Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Sun Sep 23 2018 Valid 12Z Sun Sep 23 2018 - 12Z Tue Sep 25 2018 ...Heavy to excessive rainfall possible from the lower Mississippi Valley to the Mid-Atlantic... ...Elevated to critical fire weather threat continues across the Central Great Basin and the Central Rockies... Expect rounds of heavy rainfall to continue the next few days along a nearly stationary frontal boundary draped from the lower Mississippi Valley to the Mid-Atlantic. The WPC excessive rainfall/flash flood outlooks place much of this region within a slight risk on Sunday, with a marginal to slight risk continuing on Monday as well for the Ohio Valley and central Appalachians. South of this boundary, the threat for showers and thunderstorms will be possible into the early work week within a warm and humid airmass. And to the north, strong Canadian high pressure slides in which should keep temperatures near or below normal across much of the Northeast the next couple of days, with a handful of frost advisories and freeze warnings in effect for portions of northern New England. Elevated to critical fire weather concerns will continue this week across much of the Central Great Basin/Intermountain West and into the Central Rockies where temperatures are expected to be well above normal and humidity levels remain low. As a result, numerous red flag warnings are in effect across portions of Nevada, Utah, and Wyoming. An upper level system moving across the Northwest today may bring some light and scattered showers to portions of the northern Rockies and northern High Plains. Once this system pushes into the central U.S. by Monday, it should tap into additional moisture which would increase the threat for rain and thunderstorms along a cold front from the Upper Midwest to the Central Plains. Moderate to locally heavy rainfall may be possible on Monday and into Tuesday, particularly near the low pressure area as it moves through the Upper Mississippi Valley and into southern Canada. Santorelli Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php