Thursday, March 5, 2015

59 comments:
Snow On Schedule


8:00 AM 3/5 - RADAR UPDATE (Forecaster Mike and the Winter Stormcast Team)

With moderate snow now being reported across the central Mid-Atlantic, the latest in a long series of significant winter storms is on schedule. Let us know you conditions - temperature, precipitation type, and if snowfall is sticking! For the next several hours to at least noon, areas seeing snow should expect up to 1" an hour with low visibility. 

ACCUMULATIONS - We still expect a region wide 5-8" of snow before all is said and done, with 3-6" south of route 50. Those southern areas actually have the best chance to get more than forecast of 3-6", if heavy banding occurs during the early afternoon. This is something we will be keeping a close eye on! See below for our final snowfall forecast map, and let us know how this event verifies in your area compared to the forecast.

ON TRACK? - The second wave of precipitation has arrived on schedule and precipitation rates will start to increase again. Similarly, the freezing line is progressing right on schedule. This storm trended a little later in its timing, but don't let the late start fool you into thinking it's nothing.
  • THIS MORNING - Snow, heavy at times, will continue across the region. Due to last night's rain and warm temperatures, it may have trouble sticking initially closest to the Bay (which is why we need your reports!). However, temperatures will continue dropping, reaching around 30ยบ by noon with upper 20s NW and continuing to fall.
  • THIS AFTERNOON - Snow will continue, with the heaviest snow bands dumping just a little further south than this morning. Things will slowly track further south and east before tapering off between 4PM and 7PM.
  • TONIGHT - The system moves out and it's right back into the deep freeze. Expect lows in the upper single digits to lower teens across the region (ugh).




WILL SPRING COME, EVER? - While Friday will feel like the middle of winter, we will gradually moderate. We may even see temperatures near average for this time of year by the middle of next week! (Kinda sad when that feels like summer, huh?). After that, it's a little unclear if we stay warm or retrograde back, but from now on, the cold outbreaks will get weaker and weaker. Stay tuned and stay safe today!
(Forecaster Mike)

Wednesday, March 4, 2015

92 comments:
Winter Strikes Back

3:50 PM 3/4 - FINAL SNOWFALL PROJECTIONS & STORM SCENARIOS BELOW



TIMING – Rain will move in with higher intensity this evening. start to mix with sleet for the NW counties around 10 PM-1 AM, then transition to all snow around 1 AM-4 AM. 
  • The metros will mix with sleet from 1AM-4AM and transition to all snow by 4AM-7AM with heavy snow possible across the region by daybreak. 
ACCUMULATIONS – We expect light sleet accumulations overnight, then around 5-8” of snow north of route 50. South of there, expect lesser totals. Roads will be hazardous across much of the Baltimore/DC Metro early Thursday morning, continuing through the day as temperatures drop. 

TEMPERATURES – Hovering in the lower 30s while we transition tonight, getting into the upper 20s early Thursday, mid 20s by midday, then rapidly plummeting to the lower teens overnight. 

BUST SCENARIOS – As with any forecast, there is a significant amount of uncertainty with this system. The last two years, we’ve had snow events in early March that did not live up to expectations. This system actually bears a lot of similarity to March 3rd, 2014. 

  • BAILING TO A BACHATA (20%) – The prime bust scenario would be a slow change-over to sleet and snow overnight would mean more water on the ground, warmer ground temperatures, and less snow. The cold will still come, but just a few hours later than what we expect could allow us to escape the worst of the impacts from this one. Less time in the snow means less snow falls, and less snow sticks, and most regions would fall more in the 3-5” range, struggling to get to the lower end. 
  • GOING "BIG KAHUNA" (20%) – Conversely, if we have a fast change-over to snow, and limited sleet, then much of the region is all snow well before daybreak. This allows for a burst of accumulating snow to whiten the ground again before sunrise, with ample moisture falling all as snow. This scenario could cause some people to receive over our 8” high end, with 8-10” common across the region.

11:30 AM 3/4 - UPDATED SNOWFALL TIMING GRAPHIC & OVERVIEW
  • Latest computer models including the European, GFS, NAM and others beginning to indicate a longer duration of snowfall on Thursday than first anticipated. Original ideas south of I-76 in PA to southern Maryland was snow ending by early afternoon then clearing.
  • New scenario being considered: (from central VA to southeastern PA) - a changeover of sleet/snow  to all snow by 5 AM, with all heavy snow from 6 AM to 12 PM, then light to moderate snow remainder of the afternoon, tapering after 4 PM. See Columbia, MD NWS hourly weather grid for timing in a representative location
  • This setup would significantly impact the AM and PM commute, whereas earlier ideas had more of just an AM impact with some inprovement toward the PM commute.

