Tag Archives: Severe Weather

WEEKEND WEATHER FORECAST

#weather #paweather #wx #pawx #philadelphia

Updated Sunday Forecast

Update Sun 04/02 @ 10:08 AM

Winds subside during the day. It will be sunny and unseasonably cool.

High temperature 50.0º sd 1.4º ( NBM model location Blue Bell, PA)

12z NBM Wind meteogram forecast for KLOM Blue Bell PA (Click on image for a larger view.)

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.


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—

12z NAM NEST shows elevated CAPE and Helicity northwest of the city at 6 PM. (Click on image for a larger view.)

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/kg2100
Helicity 1350 m^2/s^2655
Vertical Shear 40-4640-45
Precipitable Water 2.7″0.83”⇩⇩
Lifted Index minus 6º Kminus 9.3º
HRRR Hail Parameter 1.91.4
Peak Wind Gusts 40-5040-50
Aligned Storm Motion and Shear Vectors- ~ 90ºAlmost aligned
Jet stream level – wavyHighly cyclonic
Jet Stream 250 mb Speed – 63High 135
500mb – Highly CyclonicHighly cyclonic
Severity Parameters Impact: ⚑ indicates favors Severity ⚐ indicates Possible Severity
↓ indicates works against Severity ⇩ Significant, but less impact

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

Today’s 12z HRRR CAPE/Helicity/Radar forecast for 6 PM Saturday evening. Contours represent helicity. Max helicity South Jersey means some chance of tornadic activity. (Click on image for a larger view.)

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


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.


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/kg1900
Helicity 800-1100 m^2/s^2450
Vertical Shear 35-45 30
Precipitable Water 2.0″0.87”⇩⇩
Lifted Index (minus) 7-9 minus 8
Peak Wind Gusts 40-5040-50
Aligned Storm Motion and Shear Vectors- YESYes
Jet stream level – Highly CyclonicHighly cyclonic
Jet Stream Speed – HighHigh
500mb – Highly CyclonicHighly cyclonic
Severity Parameters Impact: ⚑ indicates favors Severity ⚐ indicates Possible Severity
↓ indicates works against Severity ⇩ Significant but less impact

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

Saturday

Rain in the morning, rapidly ending about 12-1 PM from west to east. Sunshine breaks out from the dry slot associated with the low pressure system in Canada.

A strong cold front moves through between 6 PM and 8 PM with showers and thunderstorms. Some storms. especially from Philadelphia and eastward into NJ, will be strong, although severe weather not expected. The big issue may be the winds.

The HRDPS shows a fast moving line of storms at 7 PM Saturday—

Today’s 18z HRDPS shows a line of heavy rain at 7 PM . This will be a fast -moving line. (Click on image for a larger view.)

High temperature 71.3º sd 2.7º ( NBM model location – Blue Bell, PA)

Wind Meteogram (19z NBM) for Blue Bell PA 40-53 mph winds possible (Click on image for a larger view.)

Sunday

Following Saturday’s cold front, winds subside during the day. It will be sunny and unseasonably cool.

High temperature 50.6º sd 2.2º ( NBM model location Blue Bell, PA)