894 FXAK68 PAFC 120209 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 609 PM AKDT Sun Jul 11 2021 .ANALYSIS AND UPPER LEVELS... The longwave pattern is dominated by an upper-level low situated just east of Kodiak Island and an upper-level ridge upstream over eastern Siberia and extending across the central Bering. At the surface, a 1003 mb low is currently spinning over the central Gulf with a southerly flow ahead of it continuing to push clouds and rain along the Southcentral coast. Easterly gales persist across the northern Gulf, with peak gusts of 45 kt at Middleton Island and Hinchinbrook Island. One weak shortwave embedded in the easterly flow has moved from Cook Inlet to the Alaska Range with showers from Homer to Anchorage. A second wave is pushing across Prince William Sound this afternoon. Farther inland, mid-level clouds have moved over the Copper River Basin and Susitna Valley. Scattered showers are moving over the Kuskokwim Delta from the north as a shortwave trough and surface cold front drop south from northern Alaska. Farther west, low stratus and areas of fog persist from the Pribilof Islands and eastern Aleutians west across the Bering. A weak vertically stacked low sits north of Shemya. && .MODEL DISCUSSION... Model agreement continues to improve in the near term, especially with the timing of various easterly shortwaves pinwheeling around the main upper-level low centered over the central Gulf. The 12z GFS has now trended to the other 12z models with regard to the wave lifting across Southcentral Tuesday evening through Wednesday. All models, including hi-res guidance, are indicating a band of precipitation developing over the Copper River Basin by Monday evening, moving to the Susitna Valley by Tuesday morning as another area of rain develops from Cook Inlet to Kodiak Island. The GFS does diverge from the other models Wednesday, keeping the aforementioned low lingering over the central Gulf while other guidance moves this feature east. However, given that the low is rapidly weakening, there are no significant differences in the sensible weather. && .AVIATION... PANC...VFR ceilings will persist. A stray shower or two are likely late afternoon through this evening in association with a weak upper-level wave moving overhead. Winds are expected to remain light through Monday morning. A light southeasterly Turnagain Arm wind may bend over the terminal this afternoon. An occasional higher gust is also possible; however, confidence in this is low and is not included in the TAF. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3...Sun through Tue)... The main weather player for the start of the week will continue to be the increasingly stacked and occluded low centered over the Gulf. The gale force barrier jet following the contour of the low's front will slowly diminish through tomorrow as the front gradually weakens in place along the north Gulf Coast. This same front will continue to bring steady rainfall to most coastal locations through at least Tuesday morning. Farther inland, the first of a series of easterly waves may bring enough forcing to generate a brief round of showers along the western Kenai Peninsula and perhaps into the Anchorage vicinity this evening. Rainfall chances have been increased here for this forecast update to account for this potential, but any showers will be light and short-lived with the supporting impulse racing quickly southeast into Kodiak Island by tomorrow morning. A much more robust threat for inland rainfall will move across with a deeper easterly wave pinwheeling around the low in the Gulf by tomorrow evening into early Tuesday. A band of rain will move inland from east to west as the wave axis moves across, bringing a decent surge of moisture that could result in wetting rains well away from the coast, including much of the Mat-Su Valleys and Copper River Basin. Rain will similarly end from east to west on Tuesday as the wave pivots into Kodiak Island by Tuesday afternoon. The beginnings of what could become some of the first "real" summer weather this season will start to come together with a pattern shift on Wednesday. An upper level ridge will build into the western mainland by midweek as the filling and weakening low in the Gulf finally accelerates into the AK Panhandle. This will bring a shift to northerly flow from the interior, with much warmer and drier air beginning to spill in across the Alaska Range by Wednesday afternoon. The one exception to the drying trend may be the Copper River Basin, where another shortwave tracking around the ridge from the north could bring lingering cloud cover and showers for one more day before more significant warming takes hold across the whole region later this week. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)... A quiet weather pattern will continue across Southwest Alaska over the next few days. Overall, skies will have more clouds than sun and the chance of stray showers still exists. Otherwise, the main concern is patchy fog in areas of the Kuskokwim Delta and Alaska Peninsula due to light onshore flow. The chance of fog is greatest during the second half of the nocturnal hours. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)... A fairly benign weather pattern will continue across the Bering/Aleutians. A weak area of low pressure will move into the central Aleutians on Monday, then move southeastward back into the North Pacific late Monday night into early Tuesday. This low will bring rain and showers to the central Aleutians. Winds will remain below gale force with no high seas expected. The biggest concern is areas of fog and low stratus over the Bering Sea. && .MARINE (Days 3 through 5 - Wednesday through Friday)... High pressure moves into the eastern Bering with light winds through Friday. A new low approaches the Western Aleutians on Friday, with gusty winds less than gale force spreading into the central Bering. Forecast confidence is good. A central Gulf low exits through the southeastern Gulf Thursday. && .LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)... The long term begins on Thursday with the upper-level low over the central Gulf today (Sunday) continuing to track southeast toward British Columbia. Upstream, an upper-level ridge amplifies along the west coast of Alaska. This pattern will set up a drier northerly flow across the southern mainland, with temperatures likely climbing back above normal, especially for areas away from the coast. While Thursday does look warmer, there may still be a chance for clouds and showers from the Talkeetna Mountains east across the Copper River Basin as a shortwave drops south, ejecting from an upper-level low moving east along the Canadian Arctic. On Friday, the ridge axis looks to shift slightly east, extending across the interior of the state. This shift will likely help strengthen the thermal trough, leading to even warmer temperatures. The caveat to this will be whether or not there is any influence from a potential second eastward propagating shortwave. Right now, the GFS is more bullish with the EC deepening the ridge. Either way, most of the energy with this potential feature looks to remain along and north of the Alaska Range, with any showers confined to the higher elevations of Southcentral. Model divergence grows by the weekend, but all keep some semblance of the ridge over the region. The question centers on the progression of a third shortwave from the west. The GFS and GEM are again showing this feature mainly traversing the Alaska Range, with an eventual push into the Copper River Basin by Sunday morning. The EC depicts a stronger closed low dropping from the Kuskokwim Delta to Kodiak Island by Sunday morning. In terms of precipitation, the GFS and GEM hint at another round of showers from the Talkeetna Mountains east by late Saturday. The EC, though, extends the shower activity over Southwest Alaska. Bottom line, the shift in the orientation of the longwave ridge/trough pattern will yield conditions more typical of mid-July. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...NONE. MARINE...Gale Warning: 119 120. FIRE WEATHER...NONE. && $$ SYNOPSIS AND MODEL DISCUSSION...TM SOUTHCENTRAL ALASKA...AS SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED MARINE/LONG TERM...KZ/TM