30 Day Narrative

621 
FXUS07 KWBC 311900
PMD30D
Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT Sun Mar 31 2019
30-DAY OUTLOOK DISCUSSION FOR APRIL 2019
The updated April 2019 outlook takes into account the latest numerical weather 
prediction guidance for the first one to two weeks of the month, as well as the 
subseasonal climate guidance for the Weeks 3-4 period. The overall climate 
background state is largely unchanged from the midmonth outlook. Conditions 
over the tropical Pacific continue to reflect El Nino conditions, with the 
various subseasonal to seasonal climate model forecasts depicting an 
extratropical response over the North Pacific and North America. The MJO 
continues to be weak and does not play a significant role, while soils over 
much of the central and eastern CONUS continue to be remarkably wet relative to 
normal. 
Experimental guidance that calibrates by subperiods of the month (1-3, 4-7, 
8-14, and 15-30 day periods), and then generates an aggregate monthly forecast, 
is used heavily in constructing the current outlook. The latest CFS monthly 
forecast guidance is also considered. The updated outlook is intended to 
reflect the seamless suite of official forecast guidance from Week-1 (including 
WPC forecast guidance) through the Week 3-4 forecast period.
The spatial structure of the updated temperature outlook is very similar to the 
midmonth outlook, except it is notably warmer. The latest guidance from WPC as 
well as the 6-10 day, Week-2, and Weeks 3-4 outlooks from CPC, do not feature 
any areas over the central U.S. where below-normal temperatures are favored 
with any confidence. Therefore we can no longer favor below-normal temperatures 
over parts of the central CONUS. A weakness in the above-normal temperature 
probabilities is depicted over parts of the central and southern Plains, 
consistent with the latest forecast guidance and continued above-normal soil 
moisture. Other key areas of forecast uncertainty exist over parts of the Great 
Basin, the Rockies, and parts of the northern Plains. The latest 6-10 day and 
Week-2 guidance further increases the uncertainty over the Great Basin 
extending westward to parts of northern California. The 0Z ECMWF ensemble mean 
has trended toward an anomalous trough centered over the interior West during 
Week-2, leading to only a weak tilt toward above-normal temperatures for the 
month as a whole. The temperature forecast over New England is less confident 
than in the original outlook due to the increased potential for backdoor cold 
fronts associated with the anomalous baroclinic zone forecast over eastern 
Canada.
There are some large changes in the precipitation outlook due to shorter-term 
weather forecasts. The first ten days or so of April are forecast to bring 
periods of heavy rain to parts of the West Coast associated with the eastward 
extension of a deep, anomalous trough over the Northeast Pacific. This leads to 
a two-category forecast change for parts of the Pacific Northwest. Above-normal 
precipitation remains favored over much of the central and southeastern CONUS, 
with the highest probabilities centered over Southeast Texas. For parts of the 
Northeast, there is some tendency toward above-normal sea-level pressure during 
the first part of the month, though a slight tilt toward above-normal 
precipitation during the 6-14 day period leads to an equal-chances forecast for 
the month. One exception is a slight tilt toward above-normal precipitation 
along the immediate coast. A forecast dry start to the month leads to modest 
probabilities of below-normal precipitation over the far northern Plains. There 
is a large degree of uncertainty over the southern part of the Alaska, though 
some tilt toward above-normal precipitation is still indicated for the far 
southern portions of the state. A dry-wet dipole over central and northern 
Alaska is favored, consistent with retrogression of a rex block over the North 
Pacific/Bering Strait region.
The previous discussion, issued March 21, follows below:
---------------------------------------------------------
The April 2019 monthly temperature and precipitation outlooks were prepared by 
reviewing recent surface boundary conditions, such as anomalous soil moisture 
and snow cover, coherent subseasonal tropical and extratropical variability 
including ENSO and the MJO, decadal timescale temperature and precipitation 
trends, and subseasonal and monthly dynamical model guidance. Tropical climate 
conditions continue to reflect an ongoing El Nino, with enhanced convection 
present over the equatorial Pacific near the Date Line. Predictable impacts due 
to El Nino conditions were compared for consistency with the April temperature 
and precipitation outlooks. No recognizable MJO signal is predicted by current 
dynamical model forecasts for the beginning of April, and any MJO signal 
present may be masked by current El Nino conditions over the tropical Pacific. 
Dynamical model forecasts for the month of April and for 3 to 4 weeks lead time 
into the beginning of April generally indicate troughing over the North Pacific 
to the west of Alaska, ridging over Alaska and much of western North America, 
troughing over the Southwest CONUS, and an amplified ridge and positive 
mid-level atmospheric height anomalies over parts of the eastern CONUS and the 
North Atlantic. This circulation pattern has persisted through recent 
initializations of the NCEP CFSv2 model, as well as recent week 3-4 dynamical 
model forecasts. 
The April temperature outlook indicates likely above normal temperatures for 
all of Alaska, under predicted ridging and above normal mid-level atmospheric 
heights over much of the state. In addition, lower ice cover than long term 
averages during transition seasons and above normal sea surface temperatures 
enhance the probabilities for above normal average temperatures for the month 
of April for the Aleutian Islands and the south and west coasts of mainland 
Alaska. Predicted ridging over western North America increases the chances of 
above normal temperatures for the Pacific Northwest for April as well. Greater 
than normal precipitation over the last several weeks has lead to extremely 
high soil moisture anomalies over much of the Great Plains into the Great Lakes 
region and across the Ohio Valley into the Mid-Atlantic. Snow depth is much 
above normal for parts of Minnesota, Wisconsin and the upper peninsula of 
Michigan. While dynamical model forecasts from the North American Multi-Model 
Ensemble (NMME) indicate weak probabilities favoring above normal temperatures 
for areas of the Northern Plains and western Great Lakes region, a statistical 
forecast of the impacts of El Nino and decadal trends favors near normal 
temperatures, and a constructed analog, based on current soil moisture 
conditions, favors below normal temperatures for this region. Equal chances of 
below, near and above normal temperatures are indicated in the outlook for this 
area, where tools are in conflict with one another. Individual models of the 
NMME, as well as other monthly and week 3-4 dynamical model forecasts, indicate 
a slight increase in the probabilities of below normal average temperatures for 
April from northern Texas northward across the Central Plains states into areas 
of southern Minnesota and southeastern North Dakota. This area of likely below 
normal temperatures is further supported by negative correlations between 
temperature and precipitation during spring and summer months in this region, 
current much above normal soil moisture anomalies, and forecasts for continued 
above normal precipitation into April, including week 3-4 forecasts from the 
ECMWF and CFSv2 models. Above normal temperatures are most likely for much of 
the eastern CONUS, under predicted above normal mid-level atmospheric heights. 
Probabilities for above normal temperatures are further enhanced along the Gulf 
Coast by current above normal sea surface temperatures in the Gulf of Mexico. 
Low predictability and weak signals lead to low coverage in the April 
precipitation outlook at this time. Forecasts from the NMME for the month of 
April indicate an increase in the probabilities of above normal precipitation 
for much of the Great Plains and for the Southeast region. Calibrated 
probability forecasts from the multi-model ensemble show only weak 
probabilities for much of these areas with greater skill and confidence in 
forecasts for the Southern Plains and along the Gulf Coast into Florida. This 
precipitation pattern is consistent with statistical forecasts of the impacts 
of El Nino in spring. Dynamical model forecasts and expected impacts of El Nino 
support increased probabilities of above normal precipitation for the southern 
coast of Alaska and below normal precipitation for western regions of 
Washington and Oregon. Dynamical model forecasts from ECMWF for the week 3-4 
period into the beginning of April further support these precipitation signals. 
FORECASTER: Stephen Baxter
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 May ... will be issued on Thu Apr 18 2019
These outlooks are based on departures from the 1981-2010 base period.
$$