060 FXUS65 KSLC 240234 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 834 PM MDT Fri Jun 23 2017 .SYNOPSIS...A generally dry west to northwest flow aloft will exist across Utah tonight and tomorrow. Strong high pressure aloft will return to the region late in the weekend. A brief surge of moisture will move through the area Monday. && .DISCUSSION... Water Vapor Satellite shows ridging from California into New Mexico and northern Mexico, while northwesterly flow aloft resides from the Pacific Northwest into the Northern Rockies. 400-200mb MDCARS wind observations place a cyclonic 75-105kt jet from British Columbia into the north central Plains. GOES/SLC 00Z RAOB/HRRR indicate that precipitable water values vary from 0.10"-0.25" mountains to 0.33"-0.60" valleys. With high pressure in place, benign weather once again tonight. Going forecast in fantastic shape. Just tweaked the hourly diurnal T/RH curve based on latest observations and forecast data. Also massaged the winds due to the northerly pressure gradient with high pressure building in. Winds outside of St George will be lighter than last night though. && .PREVIOUS DISCUSSION... Mountain cumulus clouds have developed across far southern Utah this afternoon, in and around the Brian Head fire. The smoke plume from the fire remains visible on satellite as the plume drifts to the southeast. As the atmosphere has become destabilized, the smoke plume appears to be growing. Winds statewide largely remain northwesterly this afternoon and some locally breezy conditions are observed. Going in to the weekend, the flow remains mostly unchanged under a building ridge and northwest flow aloft. Moisture fields are pretty meager, with mixing ratio values 3 g/kg or less. Temperatures also change very little day to day, as 700mb temps across the north range from 10-12C and across the south 16-17C. As the heat continues across the south, the going excessive heat warning remains in effect for the Dixie area in the southwest. The ridge slowly shifts over Utah and southwest Wyoming on Sunday night and Monday, as a shortwave trough pushes into northern California. Southwesterly flow will increase over the forecast area ahead of this trough, and Monday will bring a considerable warming trend for many locations, particularly across the northern half of the CWA. This increased southerly flow will help bring in some additional mid-level moisture to the area, and isolated showers and thunderstorms could initiate over the higher terrain of Utah and eastern Nevada on Monday, with the latter storms potentially drifting into northwest Utah Monday afternoon/evening. Have increased POPs slightly for this possibility, particularly across the far northwest. That said, any storms that do develop Monday will be high based, and the dry low level airmass will make gusty winds much more likely than significant rainfall. The weak shortwave passes through Idaho and northern Utah late Monday into Tuesday. This is just the beginning of a pattern change, with a mean trough setting up over the Pacific Northwest. While most of the moisture and instability generally remains north of the area through Tuesday and early Wednesday, enough low level cool air does look to filter into Utah to drop temps a bit, including ending the long string of very hot temperatures in far southern Utah. (That said, temperatures Tuesday generally decrease from "very hot" to simply "hot".) Timing differences in the global models begin to become more evident Wednesday through Friday, though the general idea is that a series of weak waves and surface cold fronts could push through the northern half of the CWA through the latter half of the week. Have generally decreased temps a bit and raised POPs for the north Wednesday and Thursday. Leaned a bit more toward the GFS timing for now, which has a cold front with decent moisture associated with it on Wednesday afternoon. && .AVIATION...VFR with clear skies overnight at the SLC terminal. North winds will become light and variable as the night progresses. && .FIRE WEATHER...Northwest winds will continue to weaken across the south and east this evening, becoming much lighter Saturday. Hot and dry conditions remain in place area wide and will continue into the weekend. A more stable air mass across northern Utah will create poor mixing and clearing indices while the south remains good to excellent for clearing. High pressure is building back across the region which will result in more widespread Haines values of 6 as the airmass becomes warmer into next week. A weak system has the potential to bring isolated showers and thunderstorms mainly across the north Monday into Tuesday, and lightning is possible as well with these storms. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 10 PM MDT Sunday for UTZ019. WY...None. && $$ PUBLIC...Rogowski/Dewey/Schoening AVIATION...Rogowski FIRE WEATHER...Dewey 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 |