Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
154 AM EDT Mon Jun 17 2019
Valid 12Z Thu Jun 20 2019 - 12Z Mon Jun 24 2019
...Overview and Guidance/Predictability Assessment...
Latest guidance indicates a persistent blocking pattern across
Canada into the northern US with the southeast Canada trough
slowly giving way to an upper ridge moving into the Great Lakes
early next week. Further upstream, a closed low drifting east
from the the northern Rockies crosses the northern Plains this
week. The low treats into Canada next weekend into early week,
with the next mid level circulation drifting southeast from the
northeast Pacific into Vancouver Island and possibly Wa State next
Mon 24 Jun. The 12-00z GFS has followed its traditional fast bias
by being faster than the 18z GEFS Ensemble Mean, 12z ECMWF
Ensemble Mean and operational ECMWF in moving the circulation
onshore and inland.
Consensus shows a closed anticyclone over the Pacific west of
northern CA that remains slowly moving through next weekend.
Teleconnections from this anomalously strong high in the northeast
Pacific lead to a downstream trough over the northern Plains.
The models are hinting that the ridge/embedded anticyclone
retrograde and drift west next weekend into early next week, which
would in turn allow the next western wave to come into the Pacific
northwest and have the trough reform there early next week.
The forecasts used a blended approach giving more weight to the
ensemble means of the 12z ECMWF and 18z GEFS Ensemble Means, with
less weighting to the operational 12z ECMWF/18z GFS, which
forecast a more progressive upper trough in the northern Plains
than the ensemble means of the 18z GEFS and 12z ECMWF.
The 18z GEFS Mean and 12z ECMWF Ensemble Means continue to show
better than average agreement over the northeast Thu and Fri
(ensemble means clustered well with the surface low track and the
18z GFS north of the means and 12z ECMWF south of the means), so
more weighting was given to the Ensemble Means of the 18z GEFS and
12z ECMWF. The 12z UKMET was the southern outlier with the
cyclone track Thu and Fri across the mid Atlantic states and
coastal waters and was given no weighting.
...Sensible Weather Highlights/Threats...
The low pressure departing the Oh Valley Thu towards the northeast
should bring widespread showers/embedded thunder across the lower
Lakes/New York/New England which tapers as the system departs Fri.
During Thu expect showers/storms to spread into the northern and
north central Plains to the mid and Upper Mississippi Valley. On
Fri 21 Jun and Sat 22 Jun another couple of rounds of
showers/storms near where moisture and instability focus across
eastern OK/southeast KS/ northwest AR up into the mid-upper MS
Valley and upper Great Lakes, as well as the northern Plains. On
Sun 23 Jun to Mon 24 Jun rounds of showers/storms are forecast to
occur across the mid MS Valley to the Oh Valley and Great Lakes,
spreading into the central Appalachians.
Over the West, the models have trended cooler over MT on day 3 Thu
and day 4 Fri 21 Jun with southwest MT having a core of
temperatures 15 to 20 degrees below normal. The cold air spreads
gradually east across the northern Plains, as on Sat the core of
the colder air is forecast across eastern MT and WY and spreading
into the western Dakotas/western NE with highs of 10 to 15 degrees
below normal.
An area of above normal temperatures is expected to be Texas for
days 4-5, which then cools with a frontal passage days 6-7, with
northwest Texas and the panhandle flipping to below normal next
Sun and Mon 24 Jun. The central US trough builds up the southeast
ridge with above normal temps next weekend into Mon 24 Jun
expected for coastal SC across southeast GA and much of Fl.
Petersen
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