586 FXAK68 PAFC 091247 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 447 AM AKDT Tue Apr 9 2019 .ANALYSIS AND UPPER LEVELS... Generally calm conditions are the rule across Southern Alaska this morning. Shower activity that produced thunderstorms yesterday evening continues across the Copper River Basin and Susitna Valley. Rain is also off-and-on along the North Gulf Coast. A pair of weak lows are also present. The stronger of the two is tracking well south of Kodiak Island. The other is a swirl of clouds northwest of Dutch Harbor. Otherwise generally mostly cloudy to cloud skies persist for much of the area as southerly flow transports Gulf moisture into Southern Alaska. The only features of note in the upper levels consist of the upper level support for the weak low south of Kodiak Island, and broad troughing over the western Bering. The subtropical jet is primarily tracking in zonal flow to the south of the Aleutians. && .MODEL DISCUSSION... The models are coming into better agreement with the track and strength of a North Pacific low that will reach peak intensity as it approaches the Alaska Peninsula and eastern Aleutians on Wednesday night. Much beyond that however, increasingly significant differences appear and quickly become worse with time. Among those differences include the strength of the low as it tracks into the eastern Bering. The GFS is the strongest with a central pressure near 960 mb. The 06Z NAM is much closer to the model consensus than its 00Z counterpart, yet it is still among the weakest solutions with a peak intensity of 968 mb. The significance of this difference mainly includes how strong the winds near Kodiak Island get when the leading front passes by Wednesday evening. It will also impact how strong the winds get on Thursday through Turnagain Arm and the gaps. While the front will be quite strong regardless of the model solution, the expected track of the parent low in a cyclonic loop should mitigate the impacts and how strong the peak winds associated with the front get on Thursday. While forecast confidence is improving, there still remains enough disagreement that it's about average. && .AVIATION... PANC... Rain showers moving over the area will continue into the early morning hours. Temporary gusty conditions are possible as well. The showers will diminish through the early afternoon, then some redevelopment is possible with afternoon heating. All activity will end towards sunset. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Monday night through Thursday)... A weak frontal boundary draped along the southern mainland slowly diminishes through the morning. Light rain showers, with snow showers along higher elevations taper off by early afternoon. Another front along the southern Gulf moves east by late afternoon. A ridge builds across Southcentral this evening keeping the region dry through Wednesday. The exception to this will be across Kodiak Island and the southern Kenai as a North Pacific front lifts north to the Bering. East to southeast winds begin to increase across the western Gulf and northerly flow for Cook Inlet Wednesday evening with pre-frontal showers before midnight. The frontal boundary makes quick progression after midnight with gusty gale force winds developing across much of the Gulf along with moderate rain. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)... A weakening deformation zone aligned over Southwest continues to bring precipitation to the interior Bristol Bay region up to the lower Kuskokwim Valley. A ridge building to the east will bring the chance for fog this morning in Bristol Bay...this will depend on whether there are enough breaks in high clouds to cool surface temperatures to the dewpoint. Showers will diminish this afternoon and steady south flow will cause high temperatures in Bristol Bay and the Kuskokwim Delta to trend several degrees warmer than yesterday. Farther inland, lingering cloud cover will limit heating somewhat. A low approaching the central Aleutians from the north Pacific will spin a front into the AKPEN Wednesday. This front will be relatively inconsequential in terms of precipitation, however expect strong southeast winds, associated with the front, with gap winds potentially gusting to 40 kt. In addition, warm air advection and downsloping will bring temperatures to the upper 40s in low lying areas of Southwest. Another front with a much deeper moisture fetch will approach Southwest Thursday. Expect another round of strong winds with this, with gusts again possibly reaching around 40 kt, but expect widespread precipitation over Southwest. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Today through Thursday)... The quiet weather ongoing across the Bering this morning will come to an end late this afternoon as the first of a pair of lows moves out of the North Pacific and into the central and eastern Aleutians tonight. As the first low weakens and tracks west, a second even stronger low will track between Dutch Harbor and Cold Bay on Wednesday night. This low will have storm force winds to its south as it reaches peak intensity Wednesday night. Widespread gale force winds are expected along the Pacific side of all of the Alaska Peninsula and eastern Aleutians. Strong southwesterly onshore winds will also impact Bristol Bay, which may result in some coastal flooding concerns. Otherwise most areas can expect gusty soaking rains through Thursday across much of Southwest Alaska. With the models rapidly diverging on the track of the low by this point, larger changes to the forecast are very possible for Thursday and beyond regarding the low track. && .MARINE (Days 3 through 5)... (Thursday through Saturday) ...Gulf of Alaska... The forecast period starts out on a very active note, with significant changes made to the forecast for Thursday into Friday. The numerical guidance has come into much better agreement over the last 24 hours, facilitating the need for these changes. In short, sustained winds will rapidly increase to storm force for most of the coastal waters Thursday afternoon, with a few hurricane force gusts a distinct possibility for the Barren Islands region, and just short of hurricane force elsewhere. Given good fetch length, seas will build into the 15 to 25 feet range, as a strong front crosses the region from southwest to northeast during the day. Conditions will rapidly improve for Friday and Saturday. ...Bering Sea and Aleutian Coastal Waters... An area of low pressure north of Adak Thursday morning will wobble eastward while becoming absorbed into a new low racing into the eastern Bering/western Bristol Bay region later in the day. Sustained gales will be common for all locations during the day, with seas averaging in the 15 to 20 feet range. The exception to this will be from The Shumagin Islands eastward, where some sustained storm force winds are likely, with some hurricane force gusts not out of the question. Here, seas will top out in the 25 to 30 feet range. Conditions will gradually improve for Friday into Saturday. && .LONG TERM FORECAST (Days 3 through 7)... The weather will become very active on Thursday, as a strong frontal system crosses the region. This front will be attached to an area of low pressure moving into western Bristol Bay. Very strong dry advection wrapping into the low. This combined with a strong 1.5 mb PV anomaly and favored left exit region jet dynamics all point to a strong downward mixing potential environment. Thus, some strong winds will develop near the Alaska Range across southwest Alaska. Here, look for sustain winds of 30 to 40 with gusts to 55 mph to be possible. For Southcentral, the main wind impacts will be felt through some passes along the Kenai Peninsula into the Turnagain Arm areas, where sustained winds of 45 to 55 mph, with gusts to 75 mph may develop. If the numerical guidance continues to portray this, a High Wind Watch may be issued for the Turnagain through Portage area. Some of these winds look to affect the southeastern half of the city as well, with the highest winds of 30 to 45 mph, with gusts to 60 mph seem reasonable. This front will also bring some fairly widespread rainfall, with the typical rain shadow locations likely just seeing some sprinkles making it across the Chugach Mountains given the strong southeasterly flow aloft. This down-sloping effect may give a boost to the temperatures though, with warm conditions expected to continue. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...NONE. MARINE...Gale Warning: 150-176, 179-185, 412-414. FIRE WEATHER...NONE. && $$ SYNOPSIS AND MODEL DISCUSSION...JPW SOUTHCENTRAL ALASKA...KH SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM/JPW MARINE/LONG TERM...PD