Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 658 PM EST Mon Nov 20 2023 Valid 12Z Fri Nov 24 2023 - 12Z Tue Nov 28 2023 ...Heavy precipitation continues late week for Southcentral and perhaps pivots into Southeast Alaska early next week... ...High winds possible for the Aleutians on Saturday... ...Overview... As the medium range period begins Friday, surface and upper lows will be stacked near the eastern Aleutians, though weakening compared to their depth in the short range. This will still direct enhanced Pacific moisture with deep southerly flow into Southcentral Alaska with heavy precipitation into Friday. Rounds of additional precipitation are likely over the weekend with a general eastward trend toward Southeast Alaska into early next week as the energy shifts east. Farther west, a large upper trough/low looks to track over the Kamchatka Peninsula with some troughing spreading east into the Bering Sea early next week. A surface low reflection that stays well west of Alaska will however push some windy conditions and precipitation across the Aleutians with a frontal passage. Meanwhile, upper ridging looks to persist across at least eastern parts of the state through the period. ...Guidance Evaluation and Preferences... The 12Z model guidance suite is reasonably agreeable with the pattern described above on the large scale, with typical differences in the details. Recent models have trended toward a quicker opening up of the upper low into a trough near the Alaska Peninsula by Saturday compared to a day ago, but still a pretty energetic feature, with just minor model differences in the exact positioning of the trough and surface low. Upper ridging farther east also has good consensus, likely extending into the Beaufort Sea, with less potential in the 12Z runs (especially the GFS) to have a shortwave suppressing it just northeast of the state. The 12Z UKMET ended up showing a farther west position of the upper high embedded within the ridge given its stronger shortwave (more like the older 00Z runs) compared to consensus. Farther west, there remains high confidence that a deep and large upper low will press east and be atop the Kamchatka Peninsula by Sunday, with a trough axis extending east into the Bering and perhaps the western Mainland with time as it elongates. The details of the surface lows and the exact extent of the trough and the energies within it are still questionable, but certainly within reason for the time period. With no particular outliers, the WPC forecast used a blend of the deterministic 12Z ECMWF/GFS/UKMET/CMC early in the forecast period, gradually incorporating and increasing the proportion of the ensemble means to about half the blend by Day 7 and just over half by Day 8. ...Weather/Hazards Highlights... Ample moisture streaming in with southerly flow east of the Aleutians to Alaska Peninsula to Gulf low pressure system will bring heavy precipitation lasting into at least Friday across Southcentral Alaska. Coastal rain and higher elevation and inland snow are forecast with this precipitation activity. The precipitation may weaken a bit into the weekend there, but numerous showers should continue within a generally unsettled pattern and onshore flow. The axis of highest moisture shifts into Southeast Alaska by Sunday and could provide heavy rain and snow to that region. A frontal system is forecast to track across the Aleutians this weekend, and strong southerly flow ahead of the cold front and winds with a westerly component behind the front could both be gusty to strong especially on Saturday. Precipitation is likely over the Aleutians as well. As the frontal system and energy aloft may push into the Alaska Peninsula and the southwestern Mainland by early next week, precipitation chances should increase for those regions and into Southcentral. Once again, overall coastal rain and inland snow are expected, but with perhaps some lower snow levels compared to late week given the troughing aloft. Temperatures across the state should be considerably milder than in the short range given the (relatively) warm southerly flow into the state and the ridging aloft in the east. Lows look to be generally 20-40F above normal, staying above 0F except in a few pockets of the North Slope and Interior, with lows in the 20s to low 40s farther south. Highs should be closer to 10-30F above normal, with actual temperatures mainly in the teens even for the North Slope, with increasing values going south into the 20s/30s/40s. Tate 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