118
FXUS21 KWNC 061851
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 06 2024

SYNOPSIS: Mid-level high pressure over the West Coast and mostly zonal flow
over the contiguous U.S. (CONUS) results in a relatively tranquil period of
weather for week-2. At the outset of week-2 a stalled frontal boundary over the
Gulf Coast leads to the potential for heavy precipitation for portions of the
Southeast U.S.

HAZARDS

Slight risk for heavy precipitation for portions of the Southeast U.S.,
Tue-Thu, May 14-16.

DETAILED SUMMARY

FOR THURSDAY MAY 09 - MONDAY MAY 13:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR TUESDAY MAY 14 - MONDAY MAY 20: At the outset of week-2 ensemble models
favor moderate ridging (troughing) over the West Coast (Great Lakes) as
depicted by 500-hPa height anomalies. The GEFS favors a much deeper trough over
the East with the axis centered over the Appalachians, while the ECMWF features
a much shallower trough over the Great Plains. Model solutions dampen both
features over the course of week-2, with weak positive height anomalies and
mostly zonal flow over the contiguous U.S. (CONUS) by the end of the forecast
period.



While there are significant differences among model solutions in the timing and
location, there is good consensus between various models with regard to the
potential for heavy precipitation. Both the GEFS and ECMWF Probabilistic
Extremes Tools (PETs) indicate at least a 20% probability of 3-day accumulated
precipitation exceeding the 85th percentile and 1 inch for portions of the
Southeast U.S for May 14-16. The ECMWF is especially bullish, with much wider
coverage of the area indicated for 1 inch total and over 2 inches possible for
portions of the Louisiana coast east to the Big Bend of Florida. There are some
indications that heavy rainfall may persist beyond May 16, but model solutions
diverge even more so, thus the hazard posted does not extend further into
week-2. Although much of this area highlighted for a risk for heavy
precipitation has been in a rain deficit and soils are becoming parched, most
of the precipitation is anticipated to be able to infiltrate into the soil
column due to soils in the area being sandy. Therefore a potential flooding
hazard is not issued at this time, although localized ponding and urban flash
flooding is possible.



In Alaska, as we move into the middle of May snowmelt season is underway and
frozen rivers are beginning to break up. This leads to the potential for river
flooding related to ice-jams. We continue to monitor the situation but
currently there are no indications of impending major river break-ups or
serious threat of ice-jamming so no flooding-related hazards are posted at this
time.

FORECASTER: Danny Barandiaran

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