071
FXUS02 KWNH 100714
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
313 AM EDT Mon Jun 10 2024

Valid 12Z Thu Jun 13 2024 - 12Z Mon Jun 17 2024

...Heat focus from the West/Southwest to the Southern Plains this
week as a Multi-Day Excessive Rainfall Threat looms for Florida...


...Guidance/Predictability Assessment...

Model and ensemble forecast spread has overall decreased over the
past few guidance cycles over much of the lower 48 with a series
of progressive northern stream systems and within a more flow
separate southern stream, slowly bolstering forecast confidence.

Guidance solutions also seem a bit better clustered with an
overall evolution of lowering heights, and highly anomalous
moisture axis, and energy over the Gulf of Mexico into Florida, but
important differences remain to offer uncertainty. Tropical system
development is not forecast by the latest from the National
Hurricane Center, but regardless, confidence in an excessive
rainfall threat for central and southern Florida is increasing.

Accordingly, the WPC medium range product suite was primarily
derived from a composite blend of the 18 UTC GFS and 12 UTC
ECMWF/Canadian/UKMET for Thursday-Saturday. Opted for smaller input
from the models in lue of more consistent GEFS/ECMWF ensemble means
at longer time frames amid growing uncertainties. The blending
process tends to mitigate variance by limiting detail consistent
with individual feature predictability. This also acts to maintain
good WPC product continuity that remains generally in line with a
similar blend of latest 00 UTC guidance.

...Weather/Hazards Highlights...

A protracted period favorable for heavy rains should continue
through later week for the Florida Peninsula as well above normal
tropical moisture pools along and south of a wavy/stalling front
with aid from upper level impulses/energy back through an unsettled
Gulf of Mexico. Uncertainties remain, but there is increasing
confidence in the looming threat with any activity/moisture feed
emanating over the Gulf. Storm total rainfall (including what falls
before the medium range period even starts) of 7-12 inches, with
locally higher amounts, is possible. WPC Excessive Rainfall Outlook
Slight Risk areas remain in place for the central to southern
Florida Peninsula. Enhanced rainfall and local runoff issues may
subsequently lift/work over the Gulf to the Central Gulf Coast and
vicinity over time to monitor.

Meanwhile, an increasing precipitation threat across much of the
central and northern Plains emerges late period as amplified
southern stream troughing ejects northeastward into the region
from the Southwest to focus lift/intstability. SPC shows a threat
for severe weather and a WPC Day 5/Friday ERO Marginal Threat area
has been introduced for the central High Plains.

Elsewhere, leading and dynamic northern stream upper trough energy
approach and passage is expected to fire convection along/ahead of
a wavy/pooling surface front from the Midwest through the
Northeast later this week. WPC introduced ERO Marginal Threat
areas from the vicinity of Chicago Thursday through northern New
England Friday as the parallel upper flow and convective axis may
lead to some repeat cells and local runoff issues.

As for anomalous temperatures, an amplified mean upper ridge slated
to slowly shift from the West/Southwest to the south-central U.S.
and parts of the East will continue to produce much warmer than
average temperatures. The highest temperature anomalies of 10-20F
above normal are forecast for the Great Basin, shifting eastward as
the week progresses into the Rockies and Plains. It will be
especially hot across the Desert Southwest and South Texas given
elevated Heat Risk and Heat Index threat values.

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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