Flooding

Warmer & Humid Tomorrow with PM T-Storms

Miguel Pierre Flooding, Severe Wx, Short-Term

A warm front move through the area tomorrow morning with some clouds. Winds turn more southwesterly south of this front, transporting a much warmer and humid airmass.  Temperatures over New York City and much of New Jersey will rise into the middle to upper 80s. However, this will be short-lived as a cold front will moving through the area tomorrow evening with some scattered showers and thunderstorms.

The 12z NAM models showing 80s for highs over much of NJ and NYC, with southwest winds. Then some showers or thunderstorms for the northwest.
The 12z NAM models showing 80s for highs over much of NJ and NYC, with southwest winds. Then some showers or thunderstorms for the northwest.

The Storm Prediction Center had issued a slight risk early this morning for these t-storms tomorrow. This was mainly in the warm sector, when instability is more likely to support severe thunderstorms. However, this afternoon look as removed the slight risk entirely. Regardless of what SPC issues, there are some factors going against widespread severe weather. Mid-level lapse rates are poor with a mostly west to southwest flow aloft. While 0-3km helicity values are in 150 m2/s2 to 200 ms/s2 late tomorrow, 0-6km bulk shear is between 25kt to 30kts with 500mb winds a little weak in the area. Clouds in the warm sector also an issue with getting more extreme CAPE values. Some models show SBCAPE near 1000 J/kg over Central and Northern New Jersey. But MLCAPE and NCAPE values are lower. This suggests CAPE will be skinny and will not support very tall updrafts. Southeast winds or sea-brezzes ahead of the warm may also keeps parts of Long Island and NJ shore, in more stable airmass. Which supports thunderstorms to weaken in this area. All this considered, I think will any severe weather will be very low and isolated. Some t-storms might strong enough produce wind gusts near 40mph. There is also very small possibility of very weak spinups (tornadoes) along the warm front nearby). But without more instability, this threat is not heightened here. Models do show very high precipitable water values over 2.20″. So any thunderstorm will be capable produce some very heavy rainfall with flash flooding in poor drainage areas.

12z NAM today precipitable water values over 2.20"+
12z NAM today precipitable water values over 2.20″+

Showers and thunderstorms will taper off later tomorrow night and clearing will take place late. A cooler and less humid airmass is in store starting on Friday. High temperatures will only reach the lower to middle 70s, despite alot of sun. Some uncertainty continues over the weekend as models stall this cold just off the Mid-Atlantic coast on Sunday. Then move a number of waves north up this frontal boundary through early next week. Details will be fine tuned as we get closer.

Hot & Humid With Strong Thunderstorms Possible Today

Miguel Pierre Flooding, Severe Wx

Yesterday south to southeast winds, transported a very muggy airmass into region. However, these winds off ocean, cause marine inversion with low clouds to develop. This kept atmosphere from mixing and less stable. Temperatures in the 80s across most of the Tri-state area. Today will be hot and humid as we much deeper westerly to southwesterly flow with 850mb temperatures near 18C this afternoon. This will likely allow for deeper mixing and temperatures to rise into the lower 90s, across much of New Jersey and into New York City. The only caveat here is that some convective debris from decaying showers and thunderstorms Western New York and Pennsylvania early this morning, works it east today.  This could possibly keep high temperatures in the upper 80s.  Closer to coast sea-breezes will develop this afternoon and keep high temperatures in middle to upper 80s.

temp13

A pre-frontal trough developing over the area, will trigger some scattered showers and thunderstorms this afternoon and early this evening. These will form over interior areas for first then move southeast towards the coast. Latest NAM model guidance is showing 2000 – 3000 J/kg of MLCAPE, 20-25kts unidirectional 0-6km bulk shear, precipitable water values 1.5″ – 2.0″ ahead of this activity this afternoon, away from the shore. This is enough instability and moisture for thunderstorms to become strong or severe and produce very heavy rainfall in a short period of time. But shear is insufficient for thunderstorms to sustain their updrafts and organize into bow lines. At this time, I expect scattered thunderstorms to be pulsing up and down in intensity. Isolated damaging wind gusts and flash flooding in poor drainage areas will be the main threats. The Storm Prediction Center has already included much of the area in a 15% slight risk. So stay tuned for any severe thunderstorm watches this afternoon or evening.

namNE_con_mlcape_012A cold front passing through the area, may trigger more showers and thunderstorms early tonight. However with the sun going down, instability will diminish. So these thunderstorms will be less capable of becoming severe. Behind this front is cooler and less humid airmass. Sunday will mostly sunny with high temperatures in the upper 70s to lower 80s. Monday and Tuesday will looking more questionable some model guidance showing a coastal low impacting the area with some rain and wind. Another post here will come later today on this system with new model data. 9/7 Update (that post will be delayed for model data today..)

