Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/18/24


Area Forecast Discussion
National Weather Service La Crosse WI
946 PM CDT Sat Aug 17 2024 .KEY MESSAGES... - Scattered showers ending this evening. Dry start to the new week. - Warming for Sunday. Temps mostly at/above normal for the new week. && .DISCUSSION... Issued at 130 PM CDT Sat Aug 17 2024 OVERVIEW: the upper level trough responsible for much of the scattered showers across the area today eases east tonight/Sunday - allowing for high pressure at the surface to build in. The upper level pattern continues to shift moving into the new week with the models showing strong continuity (within and between themselves) with edging an upper level ridge axis from the plains to across the upper mississippi river valley by Wed. How long the amplified ridge lingers and/or flattens out/becomes more zonal is uncertain. WPC cluster analysis shows a mixed bag of potential outcomes with a fairly even distribution of GEFS/EPS members in the 4 clusters. The sensible weather outcomes would still favor at/above normal temps while holding the storm track across the north (but not necessarily dry). PCPN CHANCES: current scattering of showers will decrease in coverage, gradually end this evening with loss of daytime heating and shifting of upper level trough eastward. A weak ripple a loft could shift across the region on Sunday, but most models favor sfc high pressure winning the day, keeping it dry. The dry conditions would then persist for the start of the new work week. Long range guidance starts to top the ridge with bits of shortwave energy for the later half of the week. While the brunt of the upper level forcing may hold north of the local area, associated sfc boundaries could provide a focus for pcpn development. In addition, an MCV or two could push across the ridge from nocturnal convection over the plains. Nothing clear cut at this time but warrants at least low end chances (20%) from time to time for now. TEMPS: with the ridge building in, so will warmer air - although not looking "hot". Both the GEFS and EPS suite of ensemble members suggest temps at or few degrees above normal though much of the new week. Dewpoints aren`t climbing much either, so humidity looks to be held "in check". Ensembles start to trend warmer moving into the weekend, but also show larger spreads in potential outcomes. As mentioned earlier, the models aren`t quite sure whether more ridging will persist or broader zonal flow will return - thus the range of temps. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 946 PM CDT Sat Aug 17 2024 Fog potential will be the main TAF consideration through the overnight hours and into Sunday morning. With ongoing dewpoint depression trends favoring some fog formation at KRST, decided to introduce MVFR visby reductions at the TAF site. Questions remain how low visbys can go with the 18.01z RAP showing winds off the deck to 10-20 kts which should work against more substantial visby reductions. However, when considering some probabilities (10- 40%) for IFR visbys in the 17.12z HREF, would not totally dismiss the potential for IFR reductions at KRST. Otherwise, conditions into Sunday afternoon remain VFR with few to sct low- VFR cumulus. Winds generally remain from the north at 5-10 kts. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Rieck AVIATION...Naylor
Area Forecast Discussion
National Weather Service Boston/Norton MA
1048 PM EDT Sat Aug 17 2024 .SYNOPSIS... Dangerous rip current continue due to distant Ernesto through Sunday. Spotty showers possible across western/central MA and CT tonight. Otherwise dry with low clouds and fog. Low clouds slow to erode on Sunday due to persistent onshore flow. A slow moving frontal system moving in from the Great Lakes will bring several opportunities for showers and thunderstorms Sunday evening through Tuesday. Locally heavy downpours are possible, but severe weather potential is very low. Drier weather for the middle portion of the week with cooler than normal temperatures. Warming trend for Friday into the weekend but with continued generally dry weather. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Stratus was located over the coastal waters east of MA late this evening, and is expected to move onshore overnight. Scattered showers over northern NJ and southeast NY state should also arrive later tonight as well. The last few runs of the HRRR seems to have the right idea, but perhaps is not perfect with the timing. Generally liked the focus across portions of CT and western and central MA, so used that idea to tweak rainfall chances overnight. Minor tweaks to temperatures to reflect observed trends. 730 PM Update: Starting to see stratus re-develop and/or return back landward from the coastal waters now that the sun is starting to set and the boundary layer begins to cool. The trend will be for continued SE to NW advance of stratus in general thru late evening/midnight. Still an open question on the extent of fog, but I think odds are against dense fog coverage. MOS products seem to hit the potential the hardest, but recent GFS LAMP output is starting to back off on the visbys. I`d feel somewhat more confident about about larger dense fog coverage if the near- surface lapse rates were more inverted/stable than what the NAM/RAP/HRRR indicates in the lowest 2000 ft AGL. Nonetheless, a pretty gray evening is expected with light southeast winds. Though there are a few showers in the lower Hudson Valley, they`re moving into the surface ridge axis and dissipating as they do so, and I`d expect that to continue with dry weather by- and- large. Previous discussion: Highlights * Dangerous Rip Current Risk continues. * Low clouds and stratus return. Spotty light showers across central/western MA and CT. Cyclonic flow in place with a trough parked over the Great Lakes region. A shortwave trough will lift from the eastern Great Lakes/Mid Atlantic this evening into New England tonight. A broad low is located over the central/eastern Great Lakes while we remain under persistent onshore flow. Anticipating dry and quiet weather for much of the region tonight. Will gradually see PWATs increasing to roughly 1.5 to 1.75 inches across western/central areas tonight. This is also where we will have a roughly 15-25 kt southerly low level jet impinging on the region. Did adjust our precip chances based on this setup, but think best shot for showers is across western MA and CT. Main concern is we are quite removed from strong forcing, which is why activity overnight may be spotty in nature. Wondering if some guidance hinting more at a more widespread drizzle vs showers. At this point given the moisture available went with showers. Low temperatures in the 60s. One thing we will need to keep a close eye on is the stratus deck advecting onshore across eastern areas. Some pieces of guidance, GLAMP/HRRR, show patchy dense fog moving in. Did lower our visibilities a bit in the latest update, but did not go as low as latest GLAMP/HRRR at this time. Will need to monitor as night progresses. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Highlights * Dangerous Rip Current risk continues due to distant Ernesto. * Spotty AM showers across western/central areas diminishing. Dry for much of Sun. Near to slightly cooler than seasonable temperatures. * Showers along with isolated thunderstorms spread in from west to east Sun Night into Mon. Cyclonic flow lingers across the Great Lakes and New England through this timeframe. The trough over the central/eastern Great Lakes early on Sun will slowly slide into the eastern Great Lakes/Mid Atlantic by early Mon. Another shortwave lifts from the Mid Atlantic late on Sun into New England Sun Night. A slow moving frontal system will gradually slide into Upstate NY on Sun/Sun Night. Clouds slow to erode across southern New England on Sun due to persistent onshore flow, but thinking improvement will be faster than on Sat given there should be better mixing within the boundary layer. In addition, think any lingering showers/drizzle across western/central areas Sun AM will exit as the first shortwave moves off to the northeast. High temps may be a few degrees warmer than today given the better mixing and skies clearing a tad bit faster. Highs range from the mid 70s to low 80s. Main concern along south facing beaches continues to be the high risk for rip currents due to the increased swell from distant Ernesto. Return of more unsettled weather late Sun into Mon as another shortwave lifts into the region. Will have a better shot for more widespread showers as the broad low moves into Upstate NY. Will see PWATs increasing to roughly 1.5-2 inches as the trough approaches and southerly flow increases. There is a bit more instability available with a few hundred J/kg of MUCAPE in place. Not out of the question there are some heavy downpours given the environment, but think risk greater during the day Mon. See the Long term section for more of these details. Lows in the 60s. