Monday, March 4, 2013

This. Is. Not. A. Drill.

Region faces most widespread storm since Jan 26, 2011

Forecasters Greg J., Michael N., Zachary F., Connor M., Jason M., Foot, Davies

As part of our team's pre-storm process to establish the basis for a snowfall forecast, we first introduce the data origins, that of "QPF" or "Quantitative Precipitation Forecast" The enclosed chart is based on NOAA data as rendered by the weather website

Several computer models have projected a general 1.5 to 2.0 inches of liquid for much of Virginia and Maryland, with up to 1.0 inches for southern Pennsylvania. With snow ratios expected to start "lower" due to marginal temperatures, we are anticipating much of the snow will fall at an 8:1 ratio, ending near 10:1 in western areas of the Mid-Atlantic.


The chart show indicates what is possible were this storm to "overperform" regarding both liquid amounts (closer to 2.0") and ratios. We expect snow to begin late Tuesday night, with the bulk of the heavy snow Wednesday morning to midday. This may cause ratios to decrease in areas near the coast, along I-95, with normally colder areas west of the major cities, along I-81 corridor staying with higher ratios.

BOTTOM LINE? We want readers in the Mid-Atlantic to be prepared for a heavy wet snow event that may produce 5-8 inches in the major mid- Atlantic cities by Wednesday noon. Much higher amounts of up to 12 inches are possible just west of those areas-- from southern PA to northern Baltimore County through Carroll, western Howard and down to west of DC and along I-81.

If liquid equivalent trends continue rising, and the storm begins Tuesday night as mostly snow, much of the region may face a significantly higher impact storm than is currently being forecasted by our team and other outlets.

(Forecasters Foot, Connor, Jason, Greg, Zach; Meteorologist Davies)

10:30 AM EST 3/4 : Previous update from the Winter Stormcast Team 

  • Eastern US NWS Regional HQ:  Winter Storm Watches in effect for all of central & western Maryland, northern & central Virginia, the Baltimore-Washington metro areas and southern Pennsylvania.

WINTER STORM MODE Due to the likelihood of significant winter weather within the next 48 hours,  "Winter Storm Mode" is activated for the following zones. This is to notify our readers of increased coverage and postings in affected local zones:

SYNOPSIS: After anxiously waiting for months on end for a big snowfall, it appears as though many readers in the mid-Atlantic will finally receive THE snowstorm of the year in a powder-filled last hurrah. The latest computer projections of liquid equivalents in this storm are showing a possible 1.0" or greater for the Baltimore-Washington area into southern Pennsylvania. Some models, such as the short-range NAM (North American Mesoscale) show up to 0.79" of liquid falling as snow, whereas the GFS (Global Forecast System) reduces snow liquid equivalent to just 0.49" as snow, with a disruptive 1.12" of sleet as another possibility! 

If the storm starts as all snow, then snow-to-liquid ratios may start lower, but end higher, at a point in time when the storm is at its peak in the overnight hours into Wednesday.  If so, the resulting snowfall could become a significant event for the region.
  • Bulk of the snowstorm should move through from Tuesday night to Wednesday night providing a period of heavy snow to many areas of central mid-Atlantic. The exact track of heaviest snow is still an uncertainty, but at the moment much of central and western Maryland look to be the center point.
  • This storm is likely to be a high impact event for much of the region, causing difficult travel, widespread school closures, and flight cancellations Tuesday night through Thursday morning. Below we outline the current scenarios that we see for this significant snowstorm with the first being most likely. 

SNOWFALL SCENARIOS: The map shown below displays shows our two scenarios for the heaviest snowfall amounts. If you are not in the areas, it does not mean you will not see snow, it just means that you will likely not be in the heaviest snow area. We will have additional updates and preliminary snowfall totals posted later today.

SCENARIO A (Slower storm with a northerly component, heavy snow in MD)

TIMING: In this scenario, the storm is a bit slower and is able to push further north before moving offshore. Expect precipitation to push into portions of the mid-Atlantic Tuesday evening. Snow would be heaviest through the day Wednesday before coming to an end from west to east Wednesday night.  

ACCUMULATIONS: Central and western Maryland, along with and south central Pennsylvania could see significant to high snowfall accumulations. Other areas across southern Pennsylvania could see a moderate to significant snowfall, especially across Franklin and Adams counties. Further east across southern New Jersey and Delaware, precipitation should start as rain and might change to snow for a few hours before pushing offshore leading to slushy accumulations of a few inches.  

IMPACTS:  Portions of central and southern Maryland could start as rain before changing to heavy snow. An extended period of heavy snow is likely across Maryland and extreme south central Pennsylvania (southern Adams, Franklin, Fulton, and Bedford counties) which could last for up to 12 hours. 

The snow would be heavy wet snow and given the heavy accumulations, damage would be expected for weak structures than cannot handle the weight of the snow. This would cause travel problems Tuesday night through Thursday morning across Maryland and southern Pennsylvania. Many flights would likely be cancelled on Wednesday at Dulles and BWI.

SCENARIO B (Storm departs more quickly. heavy snow stays in Virginia)

TIMING: Precipitation would begin across the mid-Atlantic Tuesday afternoon. Heaviest snow would fall across Virginia Tuesday night and taper off around midday Wednesday. 
IMPACTS/ACCUMULATIONS: The storm could push offshore before developing and not provide much precipitation to the central mid-Atlantic. This could lead to a mix of rain and snow changing to heavy snow with significant accumulations across Central Virginia. 
Further north some light to moderate snow is possible, but rain may mix in and lower accumulations. The snow would be heavy wet snow, so damage is possible if enough of it piles up on a weak structure. Travel would be affected Tuesday afternoon through Wednesday afternoon across portions of central and northern Virginia.


Unknown said...

January 2011 or January 2010? The latter is the time of the "snowpocalypse" or "snowmageddon." I don't remember any huge deep snowfalls in January 2011 (here in Frederick, Maryland which is central MD)but maybe there was. Hubby was out of the country and I'm pretty sure I'd remember having to shovel by myself after a storm like that.

ravensbbr said...

I. Love. Non. Drills.

They. Kinda. Rock.

Chris Wood...Wood you? said...
This comment has been removed by the author.
BioPat said...

Works for me, as well. I have changed my lessons for the rest of the week in anticipation of a major event. Now, LET IT SNOW!

Other items requiring attention:
1.Get vegetables for snow soup.
2.Gas up and start snow blower to get the dust out of the carb.
3.Download a good book.
4 Do the snow dance.

ravensbbr said...

BioPat, good ideas, wife just bought fixings for Cream of Crab (MD style - lots of Old Bay) and just downloaded Swiss Family Robinson free from Google Play, good to get back to a classic... to just figure out this dang snowthrower. Although if it's as heavy a snow as it could be, it'll be interesting to see if it's able to chew through it with as a high an H2O content as it could be...

BioPat said...

I've been advising my students all day to go out and get some exercise in this storm helping older neighbors and even their parents with shoveling duties. This type of snow fills the ER with heart attack victims from overloading the heart with the work needed to move heavy snow.

Julee said...

Shovel that heavy snow in layers! Top two inches, next two inches, etc.
I'm only 5 feet tall, that's the ONLY way I can do it!

My head is SPINNING from the varying snow totals! Two inches, a foot, 5 inches, ten inches. I guess we'll know for sure on Wednesday night. : P

Andy, Southern York County Pa said...

8-12 for Baltimore Metro with isolated spots getting 16.

Julee said...

You tease!