Well here we are at the end of July and the Summer has turned out VASTLY different from what most forecasters and speculators thought we would have at this time. The late Spring and early Summer months from the Plains to the East coast has been rather cool and VERY WET - especially EAST of the Mississippi River. The amount of rainfall we have seen over much of the Grain growing areas has been steady and at times heavy. When drought hysteria reached its peak in early May, the main concern was the deep, dry, subsoil moisture or lack of it, that had developed during a very dry Autumn 1999 and Winter 2000. The way things were looking was that even a "normal rainfall" during the Summer months would have produced a significant drought. Additionally, the Climate Prediction Center' s high profile news conferences convinced many traders and planners that there was going to be a serious drought over most of the U.S. this Summer. Given the established strong correlation between Strong La Nina events and above normal temperatures and below normal rainfall over of the Plains, it convinced many traders, both professional and the small timers, to take long positions.
I don' t want to harp on this too much but there are traders both at the professional and small timer that subscribe to Weather Traders Edge and have told me off losses this Spring and Summer over over $75,000. If you have not seen my May 15 Summer forecast please click HERE and I think you will be ...well "intrigued". I think its a good one --- perhaps one of my best seasonal forecasts in a while. But in this regard my opinion doesn't matter. Yours does.
CURRENT UPPER AIR PATTERN AT THE END OF JULY
In all of the maps you are about to view, there are several features for your consideration that I have highlighted. Area "A" is the western US Heat Ridge, Area"B" is the Eastern U.S. Trough, AREA "C' is the Western Atlantic Ridge ( Bermuda High) and AREA "D" is the Blocking Feature over North central Canada.
Back in early July the Eastern U.S. trough was located right along the immediate coast. However since the the July 4th holiday, the overall Upper Air pattern has been one of "RETROGRESSION" which means the overall Upper Air patterns are moving from EAST to the WEST (as opposed to the normal movement of West to East). At Fig. 1 we can see the Eastern U.S. trough over the East coast ("B")and the Heat ridge over the western Plains ("A") and the Western Atlantic ridge is way off the coast ("C"). A week later (FIG 2 July 15) we see the Heat ridge has moved into the Western U.S., the Eastern U.S. trough has shifted inland and the western Atlantic ridge has pushed to the East coast. It is also important to note the depth or amplitude of the trough which is (was) record breaking. One of the NWS offices in PA recently made the statement that the Deep Eastern U.S. Trough -- on the one on Fig 1 July 15-- was perhaps the deepest trough ever seen for July.
Fig3 shows the current pattern as we head into August. The
heat ridge is entrenched over the western US, the mother of all blocking features still
dominating Canada and the Eastern U.S. still in a rainy pattern. While it has
been hot at times in the Deep South, Richmond VA recorded only 2 days with Max
temperatures above 90 for the whole Month! Overt the northern third of the nation
Chicago. Indianapolis Detroit,
Des Moines, Columbus Cleveland, Pittsburgh, Philly, NYC, Boston did not see a single reading of 90 F the whole month. Syracuse recorded its coldest or 2nd coldest July on record with the coldest July on record for Binghamton and Wilkes-Barre Scranton PA, 4th coldest at NYC, 3rd coldest at Buffalo etc etc
Back on May 15 2000 this was my "Early Call" has to how the overall pattern would be shaping up for the Second Half of the summer season. By the term "Second Half" I refer to the period from August 1 to September 30)
CURRENT STATUS OF THE LA NINA as of July 20--- NOT QUITE DEAD YET...
The MEI chart shows that the La Nina has not yet ended. I know it was declared "dead" a while ago but clearly the La Nina --weak as it is-- is still holding on. This is rather ominous looking for the Hurricane season. The connection between la Nina events are above normal hurricane activity is well established and I do subscribe to the still debated theory that Weak to moderate La Nina events have a tendency for increased landfalling Tropical cyclones.
WILL THE PATTERN RETROGRESSION CONTINUE?
MOST LIKELY Fig5 BUT THERE IS THIS ---> Fig 6
The later half of the summer Forecast is based on 2 KEY points.
First point is whether the overall pattern Retrogression will continue or if it has ended.