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights: * Slow-moving frontal system brings mostly cloudy weather and several opportunities for showers/t-storms Mon and Tue. Severe weather potential is low, but localized downpours leading to isolated instances of flooding could be possible. Temps seasonable but humid. * Drier weather with cooler than normal temps Wed and Thurs. * Continues dry Fri into the weekend, but with a warming trend. Details: Monday and Tuesday: This is the more active period of weather in the long-term forecast period. Mid/upper level trough and its associated surface frontal system initially over NY/PA to slowly progress eastward and offshore through Tue. Although the forecast PoPs (Likely/Categorical Mon, then solid Chance for Tue) are pretty broad-brushed, guidance seems to convey some agreement in there being multiple opportunities for showers and embedded t-storms in this timeframe. One is with an approaching warm front which moves in Mon AM to early aftn with a related rise in deep moisture/PWAT values (to around 1.5 to 1.7 inches). We then should see more broader warm-sector-airmass showers and embedded t-storms for Mon aftn to evening, and while not everyone will see rains in this general timeframe, there will be showers and storms around. The final period of showers and storms, perhaps energized by disorganized trough energy over the lower mid- Atlantic region, comes in on Tue before the cold front slips offshore later Tue aftn or early night. Convective instability for both days looks to be tempered by reduced diurnal heating from lots of cloud cover, and wind shear also isn`t supportive of organized severe weather. However there should be enough instability for lightning, with forecast MUCAPEs in the 500- 1000 J/kg range. With several opportunities for showers and t-storms in this period, infused by elevated PWATs and warm cloud depths around 11-12 kft, localized instances of flooding could need to be monitored in this period; but with that said, models show varied placement of QPF bullseyes and that makes it difficult to provide any location or timing specifics at this juncture. Particularly for Tue, consideration will also have to be given to where prior heavy rain footprints took occur/where FFG is locally reduced, which are obviously unknown at this time. Trained machine- learning progs also indicate limited/marginal potential for excessive rainfall. Temperatures in this period should run near to slightly cooler than normal (could see highs only in the 70s, with upper 60s/low 70s Tue), but it won`t feel that way with elevated humidity levels until the cold front clears us out by Tue evening. Wednesday and Thursday: Cyclonic flow aloft associated with a shot of anomalously cool 925- 850 mb temps then settles in over the Northeast states, with surface high pressure supplying MUCH drier conditions. Overall a pretty pleasant stretch of weather that may feel more like a typical day in mid-September than mid-August. Will have to watch for nighttime/early morning fog potential with a pattern of clear skies, light winds favored each night and wetting rains from early in the week. Highs mainly in the 70s both Wed and Thurs, with lows in the 50s, perhaps some mid/upper 40s NW MA and the sites which typically radiate well at night under clear/calm conditions. Friday into Next Weekend: Drier stretch of weather continues into this forecast period as broad high pressure shifts seaward over the mid-Atlc waters. Warming trend closer to above normal temps then becomes more favored by late in the week into the weekend. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight: High confidence in trends, moderate in timing. Gradual deterioration toward IFR/LIFR conditions (occurring soonest with the worst categories S/E of I-95), mainly in stratus. Development of fog is still a low-confidence prospect and with GLAMP now starting to back off on reduced visbys, its coverage may end up being more sparse than last night/this morning. Light E/SE winds. Sunday...Moderate confidence. IFR stratus to start will slowly lift to MVFR with some spotty VFR as onshore flow continues. Though we may mix enough in eastern areas where we lift those lower ceilings more firmly to VFR levels. Spotty AM showers out in western areas. SE winds 5-15 kts. Sunday Night...Moderate confidence. Return of IFR to LIFR stratus and fog with persistent onshore flow. Showers and isolated thunderstorms spreading in from west to east as the night progresses. E to SE winds around 5-10 kts or less. KBOS TAF...High confidence in trends, moderate in exact timing. Gradual deterioration to MVFR stratus decks, then a return to IFR decks later tonight which continue into the early Sunday morning hrs. Slow improvement to MVFR on Sun due to persistent onshore flow. SE winds 5-8 kt. KBDL TAF...High confidence in trends, moderate in exact timing. Borderline MVFR ceilings linger heading into this evening. Spotty rain showers along with ceilings lowering to MVFR/IFR conditions roughly through 05Z. Slow improvement to higher MVFR levels on Sun due to prolonged southeasterly flow. Outlook /Monday through Thursday/... Monday: Mainly MVFR, with local IFR possible. SHRA, scattered TSRA. Monday Night through Tuesday: Mainly VFR, with local IFR possible. Chance SHRA, isolated TSRA. Tuesday Night: VFR. Chance SHRA. Wednesday through Thursday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight through Sunday Night...High confidence. Expecting persistent SE flow at 5-10 kts through the vast majority of the period. Wind gusts remain generally below 20 kts as well. Seas remain elevated due to the powerful swell associated with Ernesto. This keeps 5-7 ft seas across the outer waters through Mon, so have extended the Small Craft Advisory. This is also the case for the nearshore waters across coastal Rhode Islands where 3-5 ft seas linger. Rain showers along with thunderstorms could spread into the waters Sun Night. Outlook /Monday through Thursday/... Monday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers, isolated thunderstorms. Monday Night through Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Wednesday Night through Thursday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Risk for Rip Currents from 6 AM EDT Sunday through Sunday evening for MAZ007. High Risk for Rip Currents through Sunday evening for MAZ022>024. RI...High Risk for Rip Currents through Sunday evening for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT Monday for ANZ235-237. Small Craft Advisory until 8 AM EDT Tuesday for ANZ250-254>256. && $$ SYNOPSIS...Loconto/BL NEAR TERM...Belk/Loconto/BL SHORT TERM...BL LONG TERM...Loconto AVIATION...Belk/Loconto/BL MARINE...Loconto/BL
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
944 PM CDT Sat Aug 17 2024 ...New MESOSCALE UPDATE... .MESOSCALE UPDATE... Issued at 943 PM CDT Sat Aug 17 2024 Convective activity has shifted out of the forecast area and just some remnant convective debris is left across the south half. Several updates were made earlier to capture temps that were impacted by precip/cooler outflow so things are pretty much on track. Will updated to capture temp tweaks shortly. Focus will shift to Sunday, it will be HOT as we will reside in the lower level thermal axis. It sure looks like it will be the hottest day of the year for most locations with Highs peaking in the 98-102 range with some 100-105 very possible. As for storms, it`s not a slam dunk as the atmosphere, as often the case with volatile situations, will be right up to a point that could go either way. In the "either way" I`m referring to is just enough to convect and we get very windy storms which in-turn establish deep enough cold pools to develop additional cells and we ultimately get an organized cluster. The other way would be there`s too much dry air and limited lower level convergence that doesn`t overcome any capping resulting in few to no convective cells. While each scenario remains on the table, the latest 00z CAMs are favoring convection. While instability is not anticipated to be extreme, there`s other elements of the likely environment that are very rare for us. First will be storms developing in 98-104 degree temps. From this, there will be very steep lapse rates in the 0-3 and 0-4 km layers that will allow for efficient momentum transfer to the surface. Also between 700- 400mb there will be strong flow of 30-40kts. I`ll add in dry air in the mid levels as well which will all for more evaporative cooling as we should see Dcape values in the 1200-1600 j/kg range. So, with all that, the signal we see from the HRRR and NAM3km with strong downdraft wind signatures are very telling. Compiling all of this offers the potential for a more widespread wind event along with some potential for sig type wind gusts as well. Still more details to cover, but wanted to offer the potential and some background as to why. Lastly, timing looks to be later and main time window for this appears to be 4p to midnight. /CME/ && .DISCUSSION... Issued at 231 PM CDT Sat Aug 17 2024 Tonight through Monday... Tonight: Convection should persist through early evening, but wind down before midnight. In the wake, a quiet night will be in store, with some potential patchy fog in low-lying areas or locations that receive rainfall. With increased boundary layer moisture, persistence forecast, with seasonably warm lows in the mid-upper 70s (74-78F) are expected. Sunday-Monday: An active period of excessive heat & severe storms is expected Sunday, before a frontal zone moves through, finally breaking the grip of the heat & more seasonable & dry conditions move in next week. Synoptic & sfc pattern will consist of deep mid- level ridge centered over west TX to the southwest states while mean longwave trough persist east of the MS River Valley. This will keep perturbed northwest flow & a frontal zone is expected to sink southward into Sunday. Moisture & deep mixing is anticipated in advance of the frontal zone moving in. Guidance indicates efficient mixing up to 850-700mb layer. There are indications combined with this deep mixing, favorable thermo profiles (i.e. 28-30C vertical totals & DCAPE nearly 1800-2000 J/kg) & 25-40kt bulk shear in the mean 0-2 to 0-6km layer, southward moving organized convective clusters could contain some higher end gusts near 70mph at times & quarter size hail. Convective allowing models (CAMs) indicate some potential of gusts in excess of 50-60kts, so strong to severe storms remain a low-medium chance, where advertised "Slight" risk looks on track. The convective outlook area has been brought further southwards towards I-20, which seems to be in agreement with most guidance. With convective storm onset in the mid-late aftn timeframe, mainly between 2-4PM, high boundary layer moisture ahead of the boundary will lead to continued dangerous heat stress again into the aftn to early evening hours. With seasonably warm highs in the 98-102F range & excessive heat potential more expansive, the "Significant" area was expanded east along I-20 & southeast, with the "Extreme" taken out of the Delta, with less oppressive conditions today, while pulled eastward near east MS due to ongoing persistent dangerous heat & expected conditions Sunday. Heat headlines were maintained from mid-morning to early evening , with a heat advisory in east-northeast MS & a Excessive Heat Warning areal configuration with similar but slightly larger coverage. The Excessive Heat Warning may be able to be adjusted to the northeast but some earlier convective coverage makes this potential a low confidence forecast. Will led later shifts decide on any further adjustments. Expect storms to persist into the evening hours but could linger a little later closer to midnight. For now, timing looks mostly intact but may be able to be refined as confidence increases. Timing looks to be mid-late aftn & persist into the evening, with rain & storm chances in the isolated to scattered range (15-40%). As heights in the ridge to the west begins to fall, there will be continued surges of drier & less oppressive airmass beginning to move in the region into next week. This will help highs become more seasonable in the low-mid 90s & lows in the mid-upper 60s north of I- 20 to upper 60s to near 70F in the south into Tuesday morning. Some storms are possible but become more focused into the Hwy 84 corridor into Monday aftn to early evening. Can`t rule out an isolated strong storm in southwest MS & portions of northeast LA on Monday. /DC/ Tuesday through Friday... Post frontal passage will bring relief from the oppressive heat/humidity of the previous week. Upper/mid-lvl ridge will primarily encompass the Southern Plains/CO/NM area, placing the ArkLaMiss region on the periphery of the ridge. As a result, northwest to northerly flow allows for dewpoints to fall into the upper 50-mid 60s range across the area, lowering humidity for the area. Afternoon high won`t be as hot either, as upper 80s/lower 90s temps are expected. Low temperatures will more likely resemble early fall than summer, as low temperatures are expected to range in the 60s midweek to near 70 degrees by late week. /SW/ && .AVIATION... (00Z TAFS) Issued at 635 PM CDT Sat Aug 17 2024 Precip/storms have moved to our south and TAF sites will remain VFR for the period. By Sunday afternoon, the northern half of the area will see WNW winds with some gusts as we heat up. Storm chances will increase late, but that looks to be mainly after 21z and will hold off on including in the TAFs until timing/location fit better. /CE/ && .PRELIMINARY POINT TEMPS/POPS... Jackson 76 100 74 92 / 0 20 40 20 Meridian 74 101 71 93 / 0 30 30 10 Vicksburg 76 101 74 92 / 0 20 30 20 Hattiesburg 76 100 75 95 / 10 10 30 20 Natchez 76 100 75 92 / 10 10 30 30 Greenville 75 100 72 90 / 0 20 30 20 Greenwood 75 100 72 92 / 0 10 20 10 && .JAN WATCHES/WARNINGS/ADVISORIES... MS...Excessive Heat Warning from 10 AM to 8 PM CDT Sunday for MSZ018- 019-025>029-032-034>037-040>044-047>066-072>074. Heat Advisory from 10 AM to 8 PM CDT Sunday for MSZ030-031-033- 038-039-045-046. LA...Excessive Heat Warning from 10 AM to 8 PM CDT Sunday for LAZ007>009-015-016-023>026. AR...Excessive Heat Warning from 10 AM to 8 PM CDT Sunday for ARZ074- 075. && $$ CME/DC/SW
AREA FORECAST DISCUSSION...CORRECTED
National Weather Service Jackson KY
1033 PM EDT Sat Aug 17 2024 .KEY MESSAGES... - Below normal temperatures are expected Sunday through Wednesday behind a cold front passage late Saturday night. - Showers and thunderstorms will remain possible Sunday and Monday, especially in the afternoon and early evening, with a drying trend for Tuesday into Wednesday. && .UPDATE... Issued at 1029 PM EDT SAT AUG 17 2024 Updated grids, especially PoPs and sky for latest trends form the regional radar loops. Dropped overnight lows just slightly after impacts of evening convection. Lows may have been met, at least until the cold front pushes through the area later tonight. Temps may actually rebound just slightly through the remainder of the night. Active night, but intensity of storms have been gradually decreasing with time. However, there are still some respectable storms out there with breif, locally heavy rainfall and intense lightning. These last cluster of storms will continue to pass through eastern Kentucky over the next few hours. Will see considerably less activity overall, but the threat of at least some minimal (isolated) convection will continue through the overnight period for portions of the area. Another round of showers and storms is expected to impact the area tomorrow. Trends have been for slightly less activity Sunday and even less on Monday. The hrrr has been fairly consistent with convection being focused in the southwest tomorrow. Will continue to evaluate. Updated grids and zones have been issued. UPDATE Issued at 513 PM EDT SAT AUG 17 2024 Did a quick update to do a fairly big overall update to the PoPs given the line of storms rolling through parts of eastern Kentucky late this afternoon and evening. These have been strong to severe at times and will continue to track southeast. Outside this overall minor update for other elements. && .SHORT TERM...(This evening through Sunday night) Issued at 505 PM EDT SAT AUG 17 2024 We are seeing a notable upper low push across the Great Lakes this afternoon and this will reflect down to the mid-levels with embedded shortwaves riding through the associated trough axis across the Ohio valley. We saw a notable boundary where cumulus first developed this afternoon and this has overall been one of the main focus areas for convection this afternoon. Some of these storms have been spiting at times given the somewhat straight and concave up hodographs noted in the SPC mesoanalysis. There remains a risk of severe storms through the remainder of the afternoon and perhaps into the early evening before storms should loose better daytime heating. Outside this very little changes were needed for the near term forecast this afternoon. Tonight, most of the convection will relent through the evening, but some of the CAMs indicate possibly a bit more in the way of showers and thunderstorms into the late night hours. However, CAMs have been all over the place in the way of where convection will be and haven`t been managing the convection this afternoon well. This leads to a fair amount of uncertainty. Given this went more toward a southeastward trend with PoPs through the evening and overnight. This seems to be reasonable given the more cold pool look this is taking on. The highest PoPs will be early in the evening before tapering from west to east through the night. This trend will have to be watched given the uncertainties and lack of CAM support. Outside this overnight lows will be in the mid to upper 60s. Sunday, we will see increasing chance of showers and thunderstorms through the afternoon and evening. This as a mid-level trough deepens in the Ohio Valley and it ushers in northwest flow at the surface leading to PoPs in the 60-70 percent chance range mainly during peak heating hours. However, given the northwest flow regime these showers and perhaps a thunderstorm could continue into the evening and perhaps the night, but the HREF suggests overall the trend would be downward for showers through the night. This will have to be looked at closer in additional updates. .LONG TERM...(Monday through Saturday) Issued at 412 PM EDT SAT AUG 17 2024 The extended period will start off quite active, as an area of low pressure moves through the area on Monday. We will see showers and scattered thunderstorms rumbling through as the trough moves off to the east. The rain should taper off late in the day, and be out of the area by early Monday evening. After that, a large and well developed ridge of high pressure will settle over the region, and will bring dry and very pleasant weather to eastern Kentucky the rest of the week. A much cooler air mass will advect into the region on northwest winds through the middle of the week. In fact, we could see daytime highs in the mid to upper 70s Monday, Tuesday, and Wednesday, making it feel more like fall than mid-summer. With clear skies, light winds, and strong sunshine, the air mass will finally begin to modify on Thursday. Highs on that day should rebound to more normal highs in the lower 80s. Thursday and Friday should be even warmer, with highs on each of those days reaching the mid to upper 80s. With ridging overhead, and light winds and clear skies expected, conditions will favor ridge valley temperature splits most nights. Some valley locations may fall into the upper 40s Tuesday night and Wednesday night, with low to mid 50s everywhere else. We could also see patchy valley fog each night, especially early on after the rain event moistens everything up. The only weather hazards to speak of would be cloud to ground lightning that will be possible with any thunderstorms on Monday. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) ISSUED AT 841 PM EDT SAT AUG 17 2024 Thunderstorms are currently passing through the area. Flight conditions have been predominantly VFR outside of thunderstorms. Bases of these storms have been relatively high, above 030 AGL. However, there has been some very strong gusty winds associated with the strongest storms and VSBYS lower to less than a mile with a direct hit from any thunderstorm. Storm motion is quite high. Thus the decreases in flight categories will be short lived. Storms will continue to work through the area during the evening hours before dissipating. The stronger storms at TAF issuance were generally located south of the I-64 corridor, and that continues to be the case. Expect a lull in activity through the overnight, though some isolated to widely scattered convection can not be ruled out at any time. The next best round of showers and thunderstorms will arrive during the day Sunday, where at this time our southwestern most terminals, KSME and KLOZ appear to be most impacted. Winds will be light, around 5 kts from the west, southwest but will veer out of the west-northwest Sunday at 5-10 kts. Of note however, is that winds will be variable and gusty in the vicinity of any storms. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...RAY SHORT TERM...DJ LONG TERM...AR AVIATION...RAY
