Northwest Florida Weather (11/29/2016) - Another Severe Weather Threat

Before I begin this blog post, I'd like to extend my sincerest thoughts and prayers to those in Gatlinburg, Pigeon Forge, and surrounding areas that were affected by the wildfire. Extremely sad situation with loss of life. I'm thankful, as I'm sure many are, for the first responders' and emergency personnel's acting quickly as it could have been a lot worse.

Now, back to Northwest Florida weather information.

Well, frankly, last night ended up being a lack of rain for most areas. The good news is that we didn't have any severe weather in our area, but the bad news is that most areas didn't get much rain, if any. Why was that?

Well, last night, we were lacking instability, which some models were not picking up on. The line of storms was forecast to weaken as it moved further east, but the actual line weakened sooner than what models were thinking. Most of the better lift and instability was to our north and away from us in Northwest Florida.

So, what about tonight and tomorrow?

The Convective Outlook issued by the Storm Prediction Center (SPC). This map is valid through 6 AM CST Wednesday morning.

Parts of Northwest Florida are in the "Marginal Risk" of severe weather. This is a Level 1 out of 5, meaning we could get some isolated severe thunderstorms. But, what severe weather we might get would be closer to 6 AM Wednesday.

SPC's Convective Outlook for 6 AM Wednesday through 6 AM Thursday.

SPC has place all of Northwest Florida under a "Marginal Risk" for Wednesday. This again is a Level 1 out of 5. Isolated severe thunderstorms will be possible, with damaging winds being the main threat with any severe thunderstorms. Let's talk some meteorology!

Model sounding from the HRRR (High-Resolution Rapid Refresh) Model valid at 11 AM CST Wednesday at KVPS (Eglin AFB, FL). Focusing mostly on the left half of the image. The solid red line is the temperature profile through the atmosphere, the solid green line is the dew point profile. Pressure is labeled in millibars on the left, decreasing with height. Temperatures are labeled on the bottom in degrees Celsius. Multiple parameter are located at the bottom of the image. Image courtesy of pivotalweather.com and SHARPpy.

I personally think these model soundings are a meteorologist's best friend. There's just an abundance of information you can get from these. So, let's see what there is to see.

• Generally, there is atmosphere is abundantly moist, especially at/below 700 mb. There are two ways we can see this. First, the temperature and dew point lines are pretty close together. Second, the precipitable water (labeled PW in the parameters table) is around 1.67 inches, meaning the atmosphere is sufficiently moist. Note about the precipitable water: Basically, it's how much water would accumulate if all the moisture in the atmosphere above a point was wrung out. The moisture allows for cloud and precipitation development. Also, the more moist the atmosphere is, the higher possibility of heavy rainfall, and the rainfall can help transfer some higher winds aloft to the surface ("waterloading")
• Warm air advection through the lower portion of the atmosphere. This is a lifting mechanism. Warm air is less dense and warm air can rise.
• CAPE is high, meaning plentiful instability, allowing air to rise easily.
• Decent shear, which is favorable for thunderstorm development.
• Dry adiabatic layer from about 900 mb to the surface. (Dry adiabatic layer means that the temperature profile is parallel to the dry adiabatic lapse rate, denoted by the thin diagonal white lines going up and to the left. The dry adiabatic lapse rate is the rate at which the atmosphere cools as you proceed upward in the atmosphere if the atmosphere is not saturated.) This will allow winds to be transported downward more easily.

One note, the sounding algorithms do spit out a "possible hazard type" of tornado. I use this only as a worst case scenario. This should not be taken as there gospel truth.

So, the signals are good for at least thunderstorms, and maybe some severe storms. But there are a couple of caveats.

• Helicity is not all that impressive, meaning that there is not as much spin in the atmosphere. Thus, it does not lend itself to an atmosphere supportive of tornadoes. That's not to say it can't happen, but it's less likely.
• This model assumes that the temperature will make it to near 80 degrees at the surface. I'm not fully confident in that solution. I do think it will be warm, but I'm not sure about it being that warm. This affects CAPE, low level moisture, and that dry adiabatic layer.

