Sunrise 5:50 AM   Sunset 8:03 PM Moonrise 5:04 AM   Moonset 8:23 PM

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FXUS65 KGJT 081156 AFDGJT

Area Forecast Discussion National Weather Service Grand Junction CO 556 AM MDT Wed May 8 2024

KEY MESSAGES

- Sub-freezing temperatures for the lower valleys where vegetation is susceptible to damage is forecast early this morning. Other areas may see frosty conditions.

- Cool and unsettled weather will linger through the remainder of the week. Persistent snow over the northern mountains will bring some accumulations to the higher elevations today before the threat shifts to the south to end out the week.

SHORT TERM /THROUGH THURSDAY/
Issued at 406 AM MDT Wed May 8 2024

Cold air continued to filter southward across the forecast area early this morning as the closed low pressure system remained over the northern High Plains early this morning. Clearing was late in coming for a significant portion of the areas where Freeze Warnings were in place which has buoyed temperatures thus far.
In addition, the surface pressure gradient has proven strong enough to keep winds moving at KCNY, KBDG, KGJT and KMTJ which has also helped keep temperatures above freezing so far. That said, winds have diminished at KRIL and temperatures there were just above freezing. There's a good chance that winds will continue to keep cold surface inversions from forming which should be good news for local growers.

The Plains low drifts slowly southward today before turning east late. As this occurs, the westward flowing jet in the northern quadrant of the low causes mid-level heights to fall over the Great Basin resulting in an elongated area of low pressure over the region. Moisture will linger over the northern half of the forecast area as flow aloft, though weaker, continues to advect moisture southward. Dynamic forcing will be limited, but the cold pool at 500 mb creates sufficient instability for mainly afternoon showers, mainly over the northern mountains and portions of the central Colorado mountains. Snow accumulations will be light and fairly localized. Elsewhere, expect partly to mostly sunny skies and dry weather. Highs are expected to continue to anomalously cool with most locations 10 to 15 degrees cooler than normal.

The westward flowing jet north of the Plains low turns south over the western Great Basin tonight causing a low to close off over southern Utah early Thursday morning. Jet divergence, instability and orographics will keep light showers going along the northern border of the forecast area tonight. However, by Thursday afternoon the focus shifts to the southern half of the forecast area as difluent flow and jet divergence develops east of the low west of the Four Corners. However, enough residual moisture and instability will remain to fuel numerous showers and a few thunderstorms over the mountains and high valleys Thursday afternoon. Despite increased clouds and showers, temperatures will moderate, though highs are still expected to peak about 5 degrees below normal.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
Issued at 406 AM MDT Wed May 8 2024

A low will become cut off from the main upper level flow and continue to spin over the Great Basin through at least Friday night as a Rex Block forms over the west. This will keep moisture circulating around the low with easterly upslope flow into the San Juans and Divide mountains. The higher elevations of the San Juans look to be the most favored for some snow accumulations along with the spine of the Central Divide through Friday night. Temperatures throughout this period also look to be warming as well despite the unsettled conditions which would increase available moisture. Lapse rates will steepen and instability present. Given day time heating, this should result in scattered to widespread showers and thunderstorms, favoring the high terrain during the afternoon with some drift off the terrain into adjacent valleys from time to time.
Even though these blocking patterns have a tendency to persist, the models are showing some signals of this Rex Block breaking down by Saturday with the cut off low finally moving eastward into the Plains. Models seem to be in better agreement now than they were a few runs ago. This may be due to more shortwave energy moving across southern Canada and making its way into the northern High Plains and eventually northern Rockies by early next week.

So, conditions will remain unsettled through Saturday with some afternoon storms favoring the high terrain as we transition from the unsettled weather with the cut off low over the region to a drier northwest flow as high pressure tries to build in from the west by Sunday. Additional shortwaves try to drop in from the northern Rockies into our CWA early next week, resulting in afternoon convection mainly over the high terrain of western Colorado. High temperatures during this period will be around 5 degrees below normal Friday and Saturday, warming up towards near to slightly above normal by Sunday as the low exits, and return to 5 to 10 degrees above normal by early next week. Even though most lower elevations will return to drier and warmer conditions Sunday through early next week, showers and thunderstorms will be around each day but mostly favor mountains and high valleys. It should start to feel more like a warm Spring time convection regime.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/
Issued at 556 AM MDT Wed May 8 2024

Expect quiet weather at eastern Utah and western Colorado TAF sites. VFR conditions and light winds will be the rule. However, ceilings below ILS breakpoints will an issue for KEGE and KASE off and on for much of the day.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Freeze Warning until 10 AM MDT this morning for COZ006-007-011.
UT...Freeze Warning until 10 AM MDT this morning for UTZ022-027-029.

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