Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 722 PM EDT Thu Jul 25 2024 Valid 12Z Mon Jul 29 2024 - 12Z Fri Aug 02 2024 ...Cooler and rainy pattern across much of Alaska with locally heavy rain totals possible... ...Overview... A round of upper troughing tracking from the Bering Sea early Monday southeastward across the Mainland through midweek and troughing lingering from the North Slope to Southeast Alaska later week will be the primary driver of sensible weather next week. The mean troughing pattern will promote cooler than average weather and rain chances over the state, with some locally heavy rain. Meanwhile an upper high in the northern Pacific could build ridging atop the Aleutians next week. ...Guidance Evaluation/Preferences... As the period begins Monday, an initial upper trough will be exiting northeast Alaska with a brief bout of ridging atop central parts of the Mainland. This ridge should be short-lived, however, as another trough sweeps across the Bering Sea into the western part of the state early in the week. This second trough is on the southern side of/anchored by an upper low that will spin for multiple days just north of eastern Siberia in the Arctic. Most model guidance is in reasonably good agreement with these features through the first part of the period. The 12Z GFS was a bit of an outlier as a faster solution with the embedded upper low moving into the Gulf of Alaska around Tuesday, thus spreading precipitation into southeastern parts of the state more quickly than other guidance. The 12Z ECMWF/CMC/UKMET showed better clustering. The main trough should push farther east and south across Alaska around midweek, but models show increasing spread with its form and placement. There is still a chance that a 500mb low could temporarily close off as the energy pushes into the vicinity of Prince William Sound and the Gulf of Alaska on the southern side of the trough, but models vary with how long a closed low would last and how fast the energy gets shunted eastward. By early Thursday, the operational EC and GFS moved the low/trough/energy quickly eastward, but the AI/ML AIFS (ECMWF-based) and the GFS Graphcast as well as the 12Z CMC hold it back. A slower solution is probably more likely, and started to heavily lean toward the ensemble means that were perhaps weaker with the trough but have it farther west/slower. Models are at least agreeable with an upper high south of the Aleutians building a ridge northward for mid-late week, but there is potential for additional troughing to track across the Bering Strait into at least northern parts of the domain by late week. This will have to be resolved in future forecasts. Overall, the WPC forecast used a multi-model deterministic blend favoring the 12Z ECMWF early, with quickly increasing proportions of the GEFS and EC ensemble means as the period progressed to over half by Days 7-8 amid the increasing spread. ...Weather/Hazards Highlights... Rain chances will be widespread across the Mainland early next week near/ahead of an upper trough and surface low pressure system. The rain will push eastward across the state with time, spreading from the western Mainland into Monday, into Southcentral Alaska/central Mainland Monday-Tuesday, and into Southeast Alaska Tuesday-Wednesday. The heaviest rainfall totals are likely across portions of the Alaska Range considering the upslope enhancement on Monday-Monday night, and then into coastal areas from around Prince William Sound to Yakutat Tuesday-Tuesday night. The highest elevations of the Alaska Range may see some snow with the precipitation activity, with snow also possible in higher elevations of the Brooks Range. Behind the low system, some locally enhanced west/northwest winds are possible in favored areas near Bristol Bay and on either side of Kodiak Island likely peaking Tuesday, but not strong enough to be considered hazards-worthy. Another round of precipitation may reach western Alaska perhaps into the central Mainland into late week, with more uncertainty. Cooler than normal temperatures will prevail for Alaska next week. High temperatures are forecast to be 10-25F below average, with actual highs generally in the 50s and 60s. Lows are forecast to be less anomalous at 5-15F below normal. Temperatures may moderate to a little closer to normal, but still generally below, by later next week. The upside to the rain and cooler temperatures will hopefully be the end of fire season for most of the state. 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