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U.S. Hazards Outlook - Made September 28, 2016
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Valid Saturday October 01, 2016 to Wednesday October 12, 2016
US Hazards OutlookNWS Climate Prediction Center College Park MD
300 PM EDT September 28 2016
Synopsis: A stationary front is expected to extend from the northern Gulf of Mexico across northern Florida to off the Atlantic Seaboard during the first several days of the Outlook period. Weak surface low pressure initially in Indiana is forecast to move slowly northward and eastward during the same period. In the West, an energetic frontal system is anticipated to move across the Intermountain region, the Rockies, and the northern and central Great Plains during the 3-7 day period. In the Alaska domain, a fairly strong frontal system is expected to move across the far western portion of the state, bringing heavy precipitation to parts of that region. Elsewhere, Tropical Storm Matthew is currently moving across the Windward Islands. The National Hurricane Center (NHC) predicts Matthew will continue westward across the southern Caribbean during the next few days, and strengthen into a hurricane. This system may have a significant impact on the Southeast CONUS early next week, and should be monitored closely.
Hazards
- Heavy rain for southwestern Alaska, Sat-Sun, Oct 1-2.
- Flooding is likely, imminent, or occurring in portions of the Midwest, and southern Texas.
- Severe Drought across parts of the Eastern CONUS, Missouri River Valley, Great Plains, Northern Rockies, Intermountain West, Arizona, California, and Hawaii.
For Saturday October 01 - Wednesday October 05: A cut-off Low at 500-hPa is forecast to be centered over the vicinity of Indiana and Illinois at the start of this period. Soon thereafter, this Low is expected to weaken and lift out towards the eastern Great Lakes region and St. Lawrence Valley, signaling the end of an extended period of cloudy, cool, and wet weather for the Midwest and Northeast.
For the second half of this period, attention shifts to northern and central portions of the Intermountain West, Rockies, and Great Plains, as a vigorous mid-tropospheric trough moves across the region. Deterministic runs of the GFS and ECMWF models predict heavy rain across portions of this large area, and potentially some light snow accumulations above 6000 feet in the cold air behind the upper trough axis, especially across eastern Wyoming and northwestern Colorado. These models depict significant differences in the timing and placement of the heavier rain bands, which preclude the designation of a heavy rain area on the map at this time. Instability is expected to increase ahead of the 500-hPa trough across the southern half of the Great Plains region, which is likely to increase the chances for strong to severe thunderstorm activity. At this time, there is too much uncertainty to highlight a specific region on the map regarding severe weather.
Tropical Storm Matthew, with peak sustained winds of 60 mph (as of 11am EDT Sep 28th), is moving across the Windward Islands, heading into the southern Caribbean Sea at 20 mph. The official track from NHC continues this westward motion for the next 72 hours over the sufficiently warm waters of the southern Caribbean Sea. This warm water, combined with low atmospheric wind shear, should provide an environment that is favorable for intensification, with Matthew expected to reach hurricane status in 48 hours. By the beginning of this period, NHC predicts this system will slow down and take a fairly sharp turn towards the north, bringing Matthew close to or over Jamaica. Recent runs of the GFS (6z and 12z) and the ECMWF (0z) take this system either through the Jamaica Channel (which separates Jamaica from Hispaniola), or over the Haitian peninsula, then northward across the Bahamas. Beyond this time, the models show significant disagreements in the forecast track of Matthew, and it is too early to tell with any confidence if, and to what degree, the United States may be affected by this system. It is highly recommended that residents from the eastern Gulf Coast region to the Carolinas keep a close eye on the future progress of Matthew.
Flooding is likely, imminent, or occurring in portions of the Midwest and southern Texas from Oct 1-3. This is primarily due to rain that recently fell across these areas.
A cyclonic system, preceded by an extensive corridor of moist, southerly flow, is predicted to bring heavy rain (2 inches or greater) to southwestern Alaska on Oct 1-2. The deterministic 0z ECMWF and 6z GFS runs forecast in excess of 4 inches during this period across the vicinity of the eastern Alaska Peninsula.
For Thursday October 06 - Wednesday October 12: During Week-2, the anticipated 500-hPa flow pattern features a positively tilted trough axis from about the eastern Dakotas southwestward to southern California, a weak anomalous ridge across the eastern CONUS, a ridge over most of Alaska, and a zonally elongated trough over the Bering Sea. At this time, the only hazards that are depicted on the map with confidence are the long-term drought areas. Two areas that bear watching are the Mississippi Valley/southern Plains region, and the Southern Atlantic coast states. The first area is in regard to the possibility of heavy rain and/or strong to severe thunderstorms, while the second area is related to tropical cyclone Matthew and its future track and intensity.
According to the latest U.S. Drought Monitor (USDM) valid on September 20, the coverage of severe or greater drought (for the CONUS) increased very slightly from 7.72 to 7.76 percent during the past week. Less than 1 percent of the Hawaiian Islands is designated with severe drought.
Forecaster: Anthony Artusa
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