Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1100 AM EST Mon Feb 25 2019
Valid 12Z Thu Feb 28 2019 - 12Z Mon Mar 04 2019
...Pattern Overview...
Expect progressive and broadly cyclonic mean flow aloft over the
Lower 48. As an upper ridge initially extending from the Gulf of
Alaska into the Arctic drifts into northwestern Canada, a deep
south-central Canada upper low will descend toward the Upper Great
Lakes region this weekend and continue rapidly eastward. Flow
around this low may interact with energy from a Pacific Northwest
coast upper low that opens up as it ejects inland. The combination
of these features still offers some potential to produce an Ohio
Valley/Great Lakes into Northeast storm system Fri into the
weekend, but guidance has become more uncertain with this feature
and latest WPC progs have backed off on system strength. Meanwhile
another Pacific system will likely reach the West Coast by the
weekend. Anticipate highest precipitation totals over favored
terrain from CA to the central Rockies and with less certainty for
the eastern third of the nation, while much below normal
temperatures persist over the n-central U.S.
...Guidance Evaluation/Preferences...
Models and ensembles offer reasonable forecast clustering for
mid-larger scale systems effecting the nation, with a noticable
exception mainly over the eastern third of the country. Guidance
has increasingly broken into two forecast camps Friday into the
weekend with the GFS/FV3 and GEFS members showing substantially
more storm threat over the eastern third of country than the
ECMWF/UKMET/Canadian or ECMWF ensembles. Recent storm history, WPC
continuity, and consistent run-run GFS/FV3/GEFS guidance has
become more suspect considering expected pattern
transition/deamplification and ECMWF/UKMET/Canadian or ECMWF
ensembles guidance that has strongly trended away from having
short range closed low energy eject so bodily downstream. Given
uncertainty, WPC progs have backed away somewhat from system
development and associated heavier snow/rain threats.
Overall, opted tp composite blend the 06 UTC GEFS mean with the 00
UTC ECMWF ensemble mean to create the WPC surface fronts/pressures
and 500mb progs for the whole domain.
...Weather Highlights/Hazards...
During Thu-Fri the initial flow of moisture over the West will
bring areas of rain and higher elevation snow to about the
northern 2/3 of the region with a brief drying trend progressing
from west to east. The next Pacific system should start to bring
moisture into California by the start of the weekend with
rain/mountain snow then spreading eastward into the Rockies. For
the 5-day period expect an area of enhanced precipitation from
n-central California/southwest Oregon to the north-central/central
Rockies with highest totals likely over windward terrain of the
Sierra Nevada range.
Late this week diffuse shortwave energy may assist in producing
rainfall of varying intensity over the southern half of the East
while the northern fringe of the moisture shield could contain a
little light snow from the Mid Mississippi Valley into the
northern Mid-Atlantic. The potential development of a organized
low reaching the Northeast this weekend would initially spread
snow across parts of the northern Plains late this week with
precipitation coverage then expanding over the eastern states, but
confidence in this system is reduced as guidance forecast spread
increases. If deeper development occurs, best snowfall potential
would extend from the Midwest through the Great Lakes to New
England. Pockets of locally moderate-heavy rainfall may be
possible over the South, but thus far with no coherent signal in
the guidance for precise location/magnitude. This system may
produce strong winds over some areas, but not to the magnitude of
the system currently affecting the Great Lakes/Northeast. Expect a
period of lake effect snow in the wake of this system while
lingering moisture along southern latitudes may produce some rain
near the Gulf Coast into early next week. In the wake of this
system, a strong surge of very cold air will spread south and east
across the central/eastern U.S. from late week onward, with the
coldest anomalies spreading out from the northern Plains. Expect
best potential for daily records to be for cold daytime highs over
the northern-central Plains and Midwest during the weekend.
Schichtel
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation and winter weather outlook
probabilities are found 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