Negative AO = Cold Weather

Now, I know I keep going over this, but just look at the 00Z GFS model and you will see it happening. The GFS has been keeping it warm for so long now, building that ridge in the center of the United States. Now, here is what it looks like at 500mb:

Thats 360 hours out, yes I know...its unreliable. But even go back to 240 hours out and you can see the cold shot developing. The negative AO is starting to pan out, the cold weather is on its way. A cold and snowy eastern United States is starting to look more and more likely for mid-November and on. I forecasted snow for Anderson, Indiana on November 14th. I will stick to that forecast. And I will also stick with snow in Wichita, KS on November 21st. It might be a white Thanksgiving for much of the country, just as Joe Bastardi keeps predicting.

PS: The storm for next week, from the Tues-Thurs period, is still looking like a large scale severe weather event. Of course, mesoscale features will be very important to the event, and we will have to wait and see how the thermodynamics pan out. However, right now the trough digs deep into the plains, produces the bowling-ball of positive vorticity, plowing into the panhandles of TX/OK into Kansas, and quickly becomes negatively tilted. The makings for a severe weather event, and then possible backside snow storm are there on the synoptic scale, there is no doubt about it at this point. Of course, as we know, models can change...so we will have to keep a close eye on this.

Wet west, plains storm to come.

The dry weather the western United States has enjoyed has come to an abrupt end. Three storm system will plow into the Pacific Northwest and northern California over the next 5 days, likely leading to flash flooding and significant snows in the highest elevations. Currently the 1000-500 mb thickness values do not support snowfall, even in the Sierras, but this will change by the 2nd, and definitely the 3rd system. With SEVEN inches of liquid equivalent precipitation forecast for the Sierras by the HPC, I wouldn't be surprised to see feet of snow pile up in the highest points of the Sierras.

On top of this, wind gusts to 50 mph look possible tonight in southern California into the Sierras, and could be even stronger in the mountains from the next two storms. 500 mb winds of 80-90 knots will interact with the mountains peaks and passes, likely bringing gusts to 65 mph...or higher!

And when this third system finally plows in, the fun begins in the intermountain west and then the plains states. By day 7 a significant vort max and longwave trough will have moved into the plains, becoming negatively tilted, leading to the risk of a severe weather event. Currently the environment looks marginal, however if moisture can return sufficiently and the mid-lat low doesn't occlude too quickly, we could be in store for a classic fall severe weather event. We will have to watch this over the next 5-6 days to see whats in store. One good thing, winter weather doesn't look like a strong bet with this system, at least in the great plains. Snow will likely occur in the mountains and possibly Montana/North Dakota through day 7, but big snow storm doesn't currently look in the cards.

And then there is the LONG RANGE. The Arctic Oscillation is currently starting its dive to negative, likely beginning the trend towards colder weather in the eastern United States. Even through the models aren't currently showing it, I wouldn't be surprised to see a shift in the models for the period from Nov 10-20th. I think a cold shot is in the making. But we shall see. The Arctic Oscillation isn't always 100% right, but it is a very good indication.

It's coming....

The cold is coming! What looked like a snow storm a while ago for the high plains and then turned to a mix or rain and snow has now changed back to a snow storm....possible blizzard Tuesday night into Wednesday. The weather service is now forecasting somewhere between 4-12 inches of snow in central Nebraska! Winter is going to make its first big showing in the central US this week.

The 500 mb low producing this storm will drive south tomorrow, pushing with it a cold front that will go as far south as the Gulf Coast. Winds behind the front will be gusting to 60 mph...or even higher...with sustained winds easily in the 30s or 40s in northeastern Colorado into Nebraska and south into Kansas/Oklahoma/Texas. The strongest winds and highest gusts will be in northeastern Colorado. Thunderstorms, likely some severe, will develop along and head of the front with such strong upper-level forcing and decent moisture return. Already today some severe storms developed in New Mexico...and this was only from a small shortwave trough travelling through the southwest at 500 mb.

