Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 500 PM EDT Sun May 24 2020 Valid 12Z Thu May 28 2020 - 12Z Mon Jun 01 2020 ...Guidance/Predictability Assessment... Alaskan medium range forecast predictability remains above average due to a relatively stable and blocky larger scale flow regime, but there has been more uncertainty with offshore lows. Run to run continuity has improved over the last two days, but forecast spread still increases steadily after Thursday with small-mid scale weather features embedded within the larger scale flow. Accordingly, the WPC Alaskan medium range product suite was primarily derived from a composite blend of the 12 UTC GFS/ECMWF for improved detail along with the GEFS/ECMWF ensemble means and the 19 UTC National Blend of Models for better consistency. Increased blend weightings toward the ensemble means Friday onward amid growing uncertainty, but applied manual adjustments to ensure offshore low strengths consistent with upper support. This acts to maintain decent WPC continuity. ...Overview and Weather Hazards/Threats... An amplified upper-level ridge is forecast to persist from the Arctic Ocean across eastern Alaska and into northwest Canada this week. This will result in above average temperatures with anomalies upwards of 15 deg F over northern Alaska. This will enhance snow/ice melt, so please refer to your local office for any seasonal river ice flow issues. This ridge may tend to spread increasingly over a warm Interior later period. A system well south of the state over the eastern Pacific mid-latitudes should organize early week. This system has been difficult to track in guidance. However, models and ensembles now agree to lift a deepened low northward into the eastern Gulf of Alaska by Thursday. Maritime wind/rain impacts may also affect Southeast Alaska. The system should slowly weaken and meander over the northern Gulf of Alaska Friday into next weekend, blocked underneath the upper ridge. Guidance has trended slightly more offshore and holds onto an organized circulation more than shown yesterday. Meanwhile, a surface system will continue to weaken and lift northward on the western periphery of the upper ridge from the northern Bering Sea to the Arctic Ocean Thursday into Friday. This system offers modest lingering precipitation. Another low in the wake of this system into Thursday-Friday is expected to hold/spin over the southwest Bering Sea where it should dissipate. There is also still a strong guidance signal in support of subsequent development of a deep Pacific low that is slated to slowly track along with wrapping winds/rains near the Aleutians into next weekend/early next week that would also present an organized maritime hazard. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards 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