Catch me if you can.

"Catch me if you can."
- 2002 film starring Leo Dicaprio and Tom Hanks (Youtube trailer)

8:00 PM EST 2/16 - TEAM STATEMENT FOR SNOWFALL INTO THE OVERNIGHT

• Although decent bands of snow have set up across the region, uncertainty remains as to if the moisture levels of the system north of DC have enough depth to produce totals at the higher end of current ranges.
• Latest short range guidance as of 7:45 PM indicate dry air to the north is affecting snowfall rates in some areas of northern and eastern Maryland. In addition, the storm does not appear to be showing any further northward movement. 
• Extremely fine-grained snow flakes/crystals are developing in a level of the atmosphere where temperatures are between 0 and 5 F. Thus, snow ratios in the Washington DC area are estimated by computer models and visual inspection to be near 20:1, and 15:1 in northern MD. 
• The Winter Stormcast Team anticipates snowfall totals, with exception of DC metro, will stay at the LOWER end of our forecasted ranges for this event. See below for our earlier snowfall map. 

3:00 PM EST 2/16   SNOW ARRIVING IN DC METRO AND SOUTHERN MARYLAND. Further assessment of observations, short range guidance and ground reports indicates the system so far is on track to perform as expected. Dry air is slowly being eroded as moisture levels increase with the eastward approaching precipitation shield. We do not plan to raise or lower totals at this time. 

11:50 AM 2/16  TEAM STATEMENT ON SNOW TOTALS AND STORM OUTCOMES

We are cognizant that other outlets and forecasters have different snowfall totals than our map below, or are evaluating raising amounts ahead of the storm. We respect their choice to make that decision, but disagree on a different set of scientific grounds. 

Our view: Dry air ahead of the approaching precipitation will take a number of hours to overcome to achieve moistening of "the column." Evidence: Dewpoints in the region still below zero as of 1100 AM per NOAA Storm Prediction Center Mesoscale Analysis.

• Once this saturation level is reached, upper level and surface conditions can permit snow to reach the ground and not evaporate before doing so. However, a combination of recent surface observations and short range models suggests just light snow to start from Northern Virginia to DC and Baltimore by the PM commute. Heavier snow may not arrive until around 12 AM. 

• This dry air delay could easily reduce totals to the lower end of our ranges. A 1029 mb High pressure in Eastern North Carolina is also not moving out as quickly as expected.

• If we choose to adjust totals, we will first collect actual observable changes in ground truth once the system produces snow in our forecasted locations, versus using only model guidance. Based on the latest guidance, it is more likely we would hold or lower, not raise expected totals.

9:30 AM EST 2/16 - TEAM STATEMENT ON MONDAY-TUESDAY MID-ATLANTIC WINTER STORM 

It seems that storms this winter in the Mid-Atlantic this has been taking a page from the script written by Frank Abagnale Jr. If you know the incredible story, it recounts the travels of the deceivingly charming but elusive teenager whom outwitted federal officials for years while on a check-kiting scheme across the country. 

But similar to what's next for the Mid-Atlantic, reality (and the FBI) eventually caught up with Frank. The question is, will this storm dash away our hopes of one big snow like the clever thief, or will it give in at the last minute and deliver its secrets for all to see?

Summary of our projections:

• We project a 70% probability of a significant winter storm, with snowfall exceeding 4" in most locations south of the PA/MD line as indicated in our final map below.
• The bust scenarios below account for the 30% probability of a surprise and drastic change in the outcome

SYNOPSIS A storm system currently strengthening over the southern Plains will move into the Southeast tonight, and off the Carolina coast by Tuesday morning. 

• With extremely cold temperatures entrenched over the Mid-Atlantic, this will be a rare all snow event. Temperatures will range from the lower teens in central PA to the mid 20s in southern VA during the storm. 
• The precise track of this storm will result in a narrow band of significant snow accumulation, reaching some of the largest this winter season.

TIMING Snowfall will begin Monday late afternoon during the evening rush hour for the metros of the Mid-Atlantic. 

• Snow will move in from west to east. The heaviest snowfall is expected from around 10PM Monday night until 3AM Tuesday morning, before starting to weaken and taper off during Tuesday's morning rush hour.
• Some wrap-around enhancement can not be ruled out, hence why the NWS has warnings effective to 12 Noon Tuesday.

IMPACTS We are looking at a moderate to high impact event in which all snow that falls will stick. Road conditions will deteriorate Monday evening, become very hazardous Monday night, before improving during the day on Tuesday. Tuesday's temperatures still will only reach the upper 20s. This snow is expected to be of the light and powdery variety, rather than heavy, wet snow.

• Central Maryland: 4-8" between DC and Baltimore, 3-6" north of Baltimore.
• Southern MD: 4-8" near DC, 6-10" south.
• Northern VA: 4-8", Central VA: 6-10"
• Lower Eastern Shore: 6-10", Upper Eastern Shore: 4-8"
• I-95 Corridor in DE/NJ: 3-6"
• Southern Pennsylvania: 2-4"

NWS ADVISORIES

• WINTER STORM WARNINGS are in effect fo the areas noted in DARK PINK on the enclosed NWS Advisory Map. Visit the Eastern Regional HQ of the NWS to link to your area's local forecast office for current statements.

• WIND CHILL WARNINGS and WIND CHILL ADVISORIES expire this morning in Maryland as the brutal cold finally starts to loosen its grip, but will continue longer in PA and points north

BUST SCENARIOS - As always we like to stay one step ahead of Murphy's Law and let you know in advance how this forecast could go wrong. The above scenario is what we believe is "most probable". But there are some things that could emerge throughout the day Monday that may impact our forecast.

• The Big Bachata (10% Chance): How will a MD snowstorm figure out how not to snow? There is a chance the storm has trouble overcoming extremely dry air in place over the region currently. Dew point temperatures are well below 0ºF, and the storm will need to moisten the column of air before snow reaches the ground. It is possible, that dry air sucks some of the liquid out of this system and "wastes" a lot of the snow, leaving those north of Baltimore with 1-3", 2-5" falling in between Baltimore and DC, and 3-6" for southern MD.

• The Big Kahuna (20% Chance): As this storm develops offshore, it could also draw in additional moisture as it rapidly strengthens. This would create heavy bands of snow sliding across the Mid-Atlantic and surpassing our expected totals similar to what we saw almost exactly a year ago in February 2014 and on St. Patrick's Day 2014. Widespread amounts of 8-10" could show up between DC and Baltimore with 6-8" north of the city, and some areas in southern Maryland getting up to a foot of snow.

That being said, we do think the scenario outlined in the map is most likely. But since meteorology is not an exact science, it is important to express the uncertainty when it is present.

LAST PLAY OF WINTER? Spring-a-lings might want to stop reading here. Unfortunately the answer is no. A third round of brutal, arctic air is looking increasingly likely for Wednesday-Friday of this week. We will have more on this later, but it is looking possible that the temperatures may rival what we say yesterday and today. The second half of February is making up for lost time this season. Will there be better times in March ahead? Stay tuned for our long range look coming in the next several days.

Winter Stormcast Team: Forecasters Mike N., Connor M., Jason M., Mintong N., Troy A., Jolene W., Advisors Keith K., Dr. Pete W.,  and R. Foot