Valid Saturday October 31, 2020 to Friday November 06, 2020
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT October 23 2020Synopsis
: 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,
- 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
For Monday October 26 - Friday
October 30: WPC Days 3-7 U.S.
Hazards For Saturday October 31 - Friday
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
Forecaster: Anthony Artusa
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts