Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/23/23


Area Forecast Discussion
National Weather Service Burlington VT
1013 PM EDT Tue Aug 22 2023 .SYNOPSIS... High pressure builds across the region through Wednesday, resulting in a period of pleasant and mainly dry weather. A low pressure system will bring periods of rain for Thursday and Friday. Drier conditions return as we head into the weekend. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... As of 714 PM EDT Tuesday...Main change to forecast was to increase temperatures on Lake Champlain as the lake is holding onto heat well this evening. Otherwise, skies may not clear out completely in Vermont tonight but if anything they will be lingering high clouds and won`t affect much here at the surface. Still expecting lows tonight in the upper 30s to lower 50s but perhaps around 60 F on the lake. Some fog is possible tonight in the typical valley spots as winds calm. Previous discussion below: Previous Discussion...Following a terrific late summer day, mostly clear skies will result in temperatures quickly falling after sundown. Breezy north winds will also quickly subside as the boundary layer decouples and 1024 mb surface high pressure builds in from the Great Lakes. So it should turn out to be a rather excellent radiational cooling night, despite CAMs depicting some high clouds spilling over the 600 Dm upper ridge that is currently parked across the center third of CONUS. So did go with the colder MOS guidance to have temperatures bottoming out in the upper 30s to lower 40s in the typical colder hollows, mid to upper 40s for most other locations except for lower 50s across the lower St Lawrence valley and Champlain valley. Somewhat more uncertain is the coverage of radiational fog. Given how deep the mixing got this afternoon with RAP and HRRR soundings showing mixing up to 800mb (and hence the 15 to 20 mph gusts), the boundary layer is quite dry with afternoon minimum dew points in the upper 40s with even some mid 40s readings. While we expect crossover temperatures to be realized, current thinking is that fog should be limited to climatologically favored locations such as Montpelier and Saranac Lake. l sunshine, light winds and dew points in the 40s and 50s. Expect highs mainly in the 70s, except 60s for the high terrain. Clouds should be on the increase overnight Wednesday. But contingent on how quickly they move in, there is potential for radiational cooling to exert its effect with the light winds and mostly clear skies. This is especially true if the lower dew points are realized during the daytime. So it could be the case where temperatures plummet quickly after sundown, which is now before 8 PM, and then stabilize or even rise slightly after midnight. It also looks like any rain should hold off until after sunrise on Thursday. So blended in some of the colder MOS guidance to yield overnight lows in the mid 40s in the colder hollows, but lower to mid 50s across the Champlain and St Lawrence valleys. Also note that these forecast lows may happen early in the overnight hours as opposed t Heading into Wednesday, our region continues to be under the influence of cool, dry northwest flow. While some guidance shows the potential for a few showers to make it into the Adirondacks by Wednesday afternoon, the potential remains rather low so opted to keep the PoPs under slight chance (i.e. less than 15 percent). With the surface high pressure becoming centered over our region, any showers should be brief and confined to the terrain. Forecast soundings show rather deep mixing up to 800mb although with the boundary layer winds being light at 5 to 10 kt, it is a little uncertain how deep we can mix. It will certainly not be as gusty as on Tuesday. So Wednesday is arguably more comfortable for outdoor activities even though Tuesday was a really nice day to be outside. Temperature forecast is a little tricky with 850mb temperatures being relatively cool at +9C to +11C (25th percentile per the SPC sounding climatology for Albany, NY) but 925mb temperatures projected to be +15 to +18C (median range for the same sounding climatology). There is certainly potential to mix down some drier dew points from aloft, and for warmer temperatures downslope of the Adirondacks and Green Mountains due to adiabatic warming. Finally, high res guidance shows some smoke from western Canada wildfires making it to the Northeast on Wednesday. However, it will be aloft so no impacts to the air quality near the surface. It might make for a nice sunrise or sunset. No matter how one slices it, Wednesday looks to be the pick of the week with plentiful sunshine, light winds and dew points in the 40s and 50s. Expect