Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
328 PM EDT Thu Mar 21 2019

Valid 00Z Fri Mar 22 2019 - 00Z Sun Mar 24 2019

...A developing coastal storm to bring rain, interior and higher elevation
snows, and gusty winds to parts of the Mid-Atlantic and Northeast...

...A couple rounds of rain and mountain snows likely across parts of the
West during the short range, with rain moving into the Southern and
Central Plains by Friday...

...Major to historic river flooding will continue across parts of the
Mississippi and Missouri River Basins with areal flooding a threat across
parts of the Northwest and Northern Plains as well...


The main sensible weather threat in the short range with be a developing
coastal low pressure system over southeast Virginia this evening, tracking
up the East Coast through tonight and into Friday. Moderate to locally
heavy rainfall will accompany this system across the Mid-Atlantic and
Northeast with flash flooding a marginal and local threat particularly for
highly urbanized areas. A handful of flood watches are in effect across
parts of the Mid-Atlantic. Accumulating snowfall is likely well inland
across portions of the interior Northeast, where winter storm warnings
have been issued. Gusty winds are also likely across the Mid-Atlantic and
Northeast into the weekend as the storm deepens as it moves up the coast.

Meanwhile, a cold front moving across the Four Corners region this evening
will continue to produce rain and mountain snows across parts of the
Southwest and into the Southern Rockies through Friday. As moisture get
drawn northward from the Pacific ahead of the cold front, precipitation is
expected to spread into parts of the southern and central Plains on Friday
and Saturday. Another cold front entering the West Coast states by late
Friday will bring more rain and higher elevation snows to California, the
Pacific Northwest, and parts of the interior West this weekend.

Major to historic and catastrophic flooding across parts of the Missouri
and Mississippi River Basins will continue through the short range due to
ongoing effects following a period of rapid snow melt after heavy rainfall
last week. Flood warnings and advisories remain for parts of the region.
By Saturday, light rain will be possible across areas seeing the highest
impacts, which will only exacerbate ongoing flooding. Areal flooding is
also a concern across parts of the Northwest and into the Northern Plains
as warmer temperatures the end of this week lead to accelerated snowmelt
and the potential for ice jams.

Snell

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
334 PM EDT Thu Mar 21 2019

Valid 12Z Sun Mar 24 2019 - 12Z Thu Mar 28 2019

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

Today's guidance continues the recent general theme aloft of
strong mean ridging over western Canada and/or Alaska, periodic
downstream troughing, and features progressing from the eastern
Pacific into/across the Lower 48. Recent model/ensemble runs have
displayed some significant differences/trending with individual
western-central U.S. features that continue eastward and affect
the forecast over the eastern half of the country. Guidance has
been a little better behaved for a fairly deep eastern Pacific
trough/embedded upper low that should reach the West by Wed-Thu
but typical amplitude/timing differences still exist.

The forecast over the eastern half of the Lower 48 depends on
specifics of a compact upper low over the north-central Plains and
Interior West energy as of early day 3 Sun, and perhaps to some
degree Canadian troughing that dips into the Great
Lakes/Northeast. Over the past day there have been some trends
toward more emphasis on the Plains feature and less on the western
energy. This has led the ECMWF/CMC and their means in particular
to trend faster with associated low pressure crossing the
mid-lower latitudes of the central/eastern states during Sun-Tue.
The adjustment brings the guidance cluster closer to the prior
GFS/GEFS scenario that was fairly progressive. However by early
Tue the 00Z ECMWF/ECMWF mean may have overshot the trend just a
bit, favoring partial inclusion of the 12Z/20 run as part of a
consensus blend that includes the 06Z GFS and 00Z UKMET/CMC into
Tue. The 00Z GFS was slightly faster. It remains a close call as
to whether the Canadian/Northeast U.S. trough may influence the
southern stream system. Recent trends for the amplitude of this
trough are mixed.

