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U.S. Week-2 Hazards Outlook - Made October 23, 2020 | About the Hazards Outlook
| Composite Map Day 8-14 |
Experimental Probabilistic Outlooks |
 |
Valid Saturday October 31, 2020 to Friday November 06, 2020
US Hazards OutlookNWS Climate Prediction Center College Park MD
300 PM EDT October 23 2020
Synopsis: The Week-2 U.S. Hazards Outlook features mid-level low pressure over Alaska and near the Eastern Seaboard of the contiguous U.S., with moderately strong mid-level high pressure over the western three-quarters of the CONUS. A weak, low-amplitude ridge is predicted across the Bering Sea.
Hazards
- Moderate chance of much below normal temperatures over much of eastern New York and New England, Sat, Oct 31.
- Slight chance of much below normal temperatures over the Upper Great Lakes region, and most of the Northeast, Sat-Wed, Oct 31-Nov 4.
- Slight chance of much below normal temperatures in south-central and southeastern Alaska, including the Southeast Panhandle region, Sat-Fri, Oct 31-Nov 6.
For Monday October 26 - Friday October 30: WPC Days 3-7 U.S. Hazards
For Saturday October 31 - Friday November 06: A moderately strong 500-hPa ridge is predicted to extend across most of the CONUS during Week-2, and a mid-level trough is forecast near the Atlantic Coast. The flow pattern is expected to be very progressive, with embedded smaller-scale short wave troughs. These individual short waves are much more difficult to time accurately. A rapidly deepening trough is forecast across Alaska during this period.
Several brief intrusions of anomalously cold air are anticipated across the Great Lakes and Northeast during Week-2, in association with a nearby trough. A slight chance (20%) of much below normal temperatures (15th percentile or lower for the minimum temperatures) is indicated for parts of the Upper Great Lakes region and Northeast, from Oct 31-Nov 4. A moderate chance (40%) of much below normal temperatures is specified for much of eastern New York and New England on Oct 31. ECMWF and GEFS reforecast tools indicate temperatures could bottom out below the 10th percentile of the historical minimum temperature distribution. In addition, both reforecast tools predict a 20%-40% chance for the overnight low temperatures in the depicted moderate risk area to fall to, or slightly below, 20 deg F.
In Alaska, there is increasing model support for forecasting a slight chance (20%) of minimum temperatures falling below the 15th percentile during Week-2. The area includes south-central and southeastern Alaska (including the Southeast Panhandle), and southern portions of the Central Interior. The ECMWF ensemble is significantly more bullish than the GEFS, in terms of the predicted spatial coverage and magnitude of this anomalously cold air. The introduction of this slight risk area of much below normal temperatures is a result of today’s model runs forecasting a rapidly amplifying mid-tropospheric trough during this period.
Very early in the Week-2 period, a frontal zone moving off the Atlantic Coast is forecast to bring precipitation to parts of the Mid-Atlantic and Northeast, but the amounts are expected to fall short of hazardous criteria. Though no precipitation hazards are specified today across the U.S., one area that will be monitored more closely moving forward is the Great Lakes region. For now, rain or wet snow showers are expected to the lee of the Lakes with any cold air advection during Week-2, with no significant lake-effect snow events.
Forecaster: Anthony Artusa
$$ Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Resources
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts