Hot, dry, and windy on Thursday, 9/26/19

Highlights:

Near-critical fire weather conditions are possible over southwestern SD tomorrow. A strong cold front will then move through tomorrow evening.

Discussion:

We are expecting a hot, dry, and breezy day tomorrow across Fall River, Custer, and Oglala Lakota Counties. Temperatures are expected to reach the mid-80s, minimum RH will drop into the 13-20% range, and west-southwest winds from 10-20 mph are likely with gusts to 30 mph possible. 

A dry cold front will then move through the state tomorrow evening. This will bring a period of breezy northwest winds, gusting to 20-35 mph over southwestern SD. Keep this evening wind shift in the forefront of your mind if there is an ignition. Cooler and more humid conditions will prevail on Friday with the breezy northwest winds continuing through midday. Showers are expected Friday night and Saturday.

Fuel conditions are not yet critical but the Cottonwood Creek fire last week (9/17) did grow to 57.54 acres showing that there is some potential for fire growth in that area of the state. Quoting Jay Wickham from Monday’s Weekly Weather Update, “There are some areas in the southern Black Hills where the grass has cured but most of the herbaceous vegetation will probably remain green until we receive some hard frost.  Wind will be the driving factor for any fire to be able to spread.” The neighboring counties in WY are under a Fire Weather Watch for Thursday but no Fire Weather Watches or Red Flag Warnings have been issued by the NWS for areas of SD as of yet. 

Lightning today and tonight

Showers and thunderstorms are moving through portions of the Pine Ridge Reservation. Additional showers and thunderstorms are now moving into western SD from WY. These storms are moving quickly to the north-northeast, are producing frequent lightning and gusty winds, but are not putting down much in the way of rain. I expect these storms to continue through the evening.

The fuels are not yet favorable for large wildfire growth but it wouldn’t surprise me to see several ignitions from this event. Watch for holdovers in the coming days as well.

August fire potential very low

July has come and gone and it was another wet month across SD. Nearly every location statewide received a surplus of moisture mitigating any wildfire concerns for the month. Some areas even saw 4-6 inches of moisture above the monthly average!

The recent rains combined with the forecast for cooler and wetter than average conditions should keep us clear of any large wildfires through at least the month of August.

You can find my full monthly assessment here: http://www.ias.sdsmt.edu/clabo/Fire_Weather/Monthly_Update.pdf

Impending hot weather and fire danger

A large upper level ridge will set up over the Rocky Mountain Region in the near term and this will bring above average temperatures to large swaths of the central and northern Great Plains as well as the Rocky Mountains.

Generally, above average temperatures in mid-July would concern me as a fire meteorologist. But conditions are still not favorable for large fire growth. To get large wildfires across SD, including the Black Hills, during July we need to have several elements in place:

1. Drought conditions (or long-tern precipitation deficits). Drought leads to dry soils and the desiccation of the larger fuel classes. However, we do not have drought or even abnormally dry conditions anywhere across the state. Below are the 120-day departure from average precipitation and the current US Drought Monitor for South Dakota. 

2. Short-term precipitation deficits. Short-term precipitation deficits lead to the drying of the fine fuels and the needle cast/litter on the forest floor. These are the main contributing factors to large fire spread. But we do not have any precipitation deficits in the short term. In fact, flooding has been more of a concern. The top figure shows the observed departure from average precipitation over the past 30 days and the bottom figure shows the radar-derived 30-day precipitation total for the state.

3. Hot temperatures. A continued period of hot temperatures is required to get large wildfire growth during the summer as it contributes to stress and an earlier drying of the fine fuels. Recently, we've seen below average temperatures (top figure) along with those above average precipitation totals. But, as stated previously, we are expecting hot temperatures in the near future (bottom figure). 

4. Available fuels. To get big wildfires, you need fuels that are sufficiently dry to carry wildfire. And this year are fuels continue to be extremely green. The VegDRI product is a good tool to use to determine overall fuel dryness and this year it is showing exceptionally green fuels (figure below). The yellow "pre-drought stress" vegetation condition over portions of western SD is more likely due to a big sweet clover crop that appears yellow to remote sensing tools. The fuels are just not dry enough to support wildfire growth. 

Summary: In short, we are still looking at below average large wildfire potential through the month of July. If the hot temperatures continue this month AND we see below-average precipitation, the wildfire potential might start to climb during August. But the long-term forecasts do not favor that scenario. So get outside, enjoy the hot weather, and always remember to be fire safe regardless of environmental conditions. 

Alberta wildfires bring smoke to SD

Several massive wildfires are currently burning across northern Alberta with the Chuckegg Creek fire being the largest at 150,000 hecatres (370,658 acres).

These fires are sending plumes of smoke to the southeast where they are impacting air quality and visibility across the north-central US.

The closed 700 mb low over Iowa is bringing northeasterly winds to South Dakota which is allowing the smoke to travel across the state.

And visible satellite really picked up the smoke this morning when the sun angle was low.

May wildfires are not out of the norm for Alberta. Recall the Fort McMurray wildfire of early May 2016 https://en.wikipedia.org/wiki/2016_Fort_McMurray_wildfire.

So if you see or smell smoke across the region, realize it is not of local origin.

A wet two weeks

It has most definitely been a wet two weeks across South Dakota with most stations reporting over 200% of their historical averages for the period.

But even this map doesn't tell the whole story. Looking at actual precipitation amounts reveals how wet it actually has been across the state.

Nearly all of western SD has received 2-4 inches more rain than what is average for the period. This has led to widespread flooding near creeks and rivers with significant ponding across the prairies. Fortunately the forecast is calling for relatively dry weather over the next 7-14 days.

Regardless of the upcoming 'dry' period, I do not expect anything close to enhanced fire danger. It's been too wet for too long and the fuels are too green to burn. This wet period will likely keep our fire potential low for at least the next 30 days.

Thunderstorms today/tonight

Showers and thunderstorms are expected to develop across the Black Hills and western SD this afternoon and continue through the overnight hours. Thunderstorms imply lightning and that implies the potential for ignitions. The forecast radar reflectivity image for 1800 hrs tonight is shown below.



Although greenup has started, it has not progressed far enough to mitigate the fire risk presented by the dead grasses from last year's growing season. With the Lone Tree, High Plains, and Coyote Fires all occurring over the past week, we should be cognizant that a few lightning strikes may pose a threat for wildfire ignitions.

Luckily, these storms should come with showers but that in of itself does not preclude a fire threat. Lightning can strike outside the main core of the storm and holdover ignitions are possible. Total estimated precipitation through noon tomorrow is below.



Stay aware and don't be surprised if we see a few fires pop up tomorrow.