textproduct: Fairbanks

SYNOPSIS

Two features will dominate the forecast: a trough near the northern GoA moving north-northeast into the Tanana Valley and Yukon Flats, and a broad, weakening low pressure in the Bering Sea. The trough is expected to move into the Yukon by Thursday morning, with the weakening low moving near the YK Delta. A front associated with the weakening low will move northward over the Alaska Range, generating gusty winds in interior passes.

KEY WEATHER MESSAGES

Central and Eastern Interior... - An increased chance of precipitation today as a system moves north across the Interior. This will set up daily chances for isolated showers. Chances for thunderstorms increase to around 30% in the Central Interior by Saturday.

- Seasonably warm temperatures are expected to continue across the Interior through much of the week.

West Coast and Western Interior... - Gusty S-SE winds are expected to continue through Wednesday night and into Thursday morning across the West Coast.

- Showery conditions are expected along the Lower Yukon and Yukon Delta regions throughout the week. Mostly light showers are expected Wednesday night, with the possibility of moderate showers Thursday. These showers will be mostly rain, especially nearer the Western Interior, but some periods of snow and light wintry mix are possible near St. Lawrence Island and the Bering Strait Coast.

- Increased thunderstorm potential around 15% on Friday, primarily for the Middle Yukon Valley and Upper Kuskokwim Valley, with chances increasing to 30% on Saturday

North Slope and Brooks Range.. - Breezy northeasterly winds along the Western North Slope weaken slightly and shift more easterly. E to ENE winds 15 to 25 mph are expected across the Arctic Coast through the rest of the day.

- Diurnal showers along the southern portion of the Brooks Range are expected to continue through the week. Little to no precipitation is expected for the North Slope

- Chilly temperatures persist with highs in the 20s and lows in the teens along the North Slope. A gradient of temperatures across the Brooks Range with highs in the 50s to near 60 along the southern slopes and low 40s for the northern slopes.

FORECAST ANALYSIS AND DISCUSSION

A weakening, occluding low continues to work its way up the Aleutians, entering Bristol Bay Thursday morning. Ahead of this low, a warm front will swing across the YK-Delta late beginning early Thursday morning. Cold air will continue to be advected from the north across the Bering, which will allow for mixed precipitation chances to continue St. Lawrence Island and the Bering Strait primarily during the morning hours, before solar heating transitions any snow to mostly rain.

This new low over Bristol Bay will eventually take over as the main driver for the broad troughiness across much of the state. With this, a series of shortwave will wrap around this low which will allow daily chances for scattered showers and isolated thunderstorms to continue across much of the state through the end of the week. A more pronounced line of energy will begin to work its way north, by Thursday, as it stretches from the YK-Delta to the Eastern Interior. This will help tighten the gradient and allow for another round of gap winds through the Alaska Range on Thursday. The main bulk of the energy will work its way into the Kuskokwim valley on Friday, setting up the next chance for isolated thunderstorm, with current probabilities around 15%. The best chance for storms, Friday, will be across the Central and Western Interior.

Looking over the North Slope, high pressure continues to linger off the northern Arctic Coast. Cooler temperatures, breezy east winds, visibilities of 3 SM or less, and low cloud ceilings are expected to continue as the overall pattern is not expected to change much over the next few days.

As the end of the short-term period rolls in, models are showing the potential for a shortwave to peel away from the main low and work its way east across the Gulf. A thermal trough is expected to develop, with easterly flow across portions of the Interior by the start of the weekend, which is favorable for thunderstorm development for the western interior.

FIRE WEATHER

Broad southerly flow with a upper level shortwave trough will work its way north northeast, bringing increased PoPs and increased chances of wetting rain for the lower Tenana Valley and Yukon Flats up to the Brooks Range through Thursday. Downsloping and drying winds looks to limit PoP chances around the upper Tenana Valley including Delta Junction. Wind gusts up to 55 mph, lack of PoP, and drying down to 35% relative humidity raises the fire concern for the aforementioned area; however, not expecting critical fire weather conditions on Thursday.

For the western Interior, a front extending from the low pressure moving into the Kuskukwim will bring increased PoPs, although accumulations from showers look to be light. Wind gusts look to increase along the front, with wind gusts expected to stay under 35 mph. Temperatures in the mid to upper 50s and minimum relative humidities between 40-50% look fairly consistent the weekend.

HYDROLOGY

Yukon River: The breakup front on the Yukon has passed Russian Mission. As of 5pm AKDT Tuesday, an ice jam 10 miles downstream of Russian Mission remains in place. It is made up of about 3 miles of large intact ice sheets extending from Roosevelt Island to Seven Mile. River Watch overflew the ice jam at noon Tuesday and again at 5pm and saw no change. About 60 miles of chunk and pan ice extend from the head of the jam upriver past Holy Cross. The most extensive flooding is occurring at Holy Cross and in the lowlands between Holy Cross and Anvik. Most large Yukon River ice jams during recent years decay, erode and fail within a few days. The current jam at Russian Mission is going on day 3.

Flood warnings remain in effect for Russian Mission, Holy Cross, and Grayling. A Flood Advisory is in effect for Anvik. Extensive flooding of the lower portion of Holy Cross community was occurring Tuesday, including the Holy Cross runway. Water remains high on the Yukon upriver from the breakup front due to snowmelt and the Yuki Ice Jam release. As of noon Wednesday the River Watch Team reported that the river slows down around Anvik and that the backwater from the jam seems to have extended to Anvik.

When the ice jam releases there will likely be a period of water level rises and dense ice runs at Russian Mission for at least 24 hours as the backwater flows past there. Downriver of the ice jam towards Marshall the ice is rotten and river levels are low.

Chena: The Chena River continues to respond to warmer temperatures with higher elevation snowmelt leading to rivers running higher than normal, but likely remaining below action stage.

Additional Information: Visit www.weather.gov/aprfc for the latest hydro information.

Please report observed flooding to local emergency services, law enforcement, or to the National Weather Service when you can do so safely..

EXTENDED FORECAST DAYS 4-7

For late Saturday through next Wednesday. At the start of the extended forecast period late Saturday, the overall pattern across Alaska will have shifted more towards broad troughing. The previous dynamic of higher pressure to the northeast and lower pressure to the southwest remains, but has significantly weakened. What was previously the low in the Bering Sea slowly weakens and stretches east becoming the base of the broad trough over the state. Into the weekend the forecast becomes significantly less certain with a far wider range of possible interactions between new low pressure systems moving into the Bering and the weaker, broader trough.

Most likely temperatures remain similar to this week across the Interior and North Slope and the larger variance will lie within wind strength and precipitation early next week. By Tuesday another low is likely to have settled into the eastern Bering Sea once again shifting the trough axis further west. Models have a larger range of possible locations and strengths for this next system than previous forecasted lows and so impacts are harder to gauge. Many of the same hazards seem this past week are possible though with strong southerly winds through the Alaska Range passes, waves of showers with occasional embedded thunderstorms, and gusty easterly winds across the North Slope are all possible next week.

Coastal Hazard Potential Days 3 and 4...None

AFG WATCHES/WARNINGS/ADVISORIES

AK...Flood Watch for AKZ826-830. PK...Small Craft Advisory for PKZ801-850.