highs mainly in the 70s, except 60s for the high terrain. Clouds should be on the increase overnight Wednesday. But contingent on how quickly they move in, there is potential for radiational cooling to exert its effect with the light winds and mostly clear skies. This is especially true if the lower dew points are realized during the daytime. So it could be the case where temperatures plummet quickly after sundown, which is now before 8 PM, and then stabilize or even rise slightly after midnight. It also looks like any rain should hold off until after sunrise on Thursday. So blended in some of the colder MOS guidance to yield overnight lows in the mid 40s in the colder hollows, but lower to mid 50s across the Champlain and St Lawrence valleys. Also note that these forecast lows may happen early in the overnight hours as opposed to just prior to daybreak. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... As of 356 PM EDT Tuesday...We remain on track to see widespread rain during this period, especially Thursday night. During the day, temperatures should rise nicely before clouds thicken, with locations over our southern and western zones more likely to see an early high temperature before cooling a bit into the 60s. This temperature and cloud pattern will be attributed to a mid-level warm front approaching from the southwest while an upper level shortwave rounding the big ridge over the middle of the US approaches from the northwest. While a stronger upper level wave passes to our south and west over Pennsylvania, progged 700 millibar vertical motion over our region looks ample. This isentropic lift will initially produce only widely scattered precipitation with dry air in place. However, in combination with low level southerly flow expect skies to quickly cloud over, but height falls and increasing surface convergence will help precipitation blossom. While a general thunder and marginal excessive rainfall risks do exist during this period, these risks appear quite low at this time. Near surface winds will tend to be southeasterly, which will tend to bring in marine air and keep our air mass fairly cool and stability high to limit convective potential. For now, have continued to have a slight chance of thunder overnight in our southern areas, consistent with some very elevated instability at the top of a nearly isothermal, saturated low level atmosphere. If frontogenesis was to linger in a particular area long enough, we could see some heavier rainfall amounts than currently indicated. Some ensemble members of global model guidance show strips of 1 to 2" over 6 hours, for instance. However, hourly rainfall rates in this setup are unlikely to support flash flooding. It will bear watching though in the coming days. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 356 PM EDT Tuesday...Widespread rain will tend to become scattered showers on Friday with cloudy skies holding temperatures in the 60s, with best odds of coolest conditions in eastern Vermont where low clouds and occasional rain showers are most likely to linger all day. After a lousy stretch of weather late in the week, another batch of dry Canadian air should return by Saturday evening leading to dry weather for Sunday and Monday. Perhaps another weather system arrives on Tuesday, but predictability is too low to offer anything other than a general chance of showers at this time. Temperatures through the period will be below normal due to a combination of below normal upper level heights and northerly low level flow. With temperatures dependent somewhat on timing of the responsible cold front, there is some model spread in how warm of a day Saturday will be as well as convective chances. Given the uncertainty, have a slight chance of thunder during the afternoon nearly areawide for the scenario in which a boundary moves through during peak heating. However, looking at global model clusters, the amplitude of the upper level trough that helps push the front through explains the uncertainty more than timing - there are some warmer solutions and some cooler ones. The warmer ones, which are dominated by EPS members, are associated with enough instability to see thunderstorms. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... Through 00Z Thursday...VFR conditions are expected through the TAF period. Some patchy IFR possible at KSLK and KMPV from 06-12z due to Valley fog. Mostly clear skies with a few passing clouds with winds less than 5 kts or calm overnight and W around 5 knots aft 12z. Outlook... Wednesday Night: VFR. NO SIG WX. Thursday: VFR. Chance SHRA. Thursday Night: Mainly MVFR, with areas VFR possible. Likely SHRA. Friday: Mainly MVFR, with areas IFR possible. Chance SHRA. Friday Night: Mainly MVFR, with areas IFR possible. Chance SHRA. Saturday: Mainly MVFR, with areas IFR possible. Slight chance SHRA, Slight chance TSRA. Saturday Night: VFR. NO SIG WX. Sunday: VFR. NO SIG WX. && .EQUIPMENT... The Plattsburgh ASOS located at the Plattsburgh International Airport is back in service, however, the St. Johnsbury, Vermont, site is now down for the foreseeable future. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Chai NEAR TERM...Chai/SLW/Storm SHORT TERM...Kutikoff LONG TERM...Kutikoff AVIATION...Chai/SLW EQUIPMENT...WFO BTV
Area Forecast Discussion
National Weather Service Charleston SC
904 PM EDT Tue Aug 22 2023 .SYNOPSIS... A weak front will advance down through the region on Wednesday. High pressure then rebuilds for the latter half of the week, with another front possible early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Very few changes were needed for the late evening update. Lows were nudged up a degree or so in a few spots, especially over Southeast Georgia and along the coast given incoming guidance is trending a tad higher with temperatures overnight. Satellite and surface observation show a backdoor cold front working south across eastern North Carolina and will drop south into parts of the Midlands and Pee Dee shortly. The front is on target to push south of the Santee River just before daybreak Wednesday. Low-level moisture pooling ahead of the front coupled with some weak QG-forcing will likely support a band of showers/tstms with and just behind the wind shift, most of which will largely remain just offshore. Pops through sunrise will range from 20% as far west as a Saint George-Walterboro- Hilton Head line to 40% along the Charleston County coast per the latest trends noted in both the RAP and H3R. It will will be warm and humid night with lows from the mid 70s well inland and across areas adjacent to the Santee River to the lower 80s at the beaches and Downtown Charleston. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Pattern Synopsis/Forecast: Large upper level ridge will remain the dominant player across the CONUS through the mid week period with 590+ DM heights stretching across the southeast states. Surface high pressure will be building across the northeast/mid Atlantic region, helping to drive a backdoor front down through the southeast (in very wedge like fashion). There will be a narrow corridor of QG- forcing for ascent along the boundary sliding down through the region which might present a narrow window of opportunity for some shower activity on Wednesday, particularly late morning and through the afternoon across the southeast Georgia counties with the aid of daytime heating. Otherwise, with the shallow "cooler" air spreading into the region, temperatures will ease back into the middle to upper 80s for highs...to the lower 90s across the far southern Georgia counties. But the key will be the lowering surface dewpoints which will make it feel a bit more comfortable than in recent days. Thursday through Friday: Surface high pressure and modestly drier air will wedge it`s way down into the southeast and remain the main players to finish up the week. Dry weather anticipated. Daytime max temperatures will creep back into the upper 80s to lower 90s for Thursday and back into the middle 90s for Friday, cooler near the coast. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Anomalously strong upper level ridge is expected to begin weakening while retrograding into the southwest CONUS during the latter half of the weekend, and further weakening next week. This...in response to strong short-wave energy digging through the Great Lakes and into the Northeast CONUS and eventually carving out some modest troughing through the southeast states next week. Franklin will be passing up through the western Atlantic late this weekend through early next week. At this juncture, we are not expecting any direct impacts, although we might eventually get some stronger northeasterly flow and bigger swells. Will continue to monitor. As far as details: Another boundary will be pressing into the region by Saturday before stalling across inland areas. Along with developing troughing aloft, this will lead to a bit more unsettled conditions than we`ve had in recent times with precip chances increasing later Saturday and lingering through the first half of next week. Saturday will be the warmest/hottest day. In fact, blended guidance continues to paint max temperatures above 100F across inland areas, especially across southeast Georgia. I`m not prepared to go that hot just yet, but I will maintain mid to upper 90s in the forecast and a few locations touching 100F. Beyond Saturday, daytime temperatures should be easing back to around or even slightly below normal for the Sunday through Tuesday timeframe. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/... 23/00z TAF discussion: KCHS/KJZI/KSAV: VFR for much of the period. A band of mid-level clouds with cigs BKN050-080 will impact all terminals Wednesday morning as a backdoor cold front drops south. Isolated to perhaps scattered showers will accompany the front, but confidence for any impacts remains too low to justify anything more then VCSH roughly 10-16z at KCHS/KJZI and 12-18z at KSAV at this time. Gusty northeast winds will also occur behind the front with gusts 18-20 kt. Skies will clear late morning into the afternoon. Extended Aviation Outlook: VFR conditions will largely dominate through the rest of the week. A boundary will press into the region this weekend bringing increasing precip chances. This will result in possible flight restrictions beginning on Saturday. && .MARINE... Tonight: A weak pressure pattern early will favor a continuation of light southeasterly winds during the first half of the night, generally around 10 kt or less. Later tonight, a front will approach the region from the north, strengthening the pressure gradient and bringing a northeasterly surge across South Carolina waters toward daybreak. Winds off the Charleston County coast will ramp up into the 15-20 knot range by sunrise Wednesday with gusts approaching Small Craft Advisory levels thereafter. Seas will average 2-3 feet, then build up to around 4 feet off the Charleston County coast late tonight. The pressure gradient will tighten along the mid Atlantic coast and into the southeast coast Wednesday through Thursday, behind a boundary that will advance down through the region. This will result in stronger northeasterly flow and increasing seas across the coastal waters. Conditions are looking to push Small Craft Advisory levels, especially in the Georgia outer waters where seas will run around 6 feet. We will be hoisting a Small Craft Advisory for all coastal waters beginning Wednesday morning and lasting into Wednesday night. Winds and seas subside for late week and into the weekend. Late weekend into next week: Tropical Cyclone Franklin is expected to progress northward through the western Atlantic. Higher seas, stronger swells and stronger northeasterly winds will be a possibility during this time. Rip Currents: The combination of gusty northeast winds and NE swell will lead to a Moderate Risk for rip currents at all of our beaches on Wednesday. Additionally, longer period swell generated from distant tropical systems should begin moving through our waters late this week and into next week, which would bring an elevated risk of rip currents. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory from 6 AM Wednesday to 1 AM EDT Thursday for AMZ350-352. Small Craft Advisory from noon Wednesday to 1 AM EDT Thursday for AMZ354. Small Craft Advisory from noon Wednesday to 6 AM EDT Thursday for AMZ374. && $$
Area Forecast Discussion
National Weather Service Cleveland OH
915 PM EDT Tue Aug 22 2023 .SYNOPSIS... High pressure will drift east of the area tonight. On Wednesday, low pressure developing over the Upper Midwest will lift a warm front across the area before it meanders southeast towards the area through Thursday. The low will push a cold front across the region Thursday night. High pressure should return over the weekend. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... 915 pm update... No forecast changes were needed at this time. 645 pm update... There no adjustments needed with this evening`s near term forecast update. Previous discussion... Surface high pressure over the area with a large upper high over the Plains will foster dry weather through tonight with cloud cover increasing from the northwest. Overnight lows will fall into the upper 50s to lower 60s. By Wednesday morning, a shortwave will round the ridge and push southeast across Lake Erie and into the CWA and most CAMs portray an initial round of showers/thunderstorms accompanying this disturbance. Still some uncertainty in how well convection holds together and how high coverage will be as precip pushes south throughout the morning, especially since the atmosphere over the CWA will be well-capped. Maintained slight chance to chance PoPs with this update, but may be able to highlight a few areas with higher PoPs in a subsequent update as guidance continues to align. Any storms would likely be elevated with a low-end severe threat. Instability increases Wednesday evening into Wednesday night as a warm front lifts into the CWA and a LLJ develops along the lakeshore and especially across far NE OH/NW