Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
068 FXAK68 PAFC 081353 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 553 AM AKDT Sat Jun 8 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through Monday night)... Key Messages: 1) A Flood Watch remains in effect for Kodiak Island through late Sunday night. The forecast remains on track for periods of moderate to heavy rain, with 3 to 6 inches of rainfall expected along the east side of Kodiak Island. The heaviest rain will be during the day today and then during the day on Sunday. Urban and small stream flooding are possible. Landslides are also possible in areas of steep terrain. 2) Interior Southcentral from the Mat-Su to the Copper River Basin will see some of the warmest temperatures of the summer this afternoon, with widespread 70s. Temperatures will then trend cooler Sunday through Monday, though dry conditions will prevail for most of the region. 3) A major storm system approaching the Gulf of Alaska today will bring high winds and waves to most of the Gulf coastal waters. Strong gusty winds will also spread inland this afternoon and evening, with particularly strong winds through Portage Valley and Turnagain Arm. Travelers should use caution if driving through these areas. A look at satellite imagery this morning shows a vertically stacked low approaching the southern Gulf of Alaska, with an atmospheric river tracking up the east side of the low then westward toward Kodiak Island. Moderate rain has been falling in Kodiak City for much of the night, with over three quarters of an inch of rainfall recorded thus far. Strong winds have developed across much of the Kodiak Island waters, with surface observations and satellite winds overnight indicating 25 to 35 kts over most of the area. Winds are beginning to strengthen along the north Gulf coast and into Cook Inlet this morning as the entire storm system shifts northward. Meanwhile, a high amplitude ridge extends from British Columbia to the Alaska Interior, with the ridge covering much of Southcentral this morning. High clouds are tracking up the west side of the ridge and cover all of Southcentral. Temperatures across the region range from the mid 30s to mid 40s. The forecast is very much on track for what will be a hazardous weather day across much of the region today. A subtle change is that the approaching Pacific storm and upper trough are further north than models had advertised the past few days. As a result, the upper ridge is also further north and will have less influence on Southcentral`s weather today. The result of this is more clouds over Southcentral, slightly cooler temperatures (though still quite warm over interior Southcentral), and a faster arrival of rainfall along the north Gulf coast and eastern Kenai Peninsula later today. What hasn`t changed is that Kodiak Island remains the focal point for the heaviest rainfall this weekend. One notable change to the forecast with updates made last evening and early this morning is to up some of the gap winds this afternoon and evening. The general ingredients for strong and gusty winds remain the same: the low and surface front weakening as they track westward across the Gulf and toward the Alaska Peninsula; high pressure building in behind the low and surging northward into Southcentral leading to pressure rises; the tail end of a strong upper level short-wave lifting northward across Southcentral; and steep low level lapse rates due to warm surface temperatures. The aspects that look more impressive than in prior days include the overall strength of the low level flow over Southcentral and the lapse rates in the lower atmosphere (many forecast soundings show 5000 feet or more of dry adiabatic lapse rates starting from the surface). The reason for both of these is likely the further north position of the trough and ridge, with cooler temperatures aloft moving in from the Gulf coincident with the pressure rises. Bottom line, there is good potential for some unusually strong winds and in some locations out of an unusual direction. The prevailing low level flow will be easterly and gusty easterly winds could mix down to the surface for many coastal locations including Cordova, Valdez, Seward and most of the Kenai Peninsula. Seward is the most interesting because strong easterly winds are not common. Some of the strongest winds will be through the typical gaps, including Portage Valley, Turnagain Arm, and the Knik River Valley. A Special Weather Statement has been issued to highlight the strong winds through Portage Valley and Turnagain Arm, which can be particularly hazardous to high profile vehicles such as RVs and fishing boats on trailers. Once the winds move into Southcentral this afternoon and evening, they will tend to linger into the overnight hours. This means temperatures will remain more elevated tonight than normal. Sunday will see a weaker repeat of today, with a new low tracking south of Kodiak, sending another front northward across the Gulf. This will lead to the second round of moderate to heavy rain for Kodiak Island. The front will weaken as it nears the north Gulf coast, but bring another round of rain to coastal Southcentral Sunday night. Inland portions of Southcentral will remain dry, with some breaks of sun. However, with cyclonic flow firmly in place aloft, expect marginally cooler temperatures. Gap winds will also redevelop during the day Sunday as a coastal ridge strengthens ahead of the approaching front. Winds will not be as nearly strong or widespread as they will be later today. Looking to the new work week, low pressure will continue to spin south of Kodiak. However, features will be weaker both at the surface and aloft, so rainfall for Kodiak will be much lighter. There are hints of some weak upper level short-waves moving into Southcentral from the east, however model agreement is poor. The NAM/GFS are beginning to hint at a more significant "easterly wave" Monday night into Tuesday, which would bring a return to rain and cooler temperatures for Southcentral. Stay tuned as we continue to monitor this potential. && SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA AND THE ALEUTIANS (Days 1 through 3: Today through Monday night)... Overall, the forecast remains largely unchanged since the previous forecast package. Unsettled weather will persist through the weekend and Monday as a broad, upper level low currently in between Adak and Unalaska merges with several other upper level features approaching from the North Pacific. As the resulting broad low slides southeastwards towards Kodiak Island, several upper level shortwaves rotating around the low will promote wet and windy conditions over much of the area through Sunday and into Monday. Thus, the general expectation is for coastal Southwest to see cloudier and wetter conditions, whereas interior Southwest will have warmer and drier conditions. Gusty east to southeasterly winds will persist across much of Southwest through Monday, as well. For the Bering, expect northerly winds up to small craft. Despite some minor model differences with respect to the exact details of the forecast, here are some aspects we can say with higher confidence: * Precipitation intensity will remain fairly light for communities not on the Pacific side of the Alaska Peninsula. * Several rounds of gusty east to southeast winds, with gusts as high as 40-50 mph, for interior Bristol Bay through the weekend. Highest gusts are expected on Sunday. This morning, Bristol Bay itself can also expect small crafts with gusts up to 40 mph and seas up to 9 feet. * Daytime highs climb into the high 60s and low 70s (and relative humidity dropping into the high 20s and lows 30s) this weekend for communities along Kuskokwim River. -AF/KC && .LONG TERM FORECAST (Days 4 through 7) Tuesday through Friday... The upper level low over the Gulf of Alaska/Eastern North Pacific continues its oscillations and weakens through the forecast period. Several troughs rotate along the Southcentral Coast through the end of the workweek. The Arctic high builds over the Mainland and ridges towards Southwest Alaska. Developments with this high bear further watching to check the displacement of the transient systems. A Western Bering low diverts to the Russian Arctic, while a North Pacific low works its way across the Aleutians into the Bering by Friday. Good agreement in the model guidance, with the ECMWF making some deviations towards the end of the period. Periods of rain will continue over Southcentral Alaska, and as far North as the Alaska Range through Friday. A longer term rainfall event with locally heavier rain is possible from the Southern Kenai Peninsula across Kodiak Island into the Alaska Peninsula through Thursday. Showers over Southwest Alaska, AKPEN, the Eastern Aleutians and the Pribilofs occur through the period. Locally heavy rain associated with the North Pacific low and front spreads across the Western and Central Aleutians late Wednesday through Friday. Gusty winds approaching gale force with the front as it moves over the Aleutians Thursday through Friday. -Kutz && .AVIATION... PANC...VFR conditions are expected to persist. A very challenging wind forecast is setting up for this afternoon into tonight, with a broad range of scenarios ranging from strong, gusty southeast wind at times to calm northerly wind at the surface with low level wind shear at the terminal. At this time, it appears likely there will be a short window for the pressure gradient between Anchorage and the Susitna Valley to be strong enough to briefly overcome a strong down-inlet pressure gradient developing out ahead of a strong trough moving into the Kenai Peninsula from the northern Gulf. Southeast gusts associated with a strong Turnagain Arm wind clipping west Anchorage as strong as 35 kts will be possible for a brief time, most likely between about 2z and 6z tonight. Winds will likely then bend away from the terminal briefly, but will return in a weaker state later on Sunday morning after the trough passes through and lifts north. && $$