Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 656 PM EST Sun Jan 22 2023 Valid 12Z Thu Jan 26 2023 - 12Z Mon Jan 30 2023 ...Threat of heavy precipitation along the southern coast to the Panhandle expected to last through around Thursday... ...The Aleutians toward the western mainland could see increasing chances of precipitation along with gusty winds late this week and early next week... ...Overview... As the medium range period begins Thursday, a notable shortwave around the Gulf of Alaska region will direct moisture into the Panhandle for another day of possibly heavy precipitation, mainly in the form of rain. But then a significant pattern change gets underway late week as upper ridging builds in atop the state, in response to a couple of upper troughs/lows in the western Bering Sea. This should dry out the Panhandle but create more active weather from the Aleutians into the Alaska Peninsula and western mainland by late this week. ...Model Guidance/Predictability Assessment... Model guidance has stayed reasonably well clustered for the overall pattern evolution but with typical differences in the details. Particularly early in the forecast period, there is good agreement for an upper low centered just west of the Seward Peninsula and a shortwave with its axis across the south-central mainland into the Gulf of Alaska. Then models agree on a strong ridge building into the mainland by Friday. The most impactful model differences arise on the western side of the ridge affecting western Alaska. Model guidance continues to indicate a deep and large surface low pressure system in the western Bering Sea near the Kamchatka Peninsula late week along with troughing aloft. But there has been model waffling as to how far east the trough may reach and overcome the western edge of the ridge, with differences in shortwave energies. Today's guidance seems marginally more clustered that the ridge may not budge too much. This would limit QPF and frontal boundaries to the Aleutians to Alaska Peninsula and into the far western mainland, without spreading too far into the mainland other than some light snows. Notably there is another western Bering low by early next week that creates the same sort of issue. The WPC forecast was based on a blend of the ECMWF/GFS/CMC deterministic models early on, with incorporation and increase of the ensemble means by days 6-8 given the increasing uncertainty/detail differences. ...Sensible Weather and Potential Hazards... For the short range period into Thursday, a Seward Peninsula upper low and a Gulf of Alaska shortwave along with a weak surface low pressure system will all serve to direct Pacific moisture into the Panhandle for rounds of heavy rainfall. Ridging set up there will cause temperatures to be milder than average for a precipitation type of predominantly rain for much of the Panhandle region. Temperatures are forecast to be 20-30F above normal south of the Alaska Range, with milder than average temperatures also stretching into much of the mainland as early as Thursday. Some residual moisture should make it into central parts of the mainland as well for some snow chances. There may be some cooler than normal temperatures lasting in the far western mainland Thursday in response to the Seward Peninsula upper low. By late week, ridging becoming established into the mainland as well should help moderate temperatures to well above normal across the state, with possible +30F anomalies for parts of the northwestern mainland. The exceptions will be the near-normal Aleutians and eventually the Panhandle by early next week as they see northerly continental flow just each of the ridge. Additionally, this should begin a drying trend across the Panhandle. Meanwhile, a large surface low pressure system is forecast over the western Bering Sea/Kamchatka Peninsula for the latter half of the week. While guidance continues to have this low weakening west of Alaska, frontal boundaries and shortwaves from the system are still likely to pass across the Aleutians for some enhanced precipitation and perhaps some high winds. The impacts farther east are less certain, but this precipitation and gusty winds could reach the Alaska Peninsula/western mainland. The pattern seems to repeat itself for early next week for another round of western Alaska precipitation/winds. Some available moisture could lead to snow showers over much of the mainland through next weekend, but currently only light QPF is expected. 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