Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks
NWS Climate Prediction Center College Park, MD
300 PM EDT Thu April 18 2024

6-10 DAY OUTLOOK FOR APR 24 - 28 2024

A transient 500-hPa height pattern is forecast across North America during the 
6-10 day period. At the outset of the period, troughing and negative height 
anomalies are predicted across eastern Canada and extending into the Great 
Lakes and Northeast. Amplified ridging is forecast to shift eastward across the 
CONUS with troughing developing near the West Coast in its wake. The pattern 
across Alaska is predicted to quickly transition from enhanced ridging and 
positive height anomalies at the outset of the period to more influence from 
troughing over the Bering Sea and Arctic. Near- to above-normal heights are 
predicted across Hawaii due to increased ridging over the central Pacific.

Models are in good agreement regarding near- to below-normal temperatures 
across much of  the western CONUS during the period, consistent with decreasing 
mid-level heights and increasing troughing in the region. Today’s forecast 
depicts enhanced probabilities for below-normal temperatures over much of the 
Northeast and northern Mid-Atlantic for the period as a whole, along with 
increased chances for above-normal temperatures across the interior western and 
central CONUS, and Southeast. Ridging and above-normal 500-hPa heights across 
Mainland Alaska and Southeast Alaska favor increased chances for above-normal 
temperatures across eastern Mainland Alaska and Southeast Alaska. Elevated 
probabilities for below-normal temperatures are forecast for the western 
Aleutians due to below-normal 500-hPa heights. Near-normal temperatures are 
predicted across the Hawaiian Islands.

Return flow around surface high pressure favors increasing precipitation 
chances across parts of the central and southeastern CONUS. Above-normal 
precipitation probabilities are increased over much of the West due to 
troughing forecast to develop near the West Coast. Increased southerly flow 
across Alaska ahead of developing troughing over the Bering Sea favors enhanced 
chances for near- to above-normal precipitation across the state. Near to 
below-normal precipitation chances are elevated across Hawaii due to increasing 
ridging over the central Pacific.

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: 3 out of 5, Average, due to 
generally agreement in the models regarding the mid-level pattern evolution, 
offset by lack of forecast tools due to IT outage.

8-14 DAY OUTLOOK FOR APR 26 - MAY 2 2024

The 500-hPa height pattern during week-2 is forecast to continue to depict 
amplified ridging and positive 500-hPa height anomalies continuing to expand 
across the central and eastern CONUS. Troughs are predicted across the western 
CONUS and Alaska, with the 0z GEFS being the most amplified with these features 
compared to the 0z ECMWF and Canadian. 

The prevailing mid-level height pattern across the CONUS favors an anomalously 
warm pattern across much of the CONUS east of the Rockies during late April. 
The highest probabilities for above-normal temperatures (greater than 70 
percent) are across the Great Plains and Middle Mississippi Valley, with 
decreasing chances further east as there is some uncertainty related to the 
lingering below-normal temperatures at the start of the period. Near- to 
below-normal temperatures are favored along the West Coast and Southwest due to 
more troughing. Decreasing mid-level heights favor elevated probabilities for 
below-normal temperatures across portions of western Mainland Alaska and the 
Aleutians, with near-normal temperature remaining favored downstream across the 
eastern Mainland and Southeast Alaska. Increased chances for near- to 
below-normal temperatures remain forecast across Hawaii.

The trend toward relatively lower mid-level heights across the western CONUS 
favors increasing chances for above-normal precipitation across a large portion 
of the CONUS, aided in part by increased southerly return flow over the central 
CONUS. This pattern sets the stage for multiple episodes of precipitation as 
ejecting shortwave disturbances promote a favorable environment for enhanced 
precipitation across much of the region, with the GEFS reforecast tool 
indicating a strong signal for above-normal precipitation across the Southwest 
given the lower climatologies in the region. Near-normal precipitation is 
favored along the Eastern Seaboard, farther displaced from the forcing 
upstream. Although there are some indications for below-normal precipitation, 
uncertainty regarding shortwaves emerging from the central CONUS support a 
forecast of near-normal precipitation for much of the East, except for south 
Florida where below-normal precipitation chances are slightly elevated. 
Probabilities for near- to above-normal precipitation remain elevated across 
Alaska. Near- to below-normal precipitation is favored across Hawaii.

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Average, 3 out of 5, due to good
model agreement regarding amplified ridging across the eastern half of the
CONUS and a subsequent warmer pattern, offset by lack of forecast tools due to
IT outage.

FORECASTER: Luke He

Notes:


Automated forecasts are issued on Saturday and Sunday. Occasionally manual
intervention is necessary to address quality control and consistency issues. In
these cases, forecasts are manually drawn but a full discussion is not issued.


The notation for the categorical forecast indicated on the maps is the same as
that in the tables: A-above   N-near normal   B-below


The temperature map shows regions with > 33% chance of being warmer (orange,
"A"), colder (blue, "B"), or close to (unshaded, "N"). Historical average
values for the calendar period of the forecast (dashes, "f").  Labels on the
shaded lines give the probability (> 33%) of the more likely category (B or A).
 Probability of N is always < 40%.


The precipitation map shows regions with > 33% chance of being wetter (green,
"A"), drier (tan, "B"), or close to (unshaded, "n"). Historical median values
for the calendar period of the forecast (dashes, "inches").  Labels on the
shaded lines give the probability (> 33%) of the more likely category (B or A).
 Probability of N is always < 40%.


In the southwest and other climatologically dry regions - there will be a
greater than 33.3% chance of no precipitation and occasionally even a normal
(i.e. Median) value of zero - especially during the dry seasons.  In such cases
a forecast of near normal is effectively a forecast of little or no
precipitation.


The climate prediction center uses 1991-2020 base period means as reference in
the climate outlooks.

The next set of long-lead monthly and seasonal outlooks will be released on
April 18.


Analogs to the 5 day mean observed pattern centered 3 days ago (D-3)
for the region from 20N to 70N latitude and 175E to 60W longitude
include the 5 day periods centered on the following dates:
20080411 - 19770418 - 19640426 - 19550412 - 19990405


Analogs to the 7 day mean observed pattern centered 4 days ago (D-4)
for the region from 20N to 70N latitude and 175E to 60W longitude
include the 7 day periods centered on the following dates:
20080410 - 19770419 - 19640425 - 19550412 - 19610418


6-10 DAY OUTLOOK TABLE
Outlook for Apr 22 - 26 2024


8-14 DAY OUTLOOK TABLE
Outlook for Apr 24 - 30 2024


                           LEGEND
TEMPS WITH RESPECT TO NORMAL     PCPN WITH RESPECT TO MEDIAN
A - ABOVE   N  - NEAR NORMAL     A - ABOVE   N - NEAR MEDIAN
B - BELOW                        B - BELOW

THE FORECAST CLASSES REPRESENT AVERAGES FOR EACH STATE. NORMAL
VALUES - WHICH MAY VARY WIDELY ACROSS SOME STATES - ARE
AVAILABLE FROM YOUR LOCAL WEATHER SERVICE FORECAST OFFICE.

FOR ADDITIONAL INFORMATION SEE MESSAGE FXUS06 KWBC - ON AWIPS AS
PMDMRD.

$$