Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1151 AM EDT Thu Jun 27 2019
Valid 12Z Sun Jun 30 2019 - 12Z Thu Jul 04 2019
...Overview and Weather Highlights/Threats...
Upper ridging over and/or just south of Alaska will favor a
positively tilted mean trough over the Pacific Northwest, with
progressive and low amplitude flow prevailing downstream across
the northern U.S. Farther south an eastern Pacific into southern
Rockies ridge aloft will weaken a bit after Sun-Mon. At the same
time a central Plains/Midwest ridge will merge with another ridge
building westward from the Bahamas and settling over Florida/Gulf
of Mexico and the the Southeast. Between the western and eastern
ridges an upper weakness will drift from near the western Gulf
Coast into the southern half of the Plains.
This pattern will favor three primary areas of locally
moderate-heavy rainfall. Locations from just east of the northern
Rockies through the Great Lakes/Ohio Valley will be along/north of
a wavy mean frontal boundary which will combine with shortwaves
ejecting from the Pacific Northwest upper trough to promote
multiple convective episodes. Some convection could also be
strong to severe but predictability in specifics is low at this
time. Check SPC outlooks as the details come into clearer focus.
Rainfall could extend into the Northeast/Mid-Atlantic as a front
reaches those regions by Tue. The upper weakness drifting into
the southern Plains may bring some areas of enhanced rainfall to
locations from the western half of the Gulf Coast northward. The
most common theme in the guidance is for best focus to exist near
the Gulf Coast with lower confidence pinpointing any enhanced
activity farther north. Diurnally enhanced convection will
produce pockets of significant rainfall over Florida and portions
of the Southeast.
Expect the greatest temperature anomalies to be over parts of the
northern Plains/Upper Midwest on Sun and perhaps into Mon, ahead
of a front approaching the region. Some max/min readings (greater
coverage for mins) could exceed 10F above normal. Otherwise
anomalies over the lower 48 should be in the single digits during
the period. Warmest highs versus normal mid-late period should be
over the Mid-Atlantic/Southeast while the West and Plains will
likely see near to slightly below normal highs. Min temperatures
will tend to be near to above normal over most areas during the
period.
...Guidance/Predictability Assessment...
Over the past couple days the ECMWF/ECMWF mean, GEFS mean, and to
a reasonable degree CMC have settled into a good consistent
cluster with respect to holding the Pacific Northwest mean trough
in place for most of the period. Very low confidence small scale
features within the trough still provide opportunity for
meaningful detail changes though. For the second day in a row the
06Z GFS run is significantly more eager to eject the trough than
consensus or 00Z GFS and thus could not be used in the forecast
blend. The 00Z GFS also becomes somewhat quicker to eject the
embedded low that reaches the coast around Mon but the trough that
remains through the rest of the period is similar to the majority
cluster. Meanwhile consensus shows an upper low tracking from
northwestern Canada toward Hudson Bay, with the flow on the
southern periphery possibly pushing a cold front into the extreme
northern Plains. Again the 06Z GFS becomes the most suspect
solution for this upper low late in the period, pulling the track
to the west/southwest of other guidance. Other features exhibit
lower discrepancies. A 00Z operational model blend early in the
period, transitioning to 30-40% GEFS/ECMWF mean input along with
the models late, represents consensus well for significant
features through the period.
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