Area Forecast Discussion

KEY MESSAGES

- Freezing temperatures will once again occur in portions of eastern Box Elder County and central and southwest Utah given calm and mostly clear conditions.

- Anomalous heat returns with widespread daytime highs 10 to 20 degrees above seasonal normal Monday and Tuesday, potentially threatening records.

- Gusty southerly winds will likely develop Tuesday and Wednesday ahead of an approaching system. The system will then bring cooler and unsettled conditions with valley rain and some mountain snow.

DISCUSSION

Evening satellite water vapor loop shows the influence of mid level ridging gradually building towards the area, but some mid/upper level moisture advection and cloud cover overhead at the moment. Dry conditions have persisted, with temperatures running near to slightly below normal across areas west of the high terrain, and around 5 to 10 degrees below at areas east of it.

Looking ahead to tonight, models generally support clouds clearing out with skies across much of the area becoming clear to mostly clear. Winds will also continue to relax and become light to calm in many locations. This combination will be supportive of efficient radiative cooling, especially where clouds are able to clear out more rapidly. The most uncertainty on cloud cover is over eastern Utah, and particularly the Uinta Basin. As it stands though, a period of freezing temperatures once again appears likely across portions of eastern Box Elder County, central Utah valleys, west to southwest Utah, areas of The Swell and Castle Country, and the western Uinta Basin. A Freeze Warning is in effect overnight into Sunday morning accordingly, and those with sensitive agriculture or outdoor gardens/plants will want to consider taking steps to minimize impacts.

Moving Sunday into early next week, the strong influence of mid level ridging followed by increasing southwesterly flow will prevail. Temperatures will markedly increase, with afternoon highs around 5 to 15 degrees above normal Sunday, further pushing to 10 to 20 degrees above normal Monday and Tuesday. Dry conditions are largely also favored to continue, though Monday a subtle upper level trough will shift by overhead as some meager moisture lifts through, and the combination would support some isolated afternoon showers across the high terrain.

While the strengthening deep south to southwesterly flow ahead of an approaching system will maintain anomalous warmth Tuesday, enhanced low level winds will also result in a corresponding increase to breezy conditions across the region. With skies mostly clear to partly cloudy, strong mixing will help bring widespread daytime gusts in the 25-40 mph range. As often is the case, the signal for the strongest winds is noted across western Utah, and particularly the West Desert area. In these locations, there currently is approximately a 40-60% to see wind gusts in excess of 45 mph. Less certainty is noted on wind gust potential Wednesday given the timing of the front. Some models start to bring it through overnight into Wednesday morning, limiting the stronger gusts to eastern Utah. The ECMWF Extreme Forecast Index however highlights more or less the entire forecast area with a stronger signal for anomalously strong gusts Wednesday than it does Tuesday. Would expect some increased cloud cover though. All that to say, it'll be breezy ahead of the front, and it'll be worth watching the timing as to how prolonged the gusts end up being.

Noting the aforementioned timing caveats again, the trough and associated front are generally favored to start pushing through the region sometime around Wednesday. If during the day, some destabilization with a modestly sheared environment may offer a chance at some stronger and more organized showers and thunderstorms along the front. Shower chances will remain elevated behind the front as moisture lingers and the broader cyclonic flow of the trough (along with some embedded shortwave impulses) churn through into Thursday or even Friday depending on the exact evolution of the synoptic pattern. Deeper flow looks to generally also favor a bit more of a west to northwesterly component, which may help result in some orographically enhanced water amounts at favored high terrain. While the system is seasonably cool, snow levels ahead of the front will start around 7000 ft or so, and drop to around 6000-6500 ft as colder air moves in behind it. With the moist northwesterly flow, there is around a 20-30% chance of some lake enhanced showers as well. Overall models favor the northern half of the local forecast region in terms of precipitation, with modest northern mountain snow accumulations. Around a 10-30% chance for localized areas of freezing temperatures is also once again noted behind the front at similar areas within the current Freeze Warning area.

Ensembles do also support some continuation of unsettled weather on into the weekend, though with uncertainty on the exact pattern evolution. Troughing is largely favored in some flavor, with questions to how much and where a portion may cut off south and west of the area. A more cutoff scenario (favored by ~60% of ensemble members) would support a slightly drier/milder unsettled regime, with better phasing resulting in the opposite. Still, if nothing else a return to a strong ridge dominated pattern does not appear likely in the next 10 days.

AVIATION...KSLC

VFR conditions prevail through the TAF period under generally clear skies tonight and building mid-to-high clouds Sunday afternoon. Expect typical diurnal wind, with southeast winds persisting through the night, transitioning back northwesterly after ~20z.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions prevail for all regional terminals. Expect generally light, diurnally driven winds through the TAF period except southern Utah terminals where enhanced west to southwest breezes develop Sunday afternoon and evening. Decreasing clouds overnight will give way to increasing mid-to-high level cloud cover Sunday afternoon.

SLC WATCHES / WARNINGS / ADVISORIES

UT...Freeze Warning until 10 AM MDT Sunday for UTZ103-106-114>116- 118>122-130.

WY...None.