Rtd208

You can see the precipitation is starting to expand and move east on radar so we should start seeing heavier rain/storms over the next 2-3 hours in the immediate NYC metro.

Picked up 0.22" of rain so far today.

Picked up 0.22" of rain so far today.

Picked up 0.22" of rain so far today.

Picked up 0.22" of rain so far today.

Mt.Holly: .NEAR TERM /THROUGH TONIGHT/... ...Significant flash flood and severe weather event likely to occur in much of the area today and tonight... First concern to address is precipitation/convection this morning, with long-lived storms continuing to affect northern Virginia, the DC area, and adjacent portions of central Maryland. Although the environment appears less favorable for our area, could see some strong/severe slow-moving storms move into Delmarva and adjacent portions of far southeast Pennsylvania and southern New Jersey this morning. Will be monitoring this potential closely the next few hours. The remnants of Ida will be affecting the region today and tonight, with significant impacts expected for the area. Model trends early this morning continued a slight northward nudge of the highest QPF axis, with the GFS/NAM/ECMWF in good agreement that 3+ inches of rainfall will occur near/northwest of the Fall Line (with embedded totals 6+ inches somewhere in the southern Poconos and/or Lehigh Valley and vicinity). The CMC remains farther south (almost to outlier status), with the main axis generally between I-76 and I-80. The convection-allowing models (CAMs) are in between, and these are generally in line with our current thinking this morning. There are a few reasons for favoring a slightly farther south solution to the main QPF axis. For one thing, models tend to shunt warm sectors too far northward in advance of these systems, particularly ones that are in the process of intensifying via large- scale baroclinic processes. Additionally, models tend to bias convective precipitation too far north, in association with the synoptic forcing, rather than with the ambient/pooling instability (which tends to win out with convectively-enhanced events like these). Finally, suspect upslope contributions to precipitation are being underrepresented farther southeast near the Fall Line to the I- 95 corridor. For these reasons, our latest QPF forecast did not adjust totals as far north as the consensus of the coarser NWP models. However, these discrepancies do lead to higher uncertainty with forecast totals along the I-95 corridor. For example, Philadelphia may end up anywhere between 1 and 5 inches of rain based on the array of guidance available. However, the risk of flash flooding is not only tied to total rainfall but also duration, and the CAM solutions would suggest that much of the rainfall south of the high-QPF axis will be occurring in a relatively short period of time. Excessive rainfall rates (via PWs well north of 2 inches) are likely with the main convective show late this afternoon into the early overnight hours, and will likely lead to several instances of flash flooding near the urban corridor. Therefore, despite somewhat lowered QPF for the I-95 corridor southeastward, the risk of flash flooding remains quite elevated because of the rainfall rates. The HREF guidance provides some insight here, with the 00z ensembles indicating probabilities of 1-h rainfall accumulations exceeding flash flood guidance (FFG) above 50 percent in virtually all areas northwest of I-95 in our CWA during the evening hours, despite a range of 3-5 inches in total QPF. Notably, the probabilities of 6-h rainfall accumulations exceeding FFG are above 90 percent in much of the same area, which conveys the seriousness of the flooding threat for our area quite well. Of course, that is not all. With the warm sector expected to shift northward into at least the southern half of the CWA, the ambient preconvective environment will be quite favorable for severe weather. Model soundings indicate MLCAPE 1000-2000 J/kg (closer to 500-1000 J/kg near the warm front), 0-6 km bulk shear nearing 40 kt, and SRH > 200 J/kg in the late afternoon and early evening hours. This is an environment supportive of rotating storms, with CAM simulations suggesting a mixed mode of short line segments and cellular storms. Damaging wind gusts and tornadoes are the main threats, and the SPC has nudged the enhanced risk slightly farther north given model trends this morning. Given the coverage of convection expected, the favorable environment is quite concerning, with the severe potential continuing to look more and more impressive. The main time window for severe weather is likely in the 20z to 06z time frame from west to east. Individual cells will likely move quickly north-northeast, but the overall system will move only slowly eastward, so training convection poses a flash flood risk in the southern half of the CWA. Models continue to trend faster with precipitation moving out of the region, with most areas likely drying out by daybreak Thursday. &&

Post them here.

https://www.spc.noaa.gov/products/outlook/day1otlk.html

Also some of these north/south adjustments with the heaviest rains may be just "noise" which was something that was mentioned in Mt. Holly's discussion.

I am starting to wonder if we may get the "best" of both worlds here in Middlesex County NJ. While the heaviest rain amounts may fall just to our northwest we may also have more of a severe threat here as well. So the warm front may hover around this area. We'll see.

Will wait and see what the 00z runs do as far as heavy rainfall but I am also curious to see what the SPC does with the new day 1 outlook overnight. Maybe slight risk for portions of the NYC metro since things seem to be shifting north a bit currently??

How much for Philly?

Obviously location dependent but if you don't get the heaviest rain the tradeoff will be dealing with severe weather (including tornadoes) in the warm sector. I think regardless just about everyone in the sub forum will see at least 2" of rainfall.

High for the day yesterday was 90 here. Current temp 72/DP 70/RH 94%

High for the day yesterday was 90 here. Current temp 72/DP 70/RH 94%

Picked up 0.21" of rain for the day yesterday.

High for the day yesterday was 99 here. Picked up 0.21" of rain for the day yesterday. Current temp 7/DP 72/RH 86%

High for the day yesterday was 99 here. Picked up 0.21" of rain for the day yesterday. Current temp 7/DP 72/RH 86%

The potential for heavy rain and storms overnight will depend on how much the atmosphere was overturned by the activity during the afternoon/early evening.