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September Banter 2023


George BM
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Forecast Discussion

Thursday, September 14, 2023 3:28PM EDT

Our most significant and dangerous flash flood threat in more than 50 years will begin by this evening. Through Monday parts of the region may see more than half-a-years’ worth of rainfall.

A Flash Flood Watch is in effect for the entire Washington/Baltimore Metropolitan region from 6PM this evening through Saturday though this will almost certainly end up being extended through at least Monday as forecast details for Sunday and Monday become clearer.

With a near record strong WAR, a deep trough over the Ohio Valley and moisture from Margot streaming north from the Caribbean and western Atlantic east of Florida, Pwats will rise to the 2.25”-2.5”+ range from this evening through the beginning of next week. Clusters and trains of tropical downpours/storms will move north over the region at all times of the day. With limited sunshine and high moisture content temperatures will probably only vary by about 5-10F from daytime highs to nighttime lows (Low/mid 80s and mid/upper 70s respectively). Dewpoints will remain in the mid/upper 70s throughout the period. As far as severe weather goes there will be a daily threat of gusty winds and even a brief tornado or two especially with any transient supercells given CAPE values of 1500+ J/kg and effective SRH of 150-200 m2/s2. Lack of downdraft CAPE will prevent a bigger wind threat with storms though there may be a couple of mesovort maxes that move from south to north over the region over the next couple of days which may enhance both deep-layer and low-level shear leading to a locally higher risk of a brief tornadic supercell as well as bowing segments allowing for damaging/near-severe wind gusts and a QLCS tornado threat.

The main threat by far, however, will be the very heavy rainfall rates with these downpours and storms. Given the aforementioned Pwats and CAPE any location that gets under a band of storms that trains over the area for an extended period of time may receive several inches of rain within a few hours leading to major flash flooding. Even areas that don’t get stuck under a train of convection as frequently if at all will see many individual storms or clusters over the next couple of days resulting in several inches of rain and flooding concerns. All of the above does not even account for when Margot will finally move north into the region by the Sunday PM/ Monday AM timeframe. More on that below.

Models are coming into much better agreement that by sometime Sunday Margot will make landfall along the Carolina coastline being pulled north fairly rapidly by the strong ridge of high pressure to the east and deep trough of low pressure to the west. While the exact track and timing of the center are still being ironed out, as this is still 3 days away from occurring, it’s now looking very likely that at least a majority of the Baltimore/Washington region may experience significant impacts from Margot. Ahead of Margot on Sunday the low-level shear that will be with us through the weekend will further increase leading to a higher likelihood of tornadic supercells. As the center approaches and moves over the region a solid shield of heavy rain will move through leading to an additional several inches of rain. The biggest uncertainty that remains with Margot is how strong the tropical system will be at landfall along the Carolina coast as anything ranging from a tropical storm to, in the worst-case scenario, a major hurricane is plausible. This will determine the difference between getting several inches of rain with gusty winds Sunday into Monday OR damaging to hurricane-force wind gusts teaming up with the heavy tropical rains leading to widespread tree and structural damage.

We will continue to monitor this potentially catastrophic situation with frequent updates over the next several days.

 

Forecaster Wannabe: George BM

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  • WxUSAF pinned this topic

First Fall 2023 HH.

Who is drinking what? BCBS here.

Os are on late, starting a series at Arizona. Rays are playing well again and nipping at the heels. Coming down the stretch. Should be fun.

College football is underway; NFL starts in less than a week.  Winter is coming..

Great time of year!

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21 hours ago, George BM said:

Forecast Discussion

Thursday, September 14, 2023 3:28PM EDT

Our most significant and dangerous flash flood threat in more than 50 years will begin by this evening. Through Monday parts of the region may see more than half-a-years’ worth of rainfall.

A Flash Flood Watch is in effect for the entire Washington/Baltimore Metropolitan region from 6PM this evening through Saturday though this will almost certainly end up being extended through at least Monday as forecast details for Sunday and Monday become clearer.

