Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
767 FXAK68 PAFC 181337 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 537 AM AKDT Thu Jul 18 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)... Discussion: Overall, the forecast remains on track with continued cool and wet conditions for the Mat-Su Valleys, Anchorage/Eagle River, Western Prince William Sound, and Kenai Peninsula. Eastern Prince William Sound, Cordova, and the Copper River Delta will see scattered showers this morning taper off by early afternoon with drier weather through Saturday morning. The Copper Basin may see a few showers today but will trend warmer and drier heading into and continuing through the weekend. The upper level low that has been positioned over western Alaska the past several days is finally started to drop southwards towards the southern Cook Inlet today. It is trending a bit slower on its southward trek, and as a result will likely see showers linger through Friday morning for the Anchorage Bowl and into the early afternoon for the eastern Kenai Peninsula. Light showers have also been ongoing over the eastern Kenai and Western Prince William Sound overnight as convergence increased over the Kenai Mountains and eastern Kenai Peninsula in response to a deepening upper low to the south and the aforementioned inland Alaska low to the north. Models still in fairly good agreement with taking the northern low into the southern Cook Inlet and across the Shelikof Strait/Kodiak Island today. As such, Kodiak has a better chance of seeing slightly more precipitation out of this system before it is absorbed into North Pacific low. However, a slight shift in track either west or east will result in lesser chances of precipitation. The North Pacific low will move east today before getting blocked by broad ridging over western Canada and setting up residence in the Gulf this weekend. The setup will favor warmer, and drier air pushing into the Copper Basin from the east, and moisture pooling along the northern Gulf coast. Easterly waves look to rotate around the Gulf low and with the CAPE axis pushing into the eastern Copper Basin...could see increasing chances for thunderstorms this weekend. The northern Gulf Coast will see their brief period of dry weather come to an end as rain spreads east to west along the coast Saturday morning. - PP && .SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days 1 through 3: Today through Saturday)... A pattern change will be under way shortly as a ridge of high pressure transits from the Bering Sea and Aleutian Islands towards Southwest Alaska. Generally, expect a warming and drying trend for Southwest Alaska under the ridge. For the Bering Sea and Aleutian Islands, wetter and windier conditions are on tap as a low moves in today and lingers through Saturday. The biggest changes with the evening and overnight forecast packages were to thunderstorm chances in Southwest Alaska, and to fog across the Bering Sea and Aleutian Islands. Regarding thunderstorm chances: with a robust upper level low moving from the interior towards the Alaska Peninsula today, there may be enough upper level support for isolated thunderstorms. The current forecast keeps much of this activity near the Alaska Range, but some model guidance is hinting at convective rain showers (with perhaps enough thermal instability to support a thunderstorm or two) further west in Greater Bristol Bay. For fog, the influx of warm, moist air with today`s incoming low provides a favorable environment for low stratus and fog to develop across much of the Bering Sea and Aleutian Islands. As such, have increased the coverage and severity of fog through late Thursday night. The current forecast is for visibility down to one statute mile, but visibility could be one-quarter mile or less in some areas. Still, there`s uncertainty with whether there will be a strong enough inversion for fog to be that dense; surface pressure will be dropping as the low approaches and higher pressure moves off to the east. In addition, warmer, summertime sea surface temperatures mean that near-surface air temperatures may not be cool enough for a strong inversion to develop. As such, have kept forecast visibility to 1 mile or greater for now. -KC && .LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)... An omega pattern will dominate the long-term period, with large upper-level lows situated in the Bering Sea and the North Pacific near the Gulf. Between these lows, a high pressure ridge will situate itself over Southwest Alaska. This setup will keep the Bering Sea, Aleutian Chain, and southern Alaska Peninsula active due to numerous shortwaves rotating around the Bering low. The ridge, initially over Southwest Alaska Saturday and early Sunday, will shift eastward toward Southcentral Alaska while weakening. A frontal system is expected to approach Southwest Alaska Sunday night as this ridge shifts eastward, with locally heavy rainfall possible. Confidence remains relatively low in the front`s ability to bring precipitation inland, but the coast is most likely to see rain. Showery and unsettled conditions are expected across Southwest Alaska on Tuesday as more shortwaves pass through the Bering. For Southcentral Alaska, the North Pacific/Gulf low will pull easterly waves from the Yukon into the region. This pattern will be favorable for precipitation in the Copper River Basin and the Susitna Valley. As the ridge nudges westward from the Yukon, temperatures across Southcentral are expected to rise to near to above normal values. Afternoon thunderstorms are possible from Saturday through Tuesday, although confidence in timing regarding these easterly waves are very low at this time. && .AVIATION... PANC...Rain showers expected to last much of the day and into Friday morning as a low drops southwards towards the southern Cook Inlet today. MVFR ceilings may bounce between IFR and MVFR throughout the day with VFR ceilings returning by Friday mid- morning Friday. Visibility may also dip to MVFR periodically today with light southerly winds becoming more southwesterly by 03Z. && $$