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U.S. Week-2 Hazards Outlook - Made May 10, 2021 | About the Hazards Outlook
| Composite Map Day 8-14 |
Experimental Probabilistic Outlooks |
 |
Valid Tuesday May 18, 2021 to Monday May 24, 2021
US Hazards OutlookNWS Climate Prediction Center College Park MD
300 PM EDT May 10 2021
Synopsis: Regions of mid-level high pressure are forecast across the northeastern Pacific and Great Lakes during Week-2, with mid-level low pressure possible across the Intermountain West. An advancing cold front with accompanying heavy rainfall chances is likely to cross the Central U.S. during the early portion of the forecast period. Forecast solutions featuring increased mid-level low pressure across the West would support some risk of high winds across roughly the southwestern quarter of the Lower-48 states. Mid-level low pressure is forecast over the Bering Sea which could bring a wet pattern to the southern coast of Alaska.
Hazards
- Slight risk of heavy rain across portions of the Central and Southern Plains, and the Middle and Lower Mississippi Valley, Tue-Wed, May 18-19.
- Slight risk of high winds across portions of the Central Great Basin, Southwest, Rockies, and High Plains, Tue-Mon, May 18-24.
For Thursday May 13 - Monday May 17: WPC Days 3-7 U.S. Hazards
For Tuesday May 18 - Monday May 24: The Weather Prediction Center (WPC) surface analysis for Day 7 shows a surface low pressure center near the Sandhills of Nebraska with a trailing dry line and cold front extending southward over the High Plains. As this system transits eastward the cold front is likely to overcome the dry line and become the primary focus for heavy rainfall concerns during Week-2. A slight risk of heavy rain is forecast for much of the Central and Southern Plains and Middle and Lower Mississippi Valley on May 18th and 19th tied to the advancing boundary. Discrepancies exist regarding how progressive the system is, resulting in a slower advance in the GEFS (primarily focused over the Great Plains) versus the quicker ECMWF (targeting the Mississippi Valley), resulting in the broad shape covering both days. The GEFS is also quicker to wash out the precipitation risks beyond the 18th, while the ECMWF lingers precipitation into the 19th, resulting in the two day forecast period. Flash flooding could be a concern with this system as currently observed soil moisture levels are generally above normal across the area highlighted for the hazard, while another 2-4 inches of rain are possible over the coming week per WPC.
Mid-level low pressure is forecast to varying degrees across the West in the mean Week-2 circulation field. This feature digs the furthest south in the ECMWF ensembles, while the Canadian ensembles exhibit similar height departures with some northwestward displacement. Conversely, today's 0Z GEFS has only marginally below-normal heights confined to the Northern Rockies. The more amplified solutions of the ECMWF and Canadian models would support periodic high wind risks throughout Week-2 extending across the Southwest, Rockies, and High Plains depending on the timing of shortwave activity rotating through the longwave axis. A broad slight risk of high winds is posted for these regions across the entirety of Week-2 where winds of 35+ knots are possible but difficult to pinpoint in time and space.
Anomalous mid-level troughing is forecast over the Bering Sea during Week-2, supportive of a wet pattern for areas adjacent to the Gulf of Alaska and potentially the Bering Sea. Despite this, it's a relatively dry time of year for the region and forecast precipitation totals appear unimpressive. Reforecast guidance for temperature across the state is mixed, with the GEFS generally favoring near-normal temperatures, while the ECMWF tilts strongly toward above-normal temperatures for the northern two-thirds of the state. If the ECMWF solution were to verify this could exacerbate river flooding concerns during break-up season for regions north of the Brooks Range.
Forecaster: Daniel Harnos
$$ Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Resources
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts