Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/19/21

National Weather Service Morristown TN
949 PM EDT Thu Mar 18 2021 .UPDATE... EVENING UPDATE. && .DISCUSSION... Currently the strongest convection has moved out of the eastern Tennesee Valley and diminished in strength across the region. Still expect lingering showers through the rest of tonight and into early tomorrow as satellite imagery shows the low spinning right over the Tennessee Valley. Radar melting layer algorithm and 00z soundings show the 0 degree Celsius layer is somewhere between 3500 and 5000 feet currently. This lines up fairly well this afternoons forecast and increases confidence in forecast snowfall totals in the higher elevations expected tonight. It`s likely some of the weak reflectivities on radar are already generating some light snowfall across the southern Appalachian Mountain peaks, and expect this to continue overnight. Will not make major adjustments to the snowfall forecast and still looks like the mountains will get between a dusting and up to 3 inches, with the amounts increase as you go up in elevation. ABM && .AVIATION... 00Z TAF DISCUSSION. Showers and occasional thunderstorms still moving through NE Tennessee and SW Virginia for the first few hours of the TAFs. Expect the intensity and coverage of storms to decrease, but won`t totally go away till early tomorrow morning. Gusty conditions expected to continue overnight, but the speed of the gusts should begin to diminish with the setting sun. Low pressure system will move directly overhead spreading mid and low level clouds across the entire region. With the gusty winds and the mid level clouds fog should be kept at bay, but a stray shower could briefly cause a lowering in visibilities overnight. Low ceilings will remain in place for the next 24 hours, before conditions really begin to improve just beyond this set of TAFs. ABM && .PREV DISCUSSION... /ISSUED 315 PM EDT Thu Mar 18 2021/ SHORT TERM...(Tonight and Friday) Key Messages: 1. Scattered showers and thunderstorms will develop the rest of the afternoon, and some could produce marginally severe hail and gusty winds. 2. Scattered showers continue tonight, especially across NE TN, SW VA, and the eastern mountains. 3. A changeover to snow will occur across the highest peaks of the E TN mountains late this evening into Fri morning with 1-3 inches above 5000 feet. 4. Drier air will filter in during the day Fri with much cooler temps in the low/mid 50`s. Discussion: Late Afternoon/Evening... 2 PM satellite, water vapor, and RAP analysis places the large mid/upper closed low over NW TN and SW KY with the occluded cold front crossing the Plateau. Breaks in the overcast have allowed surface temps to warm into the mid 60`s/low 70`s beneath the increasingly cold pool aloft as the mid/upper low moves E, and this has resulted in surface based CAPES building to 500-1000 J/Kg per latest SPC mesoanalysis. New convection has initiated in a broken line from the N Plateau into NE TN ahead of the cold front, and we have issued several SPS`s for pea to penny sized hail due to mid- level lapse rates steepening to 7-8 C/Km, hail CAPE increasing to 300-500 J/Kg, and WBZ heights dropping to 5-6 thousand feet. There will also be the potential for gusty winds with the strongest cells this afternoon due to unidirectional deep layer (0-6 Km) shear of 60- 80 kts, significant mid-level drying (DCAPE values up to 800 J/Kg), and melting hail. The biggest factor that is keeping the coverage isolated is the dry air started to mix to the surface behind the morning convection noted by Td`s dropping into the 50`s near the Plateau early this afternoon, as well as, subtle subsidence behind the morning convection. Overall, expect the line of convection to remain broken as it propagates ENE ahead of the cold front with a couple marginally severe storms possible. Behind this convection as the cold front moves E, scattered showers are expected to fill in from late afternoon through the evening as the mid/upper low shifts overhead and further lowers freezing heights/steepens lapse rates. Low topped convection with small hail remains possible through the evening but will quickly wane after sunset. Winds have been gusty this afternoon due to strong mixing and SW 850 mb flow of 50 kts. We have seen 30+ kt gusts in parts of the central and S Valley. This will decrease as temps cool through the evening. Tonight... The large mid/upper closed low will cross the S Appalachians early tonight. 850 mb temps cool just below 0 C tonight, and with the upper low and associated PVA overhead, as well as plenty of moisture, scattered showers will continue, especially in NE TN and SW VA, and this will mix with and change to snow over the highest peaks of the E TN mountains. As the flow becomes more northwesterly the second half of the night, some upslope enhancement will also occur. HREF members suggest 1-3 inches of snow over the highest peaks in Sevier county, which is just above the WPC forecast. Used a blend of HREF and WPC giving 1-3 inches of snow above 5000 ft tonight into Fri morning which seems very reasonable. Issued an SPS for this light snow accumulation. Lows tonight will cool into the upper 30`s/mid 40`s. Friday... A few snow showers or flurries will linger Fri morning in the mountains, but building high pressure from the NW and associated drier air will dry all areas out during the afternoon. Highs will only reach the low/mid 50`s. Garuckas LONG TERM...(Friday Night through Thursday) At the beginning of this period our area will be under an upper northwest flow while at the surface high pressure and a cooler air mass will be continuing to build into the region. This high pressure will continue to fill into the region over the weekend, with Saturday and Sunday looking dry, with slightly below normal early Spring Temperatures. By Tuesday we get a surface return flow started and the next weather system heads our way with showers increasing west to east Tuesday afternoon and evening. The overall pattern stays pretty unsettled, with another system coming out of the Gulf around Thursday, spreading moisture and rain chances towards us. Keeping thunder out of forecast for now. Temperatures Tuesday through Thursday should be mild, as minimum temps are limited by higher dew points and cloud cover. The Thursday system will be worth keeping up with--if it rides along south of us toward the Atlantic, no big deal for us. However, if it moves northward toward the Ohio Valley, it would bring a lot of moisture into our area and would need to be watched for heavy rain potential and/or severe threat. GM && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 45 56 40 62 38 / 30 10 10 0 0 Knoxville McGhee Tyson Airport, TN 45 54 35 60 35 / 50 10 10 0 0 Oak Ridge, TN 44 54 36 61 36 / 30 0 0 0 0 Tri Cities Airport, TN 42 53 30 60 31 / 80 10 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$
Area Forecast Discussion
National Weather Service San Francisco Bay Area
459 PM PDT Thu Mar 18 2021 .SYNOPSIS...Scattered showers along a cold front pushes southward through Thursday evening providing light to moderate rain to the Bay Area and the Central Coast. Rain is expected to taper off Friday morning with clearing expected Friday afternoon. A warming and drying trend is expected over the weekend and into early next week. && of 2:12 PM PDT Thursday...Widespread rain showers have returned to the Bay Area and the Central Coast along the front of a cold front. The front still over the ocean is slowly moving eastward. The bulk of the rain fall at this time has fallen over the North Bay Mountains and Valleys. Observations stations in the Valleys closer to the San Francisco Bay are a few hundredths to a quarter of an inch, farther inland valleys a quarter of an inch to a half an inch, with the Wester North Bay Mountains along the Sonoma Coast between a half an inch to just under an inch, with rain still falling. Rain has fallen through the San Francisco Bay, into the East Bay and down the Santa Cruz coastline. Rain will continue through Thursday morning and slowly move southward toward the Central Coast, leaving lingering scattered showers in the North Bay, while the bulk of the more constant rain showers will move southward. Hi-res model HRRR and local WRF keeps the rain rates below threshold at this time expected through the evening. Lingering showers can be expected through Friday morning, with clearing expected by Friday afternoon. Patchy fog is forecast to develop in more sheltered valley locations overnight with temperatures into the low 40s and isolated upper 30s. Temperatures will once again be in the 50s and low 60s on Friday as the upper level trough moves slowly southward, with drier conditions developing. By late Saturday, a ridge over the Eastern Pacific starts to develop bring warmer and drier conditions leading into the early part of the work week next week with temperatures approaching the 70s. && of 04:45 PM PDT Thursday...For the 00Z TAFs. Radar shows showers across the majority of the forecast area late this afternoon. This line of showers will slowly transition southward through the next several hours. Expect IFR to MVFR cigs and visbys with wet runways and light S-SW winds as the frontal boundary driving this wet weather shifts southward. Moderate to briefly heavy rain is possible as the front moves over the terminals and with that, brief LIFR to IFR cigs/visbys are also possible. Additionally, lighter surface winds and a 25-35kt low level jet at roughly 1500-2000 ft will bring some limited LLWS concerns to terminals through the evening. Expect ceilings to gradually fill back in in the wake of the front overnight given ample low level moisture and cooling temperatures. Patchy fog is possible through the morning for inland terminals. VFR returns by mid to late tomorrow morning with FEW to SCT clouds at mid levels. Vicinity of KSFO...S-SW winds through the evening, minor LLWS concerns with 25-35kt winds at 1500-2000 ft AGL and potentially lighter winds near the sfc. Rain and LLWS concerns back off by 02-03Z timeframe this evening though some linger VCSH expected. For tonight low level clouds redevelop to bring borderline MVFR IFR cigs btwn roughly 11-16Z, with improving conds to VFR by 17-18Z. Mid level clouds will linger through midday. Onshore winds tomorrow afternoon. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...LIFR to MVFR cigs through the majority of the period, with cigs briefly improving to VFR by late Friday morning through the early afternoon. A couple of slugs of moisture will keep intermittent -RA to +RA over the next 10 or so hours, with the first slug moving over now and the second slated to arrive late this evening. VLIFR to LIFR conds posbl after rain finally clears out into the predawn hours of Friday morning with patchy fog or very low cigs such as OVC002-OVC003. && of 04:46 PM PDT Thursday...Gusty southerly winds will gradually diminish in wake of a frontal passage late this evening and into tonight. These gusty winds will generate locally steep fresh southerly swell, creating hazardous conditions for small craft vessels through tonight. Otherwise, a light northwest swell will be replaced by a larger northwest swell resulting in hazardous conditions through Friday. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Mry Bay until 9 PM SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 AM SCA...Pt Reyes to Pigeon Pt 0-10 nm SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm SCA...Pt Arena to Pt Reyes 0-10 nm from 9 PM SCA...Mry Bay from 3 AM && $$ PUBLIC FORECAST: DK AVIATION: DRP MARINE: RGass Visit us at Follow us on Facebook, Twitter, and YouTube at: