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Northern Alaska forecast discussion 
National Weather Service Fairbanks Alaska
255 PM akdt Monday may 4 2015

Discussion...

The main forecast issue will be potential red flag conditions by
middle week...this will be addressed in the fire weather section.
Otherwise...stratus/fog issues on the North Slope...warming and
the potential for showers over the interior...as well as hit and miss
fog/stratus along the western Alaska coast.

Models...fairly good agreement amongst the 12z deterministic
models through the first 72 hours...thereafter the typical
differences between the middle/long range solutions become apparent.
For this forecast package...nudged a blend of the models against
the previous forecast.

Aloft...weak upper level low over Bristol Bay will continue to
weaken and fill through Tuesday morning. A shortwave over the
Chukchi Sea this morning will drop southeast towards the eastern
interior tomorrow...squashing the upper level ridge that is
currently over the interior south and east of its current
position. As this shortwave exits the area Tuesday night...the
upper level ridge will reestablish itself over Mainland
Alaska...remaining overhead through the end of the weekend.
Another shortwave will clip the central and eastern Beaufort Sea
coast Wednesday.

Regarding h850 temperatures...as the upper level ridge
reestablishes itself over Mainland Alaska...southerly flow will
advect much warmer h850 temperatures over the eastern half of
Mainland Alaska. By Friday afternoon/evening...both the 12z
GFS/ecwmf are forecasting +7c to +9c h850 temperatures.

Surface...the thermal trough remains somewhat undefined as it
remains just south of the Alaska Range. As the week
progresses...the thermal trough will gradually lift north. A
surface high stretches from the new siberian islands east towards
the Canadian archipelago will shift southeast towards the
central/eastern Arctic coast. Another surface high over the Gulf
of Alaska will gradually shift east and will nose northward
towards the Alaska Range by late Tuesday. The 986 low 250 nm south
of Atka shift southeast into the Gulf of Alaska and weaken through
Thursday.

Western Alaska...fairly quiet for the West Coast. Patchy fog and
stratus is still floating out in the Bering Strait and Bering Sea
per surface observations from Saint Lawrence Island and Bering
Strait coast and the modis/sport 24 hour microphysics rgb
satellite imagery. Scattered to isolated rain showers over the
lower Yukon valley this afternoon and evening with upper level low
overhead.

North Slope...fog and stratus will be the main story on the North
Slope. As was previously stated in the morning
discussion...fog and stratus will likely remain entrenched along
the North Slope since there are no strong features to force the
departure of the fog/stratus. A weak upper level shortwave will
clip the central and eastern Beaufort Sea coast Wednesday and
will generate a few isolated snow showers from the eastern Brooks
range north.

Eastern and central interior...cooler temperatures and isolated to
scattered showers are expected tomorrow over the area as an upper
level shortwave dives southeast over the interior. The possibility
for any thunderstorm activity tomorrow or even through the rest of
the week will be very low...as convective parameters remain
lackluster. As the ridge reestablishes itself...southerly flow and
good warm air advection will setup warming the interior
temperatures to above normal values. The thermal trough will shift
north and will be north of the Alaska Range by late Tuesday. This
help enhance gap flow through the Alaska Range. Looking at
individual cross sections for Broad Pass...Isabel Pass and
Mentasta Pass...using the 12z NAM model guidance shows winds
increasing through the passes Wednesday morning...to 20 to 30 kts
Wednesday evening and Thursday morning...subsiding Thursday
afternoon/evening.



&&

Fire weather...
q vector analysis shows vertical motion associated with the
frontogenesis of the upper level trough that will arrive in the
central portion of the state on Tuesday. Divergence is seen aloft
which adds credence to the upward vertical velocities. Many
ingredients are present for convective potential except for
moisture. There does not seem to be adequate moisture available to
be lifted which is indicated by the Theta-E analysis. Additionally
the convective indices are not impressive. Expect scattered
showers but not expecting any thunderstorms at this time.

On Wednesday the upper level ridge re-establishes itself and continued
drying will begin over the central interior. The thermal trough
will be positioned near the Alaska Range which will enhance gap
flow winds. Red flag conditions are possible on Wednesday over
many areas in the central interior.



&&

Hydrology...
the latest river report from Eagle this morning...reports that
the ice started to move overnight and stopped one mile upstream of
Eagle. River watch mission is still ongoing this afternoon over
the upper Yukon...so no additional updates yet. Otherwise...break
up remains to be quiet so far this season.

&&

Afg watches/warnings/advisories...
Small Craft Advisory for pkz210.
&&

$$

Discussion/hydrology...lth fire weather...cf

May 15

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