Specific to a single storm, I remember seeing news reports about Harvey being stalled or "blocked." Now that it is wandering out of existence, I wanted more details: Why Harvey stalled over Houston - World - CBC News NOTE: I had to view this in Facebook to get the audio. Perhaps @wxman might comment. My understanding from the Canadian Broadcast Corporation is: high pressure over the west (Nevada) with clockwise rotation low pressure over the east (Pennsylvania) with counter clockwise rotation jet stream passing north of both pressure systems locking the in place So in effect, the two pressure systems combined to create a southerly flow that held Harvey over Texas and Louisiana. The addressing a question about global warming, the meteorologist indicated a weak jet stream is more likely to cause similar weather patterns in the future. With winter approaching, I'm wondering if a similar pattern could result in a record snowfall? Bob Wilson
I have heard similar reasoning to other long lasting meteorological events (storms, pressure systems, etc). I'd also be interested in more information.
Smoke drifted down to the coast a month or so back. And lately from California brush fires. Evacuations still ongoing in the interior. Yeah tough fire season this year. Very little rain.
That is pretty much what happened. Upper ridging in the southwestern U.S. blocked Harvey from pushing farther inland than it did. If you recall, Harvey actually retrograded backing into the Gulf of Mexico after it had made landfall and meandered along the Texas coast for quite a while. That upper SW ridge actually pushed Harvey back to the southeast as it (upper ridge) continued to build into the southern plains. I was an operational meteorologist at the Brownsville office of the National Weather Service (BRO) in August of 1999 in a somewhat similar approaching hurricane scenario. A disorganized area of convection moved off the Yucatan Peninsula into the Gulf of Mexico similar to Harvey. The area of convection quickly organized into a tropical storm before becoming a category 4 strength hurricane ("Bret" - max sustained winds of 145 mph at one point) as it made landfall between Brownsville and Corpus Christi. Fortunately, the direct hit occurred in a sparely populated area of Texas (Kenedy County), so damage was mainly limited to uprooted trees, etc. I remember the models were initially bringing Bret up the mouth of the Rio Grande, which would have devastated Brownsville and surrounding communities. Fortunately, the models were wrong in that case. As I recall, the Gulf of Mexico sea surface temperatures (SST) were as much as two degrees C warmer than normal (warm anomaly) similar to the scenario with Harvey. Even the satellite images looked similar (very well-defined eye). However, Bret didn't stall like Harvey and continued into Mexico before a great deal of rainfall occurred in South Texas (a little less than 15" of rain was the max I remember). IIRC, the upper ridging was more to the north of that area and not directly in front of the direction of motion of Bret. As far as extra-tropical systems are concerned, yes it is possible for an upper low to become nearly stationary if it becomes cut-off from the main upper-level flow ("cut-off low"). Extra-tropical systems typically don't have the tremendous tropical moisture feed that tropical systems have. However, any systems that stall can result in excessive amounts of precip of any type.
As bisco says, we are having cool weather here. Harvey came thru I think we had 62 F high which in some places like Dulles may be record low (Dulles is "young" airport so records there not so rare). But we were cool before Harvey and cool after now into Sept, except one hot (normal) day tomorrow. And wet. We have not had to water lawns this summer. Normally we get zero rain except trop storm remnants as they pass thru.
