5.26 Late-AM Zones Update: Some Unsettled Weather for Memorial Day Weekend

Happy Friday! Low pressure that brought more rain with some thunderstorms overnight, is now moving east of New England late this morning. Clouds and showers are clearing, with drier, downsloping northwest winds, behind this system. This will support temperatures to rise into the lower to middle 70s across much the region. However, with daytime heating the atmosphere will become more unstable under a cold-pool aloft. So a few scattered showers and thunderstorms could pop up across the region this afternoon and early evening.

Then skies will become more clear overnight with temperatures dropping into the upper 40s over Interior to middle 50s over urban and coastal areas. Some unsettled weather will continue through this Memorial Day weekend. But no washouts are still expected. For Saturday, weak high pressure will be over region for much of the day. This will support more sunshine during the morning hours. Then some clouds will likely begin increasing during the afternoon, as a mid-level disturbance (shortwave) approaches from the northwest. Instability or moisture will be limited with this disturbance. But a few isolated or scattered showers are still possible by late in the afternoon or evening, especially just west and south of NYC.

NAM showing mid-level shortwave with some scattered showers moving through tomorrow afternoon.

NAM showing mid-level shortwave with some scattered showers approach the region tomorrow afternoon

High temperatures will likely be in the lower to middle 70s, with enough sunshine. But if clouds increase sooner some areas may struggle to rise out of the 60s. Some weak sea-breezes during the afternoon will likely keep areas closer to shore a little cooler as well. Then skies will begin clearing out again later Saturday night, as more upper-level ridging builds into the the region. This will allow for to temperatures drop again into the upper 40s to middle 50s, across the region.

A mixture of sunshine and clouds is now likely for most of the day on Sunday, as stronger upper-level ridge will be moving over the region. It will be a decent day overall. But surface high pressure off New England will cause more onshore winds out of the southeast direction. High temperatures are likely to range from the mid-upper 60s closer to coast to lower to middle 70s further inland, with less marine influence farther from the shore.

Then a large upper-level trough from the Northern Plains will cause the ridge breakdown Sunday night and Memorial Day Monday. At the surface, low pressure over the Great Lakes will push a warm front into region more clouds and showers likely returning by Sunday evening or overnight and then continuing into Monday morning. Some instability and moisture will be increasing over region with precipitable water values over 1.00″ again. So some thunderstorms with heavy rainfall area also possible. But no organized severe weather is an anticipated, with best upper-level dynamics passing to northwest of the region and the overnight/early morning timing inhibiting more surface-based instability.

ECMWF model with some showers and possible thunderstorms ahead of warm front Sunday night

ECMWF model with some showers and possible thunderstorms ahead of warm front Sunday night

Afterwards, there is more uncertainty on far north the warm front will push through region and on the timing of the next cold front coming through the region, from low pressure over Great Lakes as well. There are model differences in handling of another wave of low pressure developing along the Mid-Atlantic coast later Monday. If this wave is stronger, it may slow the progress of these fronts through region. This may keep the region cooler with more clouds, showers or an onshore flow.

On the other hand if this wave of low pressure remains very weak, these fronts will likely move through region faster, with more clearing and warmer temperatures at least in the 70s by Memorial Day afternoon. At this time, we are leaning towards this solution for Memorial Day, with the flow a little faster along the East Coast. But this forecast will likely be fined tuned somewhat, as we move through the holiday weekend.

Overall with ridging out West and some residual high-latitude blocking, an unsettled weather pattern will continue into next week. The pattern will support multiple disturbances rounding the base of a large upper-level trough over the Great Lakes to Southeast Canada. More convective threats are possible and temperatures each day will depend on the amount of the clouds and rainfall. Stay tuned for another zone forecast update by this evening, on the weather into next week!