The Use of Hovmoller Analysis of 500 millibar Height Anomalies for Long Range Forecasting

1. The Use of Hovmoller Analysis of 500 millibar Height Anomalies for Long Range Forecasting Robert J. Ricks, Jr. Paul S. Trotter WFO New Orleans/Baton Rouge (LIX)

2. What is A Hovmoller Analysis? • Time-Longitude or Time-Latitude depiction of a parameter. • First documented use in Tellus (1949) by Ernest Hovmoller, of the Swedish Meteorological and Hydrological Institute, Stockholm, Sweden. [Hovmoller, E., 1949: “The Trough and Ridge Diagram”, Tellus, Vol. 1, pp 62-66.] • Used to assess or diagnose the behavior of the parameter over a span of latitudes or longitudes (usually hemispheric) through time.

3. CDC Map room Interactive Pagehttp://www.cdc.noaa.gov/map/time_plot/

4. An example • Ordinate is Time (going down) • Abscissa is Longitude centered at IDL. • Analysis is 500 millibar height anomalies from daily GFS model initialization. • “Hots” are positive, “colds” are negative.

5. AWIPS image of 500 mb Height analysis from GFS initialization.

9. Why 500 millibar Anomaly? • Currently use 10 degree longitude departure from mean at a given latitude. • Readily distinguishes significant trough and ridge positions. • Easier to detect overall Rossby Wave Numbers. • Better indicator of integrity of approaching systems.

10. ANCHORS • Early persistent trough positions (quasi-stationary) • Progressive and retrogressive with wave phase changes.

11. As a Prognostic Tool? • Target longitude (90W). • Signals have nearly linear “rhythmic” trends. • Slope of signals indicative of cumulative Rossby Wave number. • Extrapolation of signals beyond analysis boundary can project future pattern.

12. Purpose • Gain insight into potentially significant events well in advance of the conventional model temporal range. • Improved Situational Awareness • Discriminate active days from ordinary days. • Improve forecaster skill over model performance • Wave phase transitions • “3 – 5 Breakdowns” • Augment Hemispheric Circulatory Oscillation assessment. • ENSO, PNA, NAO, AO

13. Pattern Recognition • Divergent signal crossings usually yield large area of positive anomalies. • Convergent signals usually indicate a retrograding anchor position, hence, a phase transition. • Lower latitude east-west signal crossings in near neutral anomaly areas indicate a tropical cyclone “seedling” – a good 10-14 day lead time. • Lunar cycle correlations • New and Full moon – density driven systems (Arctic Outbreaks) • Quarter moon – thermodynamic bias • Severe local storms • Heavy rains/flooding

14. Forecast Location x Time x x x

15. Successful Results • Successfully forecasted LA ice storm in Feb 1996 with a 21 day lead time. • Lead times of 20-36 days on Arctic air mass intrusions into the Deep South. • Routine indications of frontal passages through about 45 days. • Promising pre-tropical cyclone development and track detection

16. Hovmoller Report • “Science Sharing” newsletter • Select mailing list of NWS peers with similar interests and expertise. (about 22 folks) • Discussion on current hemispheric wave pattern. • Synopsis of latest Hovmoller analysis. • Textual Forecast discussion based on Hovmoller signal projections. • A listing of future signal crossings out usually 30-45 days, highlighting significant ones.

17. Purpose of Report • Involved must be familiar with scheme, share expertise. • Share findings based on the methodology. • Point out future significant events that may impact operations. • Briefing material for WFO/RFC staffs. • National Hazards Assessment. • ??? Interested in adding academia, external stakeholders???

18. Who is involved? • NWS Southern Region MICs, SOOs. • NWS Eastern Region Division Chief. • National Centers Point of Contact • TPC, HPB, SPC • Ed Berry, SOO & Jeff Hutton, WCM (DDC) • SRH Climate Service Focal Point • River Forecast Centers • Lower Mississippi RFC • West Gulf RFC

19. Hovmoller Report 2004-08 February 7, 2004 1200Z Coldest Air to remain North; Some Storminess South Hovmoller diagram: Current through 00Z 06 Feb 2004 Predominant long wave pattern: 1/5 at 40N; 5 at 30N 40N mean height: 5533.1M (+64.2M from last report) 30N mean height: 5738.9 M (+59.5M from last report) Gradient: 205.8M (-4.7M from last report) Next Full Moon: March 06, 0314Z Next New Moon: Feb 20, 0918Z ANCHORS at 40N: Primary 140E, secondary 90W, tertiary 50E, minors 40W, 110W ANCHORS at 30N: Primary 130E, secondary 50E, tertiary 100W, minors 30W, IDL NOTE: Analysis is made available from the NOAA-CIRES/Climate Diagnostic Center (CDC) located on the internet at http://www.cdc.noaa.gov. Analysis Discussion This analysis is quite interesting in several regards. A large positive anomaly area extended over the eastern North Pacific Ocean, serving as a significant block, thereby yielding a major breakdown in the past few days and a general wave transition from the persistent 3/6 wave of the past couple of months to a more transitory Wave 5. There still remains an overall Wave 1 at the northern latitudes that appears to be losing amplitude of late. Of particular note is the increase in average heights at both 30N and 40N latitudes, on the order of around 60M. This is occurring at a time when climatological height minima are normally realized. In comparing to last year’s heights at the same time, the 40N mean height is actually still 30M lower than this time last year, while the 30N mean height is about 30M higher than last year. This correlates well on the sensible weather of the past few weeks with very cold Arctic air masses shunting across the upper U.S., some residual cold air briefly affecting the Deep South at times, but sub-tropical jet influences moderating the region for the most part. The Gulf States have not gotten a true full latitude trough shot of Arctic air, whereby the Arctic high builds due south into Texas then spreads east. The pattern of shunts appears to be waning, but the pattern of large amplitude trough is also becoming less favorable. The signal diagnostics show a few distinctive periods of consequential weather through mid-March with several long periods of lax weather. One point of concern though is the large expanse of snow pack across much of the nation. It would not take as much fetch from the north to get really cold air settled into the Gulf States. It also opens the door for winter storm type weather, as a baroclinic zone will easily become established between the snow pack and the warmer sub-tropical jet influenced southern states. Confidence on timing these events seems high since the number of signal crossings across the U.S. has decreased to just slightly more than a handful in the upcoming 30 days. The uncertainty will lie on the amount of cold air in place at the time of cyclogenesis with these systems. .

