Severe and Snow

It looks like there really isn't too much to add from my last blog post. The snow threat has increased substantially with all of the thickness values now turning over to all snow. The soundings in South Dakota look very promising for snow as well, along with momentum transfer of up to 60 knots of winds! What does this mean? Blizzard conditions can be expected from Rapid City to Mitchell, SD and north. I wouldn't be surprised to see snowfall totals in the 6-10 inch range in much of central S/N Dakota.

The severe threat is still considerable, however the moisture return actually does not look like it will be has high as I expected. The tornado threat is still there, and we could see a few isolated tornadoes in the central northern Oklahoma to southeastern Nebraska region as the storms fire in the afternoon on Wednesday. Quickly, however, a strong squall line will develop resulting in a much greater wind threat. I wouldn't be surprised to see a vast area of 70 mph wind gusts as the line tracks through eastern Kansas/Oklahoma/Nebraska into Missouri/Iowa/Arkansas.

This is going to be a major fall storm. The strongest of the season so far. If you are in the Dakotas, make sure to keep indoors. If you are in the area with a severe threat, make sure to keep that weather radio on in the event severe weather threatens your area.

Severe Threat Wed-Thurs

A severe weather threat will materialize this coming Wednesday evening into Thursday as a strong storm system pulls out into the plains. Currently this system hasn't even interacted with the United States yet, but will pull on shore of the California coast tomorrow. The strong 500 mb trough will begin to dig into the plains early Wednesday, becoming slightly negatively tilted and bringing along a substantial amount of vorticity. The low will close off over Nebraska Wednesday afternoon and evening, deepening the low and enhancing the dynamics of the system.

Moisture return seems like it will easily be set up for a severe weather event with dewpoints already in the 50s in Wichita, KS. This will only increase as we go towards Wednesday, likely reaching into the 60s. Storm relative helicity values near 400 are predicted by the NAM Wednesday afternoon, resulting in high EHI values. The threat for supercells at initiation from northern Oklahoma into Iowa seems possible, with the greatest threat from central Oklahoma into eastern Kansas. The NAM and GFS initialize convection in the Wichita area. Could get interesting.

Quickly the strong dynamics of the system will take over, likely resulting in a substantial squall line / high wind event. However, as the storms initialize a tornado threat will be very much possible. The tornado threat could stretch from Iowa to Oklahoma before the line goes linear and moves to the east into Thursday. 850 mb winds in Kansas look to be 50 knots as the cold front and dry line approach. The triple point might move right through the Wichita area.

Out ahead of the storm on Tuesday will be a substantial synoptic wind event, with 55 mph wind gusts possible along the entire front range and much of New Mexico. Additionally, some wind gusts to 50 might occur in northern Arizona. Wind gusts to 45-50 mph could occur even in the Wichita area before storms develop on Wednesday.

A decent blast of cold air will move into the northern plains behind the storm, possibly leading to a snow event in the Dakotas. The central Dakotas look like to be the area of greatest threat currently, but knowing the last system and how it didn't quite get cold enough with much the same set up as this one...it will be close. However, the threat is there. Strong winds will also accompany any snow or rain on the backside, possibly leading to blizzard conditions if the precipitation is snow.

Also, watch out along the eastern coast as the models are now unanimously producing a substantial hybrid system that moves along the Atlantic seaboard bringing not only the threat of some heavy rainfall, but gusty conditions along the coast. The rip tide threat will be high.

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!