Area Forecast Discussion
National Weather Service San Francisco CA
549 PM PDT Sat Aug 17 2024 ...New AVIATION... .SYNOPSIS... Issued at 1102 AM PDT Fri Aug 16 2024 Seasonal to slightly cooler than normal temperatures will continue through the weekend into next week. Increased coverage of early morning marine layer stratus, fog and drizzle is likely this weekend. Less than 10% chance for thunder on Saturday. && .UPDATE... Issued at 539 PM PDT Sat Aug 17 2024 Satellite is showing some clouds still moving over our area bringing chances of some light rain near the northern parts of our area and along the coast. Therefore, our radar remains in "precip" mode to capture any convection. Currently, no lightening activity, as most of that is further northern California. No changes were made to the forecast, as conditions remain on track. SO && .SHORT TERM... (This evening through Sunday) Issued at 259 PM PDT Sat Aug 17 2024 Upper-level troughing continues to be the name of the game. Said upper-level trough is responsible for a non-zero (<10%) chance of thunderstorms today across the North Bay in addition to gusty conditions through gaps and passes. While our region is not experiencing critical fire weather conditions, it is imperative to remain vigilant when it comes to exercising fire weather safety as grasses remain dry and winds will easily spread fire. Temperatures will be near normal with tomorrow being slightly warmer than today. Stratus is expected to fill valleys and low-lying areas tonight, receding back to the coastline by tomorrow afternoon. && .LONG TERM... (Sunday night through next Friday) Issued at 259 PM PDT Sat Aug 17 2024 As the upper-level low fills, temperatures will continue to warm up through Tuesday. A brief, gradual cooldown will take place Wednesday through Friday as troughing is expected to take shape. Uncertainty with the forecast primarily lies in the amplitude of the trough - will it be a cutoff low or will it be an open wave? If it is a cutoff low, it will linger longer, the North Bay will have better chances for measurable precipitation, and onshore winds will noticeably increase. If it is an open wave, it will move through quicker with the better chances of precipitation confined to the north. Either way, any kind of troughing offshore will promote moist, onshore flow, which is a good thing. && .AVIATION... (00Z TAFS) Issued at 548 PM PDT Sat Aug 17 2024 It`s a complex pattern resulting in largely variable weather conditions this afternoon, it`s VFR inland while it`s a mix of MVFR and localized IFR (including fog, mist) along the immediate coast. Higher dewpoint air i.e. higher water vapor has arrived across much of the forecast area, surface dewpoint temperatures are in the lower to mid 60s. Additionally a layer of cool air advection aloft with the offshore trough of low pressure has moved in mostly between 925 mb (~2500 feet) and 850 mb (~5000 feet) resulting in low clouds with a mix of stratus/stratocumulus and periodic light drizzle/light rain along the coast. SFO Airport reported a trace just after 4 pm for example. For the 00z TAFs, dry weather is forecast specifically at the terminals Cool air advection aloft has weakened and deepened the marine layer temperature inversion per recent profiler data at Bodega Bay, Fort Ord and Point Sur. A loss of northwest winds and upwelling, including a still steep August sun angle and heat input into sea surface temperatures has also reduced the lower level temperature inversion to sea surface temp difference. The amount of stratus returning tonight including the development of IFR will rest largely on clear sky aloft for radiative cooling and if there`s any additional cool air advection. The 00z TAFs carry a combination of MVFR-IFR ceilings for tonight and Sunday morning, diurnal surface warming should help lift ceilings most locations to MVFR-VFR Sunday afternoon. Vicinity of SFO...North-south band of low clouds /MVFR/ with higher dewpoint air is adhering to the SF Peninsula for the evening. Post sunset cooling will be a combination of residual cool air advection and radiative cooling supporting a continuation of ceiling at the terminal for the overnight hours and Sunday morning. The RAP model is forecasting IFR during the evening, kept in inherited 18z TAF IFR ceiling forecast for 06z this evening. KHAF has reported a low ceiling & visibility in fog, thus LIFR-IFR is there on the other side of SF Peninsula. IFR 06z-16z Sunday then improving to MVFR-VFR thereafter for the remainder of the morning and afternoon. West wind near 12 knots decreasing to 5 to 10 knots tonight and Sunday morning, increasing to near 15 knots Sunday afternoon. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Same as the Bay Area, largely variable weather conditions here this afternoon. Low clouds moving in over KWVI with IFR ceiling reported, KSNS and KMRY holding onto VFR for the time being. Low clouds will initially run into late afternoon diurnal surface warming and vertical mixing with surface temperatures in the lower 70s over the southern Monterey Bay. With the weakened marine layer temperature inversion on recent Fort Ord profiler data, 00z TAFs currently advertise tempo MVFR ceilings, however may need to amend for IFR if the low ceilings over the northern Monterey Bay hold together as the ceilings move south and east. Ceilings mixing out by late Sunday morning with generally MVFR-VFR conditions during the afternoon. Onshore winds 5 to 15 knots during the period. && .MARINE... (Tonight through next Thursday) Issued at 259 PM PDT Sat Aug 17 2024 Light to gentle breezes are anticipated across most of the marine zones tonight. The exception will be across the northern San Francisco and San Pablo Bays where intermittent moderate breezes are forecast. Primary swell will continue to roll in from the west and northwest with wave heights ranging between 2 and 6 feet. Fresh to moderate breezes are expected Sunday afternoon into next week, especially near and south of Point Sur. In response, seas will increase to 6 to 8 feet across southern zones and low-end marine headlines may be needed Sunday afternoon and into early next week. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ SHORT TERM...Sarment LONG TERM....Sarment AVIATION...Canepa MARINE...Bain Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea
Area Forecast Discussion
National Weather Service Nashville TN
713 PM CDT Sat Aug 17 2024 ...New AVIATION... .UPDATE... Issued at 634 PM CDT Sat Aug 17 2024 As of 630pm, there were no storm in Middle Tennessee, but a storm over far southern KY had sent a nice outflow boundary down toward Dover and Lafayette. The afternoon has been very hot and very sunny. Thanks to strong subsidence between storms to our east and an approaching front to our northwest, the air has dried out considerably this afternoon with dew points dipping to 60 at BNA while the temperature surged to 99. The low dew points have dropped cape values down below 1000 J/kg, thus no storms and really no clouds. But, a band of much higher dew points and cape values was upstream ahead of the cold front. These greater moisture and instability values will slide into Middle Tennessee over the next couple of hours, and as the front approaches, scattered thunderstorms are expected to develop. HRRR shows this and the NAMNest really blows it up along the front. A few storms could still produce gusty winds and heavy downpours. Unfortunately, the coverage will be lower than we previously hoped, so many people wanting some rain will not get it, and it looks quite dry through the coming week. The best chance this evening will be across the Upper Cumberland. The forecast data was recently updated to reflect the hot temps and low dew points. Also, hourly pops were updated with lower expected coverage. && .SHORT TERM... (Rest of today through Sunday) Issued at 1033 AM CDT Sat Aug 17 2024 A weak upper trough has come through Middle Tennessee already this morning, and there`s another one positioned to our immediate west that will come through later on. In addition, a rather pronounced surface boundary will soon begin inching its way across the mid state. Already, the instability needed