MN Transplant

HRRR continues to advertise a later flip than the NAM. More like 15z/10am in DC. Rates are always important, but it’ll kill us if we lose the column by 7am.

Looking great! Edit - Johnson City, TN is the line right now

TDWR base scans are 0.3 degrees and the WSR-88Ds are 0.5. So, closer and lower to the ground is normally best. However, the 88Ds are more powerful. I still defer to them in light snow.

The Canadians finally thawed. 12z GDPS seems healthy precip wise. Guessing a 14Z changeover after maybe 0.7"? 12z RDPS either had something wrong with the run or with the transmission. Not on Pivotal, but it is partially on College of Dupage. Same 14z changeover timing. No precip amounts available, but looks healthy from the precip rate/type maps.

I have just enough knowledge of this to be dangerous, but high risk can correct me. Models have a dynamical core and various physics packages. About a decade ago NOAA/NWS decided to try to align all of the operational models with a single dynamical core. The FV3 was chosen but there have been some problems with it when it is run at finer convection-allowing resolution. So, the alternative was MPAS (model for prediction across scales) from NCAR. I know that NSSL has been testing out MPAS a lot and that one may end up being the dynamical core. One of the problems with MPAS, though, is that it is computing-hungry compared to FV3. So, NOAA is weighing pros and cons.

A touch of ZR at the end of the NAM Nest run, but mostly just drier. 1" QPF, pretty similar to this morning's run.

Still the NAM

NAM 3k is a hold or worse for DC. Blasts the mix line through between 12z-13z, with maybe 0.3" QPF by then.

I think everything is colder than the NAMs, thankfully.

18Z HRRR looks ok as long as you have reasonable expectations. DC loses the column just prior to 15Z with about 0.50" QPF.

Disasterclass by the GFS in the past few days. From a weak 850 low that let the cold hang in, to an 850 low near Clev/Pitt like every other model had.

ICON 10:1 trend. Slight north bleed, but serious consistency.

Hard to tell with 6-hr panels, but the ICON looks like ~15Z changeover and maybe 0.5-0.6" QPF by then. 10:1 snow maps look like a hold from 06z. Edit - if you want consistency, the 10:1 snowfall on the ICON through 18z has been between 5 and 6" for DC for the past 7(!) runs.

I really hope we don't have to cut the NAM precip by 1/3rd like we used to!

The RRFS doesn't even look plausible with the precip shield, but it is ~0.4" in DC before the flip.

It isn't necessarily whether the NAM is correct, it is that we'd hope to be narrowing the goalposts by this period. I wanted to see the NAM come back to the fold, not double down.

Minor models: FV3 remains cold. 17-18Z changeover in DC. 0.8" QPF to that point 06z HRDPS is in the middle with a 14-15z changeover. ~0.65" 06z MPAS-HTPO is about 14z, with lighter precip ~0.4"

Another interesting divergence in the models - surface temps. 00z Monday (7pm Sunday) HRRR: 27 DC, 20 Frederick NAM Nest: 28 DC, 29 Frederick RDPS: 20 DC, 17 Frederick Euro: 27 DC, 21 Frederick GFS: 23 DC, 18 Frederick

There is less than a quarter inch of precip from changeover at 12z to 18z for many of us.

Another dud of a NAM Nest run. Changeover at 7am in DC. Less than 0.4" QPF to that point.

Parent NAM (ugh) is still a morning changeover, but it looks like ~0.5" QPF, so same ballpark as the HRRR. Not a catastrophe.

The 06z HRRR was able to "beat back" the mix line in the late morning period. It doesn't happen on this run, and it is more NAM-like in flying the mix line north. Not nearly as bad as the NAM though.

DC loses the column between 14-15z, just shy of 0.5" QPF. So, the HRRR is probably a 5-7" event before the sleet.

I'm not sure that I'd completely characterize it as a "thump", given that the HRRR is 0.05" QPF per hour from 09z to 14z, but if we do score favorable ratios it'll be a nice period.

DCA made it to 10 this morning with open water surrounding it and no snowcover. That is serious cold.