April 18, 2024 3:29 PM
FXUS06 KWBC 181924 PMDMRD FXUS21 KWNC 181905 PMDMRD 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. $$