Valid Thursday, February 28, 2019 to Monday, March 11, 2019

Summary of Forecasts and Hazards

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT September 06 2024

Synopsis: Persistent, broad mid-level high pressure is predicted to extend from eastern Canada across the northeast quadrant of the contiguous U.S. (CONUS), contributing to increased chances for excessive heat over portions of this region in week-2. There is much uncertainty in the hazardous precipitation outlook across the Gulf Coast and Florida. This precipitation outlook remains unchanged from yesterday, as does the possible flood risk area over this region. Much of the uncertainty stems from the fact that the predicted tropical cyclone pattern over the Atlantic basin is far from clear. As this is also the climatological peak of the Atlantic hurricane season, it would be prudent for interests along the Gulf Coast to keep updated with the latest tropical weather conditions.

Hazards

• Slight risk of excessive heat for middle and lower portions of the Missouri River Valley, the Middle Mississippi Valley and Ohio Valley, and southern portions of Lower Michigan, Sat-Sun, Sep 14-15.
• Slight risk of heavy precipitation for much of the Gulf Coast and Florida, Sat-Sun, Sep 14-15.
• Slight risk of high winds over the Northern and Central High Plains, Sat-Sun, Sep 14-15.
• Flooding possible along much of the Gulf Coast and northern and central Florida.
• Risk for rapid onset drought for portions of the Ohio, Tennessee, and Middle Mississippi Valleys.

Detailed Summary

For Monday September 09 - Friday September 13: WPC Days 3-7 U.S. Hazards

For Saturday September 14 - Friday September 20: An anomalous mid-level ridge is predicted to extend from eastern Canada across the northeast quadrant of the Lower 48 states. Multiple models indicate maximum 500-hPa heights across this part of the CONUS range from about 30-60 meters above normal. Another anomalous ridge is forecast south of the Aleutians, with maximum heights greater than 120 meters above normal. Weak mid-level troughs are predicted for far western Alaska, near or just inland of the West coast of the CONUS, and the Southern Atlantic coast.

A slight risk (20-40% chance) of excessive heat is depicted for middle and lower portions of the Missouri River Valley, the Middle Mississippi Valley and Ohio Valley, and southern portions of Lower Michigan, Sep 14-15. This is associated with the proximity of a moderately strong anomalous ridge and positive height departures in that region. Within this slight risk area, the 0z ECENS and 12z GEFS models predict 2-meter temperatures will range from about 6-15 degrees F above normal (GEFS being the slightly warmer solution), with daytime high temperatures peaking near 90 degrees F. Given the likelihood of low dew point temperatures during this same period, and therefore cooler overnight temperatures, the highlighted excessive heat risk is considered marginal.

Across the West, a significant mid-level trough is predicted to move into the Intermountain region, with enhanced winds and possible related increase in wildfire risk. As this trough advances eastward, there is the increased potential for thunderstorm activity across the Great Plains, as this time of year features a secondary maximum in severe weather climatology.

A slight risk of heavy precipitation remains posted along most of the Gulf Coast and Florida, Sep 14-15, associated with a decaying mean frontal zone forecasted to be draped across this region. Precipitation guidance from the Probabilistic Extremes Tools (PETs) and from the uncalibrated ECENS predict three-day precipitation amounts within this valid period to reach 1 inch, though the ECENS predicts the best chance for reaching and/or exceeding this 1-inch threshold to be over the Florida Peninsula, with a drier pattern depicted for the western Gulf region. A possible flood risk area is highlighted based on the National Water Center’s (NWC) experimental Flood Hazard Outlook for days 1-7 (week-1), which depicts possible flooding along/near most of the Gulf coastal area, and northern Florida. This flood risk is expected to extend into the early portion of the week-2 time frame. There is major uncertainty with regard to potential tropical cyclone activity during week-2. This situation is compounded by the fact that the climatological peak of the Atlantic hurricane season is rapidly approaching. In addition, sea surface temperatures across the Gulf of Mexico are more than adequate in intensifying any system that may form during this period.

Deterministic model runs have indicated the possibility of a tropical cyclone over the eastern Pacific moving relatively close to the mouth of the Gulf of California during week-2. These events are sometimes accompanied by gulf surges of moisture into the American Southwest, and the likelihood of this occurring will be monitored with future model runs.

A slight risk for high winds has been extended into the first two days of the forecast period. Surface low pressure development over the Northern and Central High Plains may produce wind speeds in excess of 20 mph.

The potential for Rapid Onset Drought (ROD) continues over parts of the Ohio and Middle Mississippi Valleys, and was expanded yesterday to include more of Kentucky and parts of the Tennessee Valley. Soil moisture values in this region are within the lowest quartile (and in some cases, decile) of the historical distribution. Precipitation deficits within the last 90 days have mounted from one to as much as six inches.

In Alaska, the southern coast is favored to get above normal precipitation during the week-2 period, with up to 2 inches predicted by the ensemble means. However, this falls somewhat short of the hazardous precipitation criterion for this area (near 3 inches), and therefore no hazard is posted.

Forecaster: Anthony Artusa

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