840 FXAK68 PAFC 281437 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 537 AM AKST Sat Jan 28 2023 .ANALYSIS AND UPPER LEVELS... A broad longwave trough is situated over East Asia this morning, spreading its influence across the Bering Sea, while a ridge to its east stretches up from the Northeast Pacific into mainland Alaska. This configuration continues to place a southerly jet drawing warm, moist air across the eastern Bering Sea into Southwest Alaska. A weak cold front associated with the jet is bringing light rain to parts of Bristol Bay and primarily snow to the Lower Kuskokwim Valley as it slowly tracks eastward. Low stratus behind the front streaming in off the Bering Sea is also contributing to freezing drizzle and areas of low visibility in the Kuskokwim Delta, though radar returns associated with this appear to have faded over the past several hours. To the south, a warm front is crossing the Alaska Peninsula bringing another round of rain and warm air set to reinforce the air mass over Southwest Alaska this afternoon. Under the subsident influence of the ridge to the east, stratus has overspread much of Southcentral through the overnight hours. Though locations have yet to report any freezing drizzle, the Kenai radar depicts weak returns above 2000 to 4000 ft. The 12z Anchorage sounding showed a dry layer with dew points as low as -23C beneath the stratus that has likely kept any precipitation from reaching the ground so far. A similarly dry layer is also evident in the mid-levels of the atmosphere. With surface temperatures continuing to hover below freezing in an environment like this, any precipitation reaching the ground would likely be freezing drizzle. Along the north Gulf coast, temperatures are slightly warmer, in the mid-30s for some locations. Stratus is widespread across the marine areas from the eastern Aleutians to the eastern Gulf of Alaska. Out west, skies are fairly clear over the central/western Bering Sea with some scattered shower activity supported by cold air aloft. Additionally, A well-developed North Pacific low located approximately 700 miles southwest of Attu Island is showing an impressive satellite presentation with hints of a developing sting jet feature this morning. An ASCAT-B pass from 1039Z showed a swath of hurricane-force winds on the south side of the deepening low. Its front wraps out ahead of it as it approaches the western Aleutians, packing storm-force winds and likely hurricane-force gusts. && .MODEL DISCUSSION... Models continue to be in large-scale agreement through the short term. There has been a subtle shift to the west with the hurricane-force low tracking near the western Aleutians later today, which will have the greatest impact on the forecast with regards to how far east the winds extend on the south side of the low, and therefore how strong the winds will be near Shemya. Additionally, they have backed off somewhat with precipitation over Southcentral on Sunday. For southern mainland Alaska, the main uncertainties relate to the timing of shortwaves rounding the top of the ridge through the weekend and how this may impact precipitation coverage/amount on Sunday and Monday. && .AVIATION... PANC...VFR ceilings less than 5000 ft are expected to drop to MVFR later this morning. As ceilings lower, the environment becomes increasingly favorable for freezing drizzle, which will be possible through at least this afternoon. Pinpointing the specific timing is difficult, and it is expected to be intermittent. Ceilings may begin to lift this evening, with freezing drizzle becoming less likely. Light winds persist throughout the TAF period. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through Monday night)... A strong upper level ridge will remain firmly entrenched from the northeast Pacific to Southcentral Alaska through the weekend. Southcentral will be positioned on the top of the ridge, in the path of whatever is moving up and over the ridge. For today, a series of very weak waves riding over the ridge will cross Southcentral. Most places will stay dry, but there will be some localized very light precipitation. The western side of the Talkeetna Mountains is the best bet for some light snow thanks to southwesterly upslope flow. Secondarily, Kenai radar has indicated some very weak returns overnight from the western Kenai Peninsula up to Anchorage. The 12Z Anchorage sounding shows dry air aloft in the snow crystal growth region. With no big surges of moisture on the way, this means any precipitation which reaches the ground would likely be in the form of freezing drizzle. Have added this to the forecast in the Cook Inlet region through early this evening. Warm air advection up and over the ridge top has warmed the lower atmosphere over the past 12 hours. Another surge of warmer air will lift northward across Kodiak and the western Gulf today and into Southcentral tonight. The first round of warming pushed the max low level temperatures just above the freezing mark. The second round of warming will create a deeper layer of above freezing temperatures, a profile ideal for freezing rain. A series of weak short-waves will lift out of the Pacific toward Kodiak Island later today, bringing steady light rain, especially to the south and eastern side of the island. These short-waves will then traverse Southcentral Sunday through Monday, leading to widespread light precipitation. The aforementioned warming aloft will lead to a variety of precipitation types across the southern tier of Southcentral, with freezing rain possible over a large area that includes the Kenai Peninsula, Anchorage, the Matanuska Valley and eastward across the Prince William Sound region. Locations right on the coast will rise above freezing, but with little wind, inland valleys will struggle to rise above freezing. While precipitation will be light, there is potential that freezing rain advisories may need to be issued. Interior areas of Southcentral, including most of the Susitna Valley and Copper River Basin should remain cold enough for snow. As the short-waves exit late Monday, the upper ridge will become reestablished over Southcentral, leading to drying and cooling. A short-wave moving in from the Bering Sea will push up against the west side of the ridge, leading to continued steady rain for Kodiak Island through Monday night. Depending on exact position and strength of the ridge, precipitation could move eastward into the Cook Inlet/Susitna Valley corridor. If it does make it that far east, expect the airmass to have cooled enough to produce primarily snow. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Saturday through Monday)... Things are beginning to quiet down over Southwest Alaska as precipitation tapers off along the weakening front. The Winter Storm Warning for Bristol Bay and the Winter Weather Advisory for Kuskokwim Delta have been canceled as the freezing rain threat from this front has ended. However, lingering stratus over the region is leading to freezing drizzle near Bethel. Low stratus and fog may linger over the Kuskokwim Delta (and perhaps the Dillingham area) into the afternoon, so it's difficult to say when the drizzle will end. For the Lower Kuskokwim Valley, the Winter Weather Advisory is still set to expire later this morning. As warm air aloft looks to exit more quickly, the forecast ice accumulations have diminished to a trace. More precipitation arrives by Sunday as moisture streams into Southwest Alaska from a low in the North Pacific. It's difficult to hone in on precipitation amounts and timing given the disorganized nature of this moisture. However, given the southerly to southeasterly flow, there is decent forecast confidence in higher precipitation amounts along the Pacific side of the Alaska Peninsula and along southeastern slopes of the Kuskokwim Mountains due to upslope enhancement. Precipitation will be further enhanced late Sunday into Monday as a front moves in from the Bering Sea. Overall, while there remains potential for freezing rain, strong warm air advection will likely lead to a quick changeover from snow to rain. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Saturday through Monday)... A strong low and its occluded front will bring active weather to the Bering Sea and Aleutians through Monday. The main hazard associated with this 940-950 mb low will be high winds, up to hurricane force, across the Western Bering. A High Wind Warning is in effect from noon on Saturday through Sunday morning for the Western Aleutians. Confidence is high that southeasterly winds will reach or exceed 75 mph along the occluded front. Confidence is lower that southwesterly winds coming around the back side of the low tonight will also reach 75 mph, especially as shifts in the forecast low track keep the strongest core of winds further west. We will continue to monitor this storm and update the warning as needed. While the strongest winds will remain limited to the Western Aleutians, the Central and Eastern Aleutians will also experience active weather courtesy of the occluded low, which will sweep a front west to east from Saturday through Sunday night. Moderate to heavy snow/rain along this front will gradually diminish in intensity as the front weakens. Behind the front, cold air wrapping around the low will bring snow showers across much of the Bering Sea and Aleutian Chain. && .LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)... An active pattern looks to continue for the long term period. On Tuesday, models highlight an upper level trough over the eastern Bering progressing eastward across Southwest, the Alaska Peninsula, and into the Gulf of Alaska through Thursday. This looks to be the final feature that eventually results in the Gulf ridge breaking down. As a result, precipitation chances for Southcentral increase through Wednesday. Meanwhile for Southwest, the breakdown of the Gulf ridge will cause a bit of a pattern change from the previously warm southerly flow over Southwest to much colder westerly flow arriving by Wednesday. This also clears the way for a broad upper level low to arrive over the Aleutians by Wednesday. A corresponding, complex surface low develops over the eastern Aleutians and eventually tracks eastward into the Gulf by Thursday. Assuming the more southerly track pans out, this will generate colder, drier conditions (offshore flow) across much of Southwest Alaska for Thursday while the Aleutians, Alaska Peninsula, and Kodiak Island will see the bulk of precipitation Thursday. Farther west, a weak upper level ridge attempts to build over the western Bering and western Aleutians, briefly allowing for a more amplified pattern to setup on Friday. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...High Wind Warning 191. Winter Weather Advisory 152. MARINE...Storm Warning 177 178 411. Gale Warning 175 176 413. FIRE WEATHER...NONE. && $$ SYNOPSIS AND MODEL DISCUSSION...CQ SOUTHCENTRAL ALASKA...SEB SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KC LONG TERM...NS