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U.S. Week-2 Hazards Outlook - Made September 27, 2021 | About the Hazards Outlook
| Composite Map Day 8-14 |
Experimental Probabilistic Outlooks |
 |
Valid Tuesday October 05, 2021 to Monday October 11, 2021
US Hazards OutlookNWS Climate Prediction Center College Park MD
300 PM EDT September 27 2021
Synopsis: There is good multi-model agreement generally favoring mid-level high (low) pressure across the eastern two-thirds (western third) of the lower 48. There is more uncertainty regarding the potential for mid-level low pressure forming across the West, with the ECMWF ensemble mean indicating mid-level low pressure being more amplified and extending further inland across the West compared to the GEFS and Canadian. Overall the anticipated pattern favors anomalously warm temperatures across much of the contiguous U.S., with more uncertainty regarding the potential for anomalously cold temperatures across the western portions of the lower 48. Temperatures are generally not anticipated to reach hazardous criteria. There continues to be increased potential for tropical cyclone activity in the Atlantic, although no related hazardous impacts are anticipated for the contiguous U.S. at this time. Mid-level low pressure is predicted for much of Alaska, favoring cooler than normal temperatures and above normal precipitation across the state.
Hazards
- No hazards posted.
For Thursday September 30 - Monday October 04: WPC Days 3-7 U.S. Hazards
For Tuesday October 05 - Monday October 11: The 0Z GEFS, ECMWF, and Canadian ensemble means generally favor above (near) normal 500-hPa heights across much of the northern (southern) half of the lower 48. Positive 500-hPa height anomalies across the North-Central CONUS are more evident in the 0Z GEFS ensemble mean compared to the 0Z ECMWF and Canadian counterparts. This translates to the GEFS reforecast tool indicating elevated chances (greater than 20%) of maximum temperatures exceeding the 85th percentile across primarily the northern half of the CONUS during the period, whereas the ECMWF reforecast tool is significantly weaker with this potential, showing only a small portion of the North-Central CONUS reaching these values for a brief period. Despite the GEFS indicating temperatures potentially exceeding the 85th percentile, temperatures are not anticipated to reach hazards criteria, with most regions having temperatures less than 85 Deg F. Additionally, embedded shortwave troughs are anticipated to move throughout the longwave ridge pattern, which would decrease chances for warmer temperatures lasting for a long duration. Therefore, a related much above normal temperature hazard is not designated at this time.
Across the West, the ECMWF ensemble mean favors more amplified troughing extending further inland and for a longer duration compared to the GEFS and the Canadian. This is reflected in the ECMWF reforecast tool, which shows an area across western CONUS with minimum temperatures falling to the lowest 15th percentile and below freezing at the beginning of week-2, expands to the Rockies westward by the middle of the period. The GEFS reforecast tool, however, maintains chances of reaching these thresholds to less than 10%. Due to significant model differences, a much below normal temperature hazard is not posted at this time.
Due to the anticipation of mid-level shortwaves being relatively transient, no associated heavy precipitation hazards are expected at this time. As of 2pm EDT, the National Hurricane Center (NHC), is monitoring Hurricane Sam currently located several hundred miles east of the Lesser Antilles, in addition to three other disturbances that have potential for developing into a subtropical or tropical cyclone. The 0Z ECMWF ensemble mean, 6Z deterministic GFS and associated forecast ensemble surface lows do not favor tracks that would support associated hazards for the CONUS at this time but will be monitored in the upcoming days.
In the East Pacific, the NHC is also monitoring a disturbance currently located southwest of Mexico, with a 40% chance (as of 11am PDT) of developing into a tropical cyclone over the next 5 days. Should this disturbance form, there is potential for this disturbance to track near the Gulf of California, which could enhance some moisture into the Four Corners region during week-2. The ECMWF reforecast tool shows a much stronger signal for a wetter pattern for the Four Corners compared to the GEFS reforecast tool. The ECMWF reforecast tool shows at least a 20% chance of 3-day totals exceeding the 85th percentile and half an inch across a broad area of the Four Corners, including a greater than 50% chance across some of these areas of receiving 3-day rainfall totals exceeding the 85th percentile. The GEFS reforecast tool has a much weaker signal, keeping chances of 3-day rainfall accumulations exceeding the aforementioned thresholds to less than 30% and amounts remaining below half an inch. Due to significant uncertainty with this feature, a heavy precipitation hazard is not designated at this time.
For Alaska, mid-level troughing is generally favored for the state, with 500 hPa heights anticipated to be near normal. Overall, below normal temperatures and above normal precipitation is predicted for many parts of the Mainland and Panhandle for week-2. The 0Z GEFS, ECMWF, and Canadian ensemble means favor a surface low to form over the Bering Sea during week-2, extending across parts of Alaska to the Panhandle, with a potential associated frontal boundary along the Alaska Panhandle. The ECMWF reforecast tool shows at least a 20% chance for parts of the South Coast of Alaska receiving 3-day precipitation amounts exceeding the 85th percentile and 2 inches. The GEFS reforecast tool, however, does not show this signal, resulting in too much uncertainty to designate any precipitation related hazards at this time. Additionally, the wind reforecast tools do not indicate increased potential for high winds associated with this disturbance.
Forecaster: Melissa Ou
$$ Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Resources
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts