Scientific Forecaster Discussion

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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska
338 PM akdt Friday Apr 18 2014

Short term...shower activity left over from last night has
continued through the early afternoon, but has generally
diminished and some nice breaks in the cloud cover are evident in
both satellite imagery and web cameras. Farther south and
offshore into the central Gulf, a cirrus cloud shield is
advancing north and east ahead of the next low and associated
front. This system is quite large and very impressive in all
three of the major satellite channels. Model data is depicting an
Oblong low with multiple centers getting down into the low 970s
this evening before the front starts to impact the southern outer
coast. Multiple centers not visible on satellite imagery yet, but
what will evolve into the eastern center is clearly the dominant
feature. Very pronounced dry slot noted in water vapour imagery
suggesting significant potential for further development. Did not
back down at all on previous wind forecast and with the
appearance of the dry slot, more wind may be necessary in
subsequent forecasts. As it is, have a strong wind headline out
for the southern outer coast for late tonight and again tomorrow
afternoon. Coastal marine zones from Cape Fairweather south
feature easterly gales to 40 kts with a 35kt gale for Clarence
Strait. Small craft advisories for most of the remaining marine

The front itself looks like it will temporarily stall over the
southern Panhandle as the two low centers fujiwhara around each
other, but northward progress looks like it will resume during the
beginning of the extended range forecast period. Consequently,
have a dry short term forecast for much of the Panhandle once
shower activity dries up later this evening. For southern
locations, quantitative precipitation forecast values not overly excessive, even with the front
stalled, 24 hour rainfall totals ranging from 0.25 inches to
around 0.44 inches.

Cloud cover today has prevented significant daytime heating with
Hyder being the only location to see 50 degrees as of early this
afternoon. Partly cloudy conditions over the Panhandle tonight
will be a moving target, so just how much radiational cooling any
one particular location experiences will be highly variable. MOS
guidance was very low with values down to the middle 20s for northern
locations. Did not think this to be realistic, so blended European model (ecmwf)
and Gem for overnight lows, then adjusted to reflect projected maximum
dew points for today and expected low level warm air advection
from the south for tonight. European model (ecmwf) temperature curve exhibited a
slow warming trend all night, but kept with a normal diurnal
trend. Cloud cover will build back in from the south tomorrow, so
overly warm maximum temperatures for tomorrow - at or slightly above normal
for late April.

No changes to pressure or wind fields. Blended ECMWF, Gem, and
GFS at times for pop and quantitative precipitation forecast. Temperatures as discussed above. Forecast
confidence is average to slightly above average.


Long term...the low pattern in the Gulf becomes a shade more
complex as the low re-curves to the northwest Gulf of Alaska as a
secondary short wave drives southeast on the west side of the
upper level low in the Gulf. This digging trough will move the
Gulf low southeastwards early next week (monday). With the low
dissipating and moving out of the Gulf Southeast Alaska. Expect
showers to persist through Sunday...although for Saturday night
the northern Panhandle may have sufficient offshore flow to delay
or limit the amount of rain that may fall. A secondary trailing
trough will spread extra moisture across the area for late Sunday
and and Monday.

As the next feature spreads its frontal band across the western
Gulf of Alaska through the first half of next week. Southeast
Alaska looks to be dry through much of the week. I do not expect
major clearing and sunshine next week after the rains taper off as
the upper level flow is southerly or southeasterly.

Confidence is average through the forecast period. Only minimal
changes to the temperatures and a minor refreshing of the winds
and rain chances through the extended time frames.


Ajk watches/warnings/advisories...
public...strong wind from 1 am akdt Saturday through Saturday morning for
Strong wind from Saturday afternoon through Saturday evening for
Marine...Gale Warning for pkz036-041>043.
Small Craft Advisory for pkz012-013-021-022-033>035-051-052.