US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 319 PM EDT Mon May 06 2019 Valid Thursday May 09 2019 - Monday May 13 2019 Hazards: - Heavy precipitation across portions of the Southern Rockies and the Southwest, Fri, May 10. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Thu-Sun, May 9-May 12. - Heavy rain across portions of the Great Lakes, the Mid-Atlantic, the Northeast, and the Central Appalachians, Thu-Fri, May 9-May 10. - Heavy snow across portions of the Southern Rockies, the Central Rockies, the Southern Plains, and the Central Plains, Thu, May 9. - Severe weather across portions of the Lower Mississippi Valley, the Tennessee Valley, the Southern Plains, the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley, Thu, May 9. - Flooding possible across portions of the Central Plains, the Central Appalachians, the Northern Plains, the Great Lakes, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains. - Flooding occurring or imminent across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Great Lakes, the Middle Mississippi Valley, the Upper Mississippi Valley, the Southern Plains, and the Ohio Valley. - Much below normal temperatures across portions of the Southern Rockies, the Central Rockies, the Southern Plains, and the Central Plains, Thu-Fri, May 9-May 10. - Heavy precipitation across portions of mainland Alaska, Thu-Fri, May 9-May 10. Detailed Summary: Over the contiguous U.S., the primary concern for this period will be the potential for heavy to excessive rainfall across the Tennessee Valley, lower Mississippi Valley and eastern/southern Texas. A strong cold front moving across the east-central states Thursday is expected to stall out as it pushes into the southern Plains and lower Mississippi Valley and basically remain quasi-stationary over this area through much of the weekend. A series of short waves rotating around and ejecting from slow moving upper low in the southwestern U.S. will interact with deep Gulf moisture and a highly unstable air mass to support multiple rounds of organized heavy showers and thundershowers. There's some uncertainty among the latest model guidance as to the exact north-south positioning of this front, but the general consensus supports the heaviest axis of rain from eastern/southeastern Texas across central/northern Louisiana into central Mississippi. At this time, 4-day totals of 5-10 inches are possible from Thursday through Sunday, with isolated higher amounts likely. Particular concern is over eastern Texas and western Louisiana where rainfall over the past 2 weeks has averaged 200-300% of normal and soils are already relatively saturated. Farther to the west behind the abovementioned cold front, a Canadian air mass will build in across the central and southern Plains and Rockies Thursday-Friday, with temperatures (especially daytime highs) upwards of 15-20 degrees below normal expected. Along with the cold air, there's the potential for moderate to heavy snowfall from central Colorado southward into northern New Mexico Thursday in response to broad upper divergent flow downstream of the southwestern U.S. closed low. On Friday, a strong short wave ejecting out of this closed system along with plenty of ambient moisture may bring heavy precipitation (snow at the highest elevations) across western New Mexico. Confidence in this latter hazard area is lower as there are rather large differences among model forecasts, however did want to highlight it given that some ensemble guidance suggests the forecasted maximum amounts could exceed the 99th percentile of model climatology for this period. Across the northern mid-Atlantic states and Northeast, strong southwesterly flow ahead of a cold front will transport deep Gulf of Mexico moisture over a retreating warm front and support heavy overrunning showers and embedded thundershowers Thursday into Friday. The attendant trailing cold front is progressing at a relatively good clip, so rainfall totals will mostly be in the moderate range (about 1-2 inches), but locally higher amounts could result in isolated runoff problems. In Alaska, a surface low quickly deepening along a north-south aligned frontal system will bring the threat for moderate-heavy precipitation along the south-central mainland Thursday-Friday. Models indicate the main threat will be around Kodiak Island to Anchorage Thursday, then farther east along the coast early Friday. Overall, this is a fairly marginal threat case, with liquid equivalent totals forecast by model guidance mostly in the 1-2 inch range both days. However, we did want to highlight the system as the associated strong mid-upper level dynamics could result in locally high precipitation rates. Klein