Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
203 AM EDT Fri Jun 1 2018
Valid 12Z Mon Jun 4 2018 - 12Z Fri Jun 8 2018
Pattern overview and guidance evaluation
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The forecast period begins on Monday with an upper trough over the
Pacific Northwest, a ridge axis encompassing the central U.S., and
a developing trough over the eastern U.S. with a surface low
offshore. This overall synoptic scale pattern is expected to hold
through much of the upcoming week, with disturbances tracking
across the northern tier of the U.S. around the northern periphery
of the upper ridge that will be building over the southern plains.
In terms of the model guidance, the greatest uncertainty exists
over the northeastern quadrant of the nation early in the week
with two separate low pressure systems. The one of greatest
interest will be a possible nor'easter southeast of New England
through early Tuesday, and there has been a trend for this to be
closer to the coast and slower to depart the region. The
deterministic ECMWF, GFS, UKMET, and CMC are now northwest of the
ensemble means, and closer to the coast. Farther upstream across
the northern plains and Midwest states, the models are having
difficulty with the progression of embedded shortwaves in the
northern stream flow that eventually amplify the large scale
trough over the eastern U.S. The guidance continues to agree well
on the placement and amplitude of the upper ridge over the
southern plains.
In terms of the WPC forecast, some of the deterministic GFS and
ECMWF was incorporated for the first half of the forecast, and
then mainly ensemble means by next Thursday and Friday. Some
previous WPC continuity was used given the noteworthy changes in
deterministic model runs.
Weather highlights and hazards
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The best prospects for noteworthy precipitation across the
continental U.S. will be from the Great Lakes to New England in
association with the upper low and trough, along with a surface
low developing offshore. There has been a trend for heavier
rainfall from this coastal low to affect parts of the northeast
U.S., with the possibility of a late season nor'easter affecting
coastal New England for early next week. Another area of
concentrated showers and storms is expected across the Dakotas and
the Upper Midwest by the middle of next week as a disturbance
crosses near the Canadian border. Model guidance is also
signaling possible mesoscale convective systems (MCS) developing
from Oklahoma and propagating southeast in northwest flow aloft
early in the week.
In the temperature department, the heat wave across Texas and
Oklahoma is forecast to continue going into next week owing to the
building upper level ridge in place and dry conditions.
Widespread highs exceeding 100 degrees are expected as far north
as Kansas early next week, and a few locations may approach 110
degrees over western Texas. Some record high temperatures are
likely during this time. Above normal temperatures are also
expected across the Rockies and extending northward across the
north-central U.S. More pleasant temperatures can be found for
the Northeast U.S. and the Pacific Northwest, which will be under
the influence of the upper level troughs. After an unusually warm
month of May, the beginning of June appears to be below average
for temperatures next week from the mid-Atlantic and extending
northward to New England, with cooler northerly flow behind the
low pressure system offshore.
WPC medium range forecasts of 500 mb heights, surface systems,
weather grids, quantitative precipitation, and winter weather
outlook probabilities can be found at:
http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
D. Hamrick