WPC Medium Range Archive
Medium Range Products Valid On:
(Day 7 PMDEPD: Valid 09/29/2022 to 10/03/2022)
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
346 PM EDT Mon Sep 26 2022
Valid 12Z Thu Sep 29 2022 - 12Z Mon Oct 03 2022
...Hurricane Ian is forecast to intensify over the eastern Gulf of
Mexico then slow as it tracks off the Florida Gulf coast later
this week, increasing the threat for excessive rain from Florida
into the Southeast among other tropical cyclone impacts...
Confidence is increasing in a slower Ian tracking over the
northeast Gulf near or along the Florida Gulf coast Wednesday into
Friday. The system is forecast to weaken prior to landfall, but
the slower system will increase the risk for excessive rainfall
for Florida into the Southeast. Please see the latest WPC and NHC
products for more information on Ian forecast and impacts.
Elsewhere, the progression of of an eastern Pacific trough/low
over the northern Rockies Thursday and the northern Plains over
...Guidance Evaluation/Predictability Assessment...
A slower and a bit farther east track to Ian from Thursday and
Friday then becomes more uncertain east-west with the 12Z ECM
farther west and the 12Z GFS farther east (and the 12Z UKMET even
farther east). However, all 12Z guidance has come in slower and
gaining less latitude this weekend before sliding east early next
week. Remarkable agreement between the 00Z ECMWF and 06Z GFS gave
confidence in relying on those models through Day 6 for both the
frontal progressions across the CONUS and QPF over the northern
Rockies and the heavy Ian-related QPF in the Southeast. That
agreement continues with the 12Z ECMWF/GFS, particularly for the
ridge developing up the West Coast Friday and low/trough this
weekend over the north-central Rockies. The 12Z CMC/UKMET continue
to differ from the GFS/EC consensus like they did at 00Z, so those
models were replaced with the GEFS and ECENS means for Days 6/7.
Hurricane Ian is forecast produce notable rainfall and wind
threats during the period to Florida and the Southeast. A stalling
front over FL will then lift north with the system. Strong high
pressure tracking from the Great Lakes and stalling over the
Northeast into Saturday and then reinforced with high pressure
from Hudson Bay to New England Sunday/Monday will help to enhance
the winds/onshore flow to the north of Ian. The heavy rain threat
lifts from northern Florida Thursday night through Friday, with
the QPF focus over the Carolina Coast Friday before lifting toward
and into, but possibly not through the Mid-Atlantic over the
weekend into Monday. The experimental Day 4 Excessive Rainfall
Outlook maintains Slight/Moderate Risk for northern Florida into
southeast Georgia. A Day 5 Moderate Risk has been raised from the
greater Charleston to greater Savannah metro areas with the Slight
Risk continuing for far northern Florida, much of Georgia, all of
South Carolina, and southern North Carolina.
The combination of anomalous moisture and the upper trough/low
emerging from the Northwest should produce areas of locally heavy
rainfall in portions of the Four Corners states and up the central
to northern Rockies Thursday/Friday. This spreads onto the
northern Plains Saturday into Sunday. Snow Levels drop to around
9000ft in the northern Rockies under this upper low.
Cloud cover/rain from Ian and Canadian High pressure farther north
will make most of the eastern CONUS with max temps as much as
10-15F below normal into this weekend. The northern High Plains
will be quite warm on Thursday with max temps least 15F above
normal. This moderates a bit as it shifts east over the rest of
the Northern Plains Friday/Saturday. The upper trough/low drifting
into the Rockies/High Plains will bring moderately below normal
highs in its vicinity Friday/Saturday with above normal
temperatures returning to the Pacific Northwest coast
Saturday/Sunday under the building ridge.
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
- Heavy rain across portions of the Southeast, the Mid-Atlantic,
and the Southern Appalachians,
Fri-Sat, Sep 30-Oct 1.
- Heavy rain across portions of the Southeast and the
Mid-Atlantic, Thu-Fri, Sep 29-Sep 30.
- Flooding possible across portions of the Southeast.
- Flooding occurring or imminent across portions of the Southeast.
- High winds across portions of the Southeast and the
Mid-Atlantic, Thu-Sat, Sep 29-Oct 1.
- High winds across portions of the Mid-Atlantic, Sat-Mon, Oct
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, experimental excessive rainfall
outlook, winter weather outlook probabilities and heat indices are