Solid disco in LWX AFD:
Thereafter, forecast uncertainty begins to increase as we move into Thursday and Friday. On Wednesday, a strong cyclone in the Gulf of Alaska will build a downstream ridge, which is modeled to progress
eastward into the CONUS with an appreciable forward speed. As this ridge builds downstream, it will perturb the downstream waveguide, which has been relatively stagnant over the past week. In response to
the ridgebuilding, troughing will dig into the Desert Southwest/Four Corners region Wednesday night, and then progress eastward onto the
Southern Plains Thursday into Thursday night. Meanwhile, the upper ridge will progress eastward and interact with a downstream upper low over Hudson Bay. Exactly how this complex process plays out will
have a major impact on our forecast. The 00z Euro and 00z Canadian have the ridge progress eastward at a higher forward speed than the
trough within the southern stream. As a result, the ridge cuts overtop of the shortwave trough as it closes off, effectively keeping it suppressed to the south as it progresses eastward. In
these scenarios, the potent upper level shortwave progresses directly overhead, with an intense area of low pressure at the surface progressing to our south. The 00z GFS on the other hand,
doesn`t have the upper ridge build overtop the southern end of the trough, and maintains one coherent north-south oriented wave from Canada down into the Southern Plains. This scenario allows the southern stream shortwave to amplify further and gain more latitude as it progresses toward the east. This scenario results in a very intense area of low pressure tracking off to our north and west.
Such a scenario would place us on the warm side of the system, and would result in temperatures climbing into the 60s or 70s, along with heavy rainfall, and potentially even severe thunderstorms. The scenario depicted by the Euro and Canadian on the other hand would produce a significant amount of snowfall across the area, with temperatures holding in the 30s.
In both of these scenarios, Thursday would have relatively quiet weather, with northwest winds, and potentially a few showers. The main forecast uncertainty on Thursday would lie in the high temperatures forecast. Ensemble guidance has highs on Thursday ranging from the 40s to the 70s. The higher impact weather, whether
it be in the form of heavy rain and thunderstorms, or snow, would move in on Friday and last into Friday night.
With such a highly uncertain and complex forecast, it`s important to think probabilistically. The deterministic models described above span the phase space of potential outcomes outlined in the ensemble guidance. The system being suppressed far to our south and completely missing us (as some ensemble members showed yesterday) appears to be off the table. The two main scenarios now entail the low passing to our north and west, and us ending up on the warm side of the system, and then the low passing to our south, and us ending up with wintry precipitation on the cool side of the system.
In terms of temperatures, these solutions range from highs in the 70s, to highs in the 30s. As a result, our deterministic forecast (that you see in the point and click forecast on our website) is a middle of the road solution and calls for highs in the 40s/50s, and rain across much of the area (since you can`t have snow with temperatures in the 50s). Nonetheless, the chance for snow is a very real one.
Digging a bit into the probabilistic phase space, and individual ensembles, both the EPS and GEPS trended colder and snowier with the 00z model cycle, especially across the northern half of the forecast area. The EPS and GEPS now shows a greater than 50 percent chance for accumulating snow across nearly all of the forecast area, as well as a greater than 50 percent chance for more than a half foot of snow across far northwestern portions of the forecast area (Potomac Highlands and western Maryland). The GEFS on the other hand stand in stark contrast to the EPS and GEFS. The GEFS actually trended warmer, and less snowy, with very low probabilities for any snow, let alone significant snow. Oftentimes, the GEFS tends to follow trends in the GFS very closely, so this trend is somewhat unsurprising. In all of the respective ensembles, probabilities for snow are greater further off toward the north and west, and lesser as you progress further off toward the south and east. At the moment, this is a very challenging and highly uncertain forecast for
Friday. We`ll continue to monitor trends and adjust our forecast accordingly as we progress through the week.
