Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Thu Apr 04 2019
Valid 12Z Sun Apr 07 2019 - 12Z Thu Apr 11 2019
...Overview...
An ongoing progression of Pacific systems into and across the
Lower 48 will bring active weather to a decent percentage of the
country. The southwestern U.S./southern Rockies appear to be the
one area that should have fairly dry weather. A leading upper
trough over the central U.S. Sun and its associated surface system
will spread a broad area of precipitation across the eastern half
of the country Sun-Tue with some areas of heavy rainfall possible.
During that same time frame expect a strong jet aimed at the
northwestern states to bring areas of enhanced precipitation to
the northern half of the West Coast inland to the northern
Rockies. A dynamic upper trough forecast to crest the West Coast
by Tue will continue inland to push a main precipitation focus
eastward to the north-central Rockies then north-central
Plains/Mississippi Valley and eventually the Ohio Valley and Great
Lakes. There is an increasing guidance signal that this potent
trough may support strong central U.S. storm genesis Wed-Thu. This
presents a risk of wrapping enhanced snows from the Rockies to the
north-central Plains/Upper Midwest, albeit with marginally cold
air. Over the south-central U.S., guidance may be underestimating
an additional threat of strong to severe thunderstorms along a
trailing cold front. Meanwhile upstream, upper level trough energy
reaching the northeastern Pacific may also approach the West Coast
with some unsettled weather around next Thu.
...Guidance Assessment/Preferences...
The WPC medium range product suite was primarily derived from a
composite blend of the 00 UTC GFS/ECMWF and GEFS/ECMWF ensemble
means. These guidance options seem fairly well clustered with the
forecast evolution of mid-larger scale systems. A composite blend
mitigates recent issues with guidance to maintain acceptable
continuity with the embedded smaller scale systems and stream
interactions.
...Weather Highlights/Hazards...
Strong flow aloft across the Northwest will promote areas of
terrain-enhanced rain and higher elevation snow from northern
California and the Pacific Northwest into northern Rockies from
Sun into early next week. Current guidance suggests best potential
for heaviest activity will be centered along the West Coast near
the California/Oregon border and the Oregon Cascades. By Tue the
upper troughing moving into the West will begin to shift the best
moisture focus eastward into the Great Basin and northern-central
Rockies. Continued progression of this system should spread
precipitation across the north-central Plains, Mid-Upper
Mississippi Valley, and eventually Ohio Valley and Great Lakes by
Wed-Thu. Some activity may be heavy and areas with ongoing
flooding concerns will need to monitor this system. A period of
low level upslope flow may add to totals over the
eastward/northward facing slopes of the Rockies. In addition
stronger trends for Wed-Thu low pressure in latest guidance raise
the potential for strong winds to be an issue over some areas.
There is also a threat of snow in the northern periphery of the
wrapback precip shield from the n-central Plains to the Upper
Midwest.
The eastern half of the country will see a broad area of
precipitation with the system progressing eastward from the Plains
Sun onward. Ample flow of moisture from the Gulf will promote
areas of heavy rainfall. Best potential for highest totals will be
over/near the Lower Mississippi Valley and central Gulf Coast
region and southern Appalachians. Convection may be strong to
severe over southern areas. Check SPC outlooks as specifics become
better resolved over the coming days. Significant rainfall is also
possible from the Ohio Valley into northern
Mid-Atlantic/Northeast. There are still significant detail
uncertainties with this system so confidence in location/magnitude
of heaviest rainfall remains somewhat lower than desired. Snow
should be confined mostly to northern New England Mon-Wed in this
pattern as moisture advects northward into a cooled/receding
surface ridge.
The warm sector of the central-eastern U.S. system Sun/Mon will
offer some much above normal temperatures. Morning lows will be
particularly anomalous with many locations 15-25F above normal Sun
into Tue and some daily record warm low values may be challenged.
The main upstream system will then spread a period of anomalous
warmth across the Southwest then southern Plains and
South-Southeast U.S. next week.
Schichtel
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