A blend/consensus approach looks reasonable for depicting the
evolution of the amplified trough/embedded upper low settling over
the eastern Pacific during the first half of next week and then
opening up with progression inland. The overall upper low
contains multiple small shortwaves whose scale results in low
predictability for those details. By Wed-Thu the models and
ensembles have varied somewhat with amplitude/timing as trough
energy progresses into the West. Recent ECMWF runs and their
ensembles have tended to be on the faster side of the overall
spread in the past day and the 00Z ECMWF looks particularly fast
in bringing height falls into the northern Plains by Thu. The
ECMWF mean has trended slower over the past 24 hours and the 06Z
GFS is a bit slower than the 00Z run so preferences for this
feature late in the period tilt more toward the latest ECMWF
mean/06Z GEFS mean/06Z GFS and 12Z/20 ECMWF.

Downstream from an upper high expected to close off over eastern
Alaska and the Yukon, there is decent agreement that an amplifying
trough over central Canada will push a cold front into the
northern Plains around day 7 Thu. There have been enough spread
and variability for the character of the upper ridge to suggest
some future guidance adjustments are possible over the northern
U.S. and southern Canada during the latter half of the week.


...Weather Highlights and Hazards...

One or more waves progressing across the eastern half of the
country will produce areas of mostly rain Sun-Tue, with
thunderstorms possible from the southern half of the Plains into
the Southeast. Some rainfall could be locally moderate/heavy but
recent faster trends suggest that any intense activity should be
fairly brief. At the same time the faster progression of moisture
may limit any snow in the northern part of the moisture shield to
farther north latitudes than previously anticipated--due to a
higher proportion of moisture crossing the East ahead of the
colder air pushing southeast from Canada.

Mostly during Sun-Sun night an initial western U.S. shortwave will
generate mountain snow/valley rain over the Great Basin and
northern-central Rockies. Some of this rain/snow may extend into
the northern Plains. The system settling into the eastern Pacific
during the first half of next week will likely bring multiple
surges of moisture into the West Coast and extending into favored
terrain farther inland over northern/central parts of the West.
The first round of enhanced precipitation should commence by Sun
night-Mon. By Thu there is some uncertainty over the exact
character of upper flow along the West Coast, lowering confidence
in how much precipitation may persist over the West Coast states
at that time. Guidance is persistent in showing best potential
for highest precip totals from northern California/extreme
southwest Oregon into the Sierra Nevada. The combination of
events will provide less extreme but still significant totals over
the northern/central Rockies.

System progression will lead to variable temperatures over many
areas during the period. Expect warmest anomalies to be for
morning lows from the Rockies into Plains/Mississippi Valley
Sun-Mon and then for max/min readings from the Interior
West/Rockies into the Plains/Upper Mississippi Valley Tue-Thu.
There may be fairly broad coverage of plus 10-20F anomalies over
the central U.S. by next Thu. Parts of the east should see
temperatures at least 10F below normal for a brief time around
Tue-Wed.

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 precipitation across portions of California, the Central
Great Basin, the Pacific Northwest, and the Southwest, Mon-Thu,
Mar 25-Mar 28.
- Flooding possible across portions of the Northern/Central
Plains, the Upper/Middle Mississippi Valley, and the Great Lakes.
- Flooding occurring or imminent across portions of the
Northern/Central Plains, the Mississippi Valley, the Tennessee
Valley, the Great Lakes, and the Ohio Valley.
- Flooding likely across portions of the Northern/Central Plains,
the Upper/Middle Mississippi Valley, and the Great Lakes.
- Much above normal temperatures across portions of the
Northern/Central Plains, and the Upper/Middle Mississippi Valley
Wed-Thu, Mar 27-Mar 28.

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
824 AM EDT Thu Mar 21 2019

Valid 00Z Fri Mar 22 2019 - 00Z Fri Mar 29 2019

Upper ridging and above average heights will slowly slide eastward
along 20N over the next week with troughing to its north and the
northeast eventually making its way toward Hawai'i. A frontal
system will stall and dissipate just north of the area (or near
Kauai) through the weekend as trades increase late tomorrow
through perhaps next Tue due to strong high pressure to the north.
Precipitable water values likely stay below average with values
near one inch with scattered windward/mauka showers and generally
light accumulations. Models/ensembles were in good synoptic
agreement through about next Wednesday before timing differences
in the next upper trough expand. The 00Z GFS/ECMWF represent a
reasonable blended solution near the ensemble consensus with a
front that may approach Kauai from the northwest by late
Wednesday/early Thursday.

