Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 PM EDT Fri Oct 4 2024

Valid 12Z Mon Oct 07 2024 - 12Z Fri Oct 11 2024

...Potentially hazardous heat will persist across the Southwest
through Monday...

...Chances for heavy rainfall across the Florida Peninsula will
increase into next week...


...Overview...

The upper pattern over the CONUS next week should settle into a
slower-evolving pattern dominated by mainly large scale features.
An upper ridge slowing moving from the Western to Central U.S. will
support much above normal temperatures while a trough settling
over the East (anchored by an upper low that may track over or near
New England) will bring a cooler trend. The leading edge of a
Pacific trough will produce gradual height falls over the Pacific
Northwest into late next week and bring some precipitation to the
northern parts of the region. Farther south, expect the main
rainfall focus over the Lower 48 to be over parts of Florida, due
to the combination of abundant tropical moisture in addition to
Gulf
of Mexico low pressure 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,
with the 00Z/06Z GFS runs north of the CMC/EC, but a general model
compromise seemed to provide a good middle ground solution. Timing
of the next trough into the West and weaker shortwaves ahead of it
become uncertain toward late next week. The 00Z ECMWF was a bit of
a western/slower outlier with the trough axis compared to the
other operational models and many AI/ML models. The WPC forecast
started with a blend of the deterministic 00/06Z models and
increased the proportion of the ensemble means into the latter part
of the period as overall spread increased.

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. Recent 12Z
ECMWF/GFS/UKMET runs have converged in showing a developing
tropical or subtropical system moving northeastward through the
Gulf, crossing the central Florida Peninsula sometime on Wednesday,
and moving into the western Atlantic for later week. This general
agreement is relatively new and is thus uncertain, but tropical
development is seeming more likely than it did with the 00/06Z
model suites. In coordination with NHC, did discount the 12Z CMC
with its low spinning in the Gulf for ten days, since this was an
outlier and seems unlikely given the close proximity to a frontal
boundary that should help steer it east at least eventually. Even
within the EC/GFS/UK general cluster, there are differences with
the track and central pressure of the low, which affects the QPF
amounts. This cycle's WPC QPF amounts trended down across the Tampa
Bay to Orlando corridor compared to the NBM because of the 00/06Z
models were south with heavier amounts, but this may have been a
mistake considering the 12Z models trended up in those areas.
Uncertainty in tropical development across the Gulf remains high.
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 funnel into a couple of west-east
oriented wavy fronts 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/Monday-Tuesday. Heavy rain potential may continue into
Wednesday at least. Possible tropical system approach could further
enhance precipitation, so stay tuned to NHC and WPC forecasts for
updates.

Elsewhere, the frontal system moving into the Northeast on Monday
should generate moderate rainfall there, and some lake-enhanced
rain is possible in westerly flow behind it through midweek. 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 on Monday, with some
highs at least 10-15F above normal, more into the Plains by
Tuesday-Friday when some northern locations could reach 20-25F
above normal. Expect numerous daily records for warm minimum and
maximum temperatures, especially over the Southwest through Monday.
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 Monday to
near or somewhat below normal 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.


Tate/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