Extended Forecast Discussion NWS Weather Prediction Center College Park MD 232 PM EDT Mon May 27 2024 Valid 12Z Thu May 30 2024 - 12Z Mon Jun 03 2024 ...General Overview... The upper level pattern across the continental U.S. will be featured with a trough over the Northern Rockies, a ridge over the Upper Midwest, and a trough over the Northeast U.S. for the beginning of the forecast period Thursday. Both of these troughs move rather slowly eastward through Saturday, while the southern tier states have more zonal flow aloft. The trough crossing the Rockies will be accompanied with a surge of moisture from the Gulf of Mexico ahead of an approaching frontal boundary, and this will fuel multiple rounds of heavy rain and thunderstorms from northern Texas to the central Plains for the second half of the work week. The trough then reaches the Upper Midwest by next weekend and then lifts northward into Canada, while the upper ridge rebuilds across Texas late in the forecast period. ...Guidance/Predictability Assessment... Latest model guidance remains in good overall synoptic agreement for much of the period, but with some lingering uncertainties in timing of individual systems. There was good enough agreement the first half of the period for an equal blend of the latest deterministic solutions. After this, models agree an upper low south of the Gulf of Alaska will send a shortwave or two into the Pacific Northwest this weekend/early next week but disagree on the timing and amplitude of this evolution, leading to models becoming out of phase with each other. Transitioned towards more of the ensemble means the second half of the period given the uncertainties. Overall though, this maintained good agreement with the previous WPC forecast. ...Weather/Hazards Highlights... Numerous showers and thunderstorms are likely across much of the central and southern Plains going into the second half of the work week as a warm front lifts up from the western Gulf and advects copious moisture northward. This will also be in tandem with increasing lift afforded by an incoming upper trough from the Rockies. A broad Marginal Risk area continues for the Day 4 Excessive Rainfall Outlook period Thursday from central Texas to the eastern Dakotas. There is an embedded Slight Risk, which was expanded northward from the initial overnight issuance, from north- central Texas into southeast Nebraska, where MCS activity is most likely to develop. Additional heavy rain is expected on Friday across many of these same areas and eastward, and so maintained a broad Day 5 Marginal Risk area from northern/eastern Texas and the lower Mississippi Valley to the Upper Midwest. There will likely be the need for a Slight Risk area during this time in future updates, but the differences in QPF maxima among the guidance preclude having any Slights at this time. Some strong to severe thunderstorms are also likely. The potential exists for 3-5 inches of rainfall through late Friday for some of these areas that get repeated rounds of convection. General troughiness across the northern states should continue to allow scattered summertime convection across the central Plains- Mississippi Valley region through the weekend and into early next week as well. Another trough just off the West Coast should also bring in a round of rainfall to parts of the Pacific Northwest late weekend. Hazardous heat is expected to continue across South Texas through much of the period with daytime highs in the low-mid 100s (and even higher heat indices) indicating a major to localized extreme heat risk. Hot and humid conditions are also expected to continue across much of the Gulf Coast region, including the Florida Peninsula, going into the end of the week, but a few degrees cooler compared to what is happening now. The opposite will hold true from the Great Lakes to the Mid-Atlantic and Northeast as a relatively strong cold front heralds the arrival of a high quality airmass with pleasantly cool conditions and lower humidity to close out the week. There will likely be some showers across the northeastern quadrant of the nation in conjunction with the trough/upper low that passes through the region. Cooler weather is also expected from the Pacific Northwest to the Northern Rockies courtesy of the upper trough moving overhead, and then a return to warmer conditions for much of the Western U.S. by next Sunday. Santorelli/Hamrick Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw