An approaching strong cold front, and associated mid and upper level disturbance, will bring heightened chances for rain into the area from tonight into Thursday morning. However, the event will be made more significant by a plume of moisture, surging northward along and ahead of the frontal boundary. Forecast models indicate a strengthening low level jet stream and transport of this moisture. Precipitable water values (the amount of water in the atmosphere) will be high — in the 95th percentile for October.
The moisture will begin surging northward later this afternoon and evening. Forecast models indicate the best lift for precipitation will remain to our west until the latter part of the afternoon. At that point, from west to east, chances for showers and thunderstorms will increase. Initially, downpours will be scattered. But over time tonight, the support for heavy rain will expand and moisture will continue surging northward. Rain will develop from southeast to northwest, with widespread heavy rain likely throughout the area overnight.
As the moisture transport continues, Precipitable Water values are forecast into increase to 2 or higher. The latest NAM indicates Precipitable Water values of 2.1 to 2.2 throughout the area during the early morning hours of Thursday. That lies in the 95th percentile at KOKX in October. It is here that isentropic lift will be maximized, so we’re anticipating some very heavy rain throughout the area during the early morning hours.
Localized flooding is likely, especially in poor drainage and low-lying areas. We are anticipating the possibility of widespread delays during the morning commute, especially as this area of very heavy rain passes through New Jersey and the NYC Metro Area near or just before rush hour.
Forecast models are currently in good agreement that the heaviest rain will surge through the area during this time. Interestingly, it appears there will be an initial surge of moisture late tonight, followed by a secondary surge from the southeast in the early morning hours on Thursday.
This is likely indicative of the low level jet strengthening, on the east/southeast side of the upper level disturbance which will be situated over the Ohio Valley at that time.
Additionally, while not likely to be widespread or significant due to low instability, forecast models indicate isolated potential for severe weather within this band of heavy rain. Strong winds just above the surface will have the potential to mix down during any stronger storms. The Storm Prediction Center suggests at 5% risk for severe thunderstorms in our area (relatively low), and notes the following concerns:
CONVECTION SHOULD CONTINUE DEVELOPING THIS MORNING INTO THE AFTERNOON FROM ERN NC THROUGH THE MID-ATLANTIC AND SRN NEW ENGLAND ALONG EWD ADVANCING FRONT AND PRE-FRONTAL BOUNDARY. WHILE STRONGER FLOW ALOFT WITHIN UPPER LOW CIRCULATION REMAINS IN POST-FRONTAL REGION...DEEP-LAYER WINDS ARE MODERATELY STRONG IN VICINITY OF DEVELOPING LOW-TOPPED CONVECTION BUT ARE GENERALLY PARALLEL TO THE LINE. THE 11Z VWP FROM STERLING VA INDICATES LARGE 0-2 KM HODOGRAPHS AND 45 KT 0-6 KM SHEAR SUPPORTIVE OF OCCASIONAL ORGANIZED STRUCTURES INCLUDING BOWING SEGMENTS AND MESO-VORTICES. SOME INCREASE IN STORM INTENSITIES ALONG THE LINE MIGHT OCCUR WHERE THE BOUNDARY LAYER CAN UNDERGO AT LEAST MODEST WARMING...WITH PRIMARY THREAT BEING SPORADIC DAMAGING WIND AND A BRIEF TORNADO OR TWO. HOWEVER...THE VERY MARGINAL THERMODYNAMIC ENVIRONMENT IS EXPECTED TO SERVE AS A LIMITING FACTOR FOR A MORE ROBUST SEVERE EVENT.
Stay tuned over the next several hours and into Thursday for updates and additional information. We’ve scheduled a live blog for tonight, beginning at 9:00pm, to serve as a place where you can track the incoming rain and storms while staying prepared for any hazardous conditions. As always, stay tuned to our social media accounts for up to the minute information.