Valid Wednesday February 08, 2023 to Tuesday February 14, 2023
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM
EST January 31 2023
Synopsis: Surface low development over the
Great Plains, combined with enhanced moisture flow from the Gulf of Mexico
increases the risk of heavy precipitation over the southeastern Contiguous U.S.
(CONUS) early in the period. Forecast mid-level low pressure is expected to
bring below (above)-normal temperatures (precipitation) over many portions of
the West, with slight chances for heavy precipitation and high elevation
snowfall late in week-2 across some areas.
Hazards
- Slight risk of heavy precipitation for portions of the Great Plains,
Mississippi, Tennessee and Ohio Valleys, Southeast, and Mid-Atlantic, Wed-Fri,
Feb 8-10.
- Slight risk of heavy precipitation for portions of California, Sat-Tue, Feb
11-14.
- Slight risk of high winds for portions of the West Coast and the Great
Basin, Sat-Tue, Feb 11-14.
- Slight risk of heavy snow for the higher elevations of the Sierra Nevada,
Sat-Tue, Feb 11-14.
- Slight risk of heavy snow for the higher elevations of the Four Corners,
Sun-Tue, Feb 12-14.
Detailed SummaryFor Friday
February 03 - Tuesday February 07:
WPC Days 3-7 U.S.
Hazards For Wednesday February 08 -
Tuesday February 14: There is generally good agreement among the dynamical
model mean week-2 500-hPa height anomaly forecasts featuring amplified ridging
overspreading the central and eastern CONUS, with weak troughing upstream over
the West. Relative to yesterday, both the GEFS and ECMWF ensembles have backed
off on the strength of the mean troughing across the West. Analysis of the
daily evolution of mid-level heights now shows a more transitional pattern over
this part of the country, though models still hint at troughing becoming more
pronounced towards the end of the period. Notably, the strongest negative
mid-level height departures in the ensembles are favored over the higher
latitudes of North America, with the mean pattern becoming more in-line with
both positive phases of the Arctic Oscillation (+AO) and North Atlantic
Oscillation (+NAO). As a result, the favored absence of Arctic air intruding
upon the CONUS is likely to reduce the risk of much below normal temperatures,
with much of the mean flow favored to be more of Pacific origin for much of the
country during week-2.
By the middle of next week, a shortwave trough ejecting from the Rockies is
expected to induce a surface low over Southern Plains. With surface high
pressure likely established over the eastern CONUS to promote ample return flow
from the Gulf, conditions remain conducive for heavy precipitation over the
southeastern CONUS early in the period. A slight risk of heavy precipitation
remains issued for Feb 8-10, and is expanded to include parts of the
Mid-Atlantic where reforecast tools show at least a 20% chance of 3-day totals
exceeding the 85th percentile. Deterministic solutions continue to depict
dewpoint temperatures reaching the lower to mid-60s in the warm sector of the
surface low, suggesting an increased potential of thunderstorm activity over
portions of the Gulf States. These solutions also show the potential for
accumulating snow on the backside of the low over the Plains and Midwest,
however reforecast guidance remains less supportive of liquid-equivalent
amounts exceeding hazard criteria, precluding a heavy snow hazard. Regardless
of whether heavy precipitation is realized, the anomalously wet conditions
favored over the Lower Mississippi Valley during week-2 may exacerbate
saturated ground conditions and trigger localized flooding, particularly over
southern Louisiana and Mississippi where soil moisture content and streamflow
are registering in the highest percentiles. Later in the period, both the GEFS
and ECMWF ensembles show signs of additional surface low formation in the lee
of the Rockies. While this is evidenced by the return of increased
precipitation amounts across the Plains and Mississippi Valley in the raw
guidance, particularly in the ECMWF, no corresponding precipitation hazards are
issued due to a lack of support from the GEFS reforecast tool.
Relative to previous guidance, more anomalous mid-level ridging is depicted
over western CONUS in the GEFS and ECMWF ensembles early in the week-2. While
some anomalously cold air is favored downstream of the ridge axis, several
temperature tools have become more modest with the predicted negative
temperature departures. Similarly, both the GEFS and ECMWF reforecast tools
depict less spatial coverage of probabilities for temperatures falling below
the 15th percentile across the West throughout the period compared to
yesterday, prompting the removal of the slight risk of much below normal
temperatures in today's outlook. Some of the cold signals in percentile space
return over the parts of the southwestern U.S associated with more anomalous
troughing and northwesterly flow favored later in the period, but remain
marginal at this time.
In regards to heavy precipitation potential in western CONUS, there is
considerable disagreement in the latest reforecast guidance. The GEFS
reforecast tool remains muted with the heavy potential until the middle portion
of week-2, whereas the ECMWF reforecast tool introduces a robust signal from
the Pacific Northwest to California, likely tied to a deeper trough extending
from the Gulf of Alaska in the ECMWF ensemble mean on day 9 (Feb 9). Later in
the period, there is slightly better agreement, depicting increased chances of
3-day amounts exceeding the 85th percentile over portions of California and the
Great Basin. Given the increased alignment among the ensembles' mid-level
height pattern during this time, a slight risk of heavy precipitation is posted
over parts of California, as well as a slight risk of heavy snow over the
higher elevations of the state, from Feb 11-14. At the base of an amplifying
trough, a broad slight risk area of high winds remains posted over the West,
which is also supported by the ECMWF reforecast tool's increased chances of
winds exceeding the 85th percentile. A slight risk of heavy snow also remains
posted over the Four Corners region (Feb 12-14) where there is continued
support from Snow Water Equivalent (SWE) reforecast tool indicating totals
exceeding the 85th percentile late in week-2.
Over Alaska, periods of increased onshore flow are expected to promote
above-normal precipitation over the southern Mainland and Panhandle throughout
the period. Both the GEFS and ECMWF reforecast tools show increased chances for
3-day accumulations exceeding the 85th percentile, however amounts are not
expected to exceed hazard criteria, therefore no corresponding hazards are
issued.
Forecaster: Nick Novella
$$
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Resources
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts