A deep, anomalously strong upper level trough and associated surface low dug southward across Western Alaska. As a result, nearly the entire atmosphere across Southern Alaska shifted to southwesterly flow, which brought copious amounts of Pacific moisture into Southern Alaska.
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The episode as NWS AFC wrote it up.
A deep, anomalously strong upper level trough and associated surface low dug southward across Western Alaska. As a result, nearly the entire atmosphere across Southern Alaska shifted to southwesterly flow, which brought copious amounts of Pacific moisture into Southern Alaska. This rainfall combined with already high water levels due to snowmelt from anomalously warm temperatures earlier in the month.
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 Jul 10, 3:56 AM AKST, 4 hours 6 minutes earlier.
Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 456 AM AKDT Tue Jul 10 2018 .ANALYSIS AND UPPER LEVELS... A broad upper level trough is still in place over much of the state this morning. The slow-moving 991 mb surface low has inched inland over Kipnuk and radar indicates rain is still falling over much of southwest Alaska and the AKPEN. The effects of this low are also reaching Southcentral as the leading edge of the front has remained nearly stationary overnight in the central Gulf. This southerly flow continues to pump moisture into the southern Mainland this morning with rainy conditions observed along the entire Gulf coast and into the Mat-Su Valleys (though very little rain has been observed in the Anchorage area due to downsloping). Gusty southeast winds are still occurring along the coastal areas of Prince William Sound and in localized areas across the Matanuska Valley. Behind the low, drier northwest flow has increased, allowing for some areas of dissipating cloud cover in the southern Bering. && .MODEL DISCUSSION... Models remain in good agreement with the timing and strength of the low moving inland over the southwestern part of the state. Uncertainty arises mid-week as a Kamchatka low enters the western Bering and a North Pacific low approaches the Aleutians from the south. At this time, the GFS has a more easterly position for both of these lows, while the NAM hangs back to the west. By the end of the week, models disagree on the timing and location of the convergence of these lows over the southern Bering. However, one noticeably consistent feature is a ridge ahead of these lows (to the east) that lifts over Southcentral toward the end of the week. && .AVIATION... With down-inlet flow pulling the Turnagain Arm winds further away from PANC and the overall southeasterly pressure gradient weakening, winds at PANC have switched to light northeasterly early this morning and precipitation is having an easier time holding together as it spreads over the terminal. Southeasterly winds will return around midday and then gain more of a southerly component as the afternoon and evening progress. In addition to this shift in wind direction, an increase in instability will aid in bring more numerous showers training over the Anchorage area with heavier showers having the possibility to briefly lower conditions to MVFR at times. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)... The upper low centered over the Kuskokwim Delta will be nearly stationary today, drifting only very slowly eastward. A fairly strong trough associated with this low will push through Southcentral today, brining rain and showers to much of the area. This trough will then slide east of the area this evening. Tonight the main upper low will accelerate eastward, becoming an open trough by Wednesday morning as it pushes through Southcentral. This will bring more showers over the area. The trough will then slide east of the area Wednesday night, and a ridge will begin to move in behind it. Showers will taper off and/or end as a drying trend begins. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)... The weakening low over the Kuskokwim Delta will continue to support cool and cloudy conditions characterized by widespread showers across the southwest mainland through tonight as it tracks eastward towards the Alaska/Aleutian Ranges. Showers will diminish in coverage from west to east on Wednesday as the low departs to the east, with partial clearing allowing afternoon high temperatures to creep back up towards seasonal normal values. The respite from the cool and wet pattern will continue into Thursday as weak transient ridging moves through the region in advance of the next system developing in the Bering. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)... Weak cold advection on the back side of the low sitting over Southwest AK will continue to support scattered showers across the eastern half of the Bering today before tapering off by late evening as the system moves off to the east. Attention then turns to a pair of systems poised to enter the western Bering as another low drops out of eastern Russia this evening and then a North Pacific disturbance move over the Central Aleutians late Wednesday. These two systems will phase with one another and bring another round of rainy and windy conditions to the central Bering before moving inland late Thursday. && .LONG TERM FORECAST (Days 3 through 7)... The long term forecast periods begins Thursday evening with a departing upper level trough moving into Canada and a deepening low over the Bering Sea. The models have dramatically slowed down the eastward progression of the Bering low, so it now seems that Thursday looks to be a nice "break" in the weather across Southern Alaska as shortwave ridging builds inland. The Bering warm front will then move into Southwest on Thursday night and early Friday then make quick eastward progress into Southcentral by Saturday. The low will merge with a series of shortwave troughs moving down from the Arctic region, so it does seem that the low will linger over Southern Alaska through at least Monday before moving east and weakening. Models continue to strongly hint at some form of Bering ridging building in early next week which means warming and inland drying seem increasingly likely. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...Flood Advisory 145 MARINE...None && SYNOPSIS AND MODEL DISCUSSION...KO AVIATION...JR SOUTHCENTRAL ALASKA...BL SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB LONG TERM...Ahsenmacher
SPECIAL WEATHER STATEMENT National Weather Service ANCHORAGE AK 836 AM AKDT Tue Jul 10 2018 AKZ161-110200- Bristol Bay- Including the cities of King Salmon, Dillingham, Naknek, and Pilot Point 836 AM AKDT Tue Jul 10 2018 ...HIGH WATER ALONG ILIAMNA RIVER NEAR PEDRO BAY THROUGH TUESDAY EVENING... Periods of rain continue to affect the Aleutian Range east of Lake Iliamna, maintaining high water levels along the Iliamna River near Pedro Bay. This is causing water to flow on to Pile Bay-Williamsport Road. After a period of dropping river levels, the latest rain has once again causing levels to rise. Thus, the amount of water flowing on to Pile Bay-Williamsport Road will increase. Rain will continue today before lightening up this evening. River levels have likely peaked and will slowly fall through the day. Dry conditions will move into the area Wednesday night through Thursday allowing for more significant drop in water levels.
The national radar mosaic for the moment the first event began.
2 flood. Local standard time, as filed.
The dike eroded along Sawmill Creek causing flooding on 2 properties in the Clyde King Subdivision to flood; 1 house has 1.5 ft of water.
The Yentna and Skwentna rivers, already high due to snowmelt, were expected to reach near bankfull during the second week of July as the weather pattern turned wetter. On July 10th, a local lodge near the confluence of the Yentna River and Lake Creek reported flooding in cabins and outbuildings resulting in 18 inches of water getting inside. The Flood Advisory was issued as a result of this report. Later that same day, an update from Lake Creek was received saying that the river had risen to 2-3 feet above the bank and that most of the property, including numerous water front lodges, were flooded.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Alaska in 2018Every state in 2018This day in weather historyWarnings in Alaska, July 2018
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: 776284, 776285.