With a near record strong WAR, a deep trough over the Ohio Valley and moisture from Margot streaming north from the Caribbean and western Atlantic east of Florida, Pwats will rise to the 2.25”-2.5”+ range from this evening through the beginning of next week. Clusters and trains of tropical downpours/storms will move north over the region at all times of the day. With limited sunshine and high moisture content temperatures will probably only vary by about 5-10F from daytime highs to nighttime lows (Low/mid 80s and mid/upper 70s respectively). Dewpoints will remain in the mid/upper 70s throughout the period. As far as severe weather goes there will be a daily threat of gusty winds and even a brief tornado or two especially with any transient supercells given CAPE values of 1500+ J/kg and effective SRH of 150-200 m2/s2. Lack of downdraft CAPE will prevent a bigger wind threat with storms though there may be a couple of mesovort maxes that move from south to north over the region over the next couple of days which may enhance both deep-layer and low-level shear leading to a locally higher risk of a brief tornadic supercell as well as bowing segments allowing for damaging/near-severe wind gusts and a QLCS tornado threat.

The main threat by far, however, will be the very heavy rainfall rates with these downpours and storms. Given the aforementioned Pwats and CAPE any location that gets under a band of storms that trains over the area for an extended period of time may receive several inches of rain within a few hours leading to major flash flooding. Even areas that don’t get stuck under a train of convection as frequently if at all will see many individual storms or clusters over the next couple of days resulting in several inches of rain and flooding concerns. All of the above does not even account for when Margot will finally move north into the region by the Sunday PM/ Monday AM timeframe. More on that below.

Models are coming into much better agreement that by sometime Sunday Margot will make landfall along the Carolina coastline being pulled north fairly rapidly by the strong ridge of high pressure to the east and deep trough of low pressure to the west. While the exact track and timing of the center are still being ironed out, as this is still 3 days away from occurring, it’s now looking very likely that at least a majority of the Baltimore/Washington region may experience significant impacts from Margot. Ahead of Margot on Sunday the low-level shear that will be with us through the weekend will further increase leading to a higher likelihood of tornadic supercells. As the center approaches and moves over the region a solid shield of heavy rain will move through leading to an additional several inches of rain. The biggest uncertainty that remains with Margot is how strong the tropical system will be at landfall along the Carolina coast as anything ranging from a tropical storm to, in the worst-case scenario, a major hurricane is plausible. This will determine the difference between getting several inches of rain with gusty winds Sunday into Monday OR damaging to hurricane-force wind gusts teaming up with the heavy tropical rains leading to widespread tree and structural damage.

We will continue to monitor this potentially catastrophic situation with frequent updates over the next several days.

 

Forecaster Wannabe: George BM

I absolutely love this, George BM! I look forward to it every month! You need followup assessments. This is great stuff and YOU ARE NO WANNABE forecaster. The National Weather Service should be feverishly taking notes! Hint hint, Millville Wx!

 

On another note: Mid Atlantic is enjoying 72/53 weather right now. Autumn is arriving ahead of schedule in your region. Everything is on track. Progressively cooler and rainier weather will ensue, deepening gradually into chilly then colder weather, with phase change conditions first developing in November, earlier in the mountains. December will see snow in Washington DC, with a debilitating White Christmas and possibly a NYE encore. Some communities particularly in higher terrain may end up with a white Thanksgiving in 2023! The New Year will be devastating both in terms of extreme snows and in terms of Vodka Siberian cold. Weather will be troffy well into June 2024 in the East. This means YOU, Mid Atlantic!

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After working at the brewery today, I went down and watched the team introductions of the Maryland Cycling Classic. Pretty cool to meet so many pro cyclists. Unfortunately the beer at the event was pretty blah so I had to stop back at the brewery on the way home to cleanse my palate.

Looking forward to the race tomorrow.

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39 minutes ago, Rhino16 said:

I could use another Jebman blizzard scenario to get the snow brain racing.

LOL, but I could NEVER do a professional writeup like GeorgeBM.

