Saturday, February 28, 2015

Roaring into March

Roaring Into March

6:30 PM 2/28 - For the winter weary out there, although this next system is not exactly a "storm," it is going to speak volumes about why wintry weather requires adjusting to changing conditions. Failing to do so results in avoidable consequences, the risks of which were widely advertised well in advance.

Although the current NWS advisory map shows "only" Winter Weather Advisories for most of the Mid-Atlantic, we can sum up in two words what we believe conditions will closely resemble: LAST SATURDAY. 

Thus, our forecast and urging to be prepared on Sunday seems a virtual repeat of occurred throughout the region on Saturday 2/21:
  • Cold surface air in the teens and low 20s Sunday morning will allow for moisture overrunning at upper levels to fall as snow for the first 5-6 hours. The snow will stick on contact and create slippery road conditions within an hour.
  • Snow intensity will increase as the day progresses, and more travelers on the roads will confound the situation and hampering road crew efforts to address the snow.
  • Areas where less extensive pre-treatment of roads than otherwise might be expected for a weekday could lead to rapidly deteriorating conditions under 1-3" of snow followed by sleet and freezing rain.
  • The current precipitation and surface map projection for 7 AM Sunday indicates a widespread snow and ice situation affecting much of the Midwest, Ohio Valley and Mid-Atlantic states. 

By 1 PM Sunday, the widespread ice and snow is expected in these regions, continuing into the evening hours.

We hope that travelers and those holding Sunday service will make prudent and well-informed decisions whether adjustment to changing conditions is a more prudent action than "staying the course" if "ground truth" clearly presents a hazardous environment to the region by daybreak. Twice this winter, Sunday had an unpleasant outcome for many. We would prefer not to make it three.

Mr. Foot, Forecaster Mike Natoli and the Winter Stormcast Team

The hits keep coming

"And the hits just keep on comin'..."
- 1972 Album by the Monkees singer Michael Nesmith

Image source: NOAA Precipitation Projections for 7 PM Sunday 3/1

9:10 AM 2/28 - Updated team statement in progress. Synopsis of forecast concerns:
  • Significant cold surfaces in the Mid-Atlantic will be retained into Sunday as moisture overruns at upper levels. Precipitation will begin Sunday afternoon as mostly snow north of I-66, with sleet and freezing rain DC metro east. 
  • By evening, most precip will turn to freezing rain as upper and near surface temperatures warm to near 32 F -- continuing overnight into the Monday morning commute.
  • We disagree with the low-hazard assessment of this event as currently portrayed by the Sterling VA NWS as of 9:15 AM 2/28. The lack of a posted Hazardous Weather Outlook conveys a false sense of security to the public that a slight amount of freezing rain would not pose a measureable risk of hazardous travel. 
  • The 0.005" of freezing rain which occurred on Sunday morning, January 21 is evidence enough that the next 24-36 hours present an increasing risk of impactful weather to the Mid-Atlantic, as is currently depicted by the NOAA Weather Prediction Center.

Thursday, February 26, 2015

Southern Snow Surprise


Southern Snow Surprise...

  • Snow will fall rapidly and accumulate quickly due to cold surfaces. Up to 1" an hour is possible between 6 and 8 AM from the I-66 corridor to the I-95 corridor, including northern and central Maryland. Accumulation is expected to reach southern PA counties.

1:10 PM EST 2/25 - The climbing and expanding NWS Warnings, Watches and Advisories associated with the southern winter storm has no doubt set many to wondering about this system:
  • How much farther north might this storm track go?
  • Is there any potential for this system or "over or under" perform, and leave (or take away) a bigger surprise than current;y expected? 
We will address these two issues in the team statement below. We are not expecting a major snowstorm for the central and northern Mid-Atlantic, as most of the action should stay "south of DC" and centered on the Richmond metro area to the eastern shore. However, the problematic timing of this next potential event presents concern for the AM commute.

SYNOPSIS - The widespread winter storm which has been impacting the Deep South with extensive snow and ice will generally be kept to the south of the central Maryland region. 
  • However, we won't avoid seeing some snow from it. Tonight, Lows in the Mid-Atlantic will fall to the mid 20s overnight with increasing clouds ahead of the storm system passing by late. 
  • Precipitation on the northern edge of the system may bring light accumulations early Thursday morning. Though the Baltimore metro region will be on the periphery of the significant snow, it is worth mentioning as this system could cause some travel problems in the AM hours. 
  • A general rule with this event: The further south your location in the region, the more likely you are to see accumulating snow.
TIMING - Light snow in the metro area is expected by 3 AM Thursday, ending by 10 AM Thursday. 

ACCUMULATIONS - South of DC/Baltimore, we expect 1-2" of snow, with higher amounts near and east of the DC metro region. For Northern MD counties that border PA, snowfall will be lighter the farther your location is from the system. A dusting (or "Coating" up to 1" is possible.) 

HAZARDS - The timing (of course) during the AM rush will make for some difficult travel, especially south of the metros. Use caution on the roads if snow is falling, and give yourself a little extra time to get to work. Those north will have it a little easier, but if the storm trends just a little bit north, that could change. 

BUST POTENTIALS - What can go wrong with this storm? Unlike the last storm, the temperatures don't really matter much with this one. It's all about the track of the storm and extent of the precipitation field. 

  • THE BIG KAHUNA (20%): The computer model guidance has been trending significantly further north with each run lately. If this continues and the storm ends up even further north of where we expect, central MD isn't just on the fringes anymore. The excess moisture easily overcomes the dry air in place. This scenario could bring easily a significant snow south of the metros and accumulating snow to the north. Travel would be heavily impacted Thursday morning in this scenario. 

  • THE BUMMED BACHATA (15%): On the other hand, if the northerly trend in guidance abruptly reverses and the storm ends up south of expectations, northern MD ends up receiving no snow, while just a dusting reaching those south of the metros. This scenario would occur with a more southerly track of the low, or if the northern extent of the precipitation field doesn't reach as far as we expect. 

The situation with this storm could rapidly change (because it has been already), so stay with us for updates! We will keep you informed of the latest information.

(Map and Statement by Foreacaster Mike, Analysis and Forecasts by the Winter Stormcast Team