for additional convection is in place, and the dynamics will be there with the surface and upper patterns being what they are. Most of Middle Tennessee remains under a marginal risk of severe storms today & tonight, with a portion of northeast Middle Tennessee under a slight risk. So the next several hours may be somewhat busy weatherwise, but the activity looks to diminish during the overnight hours, with maybe some lingering cells over the Cumberland Plateau early Sunday. Temperatures tomorrow will be several degrees cooler than today owing the air mass change coming with the fropa. && .LONG TERM... (Sunday Night through next Saturday) Issued at 1033 AM CDT Sat Aug 17 2024 Rain chances after tomorrow will be virtually nonexistent. High pressure will dominate our weather pattern next week, with temperatures hovering below seasonal norms until maybe Friday. Even looking out to 240 hrs., there is only high pressure. So once this weekend`s active weather system departs the region, we`re headed back into a dry pattern for the foreseeable future. && .AVIATION... (00Z TAFS) Issued at 713 PM CDT Sat Aug 17 2024 VFR generally thru 18/24Z. CSV obs since 17/1853Z, AMD NOT SKED removed. Convection moving thru SE/SC KY. Lightning activity noted, but if SEWD progression continues, low confidence per more stability across our area to mention prevailing shwrs/tstms, mentioned only vcnty shwrs. Convection should dissipate by 18/04Z. MVFR patchy fog formation possible all terminal sites 18/09Z-18/14Z. Shwrs/tstms possible SRB/CSV after 18/18Z, but low confidence prevailing shwrs/tstms, mentioned only vcnty shwrs. && .PRELIMINARY POINT TEMPS/POPS... Nashville 72 89 68 86 / 40 20 0 0 Clarksville 69 87 65 84 / 40 10 0 0 Crossville 64 80 61 77 / 50 50 10 10 Columbia 71 90 66 87 / 20 10 0 0 Cookeville 66 80 63 78 / 50 40 10 10 Jamestown 65 79 62 77 / 50 70 20 20 Lawrenceburg 70 89 66 86 / 20 10 0 0 Murfreesboro 70 89 67 86 / 40 20 0 0 Waverly 69 88 66 86 / 30 10 0 0 && .OHX WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Rose LONG TERM....Rose AVIATION.....JB Wright
Area Forecast Discussion
National Weather Service New York NY
1030 PM EDT Sat Aug 17 2024 .SYNOPSIS... A weak low tracks slowly eastward through the Great Lakes region tonight, and approaches Sunday. Meanwhile another low develops during Sunday over southeastern Pennsylvania and eastern Maryland. This low then deepens Sunday night into Monday and tracks northeast bringing a cold front across the area late Sunday night into Monday. A secondary frontal passage moves through Tuesday. High pressure builds in for the middle and end of the week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Forecast generally on track. Made some adjustments to PoPs over the next few hours to account the latest radar trends. There is still the potential for one round of moderate to heavy rainfall late tonight into early Sunday morning. The Flood Watch remains in effect for NE NJ into the Lower Hudson Valley at 06z and continues through into Sunday night. The 00z HRRR has backed off on its depiction from earlier of a more organized band of heavy rain across the watch area early Sunday morning. Heavy downpours may end up more scattered, but would like to see the rest of the 00z CAMs before making any changes to the rest of the forecast. Rainfall rates may peak late tonight around 1 inch per hour. Isolated flash flooding is also possible a little farther to the east, into New York City and Putnam and Westchester counties, with poor drainage and urban flooding possible. With the upper ridge remaining into the western Atlantic, showers will continue to struggle to move eastward across Long Island and CT with many locations remaining mostly dry out east through the night. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/... A Flood Watch is in effect from late tonight, 06Z Sunday, through late Sunday night, 06Z Monday, for the potential for scattered flash flooding, urban and poor drainage flooding, and possibly fast responding streams of northeastern New Jersey. Rainfall rates could be near 1 inch per hour, and at times approach 2 inches per hour. Total rainfall in the watch area will be around 2 inches to 2.5 inches with locally as much as 3 inches possible. This will be with a slow moving frontal system and with training showers and isolated thunderstorms, as the flow nearly parallels the trough. Also, precipitable waters increase to just over two inches Sunday, and warm cloud process increase along with a 20-230kt low level jet during Sunday and into Sunday night. This system will be slow moving eastward as downstream riding remains across the western North Atlantic. An then during Sunday a frontal wave develops near the mid Atlantic coast, across southeastern Pennsylvania into the Delmarva. This low provides lift for heavy rainfall as this low tracks slowly northeast to east across northeastern New Jersey into New York City and then to the northeast of the area during Monday. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... The area remains under a large-scale trough with vorticity maxima moving through Monday night and into Tuesday. As the trough tries to lift during the day on Tuesday, additional energy descends from the north to allow for another round of forcing. At the surface, this should translate into the form of a secondary frontal passage that brings another round of showers with possible embedded thunderstorms, especially Monday night into Tuesday morning. Any residual showers should diminish into the afternoon on Tuesday with the passage of the surface cold front. There is still some uncertainty as to how quickly the trough lifts with the upper-level energy rotating over New England, but consensus has been that the trough departs late Wednesday into Thursday and ridging begins to move over the area from the west. At the surface, a relatively strong high pressure system builds into the Mid- Atlantic and Northeast from Wednesday through the weekend. This will provide fairly calm and dry conditions through the rest of next week. This high pressure will be accompanied with primarily N/NW winds and a much cooler airmass. The airmass should be fairly anomalously cool for middle to late August. High temperatures on Tuesday and Wednesday may not rise out of the upper 60s to low 70s for much of the area. Even coastal areas, highs will only be in the low to maybe middle 70s. Lows Wednesday night and Thursday night will likely be fairly chilly, with some locations for the interior and outlying areas possibly dropping into the low 50s or upper 40s, depending on the strength of any radiational cooling. Temperatures will gradually moderate into late week and the weekend with highs by Friday and Saturday rising back into the upper 70s to low 80s. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... A frontal system slowly approaches the terminals through the TAF period. VFR to start for NYC terminals on north and west with MVFR with some local IFR further east. Conditions should slowly lower to MVFR overnight at all terminals. Scattered showers are possible at any time through 09z, especially from KISP and KBDR on west. More widespread showers 09-15z, possibly heavy at times, are expected especially NYC terminals on north and west. MVFR conditions are likely to continue through Sunday evening although there could be some brief improvement to VFR at times in the afternoon. Showers remain possible into Sunday evening, especially along and west of the Hudson River corridor. Further east, a brief shower is possible, but the most widespread shower activity likely holds off until after 00z Monday. There could be an isolated thunderstorm early Sunday morning, mainly NYC metro terminals on north and west. Potential for thunderstorms increases a bit Sunday afternoon/evening for the same terminals and have included a PROB30 for this time period. Winds will mainly be SE around 10 kt or less through the TAF period. Coastal terminals could see winds a few kt higher at times, especially Sunday afternoon. There is also a chance for a few gusts 15-20 kt Sunday afternoon. ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty... Timing of return to MVFR may be off by 1-3 hours. Amendments for changing flight categories likely through the TAF period. Isolated thunderstorms possible 10-16z Sunday. Timing of PROB30 TSRA Sunday afternoon and evening may be off by several hours with adjustments likely. OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY... Sunday night: Showers with possible thunderstorms. MVFR to occasional IFR conditions. Monday: Showers with possible thunderstorms, especially afternoon and evening. MVFR or lower at times. Tuesday: Mainly VFR. A chance of showers with MVFR possible. NW wind gusts 15-20 kt. Wednesday-Thursday: VFR. Detailed information, including hourly TAF wind component forecasts, can be found at: https:/www.weather.gov/zny/n90 && .MARINE... Rough ocean seas and long period swells, 12 to 15 second, will persist this weekend and into early next week as distant TC Ernesto passes well offshore in the open Atlantic. This will also lead to rough conditions around inlets. Please refer to the National Hurricane Center for official forecasts regarding Hurricane Ernesto. A Small Craft Advisory is in effect for the ocean zones, and was extended through Monday night. Elevated wave heights on the ocean zones will allow for SCA conditions to continue Monday night and possibly into the day on Tuesday with some marginal wind gusts near 20-25kt with the passage of a cold front. Late Tuesday, wind diminish and wave heights should fall below 5 feet. Sub-SCA