Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 638 PM EST Mon Nov 04 2024 Valid 12Z Fri Nov 08 2024 - 12Z Tue Nov 12 2024 ...Active pattern featuring multiple northeastern Pacific low pressure systems will bring periods of precipitation and gusty winds to the Aleutians, southern coast, and Southeast through the period... ...Overview... With an Arctic high in place to the north, the period will feature an active, progressive pattern over the northeastern Pacific/Gulf of Alaska with multiple low pressure systems passing just to the south of the state. An initial system over the Gulf late week currently shows the best chance of heavy precipitation along portions of the southern coast into Southeast Friday and potentially lingering into Saturday. Additional systems upstream look to bring further rounds of precipitation and gusty winds, but with uncertainty over how impactful they may be given a trend for each to take a more southerly path further away from the state. Meanwhile, some gusty winds and blowing snow may linger late week for the North Slope with a tight surface pressure gradient over the region. Precipitation chances otherwise should remain very widely scattered across the western coast/Interior/North Slope, with a cooling trend for temperatures this weekend into early next week. ...Guidance Evaluation/Preferences... Overall the latest model guidance is in reasonably good agreement featuring a progressive, active period in the northeast Pacific and into the Gulf of Alaska with a parade of multiple low pressure systems. A deepening/consolidating low pressure system connected in part to the remnants of TC Kong-Rey will pass over the Aleutians early next week and bottom out on Tuesday as it moves into the Bering Sea. The system will weaken but a trough of low pressure will remain along the western coast/Bering Sea into the start of the forecast period (Friday Nov 8 - Thursday Nov 12). A steady area of high pressure over the Arctic will keep activity to the south, with multiple systems expected to track northeastward from the Pacific along/south of the Aleutians and into the Gulf of Alaska on the southern side of this mean troughing/low pressure. The deterministic models were well clustered with an initial upper trough/surface system over the Gulf of Alaska Friday. However, the ECMWF is more aggressive with additional energy reinforcing the upper troughing and aiding development of a secondary low lifting northward towards Southeast Alaska. The means hinted at least at a deeper trough remaining in place through Saturday, which may prolong precipitation chances over the Southeast. Meanwhile, another system upstream over the northeastern Pacific will pass south of the Aleutians and approach the Gulf of Alaska. Guidance showed some disagreement in the consolidation of surface low pressure, but generally good clustering in terms of position and track eastward. Given generally good deterministic agreement, a composite blend of the 12Z ECMWF/GFS/CMC was used for the updated forecast during this first part of the period, with a favor towards the ECMWF to account for this lingering trough along Southeast Alaska. As the next system enters the Gulf of Alaska, yet another upper-low and accompanying surface low pressure system upstream will approach the western Aleutians and track to the south late weekend and into the start of next week. The guidance shows increasing spatial disparity on position/movement but with the ECMWF most in line with the ensemble means. For this period, a blend favoring the ECMWF with contributions from the 12Z GEFS mean/00Z ECens mean to account for decreasing contributions from the CMC/GFS is used for the forecast. The means eventually show a faster track of the system eastward, even ahead of the ECMWF, so contributions to the blend from the means were increased to end the period. It should be noted that while the pattern itself appears to be well handled in the guidance, timing of the individual systems as well as an increasing southerly trend will effect eventual precipitation amounts and potential for gusty winds across southern parts of the state. ...Weather/Hazards Highlights... A busy mid-week will feature heavy precipitation along the southern coast from the Kenai Peninsula east into Southeast Alaska ahead of a low pressure system in the Gulf of Alaska, which should linger into Thursday and potentially Friday. Thereafter, an active, progressive pattern featuring two additional Pacific systems will promote additional rounds of precipitation and gusty winds moving west to east through the weekend and into early next week for the Aleutians east along the southern Coast and into Southeast Alaska. The potential for heavier precipitation and stronger, gale force winds is more likely with the first system expected Saturday-Sunday which looks to track closer to the state than the next system early next week. Meanwhile, a tight pressure gradient across the North Slope between troughing to the south and a stagnant Arctic high to the north will cause some breezy easterly winds and blowing snow/blizzard conditions mid-week before easing late week and into the weekend. In general, some very widely scattered lighter snow showers will be possible inland and along the North Slope through the period, but precipitation chances overall look to be focused further south ahead of and along the active offshore storm track. Most locations of the Interior to the North Slope will see above average temperatures mid- to late week, with the possible exceptions of southwest Alaska, parts of the higher mountain peaks, and southern portions of the state showing cooler than average temperatures as multiple systems move through. Forecast high temperatures will generally be in the teens to low 20s for the Interior and North Slope, upper 20s for the western coast, and 30s and low to mid 40s in southern areas. Heading into the weekend, Arctic high pressure pushing further south will bring a cooling trend with below average temperatures for most areas by early next week, with highs falling into the teens/low 20s along the west coast and single digits in the Interior. Putnam 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