PA. Additional showers and thunderstorms will likely develop ahead of the warm front, however additional storms may develop wherever boundaries from dissipated early-day convection settle. Despite the unfavorable diurnal instability, there should be sufficient lift, moisture, and wind shear for at least semi-organized storms (perhaps even an MCS if the latest HRRR is correct) to develop somewhere over or near the CWA and push south late Wednesday night. PoPs peak across NE OH and NW PA Wednesday night, but a few models including the NAM have suggested that there`s potential of convection remaining to the east of the CWA. Unfortunately, as with many scenarios with this kind of setup, the outcome will heavily rely on mesoscale features that have yet to be resolved. Stay tuned for updates and refinements in the forecast. As far as hazards go, gusty winds and large hail will be the main severe weather threats, but there may be a low-end threat of quick spin-ups if an MCS or QLCS manages to develop. Regardless of storm mode, flooding will be concern as PWATs climb to around 2 inches, especially if storms manage to move parallel to the warm front thanks to the northwest flow aloft. The 12Z NAM (which tends to run a bit moist) has a strip of PWATs near record values of 2.5 to near 3 inches across NE OH and NW PA for a brief period overnight Wednesday. Torrential rainfall rates are certainly a possibility. There will be quite a gradient of temperatures across the area Wednesday: highs will be in the mid to upper 80s across NW OH with temperatures gradually decreasing to the east; highs will likely be in the mid to upper 70s across NE OH/NW PA. Warm air advection will keep temps in the 60s and low to mid 70s Wednesday night. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... NW`erly flow aloft and embedded shortwave disturbances are expected to impact our CWA Thursday through Thursday night, along the northeastern periphery of a heat dome and associated strong mid/upper-level high pressure ridge centered in vicinity of the southern Great Plains. At the surface, weak net-troughing accompanying the shortwave disturbances resides in our CWA and a cold front is still forecast to sweep SE`ward through our region Thursday night. A tight gradient in 850 mb temperatures is expected toward the WSW on Thursday and greater cloud cover is expected farther east, where the influence of the aforementioned shortwave disturbances should be greater. Late afternoon highs should reach mainly the lower to mid 80`s in NW PA, the mid 80`s to lower 90`s in NE OH, and the lower to upper 90`s farther west. The hottest highs are expected in our I-75 corridor counties. Low-level warm/moist air advection from the Gulf of Mexico will likely allow surface dew points to surge into the lower to mid 70`s. Given this high humidity and trends in our high temperature forecast, issued an Excessive Heat Watch for western portions of our CWA, along and just east of I- 75. This is where heat indices may reach 105F to 110F for at least two hours Thursday afternoon into the early evening. Overnight lows should reach the 60`s to lower 70`s around daybreak on Friday as weak low-level cold/dry air advection follows the front. Periodic, scattered, and organized showers/thunderstorms are expected on Thursday, especially east of I-71, and across our whole CWA Thursday night as low-level convergence/moist ascent along pre- frontal surface trough axes and the cold front interact with moderate to strong MUCAPE amidst moderate to strong deep layer bulk shear. Steep mid-level lapse rates and dry mid-level air accompanying an EML combined with steep low-level lapse rates stemming from diurnal convective mixing of the boundary layer should yield moderate to strong DCAPE during the afternoon through at least early evening hours of Thursday. Therefore, severe thunderstorms with damaging convective gusts are possible. Melting levels above 10.5kft AGL should limit the severe hail threat, although can`t rule- out marginally-severe hail with the strong, rotating updraft of any supercell. Torrential rainfall is expected with showers/storms given forecast PWAT`s near 1.5 to 2.0 inches in the warm sector and warm cumuliform cloud depths exceeding 10kft. Those PWAT values exceed the 90th percentile in the sounding climatology for nearby upper-air stations. Friday through Friday night will also feature NW`erly flow aloft, embedded shortwave disturbances, and net surface troughing impacting our CWA as the aforementioned mid/upper-level ridge retrogrades W`ward slightly. Isolated showers/thunderstorms are possible, especially Friday night, when a stronger shortwave trough should approach from the Upper Great Lakes and atmospheric moisture and instability, including elevated CAPE, remain sufficient. Late afternoon highs should reach the upper 70`s to lower 80`s in NW PA and primarily the 80`s in northern OH. Overnight lows should reach the 60`s around daybreak Saturday. && .LONG TERM /SATURDAY THROUGH TUESDAY/... The strong shortwave trough aloft and accompanying surface trough axis should advance SE`ward across our CWA on Saturday and be accompanied by isolated showers/thunderstorms. Late afternoon highs should reach the 70`s to lower 80`s. Odds favor fair weather Saturday night through Tuesday as NW`erly flow aloft and embedded shortwave troughs persist, yet an expansive surface ridge builds gradually from the north-central U.S./Upper Great Lakes and is accompanied by stabilizing subsidence and a drier low-level air mass. Overnight lows are forecast to reach mainly the 50`s Saturday through Monday nights. Daytime highs should reach the 70`s on Sunday and Monday, and the 70`s to lower 80`s on Tuesday. && .AVIATION /00Z Wednesday THROUGH Sunday/... Overall, VFR conditions are expected for this TAF update tonight into Wednesday. Mostly clear to fair weather skies are expected. There is some uncertainty about a complex of storms, maybe a MCS, rolling out of southeast Michigan into northern Ohio and NW PA late Wednesday morning into the early afternoon. With that uncertainty, we have not mentioned this potential in the TAFs with this update. Light northerly to northeasterly winds 5 to 10 knots this evening will become light and variable overnight. Southerly winds 8 to 12 knots will resume Wednesday morning through the rest of the TAF period. Outlook...Non-VFR possible in multiple rounds of thunderstorms Wednesday evening through Thursday. Additional non-VFR possible in showers and thunderstorms Friday into Saturday. && .MARINE... Wind speeds around 5 to 15 knots and waves of 3 feet or less are expected through this weekend. A ridge lingers before a warm front drifts northeastward across Lake Erie Wednesday through Wednesday night. Northeasterly to easterly winds veer to southeasterly with the approach of the warm front. Behind the warm front, winds veer quickly to southerly and then to southwesterly through Thursday. A cold front should sweep southeastward across the lake Thursday night and cause winds to veer to northwesterly and then to northerly by daybreak on Friday. Primarily northerly to northeasterly winds are expected for the rest of Friday through this weekend as another ridge builds gradually from the Canadian Prairies. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...Excessive Heat Watch from Thursday afternoon through Thursday evening for OHZ003-006>008-017-018-027-036. PA...None. MARINE...None. && $$ SYNOPSIS...Maines NEAR TERM...Griffin/Maines SHORT TERM...Jaszka LONG TERM...Jaszka AVIATION...Griffin MARINE...Jaszka
Area Forecast Discussion
National Weather Service Des Moines IA
1029 PM CDT Tue Aug 22 2023 ...Updated for the 06z Aviation Discussion... .DISCUSSION.../Tonight through Tuesday/ Issued at 300 PM CDT Tue Aug 22 2023 Key Messages: -Heat continues today through Thursday; Excessive Heat Warning in Effect -Potential for patchy fog Wednesday morning, mainly east Any signs of the fog and stratus that developed across the area this morning have all but dissipated, leaving only some low cumulus in the far southeastern portions of the state. With skies clear and the boundary layer mixing out early this afternoon, breezy winds have picked up and temperatures have quickly warmed. Most sites are now in the upper 80s to low 90s with associated dew points in the upper 70s to low 80s. Highs are expected to peak in the upper 90s this afternoon, resulting in heat index values well exceeding 110F. A few AWOS sites in west central Iowa continue to show erroneous dew point observations, which are resulting in unrealistic heat index values over that area. While temperatures will cool as the sun goes down, A/C units will have little time for recovery tonight as lows only reach the mid 70s to low 80s. With the amount of moisture present, it is possible we will see fog and stratus developing again in the early morning hours and lasting into the mid morning before burning off as the boundary layer mixes. Deterministic guidance isn`t overly bullish on this developing, but as mentioned in previous AFDs, the HREF seems to again be showing a weak signal in its low cloud probability product, hinting at another night of at least some stratus development. HREF fog probabilities show a slightly more eastern trend than last night, putting the most favorable area over east central and eastern Iowa. Our heat continues tomorrow, with this being the best chance for the area to reach triple digit temperatures. Soundings from the NAM, HRRR and RAP all show a deeply mixed boundary layer with strong south southwesterly flow resulting in hot and uncomfortable conditions at the surface. This will likely be the warmest day of the week, and potentially of the year so far, so it`s important to not become complacent with your heat safety precautions. Overnight temperatures tomorrow night and into Thursday will again be quite warm, with the low temperatures better resembling our normal high temperature for this time of year. Thursday`s temperatures become a bit trickier as the upper level ridge breaks down and a shortwave passes over the area. This will bring with it a cool front along the northern edge of the ridge, limiting high temperatures, especially in northern Iowa. Confidence is low on how far south this cool front will drop into the state and how soon this will occur. The recent trend in guidance has been cooler in the north for Thursday, suggesting a slightly earlier arrival of the boundary. Of course, the arrival of said cool front is not a cut and dry indicator of temperatures, as insolation and pooling moisture along the boundary may still result in uncomfortable conditions as it arrives. Therefore, if cloud cover can develop along the boundary, it is likely that the lack of insolation will allow the cold air advection to keep temperatures more comfortable. Conversely, lack of cloud cover may still result in 100+ heat indexes. With the trend in guidance towards cooler temperatures in the north, went ahead and slightly reduced high temperatures in these areas. However, due to differences in heat headline criteria between ourselves and surrounding northern offices, as well as the prolonged duration of hot temperatures, maintained collaboration by upgrading the excessive heat watch to a warning through Thursday. Confidence is low that these northern counties will reach the 105F criteria for our area but conditions will likely still be uncomfortable. The rest of the area south of the boundary will still be hot on Thursday with temperatures in the upper 90s and heat index values over 105F. Fortunately, some relief is on the horizon. As the cool front passes through the rest of the area Thursday night, high temperatures will become slightly more bearable on Friday. However, conditions still remain dry with only a slight chance for a few showers/storms as the boundary passes through early Friday. Soundings aren`t overly conducive for precipitation with a prominent warm nose and dry air still present aloft, keeping us dry through the end of the week and into the weekend. Highs will continue to fall towards more seasonal values through the weekend and into next week. && .AVIATION.../For the 06Z TAFS through 06Z Wednesday night/ Issued at 1024 PM CDT Tue Aug 22 2023 VFR conditions currently prevail across central Iowa. 03z observations have shown a general visby degradation as fog begins to develop once again within the abnormally humid environment. Model guidance suggests the highest chances to see categorical reductions will be in southeast corner of the forecast area including KOTM. Conditions may be a repeat of Tuesday morning which saw a few hours of visby down into IFR/LIFR. Elsewhere the potential for sub-VFR visby or even sct/bkn low clouds is much more uncertain. && .DMX WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 7 PM CDT Thursday for IAZ004>007- 015>017-023>028-033>039-044>050-057>062-070>075-081>086-092>097. && $$ DISCUSSION...Dodson AVIATION...Martin
Area Forecast Discussion
National Weather Service Green Bay WI
1037 PM CDT Tue Aug 22 2023 Updated aviation portion for 06Z TAF issuance .SHORT TERM...Tonight and Wednesday Issued at 250 PM CDT Tue Aug 22 2023 The latest RAP analysis and satellite/radar imagery show elevated showers and thunderstorms slowly exiting northeast Wisconsin early this afternoon. Meanwhile, temperatures have been slow to rise over many parts of northeast Wisconsin in part due to southeast winds, ample cloud cover, and positioned northeast of a warm front. This warm front was roughly located north of Minneapolis to the Wisconsin Dells to Madison at 19z. As this warm front surges northward, thunderstorm chances and excessive heat are the main forecast concerns through Wednesday. Tonight...The warm front will progress northeast and into far northern and northeast WI by 7 am Wednesday. Like last night, a 40+ kt low level jet is expected to develop and initiate convection, this time over the central Upper Peninsula from late evening into the overnight. Cloud layer flow will remain out of the northwest which would track any storms over far northern Door county. Small