Winter MESS 2011

...WINTER STORM WATCH IN EFFECT FROM THURSDAY AFTERNOON THROUGH THURSDAY EVENING...

Complications in this forecast…how warm do we actually get at the surface tomorrow? I’ll try to address that right off…MOS shows high temps reaching well above freezing tomorrow afternoon with NAM at 35 and climbing to near 40 overnight, and the GFS at 40. Now…as was the case with the last system, it’s kinda foolish to rely too much on MOS for a situation like this, but I like to go ahead and look at it anyway because at the same time, it would be kind of foolish to NOT look at it. Raw guidance is where I will base most of the forecast on once again though. Raw NAM keeps us at or just below freezing all day Thursday and warms us overnight and puts us back above freezing by early Friday morning. Raw GFS has a slightly warmer look and would imply more of a mix of sleet/freezing rain/rain as it kinda bounces around the freezing mark all day, whereas NAM would imply more freezing rain/sleet all day tomorrow and changing to rain overnight Thursday. I personally don’t really see any reason for it to warm much tomorrow with the lack of insolation and any kind of warm air advection at the surface. With that said…my own personal thoughts are that we will be dealing with primarily a freezing rain/sleet event here in Meridian for most of the day tomorrow then gradually mixing in rain overnight and eventually switching over to all rain early Friday morning. However…if I’m wrong, and we do warm above freezing tomorrow, then it will likely be mostly a very cold rain. Either way, though, it looks like it will be a very nasty next few days and potentially hazardous to people on the roads.

So…when will this happen? Models are in decent agreement on this part and it looks like precip could be falling as early as early afternoon, however there is a bit of a dry layer aloft that may delay the precip somewhat.

So…what I’m thinking…tonight we will stay mostly cloudy…lows will drop into the mid-upper 20s (~26) and temps should remain fairly steady around freezing throughout the day Thursday (I personally don’t think we will get above freezing until late tomorrow night). Precipitation will continue across the southeast during the morning hours and will gradually spread northward affecting us here possibly as early as early afternoon…starting as freezing rain/sleet more than likely and unless we do get above freezing, which I don’t think we will, it will remain as freezing rain/sleet throughout the day. We will gradually warm above freezing into overnight Thursday and gradually switchover to all rain that will linger into Friday night. I don’t see ANY snow for us here during this event. Again, this is a very fragile forecast and any small error in the warmer direction in temperature prediction would mean a big difference in precipitation type…basically…if we get above freezing tomorrow, we will likely be dealing with mostly a rain event…

I may update this a bit if 0z model data looks any different...

Winter Storm 2011

...Significant winter weather event on the horizon for Sunday into the early part of Monday...A Winter Storm Warning has been issued from 9 AM Sunday to 6 AM Monday morning...

On water vapor imagery as of about 5:45 PM, you can see the upper level low pushing across New Mexico and into western Texas already streaming moisture across southern Texas and southern Louisiana, and a surface low appears to have already developed across northern Mexico in response to this. This surface low will be the major player in our weather the remainder of this weekend as it tracks along the extreme northern Gulf of Mexico very near to the Gulf coast.

Lets just dive right into the models now. First off, this is a very difficult forecast to make and here's the reason...if models are off by just a few degrees, it will make a ton of difference. It seems to me that right now the best chance for snow here will be during the early afternoon hours of Sunday. The reason I say this is because it looks like we will start out with an area of the atmosphere that is warm and also quite dry so effects of evaporation and melting should act to cool this layer. The "1/3 rule," would suggest that effects from evaporation alone would be enough to cool this, however it looks like warm air advecting into this layer may be too strong to put the entire column at or below freezing...however there looks to be a period of a few hours during the early afternoon that it may cool enough for us to see mostly snow here. This is where the forecast really gets kinda tricky because the column gets so close to freezing, so I think snow/sleet mix is the best call during this time. By later in the afternoon/early evening, we should make a switch over to our icy scenario which will likely start as a freezing rain/sleet mix. We then start to lose moisture in the snow growth region by late evening and the melting layer becomes very pronounced at 4 degrees C and up. Surface temperatures are still forecast to be below freezing during this time so it looks like we will switch over to pretty much all freezing rain by late tomorrow night and looks like it will continue through the early part of Monday. This is all based off the NAM model...if you go by the GFS model then the solution appears much more simple...all freezing rain/sleet with a switchover to rain early Monday. I personally think it be mostly ice here with very little snow. Now...one problem I see is the spread in forecast surface temperatures. MOS ranges from 34 to 37 for highs while raw guidance is near or just below freezing...if surface temps get above freezing then there will likely be rain mixing in as well (WHAT A MESS!!). However it's kinda foolish to lean too much towards MOS numbers for this situation because this is one event where it will really struggle, and the fact is, the overall trend with this has been cooler, so I personally don't think we will get above freezing especially if clouds begin building in early enough. Now...another problem I see with this is going to be the winds. A tightening pressure gradient in response to the approaching surface low will make for some pretty strong winds between about 15 and 20 knots, so if this is mostly an icing event, that could be a real problem as it will make it easy to bring down limbs and could cause some serious problems with power outages. A bit of good news, though, is that Monday should get us back above freezing and whatever ice accumulations there are should melt off.

Bottom line...clouds should start to build in overnight tonight, then by early afternoon tomorrow, we will likely start to see a sleet/snow mix. Later in the day, we should begin to switch over towards more of a sleet/freezing rain mix, then turn to primarily freezing rain overnight and into early Monday morning...accumulations of ice possibly up to a half inch...breezy conditions could put wind chills down into the teens...The further north you go, the more likely you will see mostly all snow, the further south you go, the more likely you are to see more rain...

