Valid Thursday October 12, 2023 to Wednesday October 18, 2023
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT October 04 2023Synopsis
: Confidence is increasing regarding
an active southern stream early in week-2, which favors enhanced precipitation
chances across portions of the Southeast, particularly Florida. Today’s models
are not depicting as much of a northward component compared to yesterday
resulting in relatively lower precipitation amounts inland across the Tennessee
Valley, allowing the Rapid Onset Drought (ROD) risk to remain in place. Toward
the middle of week-2, interaction with northern stream energy may lead to the
development of a surface low pressure system near the Northeast bringing
enhanced chances for heavy precipitation up the Eastern Seaboard. While
increased precipitation chances are still likely across the Pacific Northwest
throughout week-2 due to mid-level low pressure over the Northeast Pacific,
daily precipitation totals are not forecast to reach hazards thresholds.
- Slight risk of heavy precipitation across
portions of the central Gulf of Mexico coast, Florida, the Southeast, and the
southern Mid-Atlantic, Thu-Sat, Oct 12-14.
- Slight risk of heavy precipitation across portions of the Mid-Atlantic and
Northeast, Fri-Sun, Oct 13-15.
- Slight risk of much below normal temperatures across portions of western
Mainland Alaska and the Alaska Peninsula, Thu-Sat, Oct 12-14.
- Rapid Onset Drought (ROD) risk over parts of the Lower Mississippi and
Tennessee Valleys, and Southern Appalachians.
For Saturday October 07 - Wednesday October 11: WPC Days
3-7 U.S. Hazards For Thursday October 12 -
Wednesday October 18:
Today’s dynamical models are depicting a more
amplified 500-hPa height pattern during week-2 compared to yesterday, with
troughing favored across the eastern CONUS, ridging over the western CONUS, and
another trough over the eastern Pacific and Alaska. The trend toward more
troughing in the East leads to increasing confidence for heavy precipitation.
Additionally an active southern stream is forecast, with moisture from tropical
systems in the Eastern Pacific being ejected eastward toward the Gulf of Mexico
and Southeast by the start of week-2. By the middle of the period, interaction
with the trough over the East may pull some of this moisture northward, with
the 0z ECMWF ensemble favoring surface low pressure to develop across the
Northeast around Oct 14 bringing a substantial precipitation event to parts of
the region. The 0z GEFS is further offshore, and would spare the northeastern
U.S. from the heaviest precipitation. The ECMWF and GEFS Probabilistic Extremes
Tools (PETs) indicate at least a 20 percent chance 3-day precipitation totals
exceed the 85th percentile and 1-inch extending from the Southeast up through
parts of the Northeast, with higher probabilities in the ECMWF PET given the
higher precipitation amounts forecast, particularly across Florida and the
Northeast. Given the uncertainty regarding multiple interacting features, only
slight risks of heavy precipitation are posted across the Eastern Seaboard.
Further, around the New York Metropolitan area and southern New England heavy
precipitation and flooding in the past week along with additional precipitation
forecast during week-1 favor a sensitive area for additional precipitation in
week-2. Two separate areas are highlighted to address the favored temporal
progression. The first is across the Central Gulf of Mexico Coast, Southeast,
and southern Mid-Atlantic for Oct 12-14, and the second extends northward
through the remainder of the Mid-Atlantic and Northeast for Oct 13-15.
The potential system across the Southeast favors cutting back the Rapid
Onset Drought (ROD) risk across the Southeast close to the Gulf of Mexico
coast. However, both the ECMWF and GEFS ensembles do not bring much
precipitation northward into the Tennessee Valley, instead sliding most of the
moisture eastward across the Southeast and Florida, and then potentially up to
the Northeast. Therefore, the Tennessee Valley is not forecast to have as much
precipitation as points farther south and east, allowing the ROD risk to remain
over this region.
Persistent mid-level troughing is forecast over the Northeast Pacific,
which favors elevated chances for rounds of precipitation across the Pacific
Northwest throughout week-2. The ECMWF PET has backed off its elevated
probabilities for 3-day precipitation reaching the 85th climatological
percentile early in the period, and while probabilities in the GEFS PET remain
above 20 percent, precipitation totals in the uncalibrated guidance are not
particularly noteworthy, and the strongest atmospheric river signal based on
the GEFS and ECMWF Integrated Vapor Transport tool occurs during week-1. Due to
these decreasing signals, the slight risks for heavy precipitation and high
winds are discontinued across the Pacific Northwest. Although generally wet
conditions are favored due to the onshore flow pattern, particularly across
coastal Washington, it is less likely daily totals in week-2 reach hazards
Persistent mid-level troughing forecast across Alaska favors below-normal
temperatures across much of the state. The ECMWF and GEFS PETs continue to
indicate at least a 20 percent chance of minimum temperatures falling below the
15th climatological percentile and 20 deg F across much of western Mainland
Alaska and the Alaska Peninsula, supporting a slight risk of much below normal
temperatures, Oct 12-14. This could lead to increasing freeze-up of rivers and
lakes. As this trough retrogrades later in week-2, chances for heavy
precipitation are likely to increase across Southeast Alaska. However, hazards
criteria is not forecast to be reached.
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts