textproduct: Cheyenne

KEY MESSAGES

- Critical Fire Weather conditions expected Sunday and again Monday as humidities dive into the single digit values.

- Pattern change alongside a chance at some precipitation including storms and snow expected mid through end-week timeframe.

SHORT TERM /THROUGH TUESDAY/

Issued at 328 PM MDT Sat Apr 18 2026

Minimal changes to the overall forecast package this afternoon aside from the upgrade of a Fire Weather Watch to Red Flag Warning for Sunday into Monday. For today, Red Flag Warning is verifying as breezy winds alongside low RH values into the mid to low teens are ongoing under a ridge of high pressure that is expected to dominate into the early week timeframe. A few weak echoes are seen on radar in Dawes County, but outside of providing some clouds and possible virga it is unlikely precipitation is making it to the ground with the dry conditions present. Overnight we will see clear skies help contribute to another cold spell with temperatures around or just below freezing across the region. Moving into Sunday, while winds will abate, the incredibly dry conditions with RH values dropping into the low teens to single digits alongside the chance of a breeze or two is enough to warrant concern for critical fire weather conditions. And overnight recoveries will be very poor Sunday night into Monday followed by a much windier and even more critical fire weather day on Monday. Therefore, the Red Flag Warning felt necessary to account for this incredibly dry and hazardous period for new fire starts.

Outside of this, sensible weather concerns remain minimal. Temperatures on Sunday will return to spring-like with highs in the 60's to 70's, and by Monday we may start to see a more summer-like day as temperatures continue to rise into the upper 70's and low to mid 80's, around 15 to 20 degrees above normal for this time of year and in some locations beginning to approach record highs.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Issued at 328 PM MDT Sat Apr 18 2026

A high amplitude upper level ridge will be responsible for the prevailing conditions to start off Tuesday. Unsurprisingly, this ridge will bring along with it dry and sunny conditions. We start off the day in the upper 30s to low 40s across much of the area. Temperatures reach the 70s in the mountain interior and mid 70 and 80s over SE WY and the NE Panhandle. This is a good 20 degrees above average for this time of year and within the 90th percentile of 700mb climate per the NAEFS. Some sites, particularly in valley regions of the Nebraska Panhandle, may overperform and tie their record highs. As usual with unseasonable warmth our relative humidity values are also expected to be low during the day, reaching the low teens. Winds should be on the lighter side given the ridge passing overhead, but given the dry preceding conditions and the tall mixing heights of nearly 14 kft, the fire threat is still a concern. RH recoveries overnight are poor.

Ensemble models are in good agreement of a closed low moving in over the Pacific Northwest Wednesday and our upper level ridge moving east. We will be in the southwesterly flow regime of the low pressure system by this point. We can expect increasing upper level cloud coverage from west to east overnight Tuesday and through Wednesday. Temperatures appear to be about the same as Tuesday, perhaps slightly cooler with the increased cloud cover. Dry conditions continue as well, with minimum RH values reaching the teens once again in the afternoon and evenings. However, the winds are a much bigger concern when talking about fire potential. ML high wind products are indicating an elevated probability of high winds over our wind prones (~40% of exceedance). Meaning gusts of 40 to 50 mph are likely to be felt over portions of our CWA, particularly over the interior mountain ranges. Meteorologically this increase in winds is in response to lee cyclogenesis to the north of the area. A dryline may take shape in the evening across the Nebraska Panhandle. While we are at long range here, some ML guidance are starting to pick out elevated thunderstorm potential along this dryline, with numerical grand ensemble giving about 50% chances of MUCAPE reaching above 100 J/kg currently. The vertical profiles in this environment are trending towards dry at the surface with deep layer mixing. Inverted-v soundings may support a wind threat with any high based convection. Again, we are a ways away, so guidance may change. This may also have further implications on anticipated fire weather conditions as little precip is likely to make it to the surface. Additionally any thunderstorms may increase the threat of dry lightning or influence on surface winds.

Overnight winds increase as the mid level low moves off to the northeast and a Pacific cold front moves through. Aloft we are still at the base of the upper level trough. Along this base are likely to be a few embedded vorticity maxima that may provide more forcing for ascent for the next few days. There is a bit more uncertainty on the amplitude of the remaining troughing. Cluster analysis of ensembles seem to paint GEFS members as being more supportive of deeper maximums and ENS and GEPS members with weaker lobes where most of the energy parts with the Wednesday system to the northeast. What this means to us is a slight increase in precipitation probabilities tied to stronger upper level solutions. Regardless, probabilities of seeing measurable precipitation over a large portion of our CWA remains low, except for maybe the mountains. Temperatures are likely to cool in combination of increased cloud cover and the Pacific front which hopefully will keep us out of widespread fire weather conditions, though portions of the southern NE Panhandle may have RH values in the 20s during the day.

Models are advertising an arctic front sometime overnight Thursday which may push us towards more seasonable temperatures Friday. Model spread remains high at this range in terms of upper-level features. Thus while precip chances remain elevated, the amount is still in question. Saturday appears to be much the same as Friday weather wise.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 531 PM MDT Sat Apr 18 2026

Some lingering gusty conditions at terminals before winds calm after sunset. Clear skies are expected overnight at the Nebraska terminals while a period of scattered mid to high level cloud coverage develop over the Southeastern Wyoming terminals after 6z. VFR conditions are expected with this cloud cover. These clouds are likely to dissipate a few hours after sunrise and clear skies are expected to prevail at all terminals for the remainder of Sunday. Winds at the NE panhandle terminals to stay generally below 15 kts through the forecast period and may be variable at times. At WY terminals gusts to 25 kts may occur in the afternoon hours.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Red Flag Warning from 11 AM Sunday to 8 PM MDT Monday for WYZ417-418-430>433. NE...Red Flag Warning from 11 AM Sunday to 8 PM MDT Monday for NEZ434>437.