wxsniss

18z HRRR still very warm at surface though, it's 33-36 for much of ESNE until ~20z 0z NAM thermals is what we want... it's as if all guidance warmed as soon as Pope posted this morning... I'm hoping we cool back in the 18z suite starting with NAM

Just looked, tbh I wasn’t totally enthused with soundings on 12z NAM for eastern SNE Kbos a tic warmer to 34-36 compared to 32-33 last night through most of event, and the best lift is often below DGZ The snowfall maps look great but verbatim on that run we’ll be really dependent on rates and robust CCB for the higher amounts

Our discussions here tonight identifying colder trends particularly for east SNE are mirroring NWS latest thoughts:

Excellent writeup and forecast. Agree with your bumping up Boston metro from 4-8 to 5-10 given almost all guidance (CMC is outlier). I won't be shocked to see 12-14 spots in eastern face of Worcester hills to 495 to NE Mass. Let's hope there won't be too much if any melting lull between overnight WAA and late morning-afternoon CCB. And no complaints if HREF scores a coup.

No drastic changes... a more southeast track and colder thermals throughout, giving a better run for ESNE/coastal CT / RI... colder and wetter 10:1, 12z left, 0z right:

Thru 42h continues a tic southeast of 12z run, thermals colder everywhere, otherwise very similar

Looks a hair south and east at 30h with colder 925s everywhere

Really tough forecast for SNE inside 495 and southeast... not just the capture but the thermals early on... 0z NAM was very cold once things wetbulb, and I think that's notable for a model that tends to be aggressive with warm intrusion. Hard not to forecast potential for double digits somewhere, most likely Worcester Hills to 495 / northeast MA. For MBY Boston suburbs... debating 4-8 vs. 6-10, pending trends overnight. I could see a tight gradient where downtown is like 5" whereas Jerry in Chestnut Hill closer to 8-10". And even then there is potential upside to those numbers if overnight is colder and CCB develops faster. Agree with Pickles I could see a lull Sunday morning ~7am-9am when it's fizzling (even drizzling) between WAA and CCB, before we crank again into afternoon.

Just tuning back... everyone in bed, back to storm! HREF really impressive, even mean snowfall. Anyone know if HREF thermals and/or snow algorithms are less reliable? I ask because mean QPF is very close to NAM, yet HREF has most of ESNE 12-18 mean snowfall. I do remember clinging to HREF snowfalls that never materialized in past storms, other storms it was pretty accurate. Warmest mean 2m Temps at 9z Sun: Snow and QPF are not strictly 10:1 so their algorithm / thermals must be more generous than NAM: Left: Snowfall, yellow = 12-15, orange 15-18 Right: QPF, light blue 1.2-1.5, purple 1.5-1.75

Coordinates for Dorchester just south of Logan, using 18z NAM, at 18z Sun catching CCB... (and earlier it looks like surface wetbulbs from 36-37 to 32-33 by 3z Sun... ie., cold run for Boston metro that though wet should accumulate):

2 wrinkles a little more prominent on this 6z NAM, and I’m thankful we don’t have more time for these to create even more forecasting havoc: 1) interaction of our trailing shortwave with the shortwaves diving down the Midwest 2) convection out east / multi-low structure robbing some of the inflow mechanics… you can see a bit of that hr 51

Thanks for updates fellas, haven't had a chance myself to look at any H5 trends... Seems solutions have stabilized away from the north tics earlier today and all give ESNE at least some CCB treatment, widespread SNE 6-12" Critical window and probably last opportunity for drastic changes would be 6z-12z guidance as shortwave energy enters BC ~6z Friday I'll be back for Euro NWS ticked a bit up at coast on 7pm update:

Hastily catching up on guidance since this morning, sorry if I missed similar posts earlier. Great post. First energy entered CA ~0z last night. This second piece looks to enter BC ~6z Friday. We've seen today how sensitive outcomes are to strength of these 2 pieces and timing of interaction. Would not be surprised to see continued volatility in guidance next 24 hours.

A hair better than 0z:

Still lots of uncertainty, but seems 0z Euro was the anomaly Gap from here to 12z GFS is a more potent trailing s/w and associated earlier capture... highly impactful variations that are easily within noise at 60h-72h

Wow Can we get an EPS/GFS blend… Glancing at surface first, I half expected to see that the lead vort had disappeared and this was entirely driven by trailing vort Now even more convinced we’re seeing highly impactful wobbles rather than clear trends

EPS (cut back ~1 inch everywhere compared to 12z):

Maybe the biggest change on this 0z vs. 12z Euro run is lead wave seems to move faster... vortmax is ~100-150 miles further east by 0z Sunday. And so the surface low is east. For example, 18z Sunday, ~50 miles east instead of over Nantucket. I don't think we have enough to call this a definitive trend vs. impactful wobbles.

This run also a tick warmer at 925 especially east... Agree 4-10" is a safe range this far ahead for much of eSNE. Still think there is a shot at >10" somewhere 128-495 or interior southeast depending on timing of interaction. But we need to see more support for that tomorrow, otherwise today's most bullish runs were a flash in the pan.

Definite step back from 12z Euro... interaction with trailing energy occurred too late But, we at least appear to be stabilizing the floor of a solid region-wide warning event, which appears on all guidance. The double-digit ceiling is critically dependent on that infusion of trailing wave, and on this 0z Euro the lead wave scoots east / that interaction is delayed. This will fluctuate and definitely still on the table. Ironic that GFS is now the most robust (at least for SNE).

Shifted east with lead wave compared to 12z... the mitigating factor mentioned earlier if trailing wave interacts later

Yeah pieces look perfectly positioned on that 84h NAM for injection of the trailing vort and capture for a big hit eSNE. That scenario is shown on most global guidance at this point. The main mitigating factor on current guidance is if it happens too late... 6z GFS is a good example where the trailing energy arrives too late and the system bombs out too far east

Fwiw nice hit clown range 0z NAM, much improved from 18z NAM

Energy is entering CA 18z-0z tonight, so this 18z GFS (and definite step towards Euro with more robust initial wave and capture by trailing wave) is a very promising trend to start the evening

925mb -4 to -5C much of pike region / eastern SNE throughout event