4/04 All Zones AM Update: Strong T-Storms Possible This Afternoon, Larger Storm Likely Thursday

Happy Tuesday! Heavy rains from overnight have moved out most of the region quickly this morning, as best forcing with a strong low-level has shifted northeast into New England. Thus flood watches for New Jersey and Lower Hudson Valley have been cancelled, with more significant flooding no longer anticipated for today. It will remain mostly cloudy with some showers, drizzle or patchy fog the rest of morning, as a the warm front remains to the south.

Then clouds may break for some sunshine this afternoon, especially south of NYC, as the warm front slowly lifts northward through parts of the region this afternoon. This will help rise this afternoon possibly into the upper 50s to lower 60s over parts of Northern NJ and NYC. Further more clearing with southwest winds will cause temperatures to rise well into 60s and perhaps 70s further over Central and Southern NJ and Southeast PA. Over Long Island, Connecticut and Lower Hudson Valley it will remain mostly cloudy and cooler with high temperatures likely in the upper 40s to middle 50s.

Hi-resolution NAM model with a wide-range of temperatures from north to south of a warm front this afternoon

3km NAM model with a wide-range of temperatures from north to south of a warm front this afternoon

However, with more sunshine and warmer temperatures, the atmosphere will become more unstable especially south of NYC. This will support more scattered showers and thunderstorms over the region, as cold front and vigorous shortwave moves through this afternoon and evening. A marginal severe threat may develop this afternoon, depending amount of surface-based instability. Especially along and just south of the warm front, over parts of New Jersey this afternoon. For this reason, the Storm Prediction Center has issued marginal risk for parts of New Jersey and Eastern PA this afternoon.

Mesoscale models indicate moderate instability and strong deep-layer shear over parts, especially over Central and Southern NJ this afternoon. Also Inverted-V sounding with DCAPES between 500-1000 J/kg and steep low-level lapse rates. So main threat appear to be for isolated damaging wind gusts. Some small hail is also possible.  If this severe threat materializes for parts of the region, more individual zone forecast updates may be needed later today. Further north and east, instability will most likely be too low for severe weather. But thunderstorms with heavy downpours and frequent lightning are still possible.

NAM model showing 500 J/kg> MLCAPE with 35kt to 45kt of 500mb bulk shear over Central and Southern NJ this afternoon

NAM model showing 500 J/kg> of MLCAPE with 40 to 50kt of 500mb bulk shear over Central and Southern NJ this afternoon

Behind the cold front and vigorous shortwave, skies will clear later tonight with temperatures dropping into 40s for overnight. A ridge will build over the region with more pleasant weather conditions for Wednesday. Mostly sunny skies with light northwest winds are expected. High temperatures will be upper 50s to middle 60s over region. Which is closer to normal for this time of year.

Then a large closed low deep-upper level low will likely bring more heavy rainfall and possibly a some embedded thunderstorms on Thursday. As the upper-level low takes in negative tilt, this cause a strong baroclinic gradient with a firehose low-level jet off Atlantic. Moisture from  Gulf of Mexico and the Pacific with a subtropical jet will be streaming into the region. Rainfall totals 1″ to 3″ are likely and locally higher rainfall totals are possible with training heavy downpours. This could result in some localized flooding is possible in poor drainage and low-lying areas as well over small streams and rivers.  There is also some potential for some gusty onshore winds and coastal flooding during high tides on Thursday.

Severe weather is not expected to be significant threat with a more stable marine airmass likely over much of the region. However, there will be a higher threat of more severe thunderstorms over further south over Lower Mid-Atlantic,  where the Storm Prediction Center has enhanced risk for severe weather. These thunderstorms will likely loose some intensity as move northward into Delmarva and Central and Southern NJ. But some isolated damaging wind gusts are still possible.

GFS model showing heavy rainfall over the region on Thursday afternoon, with amplifying 500mb shortwave energy and a diffluent 300mb jet

GFS model showing heavy rainfall over the region on Thursday afternoon, with amplifying shortwave energy and a diffluent upper-level flow over Mid-Atlantic and Northeast

Rain will taper off later Thursday night and Friday, as the  best forcing with triple point low and low-level jet moves northeast of the region. But more unsettled weather with showers could linger into Friday with the upper-level low swinging through Northeast. More improving weather is likely for the weekend, as the upper-level low finally departs the Northeast. Temperatures will likely be cooler than normal on Thursday again, then moderate to near to above normal through the weekend. Stay tuned more zone forecast updates on both potential for severe t-storms today and more heavy rainfall on Thursday.