Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
346 PM EDT Fri Jun 07 2019
Valid 12Z Mon Jun 10 2019 - 12Z Fri Jun 14 2019
...One or more episodes of heavy rainfall and flash flood/flooding
threats possible over parts of the Appalachians/East Coast states
next week...
...Overview and Guidance/Predictability Assessment...
During Mon-Wed guidance agrees in principle that initially weak
Pacific shortwave energy reaching western North America by early
Mon will steadily amplify toward the east-central U.S. as a ridge
builds into the western part of the continent. This evolution
will occur behind a couple leading features--a Southeast
U.S./eastern Gulf trough and separate northern stream shortwave.
The overall combination will lead to one or more periods of
enhanced rainfall over some areas of the East. By Thu-Fri details
aloft over much of the Lower 48 become increasingly uncertain but
most models/ensembles show a general theme of diffuse shortwave
energy moving into the West while the amplified/reinforced eastern
trough that persists into Thu becomes more shallow on Fri as it
lifts northeastward into Canada.
From day 3 Mon into day 5 Wed a blend of the 06Z GFS/00Z ECMWF
(and some varying weighting of the 00Z UKMET, 06Z GEFS mean, 00Z
ECMWF ensemble mean and continuity) represented the synoptic
consensus well, while yielding an intermediate solution for
important smaller scale differences that are within typical error
ranges--and have below average predictability--for the time frame
of interest. In particular some of these differences affect the
location/intensity/duration of heavy rainfall over the East.
Broadly speaking most models and ensemble means have shown fairly
stable evolutions over the past 24-36 hours with no pronounced
trends evident. In this scenario, a consensus solution often
performs best.
During the latter half of the period there are multiple detail
questions that arise: whether the sharpening trough energy
reaching the Mississippi Valley around midweek closes off a low
for some period of time (a solution somewhat in the minority thus
far), the evolution of energy over Ontario, and the particulars of
multiple pieces of energy that will comprise the overall diffuse
shortwave trough moving into the West. Increased weighting of the
06Z GEFS mean and 00Z ECMWF ensemble mean guidance helped to
downplay the less confident details within the more agreeable
large scale evolution. This resulted in only some minor changes
to the previous forecast mostly in system timing.
...Sensible Weather Highlights/Threats...
Expect highest rainfall totals for the full Mon-Fri period to be
over an area encompassing the eastern Great
Lakes/Appalachians/East Coast states. Early in the week a
north-south front heading into the East and wavy front over the
Southeast will provide focus for rainfall. The trailing front and
embedded wave(s) will likely stall over the Southeast Tue-Wed and
finally be dislodged as the upper trough amplifying into the East
brings another surface low/frontal system into and through the
region. Over the central third of the U.S. there will likely be
areas of showers/storms with some moderate to heavy amounts but on
a more localized scale. Low level upslope flow may enhance
rainfall over the southern High Plains early in the week and a
frontal system/low pressure may bring rainfall to portions of the
northern half of the Plains and points east from Mon night or Tue
through midweek. The shortwave energy moving into the West late
in the week may promote scattered convection with some activity
possibly reaching the Plains as well.
The upper ridge building into the West early-mid week will bring
very warm to hot temperatures to the region, with fairly broad
coverage of plus 10F and greater anomalies Mon-Wed. Readings will
begin to moderate later in the week as heights aloft decline.
Expect highest temperatures Tue-Wed with locations along the
Medford-Portland corridor seeing the best potential for highs 20F
or more above normal. Daily records for highs/warm lows will be
possible over the West Coast states as temperatures climb into the
90s and perhaps near or just over 100F which will likely be the
hottest temperatures so far this year. Meanwhile the pattern will
tend to favor below normal temperatures over most of the central
U.S. aside from a possible trend toward normal by Fri.
Clouds/rainfall should produce a decent area of minus 10-20F
anomalies for highs over the southern High Plains on Mon (only in
the 70s). The East will see above normal mins early in the week
ahead of the lead front but otherwise should see near to below
normal min/max readings as the frontal systems lift through the
region.
Fracasso/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
Hazards:
- Heavy rain across portions of the Northeast, the
Central/Southern Appalachians, the Mid-Atlantic, the Great Lakes,
and the Ohio Valley, Mon, Jun 10.
- Heavy rain across portions of the Southeast, the
Southern/Central Appalachians, and the Mid-Atlantic, Tue-Wed, Jun
11-Jun 12.
- Flooding possible across portions of the Mid-Atlantic and the
Southern Appalachians.
- Flooding occurring or imminent across portions of the Plains,
the Mississippi Valley, the Great Lakes, the Northern Rockies, the
Northern Great Basin, and the Ohio Valley.
- Flooding likely across portions of the Central Plains and the
Central Great Basin.
- Excessive heat across portions of the Southern Plains, Mon, Jun
10.
- Much above normal temperatures across portions of the
Central/Northern Great Basin, the Northern Rockies, California,
and the Pacific Northwest, Mon-Thu, Jun 10-Jun 13.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Tue-Wed, Jun 11-Jun 12.
- Heavy rain across portions of the Alaska Panhandle, Mon-Wed, Jun
10-Jun 12.
- High winds across portions of the Aleutians, Tue-Wed, Jun 11-Jun
12.
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