Scientific Forecaster Discussion
000 FXAK69 PAFG 172312 AFDAFG Northern Alaska Forecast Discussion National Weather Service Fairbanks AK 312 PM AKDT Tue Sep 17 2019 .SYNOPSIS... A low pressure center over Bettles that is causing heavy snow there, will move to near Barter Island tonight. Heavy snow over the Dalton Highway from Finger Mt north to Sagwon will be diminishing late this afternoon, and heavy snow in zone 218 east of the Dalton Highway will diminish late tonight. A weather system moving north over southwest Alaska tonight will bring rain to the southwest Interior and western Alaska Range tonight, and then bring rain to much of the Interior on Wed and Wed night, except for the southeast Interior which will be under southwesterly chinook wind conditions Wed and Wed eve. Thu will see scattered showers over the Interior. Fri will see another low pressure system move north into the Gulf of Alaska, and then continue north over the Eastern Interior on Sat. This will bring rain to most of the Eastern Interior Late Fri into Sat, with snow over higher elevations. Aloft... A long wave pattern consists of a trough that stretches from Mainland Alaska southwest over the Bering Sea, and a long wave ridge over the Gulf of AK and South Central Alaska. The ridge will push east over Western Canada and SE Alaska by Thu and then remain there through the weekend. H500 Heights will remain low over NW Alaska, and gradually fall through the weekend over the remainder of Northern Alaska. What this means on the big picture is that conditions will cool to seasonal norms in most areas, and be mostly wet. Expect snow from the Brooks Range north, with mixed rain and snow along the Arctic Coast and West Coast, while the Interior has rain, which could be mixed with snow at times, through the weekend, but could see accumulating snow at elevation. A low aloft near Coldfoot will move to Arctic Village by 10 pm Tue, to Barter Island by 4am Wed, then move north of the Arctic Coast Wed and Thu. This feature has strong vertical motions and Mountain with it and is causing heavy snow. Expect another several inches of snow along its track northeast of Coldfoot tonight. Snow should be ending SW of Coldfoot in the next several hours. This scenario has led us to continue the snow advisory for zone 218 east of the Dalton Highway through midnight, while the snow advisory for the Dalton Highway West in zone 218, and zone 219 will end at 4pm. The Snow warning for zone 206 will continue through 6pm as the area from Atigun Pass north will likely get upslope snow for several more hours. A second low aloft over the Chukchi Sea will move over Point Hope tonight, and then persist there into Fri. This will cause isolated to scattered snow showers over the area from Point Hope to the Bering Strait as the cold air associated with this low. This feature will also induce a surface low under it which will be addressed in the surface section below. Surface... A 1002 mb low will develop near Point Hope tonight and then persist into Fri. This will cause some N-W winds of 15-20 kt over the Chukchi sea late tonight through Fri. Winds are expected to be light enough to not cause any significant waves or surf. A 1006 mb low 100 NM north of Barter Island will deepen to 998 mb by 4pm Wed, then move to 60 NM north of Utqiagvik as a 1002 mb low by 4pm Thu. Snow occuring with this low will taper off to Scattered showers showers Wed. A 1005 mb low near Coldfoot will move to Arctic Village as a 1005 mb low by 10 pm Tue, then move north an merge with the previously mentioned low north of Barter Island on Wed. An Arctic cold front that extends from Old Crow to this low near Coldfoot, then to Fairbanks and to the Yukon Delta, will move by 4am Wed to Inuvik to Eagle to Fairbanks to the Yukon Delta. The front will then retreat north over the Interior to the Brooks Range as the next incoming system pushes it now on Wed, while the portion of the front along the West Coast drops south of the YK Delta on Wed. Snow will track northeast with the low center tonight, giving another several inches of snow northeast of Coldfoot, while isolated to scattered rain and snow showers occur along the cold front tonight. A just west of St Paul Island will move to Kuskokwim Bay as a 986 mb low by 4am Wed, to McGrath as a 991 mb low by 4pm Wed, to near Tanana as a 1007 mb low by 4am thu, and to near Battles as a 1004 mb low by 4pm Thu. An occluded and warm front stretching NE from this low NE over SW Alaska will move to Bethel to Denali to Northway by 4am Wed, to McGrath to Old Crow by 4pm Wed, to Tanana to Old Crow by 4am Thu, and to Bettles to Arctic Village by 4pm Thu, then dissipating. The Arctic cold front will extend south from the low near Tanana at 4am Thu, then from Bettles to Denali by 4pm Thu, then remain stationary into Fri. Expect rain to spread northeast over the SW Interior and Western Alaska range tonight with the low and front, and over the remainder of the southern and Eastern Interior on Wed and Wed night, then linger as scattered showers into Thu. Precip may start as snow north and west of the Arctic front, then change to rain as the Occluded/warm front overrides the arctic air. Rain may mix with snow Thu along the returning arctic cold front. On Fri...A strong low moving north to the northern Gulf of Alaska will spread clouds and a chance of rain to the Eastern Interior. This low will continue north into the Eastern Interior by Sat, and will likely cause rain and high elevation snow across the Eastern Interior on Fri night and Sat. && .DISCUSSION... Models initialize well aloft at 12Z, and show similar solutions through 4pm Fri. Models show precipitation fields in general agreement, and we prefer to use a blend of the NAM and GFS precip fields for both areal coverage and precip amounts. At the surface at 15Z, models verify a few mb too weak on the surface trough north of the Eastern Arctic Coast. As a result, models verify winds directions almost 180 degree off in direction. Since this trough will likely persist, and intensify tonight and Wed as the low aloft moves northeast over it and helps to intensify it, expect winds to remain Westerly in zones 203 and 204 and to be 3-5 kt stronger than models would indicate for tonight and Wed. Otherwise, models show similar solutions through Fri and we will go with a blend of the GFS and NAM for winds. Bottom line is we will use a blend of the GFS and NAM, but keep west winds in zones 203 204 tonight and Wed and bump up speeds from what models indicate. FIRE WEATHER... Temperatures cooling to near normal this week. RH values should remain above 40% this week. Could see winds conditions Wed in zone 226 and 224 between Dot Lake and Tok with winds southwest gusting to 40-50 mph on Wed. Coastal Hazard Potential Days 3 and 4...None. && .HYDROLOGY... Rivers continue to slowly fall or have leveled off. No areas of concern at this time. && .AFG WATCHES/WARNINGS/ADVISORIES... Wind Advisory for AKZ224-AKZ226. Winter Storm Warning for AKZ206. Winter Weather Advisory for AKZ218. Small Craft Advisory for PKZ200-PKZ210.