The Northeast including areas around NYC, Washington DC, etc (as well as far southeastern Canada) look like getting a battering from an outbreak of severe thunderstorms overnight Sat through Sun (Australian time). It's a particularly nasty setup with the biggest threat being damaging winds of the derecho kind... but also a chance for tornadoes where there's breaks in any squall lines & hail. SPC currently has much of the Tri-State region in a Moderate Risk area for severe storms.
Below is the output from the SREF ensemble for 7am Sun morning (AEST) showing the conditional probability of convective precipitation falling in the presence of the SPC's Derecho Parameter equalling or exceeding 1.0 (which typically indicates the presence of favourable ingredients for derechoes).
Here's an excerpt from the current SPC convective outlook:
POTENTIALLY SIGNIFICANT DAMAGING WIND EVENT IS EXPECTED ACROSS MUCH
OF THE NERN U.S. SATURDAY. LATEST MODEL GUIDANCE...ESPECIALLY THE
NAM/ECMWF...SUGGEST SHORT-WAVE TROUGH OVER THE UPPER GREAT LAKES
WILL DIG INTO LOWER MI BY 08/12 BEFORE EJECTING NEWD IN A NEGATIVELY
TILTED FASHION AND DEEPENING OVER SERN ONTARIO/WRN QUEBEC. 90-120M
12HR HEIGHT FALLS WILL SPREAD ACROSS WRN/UPSTATE NY DURING THE DAY
ENSURING A STRONGLY FORCED AND CONVECTIVELY-ACTIVE COLD FRONT.
ALL INDICATIONS FAVOR A SQUALL ALONG THE WIND SHIFT AT SUNRISE FROM
SRN ONTARIO SWD ACROSS OH...TRAILING INTO THE TN VALLEY.
OF PARTICULAR CONCERN IS THE EXPECTED MID LEVEL JET THAT SHOULD
INTENSIFY AS IT EJECTS ACROSS WRN PA TO SPEEDS IN EXCESS OF 70KT
OVER UPSTATE NY BY 09/00Z.
FORECAST SOUNDINGS FROM NRN NJ NWD THROUGH
THE HUDSON VALLEY SUGGEST TORNADOES ARE POSSIBLE IF DISCRETE
SUPERCELLS CAN EVOLVE AHEAD OF THE MAIN LINE AND WITH CIRCULATIONS
WITHIN THE LINE.