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The weather pattern we're locked into right now is one that features large temperatures changes over our region every several days. A few days of 20s and 30s are soon followed by the 40s and 50s, and so on. The movement of weather systems across the country in recent weeks has created spells of "anomalous" weather that just haven't stuck around that long. The forecast models are indeed suggesting this kind of regime will continue for the next 1-2 weeks at least. As they say in Kansas, if you don't like the weather, wait a few days.

Part of the reason for the big temperature jumps is the fact that we're sitting very near the dividing zone (or front) that separates Winter from Fall. As disturbances move along the front, which they tend to do, they deform it like a wave rolling along the ocean. After spending a few days in the trough (cold part) of that wave, we'll get near the crest (warm spot) for a bit. Without those transient systems slowing down, and without substantial movement of the frontal zone they're tracking along, around and around we go. Like a broken record.

Perhaps the most consistent meteorological feature of this pattern has been the lack of precipitation. A surplus of rain over the Spring has turned into a deficit of nearly 5 inches for the 2010 calendar year. And as we look into the forecast model solutions for this upcoming week, it's quite possible that any rain or snow we do get will not be significant.

Aside from providing us with sunny days and clear nights, the dry pattern has also been responsible for allowing our morning lows to plummet well beyond what a typical diurnal swing would give us. Cloudless days with high temperatures in the 40s have been accompanied by lows in the lower teens -not the middle 20s that one might expect with a high of 43. Clear skies, light winds, and a dry atmosphere are the perfect recipe for very cold nocturnal temperatures near the ground.

Until there is a shift in the global circulation, which doesn't look like it'll happen in the next 1-2 weeks, it's a good bet to figure on a dry December with some good cold shots and a warm burst here and there. Status quo.

After a mild stretch (especially for the beginning of November) we are about to see those temperatures come to an end. With that, you can expect our first rainfall for the month of November.

It looks like your Thursday will be the transition day between those warm temperatures and much cooler air that will sliding into place. It will also be the start for rain showers, especially toward the afternoon.

Our best chance for rain will be on Friday as the actual cold front swings through the area. Temperatures will struggle to make it to 50° with clouds and scattered showers likely. The latest model runs show some different solutions to this setup. Most models are showing the rain picking up for the afternoon and evening. If you have plans for the afternoon, there is some hope. There are outliers (models that don't agree with the others) that are working to slow the progression of the front into the area.

If that model run holds true, you can't rule out light rain through the first part of the day. What it does mean is that there is a chance that the bulk of the rain would not be in place until 7 or 8 in the evening. I think that is far-fetched at this point. You can count on this, though. We are looking at the end of those unseasonably warm temperatures.

The "massive" Midwest storm that swept the media's imagination into a frenzy early last week was actually not massive at all. In fact, at 956 mb, it set our national record for the lowest pressure in a nontropical system. According to the National Weather Service, this minimum pressure broke the old record of 28.28" (958 mb) set on Jan 26, 1978 during the Blizzard of 1978 (aka the Cleveland Superbomb). This mark was also lower than that observed during the March 1993 Superstorm (aka "The Storm of the Century"), the "Witch of November" storm that sank the Edmund Fitzgerald in 1975, and even the Columbus Day Storm of October 1962. That technically classifies this storm as exceptionally empty, to a record degree. That's right. It set our national record for a mass deficit in a nontropical storm. But I understand calling it a massive storm. It certainly created impacts on a "massive" scale.

The real issue is that its comparison to a hurricane makes no meteorological sense. Even if the comparison is based solely on wind speed, the analogy is still not accurate. The highest official gust in the storm was measured at 79 mph in Sherwood, Wisconsin. Sustained winds were much lower than that. Technically this is low- to midrange tropical storm strength. Ok, fine. So it didn't quite "measure up" to a hurricane. But the dissimilarity runs much, much deeper than that.

Midlatitude cyclones are remarkably unlike hurricanes for many reasons. They have different dynamics, thermodynamics, microphysics, different physical scales, and on and on. These nontropical storms owe their existence to vertical wind shear (and the "instability" thereof), and hence require strong temperature contrasts to grow and survive. They can develop anywhere -land or sea- (except very near the equator), and do so essentially every day somewhere on the planet.

Hurricanes are comparatively rare phenomenon that can only survive in a tranquil maritime environment. Their development is rooted in the transfer of heat from the ocean via a complicated air-sea interaction. They HATE wind shear and the associated temperature contrasts. The circulation that really defines the tropical cyclone is largely driven by mid-level heating from thunderstorm clusters ... which are not rooted in the kind of pre-existing "instability" that nurtures our thunderstorms here on the continent (where it's cold aloft). Instead, the mid-level heating comes from a self-induced transfer of heat from the ocean surface. Complicated, I know, but these storms are not like our Kansas storms which thrive on cold air aloft. They have to create their own "instability" through a wind-induced exchange of heat from the ocean. The bottom line is that the hurricane machine is derived from a very different set of processes than the kind that creates the "massive" midwest windstorms.

