... High pressure off to our south and east will continue to shift further offshore as a cold front approaches from the west. The front will cross the region overnight into Friday, followed by an additional weaker front on Friday. Dry and seasonable temperatures are slated for the weekend. However our next system may arrive by early next week.
NEAR TERM /THROUGH TONIGHT/... 9:45 AM UPDATE: A potent little cutoff upper-low is visible on the water vapor satellite imagery this morning over WI/IL. Surface low pressure is located over northern MI as well, with a cold front extending southward through IN, western KY and western TN. As these features move eastward, we will start to see the influence of the approaching cold front, which is outlined in the previous discussion below.
PREVIOUS DISCUSSION: While high pressure remains off to our south and east. The influence of the high will still keep conditions status quo for much of the day. Light and variable winds will become more southerly as daytime heating ensues. As a result, highs today will be the warmest of the week with many locations reaching the mid to upper 70s with cooler conditions across the mountains.
While skies are expected to remain mostly clear, clouds will gradually increase from the west later this afternoon as the front inches closer to our western borders. Ahead of the trailing cold front, some showers and storms are expected to develop over the Ohio Valley, approaching the Appalachians by late afternoon. While there will be some shear present, instability remains quite limited with only 100-200 J/Kg of CAPE over far western MD. More so, guidance has been consistent in regards to showers developing around sunset. Given the loss of daytime heating, don't anticipate much in terms of convection. Therefore any storms will be in a weakening state as they reach our forecast area. In fact, with much of the forcing to our north and a developing downslope component, most of the shower activity will likely fall apart as the front crosses the mountains. However, a few showers may survive to the Blue Ridge and across northern Maryland during the evening/early night. The cold front will push through overnight, and a secondary shortwave from North Carolina could produce a shower or two across southern Maryland overnight through Friday morning.
SHORT TERM /FRIDAY/... Closed upper level low over the Great Lakes will continue to retrograde in place Friday. As a result, a second surge of shortwave advection will move eastward across the region. Any precip chances seem minimal on Friday, with the exception of some upslope showers across the Alleghenies. The low will slowly shift northward on Saturday as high pressure returns for the weekend.
LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... To finish out the upcoming weekend, a broad negative height anomaly will remain over southeastern Canada with cyclonic flow extending southward into the Mid-Atlantic and New England. This region of lower heights is forecast to shift eastward through the day with brief height rises in the wake. At the surface, an initial ridge of high pressure will ensure a chilly start to Sunday before the anticyclone moves offshore. Seasonable conditions can be expected with highs in the mid/upper 60s along I-81 and east of the Blue Ridge. Clouds are likely to increase in coverage later in the day as southwesterly warm advection ensues. As the associated warm front approaches from the west, some showers may overspread the region, particularly toward the evening hours and into the night. The increased cloud cover and showers will raise nighttime temperatures to around 5 to 10 degrees above average.
Somewhat innocuous troughing ejecting out of the Central Plains and Middle Mississippi Valley on Sunday evolves into a more potent system across the Great Lakes/Ohio Valley by Monday. Its position is a bit variable between deterministic models, but the solution is becoming more consistent. The associated warm frontal precipitation with this cyclone is likely to migrate north toward the Mason-Dixon Line on Monday. Eventually the attendant cold front sweeps through the I-95 corridor late Monday/early Tuesday which would bring additional showers to the region. The ultimate fate of this system is rather nebulous given the variety of solutions shown by ensembles. Ensemble spaghetti plots depict a host of closed height contours indicative of a cut-off upper low solution. Where this feature closes off and for how long will provide details on the forecast through at least mid-week. There are some very amped up ensemble members so this all bears watching. For now, expect continued shower chances and seasonable temperatures. The difference between the 10th and 90th percentile members of the NBM is roughly 20 degrees. This shows some of the volatility of next week's forecast.