textproduct: Fairbanks

SYNOPSIS

The active weather pattern continues unabated, with periods of rain expected for most of the Interior through the foreseeable future. An atmospheric river and its associated systems will move through Friday and Saturday, bringing with them periods of moderate to heavy rain, with some river rises expected, especially along smaller streams in the interior. Although overall daily rainfall totals diminish in the immediate wake of the atmospheric river, a broad area of troughing will set up from Sunday into early next week and send additional systems into the area. A stronger system will move up from the Kuskokwim Delta area on Tuesday. The one positive aspect of the rain will be warming temperatures, as repeated rounds of SW flow help push back the cooler arctic airmass that had previously set up over the Interior.

KEY MESSAGES

Central and Eastern Interior...

- Rainfall is expected to be moderate to heavy at times Friday and again Friday night into Saturday as an Atmospheric River associated with a low in the Bering continues to supply deep moisture to the Western and Central Interior.

- Total rainfall of 1.00 to as much as 2.50 inches of rain will be possible over the course of the next few days, with isolated areas at elevation potentially seeing 3.00+; this represents annual return intervals of up to 10 or even 25 years for some locations.

- Local main stem rivers will see significant rises, but should be able to handle the expected excessive rainfall. However smaller streams and rivers that feed the main stem rivers could experience minor flooding.

- Despite the deep moisture push, portions of the Upper Tanana Valley and Fortymile region will remain mainly dry, barring a few showers.

- Warmer conditions are expected in the days to come, especially in areas where the rain is less intense.

West Coast and Western Interior...

- Rainfall coverage diminishes along the West Coast for Friday, returning Friday night as another wave arrives. However, parts of the Western interior will continue to see periods of moderate rainfall Friday through Saturday.

- S/SW winds along the Yukon Delta coast and into the Norton Sound will diminish somewhat in speeds to between 20 and 30 mph. However due to a long fetch of these southerly winds through the Bering, water levels are expected to continue to rise, especially for the Norton Sound where High Surf Advisories remain in effect through Saturday morning.

- Water levels could potentially reach 2 to 4 feet above the normal high tide, with highest levels expected around Golovin and Elim Friday morning. A secondary water level rise is expected Saturday morning around the time of high tide.

North Slope and Brooks Range...

- Winter's chill will weakens through Saturday as the warm front pushes north, although a low north of the Arctic coastline will continues to bring bands of mainly light snow to portions of the North Slope.

- Snow will develop at higher elevations, but the moisture plume is expected to shift eastwards with time, allowing for most of the snow over the Brooks Range to shift eastwards as well. Accumulations should remain rather light ranging from 1 to 3 inches depending on elevation.

- Temperatures will hold steady through the first half of the weekend, with highs in the 30s/40s and lows in the 20s/30s. High elevations of the Brooks Range tonight could drop to around 10-20F with wind chills down around 0-10F. Temperatures warm throug the latter half of the weekend.

SHORT TERM /THROUGH MONDAY/

A very active weather pattern has set up across northern Alaska, with current satellite and radar imagery showing an atmospheric river moving up from the SW over the Wood Mountains and into the Interior. Over the past 24 hours, an increasing number of instrument sites across the Western Interior are approaching an inch of rain already, with more on the way for Friday as the atmospheric river and its embedded systems slowly steer eastward as they displace the ridge over the Gulf of Alaska.

Periods of moderate to heavy rainfall will remain widespread through Saturday, backed up by a saturated atmospheric column, with soundings confirming that much of the Interior south of the Brooks range is saturated up through at least 500 mb, which is helping to maximize stratiform Bergeron-Findeison driven precip processes. Coupled with the widespread warm air advection which is displacing the previous early-season arctic airmass, it is entirely possible for parts of the central and western interior to see 5-10 year 48 hour average return intervals from this system, with upwards of 25 year ARIs not out of the question for some locations. The 1-2.5 inches of rain expected to fall through Saturday will bring with it river rises, and while major rivers are likely to absorb the rainfall without too much difficulty, smaller creeks and stream could see more substantial rises, with sandbars potentially becoming covered in water.

The atmospheric river will finally wind down through late Saturday into Sunday, as a low moving up north along the plume of moisture cuts off the source - though not before bringing one final round of moderate to heavy rainfall, along with the chance for some isolated thunderstorms in the 30 mile country on Saturday. Sunday will feature a lull in the previous pace of the active pattern, with the prior system departing off to the N. A weak warm front moving up in its wake which was spun off of an occluding low in the western Bering will keep some chances of rain in the forecast, but rainfall totals will be substantially lower. A broad area of troughing setting up across northern AK as we start the new week will set the stage for additional systems to move through the region. For more information, see the long term forecast discussion.

