June 24, 2013: Stormy Pattern Begins Today

Forecast Highlights:

As a hot and humid air mass spread into the region, temperatures peaked in the upper 80s to mid 90s away from the coast, which along with humid conditions resulted in heat index values reaching the mid to upper 90s. Scattered storms formed across parts of the region today, only the first day in what is likely to be a long stretch of stormy conditions as a frontal system stalls over the East Coast, resulting in a risk of storms for most days into the first week of July.

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Tonight - Thursday: Heat, Humidity Continue

Scattered storms affected the region earlier this afternoon and evening; most of the storms focused over New England, while cloud cover associated with a severe thunderstorm cell over central NJ lowered instability in NYC; most of the area stayed dry, although an isolated strong storm affected Queens and Nassau county early in the afternoon, with another strong cell in Orange, N Westchester counties in NY and interior SW CT in the evening hours.

Partly sunny skies are expected to continue for Tuesday and Wednesday with a risk of scattered afternoon/evening storms both days, especially away from the coast. The highest risk of severe weather will remain north of the area, although storms could still be strong with gusty winds and heavy rainfall. High temperatures are expected to reach the mid to upper 80s near the coast and the upper 80s to mid 90s for the rest of the area, with heat index values again reaching the mid to upper 90s. By Thursday, as a frontal system approaches the region, more cloud cover is expected to spread in with slightly cooler temperatures, in the mid 80s to low 90s, and a slightly higher risk of evening and overnight storms, especially west of NYC.


Friday - Early July: Stormy Pattern Sets Up

The pattern becomes increasingly active starting during the late week as the flow becomes more amplified over North America. Strong ridging will persist in the western Atlantic, remaining nearly stationary for the next 7-10 days, while a trough becomes amplified over the eastern half of the US with the trough axis likely west of the Appalachians. In between the eastern US troughing and a cutoff low off the W US coast, strong ridging will amplify and become stationary over the western US with 500mb heights up to 597+dm resulting in extreme heat, possibly record breaking. Overall, this setup of western US/western Atlantic ridging and eastern-central US troughing will persist through the next 7-10 days, if not beyond, which along with a stalled front over the eastern US and a southerly flow bringing tropical moisture up the coast, will result in a stormy time period for the region with most, if not all days featuring a risk of scattered rain/storms and heavy rain through the end of the month into the first week of July. If the latest model guidance verifies, parts of the region may end up with several inches of rain by the time this pattern ends in early July.

The main uncertainty at this time is regarding where the stalled frontal system sets up; some of the earlier GFS runs have been more progressive, pushing the front further east and shortening the duration of the wet time period, but has since trended towards the slower ECM and CMC with keeping a risk of rain every day through the end of the run. At this time, I am siding towards the slower ECM with keeping a risk of scattered storms through the beginning of July; with this expected setup, not every location in the area will have rain every day, and it will not rain throughout the entire day, but most, if not all days are likely to have at least a risk of scattered rain and thunderstorms, which could be heavy considering high precipitable water values; at this time, a particularly higher risk of widespread storms exists for Friday and the weekend. With this wetter pattern, Central Park, which has seen little rain since the three consecutive heavy rain events in early June and is currently standing at 9.81" for the monthly rain total, is likely to break the record for the wettest June on record, which is 10.27" set in 2003. Temperatures are expected to cool down compared to the first half of this week, likely ending up around average, generally in the low to mid 80s on most days. Stay tuned for more information on this pattern over the next few days.