Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT Tue Jun 30 2020


30-DAY OUTLOOK DISCUSSION FOR JULY 2020

The updated outlook for July 2020 utilizes the most recent dynamical model 
guidance across time scales and any change to the land surface state to modify 
the mid-month outlook release. For temperature, most of the forecast domain 
remains favored to see above-normal monthly mean temperatures for July 2020, 
although the probabilities in some areas required adjustment as well as a small 
region of elevated odds for below-normal temperatures was included in the 
update in the Pacific Northwest. Current troughing in proximity to the Far West 
and West coast decreases odds for above-normal temps for areas in California, 
the central Great Basin, central and southern Rockies and the Southwest, while 
introducing the small region of below-normal temperatures referenced above. 

Probabilities for above-normal temperatures are increased in the northern 
Plains, Great Lakes, Ohio Valley and Southeast from the mid-month outlook due 
to expectations of ridging during much of the month. Forecast coverage and in 
some areas probabilities for above-normal temperatures are decreased for Alaska 
as a result of the latest forecast guidance showing greater uncertainty in this 
area as compared to earlier in the month.  

Favored above-normal monthly total rainfall for parts of the lower Mississippi 
Valley, Southeast, lower Ohio Valley and lower Mid-Atlantic remains unchanged 
from the mid-month outlook. Elevated odds for below-normal rainfall originally 
focused in the north-central Rockies has been shifted southward and and 
expanded to include much of the central Great Basin, central and southern 
Rockies and Southwest. This area stretches eastward to include parts of the 
central Plains. Forecast troughing along the central West coast is not 
conducive for the climatological development of the Southwest monsoon ridge and 
so odds for a delayed and weaker onset of the Southwest U.S. monsoon are 
elevated and so favor enhanced odds for below-normal rainfall in this region 
for July. 

The main core of the westerlies are forecast to run across the northern Rockies 
and northern Plains which favors modestly increased odds of above-normal 
rainfall in this region. Downstream of the central CONUS ridging favors a 
likely mean relatively dry zone to the east which is supported by most 
dynamical model guidance and so favors below-normal rainfall for parts of the 
Great Lakes northern Ohio Valley eastward to parts of the Northeast and New 
England.

********* PREVIOUS DISCUSSION FROM MID-MONTH OUTLOOK RELEASE ***************

The July 2020 temperature outlook depicts elevated probabilities for 
above-normal monthly mean temperatures for the entire forecast domain. Nearly 
all information considered in preparing the temperature outlook pointed to 
warmer than normal conditions at varying degrees for Alaska and the CONUS. 
Current land surface conditions, dynamical model forecast guidance, statistical 
based tools as well as long term positive temperature trends in most areas 
supported the outlook. In addition, potential persistent enhanced convection in 
the Indian Ocean tends to favor positive 500-hPa heights for considerable areas 
of the CONUS during the summer months and so further tilts the odds toward 
warmer potential conditions in July. 

The greatest odds for above-normal temperatures are forecast for a region in 
the south-central Rockies where dynamical model guidance, long term trends and 
extreme drought conditions favor above-normal temperatures. Both dynamical 
model guidance and long term trends supported the forecast for most of the 
western CONUS along with considerably drier than normal conditions in many 
areas. Similar factors also supported above-normal temperatures for the 
Northeast, eastern Great Lakes and the mid-Atlantic region for the month of 
July. 

As is often the case, the interior portion of the country shows considerable  
uncertainty, lower confidence and so lower forecast probabilities. The 
temperature forecast from the CFS favors near to below-normal temperatures for 
much of the central CONUS. This is considered overdone given recent conditions 
and forecast factors for July from other sources and forecast tools so was 
considered an outlier and ignored. Even so, the northern portion of this area, 
which stretches from the western Great Lakes and upper Mississippi Valley to 
the Gulf coast, had less forecast guidance consistency along with elevated soil 
moisture conditions so odds for above-normal temperatures are considerably 
tempered in some of these areas. Anomalous land surface wetness and favored 
above-normal precipitation for the month of July also reduce odds for 
above-normal temperatures in the lower Mississippi Valley, Tennessee Valley and 
Gulf coast states. 

Elevated probabilities for above-normal temperatures are also forecast for 
Alaska due to consistent forecast tools as well as current above-normal sea 
surface temperatures in the Bering Sea and other nearby waters which result in 
slightly higher odds for above-normal temperatures for areas of western Alaska.

For precipitation, the July 2020 outlook indicates considerable uncertainty, 
lower forecast confidence and so reduced forecast coverage. Above-normal 
precipitation is favored for the Gulf Coast, Southeast, Tennessee Valley to the 
mid-Atlantic. This forecast is driven by potential influences from current 
subseasonal coherent tropical variability (MJO, atmospheric Kelvin wave 
activity, etc.) and any subsequent tropical disturbances and moisture as well 
as the majority of dynamical model guidance from the NMME, data from the IMME 
predecessor, Copernicus data, as well as some statistical forecast guidance. 
The CFS precipitation forecast was considered an outlier and was discounted. 
Week 3-4 model guidance was mixed in this region as well so probabilities are 
quite modest for this half-month lead outlook. 

Support for below-normal precipitation for the north-central Rockies to the 
northern Plains is modest, but is included due to long term negative 
precipitation trends, some support from dynamical model guidance, and  
anomalously dry conditions potentially limiting local recycling of 
precipitation. There remains a high degree of uncertainty for the timing and 
strength for the start of the Southwest U.S. monsoon this year. 

There is a modest tilt in the odds for above-normal precipitation for western 
Alaska based on model guidance and above-normal sea surface temperatures in 
nearby waters. Equal-chances (EC) is designated in remaining areas where the 
forecast probabilities are not effectively different from climatological 
probabilities for either above-, near- or below-normal monthly total 
precipitation amounts.

FORECASTER: Jon Gottschalck

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 16 2020

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