ers-wxman1

Source region of the cold airmass, extent of the cold air, depth of freezing layer, are we drawing from a true arctic airmass, wind direction...how long we hold onto the airmass etc. if we are filtering air from single digit temps with dry dews then cold air hangs in longer etc. this air mass starts around 30, not much room.

Very marginal airmass, shallow, and it retreats quickly. So the maps might show the wedge all the way into Georgia, but knife deep, not much reinforcing cold to the north. Nothing aloft to reinforce the cold. heavy precipitation also has latent heat release which warms the column as well.

This is the 500 low and lift depiction. Noted this in a post earlier. Ideal for us would be a deepening 500 low closing off just to our south and phasing. Above is a progressive low, good forcing but strung out and best lift to our north. Not ideal for a good column.

Not my office anymore, but gut feeling is they’ll be coming down.

Only out to 24h on TT

Changes likely by morning.

That’ll get replaced with a heat advisory after they see the GFS

If you somehow avoid the sleet transition I think you can see 12+.

I think Frederick MD will see solid warning level snow. 5-8 on the front end thump before sleet transition, maybe another 2-4 on the transition back to snow.

Track of the surface low also not necessarily the most important factor. Classic snow events for the Mid Atlantic need a strengthening upper low closing off , deepening coming near or just south of our area. This is a progressive vigorous punch and not much phasing for our area, best dynamics go north in the CCB.

I know everyone is analyzing a stronger CAD with each model cycle, but it really is not going to matter. This is not a true arctic airmass and the cold air being dammed in is marginal at best. Source is not deep. Hence we hold on to the front end thump then the shallow cold rapidly erodes. This is why we are seeing such fast changeovers today. Upper level low also not closed and is weakening as it approaches our latitude. That isn’t favorable for the column either. It’s a tough storm for our area outside the favored zones, even some of these areas north of I-70 into southern PA unfortunately will change to sleet for a while. December modified cold airmass not ideal.

Our best shot for heavy snow outside the favored areas well north and west will come on the front end thump. The CAD unfortunately is marginal and not deep which will erode quickly after 18z. Some areas such as nova, central MD, north of 70 could pick up 3-5 in the first 3-4 hours of the event before changing to sleet then rain. Need the thump. Wrap around CAA never set in stone and it appears the best forcing per the upper low energy will be north of the area in PA/NJ. Lighter snow on the backside for our area, let’s hope we can keep more forcing before everything shifts out.

Perhaps you should take an introductory course in NWP so that you can actually learn how to interpret a model. Or perhaps read up on some of the material discussed earlier on how to use the NAM at this range. You don’t look at the exact amounts, you watch the trends and the evolution and what the run to run differences/similarities are. Rarely does anyone take one model 100% for qpf, it’s always a blend. Most important information is how the model is handling the moving pieces that will become the weather event. These higher “snowfall” amounts you are seeing do not take into account sleet/ice which can jack up the amounts. What I take from the run is the penetration of the warm air...good front end thump then more expansive mixing and rain then this AM.

Do you actually have a clue what you are even saying?

This is a very good analysis.

I posted this by accident in the long range forum and meant it to be here... I’m happy to post here but every time I post anti snow or show a trend and give an analysis it’s taken as negative or harsh. I watched over the weekend at day 5 model hugging the snowiest solutions, it’s rare for it to work out that way area wide especially with such a marginal temperature setup. Conversations among colleagues can get like this...diverging opinions and Mets can be sensitive I will say that. But inevitably, the very grids a forecaster makes come from a blend of every model you see out there including the NAM, SREF, GFS, EURO etc its a blend of all and ensembles. You can gain clues into how a system is evolving from the NAM even at 48 and 60 hours. Take all the runs today...all of them are trending toward a well north and west setup of snow, rain more dominant east and you can’t just toss the NAM it’s showing this consistently run after run.

I agree. Thanks for sharing this. I can see what you are saying for the eastern areas, though I am saying generous snow amounts just well north and west.

I definitely agree

Get a grip! I accidentally posted here instead of the other thread.

My apologies. Wrong thread.

I’m happy to post here but every time I post anti snow or show a trend and give an analysis it’s taken as negative or harsh. I watched over the weekend at day 5 model hugging the snowiest solutions, it’s rare for it to work out that way area wide especially with such a marginal temperature setup. Conversations among colleagues can get like this...diverging opinions and Mets can be sensitive I will say that. But inevitably, the very grids a forecaster makes come from a blend of every model you see out there including the NAM, SREF, GFS, EURO etc its a blend of all and ensembles. You can gain clues into how a system is evolving from the NAM even at 48 and 60 hours. Take all the runs today...all of them are trending toward a well north and west setup of snow, rain more dominant east and you can’t just toss the NAM it’s showing this consistently run after run.

If the NAM is “out of range” and mauls the area with snow it’s hugged and adored by all and they can’t wait for the next run, much the same over the weekend with the GFS and Euro giving 15-20 inches “out of range” at day 5 with 90 pages of comments. When the NAM is unfavorable and analyzed its bad, out of range and nobody wants to see it or hear about it.

If the NAM is “out of range” and mauls the area with snow it’s hugged and adored by all and they can’t wait for the next run, much the same over the weekend with the GFS and Euro giving 15-20 inches “out of range” at day 5 with 90 pages of comments. When the NAM is unfavorable and analyzed its bad, out of range and nobody wants to see it or hear about it.

It’s not gospel, it’s indicative of the evolution of the pattern. The model is not worthless beyond 48 hours. I happen to work with the hard working employees that spend millions to make these models run year round, that dedicate their lives to making NWP better and people just trash them like it’s a wind up toy.

This is ridiculousness!