Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 636 PM EST Tue Jan 09 2024 Valid 12Z Sat Jan 13 2024 - 12Z Wed Jan 17 2024 ...Stormy conditions for southwestern Alaska... ...Overview... An upper ridge axis stretching from the east Pacific northward into the eastern Interior will cause the main storm track to focus across the Bering Sea and western Alaska late this week, leading to an active and windy pattern as multiple low pressure systems move through the region. One particular low will follow a more southerly track across the Alaska Peninsula to Kodiak Island for some enhanced winds and precipitation there late week. The upper ridge will promote milder than normal temperatures across most areas, with the exception of the eastern Interior and Southeast Alaska where continental flow ahead of a trough will bring in cold air. The upper ridge will likely break down early next week, with increased precipitation chances along the southern coast into Southeast Alaska, and potentially into portions of the Interior as well. ...Guidance Evaluation/Preferences... The latest runs of the guidance still have a decent handle on the synoptic pattern during the beginning and middle periods of the extended forecast. Through this period there will be an amplified ridge over the eastern mainland with mean troughing along the Bering Sea/Aleutians and into the western Gulf of Alaska. Over the weekend the upper-level weakness/inverted trough will shift into the eastern Interior/North Slope which will aid in weakening/breaking down the ridge along the North Slope. There continues to be model differences on how far west the ridging will shift. The GFS is the most aggressive with this feature. Upstream over the Bering Sea, there is general agreement in bringing the upper-level trough over the Bering Sea eastward along the southern coast and over the Gulf of Alaska, helping to break down the interior Mainland ridge from the west. The CMC significantly lags the other guidance in this progression. Towards the end of the period, both the GFS and ECMWF as well as the ensemble means agree that mean ridging will build in over the Aleutians following the departure of the upper-level trough to the east. However, the guidance is significantly out of phase to the east, with the GFS more progressive with the upper-level trough, taking it into western Canada, while troughing lingers over the Gulf of Alaska in the ECMWF. On the other hand, the GEFS mean is slower with the progression of this trough over the Gulf, while the ECens mean is more in line with the deterministic ECMWF. The latest WPC forecast had an initial starting point that used a composite of the ECWMF/GFS/CMC/UKMET but quickly transitioned to heavier weightings of the ECWMF/EC ensemble means while dropping the UKMET and greatly reducing the GFS/GEFS mean. The ECWMF/EC ensemble means made up 70% of the blend by the end of the period. ...Weather/Hazards Highlights... Moderate to heavy rain will likely linger into Saturday across the Alaska Peninsula and into southwestern portions of the Mainland. The amplified pattern will keep winds rather gusty with a tight surface pressure gradient focused along western portions of the Mainland, as well along the North Slope. The strongest gusts are expected Friday across portions of the Alaska Peninsula into southwestern Alaska as the low pressure system passes through, and along eastern portions of the North Slope Saturday into Sunday as the northern portion of the interior ridge breaks down. The combination of snow, particularly away from the coast and into higher elevations, as well as the gusty winds could lead to some blizzard conditions. Despite some disagreement with respect to timing in the guidance, the upper trough/surface low are expected to continue eastward along the southern coast of Southcentral Saturday and eventually towards Southeast by Sunday, with some areas of heavy precipitation possible, but not particularly anomalous for this time of year. Initially dry conditions will prevail for the eastern portions of the Interior with the upper ridge in place, however the approach of the upper trough/low pressure system over the Alaska Peninsula/southwest and along the southern coast may allow for at least some moisture/precipitation to spread inland into western and central portions of the Interior. Another system upstream over the Bering Sea will also potentially bring an additional round of precipitation to the western coast and Interior early next week. The western two-thirds of the Mainland will see milder than average temperatures, with the highest anomalies across northern and western portions of the Mainland. Above normal temperatures will expand eastward into the weekend. Meanwhile, portions of the eastern Interior will be running below average as the noted inverted trough over the Yukon expands into eastern portions of the state over the weekend. Southeast Alaska will also see cold/below normal temperatures with northeasterly flow ahead of the ridge axis, but temperatures may moderate closer to normal there by next weekend. With the potential pattern change into early next week, temperatures across the Mainland are likely to cool closer to normal as well. Campbell/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