Hot & Humid, with Severe T-Storms for Parts of the Northeast Today

Good morning! Happy Tuesday! Today will be hot and humid for much of the Northeast, as a Bermuda-type high pressure sets up off over the Atlantic. Some areas of patchy fog will burn off early this morning. Then partly to mostly sunny skies with southwest winds are expected for the rest of the day. Temperatures will rise in the upper 80s to middle 90s this afternoon. Temperatures will be little cooler with sea-breezes closer to the shores. High humidity with some dewpoints in the low to mid 70s, will support heat index values in the upper 90s to lower 100s. Particularly over I-95 corridor between New York City and Philadelphia, where heat advisories are in affect for today.

But this oppressive heat and humidity will be short-lived as a strong cold front and upper-level trough will be approaching from the Great Lakes today. Moderate to strong instability will be building with more daytime heating and more tropical moisture streaming northward. This could support some isolated showers and thunderstorm to develop anywhere and anytime during the today. However, more widespread showers and strong-severe thunderstorms are likely over Interior parts of New York and Pennsylvania this afternoon, as more dynamics with the cold front moves into those parts of the Northeast initially.

Despite some weak mid-level lapse rates, which often limit more high-end severe weather potential, some organized strong to severe thunderstorms are still possible.  Strong wind fields and lowering heights will result in deep-layered and large scale forcing for thunderstorms to organize into squall/bow lines with damaging wind gusts. Model soundings also indicate winds will be veering with heights with 40-50kt low-level jet along a pre-frontal/surface trough and low LCL heights will also support a threat for some supercells with isolated tornadoes. Especially with the core of low-level jet over Western or Central New York State.  Thus the Storm Prediction has issued an slight and enhanced risks for severe weather this afternoon for much of the Interior Northeast. We will be monitoring the threat closely today.

NAM model showing high instability over parts of Northeast with MLCAPE near 2500 joules. But strongest bulk shear around 40-50kts over Western NY

More forcing with more heights falls and jet streak energy will be moving into Southeast New York, New Jersey, and New England by early tonight. Some scattered showers and thunderstorms are possible, as some instability remains with very muggy tropical-like airmass over the region into late evening and early overnight hours. However, instability from daytime heat will lowering and best forcing may to northwest. So any severe weather will likely be more isolated or marginal. Locally heavy rainfall with flooding and some frequent lightning will likely be the bigger threat, with tropical moisture remaining. Otherwise partly cloudy skies are expected tonight with low temperatures 60s over the Interior and lower 70s over the urban and coastal areas.

The cold front will finally pass through early Wednesday morning. Behind it, high pressure from Central Canada will build into Northeast and Mid-Atlantic region, with skies clearing for more sunshine by the afternoon hours. A much cooler and drier airmass will begin to settle in on Wednesday. But northwest downslope winds will support high temperatures in the lower to middle 80s. Which is still close to normal for late August. Overall it will be pleasant late summer day.

GFS ensembles 500mb height anomalies forecast for later this week

Then temperatures will be running below normal for rest of the week, as some anomalously low mid-level heights remain over the much of the Northeast and Mid-Atlantic region, due more ridging out west. Pleasant weather will continue with some sunshine and clear skies each day and night. Daytime highs will generally range from the middle 70s to lower 80s, Overnight lows will be could get down into 40s or 50s, especially over the Interior areas. Another reinforcing shot of cooler, dry air will likely keep temperatures below normal for the weekend, as well. Stay tuned for more premium forecast updates on the main dashboard  and with more articles to come during the week.