You guys ARE gonna get snow blizzards late this year and early in 2024. This winter is going to be a doozy for the Washington Metropolitan Region. That subtropical jet stream will be supercharged by the El Nino plus unprecedentedly high ocean surface temps. It will be a raging beast! The Nino will bring colder than normal temps to the Mid Atlantic, and snow after snow after snow will descend upon the Mid Atlantic resulting in multiple snowmageddon scenarios. The subtropical jet will rage and will be in full-on Beast Mode, because of the very high SST's. This is going to be a memorable winter for the Washington area. Some ocean surface temps have been in excess of 100 degrees off Miami, FL! Imagine what this is going to do for developing storms off the southeastern coast! Mix that up with cold airmasses moving south from Canada late this fall and you get instant wintry mayhem! Some places in Western Maryland will get Palisaded by snow rates! That subtropical jet stream will be a serious, serious BEAST!

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GEORGE BM --- I expect a follow up on your forecast that you posted at the top of this Banter Thread.

Storm is getting stronger, probable Cat 4 Hurricane by the time it hits the Carolinas. Record rainfall imminent for much of the Washington Metropolitan Region. Storm will slow significantly and buzzsaw the coast horrifically. Many a weather enthusiast will be up all night and much of the following day watching the storm and trying to perform jebwalks in the teeth of the tempest.

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9 hours ago, nw baltimore wx said:

Who’s going to be the first jurisdiction to announce early closings for tomorrow because of heat?  I think it will be Baltimore City, though I read that they’ve apparently got AC in all but around ten schools. 

:sizzle:

Baltimore county has already canceled all after school activities. <_<  I mean we are not even under a heat advisory. 

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21 hours ago, nw baltimore wx said:

Who’s going to be the first jurisdiction to announce early closings for tomorrow because of heat?  I think it will be Baltimore City, though I read that they’ve apparently got AC in all but around ten schools. 

:sizzle:

This is what BCPS is doing:
 

Grades 2-12: Students who attend schools without air conditioning will engage in synchronous virtual (live at home) learning. Schools will implement virtual learning plans and ensure students have access to laptops.

Kindergarten and grade 1: Students will attend school in person on an early release schedule. Their learning spaces will be moved to rooms with air conditioning and City Schools will provide additional cooling support for those classrooms. Transportation and meals will be provided as usual.

Pre-kindergarten: Students who attend schools without air conditioning will engage in asynchronous virtual (at-home) learning. Early learning staff will be available virtually to support these young learners.

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19 minutes ago, H2O said:

Back in my day we had no ac so not only did we have to go to school but we also had to shovel coal into the boilers they ran to cook lunches and make hot water for the insane asylum next door.  

I remember sweating our a$$e$ off in elementary and middle school.  They would open the large windows in the old buildings if the wood panes didn't stick, but all that did was let the flies come in and bother us.  

We also had a 2nd recess back then, maybe to get the stink out of the classroom for a little bit.....:-)

 

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Hell of a closing weekend at the pool. Place was mobbed yesterday, and was probably the most fun of any days we had all summer!

Definitely a bummer to know we won't have any more long weekend days of just chilling with friends around the pool, but it does get us started on Friday happy hours on the cul-de-sac!

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1 hour ago, mattie g said:

Hell of a closing weekend at the pool. Place was mobbed yesterday, and was probably the most fun of any days we had all summer!

Definitely a bummer to know we won't have any more long weekend days of just chilling with friends around the pool, but it does get us started on Friday happy hours on the cul-de-sac!

Our pool was hopping too, but they are open for two more weekends (and 4-8pm during the week).  

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Just now, MN Transplant said:

Our pool was hopping too, but they are open for two more weekends (and 4-8pm during the week).  

DC DPR is keeping two pools open through Sept 21 (Hearst in N Cleveland Park and Oxon Run Pool in Anacostia.  A bunch of spray parks are also remaining open until then.

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9 minutes ago, MN Transplant said:

It is all about finding lifeguards.  

yeah I think that was one of the big issues with a story last month from ATL where all their pools were closing but a couple in the first week of Aug - no lifeguards because the kids were all back in school.  Which begs the question, why are schools in the SE starting school in early August?

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