US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 349 PM EDT Fri Jul 30 2021 Valid Monday August 02 2021 - Friday August 06 2021 Hazards: - Heavy rain across portions of the Southeast and the Lower Mississippi Valley, Mon, Aug 2. - Heavy rain across portions of the Southeast and the Mid-Atlantic, Mon-Thu, Aug 2-Aug 5. Detailed Summary: During the medium range period (Monday, August 2nd - Friday, August 6th) the upper-level pattern is forecast to consist of significant troughing over the eastern half of the CONUS that gives way to the development of a cut-off low over the Ohio Valley mid-week. Conversely, in the west strong ridging aloft is expected to be in place at the start of the period before weakening as low pressure off the coast of British Columbia disrupts the flow regime and eats away at the adjacent high pressure. For the majority of next week all eyes will be on the Southeast and Mid-Atlantic where a frontal boundary will likely remain locked in place, delivering a significant amount of rain to the East Coast. It all begins on Monday when a cold front extending from North Carolina to central Texas brings showers and thunderstorms to the southern states alongside a dissipating stationary boundary. Over the next couple days the western edge of the front will be quickly forced south to the Gulf Coast by a digging upper-level trough working in tandem with southward moving surface high pressure. It is during this time states located in the Lower Mississippi Valley as well as Alabama will receive the most rain, with 1 to 2+ inch accumulations in 24 hours possible. Given the high soil moisture and above to much above normal streamflow in these areas, localized flash flooding may occur. Although the frontal boundary is expected to deliver more rain to the Gulf Coast as it becomes quasi-stationary for the rest of the period, any heavy rainfall will likely remain offshore. In contrast to the evolution of the western half of the cold front the eastern half is forecast to slightly swing to the southeast, but remain predominantly stationary, as a low pressure wave along the boundary lifts north into Georgia on Tuesday. Sandwiched by high pressure on either side, the front is forecast to settle in over the Florida Panhandle, Georgia, and the Carolinas as a quasi-stationary boundary for the remainder of the period, leading to a multi-day heavy rain event over the Southeast and Mid-Atlantic. Four-day rainfall totals of 3 to 6 inches, with isolated higher amounts, will be possible from the Florida panhandle through southern Virginia. These high accumulation totals combined with already wet soils will make the risk of localized and urban flash flooding a significant concern. Out west showers and thunderstorms driven by the influx of monsoonal moisture, diurnal heating, and favorable dynamics will continue across the Rockies and High Plains through Wednesday night. Though rainfall totals are forecast to be on the moderate side throughout these regions, there is potential for isolated instances of heavy rain to occur. Additionally, fueled by the inland transport of moisture from the Gulf of Mexico, surface troughs over New Mexico and the Sierra Madre are expected to generate showers and thunderstorms with moderate to sometimes heavy rainfall across southeastern New Mexico and western Texas on Wednesday and Thursday. No significant temperature anomalies or extremes are anticipated over the CONUS during the medium range period. In fact, across the country daily highs are forecast to remain close to or below normal, save for the Northern Plains and Upper Midwest which will experience daily highs a few degrees above normal. No hazards have been posted for Alaska on today's graphic, however, there are multiple instances of potentially heavy rain during the period that are worth mentioning. The first of these instances will occur on Tuesday, when a small portion of the Alaska Panhandle that borders the Yukon Territory may receive up to 2 inches of rain, with isolated higher totals, ahead of a cold front moving south through the eastern Interior. The following day a low pressure/frontal system is expected to settle over and bring heavy rain to Graham Island, some of which may spread north into the very southern tip of the Panhandle. While deterministic models are in agreement with rainfall totals of 2+ inches affecting the area, ensembles point to the heaviest rain being farther south. Due to the uncertainty among the deterministic and ensemble forecasts, it was decided a heavy rainfall area will not be included on today's graphic. Meanwhile on the other side of the state, a cold front progressing east through the Alaska Peninsula is forecast to bring rain to the region, with the heaviest rainfall likely occurring in the northern portion. While most of the rain is anticipated to be moderate in nature, some isolated areas could experience heavy rain with totals between 1.5 and 2 inches. As the cold front makes its way through the western Mainland on Thursday and Friday, heavy rain will also be possible over the Southwest and Southcentral regions. However, a high degree of uncertainty exists regarding where the heaviest rain will fall and how much due to discrepancies among the models, precluding the inclusion of a hazard area at this time. Temperature-wise, for the first half of the period daily highs are forecast to sit 10 to 15 degrees above normal before leveling off by the end of the week. In spite of the anomalous heat, temperatures are not expected to exceed 85 degrees and will thus remain non-hazardous. Zavadoff