617
FXUS02 KWNH 080709
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
308 AM EDT Sat Jun 8 2024

Valid 12Z Tue Jun 11 2024 - 12Z Sat Jun 15 2024

...Hot temperature shift from the West/Southwest to the Plains next
week as downstream heavy convective rainfall threats affect the
south-central states and from the Gulf of Mexico into Florida...


...Overview...

There is now better agreement in the guidance that an elongated
upper low over southern-eastern Canada will split early next week
with a trough moving through the Northeast into Tuesday and a
compact closed low getting left behind over south-central Canada
and the far northern U.S. tier. This energy should linger before
becoming absorbed by an additional shortwave energy approach from
western Canada. This progresses eastward mid-late next week with
troughing extending southward through the East.

Slow moving southern stream energy will keep unsettled conditions
and heavy rainfall potential particularly across the southern
Plains and lower Mississippi Valley early-mid next week, with an
inherent stronger threat signal for a multi-day wet period across
the Florida Peninsula along with building energies and convection
to monitor over a warmed Gulf of Mexico.

Upper ridging over the West/Southwest will gradually work into the
south-central U.S. with summer heat as a closed low works slowly
to the Southwest from the tropical East Pacific. Meanwhile, the
pattern will favor multiple but mostly dry Pacific upper trough and
cooling frontal intrusions across an unsettled Northwestern U.S..

...Guidance/Predictability Assessment...

Recent guidance forecast spread and run to run continuity issues
have drastically improved over the past few run cycles for at least
the first half of the upcoming medium range forecast period. This
bolsters forecast confidence back to near normal levels overall,
albeit still with standard and widespread warm season variances
with convective focus with local interaction and placement.

Accordingly, the WPC medium range product suite was primarily
derived from a composite blend of reasonably well clustered
guidance from the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian models
valid for Tuesday into Thursday. The latest 00 UTC models remain
in line for this period. Growing forecast spread seems manageable
but sufficient to favor a switch to better compatible guidance from
the GEFS/ECMWF ensemble means at longer time frames to best depict
the more predictable pattern/weather features and keep continuity.

...Weather/Hazards Highlights...

A wavy front across the south-central Plains and vicinity will
combine with slowl moving upper energy to continue a threat for
heavy rainfall into Day 4/Tuesday from wettened Oklahoma to
northern Texas, with additional threat shifting into the lower
Mississippi Valley into Day 5/Wednesday. WPC Excessive Rainfall
Outlook (ERO) Marginal Threat areas are depicted for each day. A
multi-day period favorable for heavy rains will also develop
across the Florida Peninsula starting Tuesday as well above
moisture pools along/south of a the wavy/stalling front with some
aid from weak upper level impulses/energy. There is a lot of
uncertainty in the details and much of the state is in a drought.
Still, some threat for high rain rates exists, and its possible
much of the threat may manifest for more susceptable urbanized
areas. Day 4/5 WPC ERO Marginal Risk areas have been introduced to
include the central and southern Peninsula to account for the
uncertainty, with a looming threat into later next week as well
there and with any activity/moisture feed eminating over the Gulf.

An amplified mean upper ridge slated to slowly shift from the
West/Southwest to the south-central U.S. will continue to cause
much warmer than average temperatures. The highest temperature
anomalies of 10-20F above normal are forecast for the Great Basin,
warming a bit and expanding eastward as the week progresses into
the Rockies and Plains. Temperatures will also rise a few degrees
in the Desert Southwest to bring some temperatures back above 110F,
with heat risk threat levels mostly at moderate to major levels.
Heat should build again across south to south Texas as well, with
heat indices back up to around 110.

Schichtel


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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