Extended Forecast Discussion NWS Weather Prediction Center College Park MD 312 AM EDT Tue May 31 2022 Valid 12Z Fri Jun 03 2022 - 12Z Tue Jun 07 2022 ...Heavy rain threat increasing over Florida due to tropical moisture inflow and a possibly forming tropical system... ...Overview... While the overall pattern across much of the lower 48 will remain fairly stagnant late week into early next week, with West Coast troughing and a south-central Canada upper low sending some low amplitude troughing across the central to eastern U.S. But the main notable feature to watch during the medium range period will be the possibility for a tropical cyclone to develop over the northwestern Caribbean Sea/southeastern Gulf of Mexico partially from energy from what is currently Tropical Storm Agatha over Mexico. At this time, a low track northeastward near or over the Florida Peninsula is possible, but with fairly low confidence in the track, timing, and strength of a tropical system. Regardless, heavy rain is possible late week into the weekend with moisture streaming ahead of this potential system and then near its possible eventual track. ...Model Guidance Evaluation/Preferences... Recent model guidance is in reasonably good agreement for the overall synoptic pattern late this week. An upper low spinning offshore of British Columbia shows good consensus with its position and a slow drift northward through the weekend, with general troughing for the U.S. West Coast shown by all the guidance. There are some differences arising by Monday of next week though--GFS runs have been persistent in indicating shortwave troughing tracking into the north-central U.S. whereas the ECMWF/CMC runs hold the energy back across the Northwest, yielding ridging in the Rockies to High Plains. Preferred the latter at this time given the GFS can have a bias for faster systems sometimes, but there is quite a bit of spread from the ensemble members, lowering confidence. Meanwhile the south-central Canada upper low is forecast to persist but be slowly weakening and possibly elongating at times. While on the large scale this seems in good agreement, shortwave troughing stemming from that feature could push a series of fronts across central and eastern parts of the U.S. and provide foci for rain/convection, and these details are more variable among guidance. But with the reasonable large scale agreement, the WPC forecast utilized a blend of the 18Z GFS and the 00Z ECMWF, UKMET, and CMC for the early part of the forecast period, incorporating some GEFS and EC ensemble means later in the period and reducing the deterministic GFS component. Notable model differences continue to be seen with the potential for a tropical system to develop in the southeastern Gulf/northwestern Caribbean. The general trend over the past day or so has been for a faster track of a tropical low ejecting northeastward out of the large, complex area of low pressure over the Bay of Campeche/Yucatan/northwestern Caribbean. The deterministic GFS and CMC runs have always been faster than the ECMWF runs, with considerable timing spread in ensemble members. But each ECMWF run through the most recent 00Z run has shown a faster trend, and model guidance indicates a system could reach Florida by Saturday if it develops, then track into the western Atlantic. Timing and track differences are also related to the strength of the possible system. The ECMWF shows a stronger low with more consolidated energy than the CMC and GFS, with a track farther north across central Florida rather than southern Florida or the Florida Straits like other guidance including the GFS/CMC and many GEFS ensemble members. Overall there is ample uncertainty with the possible development of a tropical cyclone and its strength, track, and timing. See NHC tropical weather outlooks for more on this system's potential for development and stay up to date with the latest forecasts. ...Sensible Weather/Threat Highlights... Tropical Storm Agatha has currently moved into Mexico and will weaken quickly over unfavorable terrain there. But its associated deep tropical moisture will stream into southern Florida Friday, increasing the likelihood of rain and thunderstorms becoming more frequent and widespread, first ahead of the remnant disturbance and then with the potential for a tropical low to develop (possibly partially from Agatha's remnants) and track over or near the state. Moisture aloft from the far eastern Pacific and lower level moisture from the Caribbean should lead to heavy rainfall, even if the system's timing is in question. Even in the cyclone's wake, its convergent tail appears to be stuck in the vicinity of South Florida and the Keys, keeping the threat of moderate to heavy rainfall in play into early next week. Slight Risks are in place in WPC's experimental Days 4 and 5 Excessive Rainfall Outlook. Elsewhere, rain chances are expected to increase in the Northwest late week into the weekend given the trough axis near the West Coast and onshore flow. However, the Southwest should remain dry and hot, with Death Valley expected to meet or exceed 110F high temperatures this weekend into early next week. Farther east, fronts are expected to spark rounds of showers and thunderstorms across the central and eastern U.S., with the Carolinas an area of focus on Friday and parts of the Plains and Mississippi Valley seeing convection Friday into the weekend and early next week as fronts meander there, with the usual uncertainties in placement. A relatively flat pattern aloft compared to the more amplified short range period should produce lesser temperature anomalies late this week into early next week. Cooler than average spots will be across the central/southern Plains Friday with rain cooled air, but should switch to above normal in Texas by 10-15F by early next week. Periodic troughing in the northern tier should lead to slightly below average temperatures by around 10F. The western U.S. could be warmer than normal by 5-10F late in the workweek but cooler temperatures are forecast by the weekend under the troughing influence and as a cold front moves through the area. Tate 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