Category 2 Storm Alert!
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At 8:35 we are starting to see mixing enter the radar in the NYC area. Precipitation is also becoming more light and scattered as the precipitation shield dissipates.
Am expecting to see snow/mix turn over to rain around 9:10-9:40 window, then rain (heavy downpours at times) should remain in the area for another 90 minutes or so.
For areas north of the city (white plains/westchester), the changeover should occur around the same time to a icy mix before pushing out of the area around 10:30p.
There were plenty of indicators prior to the run up (please research the prior blog entries) yet as you see it unfolding it was an easy sell to go ahead and suggest it made sense to increase expectations.
The dynamic and evaporative cooling processes were expanding the colder pockets in the atmosphere and redirecting the warmer windflow preventing it from surging in to evict the colder ptypes. It is what you refer to as a runaway.
Am expecting to see snow/mix turn over to rain around 9:10-9:40 window, then rain (heavy downpours at times) should remain in the area for another 90 minutes or so.
For areas north of the city (white plains/westchester), the changeover should occur around the same time to a icy mix before pushing out of the area around 10:30p.
There were plenty of indicators prior to the run up (please research the prior blog entries) yet as you see it unfolding it was an easy sell to go ahead and suggest it made sense to increase expectations.
The dynamic and evaporative cooling processes were expanding the colder pockets in the atmosphere and redirecting the warmer windflow preventing it from surging in to evict the colder ptypes. It is what you refer to as a runaway.
Started to see the two pieces of energy that would swap tracks.
Our surface features may share a pressure field and isobars but the system is comprised of two circulations that will swap courses.
The easterly one from the Gulf will track that bend in the isobars to the north and east and expand the occlusion zone as our inland low hits the coast and turns north and deepens rapidly. This is the feature that brings those winds up.
The easterly one from the Gulf will track that bend in the isobars to the north and east and expand the occlusion zone as our inland low hits the coast and turns north and deepens rapidly. This is the feature that brings those winds up.
You can see 'em on radar. We can also see the damage done by the higher precip rates, the low dewpoints and humidity levels that allowed even further dropping of the dewpoints and wetbulb as the interior held on much longer as snowfall.
At the lower layer of the atmosphere we can see those gains made as the 0C line held firm and the windflow denied timely eviction. This just wouldn't be a system (and you can read plenty back in prior blogs to find it) that would have a strong surge northward.
The warm surge would only come with the advance of the low itself of which is now on the move north into the region which is why you're finally seeing those changeovers in the Mid-Atlantic zones.
This same process keeps areas north locked in cold longer and they too will only switch as the low advances and not in your typical southerly surging fashion. A lot of factors drove this. The high placement. The elongated suppressive environment well north behind storm number three. Our occlusion development in the system itself.
The warm surge would only come with the advance of the low itself of which is now on the move north into the region which is why you're finally seeing those changeovers in the Mid-Atlantic zones.
This same process keeps areas north locked in cold longer and they too will only switch as the low advances and not in your typical southerly surging fashion. A lot of factors drove this. The high placement. The elongated suppressive environment well north behind storm number three. Our occlusion development in the system itself.
At 700mb the dry punch is coming and the expansion leading to the occlusion and separated tracking of the surface lows. Also note the extreme wind burst here that is bumping up against the changing and slowed wind streams to the north.
The wind has nowhere to go and is forced upwards enhancing your lifting and frontogenesis and precipitation production.
The wind has nowhere to go and is forced upwards enhancing your lifting and frontogenesis and precipitation production.
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Aloft while the jet isn't negative tilt nor featuring a major switchback in presentation that would be irrelevant as to whether or not the system would produce high end. Many other factors in the lower to mid levels drove what we have here. You don't always need everything to exist in order to perform. Yet even said we have a nice jet streak rounding the trough. We have the nice divergent pocket well aligned aloft. We have the strong jet entrance region..the baroclinic leaf signature. All plenty to vent the high end lower layers of the atmosphere to produce our system. |
Read back through many blogs showing the low dewpoints but also the low humidity levels allowing dewpoints to fall even further as evaporative cooling takes place upon precipitation advance.
What transpired over the Mid-Atlantic will also transpire over New England this evening. At first maybe some rain or mixing that will quickly cause temperatures to drop and over to heavy snowfall before any other ptypes push in.
As in the Mid-Atlantic we'll see another cold wedge and pocket develop, deepen, and anchor into southern New England of which will only evict upon actual arrival of the low center itself.
What transpired over the Mid-Atlantic will also transpire over New England this evening. At first maybe some rain or mixing that will quickly cause temperatures to drop and over to heavy snowfall before any other ptypes push in.
As in the Mid-Atlantic we'll see another cold wedge and pocket develop, deepen, and anchor into southern New England of which will only evict upon actual arrival of the low center itself.
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While all signs pointed to leaning colder, triggering further south and west, and pushing frozen ptypes and their durations further south and east in the end we still had to keep pushing higher as the morning events wore on and showed themselves.
Even when you know its coming it can still take you by surprise in how well these dynamic/evaporative cooling events can become a runaway. I wrote about this a few times and the hows and whys to look for it. Also wrote how guidance was likely missing the point on the south east fringes, depicting rain or quick frozen ptype eviction, and should be adjusted otherwise. Once guidance got the hint, and the system was doing it in real time, your forecasts come up to match in those south east zones. Major winter storm continues throughout the overnight across the North East Same goes for the very S&E southern fringes of these values from SEPA through New Jersey, Long Island and southern CT/RI/MA. While we will see brief onset then switchovers I still think it may be heavy enough to allow for accumulations where not shown here. |
