UPDATE ON MID-ATLANTIC SNOW - SATURDAY NIGHT

The latest data is significantly different than earlier today. The NAM still shows the most plausible precip field. It shows the persistent band of snow reaching all the way to the coast. However, it has shifted the snow band about 50 miles south. Although I anticipated a southerly trend, this is again too much. 

I would shift this map up about 20 miles. I would also take a couple inches off the totals in Central Virginia. I'm not expecting a 10:1 snow-to-rain ratio for the entire event (warm ground and surface temps and the possibility of some sleet).

I want to also mention that I think it's odd how the NAM/GFS MOS data keep dew points near 30 all day tomorrow, yet when it starts raining, they keep surface temps in the lower 40s. That's nonsense! Temps will rapidly fall at the onset of precipitation from evaporative cooling. Dew points tonight are in the mid 20s, so the models are already wrong...just food for thought.

I might as well stick with my 3 to 6" forecast in the Richmond metro area. Isolated areas will pick up more.

RPM also shifted south.

GFS is either going to be hailed as the best model ever or it's going to be considered the ultimate bust machine. This model stands alone with its' forecast in Central Virginia...1" or less. Wow! I still can't think of a reason why the snow band would completely dissipate as the storm system strengthens. It just doesn't make sense. If the GFS is right, I will gladly eat crow on Monday. Again, I would rather get people prepared for this storm than downplay it.

WEATHER UPDATE ON MID-ATLANTIC SNOW - SATURDAY AFTERNOON

After looking at the latest data, I still like the NAM solution to this event. It generally matches what the ECMWF has been showing all along. With that said, the maps below represent a 10:1 snow-to-liquid ratio. Parts of this event will have a lower ratio due to wet snow, warm ground temperatures and the possibility of some sleet. I would take off a couple inches from the NAM totals for Central and Eastern Virginia.

I'm keeping with my 3 to 6" forecast for Richmond. Isolated areas in Central Virginia will get more.

RPM also shows a plausible solution, though I'm sad that the 12Z data is unavailable. The 15Z data shows an explosion of 6 to 8" of snow in Central Virginia. This is probably caused by the rapid strengthening of the storm as it moves off the coast. Precipitation rates will increase and bring colder air down from aloft. 

The GFS continues to change its' solution each run. The key here is the strength of the storm. GFS never has the central pressure dropping below 1000 MB unlike the NAM and ECMWF, which have the pressure dropping to 996 MB. A weaker storm means weaker cold air advection - both horizontally and vertically.

I'm not buying this solution. This storm "over-achieved" what the models predicted here along the West Coast, so the same could occur farther east. I think it's better to be prepared for a snow event than to be surprised Monday morning with 6" of snow on the ground. Worst case scenario...GFS is right and I'm eating crow Monday morning.

WEATHER UPDATE ON MID-ATLANTIC SNOW - FRIDAY NIGHT

Here are some brief thoughts on the latest data:

• GFS is out to lunch. How can the band of snow magically disappear once it moves into the eastern half of VA? However, if it continues to show the same scenario for tomorrow's 12Z and 00Z runs, I might be a little worried.
• What happened to the NAM? I expected a slight shift south, but this is ridiculous. I expect a dramatic shift back northward tomorrow morning.
• ECMWF has shifted *slightly* northward. Wobbling is to be expected as the storm approaches. ECMWF ensemble never ceases to amaze me when it comes to these type of storms. It's the best medium to long range forecasting tool.
• RPM snow accumulations match the ECMWF storm track. It has the best solution this evening.

Right now I'm keeping with my 3 to 6" forecast for Richmond. Here are factors that can ruin my forecast: 

1. Surface temperatures
2. Ground temperatures
3. Prolonged period of sleet
4. Shift in the track of the storm

The data tomorrow will be more reliable, so don't get too excited (or sad) until then.