5.18 Late-AM Zones Update: More Heat and Isolated T-Storms Possible into Friday

Good morning! More summer-like weather continues today. It will be hotter in many areas, than on Wednesday. 850mb temperatures around 17░C to 19C with southwest winds will support highs in the lower and middle 90s, away from the coast today. More record highs will likely be set again across the region.  Humidity will be higher, but not oppressive. Sea-breezes will keep coastal areas, such as Long Island and NJ shore cooler again today. But even these areas temperatures may reach the 80s, with a stronger southwest flow today.

A few isolated showers or thunderstorms are possible is afternoon and evening as instability builds along pre-frontal or thermal trough, especially northwest of NYC. But some stout mid-level capping and limited low-level moisture, will likely keep the much of the region dry. Later tonight, it will be partly cloudy, warm and humid. Overnight lows will be in the 60s in the suburbs. But temperatures will not fall out of the 70s again over NYC other urban areas.

By Friday a shortwave trough moving out the Great Lakes will flatten the ridge over the Northeast. But it will remain very warm and a little humid, until a cold front arrives during the afternoon and evening hours. More west-northwest downsloping winds during the afternoon, will help temperatures rise back at least back into the mid-upper 80s in many areas. Including along the coast, where sea-breezes are less likely to develop tomorrow afternoon. There is chance that some spots, especially southwest of NYC, could hit 90 degrees again.

Not too much activity is expected with the cold front. More deep-layered shear and upper-level forcing will passing be north of the region. Low-level moisture will also be limited. But with some instability, a few isolated scattered showers and thunderstorms are still possible during afternoon and early evening hours. The main threats from any thunderstorms are some briefly heavy downpours and frequent, cloud to ground lightning.  Some steep low-level and mid-level lapse rates isolated strong, gusty winds and some hail can’t be ruled out. However, it’s also possible that some stout mid-level capping with an EML over region, keeps most of the region dry. Overall no organized severe weather or flooding hazards are currently anticipated. But we will keep monitoring for any significant changes.

After the cold front passing it will turn cooler and much less humid tomorrow night. High pressure from Southeast Canada builds into the region this weekend. This will provide more pleasant, dry weather for most of the weekend. Some sunshine is expected each day with highs in generally in the upper 60s to lower 70s over the region. Onshore winds could keep some coastal areas a little cooler. Saturday night will partly cloudy and cool with low temperatures upper 40s to middle 50s over the region.

Then another storm system associated with upper-level trough over the Great Lakes will likely impact the region. Some showers are possible as warm front lifts northward through region later Sunday night.  Then more numerous showers and thunderstorms are possible by Monday cold front approaches the region. More dynamics and moisture with this front may support more heavy rainfall over the region. But poor frontal timing and some cloud cover, may mitigate instability for more organized severe weather. Temperatures may warm back well into the 70s, depending on how much sunshine there is Monday.

As we’ve been discussining this week, some more unsettled weather is likely for later next week and perhaps into Memorial Day weekend, with high-latitude blocking and west-coast ridging support more troughiness over the Eastern US. More prolonged heat and dry weather is not anticipated. However, confidence this far out, is very low on more forecast details each day. So stay tuned more zone forecast and other updates, as we get closer.