Fracasso

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
850 PM EDT Thu Mar 21 2019

Day 1
Valid 01Z Fri Mar 22 2019 - 12Z Fri Mar 22 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MID-ATLANTIC STATES...

...Mid-Atlantic States...
Mid level frontogenetic forcing along and ahead of a frontal
boundary extending from southeast VA into central and southeast PA
has resulted in a slow moving axis of heavier rain extending along
the front. For the most part, hourly rainfall rates have averaged
between 0.25 and 0.50 inches, with the best instability remaining
southeast of the banding. As a closed mid level low forms over the
Mid Atlantic states, the area of mid level lift moves slowly north
into central PA and northern NJ.

With instability remaining the limiting factor for higher hourly
rainfall rates, a general 1.00/1.50 inch rainfall is expected from
central PA into northern NJ before the frontogenetically forced
banding begins to weaken in place or drift slowly northeast with
time. Three hour flash flood guidance values are as low as
1.00/1.50 inches extending from western VA across western MD into
central PA, with another area of lower flash flood guidance
extending from near KPHL to the NYC metro areas. Since three hour
flash flood guidance values could be met or exceeded in these
locations, the Marginal Risk remains in place. The consensus of
high resolution guidance suggests that the highest rainfall rates
(generally between 0.25 and 0.50 inches) begin to wane after
22/03z.

Convection forming along a weak boundary (with several small waves
running along it) east of the southern DelMarVA coast has weakened
as it has moved north, away from the instability along the western
edge of the Gulf Stream. Its trajectory would place this activity
over portion of eastern NJ across portions of western Long Island
in the 20/02z through 22/06z time frame (which is supported by the
most recent runs of the HRRR). However, it is unclear where the
deep convection could survive the trip across the cooler waters
closer to the coast here (as it becomes elevated and weakens). If
it does, the higher rainfall rates could impact areas with lower
flash flood guidance, extending the flash flood threat into
western Long Island NY.

Based on this, the Marginal Risk was extended into this area, as
the convection is upstream of areas with lower flash flood
guidance. However, if the convection does not reach the NJ coast
intact, rainfall rates would be insufficient for flash flooding.

Hayes

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Thu Mar 21 2019

Day 2
Valid 12Z Fri Mar 22 2019 - 12Z Sat Mar 23 2019

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

Hurley


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
358 PM EDT Thu Mar 21 2019

Day 3
Valid 12Z Sat Mar 23 2019 - 12Z Sun Mar 24 2019

...THERE IS A MARGINAL RISK OF FLASH FLOODING OVER PORTIONS OF THE
LOWER MISSOURI VALLEY...

...Eastern Nebraska, northeast Kansas, northwest Missouri,
southwest Iowa...
A synoptic scale system coming across the Rockies will become
somewhat better organized as it moves over the Plains and spreads
precipitation over an area which is very sensitive to any
precipitation on Day 3.

Precipitation forecasts from the models are pretty modest and
would, under most instances, not warrant a risk area of excessive
rainfall. The modest model-QPF is consistent with limited
instability shown by the NCEP guidance. The global guidance
continues to show Lifted Index values of 0 to -2C and Best Cape
values of 250 to 500 J/kg nosing into the outlook area (especially
southern portions -- i.e. northeast KS and northern MO) Saturday
night into Sunday morning ahead of the next system as the
pre-frontal south-southwesterly flow increases to 30-40+ kts. The
magnitude of low-level frontogenesis and moisture flux east of the
system coincides with a modest spike in PW values (aoa 0.75"),
supportive of locally higher precipitation rates than shown by the
21/12Z models given the projected thermodynamic environment. These
higher rainfall rates would be occurring over an area where flash
flood guidance values are as low as 1 inch in 3 hours in spots.
Therefore, additional, more localized areas of excessive runoff
will be possible.

Hurley


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
329 PM EDT Thu Mar 21 2019

Valid 00Z Fri Mar 22 2019 - 00Z Mon Mar 25 2019

...CA/Great basin/Rockies...
...Days 1-3...

