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Weather Wonk Time

Jason Samenow @ 11:24 PM

A Wonkish Forecast

Normally my forecast commentaries are pithy during summer. The discussion that follows is a departure from this as we have a very complex weather pattern setting up...

The old frontal boundary that provided us with welcome relief from the excessive heat has stalled just to our south, complicating the forecast now through Sunday. Rain producing waves are going to move along this front, but how far north is the rain shield going to get? Will a large area of high pressure to the north suppress the rain to the south? Which wave will be the biggest rain producer and when? Model guidance is all over the place making this the most difficult forecast I can recall since late February . One model, the NAM, forecasts about 0.5" of rain between 8am this morning and 8pm Sunday. Another model, the GFS, forecasts about 7.0" of rain during this period.

My weather forecasting professor at UVA, Pat Michaels (yes the same Pat Michaels who's the well-known climate contrarian) taught me that when you have computer models that don't agree, look out the window. In other words, consider the current conditions, and see which model best reproduces them and make a judgment accordingly.

Without getting into too much detail, it would appear to me that the NAM better reflects reality than the GFS (or in weather speak: it's initializing better), so I am tempted to believe the NAM has a better handle on the forecast. Furthermore, the GFS precipitation bullseye over DC is likely overdone and may represent a feedback problem with the model. Lastly, other models do not support the GFS's aggressive (bordering on unrealistic) rainfall amounts. Generally speaking, I believe the high to the north will keep the heaviest precipitation south of our area. When all is said and done, I believe we'll see only between 0.5" and 1" of rain over the weekend.

As far as timing, I would expect the best chances of rain this afternoon and tonight and on Sunday morning into the early afternoon. Here are the daily details:

Today: Mostly cloudy, with a 50% chance of rain (the NWS "digital forecast" shows a 99% probability of rain as I write this). High near 80.

Tonight: A 50% chance of rain. Low near 70.

Saturday: A 30% chance of rain in the morning, mostly cloudy in the afternoon. Highs near 80.

Saturday night: A 40% chance of rain towards dawn. Low near 70.

Sunday: Mostly cloudy with a 40% chance of rain, especially in the morning. High near 80.

I will concede my confidence in the forecast is much lower than usual. Please check back for updates late this afternoon and each weekend morning.

Weather Wonk Weekend in Baltimore

As far as I know, this is a first: An on-line weather community has organized its own conference. About 100 weather hobbyists and meteorologists from up and down the East Coast will attend (including yours truly). The Conference, to be held near Baltimore Washington International Airport, will feature a series of entertaining and educational presentations including a slideshow from photographer Kevin Ambrose and a talk by Weather Channel Winter Weather Expert Paul Kocin.

Weather Wonk Week in DC

Not to be outdone, next week (August 1-5) the American Meteorological Society is hosting a meteorology conference trifecta right in our backyard:

The 21st Conference on Weather Analysis and Forecasting
The 17th Conference on Numerical Weather Prediction
The 34th Conference on Broadcast Meteorology

Last I heard, close to 500 meteorologists will be attending these conferences (including yours truly, again). Many of the top TV forecasters from across the country will be in town as well as some of the nation's preeminent weather forecasting researchers.

Odds and Ends

  • Chillin': Is your office freezing cold? Well, you're not alone according to this Washington Post article.
  • Harvey by Sunday?: Don't rule it out. The National Hurricane Center says the wave east of the northern Leeward Islands could develop into a depression in the next couple days. If Harvey forms over the weekend, that will have given us an unprecedented eight named storms in the Atlantic Basin through July.

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