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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made July 13, 2018

 Days 3-7Days 8-14Probabilistic Days 8-14
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Categorical Outlooks
Experimental Probabilistic Outlooks (Information)

Valid Monday July 16, 2018 to Friday July 27, 2018

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT July 13 2018

Synopsis: Broad mid-level high pressure is initially forecast across the lower-48 states during the outlook period, that is anticipated to transition towards high pressure over the West and low pressure over the Great Lakes which is maintained through Week-2. At the surface, a cold front is forecast to stretch from the Great Lakes to the Central Plains at the beginning of the period and move southeastward throughout the 3 to 7 day period. Another cold front is predicted to enter the Pacific Northwest and Northern Plains by the middle of the 3 to 7 day period. Surface high pressure is forecast across the Western Slope of Colorado throughout the period, which may help pump heat and moisture into the West. Elsewhere, a surface low is forecast to shift from the Bering Sea into the Gulf of Alaska and linger throughout Week-1.

Hazards Detailed Summary

For Monday July 16 - Friday July 20: A cold front is forecast to stretch from the Great Lakes to the Central Plains at the beginning of the period and move southeastward throughout the 3 to 7 day period. This cold front is likely to bring wet weather to parts of the eastern half of the CONUS, with the best chances of heavy rain (exceeding 1 inch in 24 hours) across portions of portions of the Southern Appalachians, the Central Appalachians, the Ohio Valley, the Mid-Atlantic, the Northeast, and the Tennessee Valley, July 16 to 17, as well as coastal parts of the Carolinas Jul 18 to 19.

A small region of excessive heat is possible across interior portions of the Northeast on the 16th, aided by enhanced southerly flow in advance of the passing cold front. Daily high temperatures in the low 90s are forecast across upstate New York, Vermont, and New Hampshire with this event, with these values having been previously shown to drive an increase in heat-health issues and hospital admissions for the region.

As the cold front boundary moves to the Ohio River, warm and moist conditions are forecast to its South, along and to the West of the 500-hPa high. Excessive heat is forecast for portions of the Central Plains, the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley, on the 16th through 18th due to the Gulf moisture overspreading the already warm conditions. Widespread heat index values of 105 degrees F (heat advisory criteria for much of the region) or more are anticipated, with values above 115 degrees F possible in some places in the Lower Mississippi Valley and Southern Plains. The northern periphery of heat across the Middle Mississippi and Ohio Valleys is expected mainly for July 16, with overnight lows likely to only drop into the upper 70s. The cold front is forecast to approach this region on the 17th, helping to limit the duration of the heat event. Parts of Virginia, the Carolinas, and Georgia may experience heat index values of 105 Deg F and greater Jul 16 to 17. However, an excessive heat area is not specified over this region since these heat index values are not as uncommon and are expected to be relatively brief. Given the oppressive heat in the forecast for these regions, outdoor activities are advised to be avoided if possible during peak daytime heating. It is in the best interest of those needing to be outside in the heat to take frequent breaks, seek shady areas, and pay close attention to their hydration levels.

Persistent 500-hPa ridging with above-normal heights over the Western U.S. is forecast throughout the outlook period. This scenario is supportive of continued excessive heat for much of California, the Central Great Basin, the Pacific Northwest, the Northern Rockies, and the Northern Great Basin July 16 to 19, as the cold front dropping through the Plains is forecast to be unable to make it west of the Rockies. Here, daily high temperature anomalies of +12 to +16 Deg F are forecast, helping to drive many lower elevation areas to the upper-90s or potentially triple digits. No record temperatures currently appear likely to fall with this event for the region, despite the anomalous warmth.

Amplified mid-level ridging may support excessive heat across parts of the Desert Southwest, July 20. Maximum heat values in this area may reach 110 Deg F or greater.