Here is what the HRRR model (the same one the sounding is from) predicts the radar will look like:

HRRR predicted 1 km reflectivity valid from 8 PM CST Tuesday through 11 AM CST Wednesday.

The HRRR only goes out 18 hours. It shows a line of thunderstorms (potentially strong to severe) entering Northwest Florida around 9 AM (+/- 2 hours). But the general trend looks to be slow weakening as it moves further east.

So, again, this is just one run of one model. Just one tool in our toolbox. Let's take a look at one other model.

This is a model sounding from the NAM valid at 12 PM CST Wednesday. Same properties as the sounding above.

So, just like the HRRR, the NAM has abundant moisture, warm air advection, decent CAPE (for this time of year), and decent shear. Now, there are a few differences. It's not as warm at the surface, thus nearly eliminating the dry adiabatic layer. Speaking of which, it looks like the dry adiabatic layer is only from 975 mb to the surface, not nearly enough for easily transporting winds from aloft to the surface. But, there is more helicity than there was in the HRRR sounding, meaning more possibility for rotation. So, what does this mean?

With lower instability, we may not see as much thunderstorm development. With fewer thunderstorms to tap into that helicity, the threat of tornadoes is lower. There could still be damaging winds with stronger storms. But what does the predicted radar look like with the NAM?

NAM predicted radar valid from 9 PM CST Tuesday through 9 PM Wednesday.

The NAM does not have as much in the way of intense convection (meaning that it may not be predicting as much thunderstorm activity). The NAM also brings in the convection later than the HRRR, closer to 12 PM. But the general trend is the same, weakening as it moves further east.

So what does this all mean for your forecast? We will probably see more scattered showers around Northwest Florida tonight, not really expecting much in the way of thunderstorm activity tonight, but can't rule out an isolated storm. Severe weather is not expected tonight. Wednesday is our better chance of rain. Showers and thunderstorms look to move into Northwest Florida during the mid to late morning and move eastward. The general trend is for the line to weaken as it moves further east. An isolated severe thunderstorm or two cannot be ruled out with damaging winds being the main threats. Widespread severe weather is not expected in our area.

Northwest Florida Weather - Rain Brings Good News and Bad News

Total rainfall through midnight Wednesday night predicted by the NAM (North American Mesoscale) model.

There is a good chance of something we haven't seen much of in Northwest Florida for quite some time. Rain! While this likely won't be drought-busting rain, 0.5 to 1 inch is not out of the question during the next couple of days. And, besides, it's more rain than we've seen in quite some time. Unfortunately, there is a down side to this rain, and that's the possibility of severe weather.

The Convective Outlook from the Storm Prediction Center (SPC) showing the possibility of severe weather across the state of Florida. This map is valid until 6:00 AM CST Tuesday.

Yes, we have the potential of severe weather tonight (Monday night) into Tuesday morning here in northwest Florida. The Storm Prediction Center (SPC) has outlined areas generally west of Highway 331 (including Escambia, Santa Rosa, and Okaloosa Counties) in a "Marginal Risk" of severe weather, meaning that isolated severe thunderstorms are possible in that area. This risk is valid through 6 AM Tuesday morning. The environment isn't too supportive of severe weather for tonight, but some thunderstorms are in the forecast. Let's take a dive into a bit of meteorology.

from pivotalweather.com & SHARPpy. This is a model sounding from the HRRR (High-Resolution Rapid Refresh) model. The solid red line in the upper left diagram is the temperature profile through the atmosphere, and the solid green line is the dew point profile. The closer the lines are to each other, the more moist the atmosphere is. On the left, the pressure levels are labeled in millibars (mb) decreasing with height, and the temperatures are labeled on the bottom in degrees Celsius. Winds are labeled on the right hand side of the upper left diagram in knots.

This model sounding (from SHARPpy) shows what the HRRR thinks the atmosphere will look like at 3 AM CST at KVPS (Eglin AFB). Let's go through some things working in favor of severe weather tonight.

