Significant Severe Weather Outbreak Saturday
Current watches, warnings and advisories.
Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.
A summer-like evening is in store for the Northeast this Friday night as broad, southerly flow ahead of an approaching cold front pumps an anomalously warm, humid airmass into the region. This cold front is associated with a sharpening mid/upper level trough diving into the Great Lakes region. As this cold front blasts into the Northeast during the day on Saturday a strong to severe squall line of thunderstorms will develop in response. The SPC has issued a moderate risk for severe weather across a large swath of the Northeast from central Pennsylvania across to western New England, including most of New York and New Jersey. Lingering showers move offshore with the frontal boundary on Sunday, leaving behind high pressure, fair skies for most and much lower humidity. This area of high pressure will persist throughout much of next week, bringing beautiful late summer/early autumn weather. A weak cold front will attempt to drop south from Canada late in the week with sparse precipitation.
A lovely evening and overnight will greet most Northeast residents this Friday night. Aside from a few widely scattered showers and thunderstorms across the coastal plain, central Pennsylvania and the Lake Ontario region, most areas will see mostly clear skies with temperatures mainly remaining in the 60's across the interior and 70's along the coastal plain. There will be an increase in high clouds after midnight from the west but any precipitation ahead of the cold front should hold off till after sunrise. Winds will be light and from the south.
SPC Day 2 Convective Outlook
The day of action will be Saturday as the aforementioned cold front approaches from the Ohio Valley. Weakening convection from overnight storms currently located over Indiana will move into western New York and Pennsylvania by mid-morning. Areas to the east should start fair with just some high clouds. This will allow for decent diurnal heating before the cold front moves into these areas during the afternoon hours. As the mid/upper support for the storm dives into the Northeast, the trough will begin to swing negative, resulting in a rapidly developing surface low pressure which will ride quickly northeast across the lake plain to the St.Lawrence valley. The southerly flow ahead of the front will increase as well, pumping a tropical airmass into the region. Hence, a rather breezy afternoon will take the edge off the high levels of humidity somewhat. Instability will increase during the day with CAPE's ranging from 500-1,000J/kg ahead of the front, not overly impressive, but combined with approximately 100dm height falls associated with the upper through should be enough of a trigger for the development of storms. Winds aloft @500mb will increase to 50-75kt, yielding about 30-40kts of shear. As storms fire during the early afternoon they should quickly organize into a squall line and push rapidly east at 45-60mph. These storms shouldn't have any trouble tapping into these stronger winds aloft as the strengthening surface low pressure system riding northeast will make for a highly dynamic atmosphere (sustained lift/updrafts). Strong, damaging winds up and down the length of this squall line should be the biggest severe threat on Saturday. In addition to the strong wind threat, there may even be a few tornadoes in supercell thunderstorms which develop out ahead of the main line of storms. This is a low threat due to lacking instability and convergence ahead of the frontal boundary itself but the threat is there. The fast movement of the line of storms should prevent significant flash flooding concerns but with the tropical airmass in place and precipitable water values reaching as high as 2" localized areas of flash flooding may ensue. High temperatures will range from the low to mid 80's along the coastal plain with mostly 70's across the interior. Temperatures should drop into the 60's and upper 50's with the passage of the front.
By the evening hours on Saturday the frontal boundary and its associated squall line should be moving into western New England and southern New Jersey. These storms will be in the process of weakening with the loss of daytime instability and the surface low pressure moving further north into Canada. Despite this weakening trend there will still be strong winds aloft and the potential for convection to mix these winds down to the surface. But any damaging winds won't be nearly as widespread as areas across Pennsylvania and New York receive during the afternoon hours. Total rainfall from these storms should range from a half inch to an inch and a half with higher amounts over two inches in localized spots. Low temperatures will range from the 40's and 50's across the western portion of the region behind the front with 60's and 70's in the humid airmass out ahead of the front.
The front should continue to push offshore during the morning hours on Sunday with any lingering precipitation confined to areas from eastern Massachusetts and Cape Cod to downeast Maine. A refreshing breeze from the northwest around 10mph should usher in a much cooler and drier airmass. A few showers may develop over the higher elevations under the axis of the upper trough and downwind of the Great Lakes but most areas should see plenty of sun. High temperatures will range from the 60's across the interior with 70's along the coastal plain. A few locales across the higher terrain may remain in the 50's.
Winds will die down Sunday night, with clearing skies and a dry airmass overhead ideal radiational cooling conditions will be in place. Temperatures should drop into the 40's across much of the interior with a few lows in the 30's across the higher terrain. This may lead to widely scattered areas of frost across these regions. Along the coast temperatures will be closer to 60°F due to the moderating influence of the ocean.
High pressure will remain in control throughout the mid-term period, ranging from Monday through Wednesday of next week. Mostly sunny skies and low humidity will make for stunning weather conditions, with daily high temperatures ranging from the mid 60's to mid 70's across the interior with upper 70's to low 80's along the coastal plain. The clear skies and light winds due to high pressure will lead to chilly nights with lows in the upper 30's to upper 40's across the interior with slightly milder temperatures along the coast, in the 60's, as offshore sea-surface temperatures are still rather warm - in the 70's.
The surface high pressure will slowly begin to slide offshore on Thursday with southwesterly flow increasing, helping to bring more humidity and warmer temperatures to the region to close out the week. A weak cold front will drop down into the region from Canada by late on Friday with little precipitation to speak of. This frontal boundary will wash out over the weekend as another area of high pressure drifts into the region by the weekend Highs in the 70's across the interior and 80's along the coastal plain should be common with lows in the 40's and 50's across the interior. Lows will be in the 60's and 70's along the coast.
Radar: Northeast Region Loop
Radar loop of the Northeast region. Courtesy of Weather Underground.
Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.