Saturday, January 2, 2010

Forecast Team & Storm Grade Report:
Mr. Foot, Winterman, PasadenaMatt, Poochieweather, Mr. RK


Thank you for your patience as the team just concluded an extensive analysis of the situation. Our results will be posted in segments below-- refresh several times in the next 15 minutes. This update pertains to Maryland from Harford County to Anne Arundel County to Western MD, including the WV Panhandle and Northern Virginia.

ARRIVAL By 11 PM Thursday night 1/7  (from 1/6)
ACTUAL 9:30 - 10:00 PM
11 PM to 5 AM: Periods of light to moderate snow
5 AM to 7 AM: A brief lull caused by dry slot
7 AM to 9 AM: Second band of moderate to briefly heavy snow develops along coastal portions of Bay-area counties and along I-95 northward to Cecil County, MD.
By 9 AM: Snow quickly tapers to scattered flurries until 1 PM.

Note: Northern VA and West Virginia panhandle will see an earlier stop time, and may not be impacted by the coastal deformation bands expected to develop. However as NWS advisories indicate, those areas should receive amounts at or higher than the 4" baseline due to a longer period of time when accumulating snow was falling. These regions received an earlier start time (this evening) and will be followed by an earlier end time.

As reported by Forecast Team and BCPS Crossroads Students
1 - Washington DC (Dulles Airport)
2 - BWI Thurgood Marshall Airport & Philadelphia airport
3 - Along a line from Frederick-Westminster-Towson-Belair
4 - PA/MD line to southern Pennsylvania
5 - Pittsburgh, PA ; Martinsburg, WV ; Loudon County, VA
6 - Hagerstown, MD to Garrett County, MD

Indications NWS Winter Advisories extend to central Mississippi

Snow has arrived across the Mid-Atlantic as of 10:00 PM. Short-waves embedded in the flow at 5,000 feet and higher will activate mid-level moisture transported northeast from the Gulf. This is highly evident from current radar, and we may be facing an "over-performing" event.

Wednesday evening, our team of MD high school students and PA college students investigated the upper level data from NOAA's 7pm Barotrophic Map for 850 millibars (5,000 feet): We learned that...

1. There were several upper level lows across the "ArkLoTex" becoming entrained with the shortwave coming from the midwest.
2. We calculated the shortwave locations as of 7pm last night, and projected their movement forward based on wind barb ticks showing a general 25 mph speed.
3. There are more embedded shortwaves and lows than other forecasters are anticipating. The computer models cannot detect each wave in the flow.
4. We calculated a total duration of 22 hours between arrival of first shortwave ridge along Blue Ridge at approximately 7pm tonight and departure of final shortwave by 1 pm Friday as it crosses the DelMarva.
5. Based on dewpoint depression data from the Mid-south, it appears available moisture is much higher. We believe liquid amounts will exceed .25" and snow ratios will range from 15:1 to 17:1. This suggests a total snowfall greater than 4"
This analysis was conducted using core atmospheric data from NOAA, not computer models and applying basic concepts of waves and the physics of flow.

HYPOTHESIS Based on entrainment of more Gulf moisture and more widespread influence of shortwaves moving over this precip shield, the team believes Forecaster Winterman's call of a widespread 4 to 6" is spot on. We shall issue a storm grade amount for the BWI Thurgood Marshall Airport this evening. That number will remain set for verification and cannot be changed. We have thrown down the gauntlet. We challenge other Mid-Atlantic forecasters to run the data and re-examine their conclusions. As we say in education, "the data do not lie."  This forecast is a product of the Maryland and Pennsylvania educational systems: You taught them, now they're teaching us.

IS THERE A "BUST ZONE?"  Absolutely! Any credible scientist would remind us there is a 50% or greater probabililty any hypothesis is or will be wrong. We can hear fellow forecasters saying: "Did you account for the dry slot potential if the waves separate?"  We'll examine that thoroughly tonight, just to cover all bases.

IMPACTS This event will produce accumulating snowfall across the Mid-Atlantic and along the I-95 corridor including Baltimore, Washington and Philadelphia. It is highly probable many school systems affected by this snowfall may be delayed or closed. Snow will be falling at the crucial decision time of 4 to 5 AM. Were a large school system to announce a delay at 5:00 AM, there is only a 2 hour window delay during which a re-examination of conditions can occur.

The 850 mb data clearly shows that by 7 am on Friday, the final shortwave trough that was over Mississippi at 7pm Wednesday will not have cleared the Mid-Atlantic before 7am Friday. We expect a second, heavier band of snow to develop between 7 and 9 AM before the shortwave trough moves through.

You may draw your own conclusions on what this means. This evening, the team will use core stand-alone moisture data to determine the liquid equivalent, final snow ratio and a "Storm Grade Amount" for BWI Thurgood Marshall Airport. A number of other verifiable locations across the Mid-Atlantic will be included. We will also show a cross-comparison between our numbers and other weather media providers. If our results are not met, we will be the first to admit error and tell you why. Until then, enjoy the snow!

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