• Sufficient moisture at and below 700 mb.
• Strong winds around 850 mb (winds around 40-45 knots, 45-50 mph)
• Warm air advection
• Sufficient helicity
• Sufficient shear
• Decent instability

So, we pretty much checked off all of our severe weather ingredients. But, keep in mind, this is just one run of one model, and the atmosphere doesn't always behave like we want it to. Let me discuss a bit about models. Models ingest data before their run. The model already has its initial forecast planned out, then it uses the observations and data it ingests to adjust its forecast. The model can either adjust its forecast to come closer to the observation or reject the observation. The model rarely, if ever, accepts an observation as absolute truth. This already causes inherent error. Plus, observations aren't taken everywhere, especially upper air observations. Thus, we as meteorologists have to try to figure out if the model is performing well with interpreting and interpolating data. You can see where a lot can go wrong already, but this topic is for another time. Back to severe weather.

So, with one run of one model, it looks like severe weather is a decent possibility. One thing to note is that this sounding indicates a "possible hazard type" of tornado. I generally use the "possible hazard type" as the worst-case scenario of what could happen. Remember, that is also dependent on if there are storms around. Let's look at the same model run to see what it predicts as far as future radar.

Same run of the HRRR as the model sounding came from. This is the 1 km above ground level reflectivity forecast. Essentially, this is a future radar product. This is valid through 9 AM CST Tuesday morning.

The model shows a broken line of showers and thunderstorms moving through the Florida Panhandle early Tuesday morning. Now, notice that the line in general appears to weaken as it moves further east. So, if you're in Panama City or Marianna, your severe weather chance will be lower. Before we move on, let's look at one more just to show the uncertainty.

This is the 4 km NAM (North American Mesoscale) model valid through 9 AM CST Tuesday. Showing the same product as depicted in the HRRR model animation.

You can see, this model nearly completely dissipates the line of storms before getting here. This is why there's still quite a bit of uncertainty, even in the short term forecast.

Overall, I think our severe weather threat is low tonight and tomorrow morning. Gusty winds will be the main threat with the stronger storms tonight. I can't fully rule out an isolated tornado, but I think the better chance of that happening would be to our north and west.

Going into Tuesday and Wednesday, we still do have a risk of severe weather across northwest Florida. Here are the convective outlooks from the Storm Prediction Center.

SPC's convective outlook valid from 6 AM Tuesday through 6 AM Wednesday.

SPC's convective outlook valid from 6 AM Wednesday through 6 AM Thursday

The second threat of severe weather looks to be primarily Wednesday morning across northwest Florida. Again, damaging winds look to be the primary threat with severe thunderstorms. An additional blog post will be published on this possible severe weather threat tomorrow afternoon.

Northwest Florida Weather - 11-17-2016 - Drought Worsens with Little to No Relief

Latest Drought Monitor for Northwest Florida. Map data provided by the National Drought Mitigation Center (NDMC), United States Department of Agriculture (USDA), and the National Oceanic and Atmospheric Administration (NOAA).

The latest drought monitor was released today, and it does not bring good news. Unfortunately, the drought has worsened. Much of Northwest Florida is now in a "Severe Drought." While there are no official burn bans in effect right now, outdoor burning is strongly discouraged. In fact, the Florida Forest Service is not issuing any authorizations for acreage or pile burning in the Blackwater Forestry District (Escambia, Santa Rosa, and Okaloosa Counties). The drought is highly affecting our soil moisture as well.

The Keetch-Byram Drought Index (KBDI) essentially measures the soil moisture. Above is the average value by county across Northwest Florida.

This is the Keetch-Byram Drought Index (KBDI) data from the Florida Forest Service. The KBDI assumes that the top 32 inches of soil can hold up to 8 inches of water. A KBDI of 0 means that the soil is water-logged and can't hold any additional water; on the other hand, A KBDI of 800 means that the soil is completely dry. Right now, Okaloosa, Walton, and Holmes Counties are the driest counties not only in Northwest Florida, but the entire state. This dry soil can lead to an enhanced wildfire danger. Unfortunately, there is very little in the way of rain in the forecast.

12Z (6 AM CST) run of the GFS model. Black solid lines represent isobars (lines of constant pressure). Red and blue dashed lines represent 1000-500 mb thickness. Shaded areas represent 6-hour precipitation accumulation. Fronts drawn in by myself.

