Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 AM EDT Fri Apr 4 2025

Valid 12Z Mon Apr 7 2025 - 12Z Fri Apr 11 2025


...General Overview...

A major improvement is coming to the areas that are getting
hammered by extremely heavy rainfall and severe weather Friday and
into this weekend. An amplifying upper level trough over the Great
Lakes and Ohio Valley region will accelerate a cold frontage
passage, with the boundary exiting the East Coast on Monday. Drier
and much cooler conditions will arrive behind it and likely remain
through much of the upcoming week. Meanwhile across the western
half of the country, a couple of shortwaves will pass through the
northwestern states, and then an upper level ridge tries to build
northward across the Rockies by the end of the week with a
reinforcing downstream trough across the east-central U.S.

...Guidance/Predictability Assessment...

The latest model guidance initially indicates good overall
agreement across the Continental U.S. for Monday, but differences
are already becoming apparent off the Pacific Northwest Coast with
the arrival of the next trough. A nearly multi-deterministic model
blend works well as a starting point for this time. By Tuesday,
the GFS and to a lesser extent the GEFS mean become faster and
stronger with the low pressure system developing across the Plains,
and this trend continues going into the middle to end of the week
as well.

Examination of the machine learning guidance from the ECMWF and
teleconnections with positive/negative 500mb height anomalies over
the North Pacific and North Atlantic strongly support the idea of a
slower trough evolution and progression across the Eastern U.S. for
the second half of the week. This falls more in line with the
ECMWF/ECENS/CMC solutions and the WPC forecast follows this
preferred approach, in contrast to the much faster GFS. There is
also growing model spread with shortwave energy approaching the
Pacific Northwest late in the period, so an ensemble mean approach
works well for this region by Thursday into Friday. The use of the
ECENS was increased to about half by next Friday, which still
maintaining about 25% each of the ECMWF and CMC.

...Weather/Hazards Highlights...

The heavy rainfall potential decreases quite a bit to begin next
week in comparison to what is expected this weekend. However, there
will still be an axis of deep moisture over the coastal plain of
the Southeast states ahead of the cold front, with areal 1-2 inch
totals possible from southern Georgia to the Hampton Roads area of
southeast Virginia, mainly between 12Z Monday and 00Z Tuesday,
where a Marginal Risk of excessive rainfall is in effect for the
new Day 4 period. With the exception of the central and southern
Florida Peninsula, the threat of heavy rainfall should be over by
Tuesday across the remainder of the country with no risk areas
needed. If future models trend higher with QPF over South Florida
during this time, it is possible a Marginal Risk area may
eventually be needed there.

Elsewhere across the country, rain and mountain snow makes a return
to western Washington and Oregon courtesy of onshore flow and a
couple of shortwave trough passages, but this does not look like a
major event at this time. Lighter precipitation crosses the
Northern Plains and Midwest midweek, and the next good chance of
rainfall arrives across the Eastern U.S. by Friday as a surface low
approaches the region.

In terms of temperatures, much cooler conditions are coming for the
Eastern U.S. after the strong cold front exits the East Coast
Sunday night/Monday morning. Afternoon highs are likely to be on
the order of 15 to perhaps 25 degrees below early April averages on
Tuesday from the Ohio Valley to the eastern Great Lakes,
compliments of the upper low overhead. Readings return closer to
average by late in the week for the East Coast states. Meanwhile, a
warm pattern is expected for the Western U.S. through the week with
both daytime highs and overnight lows about 10-20 degrees above
average, with the greatest anomalies over the Great Basin.

Hamrick


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw