Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Mon Mar 18 2019

Valid 00Z Tue Mar 19 2019 - 00Z Thu Mar 21 2019

...Heavy rainfall expected to persist through Tuesday night in southern
Florida...

...Major to historic river flooding will continue across parts of the
Mississippi and Missouri River Basins...

...Areal flooding is possible in parts of the Northwest to Northern
Plains...

A front lingering near southern Florida and plenty of moisture will lead
to rain across the Florida peninsula, potentially heavy. A Marginal Risk
of excessive rainfall is in place along the southeastern Florida coast.
Rain is forecast to lighten by Wednesday morning, but cooler than average
temperatures will prevail there.

Snow and rain showers are forecast from the Central Rockies into the
Central Plains Monday night and Tuesday, and rain showers will move into
the Middle/Lower Mississippi Valley and Ohio Valley on Wednesday due to a
low pressure system moving eastward. Precipitation totals will remain
light with this system. An upper-level trough will move toward the western
U.S. by Tuesday night and Wednesday, first increasing precipitation
chances in California on Tuesday evening and into the Central Great Basin
and Southwest by Wednesday. Generally, rain will fall in lower elevations,
with snow in higher elevations.

Major to historic river flooding is forecast to persist for portions of
the Missouri and Mississippi River Basins as snowmelt continues over areas
that received heavy rainfall last week. Flood Warnings and Advisories are
scattered throughout the Plains, Mississippi Valley, and western parts of
the Ohio Valley region, with a focus in Nebraska and western Iowa. Farther
west and north, areal flooding is also possible in the Northwest and
Northern Plains as snowmelt continues over frozen ground. Above average
temperatures in the Northern Great Basin and the Northern Plains will aid
in snowmelt. Ice jams are also a threat in some areas.

Tate

Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
414 PM EDT Mon Mar 18 2019

Valid 12Z Thu Mar 21 2019 - 12Z Mon Mar 25 2019

...Overview and Guidance Assessment/Preferences...

Split flow pattern is expected to persist across North America
during the extended period. Ensemble guidance shows good consensus
that a strong and blocking upper-level ridge axis initially across
the High Plains of the U.S. into Alberta/Saskatchewan will meander
in place over the next week. This will continue to split incoming
energy from the Pacific into northern stream components directed
northward toward Alaska, and southern stream components that
traverse the southern/central U.S., undercutting the ridge.
Downstream of the ridge, the Northeast will be subject to
continued mean troughing, reinforced by a series of energetic
shortwaves. Some guidance suggests that perhaps this northern
stream amplified ridge/trough pattern may begin to weaken by early
next week, but confidence in that is relatively low at this time
given increased spread among the ensemble guidance as to the
intensity and duration of the upper ridge.

Model depictions are now relatively similar with respect to the
upper low/trough crossing the Four Corners Thu-Fri and exiting
into the Plains Fri night-Sat. Farther east, solutions differ more
significantly with respect to small scale northern stream
shortwave energy traversing the larger mean trough, and the
potential for development of a compact/robust surface low off the
Eastern Seaboard Thu night-Fri. Trend in the ensemble guidance has
been toward a bit slower/deeper and closer to the coast solution,
forming a middle ground between the deeper 00Z ECMWF and 06Z
FV3-GFS and weaker/quicker 00Z/06Z GFS and 00Z Canadian/UKMET.
This blend sufficed for the west/central states as well given some
overall minor detail differences. Finally, models show general
consensus that an another shortwave/frontal system should reach
the West Coast Fri-Sat, with relatively minor timing and amplitude
differences through Sat.

Timing differences become more significant Sat-Mon in the West as
subsequent Pacific shortwaves move inland. In general, the 00Z GFS
continued to be quicker than the consensus of other guidance and
was excluded from the forecast. 06Z GFS and 06Z FV3-GFS were
slower like the ECMWF and its ensemble mean, which have been much
more consistent with the cross-continental flow over the past
several runs compared to the GEFS. Used a blend of those slower
solutions with continuity for a starting point which only resulted
in a few minor changes to the fronts, but perhaps more changes to
the PoPs given timing uncertainties of return flow from the Gulf
this weekend.


...Weather Highlights and Hazards...

Rain and high elevation snows are expected across the
southern/central Rockies Thu-Fri as the leading Pacific system
passes the region. Increasing moisture return ahead of the system
will expand coverage of showers and some thunderstorms across the
southern/central High Plains by Friday. The next system will bring
another round of rain/snow to the Pacific Northwest and Rockies
Fri-Sat, with further increased potential for rain and
thunderstorms, some of which could be heavy, from the
southern/central Plains to the Mississippi Valley through the
weekend. Above average temperatures are expected to develop by
late this week across the Upper Midwest and then gradually spread
eastward across the Great Lakes to the Eastern Seaboard through
the weekend as surface high pressure moves offshore. Maximum
temperatures ranging from 5 to 15 deg F above average are
forecast, with minimum temperatures approaching 20 deg above
average for some areas across the Midwest and Mississippi Valley.
Cooler than average temperatures in the Southwest will moderate a
bit late this weekend ahead of the Pacific system just offshore
next Monday.


Fracasso/Ryan


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

3-7 Day Hazards Bullets
- Heavy rain across portions of the Southeast, the Lower
Mississippi Valley, and the Tennessee Valley, Sun-Mon, Mar 24-Mar
25.
- Flooding possible across portions of the Central/Northern
Plains, the Tennessee Valley, the Middle/Upper Mississippi Valley,
and the Great Lakes.
- Flooding occurring or imminent across portions of the
Northern/Central Plains, Mississippi Valley, the Tennessee Valley,
the Great Lakes, and the Ohio Valley.
- Flooding likely across portions of the Upper/Middle Mississippi
Valley, the Great Lakes, and the Northern Plains.

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

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
830 AM EDT Mon Mar 18 2019

Valid 00Z Tue Mar 19 2019 - 00Z Tue Mar 26 2019

High surf warnings and advisories remain in effect for portions of
the islands today. This is the case as post-frontal high pressure
bridges to the north of the state and ushers in drier conditions
within an overall modest trade flow pattern expected to perist
into Thursday. A favored guidance composite of reasonably well
clustered model and ensemble guidance indicates that passage to
the north of the state of mid-upper level trough energies by
Friday will sag a shower focusing front to the north of the
islands, with a potential push across the state this weekend with
flow/trough amplification aloft. Post-frontal high pressure
bridges to the north of the state through this period that would
otherwise lead into an increase in trade flow and moisture/showers
underneath into the state.

Schichtel

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
222 PM EDT Mon Mar 18 2019

Day 1
Valid 1822Z Mon Mar 18 2019 - 12Z Tue Mar 19 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER SOUTHEAST
FLORIDA...

...Southeast Florida...
Deep moisture streaming north of a frontal boundary over the FL
Straits encounters marginal instability to produce convection over
portions of southeast FL, during the evening hours into the
overnight. Convection has already developed off the east coast of
FL, but thus far has remained east of the coast, closer to the
best instability located over the Gulf Stream. A 20/30 knot low
level east northeast flow is expected to push the instability over
the Gulf of Mexico to the coast of southeast FL, mainly after
19/00z.

A deep west southwest flow transports 1.75 inch precipitable water
air (which is between two and three standard deviations above the
mean) over the aforementioned frontal boundary across southern FL.
The combination of deep moisture and marginal instability is
expected to feed convection that reaches the coast after 19/00z.
Increasing low level convergence in the low level flow should
focus the convection along the southeast FL coast and just
offshore, as new convection develops in the right entrance region
of a 150 knot jet streak crossing the Southeast states.

There is a strong high resolution model signal (including the most
recent HRRR and 12z WRF ARW) showed that the convection reaching
the coast could produce local 3.00/5.00 inch rainfall amounts
along the Interstate 95 corridor from Boca Raton south to Miami.
These local rainfall amounts could result in runoff issues over
the metro areas (per collaborating with WFO MFL), so a Marginal
Risk was placed over portions of southeast FL, mainly east of the
Interstate 95 corridor.