Snow Totals

Here are the snow totals from the weather service from the recent snow event and previous blog post...

Snowy Mississippi

.....Significant winter storm looks to be on the horizon for pretty much all of Mississippi.....winter storm watches have overspread much of the southern states from northern/north central Texas eastward through Alabama....most of which I suspect will be upgraded to warnings before all is said and done.....so how have things changed? Well models are finally starting to get in decent agreement and consistency for both the strength and track of the surface low, but amounts still vary quite a bit......one is calling for between 1 and 2 inches while another is between about 4 and 6 inches. The weather service has gone up on their accumulations also where they now have roughly along I-20 to Hwy 84 getting between 4 and 6 inches, between I-20 and Hwy 82 getting between 2 and 4 inches, and north of Hwy 82 between 1 and 2 inches.....I haven't really been able to pick out much of a trend with the models depiction of precip amounts cuz they have really been all over the place, but so far from what I'm seeing, I kinda like the 2-4 inch range around here....this is just preliminary and will likely need to be adjusted, but this is just my thinking right now and also a generalization. What I mean by "generalization" is that I think these amounts will be what most locations see, but with the potential for deformation zones/banding precip, some locations could see significantly higher amounts. I think that we could see light rain echoes showing up on radar as early as early tomorrow afternoon, however I think most of it will evaporate before reaching the surface. What this will do is allow the atmosphere to moisten up and due to cooling from evaporation, it will help to cool the atmosphere. With the absence of any real southerly flow to bring in any kind of warm air at the surface or aloft as was the case with the last system, I think that evaporational cooling will have a much more significant effect than the previous snow setup we had several weeks back that turned into a complete bust. I think we will see primarily a snow event around here, but I'm seeing more indications that it could switch over to freezing rain towards the end of the event as dry air begins to get entrained into the mid levels and we lose moisture in the snow growth region. I don't think sleet will be much of a concern because I don't really see any kind of melting layer aloft that would support any partial melting of the snowflake to allow for sleet development. Bottom line....RIGHT NOW what I'm thinking is very similar to the weather service except in the area of the switchover to freezing rain at the end, but I do very much agree with their outlined zones and accumulations just maybe shifted slightly further south. This being the general idea but with isolated higher amounts if and where deformation zones/banding precip occurs. So tomorrow....I think radar will likely start picking up rain as early as early afternoon, but I don't think most of it will be reaching the ground due to dry lower levels. Once we get saturated, I think we could see a brief period of light rain or mix of light rain/snow before switching over to all snow by late afternoon/early evening and lasting through the overnight hours and finally coming to an end Friday afternoon as either a mix of freezing rain and snow or possibly all freezing rain.

Charleston, SC forecast for September 29, 2009

Well just lovely......the first wxchallenge forecast day is showing a midnight low. MOS is from 58-59.....Raw is upper 50s to lower 60s, so still some pretty good agreement amongst the models as far as tomorrow's low......highs however have a bit of a spread......Raw GFS is around mid-70s.....Raw Nam is around upper 70s and both NAM and GFS MOS is right at 80. It should be noted that I'm looking at the 12z Raw GFS and 18z Raw Nam......I will likely hold off on a final decision until the 18z GFS comes in. Locations to their northwest today that are behind the front have stayed primarily in the mid to upper 70s, so my initial thoughts right now are to go with upper 70s for tomorrow's high. Last night's 0z MOS had tomorrow's high at 81, so it has only gone down one degree......Right now....I'm thinking lows around the mid-upper 50s and highs in the upper 70s.......winds in the upper teens to near 20 kts....it looks like there will be some pretty windy conditions as the front comes in, but winds should begin to weaken some towards morning and pick back up again in the afternoon........rainfall, RIGHT NOW, is zero however, both Nam and GFS try to put a little rainfall in their area overnight tonight along the front....there is some activity off to their northwest right now...Raw GFS(12z) shows no rainfall, but Raw Nam has around 0.05 but ending before midnight, and RUC also puts some activity developing across their area after midnight, so it really looks like alot will depend on the exact timing of that front and whether or not the line will fill in.....all this is very light generally<0.07"...As I am writing this, the activity to their north appears to be dying some......I feel like it will be shortly after midnight when the front makes it through, and I think I will likely keep rainfall at nil.....but will hold off until 18z data comes out to make my final decision.........

Update......18z Raw GFS was almost exactly the same and shower/storm activity to their north/northwest continues to weaken so...........

Forecast for tomorrow......
High - 78
Low - 58
Wind Speed - 21 kts
Precip - 0.00


Today's Actuals......
High - 89
Low - 64
Max Wind - 21 (even though I didn't forecast a speed)
Precip - 0

Charleston, SC Trial Forecast for September 27, 2009

MOS is at 63-65 for the overnight low....last night reached a low of only 72 with cloudy skies and southerly winds between 5 and 10 with higher gusts.......normals are around mid-60s for lows and lower 80s for highs......I think 63 is a little too cool with winds staying between 5 and 10 overnight again....If winds go calm, though, lower 60s seem possible....skies are forecast to clear overnight and drier air is already filtering in, so it should be cooler tonight than last night......with that said I think I will go with 65 for the low and 89 for the high (MOS ranges from 87-89) since it has reached 86 today with cloudy skies....I could even possibly see 90 or better, but whateva.....

Forecast for June 16, 2009

Tomorrow.....Expect sunny skies with a low around 71 and a high around 95.

NWS............Sunny, with a high near 95. Heat index values as high as 101. Calm wind becoming west between 5 and 10 mph....low around 71.