Scientific Forecaster Discussion
Northern Alaska forecast discussion
National Weather Service Fairbanks Alaska
323 am akdt Thursday Sep 3 2015
operational model runs from the Sep 3/00z forecast cycle are in
general agreement on the upper air features out through 84
hours/4 am Sunday...and agree well with the gefs ensemble mean.
An upper level ridge over the central and western northern Alaska
Mainland will weaken Friday night through Sunday. 850 mb
temperatures will remain slightly above normal through
Sunday...elsewhere across northern Alaska 850 mb temperatures
are expected to be near normal.
A weakening short wave trough moving up the west side of
the ridge extends from the Gulf of Anadyr to near Kotzebue.
This feature will become dampened out by this afternoon as it
continue to move slowly northward. Only a narrowing band of middle
and high level clouds remains with this decaying feature.
The next incoming short wave trough extends from near
55n/170e in the far southwestern Bering Sea to near Amchitka.
The trough will move east to extend from the northeastern
Alaska Peninsula southward into the Gulf of Alaska
by Friday morning...continuing eastward across the
northern Gulf of Alaska Friday afternoon and Friday evening.
An upper low centered near 58n/170e will move eastward
to Bristol Bay by late Saturday night...undercutting
the upper level ridge over the Mainland.
Current model runs are in generally good agreement through
a 1004 mb low near Gambell will weaken to a 1008 mb low near
the Bering Strait Friday morning then dissipate Friday afternoon.
A 1027 mb high centered 150 miles north of the MacKenzie river
Delta will move to the northwestern Canada archipelago by Friday
morning. A ridge extending from the high center westward across
the Beaufort Sea will gradually weaken as it moves northward to
latitude 76n by late Friday night.
A 1005 mb low over the central Alaska Peninsula will move
to near Aniak by Friday morning then dissipate Friday
afternoon. This low will bring rain to the West Coast areas
south of Unalakleet and to the southern parts of the western
east winds 15-25 miles per hour today and 20-30 miles per hour tonight and
Friday...decreasing Friday night. West of Barrow...winds will be
less than 20 miles per hour. Little or no precipitation expected through
Saturday. Mainly clear or partly cloudy skies through
Friday...patchy stratus and fog possible at night.
Central and eastern interior...
a chance of rain or showers in the Alaska Range tonight
through Saturday...elsewhere no precipitation expected.
lower Yukon valley...rain likely developing today. Rain tonight
and rain likely Friday and Friday evening.
Upper Kuskokwim valley...rain tonight and Friday morning. Rain
likely Friday afternoon. Chance of rain or showers Friday night.
Middle Yukon valley...chance of rain in the southern parts tonight
through Saturday. Elsewhere...no precipitation expected through
rain likely most areas from the Seward Peninsula southward today.
Rain tonight and Friday over areas south of Unalakleet...a chance
of rain over other areas from the Seward Peninsula south. Winds 15
miles per hour or less through Saturday.
St Lawrence Island...
no more than scattered rain showers are expected through
Saturday. Winds...15 miles per hour or less today through Saturday. North
winds 15-20 miles per hour Saturday night and Sunday.
In the extended forecast period...
recent model runs have been showing rather volatile
results...with large differences between models and poor run to
run continuity. Both the gefs and European model (ecmwf) ensemble means from the
Sep 3/00z cycle indicate a polar vortex north of 80n with west to
northwest flow over the Arctic coast and Beaufort Sea. There is a
possibility of a more active weather pattern over the Arctic
region. GFS and European model (ecmwf) forecasts from the Sep 3/00z cycle indicate a
strong short wave trough dropping southeastward out of the Arctic
Tuesday night and Wednesday...accompanied by a 995-1000 mb
surface low. Forecast low position at 4 am Tuesday is near
75n/158w...about 300 miles north of Barrow. By 4 PM Tuesday...mean
of the GFS and European model (ecmwf) puts a 1000 mb center near 73n/149w. Gefs
ensemble spread appears to be moderate. This scenario would
produce north to northwest winds 25-35 miles per hour over the Arctic coast
Tuesday and Tuesday night with a likelihood of high surf
conditions on the Arctic coast from Barrow west. But due to the
recent variability in model runs...forecast confidence remains low
at this time. It should be noted however...GFS/ECMWF runs from
the Sep 2/00z cycle also indicated that the Northwest Arctic
coast could be affected by a moderate intensity surface system
in the same general location and time frame. The overall large
scale pattern pointing to colder temperatures north of the Brooks
Coastal hazard potential days 3 and 4...
none Saturday and Sunday. High surf conditions possible on the
Arctic coast from Barrow westward Tuesday and Tuesday night if
current GFS/European model (ecmwf) runs from the Sep 3/00z cycle are correct...with
north to northwest winds 25-35 miles per hour. Forecast confidence at this
time however remains low due to recent variability of model runs.
river levels on the chena river from the Moose Creek
downstream are still elevated but are continuing to
fall. The stage of the chena river at Fairbanks was
6.4 feet at 1 am this morning...and forecast to fall
to about 5.2 feet by midnight Saturday night.
Elsewhere...no hydrologic issues.
Small Craft Advisory for pkz235-pkz240-pkz245.
Rf Sep 15