While we do have a cold front moving through, it looks like rain will fall apart as it approaches. I am forecasting only a 10% chance of rain, and that might be a bit optimistic. Even if we do see rain, totals will be less than 0.10". Very dry air will follow behind the cold front as well as breezy conditions.

This is a model skew-T from the 12Z (6 AM CST) run of the GFS at KVPS (Destin-Fort Walton Beach Airport). Focus on the upper left diagram. The dashed white diagonal lines are temperatures in degrees Celsius. The solid white horizontal lines are pressure. As you head up the diagram, you go up in the atmosphere, and pressure decreases. The solid red line is the temperature profile through the atmosphere, and the solid green line is the dew point profile through the atmosphere.

Let's look at the above model skew-T. This is valid as of noon CST on Sunday at the Destin-Fort Walton Beach Airport in Valparaiso. It will be rather cool with this particular model only showing mid-50s at the surface at this time. But check out the dew point: 11 degrees Fahrenheit. That is bone-dry. If we go up just a little bit in the atmosphere (roughly 4,500 to 5,000 ft.) at 850 mb, it's even drier. The temperature at 850 mb is 47.3 degrees F., but the dew point is -35.5 degrees F. That is an 82.2 degree difference between the temperature and dew point.

After a bunch of math that I won't bore you with, you get this:
Relative humidity at the surface: 16.4%
Relative humidity at 850 mb: 2.2%

In other words, very, very dry conditions are expected after the cold front passes through. That coupled with winds around 10 mph could produce very dangerous conditions for wildfires. Fire Weather Watches or Red Flag Warnings may become necessary.

But that's not the only threat. Some of the coldest air of the season so far will be filtering in behind this front. Many areas could see their first freeze of the season. Here is a look at Saturday Night's forecast:

This already would be the coldest air of the season for most areas. Widespread 30s can be expected across much of Northwest Florida. But, the winds will prevent the temperatures from falling below freezing for most places. Now, not to outdo Saturday night, here's Sunday Night's forecast:

Even colder temperatures possible on Sunday night. With decreasing winds, it will allow our temperatures to fall quite a bit more. Many areas north of the bays could see their first freeze of the season. The National Weather Service in Mobile (which covers Escambia, Santa Rosa, and Okaloosa Counties) said this in their latest forecast discussion:

It will then be dry and cold over the weekend in the wake of the front and surface high
pressure building in from the north. Will monitor for likley [sic] Freeze
Watches and Warnings over the weekend...

Low temperatures Saturday night behind the cold front will fall into
the mid to upper 30s, with lows Sunday night ranging from 25 to 32
degrees inland areas, and from 32 to 38 degrees along the immediate
coast.

So, in summary, very little, if any, rain is expected through the weekend. A cold front will move through on Saturday, which will bring the coldest air of the season. Freeze Watches/Warnings will likely be issued this weekend. Very dry air and breezy conditions this weekend will lead to dangerous wildfire conditions, and Fire Weather Watches/Red Flag Warnings may be required.

NW FL Weather (11/15/2016) - Sunny & Dry, But Turning Cooler

The forecast sounds like a broken record: sunny and dry. Drought conditions continue across Northwest Florida. In fact, much of Northwest Florida is under a "Moderate Drought" (except for a small sliver of northern Santa Rosa County where there is a "Severe Drought").

Current Drought Monitor for the State of Florida. Map courtesy of the National Drought Mitigation Center (NDMC), U.S. Department of Agriculture (USDA), and the National Oceanic and Atmospheric Administration (NOAA)

This map will be updated on Thursday. Without any rainfall in the next 7 days, our drought will continue to gradually worsen. The drought is taking a serious toll on soil moisture. Here is the Keetch-Byram Drought Index for Northwest Florida.

Current Keetch-Byram Drought Index from the Florida Forest Service. Used Blackwater and Chipola Forest District maps.

The Keetch-Byram Drought Index (KBDI) measures the amount of water in the top 32" of soil. It is assumed that the maximum amount of water in that top layer of soil is 8" of water. The index goes from 0 (absolutely wet) to 800 (absolutely dry). So, Okaloosa County is currently the driest county on average according to this index with a value of 666. This means that there is 6.66" of water missing from the soil. Unfortunately, with the dry soil, this helps provide fuel for wildfires.

