Extended Forecast Discussion NWS Weather Prediction Center College Park MD 327 PM EDT Thu Jun 02 2022 Valid 12Z Sun Jun 05 2022 - 12Z Thu Jun 09 2022 ...Overview... As the medium range period begins Sunday, a tropical disturbance, for which the National Hurricane Center shows a high chance of development, should be east of the Florida Peninsula and pulling away from the U.S., but with some showers and storms possibly lingering over Florida and potentially up the Southeast coast depending on how close the low tracks to land. Meanwhile farther north, the lower 48 should see a fairly zonal pattern, but with shortwaves and surface frontal boundaries providing foci for thunderstorms and potential for heavy rainfall over much of the central U.S. and possibly into the East. ...Model Guidance Evaluation/Preferences... Deterministic model guidance is split on the location of the tropical system in the western Atlantic by Sunday morning with the 00z EC/CMC producing a low that is closer to the Florida coast than the 06z GFS and 00z UKMET which have a more progressive track. The EC suite has gradually weakened the attendant low over its past few runs while the GFS suite has remained fairly consistent. Besides small scale differences with respect to the evolution of a few shortwaves, the general trend over much of the lower 48 is for relatively zonal flow to dominate through much of the medium range period before a more amplified pattern develops late next week. The latest 12z EC/GFS have trended weaker with the bit of embedded shortwave energy forecast to propagate through the Middle Mississippi Valley on Sunday while the 12z UKMET is stronger with that piece of energy. The weaker trend continues with the shortwave as it moves into the Ohio Valley and Northeast on Monday, while the 12z GEFS actually trends deeper with the evolving shortwave. The 00z EC, 06z GFS and ensemble means tend to agree on the zonal pattern across much of the northern and central tier of the country on Tuesday. There are some timing and intensity differences with the arrival of a mean upper trough as it rotates through the Rockies and Plains next Wednesday, but the 00z EC and 06z GFS continue to agree on the timing of another shortwave over parts of the Mid-South. There's general model consensus on a ridge building over the West as a trough moves through the eastern half of the country next Thursday. A blend of the 00z EC/CMC and lesser amounts of the 00z UK and 06z GFS were favored for day 3. For day 4 the 00z EC, 06z GFS and some ensemble means were incorporated into a blend. 00z ECE/CMCE and 06z GEFS ensembles accounted for the majority of blender weighting through the rest of the period with some 06z GFS and 00z EC sprinkled in alternatingly throuh day 7. ...Sensible Weather/Threat Highlights... Though the bulk of the effects of the tropical disturbance will be in the short range period, some showers and storms could be present across Florida with lingering moisture and possibly reach the Southeast coast. Continued convergence across South Florida and the Keys could promote additional rain and thunderstorms there through at least the first half of next week, but scattered in nature. Meanwhile a weak to moderate atmospheric river this weekend aimed at the Northwest U.S. will increase precipitation chances there. This should be mainly rain as snow levels are forecast to be high, with chances for snow only in the highest peaks of the Cascades and northern Rockies. Parts of the central U.S. can likely expect the most impactful rain, however. Meandering frontal boundaries will provide areas of focus for enhanced rainfall with convection in a pattern with plenty of moisture. This looks to be most likely across northern/central parts of the Plains and into the Middle Mississippi Valley and possibly the Lower Ohio Valley. But unfortunately, models are quite variable with the placement of heavy rainfall beyond that, as the axes of enhanced rain will be highly dependent on where individual boundaries set up. The ingredients are certainly in place for heavy rainfall that could cause flash flooding, but the details of areas with the greatest threat could take into the short range to resolve, so held off on adding any Slight Risks to the experimental Day 4-5 Excessive Rainfall Outlook for now as they would almost certainly have to move around. Additionally, models have trended heavier with rainfall moving into the Northeast around Monday-Tuesday ahead of a cold front. Expect the general pattern for temperatures next week to be cooler than average in the northern tier and warmer than average in the southern tier. The northern Plains in particular could see highs 10-20F and lows around 10F below average with periods of troughing aloft. Meanwhile, much of the southern tier is forecast to see above normal temperatures by around 5-10F but reaching +15F anomalies in Texas for the first half of next week given an upper high aloft. The West Coast should be a bit cooler than normal over the weekend under the troughing influence, but moderating and warming to above normal in California and into the Great Basin and Southwest by around midweek. Tate/Kebede 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, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices are at: 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