textproduct: Fairbanks

SYNOPSIS

Fire weather is the main concern today as a low in the Western Gulf of Alaska brings an occluded front northward. It will be battling a ridge over Canada as it does so, resulting in gusty southeast winds over the Central/Eastern Interior and Brooks Range, as well as gap winds through the AK Range. Wind, warm temperatures and low humidity are the reasons for the fire weather concerns. The front will move northwest into the Brooks Range/Eastern Interior this afternoon providing isolated to scattered showers. It will run into a weak shortwave trough over the West Coast with a ridge behind it in the Bering causing breezy northerly winds over much of the West Coast. Moving into tomorrow, hydro becomes the main concern as we are expecting an abundance of rain in the Brooks Range and North Slope from Monday to Wednesday. Rainfall may be in the order of 0.5 to 1.00 inches which can cause rapid river rises, especially when combined with snowmelt from the Brooks Range.

KEY WEATHER MESSAGES

Central and Eastern Interior... - Red Flag Warnings in effect for Delta Junction and the Yukon Flats through 8PM this evening.

- Isolated to scattered showers this afternoon with the highest chance for rain expected in the Eastern Interior.

- Widespread rain moves into the southern Brooks Range tonight, continues through Monday afternoon then subsides.

- Cooler temperatures expected on Monday with highs in the upper 60s to near 70. Warming trend through Wednesday, back into the low to mid 70s across the area. West Coast and Western Interior... - Scattered showers expected this afternoon with highs in the 60s and 70s for most spots. 40s and 50s around Kotzebue Sound and the northern Seward Peninsula.

- Showers continue into Monday, mostly from Ambler/Shungnak southward along the coast and towards Hooper Bay. Farther east remains mostly dry.

- Temperatures are much cooler tomorrow, in the 50s and 60s for most spots while remaining in the 40s from Kotzebue to Wales.

- Warming trend Tuesday and Wednesday as highs return to the 70s in the Interior and 60s along the coast. A few showers are possible around but most remain dry.

North Slope and Brooks Range... - Moderate to heavy rain in the Brooks Range and North Slope from tonight through Wednesday morning. Rainfall amounts near 0.50 to 1.0 inches expected from the Central Brooks Range to Deadhorse while the Western Brooks Range/North Slope remain drier.

- Temperatures remain mild but trend upward through most of the week, potentially in the 50s along the coast late this week.

- Warm temperatures leads to snowmelt in the Brooks Range. This combined with rain may lead to areas of flooding near the rivers. A Flood Watch has been issued through Wednesday AM.

FORECAST ANALYSIS AND DISCUSSION

An occluded front associated with a low near the AK Peninsula is helping to provide gusty southeast winds across much of the Interior today. This front also supplies showers to many sections of Northern Alaska with the Central Interior remaining mostly dry due to chinook flow. Tonight, a surge of moisture from the Gulf of Alaska will move northward, then northwest over the Brooks Range. This plume of moisture is pretty anomalous and is coming with PWAT values of 0.75 to 1.00" or more which is certainly more than enough to cause rain, heavy at times. It will set up over the Central Brooks Range beginning tonight, then gradually spread north to the Arctic Coast tomorrow afternoon.

Taking a deeper dive, 500mb vorticity shows strong maxima moving northwest over the Brooks Range and North Slope tonight into tomorrow. This area of vorticity is combined with strong vertical motion at 700mb and 850mb with frontogenesis at 850mb as well. The 12z NAM depicts this vertical motion at around 10 to 20 microbars per second which is anomalously high, especially for the northernmost latitudes of Alaska. Moving forward towards Tuesday, this area of vorticity halts its northwestern progression as it gets blocked by an upper low over the Chukchi Sea and begins to pivot in place. This will allow for a north to south oriented area of moderate or heavy rain to sit over 1 spot for hours on end. Where that occurs will be the "bullseye" for heaviest rainfall totals. With every mesoscale heavy rain feature, there is uncertainty with placement and this is no different. We are anticipating a pivoting rain band somewhere in the vicinity of Anaktuvuk/Atigun Pass and between Point Thomson and Nuiqsut. Areas underneath this rain band will see totals upwards of 0.5 to 1.0" or more. This can result in localized flooding as rivers rise from the Brooks Range to the Arctic Coast.

Otherwise, generally lighter showers are expected in the Western and Eastern Interior as the Central Interior gets chinooked. Strong gap winds will persist through Monday morning then subside. Overall, after Monday the rest of the week looks to be mostly dry south of the Brooks Range. There will be a warming trend from Monday through Wednesday and beyond as a ridge builds in. Summer like weather will continue through the end of the week and into next weekend and there may be some very active thunderstorm days as well.

FIRE WEATHER

A Red Flag Warning is in effect through 8PM this evening for Delta Junction and the Yukon Flats. Expect south winds up to 55 mph in Delta Junction with min RHs around 25 to 30%, whereas the Yukon Flats will have hot/dry/windy with temperatures in the upper 70s, winds up to 25 mph and min RHs around 25%. Tomorrow will be cooler with calming winds and higher RHs across the board, leaving little to no concern for worsening fire weather conditions. Isolated to scattered showers are expected in the Eastern and Western Interior with a drier pocket in the Central Interior from chinook flow. The heaviest Interior rain will be in the Western Interior from Ambler to St. Mary's where 0.10" to 0.30" of rain is expected through Monday afternoon. The Brooks Range will be getting a soaking rain from tonight through Wednesday with localized amounts up to 1 inch. Otherwise, a warming and drying trend takes hold from Tuesday onward with minimal thunderstorm potential until Wednesday when storms begin to move back into the Interior. Towards the end of the week and next weekend, temperatures are expected to warm with some big thunderstorm potential.

HYDROLOGY

Temperatures in the Brooks Range will be warming into the 60s and low 70s for highs and staying above freezing with low temperatures in the upper 30s to mid 40s over the next several days. The Arctic Plain and Coast will have temperatures ranging from about 40F to 60F with lows in the mid 30s to mid 40s.

Rain is expected from Sunday night through Wednesday morning across a wide swath of the Brooks Range and North Slope with amounts ranging from 0.5 to 1.0 inches.

Most of the remaining snowpack is in the foothills and mountains where temperatures and rainfall will be highest. The combination of snow melt and rainfall is increasingly likely to result in river rises.

Most of the ice on the larger rivers has already moved out which leaves more room to accommodate the snowmelt and rainfall. This contrasts with last year's late breakup when the snowmelt all entered the river systems while ice was mainly still in place.

EXTENDED FORECAST DAYS 4-7

Thursday through Sunday. By the start of the extended period on Thursday, most of Alaska will be under upper-level high pressure. However, an upper-level low in the Bering Strait should prevent a ridge in the Bering from building in out of the southwest. As a result, the high pressure over the state looks to remain relatively weak through the extended. This pattern supports warm temperatures, 70s in the Interior, but also widespread afternoon convection. Thunderstorm potential in the Interior should generally increase through the latter half of the week as the pattern remains relatively stagnant until Sunday.

Sunday, models depict an arctic trough swinging west to east across the North Slope. The strength and timing of this trough is somewhat uncertain, with the 12Z deterministic ECMWF having an incredibly fast and aggressive solution, where the trough is flung southward into Northern Alaska as a low. Ensemble guidance is much more reserved with this feature, with weak ridging persisting south of the Brooks Range. I'll be treating the Euro as an outlier, but given we've had one anomalous arctic trough already this summer, I'm inclined to keep an eye on how the models handle this Arctic trough going forward.

Coastal Hazard Potential Days 3 and 4...None

AFG WATCHES/WARNINGS/ADVISORIES

AK...Wind Advisory for AKZ849. Flood Watch for AKZ804>810. Red Flag Warning for AKZ933-937. PK...Small Craft Advisory for PKZ801-850. Small Craft Advisory for PKZ806. Brisk Wind Advisory for PKZ808-855. Brisk Wind Advisory for PKZ814-815-860. Brisk Wind Advisory for PKZ861.