... A Mesoscale Convective System may impact parts of our region through early Saturday morning. Multiple fronts will impact our region through Tuesday. High pressure returns during the middle to later parts of next week.
NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 9:15 PM UPDATE: Currently across our region, only seeing some mid-upper level clouds. More menacing are the two areas of developing convection nearby. The first, closest to home, is some weaker storms to our north over east-central PA, moving due east. Some cells are starting to build further and further south in this line, and could impact western portion of our forecast in the next couple of hours. The most pressing concern is the developing MCS over the Ohio Valley. Several severe thunderstorms are present within this line. We will be watching both of these areas carefully over the coming hours.
The recent 00z run of the HRRR has started to get a better handle on the current state of convection across the Ohio Valley. With the MCS moving into a much less favorable environment, tend to believe it fizzles out as it moves out of Ohio into KY/WV. All in all though, this activity should all stay well to our west. The only thing that could happen to impact our area is that the outflow from this MCS could set off another area of convection over eastern OH (as depicted in the 21z RAP). That could then make a run at our region late overnight tonight between midnight and 4 AM or so. So, have adjusted POPs/Wx forecasts to account for current observations and to account for the most accurate guidance at the moment. All being said though, the thought is maintained that a deep layer of westerly winds will likely limit the threat for showers and thunderstorm further east of the Allegheny front. If there is any threat for severe storms, and I think that is low at this point, it should end at the Allegheny Front. This thought is still maintained in the most recent SPC severe outlook as well, keeping that area in the marginal risk category, with damaging winds the primary threat.
Notably though, overnight lows will be very mild in the mid to upper 60s to lower 70s across the region, which is about 10 degrees above normal.
SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... PREVIOUS DISCUSSION: An upper level trough will drop down into the northeast US on Saturday. A surface low associated with the upper trough will pass through the upper parts of the NE US with its corresponding front dropping into parts of NY. Our region will remain on the warm side of the front which will allow for temperatures to trend up into the mid to upper 90s on Saturday.
The threat for thunderstorms on Saturday have decreased over the past few days. The upper trough has trended further northward while an upper jet moving through PA remains disconnected from a secondary shortwave dropping into our region Saturday afternoon. The combination of CAPE values hovering around 2000-3000 across the MD/PA border along with modest shear and a shortwave moving through Sat afternoon may lead to areas of strong thunderstorms or a localized convective line. CAMS overall have trended downward with the thunderstorm coverage and I believe the main threat area will be focused along the MD/PA border which will be near the best shear. The threat for showers and thunderstorms should start to taper off after sundown with only isolated showers or storms possible into Sunday morning. Overnight lows will be mild once again in the mid to upper 60s to lower 70s.
Sunday will likely start off dry but as diurnal heating begins, temperatures will rise up into upper 90s. CAPE values will likely rise above 2000 once again, but the upper jet is expected to weakened leading to much lower shear values throughout the layer. The lack of good forcing and shear will limit the widespread thunderstorm threat but the combination of hot and humid conditions along with decent lapse rates will allow for pop up showers and thunderstorms. As CAPE values will be close to 3000 on Sunday, I can't rule out a localized strong thunderstorm threat due to pulse storms. The threat for thunderstorms should taper off after diurnal heating shuts off with only a small chance for storms Sunday evening mainly in the southern parts of our region due to an approaching low.
LONG TERM /MONDAY THROUGH FRIDAY/... Generally good agreement amongst the latest guidance suite in regards to the long term period. Confidence is increasing for the remnants of a tropical system originating in the Gulf of Mexico to track just to our south and east, away from the CWA on Monday. If this trend remains the same over the next few model run cycles, then don't foresee any hazardous impacts to the region. If the track shifts slightly more north and west, then the potential for heavy rainfall across the region would be the main hazard. However, the first scenario seems more likely at this point in time, given the advancement of a cold front which is slated to cross the region late Tuesday into Wednesday.
Hot and humid conditions continue on Monday and Tuesday with temps in the low to mid 90s for most and dewpoints in the upper 60s to low 70s. Even if the remnant low passes offshore, the unstable airmass would still poise the chance for scattered afternoon showers and thunderstorms Monday.
However, the bigger threat is Tuesday afternoon and evening as the front advances further south. A much cooler and drier airmass is present on the backside of the boundary. If the timing of the front remains the same, given the drastic differences in air masses, ample moisture, instability, 0-6km shear, and lift, would signal a potential severe weather event across the region. Flooding or flash flooding could also become an issue given high PWs.
Cooler and drier conditions are expected for the middle and later portions of next week as high pressure regains control of the region. However, heat and humidity may begin to build back into the region once again towards next weekend.