Month: July 2014

Potential for Severe Thunderstorms Late Today

Miguel Pierre Uncategorized , ,

The Storm Prediction Center has issued a slight risk of severe thunderstorms for far western parts of the area today. The rest of the area including the Northeast NJ, NYC and Long Island area are in a lower 5% risk for thunderstorms producing damaging wind gusts and large hail. An upper-level trough and cold front approaching from the west, will trigger showers and thunderstorms, late this afternoon and this evening. With a humid airmass in place and temperatures rising into lower to middle 90s today away from the shore, the atmosphere will become very unstable some of those thunderstorms to possibly become strong or severe.

Storm Prediction Center outlook for 13z Wednesday, shows slight risk for parts Upstate NY, Pennsylvania, and Extreme Western Nj
Storm Prediction Center outlook for 13z Tuesday, shows slight risk for parts Upstate NY, Pennsylvania, and Extreme Western Nj

The severe threat is greatest over Upstate New York, Pennsylvania and extreme Northwest New Jersey. Where they will be closer to an embedded 500mb shortwave trough and a 40-60kt southwesterly low-level jet streak late this afternoon and early evening. Both features will enhance shear and lift for more organized severe thunderstorms that can produce damaging winds, large hail and isolated tornadoes.  For areas closer to to I-95 corridor, with less shear and lifting later today, the threat for severe thunderstorms with damaging winds and large hail is more isolated.

12z NAM showing 40-60kt 850mb jet
Today 12z run of the NAM showing 40-60kt 850mb jet over Upstate New York  and Pennsylvania (image courtesy of College of DuPage)

The cold front will move through area tonight and tomorrow, with more showers and thunderstorms with heavy downpours. Shear and lifting will be more sufficient. But a slightly cooler and drier airmass behind front, will mean less instability for severe thunderstorms. For more organized, widespread severe thunderstorms, sufficient lifting, shear, instability, and moisture need to all come together. But forecasting how all these ingredients will come together for severe, is hardly ever simple in Northeast US, even on the same day of threat.  For this reason, I will continue to monitor this potential here today and tomorrow.

Tropical Storm Arthur, Heat & T-Storms Wed. & Thurs.

Miguel Pierre Severe Wx, Tropics

First tropical storm of the Atlantic Hurricane Season, Arthur was born today, from a disturbance that was previously discussed off the Southeast US coast.  Weaker northerly shear allowed thunderstorms organized more over the center. As of the 11pm advisory from the National Hurricane Center, Arthur has maximum sustained winds of 50mph and is pm;u drifting northward. However, very cold cloud tops near the center, seen on satellite imagery this evening, indicate that Arthur continues to get better organized and might start intensification trend soon.

1115zrbtop0

Most model guidance shows Arthur strengthening to a hurricane as it moves north-northeast near or over the outer banks of North Carolina. That area could some heavy rain and strong winds. Although, since this is lop-sided system with drier air to northwest, hurricane force wind will likely be in southeast quadrant. Then the storm will track out into the open Atlantic, well southeast of the Tri-State Area. However, Arthur will be in  right-entrance region of strong upper-level jet streak, enhancing an band of rainfall over local tri-state area during day on Friday (July 4th). Some rough surf may occur at the beaches. The rain start moving out by Friday evening. Perhaps just in time for fireworks festivities. This weekend is look beautiful with mostly sunny skies and temperatures in middle to upper 80s.

Before that we are looking at more heat and humidity to continue through at Wednesday for tri-state area. High temperatures on Wednesday will likely get between in low or middle 90s for NE NJ and NYC, with sea-breezes keeping more coastal areas slightly cooler. There is also a chance of some  afternoon thunderstorms, with a pre-frontal trough over region. Some thunderstorms may be locally severe with amount of surface-based instability shown of the guidance. However, bulk shear is little low for thunderstorms to remain well organized. So I’m not expecting widespread severe weather. Some thunderstorms may also produce some very heavy rainfall. Thursday looks wetter with cold front and upper-level streak closer,with  scattered showers and thunderstorms all day. Some thunderstorms may train and cause flash flooding.