Yard waste, soaked insulation and ductwork is still waiting to be picked up along the sides of many streets in the area. As of this writing, it’s been 11 days since the nor’easter. Before the debris is gone and our memories of the storm fade into generalities, I wanted to go through some specific memories of forecasting this storm.
For the early part of the week of November 2nd, it was becoming clear that we might see some rain “smear” up the East Coast for the following week…the remnants of Hurricane Ida. Nothing too alarming was expected because Ida was correctly expected to fall apart in the cooler waters of the northern Gulf of Mexico. But by that week’s end, a “hybrid” storm-not really tropical anymore-was showing up in computer models for the following Wednesday, November 11th.
Just a brief explanation of a computer model: A weather forecast computer model takes a “snapshot in time” of national, hemispheric, and global conditions. This “snapshot” is usually done at 7:00 AM and PM every day. This twice-daily snapshot of millions of bits of weather information is turned into math and fed into supercomputers. Those supercomputers then project the weather out in time.
Friday, November 6th: It was becoming apparent that some kind of storm would affect the East Coast somewhere between Georgia and Delaware…with the likely bulls-eye between South Carolina and Hatteras 5 days out. Models are notoriously inaccurate this far out in time. However, I ended each weathercast that day with the admonition to, “Watch this one! We could see trouble on Wednesday, Veterans Day.”
Saturday and Sunday, November 7th and 8th: Watching the models from home, there was one usually reliable model predicting an outlandish “armageddon” of a storm with 100+ mph winds, stalled for 3 days directly along the Virginia coast. Every other model was showing a modest to moderate storm still well-south of our area. The “armageddon” model was considered an “outlier”-faulty and discounted-but still being watched carefully. By the way, the actual storm did stall for nearly 3 days, but off the South Carolina coast.
Monday, November 9th: The “armageddon” computer model weakened somewhat in its projection, but was still far too strong to believe. Virtually every other computer model was still predicting a more moderate storm, still to the south of our region. I focused much more heavily on the impending storm and talked about the one computer model which was predicting an outlandish storm. But with no consensus in the computer model solutions I emphasized that, “great uncertainty remains“, and, “keep posted on this one!” After the 6:00 newscast that evening, I made it a point to confer with WAVY News Director, Kathy Hofstetter. I basically told her that, “…if this storm is closer to the worst projections, it could be very, very big.” But I also told her that going on the air to say specifically that, “this IS going to be big would be highly irresponsible, at this point.” We needed one more day for model consensus.
Tuesday, November 10th: Model consensus began to take hold…somewhat. We were likely to get a slow-moving, historic nor’easter for Wednesday and Thursday. The “armageddon” model weakened to a more realistic solution farther south…while the remainder of the forecast models strengthened considerably. At that point, tidal & wind projections indicated an event similar to a nor’easter on February 5th, 1998. 7.1 feet above baseline.
Wednesday, November 11th: Upon getting up, I immediately tuned in to WAVY and watched my colleague, Jon Cash, say that the storm could now, “rival Hurricane Isabel in tidal height.” Rushing to view the models at home, I saw that the computer models were now in almost total agreement. Tidal projections were now expected between 7.6 to 8.0 feet! Isabel was 7.9 feet. The storm could indeed rival Isabel! Those projections got refined as we approached the height of the storm, but one day out…they ended up being pretty accurate.
Thursday, November 12th: Computer model consensus continued…and so did the wind and rain. Tides were already up to moderate flooding levels throughout the morning…and fell very little at low tide around noon. After leaving home before noon and dodging flood waters, I finally drove to within a block of the WAVY studios at 12:45…then navigated “Lake WAVY” with hip waders.
The initial tidal projections were closely refined in the final hours leading up to high tide; we went with a final projection between 7.7 and 7.9 feet. High tide was expected around 5:27 PM at Sewells Point. Complicating that high tide were unexpectedly high winds (65-75 mph) right at high tide! Winds held the tide in the harbor for almost another hour…reaching a maximum high tide of 7.74 feet at about 6:20 PM.
Those winds were transported downward by a band of moderately-heavy rain. We had obviously had moderately-heavy rain with 40-45 mph winds off and on for 2 days, but it was just our luck that this particular band of rain had 65-75 mph winds just at that time! Power outages skyrocketed between 6:00 and 8:00 PM.
While rain was persistently moderate for two days (6″-10″!), storm drains can usually handle that amount of rain stretched out over that long a time. However, the tides were up…with no route for that rain water to run off through the storm sewers and into the rivers. That rainfall obviously exacerbated the tidal flooding.
By late Thursday night, rainfall had decreased to a steady drizzle. And winds had dropped back off to 40 to 45 mph. The next morning’s high tide would still be problematic, but significantly lower. I left the studio as Jon Cash was arriving at 2:30 AM…and somehow made it home through darkened neighborhoods littered with debris and stalled-out vehicles.
Hopefully, this (long!) narrative has given you an idea of the early uncertainties in the forecasting process…but also the later certainties as the storm developed and finally, to the minute by minute coverage of the worst of the storm, referred to as “nowcasting”. Hopefully also, we won’t see another storm like this for a long time to come.
November 30th, 2009 at 6:10 pm by Cheryl Nelson under Weather
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