purduewx80

I'm impressed. Crazy work day that has never gone by faster. The latest iterations of the HRRR and RPM bring convective precip farther south tomorrow morning, directly affecting NYC around 12Z/7ET. This one could go out with a bang, too.

mixing line racing north in PHL area now

Plenty of obs support the models insistence on a period of +SN in NYC this afternoon. PHL vis nearing 1/4SM now.

The upper jet associated with bombogenesis over Labrador this morning continues to impress. 300mb wind speeds at Gray, ME - only ever exceeded in Jan-Feb during the period of record: Yarmouth, NS exceeded 200KT at a few levels:

Might get pretty wild under the still-deepening upper low Friday morning. Very steep lapse rates and some CAPE showing up that are aligned with a pressure rise/fall couplet. Dynamic cooling w/ that could lead to some TSSN squalls, probably over higher terrain just W/NW/N of the city in PA, nrn NJ into New England.

you weenies should be more excited about the deep snowcover building in eastern canada w/ these systems. that will be an important source of low level cold air once we get into the nino-favored part of late winter.

The actual squall line in the warm sector will likely have tops to 40000'. May be some cloud-to-cloud lightning in the NY area (especially LI), but TS chances are much higher just to the S/SE.

Models are in near unanimous agreement on high pressure overhead Monday; perhaps you meant Tuesday? Both tomorrow's and Tuesday's systems have a redeveloping low passing near the city, PWATs above 1.5" and a low level jet focus, so the heavy rain threat is legit both days. Fortunately, they're both quick movers, so anything over ~1.5" should be highly localized.

If NAM and ECMWF are most correct for Tuesday, would expect slight risk to get expanded into the region. Shear and forecast instability (for this time of year) are impressive.

severe wx threat looks pretty legit this evening from philly/jersey into southern new england as warm advection increases ahead of the developing surface low. nose of 50kt+ llj bringing in up to 1000 units of mucape, with some good (mostly speed) shear down low. at the very least, there ought to be a few heavy showers in the vicinity of nyc around 11. hi-res in good agreement on that. soundings would also support a few thunderstorms in the region. linear convection currently near the dc area will also be worth watching as the low passes just n/w after midnight. this pattern is impressive. the gradient between the tn valley low and the eternally beefy west atlantic ridge is setting jetstream records at 250mb this evening. the PIT balloon observed 181kt at 250mb on the 00z sounding tonight, something only ever exceeded before in january (since ~1952).

The next wave coming in early Monday also is forecast to have them at 7+. With the jet max coming through early, could be a storm or two around first thing in the morning.

A lot of the 12Z hi-res has the convective look nearby in the morning. Most are focused just S/E of the city. This is obviously way over the top, but the HRRR has 80KT winds w/ this feature at JFK 12Z tomorrow. There is a gravity wave signature showing up that is likely just convective feedback, but seeing that convective signal on a number of pieces of guidance to me suggests some local "surprises" in terms of excessive wind gusts early tomorrow.

there will definitely be arrival delays and probably some cancellations due to the excessive wind gusts limiting the amount of runways they can use. your departure depends on when that plane initially gets into LGA. most NYC to ORD flights would not be canceled since these are hubs.

agree on the start time and think any heavy rain threat is primarily in the morning, ending by ~10AM. light rain and/or drizzle should continue throughout the day, however. lapse rates with the incoming dry slot during the morning hours are nothing to sneeze at. forecast soundings show up to 500 j/kg of CAPE at JFK based around 800mb, so some embedded heavy showers appear likely. thunder risk is much higher in the low-level warm sector offshore but believe chances are non-zero around here given the advection of instability on a 50-60KT low level jet.

who cares?

50mph winds are well agreed upon across Long Island and the Jersey Shore. The forecast soundings are highly supportive of the maps bluewave has posted. It's all about the gradient. The GFS had been farthest offshore w/ the low, but, as can pretty much always be expected this far out, it continues to correct closer. I suspect it will ride the coast once to the Outer Banks. Should produce significant snowfall across higher terrain well inland, as well.

ECMWF ensembles have had the right pattern for it for days. It's actually not all that different from the pattern that produced Sandy, minus the tropical input of course.

looks to be a rather wet evening for the metro. guidance hinting at overrunning cells after a bow of sorts transitions through, so i think we'll see some flash flooding in areas, mostly during the overnight.

it's chaff, likely from the air force. not precip.

LGA just observed a ~2.7"/hr rainfall rate (1.09" in 24 min actual):

forky and njwx are on the money. the low level jet currently producing convective showers in the dc area and points south is forecast to be overhead from ~midnight-9am. lwx radar is showing widespread 40kt winds aloft, with embedded 50kt maxima in convection. the hrrr, rap and other hi-res models suggest several impulses embedded in the flow will enhance showers periodically during that period. with pwats of 2-2.3", we will all see plenty of rain. as long as it clears out some behind the morning round, at least scattered thunderstorms should develop along the front tomorrow afternoon/eve. that qpf max forecast by most guidance upstate towards boston is associated with frontogenesis and will likely be narrower than most models show. there are signs of a second sfc low developing near jersey or the delmarva later tomorrow, so i think there could be a second precip max just sw-thru-e of the city.

maue is posting them on his twitter. click his link to see live updates.

hurricane-force winds showing up at ~7000' now in that developing eyewall.

exactly. i'd add that august is climo for this due to peak SSTs and weak steering flow.

JFK picked up 1.84", much of that falling in under an hour. radar estimates show around 2.5" just east of the airport. looks like another cluster of showers is building west along a very narrow wedge of untouched warm/humid air between the southern outflow boundary and the coast. JFK reporting CBs all quads, so it looks like there could be another round at the airport. may also die out just to the east.