Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
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763 FXUS21 KWNC 241757 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT May 24 2024 SYNOPSIS: Early in week-2, a weak low pressure system and trailing cold front are forecast to progress eastward across the Great Plains and Mississippi Valley. A broad area of mid-level high pressure is forecast to strengthen over the south-central contiguous U.S. (CONUS) at the beginning of June and then expand northward. This would favor above-normal temperatures for much of the lower 48 states with a chance of excessive heat for the Rio Grande Valley during week-2. A deep mid-level low and enhanced onshore flow favors above-normal precipitation across Alaska. HAZARDS Slight risk for excessive heat across portions of the Rio Grande Valley and the Southern Plains, Sat-Fri, Jun 1-7. Slight risk for excessive heat across portions of the Florida Peninsula, Sat-Mon, Jun 1-3. Slight risk for heavy precipitation across portions of the Central and Southern Plains, and Middle and Lower Mississippi Valley, Sat-Mon, Jun 1-3. Slight risk for high winds for areas downslope of the Northern and Central Rocky Mountains, Sat-Sun, Jun 1-2. Rapid onset drought risk across parts of southern Texas. DETAILED SUMMARY FOR MONDAY MAY 27 - FRIDAY MAY 31: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SATURDAY JUNE 01 - FRIDAY JUNE 07: The GEFS and ECMWF ensemble means depict a shortwave 500-hPa trough progressing east from the western to the north-central CONUS by the beginning of week-2. Their daily forecasts also feature a low pressure system tracking east from the Canadian Prairies to Manitoba with a trailing cold front. This predicted 500-hpa/surface pattern is expected to result in thunderstorms with locally heavy rainfall across parts of the Great Plains and Mississippi Valley. The highest risk for heavy precipitation has shifted south relative to yesterday and is in northeastern Texas, eastern Oklahoma and Kansas, and western Missouri and Arkansas. The slight risk of heavy precipitation (Jun 1-3) is consistent with the uncalibrated ECMWF ensemble mean probabilities for more than 1 inch and the Probabilistic Extremes Tools (PET). Since parts of this region have saturated soils from recent heavy rainfall, locally heavy rainfall may trigger flash flooding. The shortwave trough and surface low pressure along the Canadian border at the onset of week-2 may increase chances for high winds along the downslope of the Northern and Central Rockies. There are some signals among some of the ensemble members of the GEFS and ECENS for strong winds downslope of the Rocky Mountains consistent with a chinook wind event. Therefore, a slight risk of high winds is posted for downslope regions of the Northern and Central Rockies. In South Florida, there is generally continued uncertainty in the strength of the above-normal temperatures in the area. The anomalous ridge that has been focused over the region in recent days leading to heat advisory conditions doesnt appear to be as robust. However, the GEFS and ECENS PETs continue to indicate chances for temperatures to exceed the 85th percentile. And a skill-weighted GEFS/ECENS tool indicates a 20 to 40% chance of apparent temperatures exceeding the 105 deg F. Therefore, a slight risk of excessive heat remains forecast for Jun 1-3 across southern Florida. Following predicted heat relief for Texas during the early to middle part of next week, the ECMWF ensemble mean is bullish on a strengthening subtropical ridge over northern Mexico and the south-central CONUS during the first week of June. A slight risk of excessive heat is designated to areas closer to the Rio Grande Valley. Supported by the GEFS and ECENS PETs forecast at least a 20% chance of actual temperatures to exceed the 85th climatological percentile and 100 deg F through much of week-2. A skill weighted bias-corrected apparent temperature tool indicates at least 20% chances for apparent temperatures to exceed 110 deg F. Therefore, a slight risk of excessive heat is posted for all of week-2, Jun 1-7, for parts of the Rio Grande Valley. Further north, chances for excessive heat have diminished significantly relative to yesterday and the slight risk across central Texas has been discontinued. The greatest risk for rapid onset drought (ROD) during the remainder of May into early June exists for southern Texas. The ROD hazard is based on 30 to 60-day precipitation deficits, low soil moisture, and likelihood of above-normal temperatures along with the lack of a strong wet signal during the next two weeks. Multi-model ensemble means are in excellent agreement that a deep 500-hPa closed low develops over the Aleutians and southwestern Alaska by the beginning of June. This anomalous mid-level trough is likely to enhance onshore flow to southern Alaska where above-normal precipitation is favored. Since the GEFS and ECMWF PETs depict probabilities of less than 20 percent for 3-day precipitation amounts exceeding 2 inches, a heavy precipitation hazard is not posted. FORECASTER: Ryan Bolt $$