Without rain in our forecast, we focus purely on the temperatures. As the cold front moves through Saturday morning, it will not bring a substantial rain chance (right now, less than 10%). But, the front does bring cooler, drier air.

Animation of the 18Z (12 PM CST) run of the GFS model showing mean sea-level pressure (black solid lines), 1000-500 mb thickness (red and blue dashed lines), and 6-hr. precipitation accumulation (shaded). Fronts drawn in by me.

The cold front will move through Northwest Florida on Saturday morning. Temperatures will be warmer the further east you are, but will fall once the front passes. Here are your 7-day forecasts for inland and coastal regions (updated since video above):

The National Weather Service in Mobile does note that Frost and/or Freeze Warnings may be required by Sunday night. Several areas could see their first frost and first freeze of the season. Interestingly, Crestview has already had their first freeze of this season (November 11):

Believe it or not, Crestview #FLwx dropped to 32° degrees this morning, making it the first freeze this season. pic.twitter.com/Nv5QB3Jm2p

— Cameron Young (@wx_cam) November 12, 2016

So, prepare for more dry weather. Cooler weather will make its way back down to the Gulf Coast by this weekend and early next week.

NW FL Weather (11-3-2016) - Some Cooler Weather, but What About Rain?

Here's the latest webcast for Northwest Florida as of 4:45 PM, November 3, 2016. Discussion follows below:

I know that some of you are tired of the heat, and some of you are embracing it. Either way, "What goes up must come down." Temperatures will finally be settling back to being more fall-like. We won't be frigid, but it will be rather cool compared to what we had lately. But, what about our rain situation?

Across Northwest Florida, the last day of measurable rain for most of us was back in late September. In fact, Pensacola has had 37 days (as of Nov. 3) without measurable precipitation. The record for longest streak of no measurable precipitation for Pensacola is 49 days set back in 1952. It's uncertain if that record will hold.

In the webcast, I mentioned some "model uncertainty" as we head into next week. Here's a bit of what I mean.

First, we're going to take a look at the mid to upper levels of the atmosphere (500 mb, or about 17,000 ft.).

This is the GFS model out 168 hours representing what the atmosphere could look like at 7 AM Nov. 10. The shaded colors on the map represent the 500 mb heights and the black lines are the surface pressure (isobars). Generally, the lower the heights, the colder the temperatures are aloft. On this map, there is a cut-off low over the Central Plains. It is cut-off from the main flow which is to the north (where the tighter color gradient is. This gives us a southwesterly flow leading to more moisture flowing in. The increased moisture generally leads to higher rain chances. Also, there is an inverted surface trough seen in the isobar pattern over the lower and mid Mississippi River Valley. This could help produce some lift, which, again, could lead to higher rain chances.

Now, contrast the GFS to the European (ECMWF) model. This is the same map as above, just a different model. Notice, instead of a cut-off low over the Central Plains, there is generally a ridge. There is a weak cut-off low over New Mexico, Arizona, and northern Mexico. There is also a trough off the east coast, which is where the cut-off low essentially originated. The trough, basically, split into two parts, and the connection between the trough and the cut-off low weakened. In theory, this weakens any front that would come through our area. Thus, probably not a good chance of rain from this scenario. Plus, the cut-off low is too far west to give us any good influence from the Gulf of Mexico.

Unfortunately, this disparity between the models leads to very low confidence in longer term, and I do not feel like it would be wise to advertise anything greater than a 30% chance of rain next week.

Now, there are more models out there, but the GFS and the ECMWF are generally the most reliable. Both have their strengths and their weaknesses. Also, this is just one variable of the many that we could look at. The 500 mb heights is, in my opinion, the best to look at for the overall pattern. However, it is important to focus on not just one run, but the trend that the models show.  The models have consistently shown a change in the overall pattern which would allow some cooler air and possibly higher rain chances than what we've had. The GFS, in this case, is on the stronger side, and the ECMWF is on the weaker side. There is still plenty of time to watch this system over the several days to see how it evolves. I will keep you updated through these blogs and through webcasts.