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Categorical Outlooks Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards

Valid Saturday July 27, 2019 to Friday August 02, 2019

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT July 19 2019

Synopsis: Mid-level high pressure is anticipated to dominate the western half of the Contiguous U.S. during Week-2, supporting above-normal temperatures across the western third of the country. Early in Week-2, a stalled front across the Southeast and Texas may bring above normal precipitation to the western Gulf Coast. Models indicate the potential for a series of surface low pressure systems across the Bering Sea during Week-2, supporting anomalously high wind speeds across parts of western and southern Alaska during the first couple of days of Week-2. Additionally, mid-level high pressure is anticipated across much of mainland Alaska, favoring anomalously warm temperatures across the state. These warm temperatures and windy conditions may prolong wildfire risk across parts of Alaska during Week-2.

Hazards

• Moderate risk of excessive heat for portions of California, Sat-Wed, Jul 27-Jul 31.
• Slight risk of excessive heat for portions of the western third of the CONUS, Sat-Thu, Jul 27-Aug 1.
• Flash flooding possible across portions of the Four Corners region.
• Slight risk of much above normal temperatures for portions of the Alaska Panhandle, mainland Alaska, and the Aleutians, Sat-Thu, Jul 27-Aug 1.
• Slight risk of high winds for portions of mainland Alaska, Sat-Sun, Jul 27-Jul 28.

Detailed Summary

For Monday July 22 - Friday July 26: WPC Days 3-7 U.S. Hazards

For Saturday July 27 - Friday August 02: Amplified mid-level high pressure is forecast to dominate the western half of the CONUS throughout Week-2. A slight risk of excessive heat across the western third of the CONUS is highlighted, July 26 - August 1, and a moderate risk of excessive heat is embedded within over central California for the same time period. The GEFS reforecast tool forecasts a broader region of maximum temperatures exceeding the 85th climatological percentile than the ECMWF tool, but the ECMWF tool has higher probabilities (40-60%) of excessive heat over central interior California. A large spatial area was chosen due to the potential of this being a multi-day heat event.

The positioning of the mid-level ridge across the western CONUS may continue the increased likelihood of locally heavy rain across the Four Corners region during Week-2. There is good agreement between the GEFS and ECMWF reforecast tools indicating a >20% chance of some areas receiving up to half an inch of rainfall in a 3-day period. A possible flash flooding hazard is highlighted across the Four Corners where localized convection and flash flooding are possible.

Amplified mid-level troughing is predicted across the eastern half of the CONUS throughout Week-2. This trough may sink as far south as the Southeast and Lower Mississippi Valley. A stalled front ahead of this trough in conjunction with ample onshore moisture associated with a subtropical ridge over the western Atlantic Ocean increases the likelihood for rainfall across the Gulf Coast states, but our calibrated model guidance does not currently suggest that enough rain will fall to warrant a posted hazard.

There are indications that high pressure over the northeastern part of the country could lead to anomalously warm temperatures over northeastern New England during the first few days of August. However, we haven't posted a related hazard since dynamical guidance keeps maximum temperatures in the low to mid 80s.

A series of surface lows is anticipated over the Bering Sea during Week-2. This pattern favors an enhanced likelihood of high winds across parts of Alaska. A slight risk of high winds is highlighted across parts of western Alaska, coastal northern Alaska, and the Alaska peninsula, July 27-28. There is a potential for amplified ridging across parts of mainland Alaska during Week-2. Both the GEFS and ECMWF reforecast tools are in good agreement regarding widespread >20% chances of maximum temperatures reaching or exceeding the 85th to 90th percentile. A slight risk of much above normal temperatures is posted across parts of mainland Alaska, July 27 to August 1. Increased risk of high winds and much above normal temperatures may continue the risk of wildfires across parts of Alaska. According to the Alaska Interagency Coordination Center, over 1.66 million acres have burned statewide (as of July 18th, 2019) since the beginning of the year.

Forecaster: Kyle MacRitchie

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts