textproduct: Fairbanks

SYNOPSIS

The forecast continues to remain largely on track as a ridge of high pressure which has built across the western interior slowly pushes east through the weekend. Warmer temperatures reaching into the 70s and even the low 80s are expected for much of the area. A shortwave trough tracking northeast across western Alaska will continue to bring isolated showers for the West Coast and western Interior along with the Brooks Range/North Slope through Sunday. Guidance has come into broad agreement on the placement and strength of a low in the northern Bering Sea, which will slowly track east into northern Alaska with widespread rain and gusty winds early next week. High Wind Watches remain in effect for the Alaska Range passes and Delta Junction Sunday night into Monday and Tuesday where the strongest winds are expected. This system will be tapping into subtropical atmospheric river moisture, which will lead to widespread moderate to heavy rainfall totals of 1-2 inches over a 48-72 hour period, focused across western Alaska and the southern slopes of the Brooks Range. As this system gradually weakens towards midweek, winds will lessen as precipitation chances become more isolated to scattered. Ensembles are in broad agreement that the low will slowly disintegrate through the remainder of the week, with the potential for a ridge to build over the eastern half of the interior in its wake. Concurrently, temperatures that briefly cooled earlier in the week will hold steady or see a warming trend to finish out the week.

KEY WEATHER MESSAGES

Central and Eastern Interior...

- Warm and dry conditions will continue across much of the Interior through the weekend with plenty of sunshine. Highs will remain in the 70s to low 80s with lows in the 40s/50s.

- Isolated rain showers will be possible late Saturday into Sunday as a weak front tracks east over the Interior, but conditions are expected to remain predominantly dry.

- As a low from the Bering Sea tracks east Sunday into Monday, widespread rain and gusty winds will shift east across the Interior and Alaska Range. The bulk of precipitation is expected west of Fairbanks and in the Alaska Range, with driest conditions along the Alcan Border and Upper Tanana Valley.

- Rainfall totals late Sunday through Tuesday are expected to be around 0.10-0.25" around FNSB, T-0.10" east of Fairbanks to the Alcan Border, 0.25-1.00" northwest of Fairbanks, and 0.50-1.50" in the Alaska Range west of the Tok Cutoff.

- High Wind Watches have been issued for the Alaska Range passes and Delta Junction from Sunday night through Tuesday night for southerly wind gusts up to around 60 to 70 mph. Wind gusts elsewhere across the Interior will peak on Monday around 20 to 30 mph.

- As the Bering Sea low gradually weakens midweek, isolated to scattered rain showers will continue with temperatures that briefly cooled earlier in the week holding steady or seeing a warming trend to finish out the week.

West Coast and Western Interior...

- Warm and mostly dry conditions will continue across much of western Alaska through Saturday night, with isolated rain showers possible. Highs will be in the 60s to low 70s with lows in the 40s/50s, locally cooler along the West Coast.

- As a low in the Bering Sea tracks east Sunday into Monday, widespread rain and gusty winds will shift east across western Alaska. Steadier rain will reach St. Lawrence Island around midnight Sunday morning and West Coast throughout the day Sunday.

- Rainfall totals Sunday through Tuesday are expected to be around 0.50-1.50" regionwide, with locally higher totals up to around 2.00".

- Winds gusts will peak around 30 to 50 mph regionwide as the low moves in, with minor coastal impacts expected (primarily high surf) for communities along the West Coast.

- As the Bering Sea low gradually weakens midweek, isolated to scattered rain showers will continue with temperatures that briefly cooled earlier in the week holding steady or seeing a warming trend to finish out the week.

North Slope and Brooks Range...

- Isolated to scattered rain showers build in through the weekend out of the west. Highs will be in the 60s to low 70s with lows in the 40s/50s, locally cooler along the Arctic Coast. - While rainfall totals through the weekend are expected to remain light overall, steadier rain will move into the Brooks Range on Monday as moisture from a low in the Bering Sea tracks north.

- Rainfall totals Monday and Tuesday will be heaviest in central and eastern portions of the Brooks Range, where around 0.50-1.50" of rain is expected, focused on the southern slopes, as the North Slope gets downsloped and stays predominantly dry.

- As the Bering Sea low gradually weakens midweek, isolated to scattered rain showers will continue with temperatures that briefly cooled earlier in the week holding steady or seeing a warming trend to finish out the week.

SHORT TERM DISCUSSION

SATURDAY THROUGH MONDAY NIGHT. A weak shortwave trough is moving northeast through Norton Sound this morning. This will bring scattered rain showers to the Seward Peninsula and to the Western Brooks Range. As the shortwave moves across the North Slope an embedded isolated thunderstorm could be possible, these chances will be limited by the amount of cloud cover in the region this afternoon. With cloud cover limiting the surface temperatures, convection will be heavily reliant on cold air advection in the mid levels and the upper level shortwave trough to create instability. For the rest of Northern Alaska today will be generally quiet ahead of the approaching Bering Sea Storm.

Sunday afternoon the pattern will shift to the stormier side, as a 988 mb low will move towards St. Lawrence Island. This low will be accompanied by an atmospheric river with moisture originating from the tropics. As the low moves closer to the West Coast, this atmospheric river will be directed towards the West Coast and Western Interior. This atmospheric river is producing impressive returns from the ECMWF Extreme Forecast Index (EFI) with a wide swath of 0.95 to even pockets of 1.0. This paired with a shift of tails of 2, shows that this system is anomalous for this time of year. With how anomalous this system is, the models are struggling with the amount of qpf that the West Coast and Western Interior will see. There is a spread of 0.5" to 1.0" of qpf between the 25th percentiles and 75th percentiles. While 0.5" to 1.0" of qpf wouldn't make that much of difference, when we are expecting widespread 1" to 2" an additional 1.0" of qpf could exacerbate any hydrological concerns. East of Tanana we are expecting much lower rain amounts, as the Alaska Range will downslope most of the precipitation.

As the Bering Low approaches the West Coast, southwesterly winds will increase across much of the Coastline. Sunday afternoon the winds from the Seward Peninsula to the Y-K Delta will begin to ramp up with winds up to 45 mph. The strongest winds will be along the coastline. By Monday morning the pressure gradient across the Alaska Range will begin to tighten. With a gradient of 6 to 8 mbs across the Alaska Range, there is support for wind gusts up to 70 mph in the passes. Models have been steadily decreasing the pressure gradient in Windy Pass, which could see the max winds drop down to around 60 mph. As we get more Hi-Resolution model guidance we will be able to identify if that trend continues. As the Bering Sea low continues to linger in the Bering through Tuesday morning, a prolonged fetch of southwesterly winds will bring higher waters to Norton Sound. This will be highlighted in more detail in the "Coastal Hazard" section, but no significant impacts are expected.

FIRE WEATHER

Relatively warm and dry conditions continue across the Interior Saturday. Temperatures peak in the mid to upper 70s with minimum humidity bottoming out near 30% in the upper Tanana Valley and in the mid 30s to low 40s throughout much of the rest of the Interior. A large, very wet, low pressure system approaches the West Coast Sunday and brings with it two main impacts.

The first is strong south to southeasterly winds across the region, first to the West Coast Sunday afternoon, then to the Western Interior Sunday evening, and to much of the rest of the Interior Monday morning. These winds are expected to be strongest through the Alaska Range Passes where wind gusts into the 60 to 70 mph range are possible through Tuesday. A high wind watch is currently in effect for areas north of the Alaska Range, especially along the Parks and Richardson highways. There remains some uncertainty in the max strength of these strongest winds. Elsewhere gusts in the 25 to 35 mph range are possible throughout the Western Interior with gusts in that same range being frequent along the coast. The Central and Eastern Interior will see fewer gusts reaching as deep into the valleys with occasional gusts of 20 to 30 mph possible.

The second is a great deal of rain, especially throughout the Western Interior. Storm total rain forecasts Sunday through Tuesday are currently in the 1 to 2 inch range. Dry air north of the Alaska Range will limit rain totals throughout the Tanana Valley and areas east of Fairbanks are expected to see much less rain than the rest of the region. The Central Interior sees much less certain totals as the edge of the heaviest precipitation lies there with totals under half an inch currently expected near Fairbanks with higher totals nearer an inch and a half are possible farther west near Tanana and Bettles. There exists a non-zero chance of extremely isolated thunderstorms across the Western Interior amongst the rain showers Tuesday and the system weakens.

With the rain comes cooler temperatures and much more moist humidity levels. High temperatures are expected to fall into the 60 to 70 range across much of the Interior Monday with the Upper Tanana Valley and Fortymile Country remaining in the low to mid 70s. Temperatures rise slightly Tuesday as rains weaken. Minimum humidity rises well above 50 for most of the western portions of the state and above 40 for the Eastern Interior Monday. Humidities fall slightly Tuesday and further Wednesday.

HYDROLOGY

An atmospheric river arriving across the western interior late Sunday into Monday will bring river rises across smaller rivers in the west and along the Alaska Range through the first half of next week. Precipitation totals of 1-2 inches are looking increasingly likely from Sunday to Tuesday for these areas, with isolated higher amounts possible in areas of terrain. No flooding concerns are expected.

LONG RANGE FORECAST

Ensemble guidance begins to diverge on the exact details of the forecast through the second half of the week, but maintains general placement of the key features and their corresponding impacts. An occluding low over the west coast will continue to weaken, and ensemble guidance is in broad agreement on the low being likely to devolve into an open trough which anchors itself across the central and western interior. This would result in continuing chances of rain showers for much of the area, although any additional significant rain accumulations by this point would be confined to areas S of the Wrangell St. Elias mountains. A ridge anchored over the Yukon will prevent this trough from moving east, while another ridge over the Gulf of Alaska will likely prevent the trough from diving south. Ensembles have begun hinting towards the possibility that the ridge in the Yukon may extend into the eastern interior, which would bring warmer weather and drier conditions back to the eastern portion of the state. Winds will be on the lower side as the low weakens and the pressure gradient subsides, and temperatures will be cooler in the West, and warmer the further east one goes. All in all, precip chances are more likely to linger across the western half of the state while the eastern half will see better chances of warmer and drier weather.

Coastal Hazard Potential Days 3 and 4... Some minor beach erosion and high surf are possible for Norton Sound and the Kuskokwim Delta Monday and Tuesday as a 985-990 mb low over St Lawrence Island sends southerly winds up across much of the West Coast. More updates will be made available this weekend as forecast confidence in a final track and strength of the low develops, which will lead to increasing confidence on exact water level rises expected in each community. Currently water level rises above high tide look to generally be between 1-3 feet. Stay tuned for additional updates

AFG WATCHES/WARNINGS/ADVISORIES

AK...High Wind Watch for AKZ837-849. High Wind Watch for AKZ847. PK...Small Craft Advisory for PKZ811. Small Craft Advisory for PKZ812-856>858.