3:30 AM 3/4 - TEAM STATEMENT & MAP ON STORM SCENARIOS

SCENARIO A - THE ALL SNOW BIG KAHUNA (60%)   
  • Heavy rain mixes with sleet late Wednesday evening and transition to snow from NW to SE starting around 10pm and reaching the Bay by 3AM. 
  • Then, several hours of heavy, accumulating snow until Thursday morning with temperatures dropping into the 20s. 
  • By the early afternoon, this scenario would bring a significant (4+”) snowfall region-wide. Some areas could see up to 10” of snow north and west of the 95 corridor.
SCENARIO B - THE BACK-AND-FORTH BACHATA (40%)
  • This scenario would occur if the front stalls further north and cold air has a harder time moving in. Rain would continue falling through the evening mixing with sleet late at night. 
  • Then the transition to snow would occur Thursday morning from 3AM to 8AM. Snowfall would still be disruptive to the morning commute, but not quite to the high totals expected in Scenario A. 
  • Most places could still get up to a few inches for the metros, and maybe reaching the “significant” criteria north and west of the cities.
CURRENT PRECIPITATION TIMELINE FOR AREAS NORTH OF THE BAY BRIDGE
(Note: A revised timeline to be posted around Noon today)

INTELLICAST REGIONAL RADAR

4:00 PM 3/3 - OVERVIEW OF HAZARD TIMING & BASIC IMPACTS for the next 3 days for the Ohio Valley, Mid-Atlantic and Delmarva Regions. 
  • OVERNIGHT: Sleet and freezing rain this evening for areas south of I-76 transition to all rain by evening and continue into the daybreak hours as temperatures rise above 32 F by  midnight. 
  • WEDNESDAY: Moderate to heavy rain with temperatures in the 40s will lead to widespread snowmelt, runoff and some creek, low-lying and basement flooding.
  • WED NIGHT INTO THU: Rain begins mixing with sleet and snow in the evening, changing to heavy snow after midnight. Periods of heavy snow and snow-covered roads likely for the Thu AM commute. Daytime Thu temps in 20s drop to low teens overnight.

Tuesday, March 3, 2015

Meanwhile on Hoth

42 comments:
Meanwhile on Hoth

8:30 AM 3/2 - If you have been feeling like the region is beginning to resembles a Star Wars movie set, we would tend to agree. March is now the fifth straight month of wintry weather to be observed in the Mid-Atlantic. Appreciable snowfall for this season first began in mid November 2014 and show no signs of stopping.

IMPORTANT PLANNING MESSAGE FOR THE EDUCATIONAL COMMUNITY: We recognize that in some states such as Maryland, standardized testing is scheduled to commence this week and next across the state. With this in mind, we wish to provide the best available information about the weather pattern to aid school administrators in navigating this complex scheduling challenge ahead. 

This synopsis is valid for areas from I-76 in Pennsylvania south to the I-66 and I-50 corridors, including the Philadelphia, Baltimore and Washington DC metro areas. 

WHAT WE KNOW
  • MON 3/2 - Dense ice on a several inches of snowpack will begin to fracture and melt with rising sun angle. This will lead to significant runoff into the evening. Temperatures are expected to drop below 20 F for most areas of the northern and central Mid-Atlantic north of the DC metro. 
  • TUE 3/3 - Runoff will have refrozen overnight and is likely to prompt more school delays due to widespread ice in parking lots, sidewalks and sidestreets. Residual moisture ahead of a warm front will reintroduce sleet and freezing rain toward the Tuesday PM commute. See the NOAA precipitation projection below for 7 PM Tuesday night.
  • WED 3/4 - Temperatures warming to the 50s will lead the most improvements in melting of snow and ice on sidewalks, driveways and snowpack. Extensive moisture ahead of a cold front will deliver up to 0.75" of rain across the Mid-Atlantic. However, the front will be fast-moving, and turn rain over to snow Wednesday night. 
PROJECTED PRECIPITATION & SURFACE MAP FOR 7 PM TUESDAY 



WHAT IS LESS CERTAIN
  • THU 3/6 - Cold air rushing in behind the Wednesday frontal passage may change rain to snow by evening, continuing into Thursday AM. Warmer surfaces should negate some of the snowfall, so if forecasts are for 2-4" (as an example), warming and March sun angle may reduce actual accumulation to less than that. However, road conditions may be problematic again by daybreak Thursday. 
  • FRI 3/7 - Temperatures drop back to below freezing in wake of the Thursday front.  Any surface moisture, standing water or snowpack will refreeze Friday morning as highs are not expected to break 30 F for most areas.
We will continue to monitor the mid- and late-week developments and update later today when we have new information. 

If you liked our Star Wars Hoth reference, we defer the credit for the photo to this creative blogger which has a series of crafty and chuckle-worthy shots at http://media.gunaxin.com/battle-hoth/179677. Given the long and toilsome winter, it's our way of trying to use some humor to help warm hearts.

Mr. Foot, Forecaster Mike, Advisor Keith and the Winter Stormcast Team 

Saturday, February 28, 2015

Roaring into March

45 comments:
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

13 comments:
"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.