Once the 500 mb low reaches central Kansas/Missouri....possibly further south....it will stall out, developing an area of heavy snowfall in central Nebraska and thickness values sit around 540 in the central plains. Up-slope flow and a possible deformation zone will lead to the heavy snowfall and cooling temperatures. Areas of heavy rainfall from Nebraska into Missouri and Kansas look possible during the time from from Tuesday afternoon into Wednesday night. After this time frame the 500 mb low will be completely cut off for a day now, losing some of its energy and will slowly pull off to the east/northeast.

However, the low will pull moisture out of the Caribbean north towards the east coast as it begins to move again late in the week. This moisture, along with the eventual movement, will help strength the system again as it approaches the east coast, likely impacting the World Series in Philadelphia either Saturday or Sunday...or both. Not good!

And on top of all this, the Arctic Oscillation looks to change to negative by the end of the month, allowing copious amounts of cold air to flow into the eastern United States as a strong trough drives down to the Gulf Coast latitudes near Florida. It looks like snow will be likely in much of the Appalachians and the lake effect snow machine might turn on with the lake temperatures still very warm.

The weather is about to get exciting. Enjoy it!

A hint of whats to come:

Look at the Arctic Oscillation right now:

What do you see? It is currently strongly positive....and what happens towards the end of the forecast period (the red lines following the black actual number line in the top chart)? It drops! By the end of the month we are back to neutral, and still crashing. It may be more like early to mid-November when the strong cold snap occurs.

And how about that upper-low that will cut off over the central US this week? Check this out:

That's the GFS forecast displayed using Bufkit at 7 am on Thursday, Oct 23rd. It is showing snow (though the snow growth region isn't fully supporting it here) and winds to 40 mph! Wow! And where is this? WICHITA, KS! If this verifies its going to be a very impressive early season storm.

2nd Cold Shot

We had out first real big winter system last week in which areas of the west received over 40 inches of snow! However, most of the snow occurred in the higher elevations of the inter-mountain west and didn't greatly effect high population areas besides Montana and parts of Wyoming. This looks like it could change this coming week with snow possible as far south as Nebraska or Kansas.

Basically, we have the same sort of situation as last week, only the trough will be closer to the center of the United States. This will bring the cold air into eastern Colorado, Nebraska and Kansas (and places further north)....areas that didn't really get the effects of the last cold snap. It will be interesting to see what happens, but just check out the last run of the GFS and you will see a very strong 500 mb trough dive down and the cut off over Kansas. This will drive down a lot of cold 'Canadian' air into the United States. The strong dynamics of the trough and then cut off low will enhance lift, along with decent moisture return into the central US...will likely result in a nasty winter storm somewhere in the plains. Not to mention possible severe weather and the possibility of a tropical system moving towards the Gulf or Florida if the models verify. This next 4-7 days could get interesting!

Following this system, the models aren't showing much...but the Arctic Oscillation is starting to hint at a cold period coming up. Currently the AO is positive, indicating building cold air in the arctic. If it stays positive, the cold air would stay up north and not influence the US...however the models are hinting at the AO becoming negative (with a strong ridge building into Alaska) which would allow this cold air to funnel down towards the US. This might be the start of the possible cold early winter Joe Bastardi has been talking about in his winter forecast and blog. Just be ready, late November and/or early December might be very cold (at least for that time of the year). I wouldn't be surprised to see a nice early season snow for somewhere from Colorado/Kansas/Oklahoma to the mid-Atlantic at some point during that time frame. Yippie! Enjoy!

Well....

The SPC has come out with their new outlook and they are definitely not as bullish as I was yesterday. I can see what they are saying about the further north convection in KS not producing anything because of a shallow stable layer...and that's reasonable. I guess the heavy rain threat from training convection might be the only threat in this area, but if things become surface based..... I still think west TX/OK/ and now far eastern NM are the best locations. I always forget to mention New Mexico since I consider them a western state, not a plains state. However, weather doesn't care about location or time of year, only the current conditions.

SEVERE WEATHER OUTBREAK?!?

Saturday into Sunday looks like we might be in for a big event. Every variable seems to be coming together. A strong upper level trough will be bottoming out in the southwest United States with abundant vorticity. The trough will begin its movement to the east/northeast, pushing small areas of vorticity towards western TX/OK/KS and NM. A strong upper level jet max will be swinging around the base of the trough during the morning and day of Saturday, placing it over the TX/OK/KS region it the afternoon. A region of strong diffluence will also be centered over this area. On top of this, a 500 mb shortwave trough will eject out of the base of the large scale trough in the afternoon, pushing through this same region.

A strong southerly to south-southeasterly jet at 850 mb will be in place, with great backing of the winds all the way from southwestern TX into western KS. Helicity will be plenty with areas of 500-750 in KS and 200-400 in TX. Instability will be the main mitigating factor, however the models are placing a bulls-eye of 1000 J/kg in western TX, with 500-1000 stretching up into southwestern KS. Of course, any areas of clearing will allow for these values to be easily reached or exceeded as dewpoints increase into the mid 60s throughout this region. The warm front looks to be situated on the northern border of KS. I wouldn't be surprised to see a tornado risk zone in western KS due to the high helicity.

The one factor that makes me feel like Saturday might be not at big as Sunday is that the trough will only have started to shift to the east in the afternoon of Saturday. By Sunday afternoon the main vort max will start to shift more into the TX/OK area, likely with the risk reduced in western KS as cold air advection commences. Never does the trough actually go negative, but rather pulls out staying positive the entire time as the main 500 mb low tracking through the Dakotas into Canada.

This event is also a perfect example of a SCEPT (Synoptically-Forced Convective Extreme Precipitation Training) event where a Closed Upper-Level Low is present(...from my thesis). I woudn't be surprised to see areas of heavy, flooding rainfall caused by training cells nearest the region of greatest moisture convergence in the warm sector of the mid-latitude cyclone. Western Kansas looks like the most likely location, stretching into the panhandle of TX. Watch for areas of 2-4 inches in just 2-3 hours.

Basically, I think we are in for a decent size severe weather event on Saturday and Sunday. The SPC already has a slight risk for southwestern TX on Saturday, but I would not be surprised to see them extend that further north. They even have a risk area circled on Sunday in western TX as well (4 days out). A risk area circled 4-8 days out is required to be considered as a moderate risk day for the SPC to include it. I am thinking they will end up going with a moderate risk both days.

On top of all this we have the snow forecasted in the inter-mountain west and a possible tropical cyclone developing later in the week in the western Caribbean. The weather is definitely about to get interesting.

Cooler Weather for the West

Get ready for winter! A strong long wave trough is about to impact the western states, primarily causing winter havoc in Montana, Wyoming, Colorado, and the Dakotas. It looks like the first real snow of the year is on tap for the higher elevations, including even the Black Hills of South Dakota (which really aren't that high). Right now forecasts range from 6-12 inches in north central Wyoming and 2-4 inches in the Black Hills.

This long wave trough has been forecasted by the models for quite a while now. The GFS, European, and CMC all had the trough digging into the western states starting tomorrow. However, there was disagreement on the placement 3-5 days ago. The European dug the trough into southern California and Arizona, then pulling it out quickly through the Dakotas. The GFS dug the trough into the Colorado/New Mexico area and cut it off...bringing it slowly up through the Midwest. The CMC was a mix of the two, closer to the Euro.

Now the GFS has switched to the European result, digging the trough into southern California and then pulling it up quickly through the Dakotas...and then traversing west through the Midwest. This seems like a reasonable solution, and I expect it will pan out. After e-mailing with Doug, we have hypothesized that the GFS was underestimating the strength of the sub-tropical ridge int he eastern US. Thus, the GFS wanted to push the trough in a bit further to the east. When the model finally figured out the ridge was stronger, it moved towards the European solution.

