Scientific Forecaster Discussion
Northern Alaska forecast discussion...corrected
National Weather Service Fairbanks Alaska
330 am akdt Friday may 29 2015
Models...continue good short term agreement. Initialized well
against the 06z surface analysis. Middle Range is beginning to show
agreement on the development of a upper level low over the high
Canadian Arctic that drops south Saturday to be over the northeast
interior Sunday morning with the longwave trough pushing south to
the Alaska Range by Monday morning. NAM continues to work well for
the first 24 hours so will blend the first 24 hours to it
today...then use a blend of the GFS/European model (ecmwf) for the next 36 hours.
Middle Range showing more agreement between models so will use a
blend for those periods...the extended periods beyond Tuesday
still a mess so wpc guidance may be the way to go.
Aloft...at 500 hpa...a 559 dam low that developed over the upper
Yukon Flats Thursday afternoon will continue east into the Yukon
territory as the low dissipates. A sharp 573 Dam Ridge continues
to build north and slide east over the western interior and
southcentral area today and will be come stationary. A 519 dam
low in the west central Bering Sea will more northwest over the
western Bering Sea by Saturday morning and becomes stationary
through Sunday morning. A shortwave developing over the high
Canadian Arctic will move south to lie from the Canadian
archipelago to Barrow by early Saturday morning...then from
northern Banks Island to deadhorse to Point Lay by noon
Saturday...then from southern Banks Island to over the eastern
Brooks range by late Saturday evening as it weakens significantly.
A second shortwave will develop near the North Pole this afternoon
and move south to 80n 140w Saturday morning with a 536 dam
center continuing south to over deadhorse Sunday morning as it
weakens to 542 dam...and to over Fairbanks early Monday morning
at 545 dam. At 850 hpa...big changes on the horizon as the
weekend progresses. Expect some cooling today as the upper low
over the Yukon Flats moves east and pulls some colder temperatures
over the interior. Then a warm up for Saturday and Sunday before a
pretty significant cool down early next week. Temperatures 5 to 10
celsius above this weekend...but Monday they will take a dive
south of zero celsius over the northeast half of Mainland Alaska
for a couple days.
Surface...thermal trough over the upper Yukon Flats will continue
to weaken today and pull back into Canada as it loses the upper
level support. Ridge of high pressure continues to build over the
West Coast today. The ridge weakens on Saturday as thermal trough
builds west to the south of the Alaska Range. Ridging over the
Arctic will remain in place and build south over the eastern
interior tonight and Saturday. 1030 mb high over the northwest
Pacific will pull back to the south as the trough builds west
over the coast. A 982 mb low in the west central Bering Sea will
move northwest as it weakens to 998 mb Saturday morning and is
absorbed into a low in the Sea of Okhotsk early Sunday morning.
The ridging over the West Coast will drift west over the eastern
Bering Sea late Saturday night.
Arctic coast and Brooks range...patchy dense fog again today with
the stratus ceilings hanging in as onshore flow continues. Heavy
rains over the Arctic plain will taper off this morning but some
heavy rain can still be expected from the Dalton Highway east this
as the low over the Yukon Flats moves east. Almost 1.5 inches of
rain has been recorded at ivotuk overnight. It will take a day or
so for the rain to make it into the rivers...but once it does
expect rivers to rise to bankfull is some areas. Cooler
temperatures over most of the Arctic coast will only get cooler as
the weekend progresses. As the next front moves south on Saturday
expect the rain showers to turn to snow showers with a few inches
of snow possible Saturday night and Sunday east of Barrow. No
significant winds over the Arctic coast.
West Coast and western interior...decaying occluded front
making its way over the coast will continue to stretch out with
only scattered rain showers expected for the coastal areas south
of the Bering Strait and west of the middle Yukon valley. The
showers will become isolated Saturday as the front continues to
decay over the coast and eventually dissipate by Sunday morning.
Winds generally light and offshore near the coast. Some weak warm
air advection up the coast will push temperatures up a few
degrees for the weekend.
Central and eastern interior...becoming mostly clear over the
interior as the low moves east. Slightly cooler today with some
cold air advection...then warming up for the weekend before a
significant cooling event on Monday that could push overnight
temperatures Tuesday and Wednesday down near freezing from the
Tanana River North. Light winds through the weekend. Looking for
increasing clouds on Sunday over the northeast interior with a
mix of rain and snow showers over the upper Yukon Flats Sunday
evening and over the fortymile country early Monday.
Fire weather...it will be dry and cooler today so no red flag
issues today. As we continue to dry Saturday and Sunday it looks
like relative humidity values will make it into the 20 percent
range...but no winds of significance. Thunderstorms activity today
will be very minimal if any at all and be confined to east of
Chalkyitsik in zone 220 and helmut mountain in zone 218. Also
south of Chicken in zone 224 and east of Tok in zone 226. The
rains...even though they were spotty will help with Greenup and by
next week that should be reflected in relative humidity values.
Hydrology...1.5 inches of rain overnight at ivotuk on the Arctic
plain will take a day or two to be reflected in the major
Rives...but it should be enough to bring some of them to bankfull
so will continue to monitor and discuss with the river forecast
center to determine if any public advisories would be pertinent.
Gale Warning for pkz210.
Brisk Wind Advisory for pkz225.
Sdb may 15