LONG TERM /MONDAY NIGHT THROUGH THURSDAY/

A broad long-wave trough builds over the state in the wake of the atmospheric river which moved through over the first half of the weekend. With northern AK positioned on the eastern flank, prevailing SW flow will enable moisture and shortwaves to continue moving up into the Interior. The big caveat being that without the broad plume of moisture associated with an AR, day- to-day precip totals will be substantially lower. On Tuesday, the long wave trough is weakened as a ridge builds back across the Gulf, driven by downstream energy from a strengthening shortwave S of the area. This shortwave will swiftly strengthen into a full blown organized low as a strong 140+ kt jet provides upper level support, albeit its final strength will still be limited to 990-1000 mb due to the lack of a good source of cold air to tap into along its NW flank. Confidence is growing in the general location of the landfall for this new low being south of the Seward Peninsula, with the most likely location currently in the general vicinity of the Kuskokwim Delta sometime Tuesday. As the slow moves up into the interior, expect periods of widespread rain to return to areas from the Brooks Range South, with breezy conditions in the vicinity of mountain passes also a possibility. For the remainder of the week, SW flow keeps continued chances of more scattered showers and cloud cover, with the potential for a front to move out of the Bering late in the week. Temperatures will remain on the more mild side, as a more maritime airmass keeps high temperatures in the 50s or lower 60s, and low temperatures above freezing.

Coastal Hazard Potential... A low in the Bering will continue to allow for sustained southerly flow through the north Bering into the Norton Sound through Saturday. Due to the long fetch of southerly winds over open water, water levels could rise 2 to 4 feet above the normal high tide line in the Norton Sound, and 1 to 2 feet above the normal high tide line along the Yukon Delta Coast. Water levels are expected to peak Friday morning and again during the period of high tide Saturday morning. As a result we have issued a High Surf Advisory for coastal areas of the eastern Norton Sound where guidance is showing the highest water level rises at this time.

FIRE WEATHER

Some isolated showers were able to fall across parts of the Upper Tanana Thursday afternoon, ahead of the strengthening ridge in the Gulf. With this ridge expected to continue strengthening, this will continue to minimize the chance for scattered to widespread rain showers. In addition, this will set up southwesterly flow aloft which will allow for downsloping across the Upper Tanana. Not only will this contribute to the little to no precipitation, it will also help warm maximum temperatures. With temperatures warming to the upper 60s on Friday, this will also result in a slight decrease in minimum RH values. With values between 45 and 50 percent seen on Thursday, values on Friday are expected to be around 40 percent.

Another shortwave will work its way over the ridge from the southwest, moving over the Upper Tanana Valley Saturday morning. This will bring the next chance for isolated showers for the first half of the day. Depending on how much clearing there is to warm the surface after this system, there is a slight chance for very isolated thunderstorms Saturday afternoon/evening as a weaker shortwave follows behind the first.

Looking ahead to the end of the weekend, high temperatures will continue to be in the mid 60s across the Upper Tanana. A few additonal shortwaves will continue to move across the Interior as south/southwest flow is expected to continue aloft.

HYDROLOGY

A strong push of moisture across the Western and Central Interior continues through Saturday. Rainfall totals in excess of 1 inch have already fallen over parts of Western AK, and rainfall totals of up to 2.5 inches between Fairbanks, Bettles, and McGrath will be possible so expect fairly decent rises in local streams and rivers with sandbars potentially covered. Exact location of these higher amounts remain uncertain as ensemble members show a wide range of totals due to varying storm tracks, but models are still showing the area of heaviest rainfall in the lower Tanana River Basin and the middle Yukon. Given the saturation of the atmospheric column, think that the more aggressive model runs are likely to be closer to accurate regarding precip totals, with average return intervals of 2 to 5 years possible throughout much of the central and western interior through the weekend. Isolated areas could potentially see heavy rainfall more in line with 10 to even 25 year return intervals, resulting in significant rises in the smaller headwater streams that feed the Koyukuk and Middle Yukon Rivers. While there are no immediate concerns for the main stem rivers in the area, they will also see significant rises in water levels through the week as a result of the expected heavy rainfall with sandbars potentially becoming covered with water.

AFG WATCHES/WARNINGS/ADVISORIES

AK...High Surf Advisory until 11 AM AKDT Saturday for AKZ822-824. MARINE...Small Craft Advisory until 7 PM AKDT this evening for PKZ811. Small Craft Advisory until 6 AM AKDT Saturday for PKZ812-857- 858. Small Craft Advisory from 1 AM to 6 AM AKDT Saturday for PKZ813-860. Small Craft Advisory from 1 PM this afternoon to 6 AM AKDT Saturday for PKZ814. Brisk Wind Advisory from 4 PM this afternoon to 6 AM AKDT Saturday for PKZ814. Brisk Wind Advisory from 4 AM to 6 AM AKDT Saturday for PKZ815. Small Craft Advisory from 4 AM to 6 AM AKDT Saturday for PKZ815.