Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
937 AM EST Sun Feb 24 2019
Valid 12Z Wed Feb 27 2019 - 12Z Sun Mar 03 2019
...Pattern Overview...
A strong mid-level positive anomaly starting in AK will drift
northeast into the Canadian Archipelago, forcing changes
downstream, such as a consolidating mid-level vortex in southeast
Canada which, sooner or later, should settle into the Labrador Sea
early next week. Overall, this maintains a zonal-ish flow through
the medium range period.
While zonal flow can lead to milder than climatological conditions
across the Lower 48, below average mid-level heights near and west
of a cold low dropped southeast into southeast Canada continue
over the northern Plains, promising continued colder than average
temperatures for the remainder of February into early March. Any
mildness should be generally constrained across the southern tier
of the country.
...Model Preferences...
The guidance showed very good agreement overall. For the
pressures, winds, and 500 hPa heights, used a blend of the 00z
UKMET, 00z Canadian, 00z GFS, and 00z ECMWF which incorporates
slowly increasing percentages of the 00z bias-corrected NAEFS mean
and 00z ECMWF ensemble mean with time. The remainder of the
weather grids, including QPF, used a more even blend of the
deterministic and ensemble mean guidance.
...Weather Highlights/Hazards...
Over the West, expect areas of enhanced precipitation (rain and
higher elevation snow) to extend from California through the Great
Basin and into the north-central/central Rockies. There will be
two main systems of note, one arriving around the start of the
period and bringing rain/snow during Wed-Thu and the next most
likely spreading moisture across the region during the weekend.
The second system's moisture axis should be somewhat southward of
the first. Highest totals during the period should be over the
Sierra Nevada range.
Around midweek modest shortwave energy/surface waviness may bring
an area of mostly light snow across the northeastern quadrant of
the Lower 48. Another small area of rain/snow may cross parts of
the Ohio Valley/Mid-Atlantic later in the week. Then guidance is
starting to show more similar ideas for potentially strong surface
development with low pressure reaching the Great Lakes around
Saturday morning and continuing northeastward thereafter. Highest
snow potential would extend across parts of the Midwest into the
northwestern Great Lakes with meaningful snowfall also possible
over New England. Expect rain farther south and some pockets of
locally moderate-heavy activity may be possible. Slightly better
potential for highest totals will be over the Gulf Coast states
but relative maxima may be possible over other parts of the East
as well.
Continue to expect very cold temperatures centered over and near
the northern half of the Plains. Wed-Fri readings will be extreme
enough at 10-30F below normal but a stronger surge of cold air Fri
into the weekend could bring some areas to 30-40F below normal
while less extreme cold anomalies spread farther south and east.
Meanwhile Pacific flow will keep min temperatures in particular
above normal over the southern 2/3 of the West. The southern tier
states should see above normal temperatures on average but with a
cooling trend next weekend.
Roth/Reinhart/Rausch
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