Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 709 PM EDT Fri Nov 01 2024 Valid 12Z Tue Nov 05 2024 - 12Z Sat Nov 09 2024 ...Deep low pressure systems could cause high winds across the Aleutians/Alaska Peninsula and southwest Mainland and enhanced precipitation in southern Alaska next week... ...Overview... An upper low will move atop the eastern Bering Sea and vicinity as the medium range period begins Tuesday, supporting deep surface low pressure formed in part by what is currently Tropical Storm Kong-rey in the western Pacific. The surface low is forecast to cross from the northern Pacific over the eastern Aleutians/western Alaska Peninsula into Bristol Bay by Tuesday and move into the Lower Kuskokwim/Yukon regions by Wednesday, bringing high winds and heavy precipitation potential there, with heavy precipitation also spreading to its east across Southcentral to Southeast Alaska. Additional energy and surface low pressure are likely to move eastward through the northern Pacific and reinforce the trough pattern into midweek, with yet another surface low tracking similarly for late next week. This deepening and then reloading upper troughing over the Bering Sea southward into the Aleutians and northern Pacific should promote ridging developing across the eastern Mainland to Panhandle for mid- to later week, but troughing may finally reach those areas by next Friday-Saturday. Meanwhile the tight surface pressure gradient could cause strong easterly winds across the North Slope with some blowing snow. ...Guidance Evaluation/Preferences... 12Z model guidance began the period Tuesday with reasonably good agreement in showing the large and deep upper and surface lows centered over/near Bristol Bay. This was especially true for the ECMWF/GFS/UKMET, while the 12Z CMC was a bit east of consensus. However the 12Z CMC was an improvement compared to its 00Z and older runs that tracked the surface low farther southeast into the Gulf. Models show the low at about 950mb or so Tuesday morning, and moving slowly northeast inland while weakening a bit. Upstream, another shortwave will move through the northern Pacific Wednesday and combine with the southern side of the preexisting upper low by Thursday. There are relatively more timing and placement differences with this feature and its associated surface low. Today's model guidance did trend a bit faster and farther south compared to a day ago when they showed a track over the Aleutians, but the UKMET seemed to be an even faster/east outlier. A blend favoring the 12Z GFS/ECMWF worked through early Thursday, but then there is additional spread later Thursday into Friday with where the low ends up among deterministic models and ensemble members/means, farther north into Bristol Bay (ECMWF) or east into the Gulf (GFS), likely due to smaller scale energy differences that are not very predictable. It is also possible there could be multiple low centers. The next surface low moving across the North Pacific late week has even more model spread, with the 12Z CMC much slower and the 06Z GFS much faster. The 12Z GFS and ECMWF did not align great but at least both were in between the CMC and 06Z GFS, and the ensemble means focused near this middle ground on timing/placement. Overall the WPC forecast favored a GFS/ECMWF blend with lesser components of their means early in the period. Gradually included more ensemble means in the blend with time, reaching half by the end of the period given the increasing spread. ...Weather/Hazards Highlights... The deepening surface low moving from the northern Pacific northeastward is likely to cause high winds for the Aleutians and Alaska Peninsula on Monday and move into the Lower Kuskokwim and Lower Yukon regions given the strength of the low. Ahead of the low, precipitation including some heavy amounts will spread from the Alaska Peninsula and into the Southwest Mainland Monday, to Southcentral on Tuesday, and toward Southeast late Tuesday into Wednesday. The reloading upper low pattern should promote additional rounds of precipitation moving west to east across southern Alaska through late week. High wind and heavy precipitation hazards are outlooked on the Day 3-7 Hazards Chart for these threats. Meanwhile, rounds of snow showers are possible farther north through the period. A tight pressure gradient across the North Slope could also cause some breezy easterly winds and blowing snow there for potential for blizzard conditions, per coordination with the Fairbanks WFO. Most locations will see above average temperatures rising further as next week progresses, with the possible exceptions of the Seward Peninsula, parts of the higher mountain peaks, and the Panhandle showing cooler temperatures into Tuesday. In most cases the anomalies for morning lows should be greater than anomalies for daytime highs. High temperatures will generally be in the upper teens to 20s in the Interior and North Slope, with 30s and low to mid 40s in southern areas. 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