Very Warm & Humid Through Labor Day with Heavy Thunderstorms Likely

Miguel Pierre Flooding, Severe Wx

A deep southwesterly flow, will transport a very warm and humid airmass today with clouds mixing with some sunshine. High temperatures today will depend on the amount of cloud cover. Areas that see more sunshine, could get make run at 90 degrees or higher today. More clouds than sun, highs will be in lower to middle 80s. The forecast highs will compromise between middle to upper 80s. Except near the shore, a southerly winds likely keep high temperatures in lower to middle 80s. A surface trough and shortwave trough (upper-level disturbance) will trigger numerous showers and thunderstorms across the region late this afternoon and tonight.

6z NAM showing a surface temps middle to upper 80s in most areas with dews in 60s (top left). Also a shortwave trough approaching trigging showers and thunderstorms west of New York City
6z NAM model showing a surface temps middle to upper 80s this afternoon in most areas with dews in upper 60s and lower 70s , Also a shortwave trough approaching trigging showers and thunderstorms over Western parts of region late this afternoon.

Models show anywhere between 1000 J/kG and 2000 J/kg of MLCAPE with 25kt to 35kts of shear this afternoon and early this evening. This will support some thunderstorms to become strong to severe with damaging winds being the main threat. Some backing of the low-level winds this afternoon, could support an isolated, weak tornado. Especially over Northern NJ and Lower Hudson Valley. Some hail is also possible out thunderstorms. But threat for large hail is reduced somewhat with high freezing and wet-bulb zero levels. Inhibiting factors for severe weather today, are weak mid-level lapse rates and some cloud cover keeping surface-based instability from reaching extremely high levels. Also with winds more out the south this afternoon, areas near the coast will be more stable and this may cause thunderstorms to weaken. Which is why the Storm Prediction Center has the 15% slight risk northwest of NYC. Overall I’m expecting any severe weather reports to be isolated to scattered across to the region.

6z NAM model showing MLCAPE between 1000 J/kg and 2000 J/kg by early this afternoon over the Tri-State area.
6z NAM model showing MLCAPE between 1000 J/kg and 2000 J/kg by early this afternoon over the Tri-State area.

More likely than the severe weather, is potential for heavy rainfall out of thunderstorms late this afternoon and tonight with pwats (precipitable water values) near or over 2.00″.  With mostly unidirectional shear, some of training of storms with flash flooding possible in  low-lying or poor drainage areas. Depending how showers and thunderstorms setup some places could receive less than .50″ rainfall to locally one to three inches of rain.

6z NAM showing (pwats) precipitate water values 2.00" over greater over the Tri-state area
6z NAM showing (pwats) precipitate water values 2.00″ over greater over the Tri-state area

That all being said, it is not necessary to cancel plans. It will be dry, until late this afternoon for most areas and perhaps until early this evening for coastal areas. If you are at beach, park,pool, etc, be prepared to move indoor as quickly as possible, if a thunderstorm hits. Any thunderstorm whether severe or not, can produce dangerous cloud to ground lightning. Don’t take shelter under trees, as they are huge conductors of electricity. Tomorrow (Labor Day) will continue very warm and humid with mixture of sunshine and clouds. More scattered showers and thunderstorm will still be threat all day tomorrow. As the shortwave trough lingers over the area. Pwats still over 2.00″ will  support heavy rainfall out of any thunderstorm tomorrow. However, with move convective debris or clouds, this will likely keep instability lower. On Tuesday, surface high pressure will build briefly more sunshine. A deep southwesterly flow with 850mb temperatures around 18C will help temperatures rise into the lower 90s, away from the coast. A cold front and upper-level trough approaching from the west will trigger more showers and thunderstorms by Tuesday night.

Check the latest Tri-State 7-day forecast details and summary for more updates for today’s severe threat threat.

Also follow @WeathergunNY for any watches and warnings later this afternoon and night.

Have a nice Labor Day weekend!