Valid Friday June 09, 2023 to Thursday June 15, 2023
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM
EDT June 01 2023
Synopsis: Mid-level high pressure favored late
next week is expected to sustain the risk of excessive heat for portions of the
northwestern contiguous U.S. (CONUS) early in week-2. Potentially deepening
surface low pressure supports increased chances for heavy precipitation over
the south-central CONUS as well as over portions of Florida. Antecedent
anomalous dryness combined with increased chances for below-normal
precipitation continuing through mid-June increases the risk for rapid onset
drought over portions of the Midwest and extending eastward towards the Central
Appalachians. Localized flooding related to the spring thaw remains possible
for portions of the western CONUS, and along portions of the James River in
South Dakota.
Hazards - Slight risk of excessive heat for
parts of the Northwest, Fri, Jun 9.
- Slight risk of heavy precipitation for portions of the Southern and Central
Plains and Lower and Middle Mississippi Valley, Fri-Sun, Jun 9-11.
- Slight risk of heavy precipitation for portions of Florida, Fri-Sun, Jun
9-11.
- Slight risk of high winds for parts of Southwest Alaska and Aleutian
Islands, Fri, Jun 9.
- Possible flooding for portions of California, Nevada, Utah, Wyoming, and
Idaho.
- Possible flooding along portions of the James River in South Dakota.
- Rapid onset drought risk across portions of the Middle and Upper
Mississippi Valleys, the Ohio Valley, and Great Lakes.
Detailed
SummaryFor Sunday June 04 - Thursday June 08:
WPC Days 3-7 U.S.
Hazards For Friday June 09 - Thursday
June 15: By late next week, dynamical model 500-hPa height forecasts
continue to advertise a split flow pattern prevailing over the western CONUS
with more amplified troughing downstream forecast throughout much of the
eastern CONUS. Much of the amplified mid-level ridging favored over western
Canada is still expected to ease early in week-2, leading to a moderation of
temperatures and a lowered risk of excessive heat persisting over the Pacific
Northwest and Northern Intermountain regions. The GEFS and ECMWF ensembles
differ somewhat on the timing of the deamplification of this feature . However,
this cooling trend is reflected in the reforecast tools which generally depict
lower chances for maximum temperatures exceeding the 85th percentile compared
to previous guidance. A slight risk of excessive heat remains issued for day 8
(Jun 9) where there is still a 20% chance of daytime temperatures exceeding 90
degrees F, as this heat signal is expected to dissipate by next weekend tied to
the weakening and northwestward shifting positive height departures.
As the negative mid-level height departures over the southwestern CONUS are
favored to shift eastward over the Interior West later in the period, both the
GEFS and ECMWF ensembles show more of a southerly flow component ahead of the
trough axis to promote warming temperatures over portions of the Great Plains
and Mississippi Valley. Since earlier this week, reforecast tools have been
fairly consistent in regards to the onset of the increasing warm signal over
southern Texas by next weekend, with increased chances of daytime temperatures
exceeding the 85th percentile and 100 degrees F along and near the Rio Grande
Valley. While the calibrated heat tools also support this growing warm signal,
uncalibrated temperature guidance from the GEFS and ECMWF appear rather tepid,
depicting a limited coverage of weak, positive temperature anomalies over
southern and eastern Texas through the middle of the period. As a result, no
temperature related hazards are issued at this time, but will continue to be
monitored in subsequent outlooks.
In the Midwest, the ECMWF and Canadian reforecast tools indicate at least a
40% chance of temperatures exceeding the 85th climatological percentile and 90
deg F. However, due to these tools not showing enhanced risk of reaching 95 deg
F and the lack of support from the GEFS, a corresponding heat hazard is not
posted. This heat event would likely be driven by absolute temperatures rather
than being moisture driven, thus reaching hazardous thresholds would be less
likely.
For precipitation, there is fair agreement in the ensembles featuring
surface low formation in the lee of the Rockies by the outset of week-2.
Uncalibrated daily precip amounts are on the low side; however reforecast tools
continue to indicate increased chances for 3-day amounts exceeding the 85th
percentile and 1 inch to support a slight risk of heavy precipitation over the
south-central CONUS during the first several days of the period. The moist,
low-level return flow favored also increases the potential for thunderstorm
activity in this highlighted region. Farther east, raw precipitation tools
continue to point to a strong uptick in rainfall and tropical moisture over
Florida and the Caribbean tied to a weakness in the subtropical ridge and a
broad area of low pressure early in the period. A slight risk of heavy
precipitation is added over the Florida Peninsula where there is better
agreement in the reforecast tools indicating at least a 20% chance of 3-day
amounts exceeding the 85th percentile, and the uncalibrated ECMWF depicting
>40% chances for 3-day totals exceeding an inch early in the period.
Developing drought concerns persist across parts of the central and eastern
Corn Belt and adjacent areas during week-2. Antecedent conditions are quite dry
(2-4 inches below normal precipitation since early May) from the Mississippi
Valley to the Central Appalachians. Although temperatures aren't expected to be
very exceptionally warm to increase evapotranspiration rates, many areas in the
Midwest and the Mid-Atlantic are now experiencing abnormal dryness based on the
latest drought monitor, with little indications for improvement given the
normal to below-normal precipitation favored through mid-June. Therefore, the
rapid onset drought risk remains highlighted and is expanded to include
additional areas in the Mississippi and Ohio Valleys, Great Lakes, and eastward
to the Central Appalichians.
Snowmelt continues across the western CONUS after accumulating a very large
and in some cases record-breaking snowpack, inducing river flooding especially
across higher elevations for some areas in the West. As snowmelt continues in
parts of the Sierra Nevada, Great Basin, and Northern Rockies, flooding may
continue to occur along some rivers and in areas adjacent to the higher
elevations. With increased chances for above normal precipitation predicted for
much of the western CONUS during week-2, possible flooding continues to be
highlighted. Due to decreasing snow water equivalent levels across portions of
south-central and northeastern Idaho, the corresponding flood hazard is removed
in the updated outlook, as well as over portions of southern Utah, where
flooding issues are expected to ease prior to the week-2 period. Flooding is
also expected to continue along the James River in South Dakota as river levels
have been very slow to recede due to saturated ground conditions and relatively
flat topography.
In the western Pacific, tropical cyclone Mawar is forecast to undergo
extratropical transition and become absorbed in the westerlies, where an
amplification of the mid-level pattern remains favored over the Bering Sea and
the Aleutians late in week-1. While the strength of troughing aloft and surface
low is expected to weaken by the onset of week-2, there is continued support of
strengthening pressure gradients associated with this pattern and slight risk
of high winds remains issued (Jun 9) across the Aleutian Islands and portions
of southwest Mainland Alaska.
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