985
FXUS02 KWNH 050641
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
240 AM EDT Sat Oct 5 2024

Valid 12Z Tue Oct 08 2024 - 12Z Sat Oct 12 2024


...Heavy rainfall becoming more likely across the Florida
Peninsula into next week...


...Overview...

An upper trough (anchored by an upper low that may track over or
near New England) will settle over the East for a few days next
week as an upper ridge upstream tracks from the West to Central
U.S. bringing a period of climatologically warm weather. By later
next week, the leading edge of a Pacific trough will produce
gradual height falls over the Northwest with some generally light
precipitation to accompany. The main rainfall focus over the CONUS
will be over parts of Florida, due to the combination of abundant
tropical moisture in addition to a Gulf of Mexico disturbance and a
front draped across the peninsula.


...Guidance/Predictability Assessment...

Guidance continues to show some typical differences in the details
for the evolution of the upper trough settling over the East and
the anchoring low. There is some question on timing and placement
of the upper low and the associated surface low mid- to late week,
but a general model compromise seemed to provide a good middle
ground solution. Timing of the next trough into the West next
Thursday and beyond becomes very uncertain with the CMC much
quicker than the better consensus. The GFS is also faster than the
ECMWF but still within the overall spread. Prefer a blend of the
ECMWF, GFS, and ensemble means for this feature as details become
very unclear late period.

The main feature of interest during the period though is still
evolution of a possible tropical system in the Gulf of Mexico. Lows
may spin up along the frontal boundaries in the eastern
Gulf/northern Florida/western Atlantic while another feature that
is more concerning for forming a possible tropical system (possibly
partially consisting of remnant energy from what was Eleven-E in
the East Pacific) may evolve over the western Gulf. Guidance has
generally come into better agreement on the development of some
sort of tropical or sub-tropical system tracking into Florida but
remain very uncertain on the timing and north-south placement of
that. There does seem to be an uncertain slightly faster and more
northerly trend. The CMC is by far the slowest piece of guidance
and was not preferred. WPC worked with a blend of the GFS and ECMWF
which were solidly in the middle of the spread and consistent with
latest NHC thoughts as well. Please consult the NHC outlooks for
the latest information on features of interest over the Gulf.


...Weather/Hazards Highlights...

The heaviest rainfall potential for next week will be over the
Florida Peninsula, with low pressure (that could be tropical or
subtropical) over the Gulf of Mexico shifting eastward with time
but with considerable model variability on placement and timing.
Regardless of tropical development, enhanced/above average tropical
moisture will be in place and funneled into a wavy front draped
over the state. This should produce multiple days of moderate to
heavy rainfall, and Marginal Risks are in place in the EROs for
much of the Florida Peninsula for Days 4-5/Tuesday-Wednesday. If
the trends continue, it is likely at least a slight risk will be
needed, but confidence is still too low on where to place that at
these lead times. Heavy rain potential may continue beyond
Wednesday, depending on timing of any potential tropical system.

Elsewhere, the upper low over/near New England should allow for
some lake- enhanced rain within in westerly flow across the Great
Lakes. A mean frontal zone with one or more embedded waves should
reach near the northern Pacific Northwest by early-mid week,
producing some periods of light to locally moderate rain and non-
zero chances of snow in the highest elevations. Widely scattered
showers are possible at times across the Four Corners states into
parts of the south-central U.S., but anything beyond light rain is
unlikely.

The strong and persistent western-central U.S. upper ridge will
promote an extended period of well above normal temperatures over
that part of the country. Gradual eastward drift of the ridge axis
will shift the highest anomalies from the West into the Plains by
Tuesday with some northern locations could reach 20-25F above
normal. Height falls slowly pushing in over the West Coast will
support a trend toward near normal temperatures by Wednesday or
Thursday. Temperatures over most of the East should cool starting
as upper troughing sets up near the East Coast. This may lead to
frost/freeze concerns across portions of the Upper Great Lakes
region and interior Northeast, with the timing around the median to
a bit late for the first frost/freeze of the season.


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





$$