delayed in updating graphics.
most up to date graphics.
Valid Monday February 18, 2019 to Friday March 01, 2019
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EST February 15 2019Synopsis
: A strong area of upper-level low
pressure is likely to persist over western North America through late February,
while upper-level high pressure remains anchored across the Southeast. During
the next two weeks, arctic surface highs are forecast to shift south from
western Canada into the western and north-central U.S. Multiple surface low
pressure systems are expected to track across the Ohio and Tennessee Valleys
during the next two weeks. Periods of enhanced onshore flow are forecast to
affect the Aleutians, Alaska Peninsula, and western mainland Alaska through the
end of February. Hazards
Detailed Summary For Monday
February 18 - Friday February 22:
- Heavy snow across parts of
Arizona, southern Colorado, and northern New Mexico, Mon, Feb 18, and Thu-Fri,
- Heavy snow changing to sleet and freezing rain for parts of the central
Appalachians and mid-Atlantic, Tue-Wed, Feb 19-20.
- Heavy snow for parts of the mid-Atlantic and Northeast, Tue-Wed, Feb 19-20.
- Periods of heavy rain for parts of the Southeast, Mon-Fri, Feb 18-22.
- Much below-normal temperatures for much of the western U.S. and Great
Plains, Mon-Fri, Feb 18-22.
- High winds across portions of mainland Alaska and the Aleutians, Mon-Tue,
- High significant wave heights for coastal portions of mainland Alaska and
the Aleutians, Mon-Tue, Feb 18-19.
- High risk of much below normal temperatures for the interior Pacific
Northwest, northern California, northern Great Basin, northern Rockies and
northern Great Plains, Sat-Fri, Feb 23-Mar 1.
- Moderate risk of much below normal temperatures for much of the western
U.S. and Great Plains, Sat-Fri, Feb 23-Mar 1.
- Slight risk of much below normal temperatures for portions of the Central
and Western U.S., Sat-Fri, Feb 23-Mar 1.
- Slight risk of much below normal temperatures for the Alaska Panhandle,
Sat-Sun, Feb 23-24.
- Slight to moderate risk of heavy precipitation across parts of the
mid-Atlantic, Southeast, and Ohio Valley, Sat-Fri, Feb 23-Mar 1.
- Flooding occurring, imminent, likely, or possible for parts of the Ohio and
Mississippi Valleys along with Arizona.
- Severe Drought across parts of the western U.S., Alaska Panhandle, and
A vigorous shortwave trough is forecast
to eject from the Southwest early next week, promoting the development of a
frontal wave of low pressure along the western Gulf Coast by Feb 19. Moderate
to heavy snow (3 to 6 inches) is expected across the interior mid-Atlantic and
Northeast due to strong warm air advection. A strong surface high (around
1032-hPa) centered across northern New England is likely to result in cold air
damming. The GFS and ECMWF ensemble means on Feb 15 indicate 0.10 to 0.25
inches, or more, of ice accumulation in the depicted hazard area. Heavy snow at
the onset of the precipitation and a changeover to freezing rain is probable
for the Shenandoah Valley north to south-central Pennsylvania on Tuesday night
into Wednesday. Please refer to local NWS offices for the latest forecasts on
this potential winter storm.
Periods of heavy rain are likely throughout this 5-day period across the
Southeast and southern mid-Atlantic as waves of low pressure track along a
nearly stationary front from the western Gulf Coast northeast to the southern
mid-Atlantic. The deterministic 0Z ECMWF model indicates a large area of 3 to 8
inches of rainfall during this 5-day period within the depicted hazard area.
Soil moisture is currently above the 90th percentile and the upcoming pattern
of frequent, heavy rainfall may eventually lead to small stream and river
On February 18, heavy snow is expected to be ongoing across parts of
Arizona, southern Colorado, and northern New Mexico. Another shortwave trough
is forecast to cross the Four Corners region on Feb 21 and 22, renewing the
risk of heavy snow across these same areas. Snow levels are likely to be
relatively low (below 4,000 feet) with these winter storms and total snowfall
accumulations during this 5-day period of more than a foot can be expected.
The high amplitude pattern over the north Pacific and western North America
is likely to favor arctic high pressure shifting south from western Canada.
Therefore, much below normal temperatures (-12 degrees F or more) are forecast
to affect the interior West along with the Great Plains. The coldest
temperatures (below -10 degrees F) are forecast across the northern Rockies and
northern high Plains on Tuesday morning. Subzero minimum temperatures may
extend as far south as the central high Plains. Since this region is free of
protective snow cover, the bitter cold increases the risk of winterkill to
exposed wheat. Although negative temperature anomalies are forecast to be
smaller across California, the Central Valley is included in the much below
normal temperature hazard since the pattern supports a frost or light freeze
during this outlook period.
The deterministic GFS remains consistent that a surface low (around
968-hpa) enters the Bering Sea on Feb 18. Significant waves and high winds are
likely with this low pressure system across the Aleutians, Alaska Peninsula,
and southwestern mainland Alaska on Feb 18 to 19. The consistent, enhanced
onshore flow is likely to cause coastal flooding and exacerbate erosion along
the coastline of southwest Alaska. Another round of significant waves and high
winds may return to the Aleutians by Feb 22. For Saturday February 23 -
Friday March 01:
A high amplitude pattern with an upper-level ridge
(trough) over the north Pacific (western North America) is likely to persist
through the final week of February. A high risk (60 percent chance or higher)
of much below normal temperatures (lowest 15th percentile of the climatological
minimum temperature distribution) is forecast across the interior Pacific
Northwest, northern Great Basin, northern Rockies, and northern Great Plains
throughout Week-2. The GEFS probabilistic temperature tool indicates that there
is more than a 40 percent chance of record cold temperatures across the
interior Pacific Northwest and northern Great Basin early in Week-2. Even later
in Week-2, this tool indicates a 20 to 40 percent chance of record cold across
The 6Z GEFS ensemble mean features negative daily temperatures anomalies of
-20 to -30 degrees F, each day of the Week-2 period, across the northern Great
Plains. This persistent amplified pattern and successive arctic highs shifting
south from Canada support an expansive slight and moderate risk area of much
below normal temperatures across much of the western U.S. and Great Plains
throughout Week-2. Although a moderation in temperatures is expected across the
Southwest later in Week-2, the eastward shift of the anomalous upper-level
trough over western North America continues to be delayed. Therefore, little
relief from the bitter cold is anticipated across the northern Rockies and
northern Great Plains through the end of Week-2. Arctic high pressure centered
over western Canada supports a slight risk of much below normal temperatures
across the Alaska Panhandle on Feb 23 and 24.
Downstream of the longwave trough axis, multiple low pressure systems are
forecast to continue tracking along a strong temperature gradient across the
Tennessee Valley. Abundant Gulf inflow favors the likelihood of heavy rainfall
with each low pressure system. Although there may be a 2 to 3 day break from
the heavy rainfall during the middle part of Week-2, the slight to moderate
risk areas cover the entirety of Week-2 due to uncertainty in the timing of
individual shortwave troughs at this time range. The moderate risk coincides
with where the GFS and ECMWF ensemble means indicate more than 2 inches of
precipitation during Week-2 and also where rainfall is likely to be heaviest
prior to Week-2. The slight and moderate risk areas cover the entirety of
Week-2 due to uncertainty on the timing of individual waves of low pressure.
The U.S. Drought Monitor, valid Feb 12, indicates severe to exceptional
drought (D2-D4) coverage throughout the CONUS decreased to 6.23 percent.
Improvements were made across parts of Arizona, Colorado, and Utah. This is the
lowest coverage of D2-D4 since December 2017.
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts