Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Sat Mar 2 2019
Valid 12Z Tue Mar 5 2019 - 12Z Sat Mar 9 2019
Weather Pattern Overview
~~~~~~~~~~~~~~~~~~~~~~~~
A return to a more amplified upper level flow pattern is expected
across the continental U.S. for the early to middle part of next
week. The passage of a strong cold front across the eastern U.S.
by Monday will herald a much colder airmass across the central and
eastern U.S., accompanied by a pronounced upper level trough and
sprawling surface high from Canada. The presence of the eastern
U.S./Canada trough supports a broad upper ridge across the Rockies
and High Plains by midweek, which gradually flattens out towards
the end of the forecast period as the flow returns more
quasi-zonal with some shortwave perturbations passing through. An
unsettled weather pattern is expected to return across the West
Coast region as multiple Pacific disturbances move inland, with a
large scale trough expected across the Intermountain West by the
end of the week.
Model Guidance Evaluation and Preferences
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The deterministic model guidance is in above average agreement for
the Tuesday and early Wednesday time period owing largely to the
amplified flow. This especially holds true for the large scale
upper level trough anchored over the eastern half of the nation
through midweek. The main forecast challenge, similar to
yesterday, resides over the West Coast region beginning on
Wednesday with the development of a rex block over the northeast
Pacific. The UKMET is indicating a track north of the model
consensus with the next storm to affect California, and reasonably
good agreement among the other guidance. More noticeable
differences are evident as this feature crosses the Rockies and
emerges over the High Plains on Friday, with the operational GFS
well to the north of the model consensus, so more of the FV3 model
was incorporated in place of the GFS.
The forecast was primarily derived with a blend of the latest
deterministic solutions (ECMWF/GFS/FV3/CMC) as a starting point
for the Tuesday through Thursday time period. For Friday and
Saturday, the GEFS and EC means along with smaller percentages of
the FV3 and ECMWF were incorporated into the forecast process. No
major changes from previous WPC continuity were warranted.
Sensible Weather and Potential Hazards
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Much colder weather will be making headlines at the beginning of
this forecast period after the passage of a strong cold front on
Monday. A massive arctic surface high will encompass all of the
central and eastern U.S. through the middle of the week, and
reaching well into eastern Mexico. The projected departures from
early March climatology will be impressive, with high temperatures
on Tuesday on the order of 20 to 35 degrees below normal across
much of the Plains and extending eastward across the Midwest and
Ohio Valley. This equates to widespread subzero and single digit
low, and highs only in the teens and low 20s for many of those
areas. There will likely be numerous daily record lows to be
established with this arctic airmass, with the greatest potential
for this on Tuesday morning. Temperatures only slowly moderate
through midweek with anomalies of 15 to 30 degrees below normal,
and this will extend eastward towards the Mid-Atlantic and
Northeast. Although the magnitude of the cold temperatures will
abate some by the end of the week, below normal temperatures will
be the rule for the entire forecast period.
Heavy rain and mountain snow are expected to make a return to the
western U.S. by Tuesday night as an atmospheric river event
accompanies a strong Pacific low headed towards California. The
Sierra Nevada will likely get hammered by very heavy snow, thus
adding to its extensive snow pack. Significant snow is forecast
for the central and northern Rockies by Wednesday and Thursday as
the moisture plume advects inland, albeit not to the same degree
as California. Heavy rainfall across the lower elevations of
California may lead to some flooding problems, and future
excessive rainfall outlooks will have additional information as
this event enters the short range forecast period.
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