361 FXUS65 KPUB 210540 AFDPUB Area Forecast Discussion National Weather Service Pueblo CO 1140 PM MDT Fri Aug 20 2021 .SHORT TERM...(This evening through Saturday) Issued at 242 PM MDT Fri Aug 20 2021 Dry weather with breezy winds have been the main story across southern Colorado today as the frontal boundary remains stationary across the OK Panhandle stretching west northwestward to KTAD. Some cumulus has been developing along this axis this afternoon but lacks sufficient moisture and instability for showers or thunderstorms in southern CO. However high res models show showers and isolated embedded thunderstorms breaking out across portions of the southeast plains/I-25 corridor after midnight with increasing overrunning overtop the frontal boundary and increasing easterly low level winds. This is in response to an weak shortwave in increasing southwest flow aloft which moves across southern CO late tonight and Saturday morning. CAPE in model soundings looks limited (under 500 J/kg) and saturated later in model soundings rather elevated, so think these will be mainly showers with an isolated embedded thunderstorm or two. Overrunning decreases after 12z with showers gradually ending and pulling off to the northeast during the morning. Another round of showers and thunderstorms develops over the mountains in the afternoon. Coverage looks limited to the isolated to scattered categories over the mountains, with the best chances along the Continental Divide as another weak PV feature moves across in the afternoon. With dew points in the 30s to lower 40s, thunderstorms are likely to be high based with gusty winds, lightning and some brief but spotty rainfall the primary risks with thunderstorms. Will need to monitor the southeast corner of the state where southeasterly return flow may advect higher dew points westward behind the front yielding higher CAPEs, especially into the late afternoon/evening hours. Could have a strong to severe storm or two in this area late in the period depending on the timing of low level moisture return. With east to southeast flow beneath increasing southwest flow aloft...deep layer shears of around 40 kts will be present which, is sufficient for storm organization with an isolated large hail and damaging wind risk possible if storms can form given weak forcing aloft. Have included some isolated pops in there for now. Otherwise expect slightly cooler temperatures for Saturday for most areas. -KT .LONG TERM...(Saturday night through Friday) Issued at 242 PM MDT Fri Aug 20 2021 Saturday night...scattered thunderstorms could be possible over the southeast plains and northern central mountains until late in the evening on Saturday. For Sunday...a very slight chance of late afternoon/evening thunderstorms for the southeast plains. For Monday...a slight chance of thunderstorms will be possible over the central mountains. For Tuesday...a few thunderstorms will be possible over the mountains during the afternoon and plains during the evening. For Wednesday...thunderstorms will be possible throughout the afternoon and evening hours, mainly over the eastern mountains and plains. Some of these storms could become severe. For Thursday...thunderstorms will be possible during the afternoon and evening, mainly for the southern half of the CWA. For Friday...thunderstorms will be possible during the afternoon and evening. Detailed discussion: Saturday night... A trough in the longwave pattern over the NW CONUS will continue to propagate towards the region and allow for the southwesterly wind flow in the mid to upper levels to increase later in the evening. This will help to create some upper level diffluence and result in a few thunderstorms that have formed earlier in the day to move out over the plains and also allow for a few thunderstorms to be possible over the central mountains going later into the evening on Saturday. Otherwise, skies will continue to clear for other locations. Winds at the surface will continue to increase out of SSE over the plains and generally be out of the SW over the mountains and San Luis Valley. Temperatures will cool to upper 50s to mid 60s over the plains, 40s to low 50s in higher valleys, and mid 30s to low 40s in high country. Sunday... The longwave trough is going to propagate to the north of the region and this will allow for some reinforcement of drier air upstream to move over the CWA and inhibit the development of afternoon and evening thunderstorms over the mountains. Only a slight chance will be possible over the southeast plains as a weak boundary associated with the trough remains over this area during the late evening hours. Surface winds will increase out of the southwest and conditions will be drier, with lower RH values and close to critical fire weather criteria. However, with fuels being better due to antecedent precipitation over most locations, critical fire weather conditions are not expected to occur. The downsloping winds will also increase maximum temperatures, especially over the plains, where some locations in the lower Arkansas River Valley could top out over the 100 degree mark. Monday through Tuesday... Ridging will continue to strengthen preceding the longwave becoming flattened upstream over the midwestern states, and this will allow the high pressure over Texas to strengthen and bring back in some of the moisture from the monsoonal plume over the region. Therefore some storms will be possible, but more likely over the central mountains on Monday. Mid to upper level flow will also remain persistently out of the southwest, which will result in any convection to be moving towards the NE and over the plains on Tuesday during the evening. This flow will also keep downsloping winds over the plains and hot conditions in place, above the seasonal average, for most locations. Wednesday... A trough will begin to move in over the area and help weaken the ridge a bit. There will be a frontal boundary associated with this tough which could help to initiate more convection over the eastern mountains and plains during evening, depending on where the boundary establishes itself. Storms along this boundary could potentially become severe. This will also help to slightly cool down most locations a bit, returning to temperatures closer to the seasonal average. Thursday through Friday... Passage of the trough will lead to the ridge slowly building back in over the region and also the monsoonal moisture plume will have more of an influence going into the later part of next week with the chance of thunderstorms increasing over all areas, especially by Friday. -Stewey && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 1135 PM MDT Fri Aug 20 2021 VFR conditions with mainly dry weather expected across the TAF sites this period. A weak system currently moving through the region is helping to support VFR ceilings and some isolated showers across COS and PUB early this morning. Expect these ceilings and even isolated light shower development for a time early this morning, before conditions clear. With the development early this morning expected to be light and brief/isolated, have maintained VCSH in both the COS and PUB forecast. Once again, general clearing of the clouds and precip development anticipated later this morning and while can't rule out some isolated precip development later this afternoon across PUB and COS, have kept the forecast dry at this time. && .PUB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...KT LONG TERM...STEWARD AVIATION...RODRIGUEZ