Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
424 PM EDT Tue Mar 12 2019
Valid 12Z Fri Mar 15 2019 - 12Z Tue Mar 19 2019
...Overview and Guidance Assessment/Preferences...
Expect broad troughing aloft to prevail over eastern North America
downstream from a ridge that builds over the Canadian Rockies and
Interior West. Over the eastern Pacific a leading weak shortwave
will likely pass into/around the building ridge while a trailing
trough should amplify and sharpen as it approaches the West Coast.
There are essentially two larger-scale guidance disagreements.
The first involves energy initially moving into the Southwest and
eventual possible interaction with northern stream shortwave
energy amplifying into the East. Even compared to its ensembles
the 00Z CMC is rather extreme with its combined strength and fast
progression of the Southwest shortwave. Then a fairly strong
depiction of an amplifying Midwest shortwave by Sun-Mon in the CMC
(similar to the 00Z UKMET through the end of its run late Sun)
allows for a phased trough which by early Mon leads to a surface
low tracking closer to the East Coast than most other guidance.
Relative to the full array of ensemble members the 00Z CMC is on
the fringe of the envelope but not extreme enough to be considered
an outlier. The CMC scenario has sufficiently low probability not
to include in a most-likely single deterministic forecast.
However the potential for evolution to change from the current
consensus represented by the ECMWF/GFS and its ensemble means will
have to be monitored.
The second issue involves the weakening Pacific shortwave energy
that reaches western North America by around Sun. In varying ways
the latest GFS/GEFS runs (and FV3 GFS) are more enthusiastic about
the shortwave's strength passing through/around the mean ridge and
then westward/southwestward elongation of this energy into the
first half of next week. By then this evolution leads to a
flatter upper trough over the East versus most other guidance.
The 06Z GFS/GEFS mean are more pronounced with the
westward/southwestward elongation than their 00Z counterparts.
Teleconnections relative the strong core of positive height
anomalies over the western half of Canada seen in the D+8
multi-day means suggest an eastern U.S. trough that is rounded
enough to allow for some 00Z GFS/GEFS input along with the more
amplified ECMWF/ECMWF mean solution. On the other hand the
telecons support lower heights over the East than depicted in the
06Z GFS/GEFS mean and last couple FV3 GFS runs.
Based on majority clustering the forecast incorporated the 00Z
GFS/ECMWF and lesser weight of the UKMET from early day 3 Fri into
day 5 Sun. The forecast started to include 00Z GEFS/ECMWF means
late Sun and increased their total influence to 60 percent total
by day 7 Tue, with lingering operational input from the 00Z
GFS/ECMWF.
...Weather Highlights and Hazards...
The cold front crossing much of the East Coast late this week will
likely settle near the Florida Keys as a wavy stationary front.
The combination of this front and one or more southern stream
shortwaves aloft may produce periods of locally moderate or heavy
rainfall over the Florida Peninsula. Extreme southern Texas may
see some enhanced rainfall with the energetic flow aloft as well.
The rest of the East will see a drier trend as frontal rainfall
passes off the East Coast after Fri. Cool cyclonic flow will
produce some areas of lake effect snow primarily to the lee of
open waters (mostly Lake Michigan and Lake Ontario). During the
weekend light precipitation could brush parts of the Pacific
Northwest and some light/scattered activity may occur over the
southern Rockies. Otherwise the West should be mostly dry until
moisture reaches the West Coast next Tue. There may be one or
more areas of precipitation between the northern half of the
Plains and Great Lakes during the period, in association with
features progressing into the Lower 48 from Canada, but with low
confidence in timing and coverage.
Expect below normal temperatures initially over the West to
moderate with time while cool air moving into the East behind
Friday's cold front should rebound closer to normal after Sat.
The north-central and southern Rockies/High Plains may see the
most persistent cold anomalies with some locations at least 15-20F
below normal for highs through the weekend. The warming trend
over/near the West Coast states should bring readings 5-10F above
normal by Sun-Tue.
Rausch
Hazards:
- Heavy rain across portions of the Southeast, Tue, Mar 19.
- Flooding possible across portions of the Central/Northern
Plains, the Mississippi Valley, the Tennessee Valley, the Great
Lakes, and the Southern Plains.
- Flooding occurring or imminent across portions of the Southeast,
the Middle/Lower Mississippi Valley, the Ohio Valley, and the
Tennessee Valley.
- Flooding likely across portions of the Northern/Central Plains,
and the Upper/Middle Mississippi Valley.
- High winds across portions of the Great Lakes and the Upper
Mississippi Valley, Fri, Mar 15.
- Much below normal temperatures across portions of the
Northern/Central Plains, the Central Rockies, the Southern
Rockies, the Southern Plains, and the Southwest, Fri-Sat, Mar
15-Mar 16.
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