At this point, there is some concern as to whether the instability
gets to the coast, which would allow for the abovementioned
rainfall amounts to be realized. If there is a stronger signal in
the high resolution guidance for more than 5.00 inches, a Slight
Risk could be needed in later forecasts.

Hayes

Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 PM EDT Mon Mar 18 2019

Day 2
Valid 12Z Tue Mar 19 2019 - 12Z Wed Mar 20 2019

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL U.S. AND FOR SOUTHEAST FLORIDA...

...Eastern Nebraska and Kansas, southern Iowa, northern Missouri
and western Illinois...

Historic flooding is ongoing across portions of the central U.S.
and will continue to be sensitive to any precipitation for the
foreseeable future. A shortwave is forecast to pass through the
central U.S. spreading rain over the impacted region. While the
forecast amounts of 0.10 to 0.50 inch with locally higher amounts
nearing 0.75 inch would normally not cause a significant impacts
to this area, it very well may in this particular event. A
Marginal Risk was introduced from eastern Nebraska/Kansas to
western Illinois.


...Southeast Florida coast...

The strong, organized convection described in detail on the Day 1
discussion will persist into part of the Day 2 period as the deep
layer of moisture (~1.75 PW values) continues to stream north of a
stalled frontal boundary over the FL Straits- encountering
marginal instability to produce convection over portions of
southeast FL. The area of the Marginal Risk that was placed over
portions of southeast FL, mainly east of the Interstate 95
corridor (per collaboration with WFO Miami) on Day 1 was carried
over to Day 2. Heavy rainfall along the Interstate 95 corridor
from Boca Raton south to Miami could result in runoff issues over
the metro areas.

Campbell


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 PM EDT Mon Mar 18 2019

Day 3
Valid 12Z Wed Mar 20 2019 - 12Z Thu Mar 21 2019

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell





Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
422 PM EDT Mon Mar 18 2019

Valid 00Z Tue Mar 19 2019 - 00Z Fri Mar 22 2019

...California...Great Basin...Southern Rockies....
Days 1-3...

A shortwave diving through the Northern Plains tonight into
Tuesday will drive a cold front southward through the High Plains
and into the central Rockies in advance of a ridge of high
pressure. This will produce an enhanced temperature gradient and
subtly increased upslope flow to produce a few inches of snowfall
in the Colorado Rockies through Day 1. WPC probabilities are low
for 4 inches of snow, highest in the Sangre De Cristos near the NM
border.

A more robust system will approach the Southern California coast
Wednesday as a deep upper trough cuts beneath an amplifying ridge
over western Canada. A significant moisture plume shifting onshore
beneath a jet max rotating beneath the trough will spread
precipitation from California, across the Great Basin, and into
the Central and Southern Rockies by Thursday. Forcing will be
intense in the favorable upslope regions of the Sierra Nevada on
Day 2, and then the Southern Wasatch and San Juans/Sangre De
Cristos on Day 3. Snow levels will gradually climb through the
period as the ridge strengthens to the north, becoming 5-6 kft in
the California, and as high as 8 kft in NM/CO by the end of the
forecast period. This will confine the highest snowfall to the
highest terrain of the mountain ranges, but WPC probabilities are
high for 12 inches in the Wasatch and San Juans on Day 3, and
moderate in the Sierra on Day 2. Elsewhere, probabilities for 4
inches are moderate across much of the terrain above 6000 ft from
the mountains of Nevada south and east into the White Mountains of
Arizona, the northern Wasatch, and the Colorado Rockies.


...Northeast...
Day 3...

A shortwave digging through the Great Lakes Wednesday night will
produce a trough which shifts eastward through New England
Thursday. Increasing diffluence within the RRQ of a departing
100kt upper jet combined with PVA and height falls ahead of the
shortwave will produce snow in the terrain of New York and New
England on Day 3. Additionally, cold advection behind this feature
creates an environment favorable for Lake Effect snow downwind of
Erie and Ontario. The duration and intensity of forcing is modest,
so accumulations are expected to remain light, with WPC
probabilities for 4 inches exceeding 40 percent only in the Tug
Hill Plateau and Adirondacks of New York downwind of Lake Ontario.


