A Mesoscale Precipitation Discussion (MPD) is a short-term Weather Prediction Center (WPC) product that highlights an area where heavy rain may lead to flash flooding over roughly the next 6 hours. Each one pairs a map of the area of concern with a brief discussion of the mesoscale features expected to drive the rain.
Who writes it and why
The meteorological watch desk at WPC, called Metwatch, issues MPDs. WPC began providing them on 04/09/13, as short-term guidance for National Weather Service (NWS) forecast offices, River Forecast Centers, the media, emergency managers and other partners.
WPC aims to issue MPDs 1 to 6 hours ahead of time. On average a discussion covers an area roughly half the size of Kansas.
Reading one
Each MPD carries one of three confidence statements: flash flooding likely, flash flooding possible, or flash flooding unlikely. The header lists the areas affected and a valid period in Coordinated Universal Time (UTC), and the body includes a plain-language summary and a longer technical discussion.
For example, MPD 1392 of 2026 covered the low deserts of California through southern Arizona with flash flooding likely, valid from 0517 to 1115 UTC on September 29. Its discussion tied the rain to a moisture plume ahead of an upper low.
How it compares with SPC Mesoscale Discussions
The Storm Prediction Center (SPC) issues its own Mesoscale Discussions. Those focus on severe thunderstorm potential, plus some winter hazards such as heavy snow and freezing rain, over the next 6 hours with emphasis on the first 1 to 3.
MPDs cover the heavy rain and flash flood side. On a night with slow or training storms, both centers may have discussions out for overlapping areas, each answering a different question.
What it does not do
An MPD does not warn anyone. A Flash Flood Warning comes from the local NWS office when flash flooding is in progress, imminent or highly likely.
Its area is broad compared with the creeks, washes and streets that actually flood. Which spots flood still depends on where the heaviest cells set up and how the ground responds.