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HOME> Outlook Maps>Seasonal Forecast Discussion
 
Prognostic Discussion for Monthly Outlook 
NWS Climate Prediction Center College Park MD
300 PM EDT Sun Jun 30 2019


30-DAY OUTLOOK DISCUSSION FOR JULY 2019

The updated temperature and precipitation outlooks for July 2019 are based on
the expected continued influence of a weak El Nino, the most recent dynamical
and statistical model guidance, Week-1 total precipitation from WPC, CPC's
temperature and rainfall outlooks for the Week-2 and (experimental) Week 3/4
time frames, recent temperature, precipitation, and soil moisture observations,
and July climatology.

During the past week, CFS, GFS, and ECMWF model guidance have been in generally
good agreement on a circulation transition towards the typical, climatological
summer pattern across the United States. This summer pattern features mean
500-hPa long-wave trough axes near both the Pacific and the Atlantic Coasts,
and a mean ridge axis near the High Plains. West-northwesterly low-amplitude
flow aloft downstream of the ridge axis favors a pattern that is not as cool
and not as wet across the north-central states, which have experienced
excessive rainfall, saturated soils, and devastating floods during the past
30-45 days. While a reduction in precipitation seems reasonable compared to
what has fallen during the past 30-45 days, it is important to remember that
for this part of the Nation summertime is the primary time for the development
of thunderstorm clusters. These clusters (known as Mesoscale Convective
Systems, or MCS's) often develop at night, and may persist well past daybreak.
About 40-45 percent of the annual precipitation received in this region
typically falls during the warm season with these MCS's and frontal systems.
Unfortunately, the record or near-record saturated soils currently across the
North-Central CONUS has resulted in a substantial delay in the planting of
various crops such as corn and soybeans. Elsewhere, over the Southwest/Four
Corners region, July is when the western portion of the subtropical ridge
(known as the Four Corner's High) builds over this part of the country,
attended by the climatological onset of the Southwest Summer Monsoon. Given the
weak El Nino this summer, it is thought that the Four Corner's High could be
shifted somewhat northward of its climatological position, resulting in a
delayed onset of the Monsoon.

The updated temperature outlook for July favors above normal temperatures over
Alaska and a significant portion of the western CONUS. This is supported by
CPC's Week-2 and experimental Week-3/4 outlooks, and by the latest available
CFS and ECMWF temperature anomaly guidance. Probabilities for above normal mean
temperatures exceed 60-percent over southwestern Alaska, with above normal
sea-surface temperatures being a significant contributor to the temperature
outlook along coastal areas. Another factor is the prediction of mid-level
ridging and associated subsidence over Alaska and parts of the western CONUS.
Above normal (upper-tercile) temperatures are also favored from central and
southern Texas east-northeastward to include the Gulf Coast states, the
Southeast, the Upper Tennessee Valley, and the southern Mid-Atlantic. This
relative warmth is also associated with anticipated mid-level ridging, and is
also based on official CPC Week-2 and Week-3/4 temperature outlooks, and ECMWF
model guidance for these same time periods. The CFS model just recently came
into agreement with this scenario, having predicted near normal temperatures
over this region for most of the past 9 days. Farther north, below normal mean
temperatures are favored across an arc-shaped pattern that extends from Montana
and Wyoming southeastward to the Mid-Upper Mississippi Valley, and then
continues across the central and eastern Great Lakes region. The tilt in the
odds toward below normal mean temperatures is marginal over the Great Lakes
portion of this area. A weak El Nino during the summer is generally associated
with a broad area of cooler-than- normal temperatures over parts of the Great
Lakes region and North-Central CONUS. Relative to the 0.5-month lead
temperature outlook for July (issued on June 20th), the highest odds for below
normal temperatures (in excess of 40-percent) are shifted a bit towards the
west. This is in better agreement with CPC's shorter-range Week-2 and
experimental Week-3/4 temperature outlooks, and the latest 9 days of CFS runs.
The ECMWF model predicts diminishing support for the below normal temperatures
during the second half of July. Elsewhere, Equal Chances (EC) of below, near,
and above normal monthly mean temperatures is expected.

The updated precipitation outlook for July depicts a large change in Alaska
relative to the earlier 0.5-month lead outlook issued June 20th. The latest
official CPC Week-2 and Week-3/4 precipitation outlooks depict a much drier
pattern across Alaska than was indicated ten days ago, primarily due to above
normal 500-hPa heights and ridging. CFS precipitation forecasts during the past
few days in particular also support a much drier pattern in Alaska for July.
Probabilities exceed 50-percent across the southern Alaska Panhandle, which is
experiencing precipitation deficits of at least 20 inches during the past 365
days. Below normal (lower-tercile) precipitation is also favored to extend
southward across Washington, Oregon, and far northern California due to
mid-level ridging, as well as a very dry climatology. The summertime presence
of the subtropical ridge over the southern CONUS favors below normal rainfall
across much of this area. The anticipated delay in the onset of the Southwest
Monsoon is best supported by models, and official WPC and CPC rainfall
forecasts which cover all time scales out to 30-days in advance over most of
Arizona, and southern portions of neighboring states. Lower-tercile
precipitation is also favored from central and southern Texas
east-northeastward across most of the Gulf Coast states and interior Southeast.
Though the subtropical High is expected to play a role in suppressing
larger-scale areas of convection across this region, there are mixed
indications from official precipitation outlooks and model forecasts during the
constituent periods within July that this ridge will not be unusually strong or
long-lasting. However, localized and short-lived areas of flash drought are
still possible across the Southeast, especially at this time of year,
coinciding with any extended period of high temperatures and high
evapo-transpiration rates/moisture losses. In contrast with these areas of
predicted relative dryness across portions of the CONUS and most of Alaska,
there are enhanced odds of above normal precipitation from parts of the
Northern and Central Rockies eastward across most of the Northern and Central
Plains, the Middle and Upper Mississippi Valley, and Lower Ohio Valley, with an
extension southward across much of New Mexico and West Texas. This broad region
of favored upper-tercile precipitation corresponds reasonably well with
climatological MCS tracks and meandering baroclinic zones. The last 9 days of
CFS runs (valid for July) lend good support for this relatively wet region.
Elsewhere, Equal Chances (EC) of below, near, and above normal precipitation is
favored.

------- 0.5-month lead forecast discussion for July 2019 is shown below -------

For the month of July, a weak El Nino is predicted to continue. There is a 66%
chance of El Nino continuing through Northern Hemisphere summer, and a 50%-55%
chance that El Nino will persist through the upcoming fall and winter seasons.
For discussion of sea-surface temperature anomalies, as well as subsurface
anomalies, lower and upper-level winds, and convective anomalies, please refer
to CPC's Seasonal Outlook message for July-Sept. Following a brief period of
interference from westward-moving modes of tropical variability, the
Madden-Julian Oscillation (MJO) signal has renewed its eastward propagation and
the enhanced convective phase is now over the Maritime Continent. Linkages
between the MJO and CONUS impacts are generally weak in July, so the MJO is not
forecast to play a significant role in the U.S. monthly temperature and
precipitation outlooks. Multiple bouts of heavy rain over the past 30-45 days
led to very high soil moisture and flooding over much of the Great Plains and
Mississippi Valley. The July 2019 outlooks are based primarily on dynamical and
statistical model guidance, the latest available official CPC temperature and
precipitation outlooks for Week-2 and Weeks 3/4, the ongoing El Nino, very high
soil moisture, heavy rainfall observations during the past 30-days, and July
climatology.