And besides, a large fraction of the population has experienced these midwest windbags. Very few have any idea what the rare and spectacularly tempestuous conditions are like in the eyewall of a major hurricane. That is truly a frightening place to be.

In my opinion, fall has been FANTASTIC, especially by October standards. Yes, we have had our share of cold evenings, even setting records in the beginning of the month, but temperatures have been relatively close to average. Our big drawback has been a lack of rainfall.

Last winter, as you may recall, was a cold and wet one. We had record setting snow events as well as bitter stretches of cold weather. A question that I am often asked is about the outlook for the upcoming winter. My early thoughts on that question has been that we are moving out of the El Nino cycle into a La Nina pattern, which will probably bring us into a slightly warmer pattern. As for the amount of snow or rain that we pick up, that depends. It will likely be a pretty standard winter as far as precipitation.

NOAA just released their winter outlook for this upcoming season which, in essence, describes the same scenario that I described earlier. For the Midwest, NOAA outlines an average precipitation outlook with an above average temperature trend.

Temperature Outlook For 2010-11 Winter by melwellku

To break this outlook down to something that we can use is fairly straightforward. The trend is for an average precipitation outlook and above average temperatures. That translates to most of us that we could see a lot more rain than snow, and after last year's winter, I am sure that there are plenty of people that would welcome that outlook. Unfortunately, it likely won't work out quite that way.

Certainly we could see it play out exactly like that. But it only takes a couple of well-time cold snaps along with appropriate moisture and we could see the heavy snow storms that we picked up last year (Christmas Eve comes to mind, as does the late March storm that dumped snow on us).

As you probably know, there are no guarantees when it comes to forecasting weather, and that especially true when you are looking long-term. While these outlooks are reassuring, we still need to be prepared to see plenty of days that will require some shoveling.

The truth is, we are down over 3.5 inches in total precipitation for the year, and could stand to pick up some moisture, no matter what form it comes down.

What a difference a year makes. Summer 09 will be remembered in our region for its unseasonable chill, and the brutal winter of 09-10 was one for the record books here in Eastern Kansas. But those cold times seem a distant memory now. Since last winter, we've had quite a stretch of above-average temperatures in our area. In fact, monthly departures from "climatology" (a 30-year mean) have come in on the warm side since last March.

Our Warm Spring And Summer by gpostel

The abrupt shift from really cold to really warm across the United States (see footnote) occurred early last Spring, as the decline of El Nino -among other factors- nudged the global atmosphere toward a place that kept the warm air coming over the Central Plains. After only twenty five 90-degree days in the Summer of 09, Lawrence notched a more respectable 58 this season, in addition to eight 100-degree days. And while the pattern this month (October) has shown some tendency to bring an occasional cold front our way, none of the cooling has lasted more than a couple of days. Instead, the cool shots have been more than balanced by warm anomalies in between. Like clockwork, October is on pace to be the 8th warm month in a row.

However, there is some temporary hope for cold air lovers. And, oddly enough, it probably has something to do with Super Typhoon Megi in the West Pacific. This is because the weather over North America is often jolted when big hurricanes move out of the tropics and into the jetstream flow, just as Megi will do in the coming days. And for complicated reasons, the resulting pattern occasionally favors a southward penetration of "cold" air from Canada.

Some of the global weather models want to go this way late next week. It's a long way out, of course, with lots of variability in the forecast yet to be resolved, but I've seen this big picture before. The migration of strong tropical cyclones into the westerlies can indeed be a meterologically traumatic event. But I should also mention that, because this particular event appears unaccompanied by a larger movement toward a new pattern, our consequences may not last more than a couple of days. But we're used to that, right ?

*Footnote: In the global average, however, 2009 and 2010 have been extremely warm despite the regional chill observed across the United States.

In Kansas, most people think of one time of year for severe weather season... spring. In many respects that is correct. The spring storm season has some of the most violent storms that Kansas has to offer. If you think about the shear number of severe thunderstorms that we see in the region, that stands to reason. The more storms that you see, the likelihood that we will experience damaging wind, hail and the occasional tornado will go up.

The driving force for this is the jet stream. Each spring the jet stream makes the yearly migration to the north. When this happens, we a sudden spike in the ingredients that we need for thunderstorm development. The temperatures get warmer, the moisture content in the air goes up and we get upper level support from the jet stream which allows the frequency and strength of thunderstorms to go up. Cold fronts tend to be more frequent and stronger as well, which adds to the violent nature of some of these storms.

Think of the Fall as our secondary severe weather season. We still have the heat and humidity that we need for severe weather, but we are re-introducing the jet stream along with a seemingly sudden surge of cold fronts to the mix. As the days get shorter and become cooler, the jet stream will begin to once again move to the south and bring the upper-level dynamics that seemed to be missing for these storms during a good portion of July and August.