conditions are then expected with high pressure moving into the area by mid-week. && .HYDROLOGY... A Flood Watch is in effect late tonight into late Sunday night for Northeastern New Jersey and into the Lower Hudson Valley west of the Hudson River. Locally heavy rainfall is possible late tonight, and again during Sunday into Sunday night, particularly west of the NYC metro and Hudson River. The threat of heavy rainfall expands to the east into Western Long Island and portions of southern Connecticut, and with the slow movement of low pressure and lower rainfall amounts and rainfall rate was not confident enough to go farther to the east with the Flood Watch. Total rainfall amounts from tonight through Monday night range from around a half inch east to around 2 inches from NYC metro on north and west. Locally higher amounts, possibly up to 3 inches, are possible across northeastern New Jersey into the Lower Hudson Valley. Isolated to scattered instances of flash flooding are possible across the more flood prone areas of NE NJ and adjacent areas of the Lower Hudson Valley, and perhaps as far east as NYC. A more widespread threat for localized flash flooding, along with nuisance flooding of urban and poor drainage areas, sets up on Monday. No hydrologic concerns Tuesday through next weekend. && .TIDES/COASTAL FLOODING... A high rip current risk is in place through Monday. This is due to SE to S long period swells from Hurricane Ernesto. Ocean seas are forecast to be highest Sunday into Monday, with heights up to 6-7 ft. There is potential for high surf along the ocean beaches during this time frame as well as beach erosion. A new moon on the 19th as well as swell from distant Hurricane Enersto will elevated tide levels Sunday into early this week. Minor coastal flooding is expected with high tide Sunday evening across the back bays of Nassau and Western Sound along the southwest CT and S Westchester coast. Have issued a Coastal Flood Advisory for these locations. Localized minor coastal flooding is possible across southern Queens, Southern Brooklyn and lower NY Harbor. Locations may just touch minor benchmarks and a statement has been issued. Additional minor flooding is possible for high tide Monday evening and statements/Advisories will likely be needed for similar locations as with high tide Sunday evening. Please refer to NHC for official forecasts regarding Hurricane Ernesto. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Coastal Flood Advisory from 10 PM Sunday to 1 AM EDT Monday for CTZ009. NY...Coastal Flood Advisory from 10 PM Sunday to 1 AM EDT Monday for NYZ071. Flood Watch from 2 AM EDT Sunday through late Sunday night for NYZ067-069. High Risk for Rip Currents through Monday evening for NYZ075-080- 081-178-179. Coastal Flood Advisory from 7 PM to 10 PM EDT Sunday for NYZ179. NJ...Flood Watch from 2 AM EDT Sunday through late Sunday night for NJZ002-004-006-103>108. MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ350-353-355. && $$ SYNOPSIS...MET/MW NEAR TERM...DS/MET SHORT TERM...MET LONG TERM...MW AVIATION...DS MARINE...MET/MW HYDROLOGY...MET/MW TIDES/COASTAL FLOODING...
Area Forecast Discussion
National Weather Service Pocatello ID
133 PM MDT Sat Aug 17 2024 .SHORT TERM...Today and Sunday. Looking at current satellite imagery, there continues to be a deep upper level low centered just off the coast of Oregon. Over northern Utah, there is a trough with ample moisture moving northeast into our area. Look for isolated to scattered showers and thunderstorms, mainly over our southern areas along the Utah border later this afternoon into the evening. Expect gusty winds around 40 mph and up to 50 to 55 mph as well small hail and moderate to heavy rainfall under thunderstorms. Our southern areas are under an excessive rainfall outlook along the Utah border. Again, this is the area where thunderstorms are most likely as well as be the strongest. Tonight into tomorrow, models show us in the same pattern with an upper level low off the Oregon coast. Models show moisture still moving up from Utah combined with lingering moisture. Look for isolated mostly afternoon showers and thunderstorms over most of our forecast area. Look for scattered showers and isolated to widely scattered thunderstorms along the Wyoming border in our our area mainly Sunday afternoon. The biggest thunderstorm hazard will be moderate to heavy rainfall. Our eastern areas bordering the Wyoming border are in an Excessive Rainfall Outlook for tomorrow afternoon. Small hail and gusty winds are likely as well with thunderstorms tomorrow afternoon. Expect temperatures today and Sunday near normal for this time of year, mid to upper 80s with some lower 90s across our lower elevations. Wyatt .LONG TERM...Monday through next Saturday. Models continue to show lingering moisture in the area with isolated to scattered showers and isolated to widely scattered thunderstorms Monday afternoon. Our eastern areas along the Wyoming border are under an Excessive Rainfall Outlook on Monday too. Models show a drying trend Tuesday through early Thursday. Models then continue to show moisture moving back in the area late Thursday into next weekend. Temperatures will start the week near normal if not slightly above normal and will stay that way through Wednesday. Thursday temperatures will start trending downward and look to be 4 to 8 degrees below normal by next weekend. Wyatt && .AVIATION... VFR conditions expected over the next few hours with mostly clear skies. Increasing clouds and moisture will overspread the region later this afternoon and into the evening. Hi-res CAMs bring a brief period where showers, perhaps a few thunderstorms, will be possible until around 18/04-06Z. There`s quite a bit of variability however amongst the various models so don`t have a good feel for how things will transpire. Nevertheless, the forecast has VCSH everywhere except KSUN. Winds will become gusty out of the south in the SNake Plain over the next few hours. During the overnight, precip moves out, winds lessen and skies clear allowing VFR to prevail. McKaughan && .FIRE WEATHER... Moisture and clouds will surge northward this afternoon out of Utah bringing increasing chances for showers and some thunderstorms to southern and eastern portions of the forecast area. Winds will increase out ahead of this over the next few hours but RHs will also surge with the increasing moisture so no concerns for Red Flags. Sunday will see additional shower and storm development in the afternoon hours but tstm coverage looks isolated in nature so no need for any red flags that day either. Could see a bit better tstm coverage on Monday with deeper moisture before things dry out into the middle part of the week. McKaughan && .AIR QUALITY...The HRRR smoke model continues to show improvement in air quality throughout today across Custer County as the upper level flow becomes more southerly. By this evening the vast majority of central and east Idaho should be experiencing good air quality, as long as there are no new fire starts. This pattern should stay in place through Sunday and much of Monday. Wyatt && .PIH WATCHES/WARNINGS/ADVISORIES... None. && $$
Area Forecast Discussion
National Weather Service Portland OR
202 PM PDT Sat Aug 17 2024 .SYNOPSIS...A strong low pressure system offshore will bring widespread wetting rain to the area this afternoon into tonight, with concerns for localized flash flooding near ongoing wildfire burn areas. There is also a chance of thunderstorms across the area today, a few of which could produce severe wind gusts and large hail from the Cascades west to the I-5 corridor. Showers taper off on Sunday, yielding a return of mild onshore flow through much of next week. && .SHORT TERM...Now through Sunday Night...Not much change in the overall thoughts from this morning. A Severe Thunderstorm Watch has been issued for most of the counties along the I-5 corridor eastward to the Cascade crest, where the strongest thunderstorms are expected to occur. The watch is currently in effect through 9 PM tonight. Water vapor satellite imagery reveals a large and well defined upper level low offshore of the Pacific Northwest this afternoon, while diffluent southerly flow aloft is present across western Oregon and Washington on the periphery of this feature. As of 1:45 PM, numerous showers and strong thunderstorms have developed across parts of southwest Oregon and are moving northward towards Lane County. RAP analysis shows areas of 500-1000 J/kg of MUCAPE across the Oregon Cascades along with effective bulk shear increasing to 35-45 kt early this afternoon. Southerly flow will pivot a bit more southeasterly over the course of the day, helping to advect rich mid level moisture and enhanced instability into the region to set the stage for widespread wetting rain showers with embedded thunderstorms across the area this afternoon and evening. The trigger for this activity will be a potent, negative-tilt shortwave trough which will lift northward across the area this afternoon, coincident with peak heating. Temperatures will warm into the low to mid 80s in the interior valleys and into the 70s in the higher terrain today prior to the arrival of this feature, contributing to destabilization characterized by MUCAPE values of 500-1500 J/kg across much of the area away from the coast this afternoon. Additionally, strong mid and upper level wind fields will provide ample shear values to support organized updrafts for any thunderstorms that develop. Finally, all of this will occur within the left exit region of a 90 kt jet streak rounding the base of the large scale