Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
432 PM EDT Mon Oct 03 2022
Valid 12Z Thu Oct 06 2022 - 12Z Mon Oct 10 2022
A stubborn compact upper low/shortwave stuck over the Mid-Atlantic
region during the short range period will finally be departing off
the Northeast coast as the medium range forecast starts on
Thursday. In its wake, larger scale mean troughing should prevail
over eastern North America (led by a shortwave diving into the
Upper Great Lakes from Canada, possibly followed by a weaker
shortwave by Sunday-Monday) while a persistent upper ridge just
inland from the West Coast gradually retrogrades offshore. Despite
the somewhat amplified pattern, expect relatively quiet weather
conditions across most of the CONUS into the start of next week.
Exceptions will include some Southwest rainfall in response to
monsoonal moisture and a weak upper low settling just south of the
region, and a potent central/eastern U.S. cold front producing
some rain especially in the Great Lakes region along with
considerably cooler temperatures after its passage. The western
U.S./eastern Pacific upper ridge will support very warm
temperatures through the period.
...Guidance Evaluation/Predictability Assessment...
Latest models and ensembles maintain agreement for the general
pattern consisting of the western U.S. ridge retrograding into the
eastern Pacific as initial weak energy settles over parts of the
West, the mean trough prevailing over the eastern two-thirds of
the lower 48, and a weak Arizona/New Mexico upper low settling
over northern Gulf of California for a time before opening up by
Sunday or Monday.
Embedded details are more uncertain though. Models develop 12-24
hours or so of timing spread for the system affecting the
northeastern U.S. and southeastern Canada late this week into the
weekend. The 00Z ECMWF was fastest while the 00Z/06Z GFS were
slowest. Latest UKMET runs lean much closer to the slow side while
the 12Z CMC has trended somewhat faster than its 00Z run (now
closer to the ECMWF) and 12Z GFS accelerated to a compromise. Thus
it will take additional time to determine any conclusive trends.
Behind this system, 00Z through 12Z runs are showing an increasing
signal for another shortwave (possibly closed per the 12Z
UKMET/CMC) reaching the far northern tier by early day 6 Sunday.
This feature originates from around southern Alaska/northwestern
Canada on Sunday. There is enough agreement on its existence but
favor a conservative open wave depiction at this time since models
are inconsistent in its evolution. A blended approach looks good
for the weak energy dropping into the West (00Z CMC was extreme
with forming a closed low). Finally, current spread/run-to-run
variability suggest an intermediate solution for how late-period
Gulf of Alaska into Canada energy may break down the northern part
of the mean ridge. Based on guidance through 06Z, the updated
forecast started with an operational model composite for the first
half of the period and then trended to a half models/half ensemble
means blend by day 7 Monday. The primary continuity change was
introduction of the Sunday-Monday northern tier wave/frontal
system. QPF adjusted the 13Z National Blend of Models to reflect a
wider footprint for light amounts (mostly in the Great
Lakes/Northeast and southwestern U.S.) given the typically low
bias for light precipitation in the NBM.
The combination of persistent monsoonal moisture and an upper low
settling over the northern Gulf of California will produce diurnal
showers and thunderstorms over parts of the Southwest/southern
Rockies, with locally heavy rainfall possible in some spots.
Intensity and coverage may vary from day to day, with some
eastward expansion of rainfall possible by early next week as the
upper low opens up. To the north, a cold front shifting across the
Midwest and Great Lakes may bring some light rain mainly around
Thursday, and then lake enhanced showers in the westerly flow
behind the front Friday and perhaps Saturday.
Temperatures out West will be warm into early next week underneath
a blocky upper ridge, with daytime highs over the Northwest 10 to
15 degrees or so above normal. Despite the anomalies, the
resulting temperatures peaking in the 70s and 80s (90s for parts
of California) are unlikely to create any heat related hazards.
Conversely, Canadian high pressure spilling into the north-central
U.S. and expanding eastward behind the cold front will result in
much below normal temperatures shifting from the northern Plains
into the Midwest and into much of the East Thursday-Monday.
Daytime highs in some locations could be 15 to 20 degrees below
average (mainly Thursday-Saturday) while overnight temperatures
are forecast to drop into the 30s for many locations from the
northern half of the Plains into central Appalachians, and even
20s for North Dakota and northern Minnesota particularly Friday
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
- Flooding occurring or imminent across portions of the Southeast.
- High winds across portions of the Great Lakes and the Upper
Mississippi Valley, Thu-Fri, Oct
- Much below normal temperatures across portions of the Central
Plains, the Central Appalachians,
the Northern Plains, the Middle Mississippi Valley, the Southern
Appalachians, the Upper
Mississippi Valley, the Great Lakes, and the Ohio Valley, Sat-Sun,
Oct 8-Oct 9.
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, experimental excessive rainfall
outlook, winter weather outlook probabilities and heat indices are