a trof moving across the area. Rainfall could
reach 2 inches near sea level over the northwest half of the area
with locally higher amounts in the mountains. Much less rain is
expected over the far southeast area. Precip will transition to
showers late Wed night and be mainly showers for Thu. There is
potential for TSTMS for the north-central gulf Wed night but not
confident enough to include them at this point due to model
differences in intensity of the surface low and upper vort
maxima(and associated cold pool aloft). See hydrology section
below for impacts on area rivers and streams.

For the weekend and beyond, does seem like a lesser threat for
precip but this will depend on whether the ECMWF or the other
models is correct in handling of upper trof moving toward the gulf
from the northwest. Even with a lower precip threat, does not
appear to be any offshore lower level flow into early next week so
still looks like a fairly cloudy time frame.


.HYDROLOGY...Moderate to locally heavy rainfall is forecast to
spread across the northern half of the panhandle Wednesday and
Wednesday night. This will cause area creeks, streams, rivers, and
lakes to rise, including the Taiya River, which is forecast to
reach moderate flood stage Wednesday night. As a result, a flood
watch has been issued for the Taiya River, which is in effect from
4pm Wednesday through 6am Friday. Refer to the latest flood
statement and SPS for additional information.


.AJK Watches/Warnings/Advisories...
PUBLIC...Flood Watch from Wednesday afternoon through late Thursday night
     for AKZ018.
MARINE...Gale Warning for PKZ052.
     Small Craft Advisory for PKZ042-043-051.



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