516
FXUS21 KWNC 081851
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 08 2025

SYNOPSIS: An area of mid-level low pressure over the western Contiguous U.S.
(CONUS) at the outset of week-2 is favored to shift eastward, leading to
increased potential for heavy precipitation and new or renewed flooding to
portions of the Southern Plains and Lower Mississippi Valley and the
surrounding regions. Multiple days of anomalously warm temperatures may reach
hazardous thresholds at times across parts of the Rio Grande Valley.

HAZARDS

Slight risk of heavy precipitation for portions of Southern Plains, Lower and
Middle Mississippi, Lower Ohio, and Tennessee Valleys, Fri-Mon, May 16-19.

Slight risk of excessive heat for portions of the Rio Grande Valley, Fri-Sun,
May 16-18.

Flooding Possible for portions of the Southern Plains and Lower Mississippi
Valley.

DETAILED SUMMARY

FOR SUNDAY MAY 11 - THURSDAY MAY 15:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY MAY 16 - THURSDAY MAY 22: Ensemble means from the GEFS, ECENS, and
CMCE for 500-hPa heights depict an amplified trough coming ashore over the West
Coast during week-1 and spreading over the western CONUS by the outset of
week-2, along with vigorous lee cyclogenesis and a deep surface low over the
Great Plains. This synoptic setup favors moist southerly flow off the Gulf and
into the Southern Plains and Mississippi Valley, increasing the potential for
heavy precipitation across a region already impacted by repeated rounds of
excessive rainfall. The GEFS, ECMWF, and CMCE Probabilistic Extremes Tools
(PETs) for heavy precipitation all indicate at least a 20% chance of 3-day
precipitation totals exceeding the 85th climatological percentile and at least
1 inch for much of the forecast period across some portion of the Southern and
Central Plains and into the Lower and Middle Mississippi Valley. There is
better agreement among the tools today for the area of heaviest precipitation
to be centered across the ArkLaTex region but with precipitation chances
extending through much of the middle Mississippi Valley for the beginning and
middle of week-2. Therefore, a slight risk of heavy precipitation is posted for
this region for May 16-19.



The southern portions of the highlighted slight risk of heavy precipitation
have had widespread amounts of four or more inches of rain in the past seven
days and eight or more in the last 30. The current 7 day QPF shows a dry period
for the week-1 period which may allow time for soils to recover but another
significant round of precipitation could once again lead to increased chances
for flooding. Therefore, a flooding possible risk is forecast for parts of the
Southern Plains and Lower Mississippi Valley.



As this system evolves, enhanced southerly flow is anticipated to develop over
the Great Plains. There are indications of this from the GEFS and ECMWF PETs
where the forecast maximum wind speed, particularly over the Southern Plains,
indicate at least a 20% chance of 3-day maximum wind speeds exceeding the 85th
percentile through the middle of the forecast period. However, absolute wind
speeds depicted in these tools do not reach hazardous thresholds so no
associated hazard is posted at this time.



Positive 500-hPa height departures are favored over much of the southwestern
CONUS during the week-1 period, prior to the development of the previously
discussed amplified trough, which may bring excessive heat to parts of the
Southwest. These positive height anomalies are forecast to spread into the
Southern Plains by late week-1 and into week-2. Anomalously warm temperatures
are indicated by multiple models for the lower Rio Grande Valley late in week-1
and extending into early week-2 as a result of this upper-level ridge. The PETs
for maximum temperature show a strong signal for anomalous warmth in percentile
space and show 20-40% chances for temperatures to exceed 100 degF and approach
105. The NWS heat risk tool indicates major heat risk developing along the Rio
Grande at the end of week-1. Multiple days of temperatures near excessive heat
thresholds may result in expanded heat risk by the beginning of week 2.
Therefore, a slight risk of excessive heat is highlighted for portions of the
Rio Grande Valley, May 16-18. Models are showing elevated dew points along the
Gulf Coast in addition to the building heat which may lead to elevated apparent
temperatures in the area, although tools have lower support for reaching
hazardous thresholds at this time. Southern Texas will need to be monitored
throughout week-2 as the ECENS is forecasting normalized positive 500-hPa
height anomalies persisting or even increasing in magnitude by the end of
week-2 which could prolong enhanced  chances for excessive heat across the
region.



As spring continues and daily incoming solar radiation flux totals increase,
ice-bound rivers are beginning to break up in Alaska. There is no associated
hazard posted at this time but this situation will be closely monitored in the
coming days and weeks as conditions can quickly change, leading to the
potential for ice jams and associated flooding.

FORECASTER: Ryan Bolt

$$