Written by Sig Silber
At the end of every month, NOAA updates their Early Outlook for the following month – in this case April, 2018. As T.S. Eliot opined that “APRIL is the cruellest month“, the forecast for April is cruel but for different reasons than Eliot had in mind with the worst part of the area with extreme or exceptional drought maintained and the Northeast and Great Lakes forecast to be cold and wet. All of this and more is discussed in this Month-End update.
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We start with the question “Is La Nina still a factor?”
NOAA Update of their Outlook for April, 2018
NOAA has, as usual, issued an update for the month following the last day of the prior month. This NOAA update was issued today Saturday March 31, 2018. In this GEI Update Report, we present the Updated NOAA Outlook and compare it to the Early NOAA Outlook for April issued on March 15, 2018 about two weeks ago. Please note: all smaller graphics can be enlarged by clicking on them or right clicking and selecting the “view image) option.
First, I present a summary showing the prior and the new. Larger graphics follow but these smaller graphics can be enlarged.
|Prior Issued on March 15, 2018|
|Updated on March 31, 2018|
And now the larger graphics and my comments
Prior Temperature Forecast Issued on March 15, 2018
New Temperature Forecast Issued on March 31, 2018
Turning to Precipitation
Prior Precipitation Forecasts issued on March 15, 2018
New Precipitation Forecast Issued on March 31, 2018
Here is the NOAA Discussion released on March 31, 2018 with the April Update. Because this is the day after the Week 3 – 4 Release, we are assuming that todays discussion of the April Update incorporates the key elements of the Week 3 – 4 discussion so we are not including that discussion but it can be accessed here.
30-DAY OUTLOOK DISCUSSION FOR APRIL 2018
THE UPDATED MONTHLY OUTLOOK FOR APRIL 2018 IS BASED PRIMARILY ON SHORT- AND EXTENDED-RANGE TEMPERATURE AND PRECIPITATION OUTLOOKS FROM WPC AND CPC, CFS 30-DAY FORECASTS OF TEMPERATURE AND PRECIPITATION, MJO-BASED CONSIDERATIONS, RECENT SOIL MOISTURE OBSERVATIONS, THE CONSTRUCTED ANALOG BASED ON SOIL MOISTURE (CAS), SEVERAL RUNS OF THE GFS TOTAL PRECIPITATION FORECASTS FOR THE NEXT TWO WEEKS, SSTS NEAR THE SOUTHWEST COAST OF ALASKA, AND APRIL CLIMATOLOGY.
THE UPDATED TEMPERATURE OUTLOOK FOR APRIL 2018 DEPICTS ENHANCED ODDS OF BELOW NORMAL TEMPERATURES FROM ABOUT THE NORTHERN AND CENTRAL CONTINENTAL DIVIDE EASTWARD ACROSS THE NORTHERN AND CENTRAL GREAT PLAINS, THE UPPER AND MIDDLE MISSISSIPPI VALLEY, THE GREAT LAKES REGION, THE OHIO VALLEY, THE NORTHERN AND CENTRAL APPALACHIANS, THE NORTHEAST, AND THE MID-ATLANTIC. THE SPATIAL EXTENT OF THIS COLD ANOMALY IS PREDICTED AT EACH TIME-SCALE OUT THROUGH THE NEXT 30-DAYS. THE PAST 9 RUNS OF THE CFS MODEL ARE REMARKABLY STABLE IN PREDICTING THIS AREA OF ANOMALOUS COLD FOR APRIL. ENHANCED CONVECTION ASSOCIATED WITH THE MADDEN-JULIAN OSCILLATION (MJO) OVER THE WESTERN PACIFIC AND WESTERN HEMISPHERE DURING WEEK-1, AND THE WESTERN HEMISPHERE AND AFRICA DURING WEEK-2, CORRELATES WELL WITH BELOW NORMAL TEMPERATURES ACROSS THE NORTH-CENTRAL CONUS ABOUT TWO WEEKS INTO THE FUTURE. PROBABILITIES TOP 70% IN PARTS OF THE NORTHERN PLAINS, WHERE TEMPERATURE DEPARTURES OF 12 TO 24 DEGREES F BELOW NORMAL ARE PREDICTED BY WPC WITHIN THE FIRST WEEK TO TEN DAYS OF APRIL. ENHANCED ODDS OF ABOVE NORMAL TEMPERATURES ARE PREDICTED FOR MOST OF THE SOUTHERN HALF OF CALIFORNIA, THE CENTRAL AND SOUTHERN GREAT BASIN, THE SOUTHERN ROCKIES, MUCH OF TEXAS, AND THE FLORIDA PENINSULA. THE GULF COAST STATES ARE ANTICIPATED TO BE NEAR TO BELOW NORMAL DURING THE FIRST TWO WEEKS OF APRIL, AND NEAR TO ABOVE NORMAL FOR THE SECOND HALF OF THE MONTH. WITH A VARIABLE MIX OF TEMPERATURES EXPECTED, AND A MIX OF NEAR TO BELOW NORMAL SOIL MOISTURE, IT WAS DECIDED THAT EQUAL CHANCES (EC) IS THE BEST BET FOR THIS REGION. ABOVE NORMAL TEMPERATURES ARE ALSO FAVORED FOR MUCH OF ALASKA, WITH THE EXCEPTION OF THE PANHANDLE REGION, AND NORTHEASTERN ALASKA, WHERE OCCASIONAL COLD AIR INTRUSIONS ARE ANTICIPATED. PROBABILITIES FOR ABOVE NORMAL TEMPERATURES EXCEED 50% IN EXTREME SOUTHWESTERN ALASKA, IN PART DUE TO THE PROXIMITY OF RELATIVELY WARM SSTS.
