Friday, February 5, 2010

(see below for definition of this term and categories)

12:00 PM SATURDAY 2.6.2010  STORM STATUS REPORT # 3. Grade 9 students at the Baltimore County Schools' Crossroads Center calculated the following snowfall predictions on Thursday 2.4.2010 based on NOAA computer model data available at the time. Stormcaster Ryan K. has the team snowfall forecasts in the Winter Stormcast Zone.

STORM STATUS REPORT # 2: The team's current snowfall projections below are based on a new ratio of 16:1 as reported 11:30 PM Friday by Forecast Advisor Terpguy, a CoCoRaHS observer in Fallston, MD (Harford County).

OUR SNOWCAST PROJECTIONS If HPC data from map below taken verbatim, for the period 7 AM today to 7 AM Sunday:

St. Mary's to Frederick Co. to SE PA: 6 to 12"
liquid calculations: (.50 to .75" liq.) x 16
includes York-Harrisburg-Lancaster-Philly-central NJ

Anne Arundel Co. - PA/MD line - MD eastern shore: ~12"
liquid calculations: (.75 to 1.0 liq.) x 16
includes Balto Co., Baltimore City, Harford, Cecil

CURRENT LIQUID DATA Our snowcast is based the current HPC "Day 1" liquid map as of 5:00 AM, our 24 hour liquid/snow prediction 7 AM today to 7 AM tomorrow.(Click for larger version). HPC storm summary message as of 4:00 AM today.

Mr. Terpguy's snow ratio analysis
Snowfall measured: 5.5" averaged from 9 measurements.
Liquid equivalent: 0.34"   Apparent snow-to-liquid ratio 16.2:1

While this may seem outlandish to some, the culprit will be an upper level low rotating through the Mid-Atlantic during the day, tapping any available moisture in addition to the coastal storm wrap-around. Evidence of this development is clearly seen on radar.

ABOUT "KAHUNA"   A term used by Mid-Atlantic readers on this site to describe a significant snow event. Categories:
BIG KAHUNA = 6 to 12 inches
SUPER KAKUNA = 12 - 24 inches
ULTRA KAHUNA = 24" + inches
*Kahuna is defined by the Oxford English Dictionary as a Hawaiian "shaman" or advisor.

UPDATE FROM 10:45 PM FRIDAY 2.5.2010 

Blizzard Warnings are now in effect until 10 PM Saturday for large portions of the Baltimore and Washington metro areas, much of Delaware and southern New Jersey. This one storm will have such far-reaching impact on so many people across such a large area this may become a "Katrina-like event" for the Mid-Atlantic. Is that an outlandish or unfair comparsion to Gulf coast residents still recovering 5 years later? Perhaps, but take a moment to read our reporting from August 2005 before you render judgment.

Our team remains on board for 24 to 36+ inches of heavy wet snow across the I-95 corridor, central Maryland, northern Virginia and the Blue Ridge mountains. The previous post outlines our analyses and forecasts from Wednesday-Thursday 2/3-4 and original storm projections from Monday-Tuesday 2/1-2

The magnitude of this event makes one consider how we will clean it all up. What will we do in the Baltimore or Washington metro areas when 30+ inches of heavy wet snow collapse hundreds of roofs, and emergency crews are unable to reach them. What will happen when county grounds crews begin clearing school lots on Tuesday, to discover:
(A) 24+ inches of wet snow has frozen solid;
(B) Another storm could produce accumulating snow by Wednesday AM.

THE FOUR P'S OF IMPACT. The forecast team is assembling a series of 4 topics centered around the concept of what impacts the storm will produce, what public safety officials are doing to protect you, and simple steps you can take to protect yourself and your family. The discussions under each topic will be added, but before your electricity is cut by the Kahuna, consider posting in the comments your common sense suggestions for how to stay safe in the storm, and deal with the following issues:

TEAM ANALYSIS: SNOWFALL POTENTIAL  Early Friday evening 2.5.2010, the team sifted through data and generated this report on how we see the snowfall playing out in the next 24 hours. We thank Forecaster Snowlover from Franklin High School in Baltimore County for compiling this summary of the team discussion:

1. WILL SLEET MIX IN AND REDUCE ACCUMULATIONS? Some local forecasters believe that sleet will mix into the storm and in turn cut down on accumulations. Their hypothesis appears to be that due to the strengthening storm, warm air at the mid-levels of the atmosphere will cause snow to transition to ice for a period of time. Our forecast team believes that dynamical cooling will occur as the storm wraps up and keeps temperatures from warming enough to produce mixing, except along the lower eastern shore of Maryland.

Evaporative cooling is a different phenomena which helped produce the smaller snowflakes early Friday. The formation of snow crystals actually takes energy out of the atmosphere, and cools the surrounding air further. It's the same thing that happens when you step out of a swimming pool in the summer, the drops of water on your skin pull heat away from your body as they evaporate. Now that the storm is well-underway, it is dynamical cooling that will keep sleet from mixing in over Maryland & Virginia counties west of the Chesapeake Bay. We do believe that areas on the eastern shore have a greater chance for mixing, with far lower snow totals than the western shore.

2. WILL SNOW-TO-LIQUID RATIOS CHANGE? The snow ratios will play a big role in determining the final snow totals. With total liquid shown at over 2 inches in many places, the ratios could determine whether just 20 inches fall or well over 30 inches. Our thinking is that the ratios will start out at 10:1 tonight, transition overnight to 14:1 and end at 18:1 tomorrow. The ratios will increase when the storm strengthens along the coast. When a low rapidly develops along the east coast it pulls cold air into the circulation, this will cause the ratios to increase when the low also increases. The snow flake size will also be affected by the developing low. They may become smaller as morning approaches, increasing fluffy-ness of the snow.

7:30 PM UPDATE: Mr. Terpguy, a CoCoRAHS observer from Fallston, MD and advisor on this site since 2005, reported his official first ratio is 12:1.

3. WHAT MIGHT CAUSE HIGH TOTALS? Many factors will have an influence in the final snowfall totals. The snow ratios are one factor. When a storm becomes extremely strong its forward motion can slow down. The low will move at a very slow pace when it reaches the VA coast, allowing "banding" of snow to set up over the eastern Mid-Atlantic. We could see consistent snowfall rates of 1-3" per hour into the early morning hours.
Lead writer: Snowlover.
Collaborators: PasadenaMatt, Ryan K., Winterman, Dakota, Brisko, Foot, Terpguy.

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