Scientific Forecaster Discussion
Northern Alaska forecast discussion
National Weather Service Fairbanks Alaska
208 PM akdt Wednesday Jul 23 2014
Upper air...models are in good agreement with long wave trough
developing over Mainland Alaska and moving east during the next
couple of days. By Friday afternoon the trough axis will extend
from well north of the Arctic coast to over Prudhoe Bay...west of
Fairbanks...and south over the Gulf of Alaska. A short wave moving
into the long wave Sunday shows disagreement in timing and
precipitation coverage amount models...however there is agreement
in the general pattern through early next week.
Surface...low pressure over the Brooks range will weaken Thursday.
Another low will develop over the alcan border Thursday and
persist through Friday...then move slowly east into Canada through
Saturday. A front developing along the West Coast will move inland
tonight...then move slowly east over the interior as a cold front
through Friday. The front will slow as into approaches the alcan
border on Friday.
North Slope...a cool airmass for this time of year will be in
place through the weekend and possibly longer. Rain will taper to
scattered snow showers from Barrow west after midnight Wednesday
night. A change over to flurries could occur east to Prudhoe Bay
Thursday night. The airmass drys off behind the trough...so any
accumulations will be very light.
West Coast...rain will taper to light showers this evening as the
upper level trough moves east. High pressure builds in Thursday...
then a short wave moves through Saturday through Sunday...with
rainfall amounts less than those with the current system.
Interior...upper level trough moving east has already spread areas
of rain over the western interior. Rain will move east to the
central interior and south slopes of the Brooks range tonight...
then to the eastern interior Thursday and Thursday night. Rain
will change over to snow in the southeastern Brooks range at
elevations of 5000 feet Thursday...then lowering to 2000 feet
Thursday night...before rising back to 4000 feet on Friday. The
airmass will dry considerably after changeover to snow...so
accumulations will generally be less than 2 inches over that part
Coastal hazard potential days 3 and 4...none
Hydrology...rains in the Koyukuk valley will be heaviest tonight...
then taper off as an upper level trough moves east. Rainfall
amounts are not expected to cause flooding from rises of streams
and rivers in the Koyukuk valley...however streams and smaller
rivers will rise but not above bankfull. Precipitation over south
slopes of the Brooks range will also be heavy in areas...but not
heavy enough to cause flooding. Another factor will be snow...at
higher elevations...which will not drain immediately into basins.
For the western Alaska Range...models show a bullseye of
precipitation over Mount McKinley...but due to the elevation...
most of that will be snow and thus will be slower to drain.
Otherwise for the western Alaska Range...areas of rain will be
heavy enough to cause concern for possible rapid rises of
streams...so a hydrologic statement has been issued for that area.
Small Craft Advisory for pkz215-pkz220.
Da Jul 14