#weather #paweather #wx #pawx #philadelphia

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Update Sat 4/01 9:44 PM — Despite the tornadic radar ‘signatures’ seen on radar this evening (inferred from radar differential velocity), the NWS is currently not showing any actual tornado reports except off the coast, near Atlantic City—

Forecast Review

Update Sat 4/01 7:22 PM — Tonight’s storms were impressive, almost scary. Thunder/lightning was almost continuous. Small hail also thrown in for good measure. The ingredients were there. The models did well with the timing and the forecast of the severe weather possibility. The HRRR was particularly impressive, as it often is with this.

Radar with storms just entering Philadelphia 6:30 PM—

Here’s current NEXRAD radar (~ 7 PM) —

Areas of NJ will likely continue to encounter these severe storms over the next hour or so.

One more thing. The meteorologist on Channel 3 did an excellent job in covering the severe weather. Knowledgeable and impressive.

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Storm Potential Update

Update Sat 04/01 @ 10:25 AM — Updated with the 12z NAM-NEST which shows a different potential location of severe weather at 6PM—

Update Sat 04/01 @ 9:42 AM — The important 12z models (those with direct upper air radiosonde/weather balloon measurements) are just becoming available. The HRRR and RAP have become available.

Specifically, the HRRR shows chance of an isolated severe storm in South Jersey as early as 5 PM. The main line of storms moves in between 6 and 9 PM.

Here’s how the ‘severity’ parameters stack up compared to the major storm outbreak of Sept 2021—

9/1/2021 Tornado Outbreak (example of highly severe)	Todays’s Forecast HRRR 12z	Comparative Impact
CAPE 3500-4200 Joules/kg	2100	⚑
Helicity 1350 m^2/s^2	655	⚑
Vertical Shear 40-46	40-45	⚑
Precipitable Water 2.7″	0.83”	⇩⇩
Lifted Index minus 6º K	minus 9.3º	⚑
HRRR Hail Parameter 1.9	1.4	⚑
Peak Wind Gusts 40-50	40-50	↔
Aligned Storm Motion and Shear Vectors- ~ 90º	Almost aligned	↔
Jet stream level – wavy	Highly cyclonic	↔
Jet Stream 250 mb Speed – 63	High 135	↔
500mb – Highly Cyclonic	Highly cyclonic	↔

Here’s where the greatest potential for severe weather appears to be at this time (this will likely change)—

Canadian RGEM Convective (thunderstorm) Precipitation Forecast 7 and 8 PM snapshots—

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Update Sat 4/01 7:51 AM — Last night’s models continue with an increased possibility of severe weather this evening. The new 12z HRRR will become available about 9:35 AM. I’ll update before 10 AM.

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Update Fri 3/31 10:49 PM — Tonight’s models are showing storm severity parameters that are more impressive for Saturday evening’s storms than previous model runs—

9/1/2021 Tornado Outbreak (example of highly severe)	Tonight’s Forecast HRRR 00z	Comparative Impact
CAPE 3500-4200 Joules/kg	1900	⇩
Helicity 800-1100 m^2/s^2	450	⇩
Vertical Shear 35-45	30	⇩
Precipitable Water 2.0″	0.87”	⇩⇩
Lifted Index (minus) 7-9	minus 8	↔
Peak Wind Gusts 40-50	40-50	↔
Aligned Storm Motion and Shear Vectors- YES	Yes	↔
Jet stream level – Highly Cyclonic	Highly cyclonic	↔
Jet Stream Speed – High	High	↔
500mb – Highly Cyclonic	Highly cyclonic

Previously Posted Fri 8:52 PM —

Low pressure will move northeast of us on Saturday. Warm air will be brought up over us from the southwest with rain in the morning. A strong pressure gradient will bring strong and gusty winds. A dry slot from the low will bring some sunshine in the afternoon.

A fast moving cold front moves through early Saturday evening with showers and thunderstorms

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