Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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685 FXUS65 KCYS 090424 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1024 PM MDT Mon Jul 8 2024 .KEY MESSAGES... - Confidence is growing for a potentially significant heat wave to impact the region late in the week through the weekend. && .SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 300 PM MDT Mon Jul 8 2024 Quiet weather is expected through the next several days as the strong heat wave to our west begins to expand eastward. Current satellite imagery shows nearly clear skies over most of the area aside from a few shallow cumulus clouds developing. Temperatures aloft have warmed significantly over the last 24 hours, which has lead to a capping inversion around 500-mb. This, combined with a dry boundary layer will prevent convection today, aside from a virga shower over the mountains at most. While pleasant temperatures are still in place today, significant heat is now just around the corner. The ridge axis will shift a touch eastward for Tuesday leading to a range in 700-mb temperatures from +10C in the northeast to +15C in the southwest. Highs should be near normal for most of the area. The cap will be weaker tomorrow, which may allow for a few isolated showers and storms to develop over the higher terrain. Wednesday`s 700-mb temperatures will nudge upward about 2C, pushing afternoon highs a few degrees above average for this time of year. && .LONG TERM /THURSDAY THROUGH MONDAY/... Issued at 300 PM MDT Mon Jul 8 2024 A potentially significant heat wave is appearing more likely for a large portion of the region from Thursday through Monday. 700- millibar temperatures are expected to soar to between 18-22 C by Friday afternoon, peaking by midday Sunday as a highly anomalous 598-600 dam H5 ridge becomes centered over northwestern Colorado into south central and southeast Wyoming. The deterministic GFS/ ECMWF/GEM and their ensembles are in remarkable agreement w/ the strength & position of the ridge axis, especially on the days 5- 7 time scale. This is reflected quite well w/ the latest cluster analysis indicating 83% of members suggesting H7 temperatures at or above 20 deg C, above the 99th percentile & nearing the climo max per the NAEFS. The NBM spectrum is already impressive w/ the deterministic already painting a highs of 95+ F for Cheyenne and 101+ for Scottsbluff. This is particularly concerning, given the NBM tendencies to significantly under cut highs in these extreme scenarios. As such, have opted to go w/ the 90th percentile with this package, suggesting 98/106F for CYS/BFF for MaxTs on Sunday which should be the hottest day w/ the thermal ridge axis moving directly overhead. It is worth noting that that the 95th %ile of the NBM does approach all-time record territory of 100 F For CYS w/ the latest blend, a benchmark that has not been touched since the 1950s. One reason that such values are so difficult to reach in Cheyenne is the tendency for afternoon clouds to develop once we reach the mid/upper 90s, and this could very well be the case again as the models do show appreciable vort energy aloft, along the immediate edge of the ridge. This does not seem particularly convincing at this time given the extremely dry profiles, but is a failure mode that could squash our shot at a new record, which largely precludes a more conservative forecast at this time. Low temperatures are favored in the mid 60s to near 70 F, warmest in the Platte River Valley. Heat Advisories, and possibly Excessive Heat Watches may need to be strongly considered in the future if current trends hold and cloud cover appears any less likely. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 1023 PM MDT Mon Jul 8 2024 VFR conditions with mainly scattered high clouds through the next 24 hours. No weather impacts expected for any southeast Wyoming and Nebraska Panhandle airport as high pressure remains in control of the weather. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MN LONG TERM...CLH AVIATION...GCC