Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
229 FXAK68 PAFC 200042 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 442 PM AKDT Wed Jun 19 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today through Friday)... The upper level ridge continues to slide east with its axis over the Alaska Panhandle this morning. This eastward progression of the ridge will allow for the development of a more southerly flow across the Gulf of Alaska that will advect a more stable airmass over the southern half of Southcentral as well as drive a surface front from the western gulf to the northern Gulf through Friday. A diminishing marine stratus deck continues to hold over the northern Gulf and immediate Prince William Sound coast. These clouds should lift and become less expansive in coverage through the day and into Thursday as influence from the aforementioned ridge wanes. Within the upper-level trough situated over the Gulf of Alaska, embedded short-waves are swinging around the trough and into Southcentral. One such shortwave allowed for the convection observed across the Copper River Basin currently. A similar feature is expected to push across Southcentral Thursday afternoon, and with enough lingering instability, it may create the potential for isolated thunderstorms and convective showers across the northern Copper River Basin and Broad Pass regions. Generally light southerly flow will keep storm initiation on the Talkeetna mountains out of the Mat-Su valleys. Southerly gap winds through places such as Seward also expected Thursday afternoon. All-in-all little change is expected for places like Kodiak, with persistent easterly winds, clouds, and periods of light rain. -CL/TM && .SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS (Days 1 through 3: This afternoon through Saturday afternoon)... The big picture of the forecast remains largely unchanged. Generally, expect rain showers across Southwest Alaska, with overcast skies and areas of fog for the Bering Sea and Aleutian Islands. With the stronger weather systems remaining mostly out of the area, the weather continues to look relatively benign. As with yesterday, forecast confidence remains lower for the details (specifically, areas of thunderstorms and fog) as models struggle to capture the weaker upper level shortwaves driving the weather over the coming days. Starting with the fog: locations such as Shemya, Adak, Saint Paul, and Saint George saw low stratus and reduced visibilities yesterday and into this morning as a ridge of high pressure moves over the Western Bering Sea/Aleutian Islands. As the ridge continues to transit eastward, it`s likely that fog will return tonight for the Pribilof Islands and Central Aleutians (including Adak and Atka). Though confidence is somewhat low, we`re expecting fog to subside by Thursday afternoon as a weak North Pacific low approaches the Western and Central Aleutians, breaking the hold of high pressure over these areas. As for thunderstorms, high-resolution and global models alike continue to struggle with where showers and potential thunderstorms will initiate. Steadily increasing afternoon highs will help aid in thermal instability, but there remains a question of whether this instability will be fully realized if cloud cover remains in place. This, in combination with model differences as they struggle to resolve weak upper level shortwaves, is leading to continued low forecast confidence with thunderstorm locations and rain amounts. Here`s what we can say with decent confidence for Thursday and Friday afternoons: Thursday afternoon looks to be the wetter of the two days, with more widespread and likely heavier showers. The steering flow will be approximately east to west, with the Western Alaska Range, Middle Kuskokwim Valley, and Kuskokwim Delta all seeing the potential for thunderstorms. For Friday, an approximately north to south steering flow will keep thunderstorm potential mostly over Middle Kuskokwim Valley and Western Alaska Range, with the potential for storms to move south into interior Bristol Bay. There could be localized areas of greater thermal instability for Friday, which could result in more thunderstorms than on Thursday. Thunderstorm potential continues through at least Saturday afternoon, but confidence is too low to say much at this point. -KC && .LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)... Three main low centers on the upper air charts demonstrate the most energy through the forecast period. A slowly retrograding low over the Chukotsk Peninsula continues into Siberia. The second is a Western Bering low, the next of a series that have moving across the North Pacific, that will track across the Alaska Peninsula by midweek. The last is a low center just South of the Aleutians that will slide across the Southern Gulf of Alaska/ Eastern North Pacific for Wednesday. Most of Mainland Alaska is under a weak ridge which supports surface thermal troughs and areas of convection across the Interior for the entire forecast period. Showers are expected across Southcentral. A series of surface low and fronts bring mostly showery conditions along the Aleutians, Bering and AKPEN, spreading into Southwest Alaska through Wednesday. The next surface low from the North Pacific and its front enters the Aleutians and Bering Tuesday, and move over the Central portions by Wednesday. locally heavier precipitation and gusty winds up to gale force spread into the Central Aleutians. -Kutz && .AVIATION... PANC...A change in the pattern, with low pressure moving into the Gulf and a coastal ridge setting up out ahead of it will lead to a return of Turnagain Arm winds. For later today, the southwesterly up Inlet flow will still be the dominant wind. Thus, as the Turnagain Arm jet forms this evening with the establishment of an E-W oriented sfc ridge, it will meet up with the southwesterly flow and result in a more southerly component to the winds coming into PANC. Winds will likely start out with more of a SW component and back toward the SSE overnight as the Turnagain jet strengthens. As is typical, winds will die down late tonight/early Thursday with weakening of the diurnally induced pressure gradients. However, the Turnagain jet will be much stronger on Thursday and will come into the terminal earlier. As always, there is some uncertainty in the exact timing of arrival and dissipation of the gusty winds. Meanwhile, VFR conditions will prevail. With increasing easterly flow aloft ahead of a short-wave lifting northward into the Gulf, do NOT expect any chance of low clouds coming in as has occurred the last two mornings. There will be increasing mid to high clouds Thursday with just a slight chance of a passing shower - but ceilings will stay safely in the VFR category. && $$