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Categorical Outlooks Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Saturday July 06, 2024 to Friday July 12, 2024

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT June 28 2024

Synopsis: Mid-level high pressure favored over southeastern and western CONUS is expected to increase chances for excessive heat conditions during week-2. Much of the anomalous warm summertime temperatures and drier than normal conditions are anticipated to sustain the risk for Rapid Onset Drought (ROD) over parts of the Plains, Corn Belt and lower half of the Eastern Seaboard during week-2. Possible mid-level low pressure and continued rainfall over the north-central CONUS early in week-2 supports possible flooding across many parts of the Midwest. An active North American monsoon circulation and possible moisture surges into the Desert Southwest favor an increased risk of locally heavy precipitation and possible flooding over the lower Four Corners.

Hazards

• Moderate risk for excessive heat for portions of the Southeast, Tennessee Valley, and the Mid-Atlantic, Sat-Sun, Jul 6-7.
• Slight risk of excessive heat from the southern Plains eastward to the lower Eastern Seaboard, Sat-Fri, Jul 6-12.
• Moderate risk of excessive heat for the Central California Valley and into the Desert Southwest, Sat-Sun, Jul 6-7.
• Slight risk of excessive heat for portions of California, Pacific Northwest, and the Interior West, Sat-Wed, Jul 6-10.
• Slight risk of periods of heavy precipitation for parts of the Desert Southwest and Southern Rockies, Sat-Fri, Jul 6-12.
• Possible flooding for portions of southern Arizona and New Mexico.
• Possible flooding for portions of the Northern and Central Plains and Upper and Middle Mississippi Valley.
• Rapid Onset Drought risk for parts of Great Plains, Mississippi Valley, Tennessee and Ohio Valleys, Appalachians, Southeast and Mid-Atlantic.

Detailed Summary

For Monday July 01 - Friday July 05: WPC Days 3-7 U.S. Hazards

For Saturday July 06 - Friday July 12: The hazards perspective remains mostly on track since yesterday. The GEFS and ECMWF ensembles predominantly feature above-normal 500-hPa heights in the mean week-2 fields, but continue to favor near to below normal heights early in the period, likely tied to shortwave energy propagating along the longwave trough axis situated over central Canada. The ECMWF continues to be more pronounced with this development than the GEFS, favoring more northwesterly flow over north-central CONUS with a clear break in the subtropical ridge pattern extending into northern Mexico. The resultant cooler air heading into next weekend looks to quell any anomalously warm daytime temperatures throughout much of the Plains and Mississippi Valley, however the mid-level troughing predicted looks to be flanked by a pair of strong ridges centered over the eastern and western CONUS where the excessive heat risk is most likely to be prevail during the period.

Based on the latest raw and calibrated temperature tools over the eastern CONUS, a moderate risk of excessive heat remains issued across parts of the Southeast, Tennessee Valley and the lower eastern Seaboard for Jul 6-7. Probabilistic Extremes Tools (PETs) depict 30-40% chances of maximum daytime temperatures exceeding the 85th percentile and 95 degrees F, where elevated dewpoint temperatures forecast (> 70 deg F) are likely to drive high Heat Index values within the highlighted region. Given the persistence of mid-level ridging favored throughout the period, a broader slight risk area of excessive heat is issued from the Southern Plains to the Eastern Seaboard for the entirety of week-2. While the GEFS PET favors a warmer solution over the central CONUS (likely due to weaker troughing favored), the slight risk coverage is limited to the southern tier of the U.S. given the potential for cold air advection over the Midwest early in week-2.

