Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Thu Apr 25 2024

Valid 12Z Sun Apr 28 2024 - 12Z Thu May 02 2024

***Severe thunderstorms and heavy rain expected west of the lower
 and Mid-Mississippi Valley on Sunday, moving into the lower
 Mississippi Valley on Monday***


...General Overview...

The medium-range period will likely begin with a rather active
pattern Sunday morning as a low pressure system tracks northeast
across the central Plains with severe thunderstorms from the
central Plains eastward to the lower to mid-Mississippi Valley into
Monday. The upper pattern appears to become more zonal later next
week as the central U.S. trough lifts out and a moderately strong
trough passes through the Pacific Northwest and reaches into the
northern Plains. It appears that a deeper trough will edge into
the West Coast by midweek while Gulf moisture will tend to increase
and expand across the southern Plains.

...Guidance/Predictability Assessment...

The morning model guidance suite features good overall agreement
across the U.S. through much of the medium-range period. Models are
unanimous in lifting the upper trough and low pressure system
northeastward away from the Great Plains early next week but
solutions gradually show more diversity afterward as a moderately
strong upper trough moves through the Pacific Northwest into the
northern Plains. This is due to uncertainty on how fast the upper
trough will lift out of the Plains and how much the Pacific
Northwest trough will interact with the central U.S. trough.
Despite the uncertainty on the trough interactions, the ensemble
means are agreeing well that a more zonal pattern will be
established across the northern tier states midweek next week while
a deeper upper trough will edge toward the West Coast.

The WPC medium-range forecast package was based on a general model
compromise
of 40% from the 00Z ECMWF/EC mean, 40% from the 06Z GFS/GEFS, and
20% from the 00Z CMC/CMC mean, and leaning toward the ensemble
means by Days 6 and 7.


...Weather/Hazards Highlights...

The overall synoptic environment will be quite conducive for
multiple episodes of excessive rainfall across portions of the
central and lower Mississippi River Valley. There will likely be
multiple mesoscale convective systems to develop from the ArkLaTex
region to Missouri, and there is a good chance of training
convection given the slow overall progression of the frontal
boundary in conjunction with parallel flow to the trailing frontal
boundary. For the Day 4 period Sunday, the existing Slight Risk
is maintained from eastern Texas north-northeast across Arkansas
into southern Missouri where the QPF signal is highest in the
model guidance, where a multi-model signal for some 3-5 inch
totals is indicated. Storms training over the same areas with
locally higher totals are possible. There is still a good chance
for a future upgrade to Moderate Risk for portions of this region
if these model trends continue. The WPC forecast for QPF remains on
the lower end of the guidance spectrum given the influence from
the NBM. A Slight Risk area is also maintained on Day 5 centered
over northern Louisiana and into portions of adjacent states,
generally southeast of the Day 4 outlook area. The convergence
boundary is likely to linger across the region on Monday and fire
new rounds of convection, followed by an abatement in the coverage
and intensity of the convection going in Tuesday over this region.
The latest guidance has generally placed the highest QPF farther
north. The Slight was kept farther south in favor of the previous
ERO for this area.

Elsewhere across the U.S., widespread moderate to locally heavy
rain is expected from Minnesota to northern Michigan on Sunday as
the surface low lifts northeastward, and a Marginal Risk area is
planned to account for that on the Day 4 outlook. Colder
temperatures moving in across the Intermountain West and the
Rockies behind this storm system will likely result in continuing
snow showers for the higher mountain ranges of Wyoming and
Colorado, although becoming lighter. Rain and mountain snow is also
likely to make a return to the Pacific Northwest for the beginning
to middle of next week as the next shortwave trough arrives. By
Wednesday, showers and storms could once again increase in coverage
from Texas to the Central Plains.

Temperatures will also be making weather headlines as a major
warm-up is expected for a wide expanse of the country east of the
Rockies. Highs are expected to rise well into the 80s from the
Central/Southern Plains to the Ohio Valley and then reaching the
East Coast by Monday, perhaps reaching 90 degrees in some cases.
These readings are on the order of 10-20 degrees above normal for
late April, and there may be some daily record highs set. Overnight
lows will also be summer-like with lows only falling into the 60s
for many of these same areas. A modest cool-down is likely by mid-
week from the Great Lake to the Ohio Valley and Northeast, and
still remaining warm and humid across the south-central U.S. to the
Carolinas. The opposite holds true for the Intermountain West on
Sunday with readings 5-15 degrees below average, before things
moderate going into early next week.

Kong/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