The monthly temperature outlook indicates that above normal temperatures are
favored across Alaska, ranging from 33%-40% odds in the northeast part of the
state to over 60% odds in the southwest part of the state. Contributing factors
include above normal sea-surface temperatures near the coast, strong historical
temperature trends , Week-2 and Weeks 3/4 temperatures, most of the NMME model
suite, and available statistical tools. Above normal temperatures are also
favored from the West Coast of the contiguous U.S. to near the Continental
Divide, and across the Gulf Coast and Atlantic Coast states. Probabilities for
upper-tercile temperatures peak between 40%-49%. Support for this relative
warmth comes largely from the NMME PAC (Probability Anomaly Calibration), and
to a somewhat lesser extent most of the remaining inputs of the NMME dynamical
model suite, in addition to the IMME, statistical models including the CAS
(Constructed Analog on Soil moisture), historical trends , and the latest Weeks
3/4 temperature outlook. Below normal temperatures are favored across a broad
region of the Central CONUS, from Kansas, Oklahoma and northern Arkansas north
and east into the Upper Great Lakes region. Probabilities for anomalously cool
temperatures peak between 40%-49%. A significant contributor to these predicted
below normal temperatures is the very high soil moisture (95th percentile or
greater) across this area, with approximately half of this region at or above
the 99th percentile. This broad expanse of near-saturated, or saturated, soils
has been the result of frequently recurring heavy rainfall. During the past
30-days, rainfall amounts ranged from 2-8 inches or more above normal. Viewed
from a slightly different perspective, percent-of-normal precipitation ranged
from 150%-400% of normal (locally greater). Lower-tercile temperatures are
favored over the Central CONUS by a majority of models and statistical tools,
but the exact placement and size of this area of anomalously cool temperatures
is uncertain. Elsewhere, Equal Chances (EC) of above, near, and below normal
mean temperatures are forecast.

The monthly precipitation outlook indicates that wetter-than-normal conditions
are favored from southwestern Alaska northeastward across the Central Interior,
with maximum probabilities ranging from 40%-49%. This is supported primarily by
a majority of the last 9 days of CFS runs and the uncalibrated NMME, but also
the NMME PAC, both GFDL models (FLOR and CM2.1), and to a lesser extent, the
latest Weeks 3/4 precipitation outlook. Upper-tercile precipitation is also
favored over a large portion of the Central CONUS, as far south as Texas. As
was the cas e in Alaska, maximum probabilities range from 40%-49%. Of the
statistical tools, the CAS bears the closest resemblance to this predicted
pattern of upper-tercile precipitation, which also looks fairly similar to
recent observations of both heavy rainfall and very high soil moisture. The CFS
precipitation anomaly forecast for July lends some support to this area of
anomalous wetness. However, it predicts the lion's share of the rainfall to be
focused farther west, over the Pacific Northwest, the Northern Intermountain
Region, and the Northern and Central Rockies. A majority of input models for
the NMME generally predict this corridor of wetter-than-normal conditions,
though there are variations on the overall theme. The NASA, CMC2 Canadian
model, and the IMME also extended the favored area of above normal rainfall
farther west as indicated by the CFS. Finally, there is a slight tilt in the
odds for drier-than-normal conditions across most of the Alaska Panhandle, and
west-central portions of the Gulf Coast region. These areas have modest support
from the CFS, CAS (CONUS), NCAR, GFDL FLOR, and the CMC2 Canadian model. July
climatology also provides weak support for the relative dryness in the
west-central Gulf Coast region. Elsewhere, Equal Chances (EC) of above, near,
and below normal precipitation are favored.

FORECASTER: Anthony Artusa

The climatic normals are based on conditions between 1981 and 2010, following
the World Meteorological Organization convention of using the most recent 3
complete decades as the climate reference period.  The probability anomalies
for temperature and precipitation based on these new normals better represent
shorter term climatic anomalies than the forecasts based on older normals.

The next monthly outlook...for Aug ... will be issued on Thu Jul 18 2019

These outlooks are based on departures from the 1981-2010 base period.
$$

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