Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 712 PM EDT Tue May 09 2023 Valid 12Z Sat May 13 2023 - 12Z Wed May 17 2023 ...Overview... A lingering main weather feature into later this week will be a large and deep layered mean low pressure system atop the northern Pacific/Gulf of Alaska, stalled from the short range into the medium range period due to a potent upper ridge in Canada. This pattern will continue to produce unsettled weather across the southern coast of Alaska as impulses wrap moisture around the maritime low, with enhanced onshore precipitation and gusty winds but lingering for Southeast Alaska and Gulf maritime interests. This low should gradually weaken into early next week as another major surface/upper low pressure system moving through the Bering Sea is likely to lead to a round of rain across the Aleutians/Alaska Peninsula and the west coast of the mainland. Meanwhile ridging and warmer temperatures are forecast to come into Southeast Alaska, and farther north into the Interior next week, which could increase the rate of snowmelt runoff and river ice breakup and eventually lead to potential flooding threats. ...Guidance Evaluation/Predictability Assessment... 12 UTC GFS/ECMWF/UKMET/Canadian and GEFS/ECMWF/Canadian ensemble mean guidance seems compatible for this forecast period. This portends overall above normal forecast confidence, albeit tempered some by less favorable recent model run to run continuity. Prefer a composite blend that tends to mitigate consistent with predictability smaller scale system variances. Applied WPC based manual edits are intended to ensure sufficient maritime surface low pressure center depths and wind speeds muted by the blending process and forecast spread to again be consistent with overall quite favorable upper support signals. ...Weather/Hazard Highlights... The Gulf/northern Pacific low will draw Pacific moisture into southern parts of the state for late week, with enhanced precipitation totals looking most likely for Southeast Alaska easing over the weekend. Showers will linger there in a drying trend with ridging at the surface and aloft coming in early next week. Some light to moderate precipitation is also possible for Southcentral Alaska. By the weekend, another low/frontal system moving across the Bering Sea should spread rain and perhaps some gusty winds to the Aleutians and the Alaska Peninsula. This moisture is looking more likely to bring precipitation chances to the western part of the mainland by Sunday-Monday. Some showers may be scattered across much of the mainland by early next week as well. Guidance does not show very heavy amounts, but it is worth monitoring that the increasingly deep feed of moisture and Gulf system energies expected to forced northward in a channeled conduit into the mainland between the Bering system and the building downstream upper ridge may prove more efficient/slow to progress producers. The mean low dominating the northern Pacific late this week should lead to below normal highs across the southern coast of Alaska, but lows should be closer to or tending a bit above normal. However, much of Southeast Alaska could see increasing temperatures early next week as part of the Canadian upper ridge builds in. Farther north should see a mix of above and below average temperatures with not too considerable anomalies through this week. But temperatures may trend above normal for the Interior and North Slope by next week, which would serve to help rivers break up and possibly increase the threat of flooding. It will take additional time to say how much above normal temperatures could get as it will depend on the positioning and strength of the ridge. Schichtel Hazards: - Heavy precipitation across Southeast Alaska, Fri, May 12. 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