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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). What is A Hovmoller Analysis?. Time-Longitude or Time-Latitude depiction of a parameter.
Robert J. Ricks, Jr.
Paul S. Trotter
WFO New Orleans/Baton Rouge (LIX)
500 mb Height analysis
from GFS initialization.
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.
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. .
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.
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
NWS WFO Dodge City, KS