790
FXUS02 KWBC 151907
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
307 PM EDT Sat Jun 15 2024

Valid 12Z Tue Jun 18 2024 - 12Z Sat Jun 22 2024

...Record-breaking heat from the Midwest to the East Coast...
...Heavy rainfall threat along the central-western Gulf Coast and
parts of the northern tier into central Plains...


...Overview...

Guidance continues to show a strong upper ridge building over the
East through midweek and then gradually dropping a little southward
and elongating to cover the south-central Plains and southern
Rockies by the end of the week. This ridge will support a broad
area of hot and dry weather next week, with the greatest anomalies
and potential for daily (and possibly monthly) records extending
from the Ohio Valley/Lower Great Lakes into the northern Mid-
Atlantic and Northeast. Between this ridge and mean troughing along
or just inland from the West Coast, the area from the northern
half of the Plains into Upper Midwest may see multiple episodes of
heavy rainfall from a combination of a persistent wavy mean front,
anomalous moisture, and upper level impulses. To the south of the
upper ridge, upper level energy and abundant deep moisture north of
an area of low pressure (see NHC for updates) will bring the
potential for a period of heavy rain along and near the western
half of the Gulf Coast.

...Guidance/Predictability Assessment...

Most aspects of the guidance are fairly agreeable during the first
couple days or so of the period, aside from smaller scale detail
differences. By mid-late period there is more notable spread among
the dynamical guidance and machine learning (ML) models, which were
generally farther north with any semi-organized system (with a
corresponding northward/northeastward shift of rainfall emphasis).
Per coordination with the National Hurricance Center, favored the
farther south cluster of solutions with the center/centroid but
note that the heavy rainfall threat will likely extend well north.

Early-period model consensus favored a blend of 00Z/06Z models for
the forecast through midweek, followed by an increasing weight of
the 06Z GEFS and 00Z ECens mean with time. This helped to maintain
the upper ridge definition in the east.

...Weather/Hazards Highlights...

Locations from the central Plains through the Upper Midwest will
be one area of focus for heavy rainfall potential during the Days
4-5 Excessive Rainfall period covering Tuesday through Wednesday
night. During Day 4 expect convection to expand southward along a
cold front anchored by a northern tier into Canada surface wave,
with the latest majority guidance cluster favoring some small
southward expansion of the existing Slight Risk area again
(southward toward central Kansas). By Day 5 the trailing part of
the cold front may stall and eventually lift northward while
abundant moisture persists over the region. There is more spread
for convective details, yielding only a broad Marginal Risk area at
this time. The wavy front may remain nearly parallel to upper flow
through the rest of the week, maintaining the potential for
additional episodes of heavy rainfall from the northern half of the
Plains into the Upper Midwest from Thursday onward.

In the Gulf, guidance continues to show an area of deep tropical
moisture and some degree of upper level energy shifting westward
across the western half of the Gulf of Mexico and vicinity during
the Days 4-5 ERO period. There are still significant differences
for specifics of associated heavy rainfall, but a composite of
dynamical/machine learning guidance continues support a Slight Risk
area along the western two-thirds of the Louisiana coast into
eastern Texas coast on Day 4, and along the entire Texas coast on
Day 5. The southern part of the Texas coast has drier antecedent
conditions but rain rates may still be high enough to cause some
runoff issues. Rainfall along and inland from the western Gulf
Coast should trend less heavy later in the week while upstream
energy underneath the elongating central-eastern U.S. upper ridge
could lead to some rebound in rainfall over Florida/western Gulf
region but with low confidence in the details. Total rainfall per
the guidance is quite varied, showing a high-end potential but
confidence is low.

The strong upper ridge building over the East next week will tend
to produce the greatest temperature anomalies from the Midwest and
Ohio Valley/Lower Great Lakes into the northern Mid-Atlantic and
Northeast, with multiple days of readings 10-20F above normal. This
would translate to highs well into the 90s, along with lows in the
upper 60s to upper 70s providing little overnight heat relief.
Daily records will be possible within the above areas, with some
isolated monthly records possible as well. With some typical detail
differences, the axis of greatest temperature anomalies in the
current forecast shows some similarity to the 1994 heat wave that
was observed around the same time in June. Some flattening of the
northern part of the ridge by the end of the week may make the heat
a little less extreme over New England, while the central Plains
may trend a little hotter (but with single-digit positive
anomalies). In contrast to the eastern heat, lingering upper
troughing will support highs 10-20F below normal over parts of the
Interior West/northern High Plains on Tuesday with moderately cool
readings over the northern-central High Plains Wednesday. Elevation
snow will exit the northern Rockies where a heavier/wet snow will
accumulate between the end of the short range period into the first
part of the medium range. Then rising heights aloft will bring a
warmer trend to most of the West, with the region likely seeing
highs 5-12F above normal by Friday-Saturday. Moist easterly flow
should lead to two or three days of below normal highs over the
western Gulf Coast and southern High Plains by mid- late week.

Fracasso/Rausch


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





























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