The probability for significant (0.25 inches or more) freezing
rain is less than 10 percent all 3 days.


Weiss

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
414 PM EDT Mon Mar 18 2019

Valid 12Z Thu Mar 21 2019 - 12Z Mon Mar 25 2019

...Overview and Guidance Assessment/Preferences...

Split flow pattern is expected to persist across North America
during the extended period. Ensemble guidance shows good consensus
that a strong and blocking upper-level ridge axis initially across
the High Plains of the U.S. into Alberta/Saskatchewan will meander
in place over the next week. This will continue to split incoming
energy from the Pacific into northern stream components directed
northward toward Alaska, and southern stream components that
traverse the southern/central U.S., undercutting the ridge.
Downstream of the ridge, the Northeast will be subject to
continued mean troughing, reinforced by a series of energetic
shortwaves. Some guidance suggests that perhaps this northern
stream amplified ridge/trough pattern may begin to weaken by early
next week, but confidence in that is relatively low at this time
given increased spread among the ensemble guidance as to the
intensity and duration of the upper ridge.

Model depictions are now relatively similar with respect to the
upper low/trough crossing the Four Corners Thu-Fri and exiting
into the Plains Fri night-Sat. Farther east, solutions differ more
significantly with respect to small scale northern stream
shortwave energy traversing the larger mean trough, and the
potential for development of a compact/robust surface low off the
Eastern Seaboard Thu night-Fri. Trend in the ensemble guidance has
been toward a bit slower/deeper and closer to the coast solution,
forming a middle ground between the deeper 00Z ECMWF and 06Z
FV3-GFS and weaker/quicker 00Z/06Z GFS and 00Z Canadian/UKMET.
This blend sufficed for the west/central states as well given some
overall minor detail differences. Finally, models show general
consensus that an another shortwave/frontal system should reach
the West Coast Fri-Sat, with relatively minor timing and amplitude
differences through Sat.

Timing differences become more significant Sat-Mon in the West as
subsequent Pacific shortwaves move inland. In general, the 00Z GFS
continued to be quicker than the consensus of other guidance and
was excluded from the forecast. 06Z GFS and 06Z FV3-GFS were
slower like the ECMWF and its ensemble mean, which have been much
more consistent with the cross-continental flow over the past
several runs compared to the GEFS. Used a blend of those slower
solutions with continuity for a starting point which only resulted
in a few minor changes to the fronts, but perhaps more changes to
the PoPs given timing uncertainties of return flow from the Gulf
this weekend.


...Weather Highlights and Hazards...

Rain and high elevation snows are expected across the
southern/central Rockies Thu-Fri as the leading Pacific system
passes the region. Increasing moisture return ahead of the system
will expand coverage of showers and some thunderstorms across the
southern/central High Plains by Friday. The next system will bring
another round of rain/snow to the Pacific Northwest and Rockies
Fri-Sat, with further increased potential for rain and
thunderstorms, some of which could be heavy, from the
southern/central Plains to the Mississippi Valley through the
weekend. Above average temperatures are expected to develop by
late this week across the Upper Midwest and then gradually spread
eastward across the Great Lakes to the Eastern Seaboard through
the weekend as surface high pressure moves offshore. Maximum
temperatures ranging from 5 to 15 deg F above average are
forecast, with minimum temperatures approaching 20 deg above
average for some areas across the Midwest and Mississippi Valley.
Cooler than average temperatures in the Southwest will moderate a
bit late this weekend ahead of the Pacific system just offshore
next Monday.


Fracasso/Ryan


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

3-7 Day Hazards Bullets
- Heavy rain across portions of the Southeast, the Lower
Mississippi Valley, and the Tennessee Valley, Sun-Mon, Mar 24-Mar
25.
- Flooding possible across portions of the Central/Northern
Plains, the Tennessee Valley, the Middle/Upper Mississippi Valley,
and the Great Lakes.
- Flooding occurring or imminent across portions of the
Northern/Central Plains, Mississippi Valley, the Tennessee Valley,
the Great Lakes, and the Ohio Valley.
- Flooding likely across portions of the Upper/Middle Mississippi
Valley, the Great Lakes, and the Northern Plains.

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