Valid Thursday February 29, 2024 to Wednesday March 06, 2024
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EST February 21 2024Synopsis
: Model guidance favors a more
amplified mid-level low pressure over the North Pacific compared to yesterday,
supporting increased likelihood of heavy precipitation to the West Coast. An
increased potential for heavy snow in higher elevations of the Northern
Rockies, and high winds continues across much of the western contiguous U.S.
(CONUS). There is decreasing confidence in the hazards outlook by the middle of
week-2 due to increasing model divergence. A series of surface lows tracking
across the northeastern CONUS may support localized high winds and enhanced
precipitation at the beginning of the period, although there is significant
uncertainty regarding these possible storms. Over Alaska, Arctic high pressure
over the northern parts of the state may help to promote much below normal
temperatures and gap winds across the southern Mainland. Hazards
- Moderate risk of heavy precipitation for periods of heavy precipitation
for the northern half of California, Thu-Fri, Feb 29-Mar 1.
- Slight risk of periods of heavy precipitation for much of California and
the Pacific Northwest, Thu-Mon, Feb 29-Mar 4.
- Moderate risk of heavy snow for the Klamath and portions of the Sierra
Nevada Mountains, Feb 29-Mar 1.
- Slight risk of periods of heavy snow for the Sierra Nevada, Klamath, and
Cascade Mountains, Thu-Mon, Feb 29-Mar 4.
- Slight risk of episodic high winds for much of the western CONUS, Thu-Mon,
Feb 29-Mar 4.
- Slight risk of periods of heavy snow for parts of the Northern Rockies,
Wed-Sun, Thu-Mon, Feb 29-Mar 4.
- Slight risk of high winds for portions of the northeastern CONUS, Thu-Fri,
Feb 29-Mar 1.
- Moderate risk of much below normal temperatures for parts of southern
Alaska, Thu-Fri, Feb 29-Mar 1.
- Slight risk of much below normal temperatures for parts of southern Alaska,
Thu-Sat, Feb 29-Mar 2.
- Slight risk for periods of high winds for southern coastal portions of
Alaska, Thu-Mon, Feb 29-Mar 4.
- Possible flooding for parts of the northern half of California.
For Saturday February 24 - Wednesday
February 28: WPC Days 3-7 U.S.
Hazards For Thursday February 29 -
Wednesday March 06:
Multiple dynamical model ensemble means show a more
amplified mean week-2 500-hPa height pattern across much of the U.S. compared
to yesterday, but continue to be in fairly large disagreement. The ECENS
indicates a more amplified mid-level trough over the North Pacific compared to
the GEFS at the beginning of the period. By the middle of the period,, there
are increasing differences among the models regarding the evolution of this
feature. The GEFS maintains this feature near the West Coast until the end of
week-2, with mid-level shortwave troughs moving across the central CONUS
whereas the ECENS indicates the North Pacific mid-level trough shifting
eastward to the central CONUS, weakening throughout week-2. These model
differences translate to decreasing confidence in associated hazards by the
middle of the period.
The increased amplification of the mid-level trough over the North Pacific
translates to increased heavy precipitation signals for the West Coast,
especially at the beginning of week-2. A moderate risk (at least a 40% chance)
of heavy precipitation is posted across parts of the northern of California,
Feb 29-Mar 1, based on increasing enhanced integrated vapor transport (IVT)
signals in the GEFS, and the ECENS (GEFS) Probabilistic Extremes Tool (PET)
which show at least a 40% (30%) chance of 3-day liquid equivalent totals
exceeding the 85th percentile climatologically and one inch in this area. An
associated moderate risk of high elevation snow is designated for the Klamath
and portions of the Sierra Nevada Mountains, Feb 29-Mar 1. A broader area of
slight risk (>20% chance) is continued for periods of heavy precipitation for
much of California and the Pacific Northwest with a slight risk of heavy snow
for the higher elevations of the Sierra Nevada, Klamath and Cascade Mountains,
Feb 29- Mar 4. Shallow landslides and rock falls are always possible in
California during periods of heavy rainfall in winter.
As this mid-level trough moves inland, raw and calibrated guidance supports
a slight risk of periods of heavy snow across the higher elevations of the
Northern Rockies south through the northern Wasatch Range of Utah, Feb 29-Mar
4. A slight chance of high winds for much of the western CONUS, Feb 28-Mar 3,
is expanded to include southern California and more of the Southwest compared
to yesterday associated with the increased deepening of the mid-level trough
favored in the North Pacific.
A series of surface lows are predicted to track across the northeastern
CONUS at the beginning of the period. However, there is significant model
uncertainty regarding the evolution of these potential storms and associated
impacts. There may be increased potential for localized heavy snow across parts
of the Great Lakes region, Ohio Valley, Appalachians, and Northeast, although
there is too much uncertainty at this time to designate an associated hazard at
this time. A slight risk of high winds is highlighted for parts of the
northeastern CONUS, Feb 29-Mar 1, based on the potential for tight pressure
gradient associated with these storms, and support from the PETs indicating at
least a 20% chance of wind speeds exceeding the 85th percentile and 20 mph.
In Alaska, an area of Arctic high pressure is forecast across the northern
parts of the state and the Yukon, with surface low-pressure over the Gulf of
Alaska. This pattern favors increased chances of gap winds over much of the
southern Alaska coastline throughout the week-2 period. Thus, a slight risk of
high winds is maintained for Feb 29-Mar 2 across the area. The PETs show
noticeably increased probabilities for much below normal temperatures relative
to previous guidance, and indicate at least a 40% chance of minimum
temperatures falling to the lowest 5th percentile climatologically across the
southwestern Mainland and Alaska Peninsula on day 8 (Feb 29). A moderate risk
of much below normal temperatures is designated for parts of southern Alaska
south of the Interior Basin, Feb 29-Mar 1. A broader area of slight risk is
highlighted across southern Alaska, Feb 29-Mar 4. High winds across the
southern coast of Alaska could contribute to anomalously low wind chill
Forecaster: Melissa Ou
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts