Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 PM EDT Fri Jun 18 2021 Valid 12Z Tue Jun 22 2021 - 12Z Sat Jun 26 2021 ...Heavy rainfall threat for portions of coastal Southcentral next week... ...Guidance/Predictability Evaluation... The WPC Alaskan medium range product suite was primarily derived from a composite blend of relatively well clustered guidance of the 12Z GFS/GEFS mean/EC mean/ECMWF, along with some previous WPC continuity and 00Z ECMWF. Guidance forecast spread continues to indicate above normal predictability on the synoptic scale pattern. ...Weather/Threats Highlights... The first storm system during this forecast period will be weakening across the Gulf region by early next week, which will likely produce unsettled maritime conditions along with periods of rain from the Alaskan Peninsula to the southeast panhandle. A stronger storm system builds south of the Aleutians and should track slowly to the east for the middle part of next week. This would result in more widespread moderate to heavy showers from the Alaska Peninsula to the southeast panhandle as an occluded surface low will advect copious moisture northward across the region, with perhaps a few inches of rainfall possible for some areas. The weather pattern is expected to become more amplified by the Tuesday to Thursday time period as an upper level ridge builds in across eastern Alaska, which is in response to the meandering upper level gyre over the Aleutians. This will result in warm temperatures across much of the Interior next week, especially for those areas that have mostly clear skies. Cooler than average temperatures are expected for coastal areas of the Gulf of Alaska coast where cloudy skies and frequent showers will prevail. Hamrick Hazards: - Heavy rain across portions of southern Alaska, Wed-Sat, Jun 23-Jun 26. 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