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 case 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. $$