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Winter Storm Threat: Feb 7-8 (Final Call)

Much more aggressive with the totals this time around, but there is still more upside risk than downside to the forecast.

I went with a rough 50/50 blend of the GFS and Euro, with some personal touches here and there. NAM’s still out to lunch with it’s QPF and snow totals, so I didn’t even bother with it. There’s going to be some winners and losers in the low-end/mix areas as the details work themselves out. The bulk of the snow across northern MD, southern PA and southern NJ will be during the back part of the storm. The front-end could start off as snow/mix/rain in these same areas and could/should flip to rain at some point before transitioning to snow to end the storm.

Winter Storm Threat: Feb 7-8 (Initial Call)

Just going to start off by saying that forecast confidence is lower than normal. Miller B type storm will form up late tomorrow into Friday and will initially cause mixing/temp issues across the more southern areas. As the coastal intensifies, banding on the back edge of the system could bring locally higher totals from central PA to NJ, NY and maybe even down into northeast MD and northern DE. There’s plenty of risk in either direction, especially across central PA into NJ and NYC/LI.

I didn’t try too hard to figure out contouring based on strict temperature and boundary layer issue areas since there is not enough certainty to really go into that much detail yet. That’s a job that is best saved for tomorrow’s update.

Winter Storm Threat: Nov 7-8 (final call)

Made some changes to bring things a bit further east in general. I took out the 4-8 inch contour due to uncertainties in the forecast, but I do think there will be localized 4-8″ totals in eastern PA and western NJ. Confidence in the forecast is normal to slightly below normal.

Winter Storm Threat: Nov 7-8 (initial call)

Here we go with another early start to winter… but early start for who, exactly?

Well, the mountains already got a shock to the system last week as Sandy dumped as much as three feet or more of snow across West Virginia. This time around, it looks like the coastal areas will cash in more as those out west are left to deal with whatever remains of what they got last week. The latest model runs have (thankfully) converged on a somewhat reasonable solution for mid-week’s snow.

Despite the recent convergence, forecast confidence is still lower than normal as small shifts in the storm track could potentially lead to big shifts in the snow zone.

Snowfall Verification for Dec 7-8

Quite a trying forecast, but overall it wasn’t a complete loss. Verified the mountain areas and highest totals fairly well, but the more heavily populated areas left much to be desired. Looking back, I could have been less generous with the 2-4 inch range in northern MD and southeastern PA, but other than that and bringing the 1 inch cut-off further north in MD I don’t see much that I could have done to change my overall thinking for this event.

The changeover from rain to snow was fairly messy east of the mountains, and most did not even transition to 100% snow. On top of that, the snowfall ended more abruptly and sooner than I had expected, which prevented the stronger cooling to make it to the surface in tandem with the back edge of the heavier precipitation. That slightly warmer boundary layer is what turned 1-4 inches into little to no accumulation.

Going to be a little generous and give myself a C- overall, though it wouldn’t take much convincing to push that to a D+ considering the bust in south-central/southeastern PA and MD and the western edge of the snowfall.

Winter Storm Threat: Dec 7-8 (final call)

Had to make some big changes in the northern areas… the boundary layer temperatures did not cool off as much as I thought it would on the models in addition to a quicker end to the snowfall.

I think that a couple of areas will be able to top out just above 8 inches in the mountains, so I left a small area over some of the WV/MD pandhandles.

Snowfall totals should not get hurt too much after the transition to snow finally occurs as a small period of sleet during the transition could/should provide a decent base layer for the snow to accumulate on. Keep eyes and ears peeled for the possible thundersleet/thundersnow during the transition from rain, especially from the northern VA/DC region up through central PA.

Winter Storm Threat: Dec 7-8 (first call)

Think 10/29 redux, only the temps and QPF line up a bit better for the changeover on the back-end:

The upper-level vort. max is potent enough to create an area of strong dynamics along the back edge of the system, which will pull cooler air down to the surface and make it cool enough within the boundary layer for some accumulation as the coastal low forms and tracks northeastward. Some banding will allow for locally higher totals along the axis that has the greatest snowfall through the WV/VA mountains, south-central and eastern PA and northern NJ.

I took the 12z Euro Op. solution and shifted the low center northwestward to account for for some model biases, which actually lines up fairly well with the 18z NAM after that adjustment. I believe the 12z and now 18z GFS solutions are too suppressed with this system given how strong the vort. max is.

The snowfall totals could go up as the storm’s track and QPF amounts get honed in on the models.

Snowfall is expected to start in the mountains of southern WV/VA/NC Wednesday evening, working into the DC region Thursday morning and departing the PA/NJ region Thursday afternoon.

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