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Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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438 FXUS65 KRIW 171106 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 506 AM MDT Sat Aug 17 2024 .KEY MESSAGES... - A surge of monsoonal moisture will bring showers and thunderstorms this afternoon to southwestern Wyoming. Isolated flash flooding is possible. - Strong winds are likely to accompany this activity; locations east of the Divide will see the wind even when showers/storms die off late this afternoon and evening. - Shower and thunderstorm chances continue Sunday and Monday. && .DISCUSSION... Issued at 357 AM MDT Sat Aug 17 2024 Today will start off fairly uneventful as we initially stay under the influence of the dominating high to our south. Temperatures will peak a little warmer, especially east of the Divide where highs will return to the 90s. However, a strong mid-level shortwave will quickly approach from Utah after 18Z. This will advect in a notable surge of monsoonal moisture, with PWATs increasing from around a third of an inch to around or just over an inch across southwestern Wyoming. Accordingly, showers and thunderstorms will accompany the arrival of this airmass, first across Uinta County and then moving northeast to the Continental Divide by around 23Z. This activity will struggle to make it over the Divide with the loss of diurnal heating, and most of the rain associated with this activity will remain across southwestern Wyoming. Isolated flash flooding will be possible with any training storms this afternoon. The other concern with this surge of moisture is wind. Hi- resolution models are in good agreement with showing not only the convection but decently strong accompanying wind. This threat is further seen with forecast surface pressure, which shows a strong gradient setting up given the advancing cold pool / mesohigh. Wind gusts of 40 to 50+ mph are not out of the question this afternoon and evening as the showers move northeast, likely outlasting the convection and advancing east of the Divide perhaps as far north as the Bighorn Basin. Showers will be on the decrease after 03Z, mostly ending by 06Z. Sunday and Monday will see a more widespread shower and thunderstorm threat as broader shortwaves rotate around the ridge. An isolated flash flooding threat will remain given the ample moisture that will still be in place. Further ahead, the general synoptic pattern will persist, though a decrease in available moisture will keep precipitation chances a little lower Tuesday through at least midweek. Temperatures will remain on the warmer side, generally around normal to five degrees above normal for this time of year. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 505 AM MDT Sat Aug 17 2024 Light winds increase with diurnal mixing late morning and through the afternoon today. Models continue to be in agreement for a cluster of storms after 20Z/Sat in southwest Wyoming. These should push east/northeast through about 10Z/Sun. Main impact looks to be wind, with high-resolution models continuing to produce 40 to 50 mph gusts. This cluster of storms would most likely impact KBPI, KLND, KPNA, KRIW, and KRKS. KJAC looks to be on the northern edge of the clusters; have added a PROB30 group for thunderstorm chances, though confidence is low. Gusty winds 20 to 30 knots are possible for KCPR, KLND, and KRIW through the end of the TAF period, even after storms pass through. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .FIRE WEATHER... Issued at 357 AM MDT Sat Aug 17 2024 Elevated fire weather conditions are expected for much of the area this afternoon ahead of surging monsoonal moisture that will arrive to southwestern Wyoming around noon. This will bring showers and thunderstorms mainly west of the Divide, as well as strong southwesterly wind that will eventually move east of the Divide late this afternoon and evening. While humidity will increase notably, the wind will likely arrive suddenly and could cause issues for ongoing fires. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Myers AVIATION...Wittmann FIRE WEATHER...Myers