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Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
000 FXAK68 PAFC 221337 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 537 AM AKDT Fri Sep 22 2023 .ANALYSIS AND UPPER LEVELS... A deep vertically stacked low continues to drift slowly eastward and away from Kamchatka, while hugging the coast of Northeast Russia. An occluded front extends southeastward from the low and has essentially stalled over the Alaska Peninsula due to the remnants of a high amplitude ridge over the western half of the state. Despite overcast skies and lingering showers along the front, most of Southwest is currently dry with clear skies mixed with areas of patchy fog and low stratus this morning, largely thanks to the aforementioned ridge of high pressure. Things are more active over the western and southern Bering where a 120+ knot upper level jetstream spans from south of Kamchatka to across the Aleutians and back into the North Pacific before reaching the Alaska Peninsula. Numerous smaller disturbances are forecast to track within this stronger flow, skirting immediately south of the Central Aleutians through the weekend. Meanwhile, a trough remains over the Gulf of Alaska with all of the precipitation and upper-level energy being directed into Southeast Alaska. Southcentral thus remains under weak high pressure, which is likely to persist through early next week, bringing a welcomed multi- day stretch of dry and sunnier conditions to the region. && .MODEL DISCUSSION... Model guidance is in reasonable agreement this morning, especially with the synoptic features. A broad upper low over the western Bering will send multiple shortwaves across the Southern Bering and into the North Pacific over the next couple of days. There continues to be minor differences in the speed and evolution of each wave, first late Friday into early Saturday over the Alaska Peninsula, and then again late Sunday over the Western Aleutians. && .AVIATION... PANC...VFR conditions and light winds are expected to prevail today. There is potential for some patchy fog to develop near the airport this morning, but any fog should quickly dissipate with the onset of daytime heating. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)... Pretty quiet across Southcentral Alaska this morning with the only notable feature being a weak low spinning over the northern Gulf producing some scattered showers near the vicinity of the low. High pressure will continue to build in from the west as an amplified upper level ridge gradually expands over the next several days. This will result in quiet and drier weather over the weekend and likely continuing into early next week. However, it will definitely start to feel like fall with the next few days starting out with crisp morning temperatures, especially for areas that see clouds clearing out during the overnight hours. The Copper River Basin is expected to see the coldest morning temperatures this weekend with lows bottoming out in the 20s. Near normal temperatures can be expected during the day with partly to mostly sunny skies for much of the region. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today through Sunday)... Forecast remains on track. The current active pattern over the eastern Bering and Aleutians this morning will trend towards a more settled pattern through the weekend and into early next week as the longwave pattern becomes more zonal and shifts south of the area. A low in the northwestern Bering Sea extends its front across the eastern Bering and Aleutians early this morning. Winds along and behind the front will weaken today as the front sweeps well eastward of its parent low pressure system. The front will continue weakening as it lifts across the AKPen today and then into Southwest Alaska this evening, bringing a quick shift of westerly winds. Expect scattered showers for the eastern Aleutians and Bering, AKPen, and coastal Southwest Alaska through the weekend as the system gradually dissipates. Further to the west, a weak low will pass just to the south of the Aleutian Islands today, however most of the precipitation and winds should remain over the North Pacific. Widespread zonal flow is expected across the Bering and Aleutians through the weekend, with winds likely only reaching small craft at most on Saturday. By Sunday morning, an upper low and attendant surface low track into the western Bering from the Kamchatka Peninsula. Precipitation spreads eastward throughout the day and reaches the eastern Aleutians by Sunday night. Sustained winds are advertised to remain mostly below small craft. && .LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)... Key features in the long term include a deep longwave trough over the northern Bering extending southward to the Gulf of Alaska. An upper level ridge builds to the east over the Alaska-Yukon border. Model agreement beyond the midweek timeframe diverges greatly, and the GFS solution appears to be the outlier. There is higher confidence at this point in time in the EC/Canadian solution, which depicts a secondary upper level trough entering the Bering from Siberia early Wednesday. For the most part, resultant weather across Southcentral appears to be generally quiet for the middle of next week. The EC advertises a Gulf low over the Panhandle lifting northward late Wednesday. Upper level waves associated with this low may produce precipitation over the Copper River Basin through the end of next week. Farther west, would expect unsettled weather over the Bering as a low traverses from west to east and arrives over Southwest Alaska by Thursday. There is growing consensus among model solutions that a deeper trough will arrive over the central Aleutians by the end of the week, though there is little confidence on the timing and track of this feature. && $$ SYNOPSIS AND MODEL DISCUSSION...BL SOUTHCENTRAL ALASKA...PP SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AF LONG TERM...KO
