Wednesday, February 3, 2010


Recent computer model trends for liquid equivalent suggest a large portion of the Mid-Atlantic may be facing a March 18-22, 1958 scenario.  All current snow forecasts would be low by comparison. For a look at how that storm unfolded, review this report from the former U.S. Weather Bureau. What "Katrina Kahuna" means will be explained further in our "4 P's of Impact" post on public safety and preparation.

Some professional forecasters believe models may be under-estimating strength of the surface low. Between 3:53 and 4:53 PM, the low pressure center in Columbia, SC dropped from 1003 to 998, a 5 millibar drop in 1 hour. NWS offices expanded  Blizzard Warnings and may to do so again. Our team is compiling a quick scientific overview of the situation and why we believe our snowfall projections will verify.

SNOW RATIO UPDATE Any CoCoRAHS precip reporters in the path of this storm are encouraged to calculate and post snow-to-liquid ratios once adequate accumulations greater than 1" occur. Mr. Terpguy in Baltimore County will post his calculations in the comments this evening. Instead of the 12:1 we estimated, it may be closer to 18:1.

11:15 AM TEAM STATEMENT: STORM TOTAL 24 to 36 INCHES with locally higher amounts across the Baltimore-Washington metro areas to the PA line. By comparison, independent predictions made by 9th grade students at the Baltimore County Crossroads Center, whom on Thursday 2-4-2010 calculated 25.6 to 33.8 inches by Saturday 11 pm at BWI Thurgood Marshall Airport as representative location of storm impact. (Mr. Foot's grade 9 collaborating student forecasters included P1: R.W. and W.B.; P3: B.H., M.J.; P4: R.E. | Forecasts set at 3:15 PM Thu 2-4-2010)

West Virginia | Central & Western Virginia | Eastern Virginia
Baltimore-Washington  | Pittsburgh | State College | Philadelphia  | SW Ohio

Virginia 7 - 9 AM | Central Maryland - West Virginia 11 AM - 12 PM
Southern PA 1 - 2 PM | DelMarVa 2 - 3 PM | Central PA 4 PM 
Southeast PA 4 - 5 PM | New Jersey 5 - 6 PM
Northern PA 10 PM Friday - 12 AM Saturday
*Based on analysis of upper level shortwaves on NOAA's 00z (7pm 2-5) 850 mb chart

GFS*: 2.0 - 3.0  | NAM*: 2.5 to 4.0 throughout the Mid-Atlantic, suggesting this could be an extremely heavy snowfall of 24 to 36 inches across much of the Northeast I-95 corridor from Virginia to central New Jersey. The forecast team urges citizens to complete preparations now and remain off the roads this evening if at all possible.
*want to know more about all these weather acronyms, check the NWS Glossary

FRIDAY AFTERNOON & EVENING   By 6 pm, snow will be widespread across the Mid-Atlantic from Ohio to Virginia to the Jersey shore. Winds may increase overnight from the projected 20-25 mph to reach Blizzard criteria, adding to existing warnings already in place for parts of New Jersey and the DelMarVa.

SATURDAY  Heavy snow continues overnight and into the day across much of the Mid-Atlantic south of the PA/NY border, accumulating 2-3" per hour in some locations for 4 or more hours. Thundersnow, lightning and gusty winds are possible. Coastal winds increase to gale force as the secondary low wraps up along the North Carolina coast while moving slowly northeast.

By late Saturday afternoon, a widespread 20-28" snow is projected from southwest Virginia to Trenton, NJ, including the I-95 corridor of Baltimore-Washington, southeast Pennsylvania and southern New Jersey. Isolated higher amounts are possible 30-60 miles west of I-95 from northern Virginia through Carroll/Baltimore Counties into southern York, Lancaster and Chester. Additional banding overnight will raise totals above 24"

SATURDAY NIGHT - SUNDAY By Saturday evening 8-12" in New York City, ending by Sunday morning. Some mixing may occur along I-95. Areas of the coastal eastern shore and Virginia tidewater see up to 6" of snow along with sleet and freezing rain.

Strong coastal and inland winds will continue, but as snowfall tapers off, it will be replaced by significant blowing and drifting snow. Temperatures by nightfall Sunday will have dropped into the mid teens to low 20's across the Mid-Atlantic. Overnight temperatures like this will freeze solid any snow not removed, potentially paralyzing the region for a significant period of time. A statement from emergency management in Arlington County, VA summarizes the situation:
"A severe winter storm, with near blizzard conditions, is forecast to hit (the region) Friday Feb 5 through Saturday Feb 6. Be prepared to shelter in place for 3 to 5 days. Please stay off the roads. Snow crews will plow primary and secondary roads first for emergency vehicles.  It may take 36-48 hours after the snow stops before County plows can get to residential streets. Removal and treatment may take several days."
Forecast discussions from NCEP's Hydrometeo. Prediction Center
in Camp Springs, MD and local National Weather Service offices:
HPC Heavy Snow & Ice | Short Range 12-36 Hour | Prelim Extended

NWS office discussions: Sterling, VA | Wakefield, VA | Blacksburg, VA
Charleston, WV  | State College, PA | Mount Holly, NJ | New York, NY

10:30 PM THURSDAY 2-4-2010 A powerful low pressure system encompassing much of the central and eastern United States is combining with a significant influx of tropical Pacific moisture enhanced by El Nino-enhanced sea surface temperatures. This low pressure is also accessing moisture from the Gulf of Mexico and Atlantic Ocean, and will develop into a potentially paralyzing winter storm before moving off the Carolina coast by Sunday morning.

SITE UPDATE STATUS  The team and students appreciate the many important and thoughtful questions from readers. Please remember that team members are high school and college students whom partner with several adult advisors and teachers. Updates occur once the team has a chance to collaborate and independently verify data collected during the day.

Please consider the impact this dangerous storm could have on your family, students, schools and property, and make the necessary arrangements if you believe the data is not lying. If you think it's just Day After Tomorrow style hypecasting, and see this becoming the biggest bust in modern forecasting, consider a quote by Optimus Prime in Transformers 2, who said to the National Security Advisor: "What if we leave, and YOU'RE WRONG?"

What if we leave sound bite
What if we leave sound bite

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