Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Fri Oct 25 2019
Valid 12Z Mon Oct 28 2019 - 12Z Fri Nov 01 2019
...Well below average temperatures expected for much of the
West/Plains next week...
...Overview and Guidance/Uncertainty Assessment...
Guidance still shows a strong northeastern Pacific mean ridge
aloft (extending into northwestern North America at times)
supporting an amplified mean trough over the lower 48, while
another ridge persists off the southeastern U.S. coast across the
Florida Peninsula and into the Gulf of Mexico.
While there is consensus on the general pattern, models and
ensembles remain conflicted over the character of the CONUS
trough. The latest cycle yields little change in overall
clustering with the GFS/GEFS generally on their own in showing a
more progressive trough digging into the central U.S. by Tue-Wed
versus remaining guidance that has the strong western Canada flow
dropping into the West. Teleconnections relative to the strong
positive height anomaly center just off the Alaska Panhandle in
the multi-day means support a more positively tilted mean trough
such as what the ECMWF cluster depicts. In addition the pattern
already established plus recent verification and historical model
biases all appear to add up to a higher probability that the
general ECMWF/ECMWF mean/CMC/UKMET scenario should be more
correct. Recent trends/biases suggest that the 12Z ECMWF could be
a little slow with its closed low, favoring a blend with the ECMWF
mean and prior ECMWF run as well as the 12Z CMC. However the new
00Z CMC has come in with an even slower upper low. Within the
ECMWF cluster there is a signal for the ejecting western
trough/upper low to generate what could be a fairly potent area of
low pressure somewhere within the Midwest/Ohio Valley/Great Lakes
region into Canada by the latter half of the week. Among
solutions depicting this feature there has been considerable
spread and run-to-run variability so confidence in specifics is
fairly low. For the purposes of the manual forecast the 12Z CMC
and ECMWF mean along with the 00Z/24 ECMWF offered the most
similar cluster to reflect the general potential for wave
development. By late in the period the GFS and especially GEFS
mean are also questionable in their depiction of a weaker upper
ridge rebuilding over the northeastern Pacific versus the
ECMWF/ECMWF mean/CMC.
...Weather Highlights/Threats...
Areas from the Interior West through the Plains will see the
coldest temperature anomalies in the coming week. A strong front
dropping south from Canada early in the week will likely bring
highs down to 20-40F below normal, especially over parts of
Montana/Wyoming/Colorado, for Tue-Wed. Some areas will already be
20-30F below normal on Mon. Readings over the central two-thirds
of the lower 48 should moderate somewhat by next Fri but remain
well below normal. The cold temperatures Mon-Wed in particular
may challenge daily records for lows and/or cold highs. Some of
this chilly air may reach southern California and the southern
Rockies. Strong high pressure building over the northern and then
central Rockies will support a period of strong winds to its south.
Within this pattern expect the best potential for some meaningful
snow to extend over parts the northern two-thirds of the Rockies
and then across the central Plains and into the Upper
Midwest/western Great Lakes. Ejection of a fast-moving lead
shortwave may bring one area of snow from the central Rockies
northeastward during the early part of the week. Canadian energy
dropping into the West should bring another area of snow
south-southeast across the Rockies, with any areas of snow to the
east/northeast during Wed-Fri sensitive to precise track and
strength of possible low pressure. Consult the latest WPC day 4-7
winter weather probabilities for highlighted areas. Assuming a
solution closer to the ECMWF cluster verifies, the front over the
Plains will likely hang up for a time before progressing eastward
later in the week. This would allow for an increasing flow of
moisture into the eastern half of the country and the potential
for areas of heavy rainfall.
Rausch
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:
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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml