Low to Moderate risk of severe weather in Brazil

[LucasMarcomini]

HPC started talking about the risk of deep convection over central-south Brazil for a few days and now they "issued" a moderate risk of severe weather for days 2-3 and a high risk of heavy rains with potential for floodings.

Today's model discussion:

THERE IS A LOW TO MODERATE RISK OF SEVERE CONVECTION ON THE
SOUTHERN STATES OF BRASIL ON DAYS 02-03...AND A HIGH RISK OF
HEAVY RAINS.
FURTHERMORE...UNDER INFLUENCE OF THE MID/UPPER LEVEL TROUGH...A
LOW IS TO FORM ACROSS SOUTHERN BRASIL BY 54-60 HRS...WITH SYSTEM
FORECAST TO INTENSIFY/DEEPEN THROUGH 72-84 HRS WHILE IT MEANDERS
OFF THE COAST OF RIO GRANDE DO SUL/PARANA. AS IT INTENSIFIES...
THIS WILL FAVOR A STRONG EASTERLY FLOW INTO THE SOUTHERN STATES
OF BRASIL...WITH FLOW TO CONVERGE ALONG THE COAST/SERRA DO MAR.
AS THE MID/UPPER LEVEL SHORT WAVE TROUGH EVOLVES INTO A CLOSED
LOW EARLY IN THE CYCLE...THIS WILL ENHANCE CONVECTIVE
INSTABILITY. THIS...IN COMBINATION WITH ABOVE NORMAL SEA SURFACE
TEMPERATURES...WILL FUEL ORGANIZED DEEP CONVECTION AND LIKELY
FAVOR SEVERE CONVECTION. ACROSS SOUTHERN TO SOUTHEAST BRASIL WE
FORECAST RAINFALL MAXIMA OF 35-70MM/DAY. BUT...DUE TO STRONG
TOPOGRAPHICAL FORCING/MOISTURE CONVERGENCE ALONG THE SERRA DO
MAR...LOCALLY HIGHER AMOUNTS ARE EXPECTED. IN THIS AREA THE
MODELS ARE UNDERESTIMATING THE RISK/POTENTIAL FOR HEAVY RAINS.
THROUGH 72-96 HRS ACTIVITY WILL BUILD NORTH ALONG THE COAST TO
EXPAND ACROSS SAO PAULO TO MATO GROSSO DO SUL.

 

[Stephen Levine]

Thank you for posting this interesting forecast. What a joy it is for me to do this "armchair chasing" and imagine being there and ready with my camera. Please keep us posted about what transpires there for you.

 

[LucasMarcomini]

Thanks Stephen!
The HPC has reduced the risk over southern/southeastern Brazil to a slight risk.
I'll post the whole model discussion so you can have a better picture of the scenario:

NOTE: RISK OF SEVERE CONVECTION AND HEAVY RAINS WILL PERSIST
ACROSS NORTHERN BOLIVIA-SOUTHERN PERU-ACRE/SOUTHERN AMAZONAS IN
WESTERN BRASIL THROUGH 36-48 HRS.

RISK OF HEAVY RAINS REMAINS HIGH FOR THE SOUTHERN STATES OF
BRASIL DURING THE NEXT 48-60 HRS...WITH A SLIGHT RISK OF SEVERE
CONVECTION DURING THE NEXT 24-36 HRS.

MODEL COMPARISON (VALID FROM 00 UTC JAN 13): THE GLOBAL MODELS
ARE IN GENERAL AGREEMENT. THE ENSEMBLE MEMBERS ALSO CLUSTER QUITE
WELL INTO MEDIUM RANGE PERIOD. AS A RESULT...CONFIDENCE IN
THE FORECAST REMAINS HIGH.

A BROAD MID/UPPER LEVEL TROUGH DOMINATES THE FLOW OVER THE FAR
WESTERN ATLANTIC...AS IT EXTENDS BETWEEN 65W-30W AND TO THE SOUTH
OF 30S. EARLY IN THE CYCLE THE MODELS FORECAST THIS TROUGH TO
SPLIT...WITH THE SOUTHERN HALF ACCELERATING ACROSS 30W/35W. THE
NORTHERN HALF...MEANWHILE...IS TO EVOLVE INTO A SHORT WAVE TROUGH
FORECAST TO MEANDER ACROSS SOUTHERN BRASIL-URUGUAY/MESOPOTAMIA
VALLEY IN ARGENTINA. A LOW OVER RIO GRANDE DO SUL WILL ANCHOR
THIS TROUGH AT 36-60 HRS. BY 72-84 HRS THE TROUGH WILL START TO
PULL TO THE EAST-SOUTHEAST...WHILE THE SHORT WAVE TROUGH REMAINS
OVER THE SOUTHERN STATES OF BRASIL. AT LOW LEVELS A POLAR FRONT
IS TO STRETCH ACROSS THE SOUTH ATLANTIC TO RIO GRANDE DO SUL IN
BRASIL...WHILE A TROUGH IS TO MEANDER ACROSS NORTHERN BOLIVIA-
MATO GROSSO DO SUL/PARAGUAY TO SOUTHERN BRASIL. THIS TROUGH WILL
REMAIN THE FOCUS OF MOISTURE CONVERGENCE DURING THE NEXT FEW
DAYS. THE TROUGH IS TO INITIALLY CENTER ON A LOW OVER PARAGUAY.
THIS WILL SUSTAIN A TIGHT PRESSURE GRADIENT AND STRONG BOUNDARY
LAYER WINDS...WITH A SOUTHEASTERLY JET ACROSS PARAGUAY-BOLIVIA TO
SOUTHERN PERU EARLY IN THE CYCLE. THIS FAVORS A MESO SCALE
CONVECTIVE SYSTEM ACROSS NORTHERN BOLIVIA-SOUTHERN PERU/SOUTHERN
AMAZONAS-ACRE IN BRASIL. IN THIS AREA EXPECT RAINFALL MAXIMA OF
40-80MM IN POTENTIALLY SEVERE CONVECTION THROUGH 36-48 HRS.
THROUGH 60-72 HRS IT IS TO DECREASE TO 20-45MM/DAY.

FURTHERMORE...UNDER INFLUENCE OF THE MID/UPPER LEVEL TROUGH...A
LOW IS TO FORM ACROSS SOUTHERN BRASIL BY 30-36 HRS...WITH SYSTEM
FORECAST TO INTENSIFY/DEEPEN THROUGH 48-60 HRS WHILE IT MEANDERS
OFF THE COAST OF RIO GRANDE DO SUL/PARANA. ON DAY 02 WE EXPECT A
1000-1002 HPA LOW TO MEANDER OFF THE COAST. AS IT INTENSIFIES...
THIS WILL FAVOR A STRONG EASTERLY FLOW INTO THE SOUTHERN STATES
OF BRASIL...WITH FLOW TO CONVERGE ALONG THE COAST/SERRA DO MAR.
AS THE MID/UPPER LEVEL SHORT WAVE TROUGH EVOLVES INTO A CLOSED
LOW EARLY IN THE CYCLE...THIS WILL ENHANCE CONVECTIVE
INSTABILITY. THIS WILL COMBINE WITH WARM SEA SURFACE TEMPERATURES
ALONG THE BRAZILIAN CURRENT TO SUSTAIN ORGANIZED DEEP CONVECTION
AND LIKELY FAVOR SEVERE CONVECTION. ACROSS SOUTHERN TO SOUTHEAST
BRASIL WE FORECAST RAINFALL MAXIMA OF 50-100MM/DAY THROUGH 36
HRS. THROUGH 48-60 HRS IT WILL DECREASE TO 35-70MM/DAY WHILE
BUILDING NORTH ACROSS SAO PAULO-MATO GROSSO DO SUL. BY 72-84 HRS
CONVECTION ON THE SOUTHERN STATES OF BRASIL WILL DECREASE TO 20-
40MM/DAY...WHILE OVER SAO PAULO-MATO GROSSO DO SUL EXPECTING
MAXIMA OF 30-60MM/DAY. THIS IS LIKELY TO AFFECT PORTIONS OF RIO
DE JANEIRO ON DAY 04.

Some GFS charts:

 

[Tim Vasquez]

Lucas --

South America's weather network is not quite as dense as the US but still it is possible to do a good surface analysis with it. Here is how I might have forecasted a "target", though without the benefit of upper air data and soundings. This outlines a zone of better low-level shear and storm-relative flow in the red area. Looking at the satellite imagery I suspect the environment is weakly capped and this activity is rather multicellular. Also it looks like there are some outflow boundaries in the moist sector, which could make further analysis a bit challenging.

Also, sorry that these plots are not in Celsius, but you can still see the overall pattern.

