Once again we’re looking at another round of rain and thunderstorms. There’s a low threat for severe weather and an elevated threat for flooding. I sound like a broken record.
The big trough/cut-off low that has plagued our weather pattern the last few days will dig and sharpen tonight. The rather flat appearance of the trough today will become much sharper by tomorrow night and Monday.
What will govern our weather Sunday and Monday is a developing jet streak in southeastern Quebec that will result in a large area of atmospheric “lift”. Most of New England will be in the “right entrance region” of this jet streak (centered near Quebec City in the computer model forecast above) which is an area that is favored for synoptic-scale ascent. Showers and thunderstorms are likely across a broad area.
Compare the strength and location of the low level jet at 8 p.m. Sunday. Below 850mb the NAM shows the low level jet approaching 50 knots at 925mb at 00z tomorrow! All of this stems from a weak upper level disturbance over the southeast that ejects north tomorrow toward New England. For what it’s worth, the Euro and UKMet both show the LLJ like the NAM which makes me think this isn’t just the NAM being the NAM. The GFS brings the upper level disturbance over the southeast well out to sea while the other models hug the coast. You can see the PV anomaly on the GFS at 18z Sunday way out to sea – that’s why the low level jet repsonse is displaced hundreds of miles east.
Given the favorable jet dynamics, modeled LLJ (on all but the GFS), lots of moisture (PWAT values >2.2″ on the NAM), and some instability we will likely be looking at a period of heavy rain and thunderstorms late Sunday and into Monday.
The Euro shows periods of heavy rain lasting through Monday night with a strong southerly flow in the low levels of the atmosphere with a favorable location of a jet streak in Quebec as discussed earlier.
As the low level jet strengthens tomorrow late afternoon the 0-1km shear will increase rapidly and that may result in a localized severe weather threat if instability materializes as well (watch for low topped spinners!). In addition, with saturated soil and high rivers/streams we will have to watch for flash flooding. This setup could put down a significant amount of rain in some towns.
The good news is that by later in the week toward July 4th the large western Atlantic ridge will begin to retrograde and start pushing the showery weather to the west. It will remain humid with an isolated storm chance but the Wednesday-Saturday period isn’t looking half bad!