20. Oscillation Assessment The Arctic Oscillation (AO) is a slight positive phase and should trend to a moderate positive phase through February 20th. The NAO has trended to neutral after bottoming out at very strong negative at last report. The forecast of the NAO index calls for a hover around neutral through the 20th before trending to a moderate negative phase for the end of the month. The PNA is near neutral but should trend to strong positive by Feb 14th, then return to neutral by Feb 20th. All the oscillation forecasts by the mid and long range ensemble members continue to be too slow in the forecast trends when compared to the actual traces. This will probably remain the case. In addition, the large amplitude peaks in the oscillations were dampened out too much within the ensembles. Hopefully, the phase change in the hemispheric pattern may offer a higher correlation in the oscillation behavior and forecast. Forecast This will simply be an update from the previous report. The big glaring difference will be the lack of a strong or noticeable signal for the end of the month as previously stated. There are three main periods of concern for the southern states. The first will be on the 9th when three signals converge at 30N/88W. This should be a heavy rainfall episode in the Gulf States with perhaps some wintry precipitation across the northern portions of MS-AL, extending into AR and TN. The next signal comes through on the 14th with amplitude from the north, as a strong wave traverses the northern latitudes on the 12th-13th, then amplifies in phase on the 14th with the southern stream. This could be particularly cold for a day or two in the Deep South but not unlike what has been seen already this season. The next stretch of weather is between the 19th and 23rd when five signals cross. Two converge over Texas on the evening of the 18th. This could be a winter storm cyclogenesis that lays a new layer of snowpack across OK-AR-TN with a consideration of ice and sleet for northern MS and AL on the 19th. The other single signals are spread out over a three day period during the pre-Mardi Gras weekend with southern branch induced upper level disturbances imparting stratiform rain chances from the 21st through the 23rd along the Gulf Coast, before clearing out for Mardi Gras Day. A large stretch of positive anomaly heights should linger through about the 4th of March with a significant signal moves through the southern latitudes. For Mardi Gras week (February 17-24), mild weather should accompany the earlier calendar parades, but the big Mardi Gras Weekend (21-22) should be dicey with a rain threat and cooler than normal temperatures for the Endymion and Bacchus super parades. The latest analysis now shows a signal coming through on the 24th around 00Z with positive anomalies building for Mardi Gras Day. This means no rain expected for Mardi Grad Day but temperatures may be slightly cooler than previously indicated. Low 40, high 68, POP 0%, mostly sunny with scattered high clouds. Signal crossings at 40N/90W Signal crossings at 30N/90W Feb 07, 12Z Feb 09, 12Z (three crossings!) Feb 11, 00Z Feb 14, 18Z Feb 12, 18Z Feb 19, 12Z Feb 13, 12Z Feb 20, 06Z Feb 14, 06Z Feb 22, 00Z Feb 15, 21Z Feb 23, 00Z Feb 16, 06Z Feb 24, 03Z Feb 24, 12Z Mar 04, 00Z Mar 01, 03Z Mar 07, 12Z Mar 12, 00Z DISCLAIMER: This is a science sharing NWS endeavor and is in no way intended for public use without prior approval from management. This information should be used in conjunction with other conventional forecasting mechanisms and discussions from national centers. Next report will be around February 17th . RICKS

21. Long Wave Analysis ProgramJay Albrecht – WFO SEA

22. Long Wave Analysis ProgramHovmoller Tool

23. Long Wave Analysis Wave Power by Wave Number

24. Long Wave AnalysisFourier Harmonics

25. Long Wave AnalysisHeight by Latitude

26. Future Endeavors • Development of the HovPlot program • User interaction for selecting signals • Regression and Fourier Transforms computations on extrapolated signals. • Continue summer analysis to improve tropical cyclone detection skill. • Participate in National Hazards Assessment efforts. • Participate in Regional Climate Assessments.

27. Projected HovPlot Application • Define key signal crossings into a forecast area. • Apply harmonic Fourier transforms onto the signals to determine state and intensity of signal passage. • Downscaling - Make finite discrete adjustments to the 30, 60, 90 day outlooks, highlighting local episodic departures from the national forecast products.

28. Credits • NOAA Climate Diagnostic Center (CDC) – CIRES • Jay Albrecht, Forecaster NWS WFO Seattle, WA. • Ed Berry, Science Operations Officer NWS WFO Dodge City, KS • Victor Murphy - NWS SRH Climate Services Focal Point