Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 641 PM EDT Mon Jul 06 2020 Valid 12Z Fri Jul 10 2020 - 12Z Tue Jul 14 2020 ...Overview and Guidance/Predictability Assessment... The large scale pattern appears rather blocky and slow to evolve, aside from parts of the Northeast Pacific during the first half of the period when an initial wave well southwest of the Panhandle will weaken as it tracks near/south of Haida Gwaii. The best consensus of guidance shows an elongated trough aloft with a possible embedded upper low becoming established over the northern mainland in response to flow around an Arctic upper high. Farther south there will be a system over the North Pacific late this week into at least the weekend. An associated front may eventually lift into the Aleutians as the eastern side of the system is pulled eastward. This system could linger into next Mon-Tue in weakened form or be replaced by another wave approaching from the western Pacific. As is typically the case in such patterns there is considerable spread for the specifics of energy that reaches the mainland from the northeast. The 12Z CMC (bringing some mainland energy into a deep Bering closed low) and 12Z GFS (showing a second deep upper low arriving during the latter half of the period, as does the CMC) are the two least confident solutions based on the full array of models/ensembles. The 12Z ECMWF shows this second low but at least is slower than the 12Z GFS/CMC. Historically in situations of retrograding energy the deepest and/or fastest solutions tend not to verify that well. Details are murky with respect to how North Pacific low pressure may elongate/split apart, as well as possibly interact with upstream energy. Toward the end of the period the 12Z GFS is a fast extreme with a stronger system whose influence reaches the Aleutians by next Tue in that model. Overall a model-ensemble approach best resolves the various question marks that exist for the North Pacific evolution. Based the latest array of guidance through the 12Z cycle (and 00Z for the ECMWF mean) today's forecast started with a mostly 12Z operational model blend early in the period. Then the blend eliminated the 12Z CMC and transitioned GFS input from the 12Z run to the 06Z version, while increasing GEFS/ECMWF mean weight to a total 40-50 percent by days 7-8 Mon-Tue. The ECMWF component used some of both the 12Z run and prior 00Z run due to different mainland and North Pacific details which may or may not be better in the newer run. ...Weather/Hazard Highlights... The elongated upper trough settling over the mainland will lead to fairly broad coverage of below normal temperatures (especially daytime highs) during the period. Expect the greatest negative anomalies to be over the North Slope and the southeast/Panhandle. The best potential for above normal temperatures will be over the extreme western mainland near the Bering coast. Highest rainfall totals from late this week into the first half of next week should be over the southern mainland, near the Alaska Range where daytime heating along with cooling temperatures aloft should promote multiple episodes of rain. The Panhandle may see some precipitation from moisture on the northeastern periphery of a Northeast Pacific system likely to track toward Haida Gwaii late this week/weekend. Meanwhile one or more surface systems/fronts over the North Pacific may extend far enough north to bring some rainfall into the Aleutians. Rausch 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 Hazards: No significant hazards are expected over Alaska during this forecast period. 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