Spring Wx

Cold and Damp Through Thursday…More Warmth and Thunderstorms Friday

Miguel Pierre Severe Wx, Spring Wx

Strong high pressure over SE Canada has cause a strong  cold front to push south into Mid-Atlantic region this evening. We call this a “backdoor cold front”, because it comes from the northeast or east direction instead of the more common northwest or west direction. Behind the fronts, is an ocean-cooled airmass. Temperatures have drop into 40s through the region, as east to northeast winds increase to 15mph to 20mph.  Periods of rain and drizzle have also developed around the region Tomorrow and Thursday will feature periods of rain and drizzle with temperatures in upper 30s to middle 40s through the region. Which 10 to 15 degrees below normal for this time of year.

18zNAMf24

High pressure will begin moving east into the Atlantic on Thursday night and Friday morning. This will cause stronger southerly flow and the front to lift back northward as warm front. Depending on timing and progression of this warm, temperatures could rise back into 60s or 70s in parts of the area. Especially over New Jersey and New York City. A low pressure system tracking into the Great Lakes will push a cold front through area on Friday night. Ahead of this front could some showers and thunderstorms for the Tri-state area late Friday afternoon. The Storm Prediction Center has placed Central and Southern New Jersey in a 15% slight risk for severe thunderstorms on Friday. Where is more likely to be unstable enough for some thunderstorms to reach severe levels.  However, there is some risk for some strong thunderstorms some shear and marginal instability. The main threats are strong winds and heavy rainfall.

day4prob

Behind the cold front, northwest winds will dry us out for a beautiful weekend. Saturday and Sunday will be mostly sunny and with high temperatures in the lower to middle 60s. Except upper 50s near the shores, where sea-breezes will develop late.

Warm, Humid & Storms Today. More Rain & Storms Possible Wednesday Night & Thursday

Miguel Pierre Severe Wx, Spring Wx ,

With a southerly flow, today will be warmer and more humid for Tri-State area. Temperatures will rise into middle to upper 80s this afternoon, away from the coast. Scattered showers and thunderstorms will develop along trough axis approach from the west this afternoon. Best chances for showers and thunderstorm will be north and west of New York City, where lift and instability will be higher. Model forecast soundings show sufficient SBCAPE for thunderstorms to become strong this afternoon. However, weak vertical shear and poor mid-level lapse rates will limit storm organization and intensity. Also with the weak flow and PWAT near 1.80″, any thunderstorms will be moving slowly and capable of producing very heavy rainfall. Which could result in some flash flooding. Showers and thunderstorms should gradually diminish tonight. As the trough axis shifts east and instability decreases after sunset.

6z NAM model sounding for Trenton, NJ late this afternoon, for high SBCAPE, weak shear & pwat 1.77"
6z NAM model sounding for Trenton, NJ late this afternoon, for high SBCAPE, weak shear & pwat 1.77″

Tomorrow we will see more sunshine. But it will not be as warm and humid. A weak cold front will slowly pass through the area. Temperatures will still take run at 80 or above, with a deep NW flow and steepening lapse rates. A strong cap aloft will likely suppress shower and thunderstorm development during the afternoon and early evening hours.

6z NAM showing strong capping inversion tomorrow
6z NAM model sounding showing strong capping inversion tomorrow

Later tomorrow night into Thursday could get more stormy. A potent shortwave and wave low of pressure that will producing severe weather over Central Plains today and Ohio Valley tomorrow, will moving across our region. There are some models differences on the exact timing and track of this wave through our area. If this wave, tracks over Central or Southern New Jersey, it could give many of us period of heavy rain with embedded, elevated thunderstorms. A track further north than that, would put more of the in warmer, unstable airmass and vertical wind shear. Which would support strong to severe thunderstorms. At this time, much the guidance favors the southern track. But as the begins develop over Central Plains today, this could still be some changes. Stay tuned for another update late tonight or early tomorrow.

Heavy Rainfall for the East Coast Thursday and Friday

Miguel Pierre Flooding, Spring Wx

A large upper-level trough over Mississippi River valley will be taking a negative tilt. A deep southerly flow ahead of it, will transport an abundant amount of moisture from Gulf of Mexico and Atlantic moisture up the Eastern Seaboard between Thursday and Friday. At the surface, a cold front with couple of low waves running along it, will be a focus for strong convergence and instability. This will enhance an area of heavy rainfall with embedded thunderstorms. Widespread rainfall totals of 2 to 3 inches are likely from Pennsylvania southward to Georgia. Localized higher totals are possible, especially where thunderstorms train.

The 0z GFS showing 2″ -3 of rainfall for the Mid-Atlantic Region (image courtesy of College of Dupage)
The 0z GFS showing 2″ -3 of rainfall for the Mid-Atlantic Region (image courtesy of College of Dupage)

For the New York City Tri-state area, a strong high pressure centered over Western Atlantic, should keep most of the rain away until it begin shift east on Friday. Showers will likely increase from west to east during the day Friday, as the cold front slowly nears the the area. Some of these showers can produce some downpours. Then a wave forming along cold front, will enhance more rainfall Friday night. A strengthening southerly low-level jet and high precipitable water values 1.50″  will produce moisture convergence and elevated instability for more heavier showers and scattered thunderstorms.

The 0z GFS tonight showing preciptable water values over 1.5" over the tri-state area Friday night
The 0z GFS tonight showing preciptable water values over 1.5″ over the NYC Tri-state area Friday night

When all is set and done early Saturday morning, rainfall totals will likely be between 1 to 2 inches for much of the tri-state area. Locally higher totals are possible in spots where thunderstorms occur. his could cause some minor flooding in poor drainage areas. As well some renewed flooding across streams and rivers.  But major flooding is not expected. The good news is that rest of the weekend is look dry and comfortable with high temperatures in the lower to middle 70s.