Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Tue May 10 2022
Valid 12Z Fri May 13 2022 - 12Z Tue May 17 2022
...Lingering blocky pattern to extend record heat from the
Southern Plains/Lower Mississippi Valley to the Midwest/Northeast
late week along with episodes of central U.S. convection and an
emerging onshore rainfall focus to the Carolinas...
...Developing heat threat for California and the Southwest from
the weekend into next week while heat persists eastward over far
southern tier areas...
...Overview...
Guidance continues to show the large scale upper pattern
transitioning from a blocky regime late this week toward an
eastern Pacific trough, western U.S. into High Plains ridge, and
eastern U.S. trough. A broad area of much above normal
temperatures into late this week from the southern Plains into
Great Lakes/Northeast, with numerous daily records possible, will
eventually moderate over the northern two-thirds of the country as
a wavy front over the Plains (a possible focus for at least some
locally heavy rainfall) pushes farther eastward ahead of the
approaching trough. Meanwhile an upper low reaching the Southeast
by Friday will quickly open up as it lifts northward, spreading
rainfall into and north from the Carolinas. The upper ridge
building into/through the West will moderate initially chilly
temperatures over the Northwest while bringing a period of very
warm to hot weather across the southern half of the West Saturday
onward, connecting with the heat expected to persist over and near
the southern Plains. Highs may challenge daily records over some
locations across these areas.
...Guidance Evaluation/Preferences...
The 12Z/18Z operational model composite used as the basis of the
updated forecast early in the period transitioned to a blend of
the 18Z GFS/12Z ECMWF and their ensemble means by mid-late period.
The UKMET/CMC have continued their general trend toward recent
GFS/ECMWF ideas for the storm expected to reach just north of the
northern Plains as of early Friday. However the UKMET/CMC have
been straying from the other guidance for the ultimate evolution
of trailing shortwave energy initially over the Northwest, pulling
it farther south than consensus. This trait of those models
contrasts with recent GFS/ECMWF and GEFS/ECMWF mean trends toward
somewhat less amplitude of the eventual eastern trough aloft and a
stronger upper ridging building back over the southern
Plains--leading to greater persistence of the heat over that
region. Meanwhile individual models and ensemble members diverge
for details of eastern Pacific shortwave energy pushing into
western North America. In general the latest GFS runs have leaned
toward bringing lower heights into the West versus most other
guidance but not to an extreme degree versus typical
predictability/error ranges at the time frame of interest. Also
the new 00Z UKMET bears some similarity to the GFS. These
shortwave details will be important for determining the coverage
and intensity of precipitation over the Northwest.
...Weather/Threat Highlights...
Within the broad area of above normal temperatures from the
southern Plains through Great Lakes and Northeast on Friday, the
best potential for some daily records will be across the southern
tier and Great Lakes/Northeast. Highest anomalies of plus 10-20F
or slightly higher should be across northern areas from Friday
into the weekend. Meanwhile potential record heat could persist
over/near eastern Texas into next week, and may expand over more
of the southern Plains/South early next week.
The ridge building over the West will lead to a pronounced warming
trend during the weekend, with broad coverage of highs 10-15F
above normal over the southern half of the region by Sunday and
persisting into Tuesday. This heat could challenge daily record
highs over some southern areas and ultimately increase
temperatures over the southern Plains once again next week. The
Pacific Northwest and northern Rockies will be chilly on Friday
with highs 5-15F below normal, followed by some moderation.
Shortwaves ejecting from the eastern Pacific upper trough and
associated surface fronts may produce multiple episodes of
precipitation over the Northwest. Some of this activity could be
locally moderate/heavy depending on exact details which have low
predictability at this time.
A wavy front extending south from an initial storm system over
southern Canada may hang up over the Upper Midwest through
southern Plains for a time late this week as it awaits the arrival
of dynamics from the Northwest, leading to the possibility of some
moderate to heavy showers and thunderstorms over or just west of
the Mississippi Valley. Then this front will become more
progressive as upper troughing heads toward and into the East.
Some rainfall along the front could still be fairly intense but
the greater progression may temper maximum totals over the East.
The trailing part of the front should stall and may lift back as a
warm front early next week, potentially serving as a focus for
some convection. The Southeast upper low that quickly opens up
Friday into Saturday will spread an area of rain into the
Carolinas and areas to the north. Some localized enhancement will
be possible over the Carolinas/Virginia but rapid opening of the
upper low should tend to decrease the focus of moisture farther
northward.
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, experimental excessive rainfall
outlook, winter weather outlook probabilities and heat indices are
at:
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