THE UPDATED PRECIPITATION OUTLOOK FOR APRIL 2018 DEPICTS ENHANCED ODDS OF ABOVE NORMAL PRECIPITATION OVER MUCH OF THE NORTHERN AND EASTERN HALVES OF THE CONUS. THIS BROAD SWATH OF FAVORED ABOVE NORMAL PRECIPITATION DENOTES, IN A ROUGH SENSE, THE MEAN EXPECTED POSITIONS OF THE POLAR JET STREAM AND STORM TRACK. THE CONFLUENCE OF NORTHERN STREAM ENERGY WITH MOISTURE STREAMING UP FROM THE GULF OF MEXICO OVER THE TENNESSEE AND OHIO VALLEYS FAVORS PEAK PROBABILITIES IN EXCESS OF 50% FOR THAT AREA. THIS BROAD AREA OF FAVORED ABOVE NORMAL PRECIPITATION ALSO HAS THE SUPPORT OF PRECIPITATION FORECASTS AND OUTLOOKS AT LEAST THROUGH MID-APRIL, WITH A DRIER PATTERN ANTICIPATED DURING WEEKS 3,4 ACROSS THE DEEP SOUTH. THE MOST RECENT RUNS OF THE CFS ALSO LEND ADEQUATE SUPPORT FOR THIS EXPECTED AREA OF ANOMALOUS WETNESS. BELOW NORMAL PRECIPITATION IS FAVORED OVER THE SOUTHERN HALF OF CALIFORNIA, MUCH OF THE SOUTHERN HALVES OF THE GREAT BASIN AND ROCKIES, WESTERN OKLAHOMA, AND WESTERN AND SOUTHERN PORTIONS OF TEXAS. THIS LARGE REGION IS FORECAST TO BE WELL REMOVED FROM THE ANTICIPATED MEAN STORM TRACK DURING APRIL, AND IS TYPICALLY DRIER AT THIS TIME OF YEAR. BELOW NORMAL PRECIPITATION IS ALSO FAVORED OVER THE FLORIDA PENINSULA. THIS IS DUE IN PART TO APRIL TYPICALLY BEING THE HEIGHT OF THE DRY SEASON IN THIS AREA, AND TO PRE-EXISTING DRY SOILS FOR MANY AREAS. THE STORM TRACK IS ALSO FORECAST TO REMAIN NORTH OF THE SUNSHINE STATE. FINALLY, THERE ARE ELEVATED ODDS OF BELOW NORMAL PRECIPITATION FOR THE ALASKA PANHANDLE IN APRIL, DUE TO RECENT RUNS OF THE CFS MODEL, AND WHAT APPEARS TO BE A SOUTHWARD DISPLACED JET OVER VANCOUVER ISLAND AND THE U.S. PACIFIC NORTHWEST.
ELSEWHERE, EQUAL CHANCES (EC) OF BELOW, NEAR, AND ABOVE NORMAL TEMPERATURES AND PRECIPITATION ARE FORECAST, CORRESPONDING TO AREAS WHERE CLIMATE SIGNALS ARE RATHER WEAK AND INDISTINGUISHABLE FROM NOISE AND/OR WHERE THE VARIOUS MODELS AND TOOLS EXHIBIT SIGNIFICANT DISAGREEMENT.
Sometimes it is useful to see how the Monthly forecast fits with the 1 – 5 Day, 6 – 10 Day , 8 – 14 Day and Week 3 and 4 forecasts. I do not have comparable maps for the Day 1 – 5 forecast in the same format as the three maps we generally work with. What I am showing is the Day 3 Maximum Temperature and the five-day precipitation: the latter being fairly similar in format to the subsequent set of the maps I present each week but showing absolute QPF (inches of precipitation) not QPF deviation from Normal. .
Sometimes it is useful to see how the Monthly forecast fits with the 6 – 10 Day , 8 – 14 Day and Week 3 and 4 forecasts. To be complete we should look at Day 1 – 5 also. I do not have maps for the Day 1 – 5 forecast in the same format as the three maps we generally work with. What I am showing is the Day 3 Maximum Temperature and the five-day precipitation: the latter being fairly similar in format to the subsequent set of the maps I present each week. You can click on these maps to see larger versions. The easiest way to return to this report is by using the “Back Arrow” usually found top left corner of your screen to the left of the URL Box.
First the short-term Five Day Maps
Then our regular set of forecast maps.
And then Precipitation
Sometimes it is useful to compare the forecast for the current month with the three-month forecast.
April 2018 Plus April – June 2018 Outlook
One can mentally subtract the First-Month Outlook from the Three-month Outlook and create the Outlook for the last two months in the three-month period.
*The concept is that the probabilities of a deviation from climatology in the First Month and the combined Month Two and Three forecast that one derives must average out to the probabilities shown in the three-month maps.
Some Indices of Possible Interest:
Phases of the PNA pattern (N.C. State) PNA Negative is on the right. The Pacific Hawaiian High with a Negative PNA is out to sea allowing the Pacific Troughs and also Gulf Coast moisture entering CONUS. But the PNA may not be controlling this change in pattern. The part about Gulf of Mexico moisture entering CONUS is in the forecast.
We wonder how the new forcast for April might impact the Drought Situation.
The U.S. Drought Monitor is a comprehensive way of understand the drought situation for the U.S. If is issued every Thursday and reflects the conditions as of the prior Tuesday. The drought monitor is not just based on precipitation but the condition of the land so it generally reflects more than a month’s precipitation and temperature and wind.
Because of the current drought conditions we now publish a Drought Update on Thursdays. You can access the most recent report here. That report will be update tomorrow.
I now show the 30 Day and 90 Day Temperature and Precipitation History. As you can see, the lack of precipitation has persisted for a while and has gotten more extreme as has the warm anomaly relative to the time of the year.
Finally there is the issue of floods and tornados