750 FXUS65 KSLC 100955 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 355 AM MDT Wed Oct 10 2018 .SYNOPSIS...An unsettled and cool pattern will continue across the region with multiple disturbances expected to impact Utah through the end of the week. && .SHORT TERM (THROUGH 12Z SATURDAY)... Potential Impacts... * Accumulating snowfall above 6500 ft, especially this morning across the north * Winter driving conditions for northern Utah mountains, and southwest Wyoming this morning * Snow may mix in with rain down to the high benches * High elevation accumulating snowfall mainly southern and central Utah late tonight through tomorrow night Antecedent Conditions... Exceptional Drought is occurring centered across San Pete county and near the Four corners. Extreme drought continues across the remainder of central and eastern Utah and northeast of the Great Salt Lake. Severe drought is across the remaining areas, scaling down to Moderate drought across southwest Utah and near the Wyoming border. Big Picture... During the past 5 days, storm systems are progressing across the Pacific within an amplified pattern. A ridge dominates the eastern Pacific as a closed low drops into northern Utah, maintaining a trough over the Rockies. MDCARS aircraft observations within the 400-250mb layer show a 100-130kt cyclonic jet from Washington into the Four Corners. Local Observations... 00Z KSLC RAOB shows mixing up to 700mb. The column was nearly saturated above ridgetop level. Mid and upper level winds were weak to moderately strong from the west. Precipitable Water values range from 0.20"-0.40" mountains to 0.50"-0.60" valleys. A 1006mb occluded surface cyclone is near Evanston, with a 1035mb surface anticyclone across central Canada. This is creating a 13mb northeasterly pressure gradient across southwest Wyoming, providing gusty winds and an upslope component to locally enhance precipitation coverage and rates. The boundary extends to a 1004mb surface cyclone near Green River, with the attendant cold front extending southwest toward Kanab. 24 hour trends: * Precipitable Water 0.10"-0.20" higher except southeast valleys * Temperatures are 5-15F warmer south of I-80 * Dewpoint Depressions are 5-15F higher (moister) across northern Utah, 10-20F lower (drier) southern Utah Forecast... The forecast remains on track and no changes were made to the Winter Weather Advisories. The northern mountains along with southwest Wyoming are the chief locations of concern for wintry impacts. IR satellite confirms the coldest cloud tops have advanced into southern Idaho, southwest Wyoming and northwest Colorado, suggesting large scale ascent will only decrease from here. This was the expected timing per GFS Time Height charts. The soaking rain rates along the Wastach Front have come to an end. Precipitation turns showery this morning, and dissipates this afternoon and evening given strong height rises and warming aloft behind the passing storm system. Snow levels look to remain near 6500 feet today as was expected, a bit lower north and east of Salt Lake. Road temperatures at and above this elevation are currently near or below freezing. Snow may mix in with rain down to the high benches under heavier showers. Downstream (east) of the Great Salt Lake, there is a potential of seeing enhanced precipitation across Weber and Davis counties this morning. The Great Salt Lake surface water temperature is about 57F currently. Adjusted FV3 BUFKIT forecast soundings (for a 55F water temperature) suggest up to 600J/kg of Lake Induced CAPE, a NCAPE near 0.10, and Equilibrium Level up to 20kft. Cool temperatures are forecast today as at least most of the day will be overcast along the Wasatch Front. Additional energy drops into the backside of the trough (to our west) tonight and tomorrow, with a period of falling heights centered overhead around sunrise tomorrow. Warm advection will ensue, with overrunning providing a good chance for valley rain and mountain snow across southern and central Utah by tomorrow morning. A cold front will sweep southeast across Utah tomorrow night with the passage of the trough axis. Dry advection, rising heights and warming aloft will shut off precipitation processes by Friday morning. .LONG TERM (AFTER 12Z SATURDAY)... The synoptic pattern over the West at the start of the long term period will be characterized by a mid-lvl ridge centered over the Pacific with a cut-off low pinned to its south off the southern California coast. A shortwave is progged to dive southward along the eastern periphery of the Pacific ridge Saturday into Sunday. Unfortunately 00Z guidance has diverged on the track of this wave with the EC/FV3 favoring a more western track while the CMC/GFS(and majority of GEFS) favor a more eastern track. The further west solutions would both advect a cooler airmass into the area (H7 temps around -10C in northeastern parts of the area) and also come with chances of snow for northeastern parts of the area. Conversely only modest cooling is advertised in the GFS/CMC solutions with almost no precipitation chances as the wave's dynamics are focused well to our east. To account for these discrepancies went with a blended solution slightly weighted towards the cooler EC/FV3 camp this package. The potential for a frost/hard freeze in valley locations Sunday and/or Monday AM remains although this will be dependent on how cold the airmass gets (which is a bit more uncertain). Additionally the northerly pressure gradient and cold advection in the wake of this wave could result in gusty canyon winds in SW Utah Sunday into Monday AM. The pattern trends warmer and drier next week as the Pacific ridge builds inland. Although a general pattern change looks likely, one caveat would be the cutoff low mentioned at the start of this discussion. This is progged to more or less meander around the southwestern US next week, bringing cooler and more unsettled weather wherever it happens to track. However, given the decaying nature of this feature and guidance's typical struggles with cut-off lows more or less ignored it for this forecast package. && .AVIATION... MVFR conditions associated with rain, are expected to improve to VFR around 10-12Z as precipitation trends more showery the remainder of the morning at SLC, although there is a 20 percent chance MVFR CIGs persist until around 14-15Z. Expect mid-lvl Cigs to lift above 7kft this afternoon although exact timing is uncertain. Generally westerly or variable winds this morning will become more firmly northerly this afternoon. && .FIRE WEATHER... ERC values are running below the 50th percentile. A cold and wet storm will continue this morning, dissipating this afternoon and evening. Snow Levels are around 6500 feet. The next warmer but wet system will affect southern and central Utah late tonight through Thursday evening. A warming and drying trend is expected to close out the week, ahead of a sharp cold front Sunday. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Winter Weather Advisory until 9 AM MDT this morning for UTZ007>010. WY...Winter Weather Advisory until 9 AM MDT this morning for WYZ021. && $$ SHORT TERM/FIRE WEATHER...10 LONG TERM/AVIATION...Carr For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php