


Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
274 FXUS65 KRIW 140805 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 205 AM MDT Mon Jul 14 2025 .KEY MESSAGES... - Isolated to widely scattered showers and thunderstorms across northern Wyoming today, some with strong wind gusts. - A more widespread chance of showers and thunderstorms for Tuesday and Wednesday, with a few strong storms possible. - Elevated fire weather likely today and tomorrow, and again late in the week. && .DISCUSSION... Issued at 159 AM MDT Mon Jul 14 2025 The weekend was of the nice, summer variety. One warm day and one hot one with light to moderate wind and lots of sunshine for most locations. Things do turn more active today though, and this will last for the next three days. And they fall into two camps, fire weather and thunderstorms. As for today, we will have both concerns. We do have a small area of showers and embedded thunder moving into Yellowstone Park but this should be gone by morning. A cold front will be dropping through Montana today but will remain north of the state today so it will be another hot day, possibly a bit hotter with some southwest flow ahead of it. A few of the warmer spots, like Greybull and Worland may make a run at 100 degrees today and even Casper could get close. In addition, it will become breezy ahead of the front, And this brings us to the fire weather concerns. Humidity will be plenty low, falling to around 10 percent in some locations. Wind remains marginal though. Latest guidance actually has it a bit lighter than last time at this time. So, we have made the decision not to issue and Red Flag Warnings, since any critical fire weather would be brief. Elevated fire weather looks like though for roughly the southern half of the area though. And this brings us to the thunderstorm aspect. We have a marginal risk across the northeastern half of Johnson County, where the atmosphere will be a bit more moist and could bring some hail. The main threat by far today will be strong wind gusts. We have a very good set for strong to possibly high convective winds. A cold frontal boundary and shortwave approaching to increase instability. Mid level moisture will be increasing as well. Lower levels remain very dry as well very large dew point depressions, over 60 degrees in some cases. Model soundings are showing some very large inverted V signatures as well. So, any thunderstorm, shower or even cumulus cloud could produce a wind gust past 50 mph when it the updraft collapses. This would be largely across northern Wyoming this afternoon and evening. Coverage looks small though, with any location having at most 1 out of 4. But where they occur even innocent looking showers could have a strong wind gusts. All in all, a good set up for one of our "Little Green Blob" days. Thunderstorms will remain possible on Tuesday, although the main threats will shift. For one, storms look more widespread across roughly the northern half of the area. Instability parameters also looks more impressive, with CAPE as high as 1500 J/Kg and limited indices to minus 5. The big change will be moisture though. Much of the area may have precipitable water values approaching 1 inch East of the Divide and even over. For example, models give around 0.95 inches at Riverton. For reference, the mean this time of year is around 0.60 inches. This puts Riverton over 150 percent of average with this amount around the 95th percentile. So, this could lead to locally heavy rain. There will be some steering flow that will mitigate this somewhat but local flooding is a possibility. Shear isn`t the best I`ve seen but there is some so we could have some tilted updrafts and some larger hail. The main threat of this would be in Johnson and Natrona County, where we have a marginal risk along with low level east to easterly flow to bring upslope and aid in storm initiation. This will be a cooler day as well, anywhere from 10 to 25 degrees cooler depending on where the front is. This is also where the strongest storms would be, wherever the front is in the afternoon. As for fire weather concerns, these will continue across the south. However, somewhat cooler temperatures and higher humidity may mitigate this to a certain degree. The threat of thunderstorms will continue on Wednesday. However, models show less of a chance on this day. Most guidance shows drier air moving in from the west that will drop precipitable waters about 25 percent across the area. Most areas East of the Divide will continue to have a chance of a shower or storm but the greatest chance will be in the eastern counties. This will also be the coolest day. MOS guidance continues to have highs in the 50s for Buffalo but I still don`t buy it since any sort of sun that day would warm things up. It could should stay in the 60s though. This will be the coolest day across the area though, with high temperatures East of the Divide anywhere from 10 to as much as 25 degrees below seasonal averages. Warm temperatures will continue West of the Divide though with more elevated fire weather possible for Wednesday. Flat ridging then controls the weather from Thursday into the weekend. This will bring a return to near to somewhat above normal temperatures. Thursday at this point looks largely dry. Following that, a couple of shortwaves will bring chances of diurnal convection, but timing of these is still uncertain. With the flat ridging, breezy conditions will be common and could lead to elevated to critical fire weather on any of those days. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 942 PM MDT Sun Jul 13 2025 VFR conditions and mostly clear skies continue through Monday morning. A change in the weather pattern begins Monday afternoon as a weather system approaches from the northwest. There will be enough moisture Monday afternoon for some isolated showers and storms, but most will be virga showers. The best chance (30-40%) of impacts will be at KCOD and gusty wind would be the main threat. KCPR may also have an isolated shower or storm late afternoon into the evening, but the chance is only about 15-20%. Other terminals will have some scattered cumulus in the afternoon around FL100-150. There will be a bit more wind across the area Monday afternoon about 10-15 knots, with gusts of 20-25 knots at KBPI, KPNA, KCPR, and KRKS. Stronger gusts will occur where virga downdrafts and outflows develop. Wind will subside around sunset Monday evening. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued at 159 AM MDT Mon Jul 14 2025 A cold front will move toward Wyoming today, bring locally breezy condtions across central and southern Wyoming. With relative humidity falling under 15 percent, elevated fire weather is likely this afternoon. Wind gusts over 25 mph do not look widespread enough for critical fire weather though. Elevated fire weather will remain likely in southern Wyoming on Tuesday, with improve conditions in areas East of the Continental Divide. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Hattings AVIATION...Rowe FIRE WEATHER...Hattings