NY NJ PA Weather Forecasts

This Evening’s Podcast:  Tonight I discuss the day’s events including the heavy rain showers that moved through Manhattan this evening.  Also, I look at the developing Nor’easter for Wednesday night and Thursday.  Plus a change in the pattern is a foot, what does this mean for the region and are tropical influences a threat?

Tuesday, August 12th, 2008

The main focus for severe weather will be along the stationary front over the Gulf Coast.  A strong disturbance as the mid level will interact with the stationary front to produce showers and strong to severe thunderstorms.  The additional wind shear combined with isentropic lifting will lead to thunderstorms capable of tornadoes, large hail, wind gusts exceeding 55 mph, and heavy downpours.  

Meanwhile, an upper disturbance and a surface disturbance will produce scattered strong to isolated severe thunderstorms.  Dry air behind the disturbance will support the development of large hail in some of the stronger thunderstorms, however the upper level dynamics are currently not very impressive for wind shear to support severe thunderstorms.

There are two main features to keep an eye on in the Tropical Atlantic.  

The first feature is located roughly 750 miles from the Lesser Antilles.  The satellite images this morning shows that the low level circulation is much better organized and showers and thunderstorms are rapidly redeveloping around the center of circulation.  High pressure aloft will support development for the next 48 hours.  An upper level low over the Bahamas will eventually produce some northwesterly shear on the system in the next few days, however before that this disturbance has a very favorable chance of becoming a depression in the next 48 hours and a tropical storm by the end of the week.

The second disturbance is a little less organized, but has much more favorable conditions for development.  A strong ridge of high pressure will sit to the north of the tropical disturbance located roughly 200 miles east of the Cape Verde Islands.  The low level circulation is becoming more organized with showers and thunderstorms developing around the center.  With favorable conditions for development, this disturbance may become a tropical depression in the next couple of days.

Finally, the model guidance combined with the increase thunderstorm activity over Africa suggest the the Tropical Atlantic is about to significantly heat up with activity.  The Tropical Atlantic is plenty warm enough with a strong ridge situated to the north of the ITCZ to support a shear free zone through out the Tropical Atlantic.  This type of pattern has the potential to produce several Cape Verde tropical systems over the Atlantic.

The upper low that rotated through the forecast area produced some pretty impressive isolated severe thunderstorms yesterday.  The cold air aloft significantly destabilized the atmosphere while the strong disturbances rotating around the upper low produced strong wind shear.  As a result, the thunderstorms were capable of producing large hail, wind gusts over 55 mph, very heavy downpours, frequent lightning, and even a few water spouts!  The following are official storm reports from the National Weather Service:

0830 AM     HAIL             PRINCETON               40.35N 74.66W

08/11/2008  E0.25 INCH       MERCER             NJ   TRAINED SPOTTER

0848 AM     HAIL             WHITE HORSE             40.19N 74.70W

08/11/2008  E0.50 INCH       MERCER             NJ   TRAINED SPOTTER

            DIME SIZE HAIL IN HAMILTON TOWNSHIP.

0850 AM     HAIL             TRENTON                 40.22N 74.76W

08/11/2008  E0.25 INCH       MERCER             NJ   TRAINED SPOTTER

0902 AM     HAIL             5 ESE READING           40.31N 75.84W

08/11/2008  E0.25 INCH       BERKS              PA   TRAINED SPOTTER

            HAIL OCCURRED IN EXETER TOWNSHIP.

0915 AM     TSTM WND DMG     WINDSOR                 40.24N 74.58W

08/11/2008                   MERCER             NJ   NWS EMPLOYEE

            TREE LIMBS DOWN.

0953 AM     HAIL             WOODBRIDGE              40.55N 74.29W

08/11/2008  E0.25 INCH       MIDDLESEX          NJ   TRAINED SPOTTER

1120 AM     HAIL             2 SSE SCOTRUN           41.04N 75.31W

08/11/2008  E0.25 INCH       MONROE             PA   TRAINED SPOTTER

            HAIL OCCURRED IN TANNERSVILLE.

1140 AM     HAIL             4 N HOPE VALLEY         40.97N 74.97W

08/11/2008  M0.25 INCH       WARREN             NJ   PUBLIC

1230 PM     WATER SPOUT      3 NE FORKED RIVER       39.85N 74.11W

08/11/2008                   ANZ451             NJ   PUBLIC

            FOUR WATERSPOUTS SEEN OVER BARNEGAT BAY. NO BOAT DAMAGE

            REPORTED.

0750 PM     WATER SPOUT      5 NE MOUNT SINAI        40.99N 72.95W

08/11/2008                   ANZ330             NY   NWS EMPLOYEE

0924 PM     HAIL             SETAUKET-EAST SETAUKET  40.93N 73.10W

08/11/2008  E0.75 INCH       SUFFOLK            NY   PUBLIC

0735 PM     FLASH FLOOD      MIDDLEVILLE             43.14N 74.97W

08/11/2008                   HERKIMER           NY   FIRE DEPT/RESCUE

            FLOODING ON FISHING ROCK ROAD/RTE 28 IN MIDDLEVILLE

0755 PM     FLASH FLOOD      MIDDLEVILLE             43.14N 74.97W

08/11/2008                   HERKIMER           NY   EMERGENCY MNGR

            BRIDENBACKER CREEK OUT OF ITS BANKS

The local forecast discussion is updated.

The main story this morning is the departing low pressure system over southern New England, which is producing a northwesterly wind over the region.  As a result, drier air is building into the forecast area through the day with clear skies.  I can’t rule out an isolated shower with the cold air aloft, however much like yesterday.  Here are the themes in the technical forecast discussion.

1. Cold air aloft leaving?

2. Pattern relaxing slightly?

3. Models hit the switch.