We warned you about the threat for flooding during the second half of February in our long-range outlook, and this threat is already coming into fruition across portions of the Ohio River Valley. Flooding will only worsen and become more widespread this week as a spring-like flood takes place.
There are two culprits for this week’s flood risk: a trough over the West and a strong blocking high over the East plus deep tropical moisture streaming in from the Pacific Ocean. This combination will make for a very wet situation from the Southern Plains through the Mid-Mississippi Valley and into the Ohio River Valley. A trough of low pressure will practically sit over the Western US this week while a strong, Southeast ridge centers itself over the East Coast. In between these two features is a strong gradient where deep, tropical moisture all the way from the eastern Pacific moisture will funnel. Below, you can see the very bright colors on the map showing the highly anomalous water content in the atmosphere. In more latent terms, this translates to above average moisture in the region. With several upper-level disturbances moving in from the Northwest US, these will instigate the formation of clouds and eventually rain. Due to the highly-moist environment, these clouds will have ample amounts of water to work with.
Several rain events have already affected this region last week, especially in the Ohio Valley. Below are a few photos from Photographer Dave DiCello in Pittsburgh, reporting the rivers overflowing their banks, thus flooding some roadways in the city. Thankfully, the rivers in this area will subside and return back to near-normal levels by midweek. However, they may rise again by next week due to several more inches of rain on the way.
Throughout the week, we’ll highlight the specific rain events and bring you the exact timing and details, but for now we’re going to briefly describe when the different events will occur and where.
On Monday, rain showers, which will be light for most areas, will break out across much of the Midwest, Great Lakes, and Ohio Valley. That rain will consolidate into a line of heavy rain and thunderstorms that will train from the western Great Lakes through the eastern Southern Plains on Tuesday. When we talk about training, this is when heavy precipitation falls across the same areas for several hours. In this event, the heavy rain will move from south to north over the same areas without making much eastward progress. Rainfall rates may exceed two inches per hour for some locations. On Wednesday, the rain will exit much of the Great Lakes while training rain and storms continue across portions of the eastern Southern Plains into the Mid-Mississippi Valley. On Thursday, it will quiet down relatively speaking with lighter showers spanning from the Northeast through the Southern Plains. It’s not until Thursday night into Friday when the next burst of moisture may stream in, possibly leading to more heavy rain in the ArkLaTex region. It is still really early to specify where the heavy rain will occur by this time period, but understand that more rain is likely ahead in this general area during this time frame. During the weekend, another very heavy rain event may take shape. That’s really all we can tell you at this time.
When comparing the ensemble mean guidance of the American (GEFS) model and the European (EPS) model, they are agreeing very well on where the axis of heavy rain will be focused and how much rain will generally fall. This screams the threat for flooding. Remember, much of this region is experiencing dry conditions or even a drought. Typically droughts end in floods, and this certainly may be the case.