Valid Wednesday August 24, 2022 to Tuesday August 30, 2022
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT August 16 2022Synopsis
: Dynamical models are in good
agreement regarding mid-level high pressure across the western contiguous U.S.
(CONUS), and mid-level low pressure downstream over the central and eastern
CONUS during week-2. This pattern favors increased chances for excessive heat
across portions of the western CONUS and Northern High Plains. An unseasonably
cool pattern is forecast across much of the interior eastern and central CONUS
during late-August with enhanced rain chances over parts of the Middle and
Lower Mississippi, Ohio, and Tennessee Valleys tied to the aforementioned
mid-level low pressure. The southwest monsoon is forecast to remain active
early in the period, although weakening mid-level high pressure combined with
decreasing East Pacific tropical cyclone activity is expected to reduce the
amount of moisture over the region later in the period. Mid-level low pressure
forecast across Alaska favors enhanced southerly flow and rounds of heavy
precipitation along the southern coastal Mainland during week-2.
- Moderate risk of excessive heat across portions
of the Pacific Northwest, Intermountain West, Northern Rockies, and northern
California, Wed-Fri, Aug 24-26.
- Slight risk of excessive heat across portions of the Pacific Northwest,
Intermountain West, Northern Rockies, Northern Plains, and California, Wed-Sun,
- Slight risk of heavy precipitation across portions of the Central Great
Basin, Desert Southwest, and Central and Southern Rockies, Wed-Sat, Aug 24-27.
- Slight risk of heavy precipitation across portions of the Southern Plains,
Middle and Lower Mississippi Valley, Ohio and Tennessee Valleys, Southern
Appalachians, and Southeast Wed-Fri, Aug 24-26.
- Slight risk of heavy precipitation across portions of southern Mainland
Alaska and the northern Panhandle, Wed-Sun, Aug 24-28.
- Rapid-onset drought possible for portions of the Northern Plains, Northern
Great Basin, and Northern Rockies.
- Flooding possible for portions of the Four Corners Region and Southwest.
For Friday August 19 - Tuesday August
WPC Days 3-7 U.S. Hazards For Wednesday August 24 -
Tuesday August 30:
The 0z ECMWF, GEFS, and Canadian ensembles are in very
good agreement during week-2, depicting an amplified 500-hPa height pattern
across western North America, with troughing favored over Alaska, and ridging
over the western CONUS and Canada. While a slight reprieve in the heat over the
Northwest CONUS is possible late in week-1, relatively higher temperatures are
likely to return to the region early in week-2, corresponding with an increased
heat signal in the reforecast tools. The GEFS reforecast tool depicts some
areas of the Pacific Northwest and Intermountain Region having at least a 40
percent chance of maximum temperatures exceeding the 85th climatological
percentile. Both the GEFS and ECMWF reforecast tools indicate at least a 30
percent chance of maximum temperatures exceeding the 85th climatological
percentile extending southward from the Northwest to the northern half of the
California Central Valley. The reforecast tool probabilities indicating extreme
heat are higher today compared to yesterday, and the National Blend of Models
also indicates the potential for daily record high temperatures over parts of
the Northwest early in week-2 (mid to upper 90s deg F). Therefore a moderate
risk for excessive heat is highlighted across the Pacific Northwest,
Intermountain Region, and northern California for 8/24-8/26.
A broader area of slight risk for excessive heat includes all of the
California Central Valley where temperatures may exceed 100 deg F, and also
extends eastward through the Northern High Plains where temperatures may exceed
95 deg F. The ridge is forecast to weaken later in week-2 allowing the slight
risk to be discontinued after 8/28. The persistent anomalously warm
temperatures, combined with little precipitation forecast during the next week,
favors an elevated risk for rapid onset drought across portions of the Pacific
Northwest, Northern Great Basin, and Northern Plains, as well as enhanced
wildfire threat over these areas.
For much of the central and interior eastern CONUS, an unseasonably cooler
pattern is forecast due to intermittent troughing forecast over the region
downstream of the ridging to the west. Enhanced precipitation is also likely,
especially over parts of the Southern Plains, Middle and Lower Mississippi
Valley, and the Ohio and Tennessee Valleys, where a shortwave impulse is
forecast to develop along the mean trough axis around day-7 (8/23), bringing
the potential for heavy rainfall persisting into the early part of week-2. Over
time, the greatest chances for heavy precipitation are forecast to shift
eastward and southward, reaching the Central Gulf of Mexico Coast by day-10
(8/26). The ECMWF and GEFS reforecast tools indicate at least a 20 percent
chance of 3-day precipitation totals exceeding the 85th percentile and 1-inch
early in the period over parts of these areas, further justifying a slight risk
of heavy precipitation from 8/24-8/26.
The southwest monsoon is forecast to remain moderately active during the
first half of week-2. The ECMWF reforecast tool depicts probabilities of at
least 20 percent for 3-day precipitation exceeding the 85th climatological
percentile and a half-inch through the middle of the period across much of the
Four Corners Region and Southwest. The GEFS reforecast tool depicts weaker
probabilities and less coverage compared to the ECMWF, with many areas falling
below 20 percent by the middle of the period. The slight risk of heavy
precipitation is maintained from Aug 24-27 over much of the Southwest and Four
Corners region given good continuity with yesterday and the more robust ECMWF
guidance. A flooding possible hazard remains posted over much of the
highlighted region as the convective nature of precipitation could result in
localized flash flooding. It is worth noting that flash flooding can occur even
in areas that do not directly receive rainfall due to runoff of precipitation
upstream. The monsoon is expected to weaken toward the end of week-2 due to a
flattening of the ridge over the West, along with a decrease in tropical
cyclone activity over the East Pacific.
Mid-level troughing forecast across Alaska, along with associated surface
low pressure south of the Aleutian Islands, favors enhanced onshore flow over
the southern Mainland throughout week-2. The amplitude of the troughing is
weaker compared to yesterday’s guidance, with the GEFS and ECMWF reforecast
tools indicating reduced coverage of areas having at least a 20 percent chance
of 3-day precipitation totals exceeding the 85th percentile and 2 inches.
However, uncalibrated guidance from the GEFS, ECMWF, and Canadian ensembles
continue to indicate localized totals of over 4 inches for week-2 as a whole,
with the greatest precipitation chances during the early and middle parts of
the period. Several inches of snow is also possible across higher elevation
areas of the Alaska Range. A slight risk for heavy precipitation is maintained
over much of the southern coastal Mainland and northern Panhandle from
8/24-8/28 despite the weaker probabilities in the reforecast tools relative to
yesterday, given that the uncalibrated guidance continues to depict high
precipitation totals over the region.
Forecaster: Thomas Collow
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts