Sunrise 6:16 AM   Sunset 8:33 PM Moonrise 5:23 AM   Moonset 8:50 PM

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FXUS65 KSLC 082153 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 353 PM MDT Wed May 8 2024

SYNOPSIS
A downslope windstorm will impact portions of northern Utah Thursday morning into Friday afternoon. Gradually warming, with daily convection, will continue into the weekend.

.SHORT TERM (Through 18Z Friday)...An upper level low will gradually weaken over the short term forecast period...slowly shifting south and east with time.

By far the biggest impact will be the increasing likelihood of a downslope windstorm across northern Utah. By Thursday morning, modest cold air advection combined with easterly flow will begin to set up the necessary ingredients. Guidance suggests the start time will be a bit different than most windstorms, with winds increasing Thursday morning rather than Wednesday night.

Current guidance suggests that winds will increase through the day Thursday, reaching gusts in excess of 60 mph across the Layton to Bountiful corridor after 00Z Friday. For other areas such as northeastern Salt Lake County, eastern Box Elder County and eastern Cache County, this event looks more like an extended period of gusts in the 40-55 mph range.

To match this expected morphology, issued a wind advisory for all prone areas, with a high wind watch from 00Z Friday onward for Weber and Davis County. Right now, the most likely outcome (60-70% chance) would be for wind gusts to 65 mph in this area. While unlikely (15% chance), winds could gust as high as 75 mph in the Layton to Bountiful area. The peak period for strong winds is expected from 7 PM Thursday to 10 AM Friday.

As the cold air advection weakens and the easterly gradient shifts later Friday morning, conditions will gradually improve...just in time for a more summer-like pattern featuring afternoon and evening convection along the higher terrain and adjacent valleys.

Given that trees are fully or nearly fully leafed out and antecedent conditions have been quite moist, expect the threat for tree damage will be higher with this event. Those in the prone areas should secure trampolines, outdoor furniture, garbage cans, decorations and other lightweight objects to prevent projectiles that can cause property damage. Strong crosswinds may make travel difficult for RVs and high profile vehicles along I-15, Legacy and US-89 in Weber/Davis County and in the Brigham City area, especially Thursday night into Friday morning.

.LONG TERM (After 18Z Friday)...Low pressure will retrograde through Friday, and will position near the Nevada, Arizona, and Utah border Friday evening. As it does that, east synoptic winds will diminish, allowing strong downslope winds to diminish for northern Utah.

With the low cut off from the mean flow, it will not exit until later in the weekend. Scattered convective showers and isolated thunderstorms, mainly from afternoon into evening, are likely with low pressure to the southwest, strong lapse rates, warming of the day, and sufficient moisture. Showers will be most common in the mountains.

Shower coverage will be lower for the end of the weekend as the closed low will track to the east. Isolated showers and thunderstorms are forecasted for portions of eastern Utah, including the Uinta Mountains. Drier conditions will build in Monday, as ensembles are in good agreement on a longwave ridge building off the west coast. Within northwest flow, several shortwave troughs could track into southwest Wyoming and northern Utah during the week. Isolated or scattered showers, primarily in the mountains are likely with any shortwaves through Wednesday.

Temperatures Friday and Saturday will be near normal. As the closed low exits Sunday and a ridge builds to the west, temperatures throughout southwest Wyoming and Utah will warm Sunday and Monday to roughly 5-10F warmer than normal, then stay similar or decrease slightly if any shortwave tracks nearby.

AVIATION
KSLC...VFR conditions remain in place through the valid TAF period with afternoon build-ups/ low level cloud cover decreasing during the overnight hours. Northerly winds will decrease in speed and gradually shift to a south wind late this evening. That said, there is a 60% chance that light and variable winds prevail overnight. Northeast to east winds increase in speed tomorrow afternoon.

REST OF UTAH AND SOUTHWEST WYOMING
VFR conditions will prevail for a vast majority of the forecast area through the valid TAF period, with the exception of southwest Wyoming. Near KEVW, periods of MVFR to IFR conditions are anticipated as area snow showers increase overnight and tomorrow morning. Otherwise, gusty north winds are expected to develop between KCDC and KSGU tonight and diminish by tomorrow morning, with east to northeast winds increasing in speed across the Wasatch Front and southwest Wyoming tomorrow. Showers will build over terrain features during the afternoon, however, bases should remain above 5000ft AGL.

FIRE WEATHER
A slowly weakening disturbance will bring the threat of afternoon and evening showers and thunderstorms through the weekend. Temperatures will gradually warm, averaging around 5-10 degrees above normal by Sunday.

Strong and gusty downslope winds are expected Thursday morning into Friday morning from Salt Lake County north and the eastern Cache Valley.

SLC WATCHES/WARNINGS/ADVISORIES
UT...Wind Advisory from 6 AM Thursday to 10 AM MDT Friday for UTZ103- 105-107.

Wind Advisory from 6 AM to 6 PM MDT Thursday for UTZ104.

High Wind Watch from Thursday evening through Friday morning for UTZ104.

WY...None.

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