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Categorical Outlooks Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards

Valid Saturday June 01, 2019 to Friday June 07, 2019

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 24 2019

Synopsis: After an amplified pattern over most of the contiguous U.S. during week-1, zonal flow is forecast for much of the lower 48 through week-1. Mid-level low pressure is likely to develop over the Great Lakes, suppressing the mid-level high pressure over the eastern U.S. from the prior period. The heat wave expected to start over Memorial Day Weekend is likely to linger into early June. Over the central U.S., the perpetually wet pattern over the Central Plains looks like it will start to wane mid-period.

Hazards

• Moderate risk of heavy precipitation for portions of the Central Plains and Middle Mississippi Valley, Sat-Sun, Jun 1-Jun 2.
• Slight risk of heavy precipitation for portions of the Central Plains and Mississippi Valley, Sat-Mon, Jun 1-Jun 3.
• High risk of excessive heat for portions of Alabama, Georgia and South Carolina, Sat-Mon, Jun 1-Jun 3.
• Moderate risk of excessive heat for portions of the Southeast, Sat-Tue, Jun 1-Jun 4.
• Slight risk of excessive heat for portions of the Lower Mississippi Valley, the Tennessee Valley, and the Southeast, Sat-Tue, Jun 1-Jun 4.

Detailed Summary

For Monday May 27 - Friday May 31: WPC Days 3-7 U.S. Hazards

For Saturday June 01 - Friday June 07: As we round out the week for our hazards forecast, the 06z GEFS upper-level pattern finally has fallen in line with what the ECMWF has been forecasting all week. Due to this evolution, there is more confidence in today's forecast on the 500hPa height pattern and its likely impacts. Both models now indicate that negative height anomalies will likely be over the Great Lakes with the bulk of the trough northward into Canada. The ridge over the eastern US during the prior period is forecast to be suppressed southward due to this troughing, weakening the positive height anomalies and keeping them confined mostly to the Southeast. Zonal flow is predicted to dominate for most of the period over the CONUS.

With the weak ridging over the Southeast through the early half of the period, the models show good agreement of this heat wave for the region lasting through the first few days of June. As has been messaged for the past few days, we expect a dry heat prior to the period and early on, mainly through day 8. Apparent temperatures should be close to dry bulb temperatures, and could be near 100F. As we continue further into week-2, dew points are forecast to begin to rise and humidity is likely to take a role in escalating the apparent temperature or heat index. With the now closer ridge placement over the central Gulf Coast, both the ECMWF and GEFS show good agreement on the duration and placement of the warmest temperatures; however, the GEFS does not forecast heat quite as extreme as the ECMWF. Again, we are favoring the ECMWF solution for this forecast due to the run-to-run consistency throughout this week. The high risk for excessive heat over southern Alabama, Georgia and South Carolina is valid from June 1-June 3, where the greatest chance for around 100F is focused. A broader moderate risk is forecast until June 4th for the Deep South, while a slight risk for the same time period is extended north through Southern Virginia and the central Gulf Coast. With the lack of precipitation over the next two weeks and the duration of this heat event, there is a possibility of flash drought development in parts of the region, especially in the high and moderate risk regions.

Prior to this period, a ridge-trough upper-level pattern is forecast over the CONUS, leading to a mean baroclinic zone aligning from the Central and Southern Plains. The upper-level pattern is expected to become zonal over the Central U.S. early in week-2, but surface lows are forecast over the High Plains and drop over the Central and Southern Plains into the middle Mississippi Valley for the first half of the period. A moderate risk of heavy precipitation is forecast the central Plains, from northeast Texas toward eastern Missouri for June 1- June 2, where the probabilistic tools are indicating a 40% chance for rainfall totals over 1 inch. A wider slight risk is forecast further north through portions of the Midwest, June 1-June 3. Much of the region highlighted for both the slight and moderate precipitation risks is currently at 95-99 percentile for soil moisture with the anomalously high amount of rainfall it has received this spring. The deluge of precipitation that has plagued the Central Plains for the past few months makes the region extremely vulnerable to flooding, so these additional rains are likely to trigger river and flash flooding. There should be at least a break to this persistent wet pattern for the Central Plains for that latter half of week-2.

The upper-level trough forecast over the Aleutians at the beginning of week-2 is projected to propagate along the southern coast, weakening the widespread upper-level ridging over mainland Alaska. The South Coast and Aleutians are likely to have an active storm track through week-2, with the strongest system currently forecast for the beginning of June. However, rainfall amounts and winds from this system are still expected to remain below our hazardous criteria. The influence of this trough will likely wane toward the end of the period and weak upper-level ridging is forecast to build again.

Forecaster: Christina Maurin

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts