736
FXUS21 KWNC 181835
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT April 18 2025

SYNOPSIS: During week-2, anomalous mid-level high pressure is forecast across
the central and eastern contiguous U.S. (CONUS), with an area of mid-level low
pressure predicted to move into the western CONUS. This set-up favors episodes
of heavy precipitation and increased potential for thunderstorms across the
Great Plains and Mississippi Valley. Due to excessive precipitation observed in
the Mississippi and Ohio River Valleys during the past few weeks, any
additional precipitation received may trigger flooding over these areas. Windy
conditions are possible over parts of the southwestern CONUS and High Plains
associated with the mid-level low.

HAZARDS

Slight risk of heavy precipitation for much of the Great Plains and Mississippi
Valley, Sun-Tue, Apr 27-29.

Slight risk of high winds over the southwestern CONUS and High Plains, Sat-Tue,
Apr 26-29.

Possible flooding for the Middle and Lower Mississippi, and lower Ohio Rivers.

Possible flooding for parts of the Great Plains and Mississippi Valley.

DETAILED SUMMARY

FOR MONDAY APRIL 21 - FRIDAY APRIL 25:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY APRIL 26 - FRIDAY MAY 02: At the outset of week-2, a stationary
front is forecast to enhance precipitation chances across the Mississippi
Valley and possibly into the Ohio Valley and Northeast. However, this feature
is predicted to weaken, with attention turning to a shortwave trough forecast
to enter the western CONUS. This system combined with the anomalous ridging
favored over the central and eastern CONUS is forecast to lead to renewed
increased chances of heavy precipitation and thunderstorms across the Great
Plains and Mississippi Valley. The GEFS and ECENS Probabilistic Extremes Tools
(PETs) depict some areas having at least a 20 percent chance of 3-day
precipitation totals exceeding the 85th climatological percentile and 1-inch
during the first half of the period, with the anomalous ridge over the central
and eastern CONUS supporting a more northward extent of the convective
potential into parts of the Northern Plains and Upper Midwest given
above-normal precipitable water values. Therefore, a slight risk of heavy
precipitation is forecast for much of the Great Plains and Mississippi Valley,
Apr 27-29.



With copious antecedent rainfall and recurring flooding concerns for portions
of the lower Ohio, Middle and Lower Mississippi Valleys, a possible flooding
hazard remains posted mainly along the Mississippi River given the potential
for new and renewed rises in water levels during week-2. Main channels are
already very high, and thus are unlikely to have large responses to additional
precipitation. Regardless, tributaries and streams will continue to be
susceptible to renewed flooding or flash flooding if additional rainfall
occurs. Due to heavy precipitation forecast for the coming days over parts of
the Southern and Central Plains and Middle Mississippi Valley, with little
reprieve favored before the heavy precipitation risk returns, a second possible
flooding hazard is posted for portions of these regions. Any locally heavy
precipitation into week-2 could cause new or renewed flooding or flash flooding
over the complex terrain of the Ozarks as well as bring renewed streamflow
rises in the highlighted region.



The shortwave trough moving into the West and associated negative height
anomalies early in week-2 favor increased wind speeds across much of the
Southwest extending into the High Plains where a slight risk of high winds
remains posted, Apr 26-29. The ECENS PET depicts these areas having at least a
20 percent chance of wind speeds exceeding the 85th climatological percentile
and 20-mph (25-mph over portions of the High Plains). The GEFS and ECENS
uncalibrated guidance also shows some areas with enhanced probabilities for
wind speeds exceeding 20-mph further justifying designation of the hazard.



The prevailing mid-level ridge supports increased chances of above-normal
temperatures across much of the central and eastern CONUS during week-2. While
temperatures are not expected to be hazardous, there is some indication that
temperatures may approach or even exceed 90 deg F across parts of the Southeast
and Florida based on the uncalibrated 0z GEFS and ECENS ensemble means.
Additionally, calibrated heat risk guidance from the ECENS depicts at least a
50 percent chance heat indices exceed the 90th climatological percentile over
some areas, and the National Blend of Models indicates elevated potential for
record daily maximum temperatures. While excessive heat thresholds are unlikely
to be met due to the time of year, precluding a related hazard, there is
considerable concern for a stretch of unseasonably warm weather across the
region.



Outside the CONUS, above normal precipitation and temperatures are
predominately favored over southern Alaska, with below normal temperatures over
northern Alaska and the Yukon of Canada tied to an anomalous ridge center over
the Chukchi Sea. This pattern is suggestive of seasonal river ice breakup being
delayed, though as temperatures continue to warm, the eventual river ice
breakup may lead to ice jams and associated flooding in the coming weeks. Over
the central Pacific, 500-hPa troughing is favored to develop underneath a north
Pacific ridge before deamplifying later in week-2. An accompanying area of
surface low pressure is expected to bring reduced trades mainly north of the
Hawaiian Island chain, which could result in locally heavy precipitation to the
northern windward islands.

FORECASTER: Thomas Collow

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