Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 656 PM EST Sat Jan 04 2025 Valid 12Z Wed Jan 08 2025 - 12Z Sun Jan 12 2025 ...Continued stormy pattern this coming week through next weekend with heavy precipitation and strong wind threats along the southern mainland coast... ...Overview... Today's guidance maintains the theme in the mean of a persistent Bering Sea into Pacific upper trough and downstream ridge, with flow between the two features directing a series of strong storm systems that will focus heavy precipitation along the southern coast and produce strong winds over the Northeast Pacific to the southern coast. There should be a transition in storm track though, from south to north over the east-central Pacific through Thursday or so, followed by a northern Pacific to around the Alaska Peninsula path. The current extended forecast period is only a part of what looks to be an anomalously wet/snowy pattern from now to about a week and a half out in time. Expect above to well above normal temperatures over a majority of the state during the period, aside from some below normal readings through midweek over portions of the North Slope and along the western coast toward the end of this coming week and into the weekend. ...Guidance Evaluation and Preferences... A 12Z operational model composite (slightly more GFS/ECMWF weight relative to the CMC/UKMET) represented latest consensus well early in the period when the primary focus is on strongly developing low pressure that reaches a position to the south or southeast of Kodiak Island by early Thursday. As this system continues rapidly northward and weakens while North Pacific low pressure comes into the picture late week into the first part of the weekend, the GFS/UKMET begin to compare less favorably to most other guidance. Thus the forecast preferences shifts more to the 12Z ECMWF/CMC and ensemble mean (12Z GEFS/CMCens and 00Z ECens) toward the end of the week. However on Saturday the CMC strays to the slow side with the leading North Pacific system and then does not depict a potentially stronger second storm right behind it. Thus day 8 Sunday reflects 30 percent input of the 12Z ECMWF with the means comprising the remainder. Ensemble means and machine learning (ML) models have been very consistent overall in their depiction of the strong storm tracking into the Gulf of Alaska late this week (with a gradual deepening trend), while operational models have shown some typical variability in strength and track (now reaching a depth in the 950s to low 960s mb as of early Thursday). Some recent GFS runs strayed farther from consensus with a suspiciously west track, but now the main question is that the model could be a tad slow by early Friday. Remaining dynamical/ML guidance shows a little spread, with a portion of the envelope nudging a bit faster in a nod to recent ECMWF runs. The guidance average has maintained good continuity for the system expected to track a little south of the Aleutians Thursday-Friday. By Friday some spread develops for system timing, with greater divergence into Saturday. ML models diverge as well, but generally favor a progressive scenario with the system reaching a position somewhere between the southeastern Bering Sea and the Kenai Peninsula by early Saturday. The 12Z ECMWF/CMC and their ensemble means match this idea in principle, while the 12Z GFS/UKMET strayed to the slow side with the parent low. The 18Z GFS has trended somewhat closer to the preferred ECMWF/ensemble cluster that reaches near Bristol Bay by early Saturday before weakening. Thus far most solutions show another North Pacific storm coming in about a day behind the preceding one, reaching somewhere near the Alaska Peninsula by early Sunday. The ensemble means are remarkably well clustered at the moment, albeit showing a gradual eastward trend over the past couple days. Nearly all 00Z through 12Z ML models show upper dynamics becoming negatively tilted and pinching off a closed low, yielding a strong surface low averaging around 960 mb or even a little deeper by early Sunday. The ML model track is a little south of the Alaska Peninsula at that time. The 12Z ECMWF fits best within the ensemble mean/ML model theme (including the ECMWF's depth in the 950s mb), while GFS runs have tended to be more diffuse with their surface low(s). The 12Z CMC strays increasingly slow with the overall low sequence. Around 970 mb seems to be a good starting point for depth given the combination of guidance signals but typical uncertainty that far out in time. ...Weather/Hazards Highlights... Expect a continuation of long-term heavy precipitation threats along the southern coast including the Panhandle, with periods of strong winds over the northeastern Pacific/Gulf of Alaska toward the southern coast as well. The last and potentially strongest in a series of south-to-north Pacific storms will likely track into the Gulf of Alaska by Thursday-Thursday night, producing one period of focused rainfall and higher elevation/inland snow. Then a couple North Pacific systems that may track toward the vicinity of the Alaska Peninsula by the weekend should continue the sequence of atmospheric river events aimed at the southern coast. Guidance continues to show significant five-day QPF totals (early Wednesday to early Monday) from the Southcentral coast into the Panhandle, with localized maxima of at least 10-15 inches of liquid possible. Including the short term and going a little beyond the current extended forecast window, forecast totals continue to be particularly anomalous over the southeastern part of Southcentral. Elsewhere, much more modest amounts of moisture may occasionally spread areas of light snow farther north across the mainland at times, with a southwest-northeast frontal boundary providing some focus, while mean southerly/southwesterly flow aloft could support periods of brisk to strong winds to the lee of the Alaska Range. Areas from the eastern Aleutians into the Alaska Peninsula/southwestern mainland may see increasing precipitation and winds with the two systems forecast to affect the region by Friday into the weekend. Above to well above normal temperatures will prevail over most of the state during the period. The warmest anomalies should be most widespread around Wednesday-Thursday and then become more confined to the eastern half or third of the state by Friday-Sunday. Parts of the North Slope may see some below normal readings through Wednesday or so, and some locations along the western coast may trend a little below normal by the end of the week into the weekend. Rausch 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