Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
153 AM EST Mon Mar 4 2019
Valid 12Z Thu Mar 7 2019 - 12Z Mon Mar 11 2019
Weather Pattern Overview
~~~~~~~~~~~~~~~~~~~~~~~~
The amplified flow pattern that exists during the short range
forecast period is expected to transition to a more quasi-zonal
pattern across the continental U.S. by the beginning of the medium
range period on Thursday. The anomalous upper level ridge over
the eastern U.S. lifts out while an upper level trough builds in
across the West Coast region by Friday, and it will be this trough
axis that induces surface low cyclogenesis across the Plains by
this weekend. A second and weaker disturbance is likely to affect
the West Coast region by the end of the forecast period next
Monday with a more amplified pattern in place.
Model Guidance Evaluation and Preferences
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The models and ensemble means indicate reasonable agreement on the
synoptic scale for the end of the week, but not quite as good as
previous days when confidence was above average. One of the main
differences on Thursday was the CMC having a flatter 500mb height
configuration over the West Coast region compared to more
troughing evident in all of the other guidance. Both the 18Z and
00Z GFS indicate a more developed lead surface low crossing the
Ohio Valley region on Friday, whereas the model consensus and FV3
support more of an elongated surface trough.
The strong surface low that is forecast to develop across the
Plains and then track northeastward is indicating very good
agreement on Saturday morning across eastern Colorado as lee
cyclogenesis gets underway. Model differences grow significantly
by Sunday regarding the track of the surface low across the
Midwest states and then the Great Lakes region. In terms of
trends, both the EC mean and GEFS mean have trended stronger with
this storm system, and the Canadian mean more suppressed to the
south and not as strong. The FV3 is faster than the model
consensus and is not preferred beyond Saturday. There is better
agreement among the EC and GEFS ensemble members compared to the
CMC members, and the EC mean provided a reasonable idea on low
placement. Taking all of these factors into account, the forecast
was primarily derived from the 12Z ECMWF/18Z FV3/12Z UKMET for the
first half of the forecast period, and then some of the ECMWF and
EC/NAEFS mean for the last two days.
Sensible Weather and Potential Hazards
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Heavy snow will likely be ongoing across the higher elevations of
the Sierra Nevada and much of the Intermountain West and Rockies
through Friday as the strong Pacific disturbance crosses the
region. Snowfall amounts on the order of 1 to 2 feet are likely
across parts of the central and northern Rockies, mainly on
Friday. Temperatures are expected to slowly moderate across the
north-central U.S. compared to early this week while still
remaining below average.
With a large storm system likely developing across the central
U.S. next weekend, widespread rain is expected to develop from the
Gulf Coast to the Ohio Valley and southern Appalachians as a rich
supply of Gulf moisture surges northward ahead of a strong cold
front. The heaviest rainfall is likely across the Deep South and
Tennessee River Valley, where a general 1 to 3 inches of rain is
likely that may lead to some flooding issues based on the current
forecast. Depending on where the surface low develops, a corridor
of blizzard conditions will be possible across parts of the
northern plains, Upper Midwest, and western Great Lakes region.
It is still too early to mention precise locations given current
model differences. Another facet to this low pressure system will
be the potential for strong to severe thunderstorms to develop in
the warm sector, and this is something that the Storm Prediction
Center is currently monitoring.
D. Hamrick
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