The persistent warmer and drier than normal conditions over at least the past month have led to a risk for Rapid Onset Drought for parts of the Ohio Valley (eastern Corn Belt), Mid-Atlantic, Southeast, Southern Plains, and southern Central Plains. The recent heat waves across the eastern U.S. have exacerbated the ongoing dryness across these areas, and have led to Moderate Drought (D1) for many areas in the east. Much of the areas highlighted for risk of Rapid Onset Drought have seen large precipitation deficits over the past two weeks to a month and have seen large reductions in available soil moisture. There is additional risk for high evapotranspiration rates with above-normal temperatures forecast across much of the eastern CONUS. Although periodic, localized heavy precipitation cannot be ruled out due to frontal and/or daytime thunderstorm activity. Dry soils, stressed vegetation, and reduced water availability due to low ponds and streams may lead to increased impacts to agriculture and livestock, with several locations already experiencing impacts.

Upstream, there is better model agreement in regards to more amplified ridging extending from the eastern Pacific into the Interior West. Much of the accompanying excessive heat potential looks to already be established late in week-1, with double digit temperatures departures forecast throughout the Central California Valley (based on WPC days 6 and 7 temperature anomalies), and the NWS Heatrisk tool indicating red and magenta levels in the region. Leading into week-2, both the GEFS and ECWMF PETs show elevated chances (30-50%) for maximum temperatures exceeding the 85th percentile and 100 deg F during the first few days of the period. Given the growing support for excessive heat conditions in these tools, a corresponding moderate risk is introduced for the Central California Valley and the Desert Southwest for Jul 6-7. From day 10 and beyond, the strongest signals for heat weaken in the PETs over the southwestern CONUS, but point to a northward and eastward expansion of heat potential. As a result, the slight risk of excessive heat is expanded to include more of the Pacific Northwest, Great Basin, and Northern Intermountain in the updated outlook for Jul 6-10. The PETs also show heat possibly returning the Central and Northern High Plains tied to rebuilding mid-level heights late in week-2, though no hazards are posted due to uncertainty at this lead.

The shortwave energy favored over the north-central CONUS is expected to promote above-normal precipitation over many parts of the Midwest late next week and into next weekend. Although the raw and calibrated precipitation tools show the heaviest precipitation amounts timing off, a flooding possible hazard remains posted for many parts of the Midwest. Any continued rainfall heading into week-2 may worsen ongoing flooding along the Missouri and Mississippi Rivers.

Underneath the anomalous mid-level ridging favored over the southern tier of the CONUS, easterly flow from the Gulf of Mexico consistent with the North American monsoon circulation is expected to promote increased precipitation amounts over northern Mexico and the southwestern U.S. With intense daytime heating to deepen the thermal low over the Sonoran Desert, and some model solutions continuing to depict periods of dewpoint temperatures increases, there remains the potential for Gulf of California moisture surges, and a slight risk of heavy precipitation remains posted over the lower Four Corners region. This slight risk is extended to include all of week-2 based on support from the GEFS and ECMWF PETs, which indicate at least a 20% chance for 3-day amounts exceeding the 85th percentile. A flooding possible risk is also designated for southern parts of Arizona and New Mexico where stronger precipitation signals are depicted in multiple models. Precipitation is expected to be isolated and not all locations will experience heavy rainfall. However, flash flooding is possible both where precipitation occurs and in downstream valleys, particularly in and around burn scars where debris flows can be triggered by heavy rainfall.

Across the tropics, the Madden-Julian Oscillation (MJO) has been largely disorganized for much of June. However, there is good continuity in the model guidance favoring a more coherent MJO signal emerging over the Indian Ocean and propagating eastward into the Maritime Continent during the next two weeks. Historically, this evolving signal is supportive for tropical cyclogenesis in the western Hemisphere based on MJO composites during Jun-Aug, and the National Hurricane Center (NHC) is monitoring the potential for Tropical Cyclone (TC) development associated with three tropical waves in the Atlantic. Of the three, Invest 95L has the highest odds for development (currently 90% during the next 7 days). No corresponding hazards are posted given large uncertainty with eventual strength and track of the disturbance, but the tropics bear monitoring during the next several days, as the shearing environment looks favorable for further development as it approaches the Caribbean.

Forecaster: Nick Novella

$$ Please consult local NWS Forecast Offices for short range forecasts and region-specific information.

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts