Widespread precipitation fell across the Talkeetna, Susitna, Yentna and Skwenta Basins in late August as a deep, upper-level low anchored itself over the Bering Sea, sending waves of precipitation through the area. The persistent moist pattern followed a prolonged period of wet conditions over the previous months, leading to high flows and flooding across the Susitna Basin and associated rivers…
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The episode as NWS AFC wrote it up.
Widespread precipitation fell across the Talkeetna, Susitna, Yentna and Skwenta Basins in late August as a deep, upper-level low anchored itself over the Bering Sea, sending waves of precipitation through the area. The persistent moist pattern followed a prolonged period of wet conditions over the previous months, leading to high flows and flooding across the Susitna Basin and associated rivers in the basin over the course of the period.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Anchorage, AK wrote its last area forecast discussion before the first event at Aug 26, 4:11 PM AKST, 1 hour 34 minutes earlier.
Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 511 PM AKDT Sat Aug 26 2023 .ANALYSIS AND UPPER LEVELS... A broad, longwave trough remains over the over the Bering with an upper-level ridge downstream over the Alaska Peninsula. Persistent southwesterly flow between the two continues to tropical moisture from the Pacific over the Southern Mainland. The copious moisture feed is wringing out across much of the region this afternoon, as a stout upper-level shortwave and attendant occluding surface low lift across the Kuskokwim Delta. The warm front attached to the surface moved through Southcentral this morning and continues to lift north. The trailing cold front is positioned from southern Cook Inlet south over the western Gulf this afternoon and is moving east. Steady rainfall this morning is transitioned to a more showery and convective regime, especially across the Kenai Peninsula and Gulf of Alaska, as the cold front approaches. Winds have also been quite strong through the south and southeasterly gaps in response to this system. Gusts ranging from 40 to 55 mph have been reported throughout the Anchorage Bowl, Knik River Valley, and Copper River Valley as of this afternoon. These winds are expected to continue through the nighttime hours as the gradient between the low out west and the ridge to the east maintain. Farther west, showers persistent around the center of circulation over the Kuskokwim Delta. Strong southerly wind gusts are also occurring from coastal Bristol Bay to the Middle Kuskokwim Valley. Strong northerly winds and low clouds persist over the eastern half of the Bering in the wake of the low. && .MODEL DISCUSSION... Models are in decent agreement at the synoptic scale through early next week. There remains, however, some slight discrepancies with respect to a shortwave and its associated low entering from the North Pacific for Monday affecting rain timing and amounts across the Southern Mainland. Farther west, models are coming into better agreement with a low moving towards the Aleutian Islands from the Sea of Okhotsk, though some disagreements persist with how the low will phase with an incoming shortwave and interact with another trough over the northwestern Gulf. && .AVIATION... PANC...Expect VFR ceilings and vis to persist through Sunday morning with rain showers continuing through late Saturday afternoon. Expect southeasterly Turnagain Arm winds of 15 to 25 mph and gusts 30 to 45 mph to persist across the airport complex through Sunday, as well. There is still some uncertainty as to whether the gusts diminish slightly this afternoon as a cold front moves to the east. However, even if gusts do drop off slightly this afternoon, they are expected to pick back up to a similar intensity this evening and continue through Sunday morning. Gusty southeasterly winds will continue into Sunday afternoon, but are not expected to be as strong as those observed earlier today. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Tonight through Tuesday)... Overall wetter and cooler conditions are expected to continue across Southcentral for the next several days. A broad trough over the Bering and an upper-level ridge over the Gulf promote persistent southwesterly flow across the Southern Mainland. This flow has been bringing moisture north from the tropics, which has combined with sufficient upper-level energy to enhance widespread wetting rains across the region. The core of heaviest rain will continue pushing slowly east through Sunday as the trough moves to the east, parking itself over the eastern Prince William Sound. Valdez and Cordova may receive upwards of 5 inches of rain through Sunday, with more to come later next week. Multiple flood watches remain in effect for Southcentral. Elevated, gusty winds through many of the gaps and passes of Southcentral are expected to be persistent through the weekend. These include the Turnagain Arm, Knik Arm and Copper River Valley winds. The Anchorage Bowl and Glenn Highway corridor towards Eagle River will also have periods of gusty winds through Sunday. A Special Weather Statement has been issued addressing this concern. On Monday, another low tracks from the North Pacific to the western Gulf coast and returns more widespread wetting rains across portions of Southcentral. Current models track the low near Kodiak Island and the Alaska Peninsula by Tuesday morning before taking it generally over Southwest Alaska later on Tuesday. This would give areas from Prince William Sound and the Kenai Peninsula northwest through the Susitna Valley the heavier rainfall amounts, with the Copper River Basin seeing the least amount of rain. However, some slight discrepancies with the low placement and its associated upper shortwave affect rain timing and amounts. &&.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days 1 through 3)... The longwave pattern features a weak ridge moving into the central Bering from the North Pacific, between low pressure systems over Kamchatka and the Alaskan interior. Rain will continue Saturday night to Sunday morning, as an extended band of moisture flows north from the Gulf across the AKPen and into the Southwest. Monday morning, high pressure will shift to the eastern Bering and weaken as the Kamchatka low drops into the Western Bering and slows over the central Aleutians. Monday afternoon a third low pressure system moves north from the Western Gulf, bringing the next round of rain to the southwest on Tuesday. && .LONG TERM FORECAST (Days 4 through 7)... No major changes to the long term forecast at this time. Intermittent, but soggy conditions expected through the extended as moist SW-ly flow persists as multiple waves push across much of Southern AK through the week. Next major system in the extended should approach the Alaska Peninsula & Kodiak Island by Wed night before eventually moving inland into Southcentral Alaska by Thursday/Friday. Main concerns through the extended is persistent rainfall leading to saturated soils, potential river & coastal flooding, and elevated winds. With expected wet soils and gusty winds, can't rule isolated trees and powerlines down by Thursday night. && SYNOPSIS AND MODEL DISCUSSION...TM SOUTHCENTRAL ALASKA...AF SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ER LONG TERM...MB
SPECIAL WEATHER STATEMENT...UPDATED National Weather Service ANCHORAGE AK 114 PM AKDT Sat Aug 26 2023 AKZ101-111-270900- Anchorage-Matanuska Valley- Including the cities of Anchorage, Eagle River, Indian, Eklutna, Palmer, Wasilla, Sutton, and Chickaloon 114 PM AKDT Sat Aug 26 2023 ...STRONG WINDS TO CONTINUE ACROSS THE ANCHORAGE BOWL AND KNIK RIVER VALLEY THROUGH SUNDAY MORNING... A strong autumn storm system over Southwest Alaska will continue to produce gusty southeasterly winds through Turnagain Arm, the Knik River Valley, and across the Anchorage Bowl Saturday morning through Sunday morning. The strongest winds and gusts are expected through late morning and again late this afternoon through late Saturday evening. For Turnagain Arm and the Anchorage Hillside, sustained winds of 20 to 25 mph with wind gusts of 45 to 60 mph expected. For the Anchorage Bowl, Eagle River, and the Knik River Valley, sustained winds of 15 to 25 mph with winds gusts of 35 to 50 mph are expected. The strongest wind gusts for these areas will likely occur across South and West Anchorage, the S-curves of the Glenn Highway near Eagle River, and from the Palmer Airport south to the junction of the Parks and Glenn Highways. People are urged to secure loose objects that could be blown around or damaged by the wind. Prepare for the possibility of power outages. Use caution if you must drive, especially if in a high profile vehicle. For more information from the National Weather Service visit https://weather.gov/afc
Preliminary Local Storm Report
National Weather Service Anchorage AK
352 PM AKDT Sat Aug 26 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1243 PM Rain Sutton 61.71N 148.87W
08/26/2023 M1.36 inch Matanuska-Susitna AK Trained Spotter
Total recorded so far today. Rain still
falling heavily at time of report.
&&Preliminary Local Storm Report
National Weather Service Anchorage AK
359 PM AKDT Sat Aug 26 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1227 PM Non-Tstm Wnd Dmg Eagle River 61.29N 149.56W
08/26/2023 Anchorage AK NWS Employee
A few trees were blown down onto portions of
Hiland Road.
&&Preliminary Local Storm Report
National Weather Service Anchorage AK
411 PM AKDT Sat Aug 26 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1032 AM Rain 7 S Talkeetna 62.23N 150.07W
08/26/2023 M2.86 inch Matanuska-Susitna AK Trained Spotter
Storm total rainfall recorded since Thursday
8/24/23. Some ponding water reported but no
flooding.
&&The national radar mosaic for the moment the first event began.
4 flood. Local standard time, as filed.
Flood waters encroached on cabins along the Yentna and Skwentna Rivers. 2-4 inches of rain fell within the basin causing river levels to swell, and inundating land areas alongside cabins on the river's edge of the Yentna and Skwentna Rivers.
Heavy rains of 2-4 inches in the Little Susitna Basin, along with much higher rainfall amounts along the mountain headwaters, caused rapid river rises along the Little Susitna River and its tributaries. High water impacted areas around the Enchanted Forest area of Houston and at campgrounds in Hatcher's Pass.
Heavy rain across the Talkeetna Mountains caused rapid rises along the Talkeetna River. 1-3 inches of rainfall in the basin, with much higher rainfall amounts in the mountains and headwaters, kept rivers consistently high over a long period of time; this contributed to widespread flooding and areas of bank erosion in Talkeeta.
One to three inches of heavy rainfall flooded low lying areas of the Susitna Valley, including the main road that crossed Kroto and Moose Creeks. This road closure limited resident access to their homes.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Alaska in 2023Every state in 2023This day in weather historyWarnings in Alaska, August 2023
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1127109, 1127626, 1127620, 1127817.