Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 505 PM EDT Sat Oct 19 2024 Valid 12Z Wed Oct 23 2024 - 12Z Sun Oct 27 2024 ...Significant storm to bring heavy precipitation, high winds and coastal flooding threats to West/Southwest through Northern and Interior Alaska into early-mid next week... ...Overview and Guidance Evaluation/Preferences... Predictability remains above normal in showing a significant storm with long fetch moisture and high winds/waves from the Bering Sea to the Arctic Ocean along with leading coastal flooding, heavy precipitation and high wind threats inland for West/Southwest through Northern and Interior Alaska into early-mid next week. Prefer a composite of well clustered guidance of the 12 UTC GFS/ECMWF/UKMET/Canadian into Wednesday-Friday. This also acts to trend WPC guidance toward a deeper and slightly offshore shifted upstream storm from the Southern Bering Sea to the northern Gulf of Alaska into late next week to monitor. Prefer better clustered guidance of the GEFS/ECMWF/Canadian ensemble means next weekend along with limited model input amid slowly growing forecast spread and uncertainty. This maintains good WPC product continuity. ...Weather/Hazards Highlights... A main weather maker continues to be a deep and quite strong surface low moving over the Arctic Ocean and its associated trailing cold front and reinforcing flow on the backside that are slated to slam across Mainland Alaska early-mid next week. This system will bring impactful precipitation, mostly in the form of snow especially for the mountains and farther into the interior, but western/west-central areas may see periods of heavy rainfall now mostly over short term time frames. Please refer to your local NWS forecast office for advisories, watches and warnings for actionable hazards. Models continue to show the potential for several periods of focus resulting in more than a foot of snow for the western and central Brooks Range. This storm offers a significant maritime winds and waves threat across the Bering Sea and open waters of the Arctic Ocean. Highest inland winds may focus into parts of northwestern Alaska, with the highest gusts expected in the mountains. However, this will present as a widespread high wind threat well inland across the Interior and into the Brooks Range/North Slope with colder snow areas potentially having periods of local blowing snow/near blizzard-like conditions to monitor through early-mid-week. Persistent and strong onshore flow may lead to a significant coastal flooding threat as well, with focus also spreading southward through Western and Southwest Alaska. In the wake of the main storm later next week into next weekend, the overall flow pattern transitions to allow emergence of dynamic system energies set to dig southeastward across the southern Bering Sea to the Gulf of Alaska. Guidance over the past two days have overall trended more amplified with this system and the trend seems reasonable given supporting upstream ridge amplitude. This favors a deeper low pressure and frontal system to enhance winds/waves and precipitation in unsettled flow. The main weather focus inland will shift from coastal Southwest Alaska and the AKpen/Kodiak Island to coastal areas of SouthCentral Alaska, then perhaps especially Southeast Alaska heading into next weekend with advent of subsequent system energies and focus rotating around the eastern periphery of a mean Gulf of Alaska closed low position. Schichtel Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html