textproduct: Salt Lake City

KEY MESSAGES

- One more round tonight of freezing temperature for sensitive ag areas, followed by a warming trend into the weekend.

- There is a low chance (10-25%) of downslope winds for the northern Wasatch Front Thursday night into Friday morning.

- The next of daily shower/thunderstorm chances moves in next week, though with warmer temperatures in comparison to the last storm cycle.

DISCUSSION

Visible satellite imagery today shows notable fresh snow over the mountains of central/northern Utah and a more widespread dusting over southwest Wyoming including the I-80 corridor. Shallow cumulus fields can also be seen developing late this morning around all higher terrain, with more pronounced activity north of I-80 including a few weak echoes on the northern Utah radar. On a larger scale, water vapor imagery shows broad cyclonic flow over the Intermountain West with a circulation center upstream of our area over the Bay Area of California and another weak wave in the Vancouver Island vicinity.

Generally weak convection is expected the next few days with the previously-mentioned cyclonic flow lingering and the type of shallow low-level instability more typical of late March. The low center currently over the Bay Area will track through our region Wednesday (as it weakens) followed by the upstream Pacific NW wave settling in over Utah Thursday. Thus, expecting daily buildups of shallow cumulus around the mountains and a few rain/graupel showers, but low chances (generally 15% or less) of lightning. Thursday looks to have the most widespread chance of showers, with more instability available and scattered to widespread showers along and east of I-15.

With the shortwave trough digging into our area Thursday and attempting to close off around central Utah, one noteworthy aspect is the northeasterly to even easterly flow aloft that develops over far northern Utah and southwest Wyoming, which combined with cold air advection sets up a pattern that is vaguely similar to past downslope wind regimes for the northern Wasatch Front. Looking at a local forecast tool based on past research into such events and applying the forecasted pressure gradients from a few deterministic models, it suggests a 10-25% chance of occurrence. Current wind probs from the NBM are also below significant thresholds. While this does not meet the 33% threshold for us to message the thread in our Weather Risk Outlook, but it is something to keep an eye on. The potential of a downslope wind event will be highly dependent on the track of the low, and of course the track of springtime closed lows are notoriously finicky to forecast.

Heights aloft build over Utah Friday into the weekend, supporting a warming trend along with drier conditions. Temperatures will rebound from the recent 15-20 degrees below normal to 5-10 degrees above normal by Sunday. Some threat of high-based showers returns to the mountains by late Sunday though as yet another closed low, this time much larger in scale, develops off the California coast and sets up generally southerly flow aloft over the Great Basin. Ensemble cluster analysis for 500MB heights shows surprising consistency among ensemble members with the track of this feature, suggesting moisture transport aloft into our region and increasing instability going into next week. One notable difference from the last deep closed low early this week is this next round will be warmer, with temperatures tracking near seasonal norms (it will be May by that point in fact) and snow levels more in the 8 to 9,000' range.

REST OF UTAH AND SOUTHWEST WYOMING

Isolated showers will continue through the afternoon roughly north and east of a line from Park Valley to Kamas. Any showers will diminish near sunset. Aside from briefly lower ceilings near these showers, VFR conditions will continue through the region.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Freeze Warning from midnight tonight to 9 AM MDT Wednesday for UTZ114>116-118-119-122.

WY...None.