Keep in mind that severe weather can happen at any point during the course of a year. Over the course of time, Kansas has had a tornado in all twelve months of the calendar year.

After a brief cooldown during this upcoming week (Aug 23-27), when our high temperatures Tue-Thu will likely hold in the 80s, a return the 90s is expected by next weekend. These conditions, which will be several degrees above normal, should last into early September with less than usual chances for significant rains.

This is all a result of the redevelopment ... after taking a brief break this week ... of one of the characteristic patterns we've seen during the last 6 months. This pattern, where an upper-level ridge of high pressure sits over the southeastern United States, is a typical byproduct of the La Nina condition we are currently in. La Nina, which is a phase of the El Nino/Southern Oscillation phenomenon that affects sea-surface temperature patterns in the Pacific Ocean and atmospheric weather patterns worldwide, is defined by a cooling of the near-surface water temperatures across much of the equatorial Pacific Ocean. Through a complicated interaction with the overlying atmosphere, this ocean water cooling is often related to a global weather pattern that favors warmer-than-average temperatures over the Southeastern and Southcentral U.S.

Strikingly unlike Summer 09 and last Winter, when we were firmly in the midst of an El Nino that played a role in allowing cool/cold air to routinely invade the Central U.S., this relatively warm and humid pattern for much of the country (east of the Rockies) began to take shape early this Spring. It is indeed likely that La Nina has played a significant role in giving this part of the world a hot summer.

Looking ahead, long-range forecasts expect La Nina to continue through the upcoming fall and winter. It wouldn't surprise me to see our month-to-month temperature anomalies continue to follow the warm theme for the next several months at least. If nothing else, the atmosphere is in an entirely different mode than it was a year ago, and a repeat of last winter seems highly unlikely.

I suppose that it is bound to happen. It is August in Kansas after all. Extreme heat will make its return to northeast Kansas by Sunday and keep going well into next week.

Computer models are consistently putting our daytime highs into the mid-to-upper 90's through Thursday of next week, and even after that it looks like most models are only bringing a slight change to the daytime heat.

Sunday's Daytime Highs From GFS Computer Model

GFS 2 meter temperatures For Sunday by melwellku

During this stretch we hold only minimal chance for rain with only the blazing sun to deal with. So far in August we have managed to somehow avoid any measurable precipitation. We typically average 0.11" of precipitation a day. Obviously that is an average, but six days into the month we are already 0.66" down in what is typically our driest summer month.

I took some time to look back at the official numbers for July and found something that stood out to me. It took 12 days into July before we saw our first 90° day. After the 12th we had only one day that was in the 80's.

If you work outside for a living, or just plan on spending some time outdoors, remember to drink plenty of water, wear light-colored clothing, and take frequent breaks. It is also a good idea to check on elderly family or neighbors from time to time, especially if they don't have air conditioning or it isn't efficient.

I have been asked by several people over the last few days about the heat we have experienced so far in July. We certainly have had our share of hot days and when we add the humidity into the mix, it seems to make it much more uncomfortable for the vast majority of us.

Through Wednesday our average high was 89.3°. If you compare it to the daily normal for July which is 90.6° we are slightly below the normal for July. Conversely, the average low for July this year was 70.1 with the daily normal in Lawrence registering 69.7°. Looking at the numbers for the month, we are almost exactly where we would expect to be climatologically speaking.

We also have had 16 days through Wednesday that have been at or above 90° or above. Looking at the monthly averages we should have all but one day that would be in the 90's.

The forecast heading into the beginning of August looks to start out in the mid-to-upper 90's. What I find interesting is that we have not had an official high over 100 degrees yet this year in Lawrence. The last 100 degree day was on June 23rd, 2009 which as of Thursday was 402 days ago.

July is typically known for the heat and humidity that it brings to the Midwest, but that hasn't been the case so far this year. As a matter of fact the last time that we hit 90° at the official reporting station here in Lawrence was on the 28th of June when we hit 91°. Since then we have had plenty of rain and cooler temperatures rolling across the great plains.

That is all about to change for us. The latest model guidance suggests that our daytime highs will once again be in the low to mid 90's with humidity building back to the range that is considered uncomfortable to most of us.

At this point, it looks like the warmest day on tap will be Wednesday as seen from the GFS model shown below. We do seem to pick up a chance for showers on Thursday with the heat and humidity staying in place through the weekend.

Wednesday's High Temperatures

GFS_18_opUS_T2MS_0048.png

Most weather models show that heat and humidity staying in place well into next week with daytime highs ranging from the low 90's to upper 80's. If you remember from past blog posts, the main ingredients needed for thunderstorms are heat, moisture and some sort of lift. This type of setup will keep the heat and moisture in place through next week, leaving a source of lift (like a cold front) as the main variable here. It doesn't look like we will see many disturbances moving through the area for the weekend, but if we do get a weak front move through, we could pick up some strong storms along the way late in the weekend or into next week.