vortex95

Look at these GIF loops from late this aftn. Classic supercell split mirror pair in n-cntrl MD. The left split accelerates and moves N, and the right split moves ESE and is slow-moving. In a more unidirectional environmental flow w/ wind shear, the supercell splits both have an equal chance of surviving. Most of the time tho when there is directional shear present, it is veering w/ height, so that favors the right mover (cyclonic meso), and the left mover (anticyclonic meso) does not last long. Supercells by default split, but often since the right split is so favored so often from the shear profile, the left split never has a chance and is wiped immediately, so you see nothing on radar! And when overall flow is weak/disorganized over an area, the mesoscale takes over, leading to some odd storm motions and evolutions, as we see today.

FWIW, this is what it looked like just to the N of College Park at 5pm today. It tried for a brief time. Definite supercell with a long inflow band to the E. I had to take this pix through a window.

There are these wx sayings, "similar patterns breed similar storms" and "when it's good, it can be REAL good!" First, I will get this out of the way, CoastalWx is once again STEAMED this did not happen in this past winter! This storm is almost a carbon copy of the last storm, except everything is ~100 mi NW. The 500 trough evolution is ideal. The trough over the Mid-Atlantic is at first neutrally titled, and does a full 90 deg swing negative as it moves across New England. That's how you do it for a classic! The last storm did this as well. 982 mb for a central pressure over New England is very impressive for late May. I can not recall a low this deep here this late, esp. over land. Embedded tstms look to be widespread, even the cool sector of the storm. Few hundred CAPE is common across the region on the models as the storm winds up. That does not happen often w/ a Nor'easter, but given it is late May, by default you will have some CAPE around. Big R+ potential in western sections w/ the deformation. Can it look any more classic on the HRRR forecast radar valid 18z Sat? Snow once again likely in the mtns (above 4000 ft this time) and probably several inches on Mt Washington as a rather cold air mass for this time of year flushes in behind the storm.

Feedback period open through 6/26 https://www.weather.gov/media/notification/pdf_2025/pns25-37_mag_webpage.pdf Site in question. https://mag.ncep.noaa.gov/model-guidance-model-area.php

Oct 22-23, 2014 CG plot and IR attached. Blue Hill 6.18" for the storm. One thing I recall about this event is the gusty/bursty winds well before the precip stared, even inland. Why? B/c there was CAPE/lifted index negative in the region as the storm approached and the gradient increased. Much more efficient mixing down of the BL winds in such an environment, which is rarely seen pre-nor'easter in New England!

Precip plot for this past storm clearly shows the mesoscale "thingee" track over sern MA. Mesolows are notorious for enhancing rainfall. Broad rotation increases updraft strength and low-level convergence locally. The mesolow also explains the unusually high LTG density for a Nor'easter, and also the fact given it is late May, climo says there is just more convective instability around in the mean. What was amazing is the apparently the HRRR caught on to this feature 24 hr before, showing an enhanced swath of R++ S Coast of MA to BOS. Last time there was this much LTG in a Nor'easter here I think was Oct 2014. Need to check my archives on that when I get home. CoastalWx may be able to pinpoint this one!

I moved to Silver Spring MD in 2020 for a job after living most of my life in Woburn MA. The avg temp yearly in DCA is 6 F higher than BOS, and the DPs are relentless in the summer, esp along Chesapeake Bay where they get to 80 F often. My first two summers here, I was sweating a lot, but by the third summer, it was not nearly as bad. Point I am making is that the body adapts to warmer (or colder) temps in a relatively short period time w/ no ill effects. But that nothing to to what happens in the Middle East along the Persian Gulf, specifically Qehsm Island, Iran. Dew points every summer get into the 90s, and typically in August it really maxes out. Two years ago, it was 100/97 around sunrise one day and last year the same. The METAR (OIKQ) reports I have checked over time, and the temp/dp are valid based on the wind direction, SSTs, and other factors, such as FG present or not. Population of the island is 150k, and many do not have AC. Yet they do just fine or at least can handle it. So it makes what we experience in the U.S. "easy" by comparison!

Scott needs to pick one!

May 9-10, 1977. Not all elevation either. 9.5" BED and 7" PVD. The 500 mb evolution was extraordinary. Giant 500 5-contour cut-off over the NEUS. Sfc low 990 mb.

That May 1967 event was epic. 10" of snow Monadnock regions. MWN 24.9" for a record May snowfall. Minor accums into central MA w/ the latest on record flakes in the air many locations, at least going back 60 years. Winds gust as high as 90 mph on the coast and ACK had over 7" of rain. May 1967 among the coldest Mays on record for the NE. BOS was -7 F for the month.

At least CoastalWx gets this consolation "prize!" Very impressive event synoptically. I'll post later on it in more details.

So Scott, did it rain so hard in Weymouth like that time when you lived in Dorchester you were concerned about house flooding?

As CoastalWx has already lamented I bet, "why couldn't we get this 3 months ago!!!" Set up synoptically is ideal for a big snowstorm, but can't fight that it is late May. Still, I bet there will be some S+ surprises in ME/NH/VT. Excellent comma head and low track w/ max dynamical cooling aloft as 500 low passes right over the region. S/w swings around the base of the mean trough and does 90 deg negative tilt w/ a W-E elliptical, oval-sharped, closed 500 low -- about as classic as it can get for "backlash."

For May 3rd this is excellent. Not often you have this kind of widespread svr wx in early May in SNE.

Betcha didn't think it would make it to ern MA for svr!

CoastalWx better retract his MEH attitude!

Damage in Hampton NH part deux soon! ARe BOX radar reflectivities running a bit hot? Either that or GYX is running cool.

This is pretty darn good for 5/3. Microburst Hampton NH earlier.

Ignore the fact we just had a great late season snowfall in SNE. Oh, but NIMBY, so who cares? https://www.youtube.com/watch?v=w_6bAt_HwnI

I'm sure CoastalWx will agree wholeheartedly!

Blue snow is a result of the high liquid water content. You typically only see that when you dig into the snow and there is more then a foot on the ground.

Sounds like a good job for CoastalWx! Odd that the HRRR just picked that one area repeatedly. Why didn't it do it for other mtn peaks that were even higher then Brace Mtn in the area? The 3 km NAM does this systematically all the time for all higher peaks, but HRRR singnaling out one mtn for multiple runs? Not sure I have seen that before.

Crazy mountain QPF/snow bulls-eyes are a big 3 km NAM issue, but not nearly as much for the HRRR.