677
FXUS02 KWNH 070637
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
237 AM EDT Mon Oct 7 2024

Valid 12Z Thu Oct 10 2024 - 12Z Mon Oct 14 2024


...Hurricane Milton should clear Florida by Thursday...


...Overview...

By the start of the period on Thursday, Hurricane Milton should be
beginning its extratropical transition and exiting the Florida
peninsula. Much of the heavy rainfall should be offshore but some
lingering backside showers are possible still across eastern parts
of Florida. Elsewhere, an initial central U.S. ridge will continue
to bring much above normal temperatures but should suppress with
time as a Pacific shortwave moves into the region. Troughing should
build again late period across the East, as a strong low in the
Gulf of Alaska sends amplified troughing towards the Northwest.


...Guidance/Predictability Assessment...

Model guidance remains still very uncertain with Milton into the
medium range period. Although the consensus (and the official NHC
forecast track) show Milton exiting Florida by the start of the
period, some of the slower pieces of guidance (GFS and CMC) still
show Milton over or approaching the Florida Gulf Coast at that
time. The official NHC track was closest to the 12z ECMWF so that
was the favored model early in the forecast period.

Elsewhere across the CONUS, models show good agreement on the
overall large scale pattern through Friday. By the weekend, there
are still timing differences with the first shortwave into the
Northwest. The CMC is quickest with this with quite a different
evolution as it moves into the Rockies and central U.S.. The
ensemble means show more agreement with the GFS and ECMWF. A weak
shortwave should dive south and amplify troughing over the East
again Sunday into next Monday and the guidance actually shows
fairly good agreement on this, but with lingering questions on
amplitude.

WPCs forecast for tonight favored a non-CMC blend for the first
half of the period (anchored by the ECMWF which was closest to the
official NHC track for Milton). Gradually increased blending of the
ensemble means late period to mitigate increasing uncertainty.


...Weather/Hazards Highlights...

The current official forecast for Milton has it just off the east
coast of Florida by early Thursday, so much of the associated heavy
rainfall should also be offshore by then. There is still a fair
amount of uncertainty and some potential heavy rainfall may still
be impacting northeast parts of Florida into Thursday so a marginal
risk remains for that region on the Day 4 Excessive Rainfall
Outlook. Depending on Milton`s exact track, some heavy rainfall to
the north of the system may clip the Southeast coast so that will
need to be watched.

Elsewhere, a front passing through the Pacific Northwest by
midweek should produce some light rain and nonzero chances of snow
in the highest elevations. Then another round of precipitation is
likely to come into the West with upper troughing on Friday, for
moderate amounts of rain and some higher elevation snow in the
Pacific Northwest. Precipitation amounts into the Interior West
late week-weekend are more uncertain related to the evolution of
the trough.

A western-central U.S. upper ridge will continue to promote an
extended period of well above normal temperatures with highest
anomalies likely for the northern Plains on Thursday, and some
locations should reach 20-30F above normal as highs in the 80s may
extend to the Canadian border. Northern stream troughing and a cold
front could push the greatest warm anomalies southeast into the
central Plains and Mid/Upper Mississippi Valley Friday- Saturday.
Meanwhile height falls slowly pushing in over the West Coast will
support a trend toward near normal temperatures by Wednesday or
Thursday. However, temperatures around 10 degrees above normal in
the Southwest could set additional daily records though the
temperatures have moderated compared to recent days and the short
range. Meanwhile, cooler than average temperatures are forecast
across most of the East as upper troughing sets up near the East
Coast, with some potential frost/freeze concerns across portions of
the Appalachians and interior Northeast early Thursday. Expect
temperatures to moderate next weekend as the upper low scoots out
of the region, but cool again early next week underneath another
trough.


Santorelli


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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