Area Forecast Discussion

SYNOPSIS

Broad troughing continues across much of the state. Attention turns toward the Arctic low that continues to spin over the North Pole, swinging a series of shortwaves across the state. A colder airmass will begin to shift south on Sunday as part of a stronger shortwave moving south from the Arctic Low. This will set up potential for moderate snowfall across the Brooks Range on Sunday and Monday, along with isolated chances for thunderstorms across the Interior. A winter Storm Watch is currently in effect for the Brooks Range. This system will also bring in seasonably colder temperatures for much of the state which is expected to linger through the early parts of next week.

KEY WEATHER MESSAGES

Central and Eastern Interior... - Gradually cooling temperatures are expected through the weekend into early next week as increasingly scattered showers and isolated thunderstorm chances build in across the Interior. Thunderstorm chances will be confined to the Upper-Tanana today, spreading to other portions of the Interior on Sunday.

- Gusty west/southwest wind speeds will increase across the Northern Interior on Sunday. The strongest winds are expected at higher elevations with gusts up to 35 mph.

- Dependent on clearing skies, low temperatures Monday night through Wednesday night will bottom out in the 30s and 40s for most, with coldest valleys dropping to around freezing.

West Coast and Western Interior... - Dry conditions will continue across Western Alaska through the weekend, with highs cooler on the coast in the 30s/40s/50s and warmer inland in the 50s/60s/70s.

- Isolated showers will continue across some portions of the central West Coast today as northwest flow continues to bring weak shortwaves down from the Arctic.

- Isolated showers will then continue through the weekend as temperatures see a gradual cooling trend. Lows will be in the 20s/30s/40s.

North Slope and Brooks Range.. - Below normal temperatures are expected to continue into early next week north of the Brooks Range with highs/lows in the 20s/30s while warmer air remains situated to the south of the Brooks Range where highs in the 40s/50s/60s and lows in the 30s/40s continue.

- Isolated to scattered showers expected to continue across the North Slope, expanding to the Brooks Range over the weekend into next week. Light snow accumulations are expected across the Arctic Coast/Plains, with heavier amounts in the Brooks Range.

- A Winter Storm Watch has been issued for the Central Brooks Range for Sunday and Monday to capture heavier snowfall amounts along the Dalton Highway, with snowfall amounts up to around 6-12 inches and wind gusts around 30 mph at Atigun Pass.

- Temperatures will hold steady or see a cooling trend this weekend into early next week.

FORECAST ANALYSIS AND DISCUSSION

Not much has changed to the overall pattern as broad troughing continues across northern Alaska. A 500 decameter, Arctic low continues to spin near the North Pole, providing westerly flow across the state. A weak shortwave will move south from the Chukchi throughout the day, today, providing very isolated chances for showers across the West Coast. Some of the energy will get caught in the westerly flow, providing snow showers across the Brooks Range today. Some of this energy will stretch from the YK- Delta to the Yukon Flats. This sets up a frontal boundary that will provide chances for thunderstorms across the Interior on Sunday.

Troughing will slowly amplify throughout the weekend as some of the energy from the Arctic low shifts further south. Associated with this system is a cold, Arctic airmass that will move across the state along with widespread chances for showers. Looking over the Brooks Range, the southwesterly flow will slowly set up as the trough continues to dig further south across the Western Interior. This will provide a chance for moderate snowfall amounts through the central Brooks Range with Sunday and Monday totals between 6 and 12 inches expected. A Winter Storm watch remains in effect for these areas.

FIRE WEATHER

Conditions are expected to shift beginning today as upper-level troughing is expected to build into the state from the north, leading to the isolated showers and thunderstorms returning to northern Alaska. The greatest chance for thunderstorms are on Sunday for the Interior and SW Interior with the possibility of gusty winds accompanying these thunderstorms. High temperatures will begin to steadily decrease and minimum relative humidities will steadily rise over the next couple of days. This is expected to persist into mid- week as upper-level ridging begins to move into the state once again.

HYDROLOGY

Sagavanirktok River Temperatures continue as below normal, around the low 30s for a high near the coast and the mid to upper 30s for the northern Brooks Range. Going into the weekend and into next week, much below normal to possibly record breaking temperatures with lows possibly below 20 degrees and high temperatures not exceeding freezing, except near the Brooks Range where temperatures may reach the upper 30s. APRFC reports some open water for the whole river channel.

Colville River Fresh Eyes on Ice report from Thursday shows between Umiat at Ocean Point that the low is up slightly and is more turbid with fewer but bigger jams present with a lot of stranded ice. APRFC reports some open to mostly open water with mostly ice still in place by Colville Village.

EXTENDED FORECAST DAYS 4-7

The main story on Tuesday is an upper level low which is providing northwesterly flow to most spots from the Central Interior north and west while the Eastern Interior remains in southwesterly flow for much of the week. Rain will be ending in the Central Interior by Tuesday afternoon with widespread rain showers and isolated thunderstorms persisting in the Alaska Range, Upper Tanana Valley and Fortymile. Wednesday should be a drier and warmer day for most areas but scattered showers and isolated storms remain possible in the Eastern Interior. Looking at the end of the week, there is some uncertainty with the exact details but the pattern is there. Ridging appears to be increasing across Northern Alaska from the southeast, especially from Friday into Saturday bringing the potential for much warmer weather and thunderstorms. The warmer weather would include the Brooks Range and North Slope as well.

By Saturday, a nearly 590 decameter ridge will be fully developed, but the question is where it sets up. Some guidance has it over the West Coast of the CONUS while others have it south of, or directly over, Haida Gwaii. To the west of the ridge is an upper low near the Alaska Peninsula which would further promote southerly flow in Northern Alaska. Needless to say, significantly warmer weather is possible. One thing the upper level low can do is provide fronts to Northern Alaska which would come in the form of showers and storms. Nonetheless, expect warmer, more summer-like weather heading into the end of next week and especially the weekend.

Coastal Hazard Potential Days 3 and 4...None

AFG WATCHES / WARNINGS / ADVISORIES

AK...Winter Storm Watch for AKZ809. PK...None.