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Update Sat 04/22 @ 5:11 PM — The storms are moving in somewhat ahead of schedule of the HRRR and RAP models—

The Phillies game may just finish ahead of the storms. It’s going to be close.

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Update Sat 04/22 @ 10:18 AM — The latest 12z NBM, HRRR, RAP and NAM-NEST models have become available.

Here’s the trends. Storms move in between 6 PM (western suburbs areas) and 8 PM.

Heaviest rain in western suburbs and in New Jersey. The immediate PHL area appears to fall into a lull in activity of the storms.

Heaviest rain—

As for severity, below is my HRRR Severity Table—

Based on this table, I see tonight’s storms as typical thunderstorms with a chance of locally severe.

I don’t see tornadoes as likely. Largest hazard will be possible localized hail and strong straight line wind gusts.

I should indicate that the latest NAM-NEST has much higher CAPE and helicity values than the HRRR. I’ve found that the HRRR is more reliable for these sort of events and I’m going to ignore the more severe NAM-NEST forecast at this time.

Sept 1 , 2021 Tornado Outbreak (example of highly severe)	Past April 1st 2023 Tornado Outbreak HRRR 12z	Today’s 12z HRRR Forecast	Impact
CAPE 3500-4200 Joules/kg	2100	550	⚐ ⇩
Helicity 1350 m^2/s^2	655	460	⚐ ⇩
Vertical Shear 40-46	40-45	25	⚐ ⇩⇩
Precipitable Water 2.7″	0.83”	1.1″	⚐
Lifted Index minus 6º K	minus 9.3º	minus 2.3	↓ ↓
HRRR Hail Parameter 1.9	1.4	1.3	⚑
Peak Wind Gusts 40-50	40-50	35-40	⚐
Aligned Storm Motion and Shear Vectors- ~ 90º	Almost aligned	non-aligned	⇩
Jet stream level – wavy	Highly cyclonic	wavy	⚐ ⇩
Jet Stream 250 mb Speed – 63	High 135	94-100	⚐ ⇩

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Update Sat 4/22 @ 8:09 AM — Quick update. Last night’s models show the following trends: A further increase in CAPE and some areas of moderate helicity, especially in Delaware and areas north of Trenton. Some areas with strong to severe storms now appears possible.

The line of storms moves in between 6 PM and 8 PM, about an hour or so later than forecast last night. (Earlier in western suburbs.)

I’ll update later this morning before 10:30 AM with this morning’s 12z models.

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Update Fri 4/21 9:52 PM — With tonight’s HRRR just becoming available, I want to underline the possibility of a one or two widely scattered pop up storms during the mid afternoon due to increased instability.
The timing of the main line of rain and storms is mostly unchanged. The HRRR also shows a modest increase in severity parameters. Updates tomorrow morning after 10:15 with the new HRRR and NAM-NEST.

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Previously Posted Fri 7:55 PM —

A strong cold front will move quickly through our area Saturday night with showers and possibly some thunderstorms. Cooler high pressure builds in for Sunday. (Average highs this time of year are 66º-67º)

Satellite water vapor shows the position of the front and upper level low this morning—

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