Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
231 PM EDT Sat May 4 2024


As a main closed upper low tracks out of the West with additional
energies reaching the West Coast, widespread precipitation will
include some enhanced snow potential given cooled temperatures. The
higher elevations of the Great Basin into the Intermountain
West/Rockies will see May snow as the medium-range period begins
Tuesday morning. Vigorous troughing aloft in conjunction with a
potent cold front will lead to windy conditions and a threat of
high winds from much of the Rockies to High Plains as the
cyclogenesis should be well under way across the northern High
Plains into Tuesday. Precipitation is forecast to be ahead of the
system as it spreads across the northern Plains to Midwest Tuesday
into midweek. Rainfall on the west side of the strong surface low
could be heavy across eastern Montana into the Dakotas given strong
upper-level support for lift with a slowdown of the storm track.
However, this region is not particularly sensitive to flooding
concerns, and instability should be limited wrapping around the
low. A WPC Excessive Rainfall Outlook (ERO) Marginal Risk area
remains in place Day 4/Tuesday and into Day 5/Wednesday for this
area given the potential for protracted heavy rain, but likely
without widespread significant flooding impacts. Convective
rainfall is forecast to shift east into the Great Lakes and Ohio
Valley Tuesday into Wednesday with system progression and
intercepting return flow. The Marginal Risk ERO remains farther
east into the Great Lakes, Ohio Valley and down toward the mid-
Mississippi Valley for Day 4/5 as the fronts push farther toward
the east and northeast. A Slight Risk threat area remains in the
vicinity of the Mid-South Day 5/Wednesday as energy interacts with
a wavy and stalling front and combines with pooling moisture and
instability. The Storm Prediction Center also highlights a broad
area of the Midwest to Mississippi Valley/parts of the Southern
Plains for severe weather potential Tuesday and Wednesday. Beyond
Wednesday, a favorable pattern will continue for rain and
thunderstorms across the south-central states/Mid-South and
broadly onward to the East where downstream energy track may
support moderate late next week coastal low development, likely
off New England.

Much cooler than average maximum temperatures will slowly moderate
while spreading next week from the West to the northern Plains
as the closed upper low ejects eastward. But farther southeast,
mean upper ridging will meanwhile spread quite warm pre-frontal
temperatures from the South through the Appalachians/Mid-Atlantic
to threaten record seasonal values. 90s are forecast to become more
widespread across the southern tier, with temperatures over 100F
(and even higher heat indices) into south Texas and the possibility
for the first excessive heat days of the year Tuesday-Thursday
before moderation by Friday and Saturday.

Santorelli/Schichtel