Tim

 

[LucasMarcomini]

Thank you Tim!
I really am only a newbie in weather so that map is an awesome help!
00Z soundings should be up in about an hour or so, I will post them later.
The 12Z sounding from Foz do Iguaçu (It's inside the red area in your map) was no looking really impressive, but storms are going to pop closer to the 00Z ones, so things might change.

This one is from Londrina, about 300 miles to the northeast of Foz do Iguaçu

 

[Tim Vasquez]

The soundings are a little difficult to read since they're stretched vertically, but they look contaminated (perhaps rain at the station at the time). Any instability index values are probably suspect. The hodograph (which must be compared to the wind plots at the side to help determine height of the shapes) does point out good shear between the low levels and the mid levels (about 700 mb)... also for those readers who are in the US, this is using m/s, so the plots can be misleading at first glance. Double the values to get knots. This is certainly an interesting case.

 

[Tim Vasquez]

Radar page for anyone interested:
http://www.simepar.br/site/internas/conteudo/monitoramento/radar/index.shtml

Hard to tell what I'm looking at on this radar, and whether it's a composite reflectivity blurring multiple levels together or base reflectivity showing stratified convection. I'd probably check out the visible satellite imagery (as close to 1 x 1 km as possible) to get a better idea of the convective elements and whether there's any isolated cells. My impression so far is it's an uncapped precipitation event enhanced by weak isentropic lift over old outflow near or north of the cold front (that dashed line on the surface analysis above); sort of a monsoon-like system. Any stronger cells would probably be close to that surface low and further NW along the front, though that gets further from the favorable storm-relative inflow.

 

[LucasMarcomini]

Yeah Tim, I don't really trust our radar sites. They use mostly MaxCAPPI images, which are a kind of composite that shows the higher reflectivity values in the storm regardless of it's height, which causes some trouble in the identification of structures like a hook echo, inflow notch, etc.
Though in this case I belive the storms are out of range.
This link shows most of the public owned radar sites with CAPPI images, that show the reflectivity values at 3.000 meters.

http://sigma.cptec.inpe.br/radar/radargoogle.principal.logic

To the left there's a menu where you can choose between the radar sites. Some of them have more products available like 1° Reflectivity, Eco Tops and a wind field that I'm not really sure if it's similar to SRV or BV. Those products do not work in most of the radars though, welcome to Brazil..

Here you can see GOES 12 Satellite imagery updated at every 15 minutes.
http://satelite.cptec.inpe.br/acervo/goes_anteriores.jsp

 

[LucasMarcomini]

Here's the latest Goes 13 (Goes East) Full disk image:

 

[LucasMarcomini]

Here's the 00Z sounding from Foz do Iguaçu:

Hodo:

 

[LucasMarcomini]

12Z sounding from Londrina, Paraná.

Visible Goes 12 image:

 

[Tim Vasquez]

Thanks for sharing. I haven't had time to look at this event, but I find these storms outside the US interesting as we have so much access to all kinds of data. Have you heard any reports of damage in the news or seen any photographs from Brazilian weather enthusiasts? That would be interesting.

By the way, I think you should try out McIDAS V... see <a href="http://www.ssec.wisc.edu/mcidas/software/v/download.html">this</a> link. It would be very good for looking at satellite data for Brazil and would give you better graphics overall. I use it all the time when looking at international weather events since there's usually data sources that give much better real-time images than anything on the web.

Tim

 

[LucasMarcomini]

Thanks for that link Tim, I'll try it out!
There are not many weather enthusiast around here, and many of those are the kind that enjoy the winter rather than severe weather. There's a really good project going on at UFSM (Federal Universitie of Santa Maria, in Rio Grande do Sul state, south Brazil) where some students are doing some storm chasing. The project is coordinated by Dr. Ernani Nascimento, who studied at the Oklahoma University for his phd I belive. He chased the Moore/Bridge Creek tornado in 1999 too.
I have a blog with a couple of friends I've met in a Brazillian weather forum http://vortexbrasil.blogspot.com/
Also, in our partners list there is an amateur storm chasing team of meteorology students: http://www.capinchocumulus.blogspot.com/

Went a little of topic there hehe
But returning to the storms, no tornados were recorded or supercells, mostly a wind and rain only event. The airport of São José dos Campos recorded gusts of 75 mph.
I guess this was a false alarm, but I'll post if a new event starts shaping up.
Also, if anyone have any questions about the weather and weather related down here I'll be glad to answer.

Thank you

 

[LucasMarcomini]

This was shot in Rio de Janeiro. Looks like a shelf cloud