Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 739 PM EDT Sun Jun 11 2023 Valid 12Z Thu Jun 15 2023 - 12Z Mon Jun 19 2023 ...Overview... As the forecast period begins Thursday, a closed upper low is likely to be centered over the Bering Strait or so after dropping south from the northern latitudes around midweek. This will extend continued troughing over the Bering Sea to Chukchi Sea and into at least western Alaska. The troughing should keep much of the state cooler than normal while providing support for light to moderate amounts of rain. After a surface low tracks into southeast Alaska late week for some enhanced rainfall chances there, the main concern for the forecast at the surface will be the recurvature of current Tropical Storm Guchol across the Pacific and its potential to at least influence the Aleutians/Alaska Peninsula weather by early next week. ...Guidance Evaluation/Preferences... Model guidance shows fair agreement that a couple of surface lows in the Gulf of Alaska/northern Pacific on Thursday may combine or at least interact by Friday and come into Southeast Alaska. The 12Z CMC is a bit of an exception as it keeps the lows separate with a slower-moving western low. On the larger scale, recent guidance still indicates that energy from the far northern latitudes is likely to create an upper low around the Bering Strait/Chukchi Sea for the latter half of next week, with north-south oriented upper troughing extending across the Bering Sea. By the weekend the elongated upper low (possibly with multiple low centers, with models generally favoring one on the northern and one on the southern side) may tilt northwest to produce a negatively tilted trough/low with the southern end over the southwestern Alaska Mainland. There is growing spread and uncertainty with time regarding the centroid of the southern upper low. Overall GFS runs take the upper low farther south of the ECMWF/CMC by the weekend, but there is quite a bit of variability, and energy from Guchol and any phasing could play a role as well. Speaking of Guchol, the Joint Typhoon Warning Center forecast for what is currently Tropical Storm Guchol indicates the storm will recurve east of Japan and across the mid-latitude north Pacific as it transitions to post-tropical. Most model guidance agrees with its track eastward around 40N or so, reaching the Dateline perhaps late Thursday. The system may restrengthen (in terms of lower pressures, still an extratropical system) around Friday-Saturday with a general trend toward weakening early next week. The possibility for Guchol's low itself to come into southern Alaska still looks to have lower probability compared to keeping it south of the state, at least through Monday. The 06Z GFS looked particularly like an outlier with more combination of the Guchol and Bering energies, leading to the surface low tracking into around Kodiak Island by Monday. The 12Z GFS shows the low farther northeast than other guidance but not to the same extent of the 06Z run--the 12Z still kept it south of the state. Tended to favor the ECMWF position/slower track as it was well aligned with the EC ensemble mean. With the Guchol low/trough south of the Aleutians, downstream there may be a restrengthening of the northeast Pacific ridge--but today's forecast tended to maintain troughing across southern Alaska winning out over the ridge. But this interface of the ridging to the south and troughing to the north is still uncertain. In general was able to start the forecast with an even blend of the 12Z GFS/ECMWF/CMC/UKMET, but ramped up the amounts of the ensemble means, especially the EC mean, quickly by the latter part of the period given the increasing uncertainty. ...Sensible Weather and Potential Hazards... The persistent troughing over the Bering Sea (and beyond) will maintain cooler than temperatures across pretty much the entire state through this week into early next week. The Interior should generally see highs in the 60s with cooler temperatures elsewhere. There will also be some persistent chances for scattered showers across much of Alaska that should tend to be diurnally driven. Mainly light amounts are expected, with a few exceptions. One exception will likely be with the organized surface low crossing Southeast Alaska bringing enhanced rain totals there late week. A frontal system pushing through the western Mainland could also produce some more organized precipitation late week, some of which could be snow even into places like Nome/the Seward Peninsula. Interior areas of the state could see increasing coverage of precipitation, though still with generally light amounts, into the weekend. The Aleutians to Alaska Peninsula may see some rain potential by early next week depending on the track of Guchol. Tate Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html