Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 PM EDT Thu Jul 08 2021 Valid 12Z Mon Jul 12 2021 - 12Z Fri Jul 16 2021 ...Some precipitation likely to linger over the southern coast and Panhandle into next week... ...Overview... Guidance continues to show a fairly blocky pattern across the Bering Sea, Mainland Alaska, and the Gulf/Northeast Pacific. A slow-moving upper low should track from southeast or east of Kodiak Island toward the Panhandle through the week while an upper ridge over the northern/east-central Bering Sea extends into portions of the mainland. Initial weak energy farther west over the Bering will either go around the western side of the upper ridge or possibly combine with North Pacific/Aleutians energy that is more likely to flow to the south of the ridge. Meanwhile the best consensus and continuity show fast and low-amplitude flow aloft across the Arctic, tending to evolve toward a broad trough whose axis reaches the Canadian Archipelago later next week. This flow will likely support a mean frontal boundary that should be near the northern coast early in the week and then push southward into the north-central mainland by mid-late week. ...Guidance/Predictability Evaluation... Various aspects of flow over the Arctic and the blocky pattern to the south are proving to be challenging to resolve in the models. In what has become a multi-day oscillating theme, trends over the past 24 hours have led to a farther west position for the Gulf low. The GFS adjustment is particularly dramatic as the 12Z/07 run strayed to the fast side while latest runs are on the western side of the spread. The GEFS mean does offer some support for the western idea though. The ridging that extends into the mainland at least favors slow movement, regardless of exactly how far westward it starts out. A composite of 12Z model solutions seems best at this time--reflecting the westward adjustment versus yesterday while avoiding the more extreme sides of the envelope given multi-day inconsistency. Farther west, latest trends have been toward a farther south track for a weak wave that reaches the Aleutians early-mid week and then likely dissipates. Meanwhile the models have been quite varied among each other and in consecutive runs for Arctic flow details. 00Z-06Z models had generally suggested more amplified upper troughing that would push the northern mainland cold front farther south than continuity, but new runs have reverted back to higher heights. Averaging the varied solutions of recent ECMWF runs and other 12Z guidance along with the ensemble means yielded a forecast close to continuity for the front that drops into the northern mainland, along with moderate-strength high pressure to the north. Finally, models/means are showing a decent signal for upper dynamics and low pressure to consolidate over the western Aleutians/Bering toward the end of the week. A model/mean blend provided a good starting point for this potential system. Today's forecast blend started with various components of the 12Z GFS/ECMWF/CMC/UKMET early in the period and then transitioned to half models (00Z-12Z ECMWF and 12Z GFS/CMC) and half means (12Z GEFS/00Z ECens) by day 7 Friday. Offsetting differences among the models in the Arctic helped to guide the forecast even more toward the means than the explicit weight over that region. ...Weather/Threats Highlights... Today's westward adjustment for the Gulf low leads to longer persistence of precipitation over areas from near Kodiak Island across the southern coast and into portions of the Panhandle. There could be some localized 24-hour totals of at least one inch in the early part of the week. However magnitude/location will be very sensitive to the exact position of the low at any particular time and so far the model spread and inconsistency do not provide much confidence in refining important specifics. Meaningful moisture could extend somewhat farther into Southcentral as well. Elsewhere, some rainfall may accompany the front that should drop into the northern half of the mainland by mid-late week while a weak wave should spread light-moderate rainfall across the Aleutians mostly during the first half of the week. Late in the week an area of rain and somewhat stronger winds may extend ahead of a system reaching over or near the western Bering Sea. Clouds and precipitation will keep many areas along the southern coast and Panhandle below normal for temperatures during the period. Cool air behind the front dropping into the northern mainland will drop readings over the North Slope to below normal levels by Wednesday-Friday. In-between, expect highs to trend toward modestly above normal during the first half of the week and then settle back to within a few degrees on either side of normal, while lows tend to remain a little more above normal. Rausch Hazards: - Heavy rain across portions of southern mainland Alaska, Sun, Jul 11. Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards 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