The interaction between the very stubborn North central Canada block ( the area marked as "D" on these maps) and the intense Polar Vortex (hereafter known the PV) that has been rotating around the arctic regions this summer.
Earlier in July, when the Eastern U.S. trough was at its Max amplitude, the PV was EAST of the Block -- in other words located over Hudson's Bay-- and was dumping some very cold air for middle July even by Canadian standards. By the 22nd of July the PV has shifted east and was over Greenland. This enabled the Eastern US Trough to lose its amplitude and kept the overall pattern fairly flat and zonal. As we head into August the PV is currently located over NE Siberia. My concern is that when the PV slides east over the Canadian Block ( the area marked as "D") it will re-energize the Eastern US Trough and send a shot of very cool air southward.
On this basis I think there will be an early Frost over Manitoba and Ontario Canada before or around September 1. It has been too cold there in July for one NOT to be at least concerned about this threat. moreover, unlike the US Grains their planting started late and they are very exposed to the Frost threat. Traders should watch this carefully -- in particular the Wheat and Oats. This also has some implications for the US Grains as well but in anticipation of the Drought much of the US Crops were planted early so the "window" of Frost opportunity is that might do damage and rive up prices is smaller than normal.
LONG RANGE REGIONAL SPECTRAL MODEL -- A.K.A RSM
Fig 7 Fig 8
Here is the latest versions of the RSM or REGIONAL SPECTRAL MODEL. This is a rather unknown and unused model that has been developed by NCEP and the Scripps institute out in California. they run it weekly out to 30 days and it has done a really GREAT job this summer. These two panes that I have presented here are the mean (average) 500 MB patterns on a weekly basis. Note the yellow line. Fig 7 is the period from Aug 6 to 12. If you have seen the models in early August you will have seen strong indications of another large Eastern U.S. Trough developing during the period Aug 6-12. Fig 8 is the week from Aug 13-19. The pattern here has relaxed a bit but as you can see the eastern us trough has still not yet really dissipated or lifted out.
The depth of the western Atlantic ridge this summer has been very strong -- at times nearing 600 Dm. The subtropical ridge that sometimes extends from the African coast to the SE coast vicinity has been very strong, deep and will ensure long tracking tropical origin Hurricanes ( a.k.a. Cape Verde 'canes) that may not have little chance to turn out to see.
This type of pattern is also quite threatening to the East coast IF the Eastern U.S. trough is amplified when the Hurricane is approaching the US mainland. Certainly given the depth of the trough for July which, as I mentioned above, has been evaluated as one of, if not the deepest ever seen for July, then it is NOT unreasonable to be concerned that come later August, September and October the trough may be even amplified! It is possible that we may be looking at a near ideal situation --something akin to what we saw in the 50s East coast hurricanes-- pattern wise for Major East coast hurricanes. Whether this scenario is likely or not I have no idea. But I am certain about this point.
The size of the tropical waves coming off the African coast have been very large-- stunningly large IMO. Given the near TEXTBOOK "tropical conveyor" which has already been in position since mid July-- a uniform High pressure ridge extending from the Cape Verde Island to the western Atlantic Ocean-- I think there may be a large number of Major hurricanes that threaten landfall. There may be a some sort of development out by 50 or 60 longitude that will turn these developing 'canes out to sea. But I am concerned about this pattern.
Of course IF the PV is on the other side of the globe when the hurricane approaches then the eastern US trough will be fairly Flat and the long track Hurricanes may be more of a threat to Florida and the Gulf.
On the other hand IF the retrogression does continue , then a Gulf track would be more favored with a turn into the mean trough position. This could pose a real problem for the Deep south's Cotton crops and offer the risk of heavy flooding due to saturated ground in the eastern US.
WXRISK 'S SUMMER FORECAST
|PERIOD OF JUNE 1 TO AUGUST 1 +/- 10 DAYS|
|500 MB MEAN||TEMPERATURES||RAINFALL|
This summer forecast covers the period from June 1 to August 1. At the bottom of the page is the forecast for the latter half of the summer. Essentially a weak La Nina summer usually have 2 distinct phases; an early summer and late summer pattern. The early summer pattern is a continuation of the one that developed in May.
The 500 MB pattern will feature the a mean trough over the Northern Rockies and Upper Plains. This means that there will be a ridge over the West coast and off the Southeast coast (a.k.a. the"Bermuda High") and I place the Mean Jet in a southwest to northeast orientation. The southeast ridge is a text book example of the summer influence of the "Bermuda High".
Temperature wise, the Western High Plains and Northern Rockies will see below normal temps --in some areas Much below normal as they will be either under the mean jet position OR North of it in the cooler air mass. As the mean trough shifts--which it will do from time to time-- to the West coast or as far east as the Western High Plains, the ridge in the eastern Pacific will move inland bringing, searing heat to the West coast for a few days only to re-set as the next North Pacific short wave arrives.
Temperatures over the Plains will average Near normal but this is somewhat deceptive. When the mean trough is over the Rockies, MOST of the Plains' regions, the Mississippi valley and points East will have Above normal temperatures. But when the short waves from the North Pacific and Pacific NW push inland, the fronts will drive south and east into the central Plains and Ohio valley areas, producing above normal rainfall due to prolonged periods of rain as the fronts stall in an west to east direction. And this also mean Below Normal temperatures for several days in a row. So the average temperature forecast is somewhat deceptive.
I think as a whole the summer 2000 will be rather wet. The inflow of high dew points and water vapor into the Deep South is of course, nothing new. But in this position, for a prolonged period the Western Atlantic ridge will pump the very high dew points QUITE far north. I expect to see MANY days of dew points near or above 70 F over Chicago, Detroit, Syracuse, NYC. With the mean trough out by 110 Longitude the western high Plains will see Above Normal rainfall -- and damage to the wheat crop may be a real problem.
In the Northeast US, it looks to be a wet summer for New England and rather off & on temperature wise with the jet not far away and these front laying close to the region with high dew points to work with. Over the Middle Atlantic region it will be a warmer summer and mighty sticky.
With the close proximity of the 500 MB ridge off the southeast coast I think we will see 3 major effects:
Any tropical cyclone activity that moves inland from the Gulf has a good chance of causing SERIOUS FLOOD THREAT to the Tennessee valley and lower Ohio Valley. These areas are going to see Normal to above normal rainfall anyway over the next 45-60 days. A dying tropical system in the pattern I have forecasted will get stuck in a COL or weak spot in the atmosphere where no weather feature is dominated. Thus in this pattern --assuming I am right-- tropical systems would to to far away from the Bermuda high and to far south of the mean Jet. This is the recipe for serious flooding threat.
However after the pattern flip -- within 10 days of August 1 either way-- the Heat ridge that CPC has been looking for over the Plains states will set up... and this places the mean trough over eastern US. If the trough is off the east coast far enough then we may be facing a re-curving seasoning like 1995 or 1949. I will make a call later in the season about this.
THE REASONING BEHIND THE FORECAST
Even a cursory glance of my summer forecast shows that my forecast is as diametrically opposed to the the now infamous drought forecast that have been coming out of Climate Prediction center as you can have. I really respect the folks at CPC. They are some of the best long range scientists in the world, IMO. Over the last 5 - 7 years, their seasonal forecasts are MUCH improved. Their hurricane forecast in June 1999 was right on the mark and their Seasonal Winter forecast over the last 3 winters in the U.S. as close as one can be ( although they missed the significance of the Ireland Greenland Monster block that lasted 4 weeks in Mid Jan to Mid Feb).
A large part of my forecast is based on the collapsing La Nina and the overwhelming climatological evidence regarding what sensible weather conditions that occur during STRONG La Nina and WEAK La Nina events. It is well known that the strengths and location of the La Nina events have major impact upon the Summer and Winter forecast over the U.S. The recent issuance of the Middle June summer forecast from CPC is to me utterly baffling. Considering that the main premise for the HOT & DRY summer forecast that CPC has been issuing since March was that the La Nina would stay strong right through the summer. Yet as CPC is well aware of, that La Nina went through a major collapse during late April and May. That being so, why would anyone stick with a HOT & DRY forecast when the premise of the forecast (strong La Nina conditions will continue through the summer..) is no longer valid?
