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Tornadoes in California & the PANW

SpotlightForRareTornadoes said:
20 years ago, an F1 tornado ripped through South San Francisco, damaging 60 structures. Here is a news clip featuring the only footage of it.

Click to expand...

Not the only video. There used to be a second close range angle on YouTube of this tornado ripping off roof shingles. Was one of the first tornado videos I ever found on YouTube actually.
 
Last edited:
The 2023 Montebello Tornado - Two Years Later










On March 22, 2023, a high-end EF1 tornado ripped through the Montebello District of Downtown Los Angeles, damaging 17 buildings (11 severely) and injuring at least one person. The estimated wind speeds of the twister reached 110 mph as it ripped the roofs off of multiple industrial warehouses, totaling several cars, and spiraling thousands of pieces of debris hundreds of feet into the air. The worst of the damage was inflicted at the Royal Paperbox Company warehouse, where the roof was almost totally collapsed, and its HVAC unit was ejected into the air. With a borderline EF2 rating, this tornado remains the strongest in LA since the 1983 South Central Los Angeles Tornado 40 years earlier. What is very intriguing about this twister is that it occurred during a general thunderstorm risk in the area and that it's heavily implied that the same storm system would go on to spawn the 2023 Rolling Fork EF4 two days later.

1742629979866.png

This is the SPC outlook issued 30 minutes before the rare tornado touched down. Even if there is a general thunderstorm risk, that doesn't mean a tornado is out of the picture.
 
Legitimate threat for supercells with very large hail and even a tornado or two along the I-5 corridor tomorrow. Record levels of instability and more than enough shear for organized storms. In terms of forecast confidence for an environment supportive of severe storms, this is just about unprecedented in the modern era in the Pacific NW.
 
In west central Oregon here (and throughout the region), we've had some incredibly warm days -- 70s! Reaching 80 is not impossible -- so that feeds into the setup.

Then the ridge gets pushed eastward into Jacob's area of responsibility ;) and things get active for us.

The boffins don't seem especially strong on the tornado threat yet, but it is there. Per Portland's current FD:

...
Looking at the ECMWF EFI (Extreme Forecast Index) is showing values that are the highest relative to the 30 year model climatology. Also, the shift of tales value range from 2 to 5 standard deviations or to put it simply, these values are beyond what would normally be expected for this time of year. In addition, model soundings within our CWA, look very similar to what would cause severe weather out in the Central Plains of the United States as they show significant CAPE values, PWAT values as well as favorable wind shear profiles. I can say that in my near decade of time here at NWS Portland, these are the most consistent and robust model soundings I have seen for this area. Given all of this information, SPC has also put most of our CWA in the Marginal Thunderstorm Threat Category (20-40% probability) for Wednesday.

Impacts from any thunderstorms that develop on Wednesday are as follows:

Hail: up to 1 inch in diameter or about the size of a US Quarter.
Tornado/Funnel Cloud: Less than 5% probability.
Wind: Gusts up to 60 mph.
Light[n]ing

It should also be noted that while Wednesday could also be a near or record breaking day for daytime highs, that will be dependent on the amount of cloud cover. If showers start earlier than currently forecasted, then that will temper daytime highs.

Will continue to monitor as cloud cover is very challenging to forecast in this pattern.
Click to expand...
 
The current forecast discussion is an excellent explanation of the situation for science-minded lay folks who haven't encountered this setup before or who, like me, need a better grasp of the basics. (Why autotranslate -- presumably -- condemned the SPC to perdition, though...? ;) )

Essential point:

To summarize, confidence in severe thunderstorms has increased
across the CWA. The highest threat currently is for large hail,
followed by damaging winds and then tornadoes. According to
records dating back to 2002, this is the first day 2 slight risk
issued in March west of the Rockies. So, make sure you have a
way of recieving NWS alerts and have an action plan in case you
are caught in a severe thunderstorm warning.
Click to expand...

Good on both counts.

Wonder how intense things will be in the late afternoon, given sufficient insolation, to our northeast and around the Washington border area.
 
It is so amazing, though not unique, of course, to have an MD for our area!

Mesoscale Discussion 0266
NWS Storm Prediction Center Norman OK
0343 PM CDT Wed Mar 26 2025

Areas affected...Parts of western OR/WA

Concerning...Severe potential...Watch likely

Valid 262043Z - 262245Z

Probability of Watch Issuance...80 percent

SUMMARY...Supercell development is possible later this afternoon.
Large hail, isolated severe gusts, and perhaps a tornado or two will
all be possible. Watch issuance is likely.

DISCUSSION...Seasonably strong diurnal heating is underway across
western OR into southwest WA early this afternoon, with temperatures
expected to approach or exceed record highs in some areas. The 18Z
soundings from MFR and OTX depict steep lapse rates within the
850-600 mb layer, and deep-layer wind profiles supportive of
supercells. Moisture was lacking within these soundings, but surface
observations suggest somewhat more favorable moisture into parts of
western OR/WA, with dewpoints from the upper 40s to 50s F. Continued
heating will support weak to moderate destabilization with time to
the west of the Cascades, with SBCAPE potentially increasing to
near/above 1000 J/kg by late afternoon.

As an intense deep-layer cyclone well offshore of OR/WA moves
east-northeastward this afternoon, a strong mid/upper-level jet will
overspread the Pacific Northwest, further strengthening deep-layer
shear across the region. Isolated storms may initially develop near
the coastal ranges and/or the western slopes of the Cascades, with
increasing large-scale ascent supporting maintenance of storms as
they spread north-northeastward with time.

Favorable deep-layer shear will support development of a few
supercells with time. Hail to the size of golf balls or larger may
become the most prominent hazard, given the presence of elongated
hodographs, moderate buoyancy, and rather cold temperatures aloft.
Any sustained supercell could also pose some tornado threat,
especially where low-level winds are locally backed due to terrain
or storm-scale influences. Isolated strong to severe gusts may also
accompany the strongest cells/clusters. A watch will likely be
needed once storm initiation appears imminent.

..Dean/Smith.. 03/26/2025

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...PDT...MFR...SEW...PQR...

LAT...LON 43312382 46132352 47112314 47712237 47672153 47052134
45492128 44312153 43612192 43032276 43312382

MOST PROBABLE PEAK TORNADO INTENSITY...85-115 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN
Click to expand...

Moisture might be a problem.

Numbers aside, yesterday felt much muggier at this point in the afternnon than today does. Guess I forgot I wasn't in Alabama and was expecting the whole damp scuba-suit experience of high dew points again. :)
 
We've got a severe thunderstorm watch. I'm worried about Washington later this afternoon, given how convection just sort of switched on a little while ago here and is taking off (nothing warned yet, still messy but muscular-looking).

The Washington counties in the watch are:

CLARK COWLITZ KING
LEWIS PIERCE SKAMANIA
THURSTON
 
It seems to be following the later part of the timeline suggested by Seattle/Tacoma NWS this morning. This amateur wonders if the tornado threat will be highest if and when a squall line forms:

...
Timing for the possible
severe thunderstorms still looking like starting around 3 to 4 pm
in Lewis county. The storms will be moving quickly and will reach
the metro area around 6 pm give or take an hour finally getting to
Bellingham around 9 to 10 pm. Everything is still in place for the
possibility of severe storms ( hail greater than 1 inch in size
and or wind gusts 58 mph or greater ). Something to remember the
frequency of lightning is not a factor on whether a storm is
severe. The models are starting to show the storms could become
organized into a QLCS ( a ragged long squall line ) instead of
isolated hit or miss storms...
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Portland, early this afternoon, on our chances (and the parts of Washington in the Columbia River area and along the coast):

...
SPC also has a 5% chance of tornados throughout the Willamette Valley
and SW Washington lowlands, including along the I-5 corridor this
afternoon and evening. With strong CAPE values 2500-3500 J/kg, as
well as effective SRH around 150 m2/s2 and bulk wind difference
around 50-60 kt, conditions are somewhat favorable for enough
rotation to induce mesocyclonic tornado formation. Effective SigTor
(significant tornado parameter) values are around 0.5-1.0, further
indicating the possibility of tornados. While conditions are more
favorable for tornado formation than other thunderstorm systems in
recent memory, SPC risk is still only 5%, meaning this is still a
fairly unlikely occurrence.
..
Click to expand...
 
bjdeming said:
We've got a severe thunderstorm watch. I'm worried about Washington later this afternoon, given how convection just sort of switched on a little while ago here and is taking off (nothing warned yet, still messy but muscular-looking).

The Washington counties in the watch are:

CLARK COWLITZ KING
LEWIS PIERCE SKAMANIA
THURSTON
Click to expand...
Yeah, I am keeping an eye on Seattle as I have a friend who lives there. Luckily the risk for tornadoes in the Willamette Valley and Seattle Metro remains at 2%! :)
 
I know the environment didn't fully come to fruition as in some of the earlier HRRR models, but I cherry picked a non-contaminated sounding in Western WA from the 12z HRRR. And there's just a casual 3k SBCAPE and 150 3CAPE in Washington...

12zhrrr032625soundingWesternWashington.png
 
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