textproduct: Fairbanks

SYNOPSIS

A low in the Bering Sea is rapidly moving northeast towards St. Lawrence Island this morning. This system will bring impacts to a majority of Northern Alaska, including gusty winds, moderate to heavy rainfall, and minor coastal concerns. Winds will begin to increase across the Y-K Delta and Seward Peninsula by noon today, and will extend eastward as the system continues to move east. Strong southerly gap winds through the Alaska Range passes will begin early Monday morning and will continue through Tuesday. Widespread heavy rainfall of 1" to 2" is expected across the West Coast, Western Interior, and the Southern slopes of the Brooks Range. In the Eastern Interior, rainfall totals will be limited due to chinook flow, but up to 0.5" is possible within the FNSB. Once this system weakens in the middle of the week, temperatures will rise across Northern Alaska, and rain shower chances will continue.

KEY WEATHER MESSAGES

Central and Eastern Interior... - 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 0.25-0.5" around FNSB, T-0.1" east of Fairbanks to the Alcan Border, 1.0-2.0" northwest of Fairbanks, and 0.5-1.5" in the Alaska Range west of the Tok Cutoff.

- High Wind Warnings and a Wind Advisory for southerly wind gusts have been issued for the Alaska Range passes and Delta Junction respectively. From Sunday night through Tuesday night, gusts could exceed 70 mph through the passes and 50 mph at Delta Junction. Wind gusts elsewhere across the Interior will peak on Monday around 20 to 30 mph.

West Coast and Western Interior... - The low pressure in the Bering Sea is rapidly moving east towards St. Lawrence Island this morning. This low will bring gusty winds and heavy precipitation across the region through Tuesday. - Rainfall totals Sunday through Tuesday are expected to be around 1.0" to 2.0" regionwide, with locally higher totals up to around 2.50". - Winds gusts will peak around 30 to 50 mph regionwide as the low moves in, with minor coastal impacts expected for communities along the West Coast.

North Slope and Brooks Range.. - Isolated to scattered rain showers continue to slowly move across 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 0.50-2.0" of rain is expected, focused on the southern slopes, as the North Slope gets downsloped and stays predominantly dry.

FORECAST ANALYSIS AND DISCUSSION

Latest Hi-Resolution model guidance has the low in the Bering Sea at around 992 millibars (mb). This low is rapidly undergoing occlusion as it moves towards St. Lawrence Island. With the occlusion beginning it will slow down it's strengthening. The latest guidance has the low only getting down to around 990 mb, this is roughly 5 mb weaker than what model guidance was showing yesterday afternoon. With the low potentially being weaker than anticipated we could see some changes to the wind forecast across Northern Alaska. With a weaker low the gradient along the Alaska Range would be weaker resulting in winds that could be below High Wind Warning criteria. This weaker low would also lower our coastal hazard concerns. While the ensemble guidance for the surf is still 1 to 3 feet, if the southerly winds are weaker than the surf would be on the lower end of guidance. While the occlusion process is ongoing, there is still potential over the next 6 to 12 hours to continue to strengthen to around the 985 mb mark.

While there is some uncertainty now with the strength of the winds associated with the storm in the Bering, there is good confidence we are going to be seeing widespread moderate to heavy rainfall across the West Coast and Western Interior. A stout atmospheric river originating from roughly 15 degrees north will be ejected towards the western half of the state. We are expecting a wide swath of 1.0" to 2.0" of rainfall across the Western Interior and southern Brooks Range. Some areas specifically in the higher terrain and south facing slopes could see up to 3.0" of rain due to upsloping. As the warm front moves east across the Interior this swath of moisture will moves eastwards as well. As it moves towards the Eastern Interior, than it will have to contend with chinook flow through the Alaska Range. While the Upper Tanana Valley and Fortymile Country will be downsloped, in the Tanana Valley there should be enough moisture in the column to overcome the downsloping effect. Model soundings in Fairbanks later this evening are showing PWAT values near 1.25 inches, but a considerable dry layer at the bottom 5000 feet of the air column. This dry layer will have to be eaten away first in order to see rain here in Fairbanks. This will limit how much rainfall we will see in town, but any amount of shift of the low in the Bering could drastically effect the rain totals we see from the storm.

As the storm meanders in Norton Sound until Tuesday evening it will keep rain showers going across much of the Interior, even after the warm front completely weakens. With colder air aloft within the core of the system creating the potential for condition instability, the Western Interior could see an embedded isolated thunderstorm. With the slow moving nature of the low, it will continue to impact northern alaska through the end of the work week, and will be discussed more in the Extended Forecast Discussion.

FIRE WEATHER

Sunday brings a large, very wet, low from the Bering Sea to the West Coast. This low brings widespread wetting rains and gusty south to southeasterly winds across the West Coast, Western and Central Interior, and Brooks Range Sunday afternoon through Tuesday. Wind gusts up to 40 mph are possible across the West Coast and Western Interior. Rain totals Sunday through Tuesday in the 1 to 2 inch range are expected with higher amounts possible along south facing slopes. Cooler and very wet conditions through Tuesday will significantly limit any fire weather potential for the Western portions of the state.

This low also increases southerly winds through the Alaska Range passes. High wind warnings are currently in effect for the Alaska Range Passes with gusts up to 70 mph expected. Strong southerly flow will reinforce dry air just north of the Alaska Range and over the Tanana Valley which will significantly limit rainfall for areas south and east of Fairbanks. Fairbanks itself lies near the edge of the storm system and will likely see some wetting rains, but far less than areas west of Fairbanks. Current forecasts indicate rain totals in the 0.25 to 0.5 inch range, but those amounts could change rapidly if the storm moves slightly farther west (drier) or east (wetter) than currently expected. The greatest uncertainty in total rainfall lies from the Fairbanks vicinity north and east towards the eastern portions of the Brooks Range. The strong winds and relatively little rain will keep fire potential relatively higher in the Middle and Upper Tanana Valley.

The storm keeps conditions cooler and wetter for the entire region through the early part of the week. This trend is strongest in the Western Interior, where highs drop into the 60s with very high minimum humidity values, and weakest in the Upper Tanana Valley where highs drop into the mid 70s and minimum humidity values rise into the 30s and 40s. Conditions warm and dry slightly after the storm passes through the latter half of the week.

HYDROLOGY

A Bering Sea storm accompanied with a stout atmospheric river will bring widespread 1 to 2 inches of rainfall to the Western Interior and parts of the Brooks Range. Areas in higher terrain and southern slopes of terrain could see up to 3 inches of rain due to upsloping. No flooding is currently expected, but river rises are anticipated and smaller creeks and streams could become bankfull.

EXTENDED FORECAST DAYS 4-7

WEDNESDAY THROUGH SATURDAY Wednesday the weakening Bering Sea storm will begin to slowly move south towards the Gulf of Alaska, as an arctic trough moves across the North Slope. This trough will bring isolated to scattered rain showers and cooler temperatures to the North Slope and Brooks Range. With this trough being fairly slow moving it will keep the weakening low pressure over Mainland Alaska until the weekend. This will allow for continued isolated rain showers to continue through much of the work week in the Interior.

As we move into the weekend the ensembles are in fairly good agreement that another arctic trough will dip southwards out of the Chuckchi Sea and into the Western Interior. This will bring another round of cooler temperatures to Western Alaska. Where the models diverge is the strength of the ridge axis over the eastern half of the state. If the ridge axis remains in place then southerly flow will set up over the central and Eastern Interior bringing above normal temperatures. On the other hand if the ridge is able to get pushed out of the region by the arctic trough then we could see cooler temperatures return to the region.

Coastal Hazard Potential... Gusty southerly winds from a Bering Sea low will result in minor high surf along the West Coast. Water will rise 1 to 3 feet above mean high tide, with the highest water peaking Monday afternoon during high tide. These higher waters will remain elevated even during the low tide overnight Monday, by Tuesday afternoon high tide water levels will begin to decrease.

AFG WATCHES/WARNINGS/ADVISORIES

AK...High Wind Warning for AKZ849. Wind Advisory for AKZ829-830-852. Wind Advisory for AKZ837. High Wind Warning for AKZ847. PK...Gale Warning for PKZ801. Small Craft Advisory for PKZ802. Small Craft Advisory for PKZ805-806-853. Small Craft Advisory for PKZ816-817-854. Small Craft Advisory for PKZ850. Small Craft Advisory for PKZ851.