high risk

Looking at the 00Z guidance, the timing for Wednesday now appears slower which probably reduces the severe threat for those of us in central MD. Some thoughts: 1) Several CAMs show an intense, forced line of convection sweeping through during the midday hours. Wind fields are intense, but there just isn't any instability until you get south of Richmond, and it's pretty meager down there too. If there is a severe threat with this feature, it's likely well south and southeast of the DC area. 2) As the dry slot approaches and much colder air aloft overspreads the area, convection is likely to form later in the day over western VA and move eastward. Wind fields are weaker but still sufficient for a severe threat, and there may be just enough sfc-based instability for a low-end wind threat and perhaps some hail too. What's not as good is that the timing of the system reduces the instability, especially for areas on the east side of the Potomac. There is still some severe threat, but it's highest over northern VA.

The models all ingest the same weather balloon data.

Uh, because guidance shows actual sfc-based instability this far north…..

Right now, the morning threat appears to be south of the DC area. While the wind fields will be terrific, there likely won’t be sufficient time to advect the unstable air mass far enough north. For now, I agree with SPC that the best opportunity in our area is with the evening front. The wind fields will be weaker, and surface winds may start to veer a bit, but a wind threat will exist if we can get a bit of instability.

GFS has a known progressive bias.

There may be some pretty good height falls with this system, but we typically end up with very widespread clouds and showers in advance of the primary forcing in setups like these. Regardless, it's certainly nice to have something to look at as we wrap up February.

Agreed. The NAM Nest had the band falling apart as it moved east, which was a clue that the scenario shown by some of the other CAMs wouldn’t play out.

That’s not even remotely true. Several models yesterday had a band of light snow moving through the area this morning. It’s a real thing, but it’s just too light. Even if it ended up not working out, LWX doesn’t make up advisories out of nothing.

Several CAMs are showing a band of snow with the ULL pass midday Thursday. There is even bit of instability in the forecast soundings, so some heavier bursts of snow certainly seem possible. And stockage would be very efficient with the very cold temps.

We should all acknowledge as a group that, even if the NAMs are spectacularly wrong on this event, we’re going to miss them like deceased grandparents when they’re retired next year.

Yes! When the 3 km shows details differently than the 12 km, the 3 km is better way, way more than it isn’t.

Absolutely. The problem is that the mesoscale models really weren’t designed for beyond the day 2 period. That doesn’t mean that they’re useless; you just have to use extreme caution.

The wind threat is behind the cold front. Still several hours away for the I-95 corridor

Oh good. You’re back with your incessant 3rd grade understanding of NWP.

I think it's legit. The forecast soundings show potential for good mixing behind the front, and there will be some strong speeds just above the surface.

Several CAMs take most of us into the low 60s Sunday, with the NAM Nest being a notable holdout. Soundings support possible thunder ahead of the cold front.

As expected. The changes between the 06Z and 12Z GEFS were small, and both the 13 and 19Z NBM use the same cycle (00Z) of the EMCWF ensemble.

It ran on time, but they are having huge issues with getting the data to their customers, so no site is able to generate any graphics.

Of course the model ran. The problems are with the dissemination of the output.

But you're showing the parent (12 km), and I praised the nest (3 km). The parent NAM is not a very good model, but the nest is, especially at shorter ranges. I don't trust the synoptics much beyond 36 hours.

In seriousness, though, the HRRR was developed to be a model to assist with forecasting of deep convection. Is it totally useless in winter? Of course not, and we know that it led the way on lower QPF last Saturday, but at least be suspicious when it bucks most other guidance. Go back and look at simulated reflectivity from yesterday’s 12Z NAM Nest. Pretty damn good. This is one of the first models I look at for short-term winter forecasts. Too bad that its days are numbered.

New HRRR and NAM Nest runs have the late afternoon precip starting as snow or sleet for areas northern and central areas (before quickly turning to rain).

When looking at the NAM Nest (3 km), the snow product that is truest to the actual internal model microphysics is the Ferrier accumulation. It does, however, tend to run slightly low, so I like mentally blending it with the 10:1 product.

The snow depth product is notably less than 1/2 of those amounts. That product isn't the gospel by any means, but when the discrepancy between the snowfall and snow depth maps is that large, that tells me that the model really isn't producing the big snow totals suggested by those maps.

NAM parent vs. nest timing is still the difference between whether Maryland schools can open tomorrow (and dismiss early) or have to be closed for the day.