But what does this all mean? Get ready for cold weather and possible snow in the higher elevations of Wyoming (and even possibly in the valleys in this area as well), Montana, Colorado, and South Dakota. The original threat of snow from the GFS in Denver is gone now with the correct European solution panning out. However, don't worry...the Denver snow will come later this year. :)

PS: The GFS/NOGAPS/Euro are all showing a tropical system developing in the western Caribbean over the next week. The steering currents are interesting, and might even pull the system to the EAST rather than the west. This has happened in the past, so it is not unprecedented. All three models forecast a rather strong storm.

Severe Weather Threat Sunday into Monday

It looks like the weather will finally get active again. A considerable storm system moved into the western states on Friday into today and will be ejecting out into the western plains tomorrow. The dynamics and thermodynamics look decent for a severe weather event, at least on Sunday. However, many of my friend and co-workers are also interested in Monday as well. So, lets get into it.

SUNDAY:

Severe weather will almost definitely occur on this day. Already on Saturday a wind gust from a small microburst produced 59 mph winds in west Texas, and this was well ahead of the main storm system and was produced by only a small cell. What this tells me is that there is plenty of energy for a severe outbreak tomorrow with the upper-level energy beginning to move into the Texas panhandle, Oklahoma and possible southern Kansas.

The 500 mb trough will start to become slightly negatively tilted by the late afternoon into the evening hours with diffluence occurring over the TX/OK panhandles into western OK/north central TX. There might not be a 'bowling ball' of vorticity set to enter the TX/OK panhandles, but there is a considerable amount of vorticity that will be enough to help initiate storms. Backed winds at 850 mb, becoming more backed through the day as height falls ahead of the system increase, will result in a decently sheared environment. Also, a weak 200 mb wind maximum will be swinging into the area at this time. All of these variables indicate the possibility of severe weather. The question is whether or not the thermodynamic environment will be set as well.

And the answer is: quite possibly. It looks like showers, and possibly some storms, will be ongoing in the morning to midday hours, likely reducing the surface heating in far western TX. These storms, however, will put out outflow boundaries. As the storms die, or push westward, the thermodynamic environment will become more supportive of severe storms into the eastern panhandles or north west/central TX. CAPE values should reach above 1000 J/kg and 3 km helicity looks to be in the 100-200 range. This would not be the ideal environment, but still supportive of rotating storms. Add in 60F dewpoints, and storms should occur.

The mode is more difficult for me to predict. I could see some discrete cells early, likely able to rotate, but I don't see a massive tornado outbreak. Possibly one or two. However, with all of the wind energy, and knowing what occurred today, I wouldn't be surprised to see a large wind event occur if the upper-level winds easily are mixed to the surface, which seems like a good bet to me. A learning experience on my severe weather forecasting is to come tomorrow.

MONDAY

The severe weather threat might be there, but its difficult to say. The upper-level dynamics do look better, right up until the upper-level low begins to cut off around midday. At that point, the vorticity does not seem to be traversing much further west, but rather staying still in central Kansas. A diffluent flow aloft is still present, only now we have shifted towards eastern Oklahoma and Kansas, which should be the possible risk zone. Dewpoints will be nosing into the middle 60F, and 850 mb winds will still be backed. Helicity actually increases as well, approaching 400 in far northeastern Oklahoma.

The main threat to storms will actually be from the severe weather the day before. The remaining MCS will likely still be ongoing in the early to mid-afternoon hours into central and eastern KS/OK. This cloud cover will hold down the temps, thus reducing the CAPE potential. Without the high CAPE it will be difficult to have severe storms. However, if breaks in the cloud cover, or a dry slot causes a cloudless area, then heating could occur resulting in regions of higher CAPE. I think Monday will be a much more conditional situation where severe weather will be possible in areas that heated up, while heavy rainfall, due to the slow motion of the storm system as a whole, will be the primary threat from the others storms.