The first system is an upper low that crosses from NV this evening
and across UT overnight into CO Friday. Light to moderate snow
are expected along the track of the low and accompanying mid
level deformation zone from east central NV across the UT Wasatch
and then ranges of west CO.
southern Rockies. The heaviest snow Day 1 is expected in the San
Juans of CO as both longer duration snows occur plus the favored
300 mb jet crosses this evening to aid in producing higher snow
rates. WPC probabilities show a moderate risk for 12 inches in the
San Juans

On day 2, the event in UT and CO winds down as the upper trough
continues moving east, with temps too warm on the CO plains to
support snow as you head towards the KS border. Modest snows are
expected in the cyclonic shear zone and upper divergence maxima
cross the ranges of southern ID to adjacent northwest WY.
Snow picks up again the Sierra Nevada range in CA as the next in
the series of upper trough moves onshore, with upper divergence
maxima and low-mid level warm/moisture advection in the region
centered in the hours around 12z Sat.

As this trough moves further inland later Sat, the snow relocates
into the ranges of southern ID and northern UT, where favorable
difluent flow aloft supports lift from associated 300 mb
divergence maxima.
Although widespread heavy accumulations are not expected, WPC
probabilities indicate a slight risk for 8 inches in the Sawtooth
range and eastward into NW WY.
Several inches are expected in the UT Uintas due to the orographic
lift plus synoptic lift from the approaching upper trough.

...Interior New York/Northern New England...
Days 1-2...

A surface low near the Delmarva today will move northeast across
eastern New England into Maine on Friday and the Canadian
maritimes thereafter, with slow forward motion. Snow occurred in
the higher elevations of the VA Blue Ridge today and the forecasts
continue to show an elevation based event as it crosses PA into
New York tonight. The heaviest snow is expected in the band of
enhanced mid level deformation and frontogenesis from higher
elevations few the southern tier to the western Catskills of NY
and the Adirondacks.

Once the upper low passes later Friday, cold air returns from west
to east, with post frontal upslope flow allowing snow in the
Adirondacks to continue and then develop in the Green Mountains of
VT and the Berkshires of MA. A relative minima in snow is expected
in the Hudson Valley first due to initial warm temps and then
descent in the lee of the Adirondacks. A mixture of precip types
and duration provides the uncertainty in the Catskills of NY.

The highest probabilities for 4 inches of snow are across the
Adirondacks, due to the longer duration of snow . There is likely
to be significant snowfall gradient in the terrain however,
especially in the Champlain Valley of VT, which is between heavier
snow corridors in the Adirondacks and Green Mountains. WPC
probabilities show a moderate to high risk for 8 inches of
accumulation in the highest terrain.
Up in ME, the initial shot of warm advection zone then leads to a
precip type transition plus a dry slot might cross the region.
Precip transitions back to snow late Fri-Fri night as the 850 mb
low moves across downeast Maine, providing a favorable track for
western ME to get several inches of snow in the mid level
deformation band.

As the low pulls away slowly, NW flow will be favorable for
upslope snow
focuses snow in the mountains of WV, where several inches are
possible, with more weighting given to the NAM and less weight to
the 12z GFS, which has been changing its low level enough to
warrant low confidence.

The probability of significant freezing rain is less than 10
percent.

Petersen

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
334 PM EDT Thu Mar 21 2019

Valid 12Z Sun Mar 24 2019 - 12Z Thu Mar 28 2019

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

Today's guidance continues the recent general theme aloft of
strong mean ridging over western Canada and/or Alaska, periodic
downstream troughing, and features progressing from the eastern
Pacific into/across the Lower 48. Recent model/ensemble runs have
displayed some significant differences/trending with individual
western-central U.S. features that continue eastward and affect
the forecast over the eastern half of the country. Guidance has
been a little better behaved for a fairly deep eastern Pacific
trough/embedded upper low that should reach the West by Wed-Thu
but typical amplitude/timing differences still exist.

The forecast over the eastern half of the Lower 48 depends on
specifics of a compact upper low over the north-central Plains and
Interior West energy as of early day 3 Sun, and perhaps to some
degree Canadian troughing that dips into the Great
Lakes/Northeast. Over the past day there have been some trends
toward more emphasis on the Plains feature and less on the western
energy. This has led the ECMWF/CMC and their means in particular
to trend faster with associated low pressure crossing the
mid-lower latitudes of the central/eastern states during Sun-Tue.
The adjustment brings the guidance cluster closer to the prior
GFS/GEFS scenario that was fairly progressive. However by early
Tue the 00Z ECMWF/ECMWF mean may have overshot the trend just a
bit, favoring partial inclusion of the 12Z/20 run as part of a
consensus blend that includes the 06Z GFS and 00Z UKMET/CMC into
Tue. The 00Z GFS was slightly faster. It remains a close call as
to whether the Canadian/Northeast U.S. trough may influence the
southern stream system. Recent trends for the amplitude of this
trough are mixed.

A blend/consensus approach looks reasonable for depicting the
evolution of the amplified trough/embedded upper low settling over
the eastern Pacific during the first half of next week and then
opening up with progression inland. The overall upper low
contains multiple small shortwaves whose scale results in low
predictability for those details. By Wed-Thu the models and
ensembles have varied somewhat with amplitude/timing as trough
energy progresses into the West. Recent ECMWF runs and their
ensembles have tended to be on the faster side of the overall
spread in the past day and the 00Z ECMWF looks particularly fast
in bringing height falls into the northern Plains by Thu. The
ECMWF mean has trended slower over the past 24 hours and the 06Z
GFS is a bit slower than the 00Z run so preferences for this
feature late in the period tilt more toward the latest ECMWF
mean/06Z GEFS mean/06Z GFS and 12Z/20 ECMWF.

Downstream from an upper high expected to close off over eastern
Alaska and the Yukon, there is decent agreement that an amplifying
trough over central Canada will push a cold front into the
northern Plains around day 7 Thu. There have been enough spread
and variability for the character of the upper ridge to suggest
some future guidance adjustments are possible over the northern
U.S. and southern Canada during the latter half of the week.


...Weather Highlights and Hazards...

One or more waves progressing across the eastern half of the
country will produce areas of mostly rain Sun-Tue, with
thunderstorms possible from the southern half of the Plains into
the Southeast. Some rainfall could be locally moderate/heavy but
recent faster trends suggest that any intense activity should be
fairly brief. At the same time the faster progression of moisture
may limit any snow in the northern part of the moisture shield to
farther north latitudes than previously anticipated--due to a
higher proportion of moisture crossing the East ahead of the
colder air pushing southeast from Canada.

Mostly during Sun-Sun night an initial western U.S. shortwave will
generate mountain snow/valley rain over the Great Basin and
northern-central Rockies. Some of this rain/snow may extend into
the northern Plains. The system settling into the eastern Pacific
during the first half of next week will likely bring multiple
surges of moisture into the West Coast and extending into favored
terrain farther inland over northern/central parts of the West.
The first round of enhanced precipitation should commence by Sun
night-Mon. By Thu there is some uncertainty over the exact
character of upper flow along the West Coast, lowering confidence
in how much precipitation may persist over the West Coast states
at that time. Guidance is persistent in showing best potential
for highest precip totals from northern California/extreme
southwest Oregon into the Sierra Nevada. The combination of
events will provide less extreme but still significant totals over
the northern/central Rockies.

System progression will lead to variable temperatures over many
areas during the period. Expect warmest anomalies to be for
morning lows from the Rockies into Plains/Mississippi Valley
Sun-Mon and then for max/min readings from the Interior
West/Rockies into the Plains/Upper Mississippi Valley Tue-Thu.
There may be fairly broad coverage of plus 10-20F anomalies over
the central U.S. by next Thu. Parts of the east should see
temperatures at least 10F below normal for a brief time around
Tue-Wed.

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 precipitation across portions of California, the Central
Great Basin, the Pacific Northwest, and the Southwest, Mon-Thu,
Mar 25-Mar 28.
- Flooding possible across portions of the Northern/Central
Plains, the Upper/Middle Mississippi Valley, and the Great Lakes.
- Flooding occurring or imminent across portions of the
Northern/Central Plains, the Mississippi Valley, the Tennessee
Valley, the Great Lakes, and the Ohio Valley.
- Flooding likely across portions of the Northern/Central Plains,
the Upper/Middle Mississippi Valley, and the Great Lakes.
- Much above normal temperatures across portions of the
Northern/Central Plains, and the Upper/Middle Mississippi Valley
Wed-Thu, Mar 27-Mar 28.

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