Storms have blossomed over portions of northern Argentina tonight. You can see the greens and reds blow up near the middle of the satellite animation below. These storms will tend to move southeast overnight and into Friday. Very heavy rainfall will occur with these storms, leading to flash flooding.
The heaviest rainfall of 100-200 mm are expected over portions of northwestern Argentina and western Uruguay, including Buenos Aires and areas to the north. Localized amounts exceeding 200 mm will probably occur. These torrential rainfall amounts will lead to flash flooding in spots. Storms will weaken later on Friday with the flooding threat diminishing.
The first major fall storm of the season is set to impact southeast Australia through the end of this week. Accompanying the fall storm will be rain and the potential for flooding, strong winds, and mountain snow.
Wednesday
A cold front will cross the Bight on Wednesday and move into coastal southeast AU by day’s end. Gusty showers and isolated thunderstorms will accompany the frontal passage. The cold front is expected to reach Adelaide on Wednesday evening and Melbourne Wednesday night.
Thursday
The cold front will sweep across southeast Australia on Thursday. Additionally, low pressure will develop near TAS and help drive strong south to southwesterly winds across the region. Gusts of 70-100 kph are likely along the coast as well as across the mountains.
Periods of rain will accompany the strong winds in many locations. Heavy rain will be likely near and to the west of the low pressure system. The heaviest rain on Thursday will likely be across TAS, especially near the Hobart area and surrounding hills.
In additional to the rain and wind, temperatures above 1,000 meters will get cold enough for the rain to change over to snow at times. A significant amount of snow in excess of 30 cm is likely at elevations above 1,300 meters between Thursday and Saturday.
Friday
Low pressure will drift northward on Friday continuing the strong wind and rain threat across much of southeast AU. Periods of heavy rain will spread northward across southern and eastern VIC.
The moist southerly flow on the west side of low pressure will combine with increasing elevation will bring an elevated risk for flooding to the VIC hills and Alps. The threat for heavy rain and flooding will continue across eastern VIC into Saturday.
The strongest storm-related impacts are expected to lighten up by Sunday, however, lingering showers and breezy conditions are likely from eastern VIC up to the central NSW coast.
The potential for heavy rain and severe thunderstorms will exist through much of this week across central South America. Argentina, Uruguay, Paraguay, and southern Brazil are the countries most at risk for damaging thunderstorms and flooding rain.
The Setup
High pressure will setup to the east of Uruguay this week while low pressure will establish itself over the Gran Chaco region located just east of the Andes Mountains. Additionally, a second low pressure system will move into Chile later in the week.
Satellite imagery from Sunday shows low pressure off of the Chilean coast. This storm will move into Chile and eventually aid in heavy rain and severe thunderstorms across Argentina and Uruguay later Wednesday through Thursday.
The flow around the pressure systems will draw tropical moisture southward. The result will be numerous rounds of showers and heavy thunderstorms, some of which will be severe.
Initially, the heaviest rain and best chance for severe thunderstorms will exist across Paraguay and central Argentina through Tuesday. However, this threat area will shift toward eastern Argentina, Uruguay, and southern Brazil during the middle and end of the week.
The Impacts
Damaging winds, large hail, and torrential downpours capable of flash flooding are likely in the heaviest storms.
5-day rainfall totals of 100-200 mm are likely in a corridor from northern Argentina into parts of Paraguay. Outside of this area, widespread rainfall amounts of 25-100 mm are likely.
Weather models trends this weekend suggest that the period from Wednesday evening through Thursday and Thursday night may bring the greatest risk for severe thunderstorms and flash flooding.
Capital cities such as Asuncion, Buenos Aires, and Montevideo are within the threat area for heavy rain and severe storms, mainly from Tuesday through Thursday night. Other cities such as Cordoba and Rosario are also at risk for severe weather and flash flooding.
By the upcoming weekend, the risk for severe weather will end as a more tranquil fall air mass moves into the region.
The month of May got off to an active start with severe thunderstorms across the US.
The National Weather Service (NWS) recorded over 500 reports of severe weather from Colorado to New York state. The majority of the severe weather occurred across the central Plains from Texas to Iowa.
The most active day for severe thunderstorms in term of reports was on Wednesday when the Storm Prediction Center (SPC) reported a total of 232 severe weather reports.
One of the more impressive individual storms occurred on May 1st from a severe thunderstorm that produced a large tornado in Kansas. This particular tornado was captured by a storm chaser’s dash cam.
In addition to the severe storms, heavy rain and flash flooding was observed across portions of the Plains and Midwest. In just the first 3 days of May, a swath of 3-6 inches (75-150 mm) of rain fell from Iowa to Wisconsin.
The system responsible for the severe thunderstorms will be moving off of the East Coast this weekend giving a much need break from severe weather to the Central US.
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