Go figure. I cannot. Let me be clear. I am NOT dumping on the "Hot and Dry" forecast. It is quite possible that CPC may turn out right and I may be wrong. I just do not see the logic of keeping the same forecast when the underlying conditions have utterly and completely collapsed (yes Ii know about Lag time effects).
So I kind of have to take issue with the "Drought" forecast. I suspect this will be somewhat controversial to some and I suppose that is just they way I am... but in order to have a drought, it has to be NOT raining. I am fairly certain about this. I remember the day I was taught this in undergraduate school like it was yesterday. The professor said "Droughts are usually dry" or words to that affect..
TRACKING LA NINA 2000
This chart comes from the Climate Prediction center La Nina page which is the best Net site in the world regarding la Nina and El Nino events.This chart plots the biggest La Nina events since 1950. The dashed black line is the CURRENT L La Nina. At point "A" the la Nina reached its first Nadir in the winter of 1998-1999. The turn around from the monster Peak of the El Nino just a few months ago was the sharpest and fastest turn around ever seen in the El Nino- la Nina cycle. The 1998-2000 La Nina was NOT the strongest La Nina (at -1 standard deviation) but it fell from the warmest Peak, as it were. The La Nina began to weaken slightly at point "B" only to re-strengthen in the winter of 1999-2000.
Point C shows the current status of the La Nina. Note the rapid the "rise" on the dashed black line as it heads towards the zero line. The rise shows weakening and it has all occurred in the last 2 months. Therefore I think it is safe to say that we can no longer use the Climatology of "STRONG" La Nina as a forecast guide. We have to use :"weak La Nina"-- and in the June 15 discussion CPC said the same thing.
CLIMATOLOGY FOR STRONG LA NINA SUMMERS
These climo maps are pretty self explanatory. Strong La Nina has a high correlation to Hot & Dry (drought).
CLIMATOLOGY FOR WEAK LA NINA SUMMERS
Weak La Nina have a high correlation to WET and COOL. .. which is clearly what the current weather patterns are depicting..
500 MB PATTERN
500 MB PATTERN EARLY
15 - 20 MAY 2000 JUNE 2000
FIG 1 FIG 2
I will start out with a review of May and early June. This summer forecast, first issued to some private clients has not really changed much and I don't think it will either. The month of May saw a large increase in monthly rainfall totals with several MAJOR weather systems bringing heavy rains to Chicago (200% above normal) waterloo Iowa (4.50" above normal rain), Wisconsin, the eastern Corn and Soy belt etc. However, south of Interstate 80 much less rain fell and the drought was still going as the month came to a close... with more substantial rain over much of the nation east of the Rockies memorial day weekend. In fact FIG 1 shows a pattern that, I think, will be the mean pattern is going to be the first half of the summer as a whole. On the 500 MB chart there is a Flat ridge center over the southern Plains which serves to protect the drought areas from seeing much rainfall. There are 2 mean troughs --one off on the west coast and the other off the east coast (near 70 Longitude). The trough off the eastern US coast is transitory. The PJ (Polar jet) ran very active and VERY strong the whole month of May (which is typical in a La Nina event) and was constantly dropping into the central and Northern US which in turn drove strong cold fronts pretty far south and helped to make the month rainy.
This pattern has continued for much of June. In early June (figure 2) there was change. The pattern briefly amplified with a major ridge developing over the west coast of North America -- this is known as the Positive PNA pattern -- and it brought in more usually strong cold air masses that drove into the middle of the nation and placed the eastern US in the mean trough. For several days the Ridge over the Canadian & US Rockies shifted eastward and the Plains did heat up. Many locations in SD & Nebraska reach 100 to 105 for 3 or 4 days. However, this heat did not last long as more energy came in from the North Pacific and ripped the top of the plains ridge off.
The problem with a Hot and dry forecast is that the Pacific jet remains VERY strong and the flow over the central Pacific remains split. The NP oscillation has been in a positive phase as well, which means strong Pacific systems will crash into the Pacific NW and prevent any sustainable "Heat Ridge" from locking into place .