The North American Monsoon appears likely to remain active during Week-1. Heavy rain (exceeding 1 inch in 24 hours) is forecast across the Four Corners Region and Central Plains July 16th through 17th as a surge of moisture from the Gulf of California lifts northward into the region. Flash flooding is also possible with these monsoonal rains for much of the Four Corners region in areas that see persistent rainfall or lie downstream of complex terrain receiving such rainfall. The flooding risk is also extended into the Front Range of Colorado where low-level easterly, upslope flow could yield flooding concerns behind the cold front. Those planning outdoor activities where flash flooding is possible are advised to consider their routes given the elevated flooding risks. Those encountering flood waters on foot or in vehicles are advised to avoid entering them, given six inches of water can carry away an adult while 1-2 feet of water is typically sufficient to sweep away vehicles.

An active pattern is expected for nothern Alaska. Elswhere, a relatively cool, quiet period appears to be in store across Alaska during much of Week-1. Surface low pressure is forecast to develop along a stationary front across northern Alaska toward the end of the 3 to 7 day period. This disturbance may bring heavy rainfall (1 inch or greater of rainfall in a 24-hour period) on July 19.

The remnants of Hurricane Beryl continue to linger in the Atlantic, but it is not a threat to the lower-48 states. There is a disturbance currently over the Eastern North Pacific Ocean. The National Hurricane Center is indicating a 10 percent chance of cyclone formation in 48 hours, as of 11am PDT. No related hazards are anticipated for the U.S. at this time.

For Saturday July 21 - Friday July 27: The Week-2 period is forecast to be dominated by amplified mid-level ridging across the western two-thirds of the CONUS and troughing across the eastern third. This pattern favors heat across many parts of the western two-thirds of the lower 48 states. A slight risk of excessive heat is forecast to continue for western areas throughout the majority of Week-2, with some extension further southward possible into the Central Valley of California. Daily high temperature anomalies of +8 degrees F or more continue to be indicated by the GEFS ensemble mean, while GEFS reforecast support a better than 20% chance of highs above the 85th climatological percentile. Troughing across the eastern third of the CONUS favors enhanced chances for above-normal precipitation during Week-2 across this region. The greatest likelihood for above-normal precipitation is over the coastal part of the Mid-Atlantic. Mid-level ridging is anticipated to build across Alaska, favoring a shift to above-normal temperatures, compared to the cooler temperatures expected for Week-1.

This mid-level ridge may also support excessive heat across parts of the Desert Southwest. A slight chance is highlighted across the region for Jul 21 to 24, with a moderate chance identified for a smaller embedded region across the southern parts of the Desert Southwest. Parts of this area has a 20 percent chance or greater of heat values exceeding 110 Deg F and reaching the 95th percentile or greater. Maximum temperature anomalies may be 8 Deg F or greater compared to normal.

A slight risk of excessive heat is highlighted over the Southern Plains throughout Week-2, with a moderate risk across interior Texas, July 21 to 23. The cold front in the Great Plains during Week-1 is not forecast to make it this far south, resulting in lingering heat and moisture across the region. Heat risk guidance from the GEFS and ECMWF highlights parts of the identified area reaching the 95th percentile, with heat index values reaching 110 Deg F or greater. Both the GEFS and ECMWF heat tool is showing a stronger signal with greater spatial area for excessive heat across this area, compared to yesterday.

Model uncertainty continues from yesterday regarding the potential of heavy rain associated with the North American Monsoon across the Four Corners region in Week-2. Daily ensemble mean precipitation totals are generally on the order of a quarter inch or less, suggesting a more widespread, showery precipitation for the region. The Week-2 precipitation forecast indicates the most favored area for above-normal precipitation over Colorado and western parts of the Central Plains. While not highlighted on the forecast map, the flash flooding risk should continue in the first half of Week-2 across this region before things potentially quiet down.

The U.S. Drought Monitor, valid on July 10, shows a minor decrease in severe drought coverage to 16.46 percent (from 16.64 percent). Conditions over northern Missouri have deteriorated, although there is some improvement in south-central Texas along the Rio Grande.

Forecaster: Melissa Ou

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Click here to see a display of the GFS Ensemble Forecasts

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