06/22/10  4:35 PM

I’m currently doing live coverage via twitter for the single severe thunderstorm over southeastern Pennsylvania.  Should a more pressing severe threat develop for the entire region, I will enter into the more traditional live coverage mode.

Sometimes I’m not at my computer and can’t set up a live update the way I normally do, however I am able to jump on twitter and start to update my latest thoughts!  If weather in the Northern Mid Atlantic strikes, you can bet on me updating the latest details on Twitter and at the NY NJ PA Weather Twitter page!

This afternoon the atmosphere is rapidly become unstable as skies have cleared and an aggressive secondary warm front races northeast towards the northern Mid Atlantic.  A cold front entering western Pennsylvania at 1 PM is expected to move towards the region later this afternoon and this evening with strong to severe thunderstorms.

I will be doing live coverage of this potential severe event through this afternoon and evening.  You can also follow along on twitter, but all illustrations can be seen here!

View Severe Weather Potential for 5/14 in a larger map

9:01:54 AM: Rainfall is become focused along the central and southern New Jersey coast as high pressure and dry air presses south.

9:03:38 AM: Pressure falls continue to develop off the North Carolina coast extending through the Gulf Stream. A transition appears to be developing.

9:04:35 AM: Meanwhile, a more solid phase can be observed on the water vapor satellite as the upper level low with this storm moves ENE rather than E.

9:05:28 AM: The influences of the Bahamas disturbance clearly has forced this storm further north by building the western Atlantic ridge at 500 MB.

9:05:57 AM: As a result, the Polar disturbance is phasing with the Sub Tropical disturbance more completely than earlier expected.

9:06:23 AM: This is why the model guidance has trended and will continue to trend northward with the higher QPF.
9:10:12 AM: As the day continues, I expect the press down on precipitation to continue through NYC and approaching Philadelphia.

9:10:37 AM: However, as the dry air presses down, the rain along the New Jersey coast will intensify as moisture convergence increases.

9:11:12 AM: Southern and central New Jersey is in for a very wet couple of days. I will continue to update through the day via this medium.

9:11:56 AM: I’ll try for an update on thoughts at once every one to two hours, depending on circumstances of this event.

9:12:13 AM: As of now, I can say that the going thoughts from last night are working out very well.

11:07:48 AM: The rain is slowly stopping the southward trend of the early morning. Light to moderate rain will continue along the C and S NJ coast.

11:08:33 AM: The pressure gradient will increase through the day as the coastal low develops off NC.

1:23:27 PM: The new coastal low is offically taking shape off the central coast of NC where the wind vectors are rapidly converging and pressure falling

1:24:25 PM: Meanwhile cloud tops continue to rapidly cool over the northern Mid Atlantic as lifting at all levels increase.

1:25:31 PM: The increased lifting is due to the phasing of the Polar disturbance with the Sub Tropical disturbance.

1:27:01 PM: Rain is rebuilding northward and is expected to reach much of the Philadelphia metro and central NJ. Showers will in increase over NYC.

1:28:31 PM: Rain will increase in intensity over the C and S NJ coast along with sustained winds between 15 to 30 mph with higher gusts.

6:55:24 PM: Through this afternoon the storm has developed as expected as rain continued over southern NJ and PHL.

6:57:50 PM: This evening I will up grade to a new coverage format that will intergrate Twitter. The live coverage will begin between 8 and 8:30 PM.

12:36:36 PM: Through the afternoon and evening, I will be following the development of what MAY be a surprise rain event for the northern Mid Atlantic.
12:41:41 PM: One important note that I’m following is that the Sub Tropical upper low is further north and west than guidance suggested.

12:42:01 PM: The result of that could indicate a track further north and west of the forecasted guidance.

1:49:33 PM: A distirbance to watch this afternoon is over the Bahamas. This disturbance is force the Sub Tropical disturbance furher west.

1:58:48 PM: Light rain is currently entering central Virginia.

4:06:53 PM: Heavy rain continues to push north-northeast into central Virginia. A slight push east to developing in the rainshield.

4:09:07 PM: The upper low associated with this area of rain is currently moving towards the Tennessee Valley. The Polar disturbance is approaching.

4:10:10 PM: Virga is developing throughout the northern Mid Atlantic which will eventually lead to scattered showers.

4:11:37 PM: The Boundaries of moisture convergence MAY be a precurser to the heavy rain to the south to approach the northern Mid Atlantic.

4:12:29 PM: Pressure falls are developing off the Mid Atlantic coast including New Jersey.

7:31:50 PM: High pressure is finally establishing it’s influence ove the nothern Mid Atlantic, suppressing much of the heavy rain over Virginia.

7:33:28 PM: Through the evening showers will develop, especially along the cost however the steady rain will remain south of New Jersey and PA.

8:21:05 PM: Keep an eye on the heavy band of rain over southern VA. If this band of rain starts to push north in northern VA, MD, and DE then ….

8:22:00 PM: A much wetter Wednesday can be expected than currently forecasted for the northern Mid Atlantic.

10:09:29 PM: As we head into the late evening, a few interesting aspects to note.

10:10:12 PM: First, the progression of the precipitation over West Virginia and eastern Kentucky has moved very little over the past 4 hours to the east.

10:11:51 PM: A moisture convergence boundary appears to be setting up from the southern Hudson Valley through northern NJ back towards West Virginia.

10:13:10 PM: This boundary would mark the end of precipitation threat so it is clear that CT, the Hudson Valley, and NE PA will miss out on the showers..

10:16:29 PM: The latest radar echoes are currently pushing north into MD and southern Delaware however the dry air at the surface will lead to virga.

10:19:42 PM: Meanwhile, the Polar jet stream disturbance is now interacting with the Sub Tropical Jet Stream disturbance.

10:20:11 PM: In the coming hours, we’ll see if this precipitation is shunted east as expected of is allowed to push north into the northern Mid Atlantic.

10:21:01 PM: Interesting radar development the past five minutes at the lowest radar level. A line of showers is developing over eastern PA.

10:25:49 PM: If this rain continues to push north, the first type of rain intensity I expect is drizzle.

10:26:19 PM: The lower levels of the atmosphere will have to moisten up a bit before any steady rain can develop.

10:27:10 PM: For example, many locations have temperatures in the upper 50′s with dew points in the mid 40′s.

10:28:56 PM: A light to moderate ban of rainfall is moving into SE MD, DE, and central VA this hour. Rain over WV still has not moved to east.

10:29:29 PM: Moderate rain has just been reported in central Delaware.

10:35:44 PM: The latest upper level wind date continues to move from southwest to northeast from the Tennessee Valley to New England.

10:36:24 PM: The Sub Tropical Disturbance is very strong. The sinking air behind this disturbance is VERY impressive.

10:37:02 PM: This would indicate that the dominant system over the East is the Sub Tropical system and not the Polar trough.

10:39:07 PM: The disturbance over the Bahamas is having an impact on this forecast.

10:39:45 PM: I believe the Sub Tropical Disturbance is being forced to move ENE rather than east due to the influence of the Bahamas disturbance.

10:41:56 PM: Pressure falls are being reported by Penn State E-wall observations off the Mid Atlantic coast. Strong drops 150 miles east of NC coast.

10:43:24 PM: Surface winds have started to converge along the NC coast as the stationary front intensifies.

10:48:16 PM: The IR satellite picture is highlighting two areas of lifting. The first is associated with the Mid/Upper level disturbance over TN/AL/GA.

10:48:41 PM: The second is increasing lifting off the NC coast. We can see this due to the cloud tops cooling.

10:49:06 PM: The cloud tops are cooling due to air rising in these locations. I expect a new surface low to form off the NC coast in the next few hours.

10:54:11 PM: The higher level radar scans are picking up moisture convergence over central PA now as the Polar disturbance approaches. Unexpected.

10:56:28 PM: New water vapor image shows cirrus clouds over Kentucky fanning north and west as the Polar disturbance approaches, also unexpected.

10:56:59 PM: No signs of the Sub Tropical disturbance jumping due east as of the latest observations.

11:14:42 PM: Precipitation is now developing over western PA and eastern OH in response to the Polar disturbance. The next hour is going to be telling.

11:16:20 PM: Precipitation intensity meanwhile is increasing over eastern MD and DE as this rain is clearly pushing north.

11:25:01 PM: Classic signs of moisture moving north, high level echoes fanning into southern PA now.

11:27:44 PM: Strengthening pressure falls continue off the NC/VA coast this hour. The pressure falls move NE over the Gulf Stream.

11:46:15 PM: If the Polar disturbance is going to force this storm south via the high pressure system, it better do so now.

11:47:36 PM: Classic signs of phasing showing up. The most important is the enhancement of upper level winds over the Tennessee Valley.

11:47:36 PM: Classic signs of phasing showing up. The most important is the enhancement of upper level winds over the Tennessee Valley.

11:48:24 PM: These upper level winds are direction from the SSW to the NNE, illustrated by the fanning of cirrus clouds towards IN and western KY.

11:50:17 PM: Precipitation echoes are also developing with greater organization over DE and eastern PA. Some signs over central NJ as well.

12:00:50 AM: The 500 MB 00Z observations tell the story here. It is now clear the Polar disturbance has a more neutral tilt than thought.

12:01:27 AM: What this means is that the ability for the Polar disturbance to force the developing storm south and east is limited.

12:02:00 AM: As a result, moisture will be able to push north into the Philadelphia metro and the southern half of New Jersey.

12:02:46 AM: Radar, satellite and surface observations all show this trend unfolding in front of us. The models from the past few days have busted.

12:03:29 AM: What is clear is that this storm will come further north than expected, which will lead to a prolonged rain event for the C/S NJ coast.

12:04:10 AM: A full update will be issued tomorrow morning. For now, I will wrap up this live coverage.

12:04:43 AM: I leave one additional note, if this is the trend in terms of phasing for this winter, we are all going to be very busy with snow and ice.