trough, providing additional forcing for ascent across northwest Oregon and southwest Washington. Given all of the favorable factors described above, SPC maintains a rare slight risk for severe thunderstorms across the Cascades today, with a marginal risk extending westward to the I-5 corridor. For some historical context, we have to go back nearly four years to September 2020 to find the last time any portion of our forecast area was included in an SPC Day 1 slight risk. The primary severe threat will likely be damaging thunderstorm wind gusts of 60+ mph given a well mixed sub cloud layer contributing to DCAPE values of 700-1100 J/kg. That said, can`t rule out the possibility of some large hail to the size of quarters, especially farther south over Lane County where cells may tend to be more discreet early in the event. SPC maintains a 15 percent chance of both severe modes for areas in the slight risk, and a 5-15 percent chance in the marginal areas. This means that any point in the Cascades slight risk area will have a 15 percent chance of a severe thunderstorm occurring within 25 miles today, with a corresponding 5-15 percent chance within 25 miles of any point in the marginal risk area. In terms of timing, hi-res guidance has been fairly consistent over the past several runs in depicting showers and thunderstorms popping up across Lane County around 1-2 PM this afternoon and then spreading northward and reaching the Mt Hood and Portland areas approximately 4-5 PM. Activity then continues into the evening and starts to ramp down in intensity after sunset through about midnight. Shifting gears to the heavy rain/potential flooding aspect of today`s activity, the forecast remains largely on track with what has been depicted in previous model runs. Yesterday`s sounding from SLE showed a precipitable water value over 1.1", with additional moisture streaming into the area today looking to send PWATs above 1.25" and perhaps as high as 1.50" according to the higher end of guidance, which would be right around the maximum values of mid August climatology. Given the ample moisture and forcing, hi-res guidance continues to depict rainfall rates mostly topping out around 0.75" per hour, though latest HREF guidance does show a 5-10 percent chance of rates locally as high as 1 inch per hour starting to show up over some areas this afternoon. As such, will keep the Flash Flood Watch intact along the length of the Oregon and south Washington Cascades this afternoon into tonight. The primary areas of concern remain the recently burned areas associated with ongoing wildfires, but will have to also keep an eye on burn scars from past years give the slight uptick in probabilistic guidance for rainfall rates. Flood concerns in the inland valleys should remain more limited in scope to some localized ponding of water in areas that happen to see heavier rainfall rates over a prolonged period of time, but widespread flooding concerns are not expected in the lowlands. Showers will ramp down in intensity and eventually taper off from south to north through late this evening as the bulk of the energy associated with the upper level trough shifts north of the area into Washington. Could certainly see some lingering shower activity into the day on Sunday and perhaps some isolated thunderstorms into Sunday morning across southwest Washington, but any additional rainfall will be minimal. The region will start to settle back into a benign onshore flow regime by later Sunday afternoon, with highs remaining in the upper 70s to around 80 in the interior valleys. DH/CB .LONG TERM...Monday through Friday...Little change in the long term forecast as ensemble guidance continues to favor mean upper level troughing over the NE Pacific through much of next week. This will keep western Oregon and Washington in a stable onshore flow regime through the period, bringing seasonably mild temperatures with morning cloudiness and afternoon highs generally in the upper 70s. The proximity to the upper level trough will also yield continued chances for sporadic shower activity and perhaps some minimal thunderstorm potential at times, but no significant rainfall or strong thunderstorm potential is expected beyond this weekend. /CB && .AVIATION...VFR conditions prevail at 21Z Sat, now seeing start of next round of convection as a shortwave lifting north across western Oregon expected to trigger more robust thunderstorms this afternoon into the evening hours. Hires models show most active thunderstorms over the Cascades during this time. But valley locations as well have a chance for thunderstorms. Approximate timing for stronger batch of thunderstorms at TAF sites: KEUG 21Z Sat-01Z Sun, KSLE 22Z Sat-02Z Sun, KPDX 23Z Sat-03Z Sun. After that thunderstorm chances drop but not quite end until about 09Z Sun. Predominantly VFR conditions throughout, though passing thunderstorms could briefly reduce visibilities below 6SM due to heavy rainfall. Gusty erratic winds will be possible as thunderstorms pass through, with a 5-14% chance of severe convective wind gusts up to 60 mph. Frequent lightning will also be possible. PDX AND APPROACHES...Thunderstorms and showers reach KPDX around 00z Sun through about 03Z Sun, then chances drop but not quite end until about 09Z Sun. Predominantly VFR conditions throughout, though passing thunderstorms could briefly reduce visibilities below 6SM due to heavy rainfall. Other impacts of thunderstorms covered above. && .MARINE...Expect benign conditions over the waters through mid next week. Winds remain N/NW this evening then turn SW late tonight/early Sunday as surface low pressure moves through the waters. Showers pass through all waters on Saturday, with around a 20% chance of isolated thunderstorms. Low pressure remains over the NE Pacific through mid-week, maintaining SW winds. Winds are expected to remain at 10 kts or less with gusts up to 15 kts; wind-driven seas of around 4 feet. /mh /Sala && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland
Area Forecast Discussion
National Weather Service Phoenix AZ
440 PM MST Sat Aug 17 2024 .UPDATE...Updated 00z Aviation Discussion... && .SYNOPSIS... Thunderstorm chances increase today with the best chances favoring the high terrain areas of Arizona and across southeast Arizona. Isolated thunderstorms will be possible across south-central Arizona with gusty winds and blowing dust being the primary concerns going through this evening. Drier conditions are favored early next week before thunderstorm chances increase again during the middle part of next week. Temperatures will warm up early next week with excessive heat conditions possible. && .DISCUSSION... The subtropical ridge of high pressure that`s been over the region continues to gradually shift eastward and is now centered over eastern New Mexico. Meanwhile, a strong trough situated off the coast of the Pacific Northwest is leading to downstream amplification of the ridge as it shifts into the Southern Plains. Locally, this has resulted in better southeasterly flow aloft, importing better moisture into the region that will help increase our thunderstorm chances for today. Early afternoon satellite and radar trends shows more robust convection ongoing across northern Arizona and Utah as a notable vort max pushes through that region, while CU development is ongoing across southeast Arizona with a few isolated thunderstorms now popping up. Thunderstorm chances today will be greater today across south-central Arizona given the better moisture that is now in place with the 12Z PHX sounding recording a PWAT value of 1.66" and surface dew points now in the upper 50s to low 60s. HREF paintball plots support continued thunderstorm development across southeast Arizona through the rest of this afternoon with southeasterly steering flow helping to propagate thunderstorms toward south- central Arizona. Across south-central Arizona, uncertainty quickly increases in regards to thunderstorms being able to survive as they push northwestward from southeast Arizona. Forecast soundings suggest a favorable environment conducive to thunderstorm development and strong outflows with favorable CAPE values upwards of 1000-1500 J/kg and inverted-V profiles supporting high DCAPE values to around 1500 J/kg. However, there is a good deal of uncertainty around whether or not a strong/deep enough outflow boundary can survive into south- central Arizona and overcome the CIN to spark new thunderstorm activity. Previous iterations of the HRRR had supported the idea of new thunderstorm development occurring into the Valley, but the latest runs continue to back off on this. Nevertheless, any thunderstorms that were to develop across south-central Arizona this evening would be capable of producing strong downbursts. Aside from thunderstorm chances, strong outflows from southeast Arizona could lead to some areas of dense blowing dust between Phoenix and Tucson. Going into early next week, the subtropical ridge will continue to strengthen and gradually shift westward with global ensembles indicating 500 mb heights climbing upwards of 596-598 dm during the Monday/Tuesday timeframe. This will lead to temperatures warming up to around 108-114 degrees across the lower deserts with the hottest temperatures currently focused across the Valley. The warming temperatures will promote Major HeatRisk primarily around the Phoenix metro as well as the San Carlos/Globe areas during this time. Thus, an Excessive Heat Watch has been issued for the aforementioned areas. Moisture will decrease for the start of the new workweek and thus lead to lower thunderstorm chances before global ensembles show moisture increasing again midweek. There is uncertainty in exactly how this pattern will evolve, but there are indications that an inverted trough move across northern Mexico may potentially support greater thunderstorm chances during the middle part of next week. && .AVIATION...Updated at 2330Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Main aviation weather concern will be the potential for gusty thunderstorm outflow winds heading into this evening. Westerly winds aob 10 kts will prevail into early this evening before an outflow boundary from thunderstorm activity currently affecting southeast AZ pushes through the metro area. Based on the latest trends, it appears the main outflow boundary will push through between the 02-04z timeframe, with wind directions switching out of the S-SSE with potential gusts in excess of 25 kts as well as areas of blowing dust. Confidence of actual thunderstorm activity directly affecting the area terminals continues to remain low and thus not mentioned in the TAF package. Conditions should improve by the late evening hours with winds resuming the typical diurnal tendencies with easterly winds overnight through early Sunday morning before switching out of the west by the late morning hours with speeds aob 10 kts. Convective cloud bases will remain aoa 10 kts with FEW coverage becoming SCT to occasionally BKN coverage by early this evening. Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected during the next 24 hours under generally clear skies. Winds at KIPL will follow the typical diurnal tendencies while winds at KBLH will favor the south to south-southwest. Wind speeds will generally remain aob 10 kts, although afternoon gusts upwards of 20-25 kts will continue to be favored at KBLH through early this evening and once again for Sunday afternoon. && .FIRE WEATHER... The greatest thunderstorm chances this weekend will remain primarily confined to the Arizona high terrain and southeast Arizona, but isolated chances for thunderstorms along with strong, erratic outflows will be possible across south-central Arizona. MinRH values will be in the 15-25% range with fair to good overnight recoveries of 30-60%. Drier conditions with lower thunderstorm chances will start off the new workweek before thunderstorm chances are favored to increase during the middle part of next week. Outside of thunderstorm outflows, winds will tend to follow their typical diurnal patterns with some afternoon upslope gusts of 20-25 mph possible. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Watch from Monday morning through Tuesday evening for AZZ534-537-540>551-560-562. CA...None. && $$ DISCUSSION...Smith AVIATION...Lojero FIRE WEATHER...Smith
Area Forecast Discussion
National Weather Service Topeka KS
609 PM CDT Sat Aug 17 2024 .KEY MESSAGES... - Showers and thunderstorms are possible (30 to 50 percent) Sunday afternoon and evening, some of which could be strong. - Below normal temperatures are expected to start off the workweek. - The forecast has highs back into the 90s heading into next weekend. && .DISCUSSION... Issued at 222 PM CDT Sat Aug 17 2024 An upper ridge remained centered over the southern high plains per the 19Z water vapor imagery. The ridge axis extended north over the northern plains and a closed upper low was noted off the coast of OR. A shortwave looked to be lifting northeast through UT. Surface obs showed weak high pressure ridging into northeast KS from the north. Main challenge with the forecast is timing the weak disturbances rounding the upper ridge. And then there may not even be a wave spark convection per the isolated storms across central NEB which appear to be a result of some modest warm air advection in the mid levels. The 12Z operational models are converging on a common idea of a shortwave diving southeast Sunday afternoon and evening. There is a good response to this wave seen in the isentropic surfaces with increasing lift and saturation in mid levels. So confidence in isolated to scattered showers and storms is increasing and have POPs in the 30 to 50 percent range by Sunday evening. NAM and RAP forecast soundings suggest elevated CAPE values could be around 1000 J/kg. Combined with bulk shear around 50KT with effectively a straight line hodograph, there is some potential for organized updrafts and severe storms. By Monday models build a stronger surface high into the central plains with some drier air. This brings into question whether there is enough moisture for precip Tuesday night and the operational models have backed off on QPF. This has resulted in the NBM coming in with POPs less than 10 percent for Tuesday night and into Wednesday. Then the upper ridge axis begins to slide east over the central plains limiting the chances for shortwave energy to affect the area. So the only chances for precip in the forecast is on Sunday and Sunday night. The stronger surface ridge Monday should bring below normal temps for the first of the workweek. Then temps are forecast to warm as the upper ridge moves overhead and southerly return flow redevelops. This should push highs back into the 90s by Saturday. The NBM reflects these trends nicely and have not made and changes. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 607 PM CDT Sat Aug 17 2024 VFR at terminals with light easterly winds overnight and increasing high clouds by sunrise, limiting overall fog development at KTOP. Added a mention of VCSH aft 17Z at all sites with some uncertainty on timing and coverage of showers and isolated TSRA during the afternoon. Mid clouds around 10 kft are most likely with showers given lack of low level moisture with this system. && .TOP WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wolters AVIATION...Prieto
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
510 PM MDT Sat Aug 17 2024 .KEY MESSAGES... - Thunderstorm chances overnight and Sunday, with potential for strong/severe thunderstorms on Sunday. - Warm and generally dry conditions to start begin the work week. - Fire weather conditions will become a concern late Monday afternoon and again Tuesday afternoon across the western parts of our CWA. && .DISCUSSION...(This Evening Through Saturday) Issued at 111 PM MDT Sat Aug 17 2024 Current 500hpa analysis shows upper low spinning across the Great Lakes region with high pressure located across nrn New Mexico/srn Colorado. Ridge axis extends northward through central WY with much of the CWA located in northwest flow aloft between the two features. Water vapor imagery shows fairly potent s/w lifting northward through NV/UT with abundant convection associated with feature. At the sfc, weak boundary located across northeast WY dropping southeast through the Neb panhandle. West of this feature, sfc winds are generally westerly with lower dwpts, while to the east, southeast winds are found with sfc dwpts in the low to mid 60s. 850hpa low level jet increases into the 35-45kt range overnight across the SC part of the state. This is also about the time the aforementioned s/w moving through the NV/UT area moves into the region. Ensembles are showing mean 0-6km shear AOA 50kts in the 06z-09z Sunday time frame...with increasing probabilities for lightning strikes (as seen in DESI). MUCAPE values are still in the 1.0-1.5k J/kg range (again...all aloft and not surface based) during this time. Also noticed that with the new Day1 SPC outlook, the MRGL outlook has been re-drawn to include a large part of SC SD. One question that remains is will the boundary that remains in place from northeast WY through the Neb panhandle also be a focusing mechanism for storms as the s/w lifts into the region. The HRRR has been fairly persistent in developing isolated convection across the srn Black Hills separate from the expected elevated convection across the sc part of the state. With the boundary and s/w moving over, developing lolvl jet, the probabilities are non-zero. Thoughts then turn to Sunday proper. Will be dealing with any leftover convection across the sc part of the state, and if the atmos and recover quick enough for stuff to re-fire during the afternoon. By 21z Sunday a narrow corridor of MUCAPE values from 2k-3k J/kg will exist from the Black Hills to south central SD. Ensembles shows sfc dwpts in the low 60s in the corridor during the afternoon. However shear looks meager at best with 35 to 40kts seen. With an easterly sfc upslope wind cant discount something developing over the Black Hills, with isolated plains convection developing. The first half of next week will be defined by the upper 500hpa ridge staying in place across the nrn plains. Temperatures will remain above normal for the middle of August. Models are highlighting various impulses moving over the ridge, which will bring isolated/widely scattered showers/storms to the region. && .AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening) Issued At 509 PM MDT Sat Aug 17 2024 VFR conditions are expected through the forecast period. Isolated thunderstorms are possible across southwestern and south central South Dakota late tonight. && .FIRE WEATHER... Issued At 111 PM MDT Sat Aug 17 2024 While a brief recovery in RHs is expected for Sunday across northeast WY, they will once again fall to sub 20% values on Monday, especially across western Campbell Co WY. With the upper ridge in place through the middle of next week, the dry airmass and low RH values will spread into the Black Hills region for Tuesday afternoon...leading to the potential for elevated fire weather concerns. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Hintz AVIATION...10 FIRE WEATHER...Hintz