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Winter Storm Threat: March 4-5 (Only/Final Call)

Can this be the last one, please? Near normal highs are going to feel like heat waves this month.

20150304-05_MAsnow_final

Most uncertainty is going to come from the changeover from rain to sleet to snow. A slower cold push and/or prolonged sleet could cut down on totals. Regardless of the fact that there’s more downside than upside, it should be a fun storm. Once the changeover to snow does occur, the snow rates should be pretty good, so I’m not too worried about getting accumulations started in the more southern areas when the changeover isn’t until after sunrise. A layer of sleet to start should help the initial snow accumulations as well.

Winter Storm Threat: Feb 5 (Only/Final Call)

Heavy snow is expected across the northernmost parts of the forecast region, with lesser amounts the further south you go as snow at the onset of the storm battles with warming mid-levels as the storm pushes through the Mid-Atlantic. Timing of the changeover to sleet/freezing rain/rain will be critical from central PA roughly from I-80 (or even a little north of that) southward… so yeah, that’s a large area to watch for the changeover. After the storm passes, some residual moisture playing the upslope on the west side of the Appalachians could bring 1-2 inches of snow into the higher elevations of WV and the WV/MD panhandles.

20140205_MAsnowFinal

Significant (damaging) icing is possible in southern OH, southern PA, WV, VA, western MD and western NJ, which is not shown on the map. For the DC area, places around I-95 and points east should have little to no icing, but west of I-95 up to 0.25-0.5 inches of ice is possible. Further north into PA/NJ, more notable ice is possible east of I-95. My forecast map includes snow+sleet accumulation, but not ice from freezing rain.

NEW! I added a confidence bar to my map, with a scale of 1 (low) to 5 (high). I almost always write out my forecast confidence in these blog posts, but those who just look at the forecast image will miss it, so I figured I would fill in some of the negative space with some useful information. The confidence in this forecast is 2 out of 5 (low-medium).

Here is the latest ice accumulation forecast from the NWS for the LWX forecast region:

20140104_LWXStormTotalIce

Winter Storm Threat: Mar 5-7 (Final Call)

There were some detail changes due to adjustments in the storm track, which mostly affected central/northern PA, southern VA and the Delmarva Peninsula. Higher confidence in the higher snow totals brought some upscale changes to northern VA.

It’s still a low confidence forecast overall, with both upside and downside risks across most of the impacted region.

Winter Storm Threat: Mar 5-7 (Initial Call)

So here we are with another complicated setup and poor model agreement leading to a low confidence forecast. The good news is it looks like DC is finally going to get a decent storm! It only took until March…

Anyway, right now it looks like the biggest risks are along the coast and in PA and southern VA. I’ll save some of the more intricate details for the final forecast, but there is going to be some serious issues with the rain/snow line in the lower-total areas to the south, with precip. shield concerns across PA, NJ and southern NY.

There is also some upside risk west and a little north of DC, where strong banding will likely occur somewhere in there. The other big question is with the coastal low track and whether or not the more northerly GFS and bring higher snow totals to PA/NJ northward or if the more conservative Euro wins out in those areas. In that case, I decided to lean a bit more towards the Euro with the lower totals.

Some strong, gusty winds are possible east of the mountains north of the VA/NC border.

Winter Storm Threat: Mar 4-5 (only/final call)

Here’s my only/final forecast for the snow that will accumulate today into tomorrow:

 
Boundary layer temperatures are once again the main concern with this disturbance once you get east of the mountains. There is not a lot of model agreement regarding the QPF and surface temperatures with this system as it moves across the region tomorrow, which along with the QPF uncertainty makes this a low confidence forecast. The early start time (being this afternoon) is to account for the ongoing snow showers along and west of the mountains.

Snowfall Verification for Feb 4-5

The verification on this one was rather interesting… some odd shapes/placements of the snow totals:

The front-end of the system over-produced and the back edge under-produced, with some front-end banding boosting totals in central MD. Lighter rates and above-freezing temperatures kept the totals down elsewhere. Overall, I had the right idea, but with a warm boundary layer and a weak system it’s always difficult to nail the accumulations. I’d give this forecast a B- for getting the general theme right within the oddly-placed snow totals.

Winter Storm Threat: Feb 4-5 (final call)

Much better agreement on the models today. The main issues are still how warm the boundary layer is and how light the precipitation rates will be. I think plenty of areas SEE snow, but accumulations could be hard to come by outside of the higher elevations, so I cut back on my totals a bit:

 
I also adjusted the start/end times to account for the snow currently falling in OH/PA.

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