AccuChris

HRRR holding serve so far .

My gut since Friday keeps screaming 4” so I will stick to that .

It would seem the HRRR is more accurate in the real-time world…see if that continues to play out in its forecasts too.. .

CTP had an interesting take and write-up this morning about the ongoing disagreement within the models. They point to the more suppressed models focusing on a mid-level vort in northern New England enhancing drier advection from Canada versus the HRRR which cant even see that in its domain. Time will tell as always “Still quite a bit of uncertainty with 18 hours or less until first flakes. The ECMWF and Regional Canadian models are on the lower end of the snowfall total spectrum. Part of the reason for this might be that they both develop a stronger midlevel low pressure system over northern New England late Monday from a shortwave trough originating east of Hudson Bay at 00z Sunday. This could act as a kicker to bring in drier air more quickly and shorten the window for moisture advection early Monday before the Mid Atl coastal system gets nudged offshore. This shortwave trough is outside the domain of the hires models (HRRR and 3km NAM) and will remain so until the 00z Monday runs. Given that the HRRR and 3km NAM together make up about 1/3 of the NBM weighting in this time period, IF this Hudson Bay feature is indeed responsible for the lower snow totals in the ECMWF and Canadian models, it`s certainly possible that we see a shift south in snowfall totals over the next 24 hours. That said, the HRRR does represent the worst case scenario, with warning criteria (6+ inches) across much of central PA from I-80 southward, which can not completely be ruled out at this point.” .

12z WRF-FV3 also significantly cut snow totals north of the M/D line. Should these lower totals verify tomorrow, it would be a win for the Euro, UKMet and Canadian/RGEM suites for sure. Only the extended HRRR is maintaining a snowier solution farther north .

12z 3km NAM also drier overall .

12z NAM has gotten very RGEM-ish .

12z HRRR kuchera snow map .

So far so good on the HRRR .

These are what they use and its updated every 3 hours and ingests newer data from the short term meso models. It is also “bias-corrected”. They updated it in May 2024 and they tout its “most accurate” and doesnt suffer from wild one-off model swings that a deterministic model may suffer from one run to the next .

The RGEM is relentlessly unimpressive still. Either its going to score a coup here or fold like a cheap card table tomorrow .

0z National Blend of Models was a slight bump north compared to 21z .

21z SREF Plumes were quite good for the LSV. 9” in York, 8” in Lancaster, 7” in Harrisburg and 6” in Reading. Lancaster had a top member at 18” .

It all comes to SLP placement. A primary into WV and secondary off the Delmarva is a full blown major snowstorm for southern PA .

Beautiful look at 9AM Monday .

You can see the confluence is retreating up through NY on the 500mb and the closed low just rolling east. The longer that stays closed the better .

My new slogan for these snow maps moving forward is “If its not pink, it stinks”. Giggity .

18z Euro had a slight bump north .

18z GFS kuchera for next Saturday for the 24 hour period. Again this is JUST its map for next weekend .

GFS still all in on major storm Friday-Saturday next week too .

Another view of 18z GFS kuchera snowmap .

The 18z 3km NAM shows that the real business is about 75 miles wide and per that model, is centered on the M/D line. Clearly a 50 mile shift north or south will make or break our area for better or worse. Regardless, someone somewhere nearby is getting a 10-12 hour thumping with temps in the 20s .

Appears this time step has all precip offshore by then .

Im liking the 48 hour time stamp on NAM. Heavier precip field into southern PA .

12z HRRR looks very nice so far for many. 500mb also shows bowling ball rolling right along due east as well .