hail and locally heavy rain will be possible. The rest of the region should see mostly clear to partly cloudy skies and warmer conditions. Lows ranging from near 60 degrees in the northwoods to around 70 at Marshfield and Wisconsin Rapids. Wednesday...The warm front will stall over far northern Wisconsin for much of the day, placing the majority of the region in the warm sector. Under mostly clear skies, should have ample sunshine for very warm temps to occur before winds shift to the north late in the afternoon. Taking an average of 925mb temps puts highs in the mid to upper 90s over central and east-central WI. Combined with dewpoints in the low to mid 70s, heat indices of 100 too 110 look likely. Forecast highs have increased a degree or two in this forecast cycle, so will expand the excessive heat warning and heat advisory. The expiration time is not ideal, but matches neighboring offices headlines, and it can be canceled early. .LONG TERM...Wednesday Night Through Tuesday Issued at 250 PM CDT Tue Aug 22 2023 Warm and humid weather is likely Wednesday night as dewpoints remain in the 60s. Thursday will not be as hot as Wednesday, but will still be warm and humid over all but the north despite a northeast wind. An upper trough and surface cold front will move across the area Friday and bring a chance of showers and thunderstorms. There may be enough instability to get some strong or severe storms in the north where directional and speed shear are maximized. Cooler and drier weather will return for Saturday and Sunday as a large surface high moves in from central Canada. There may be enough of a northeast wind Saturday for small craft advisory conditions on the lake and bay. && .AVIATION...for 06Z TAF Issuance Issued at 1024 PM CDT Tue Aug 22 2023 Low clouds have filled in along and north of Hwy 29 this evening, with most locations showing a mix of MVFR and VFR ceiling heights. The clouds were forming north of a warm front, which was situated in central WI. Scattered thunderstorms could brush through northern Door County during the overnight hours, but it is looking more likely that storms will stay northeast of the forecast area. The main aviation concerns will be low cloud/fog/LLWS trends overnight into Wednesday morning. Have gone more pessimistic with the coverage of low clouds overnight, and trended slower with the erosion of the clouds as a warm front shifts north on Wednesday. It looks like a good bet that the front will not make it all the way through the forecast area, so low clouds will probably persist over far northern WI through the day. The main question is how low the ceilings will get overnight, as most observing sites were reporting ceilings in the 2500-3500 ft agl range late this evening. Still think ceilings may drop to IFR over northern WI, and that at least patchy fog will form there as well. Improvement to VFR may not occur until early Wednesday afternoon at the RHI TAF site. The warm front will retreat to the south as a cold front Wednesday evening, which should allow low clouds to make a southerly push again later in the TAF period. LLWS is expected to expand eastward during the overnight hours, as a SW-W low-level jet increases to 35 to 40 knots. The LLWS should wane early Wednesday as the low-level jet weakens. && .GRB WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 10 AM to 9 PM CDT Wednesday for WIZ020-030- 031-037>040-049-050-074. Beach Hazards Statement from 7 AM CDT Wednesday through Wednesday evening for WIZ022-040-050. Excessive Heat Warning from 10 AM to 9 PM CDT Wednesday for WIZ035-036-045-048. && $$ SHORT TERM.....MPC LONG TERM......RDM AVIATION.......Kieckbusch
Area Forecast Discussion
National Weather Service Grand Rapids MI
950 PM EDT Tue Aug 22 2023 LATEST UPDATE... Update .UPDATE... Issued at 949 PM EDT Tue Aug 22 2023 A complicated forecast remains for Wednesday. Strong elevated instability on the periphery of a building upper ridge and nose of a 45 kt LLJ (underneath a well-positioned right entrance region of the upper level jet) will help initiate clusters of thunderstorms across northern Lake Michigan and northern Lower Michigan very early Wednesday morning. Numerical model guidance so far has fallen into two camps: 1) A NW/SE oriented line of thunderstorms east of US 131 from around 09z to 13z or so, and 2) A W/E oriented line of storms that drops due south through the northern 2/3rds of our forecast area roughly during the same time period. Either solution is plausible, though a slight favoring is given to the first scenario given how well the HRRR handles convection and how consistent it has been showing a more arching complex of storms during the 09z-13z time frame across the eastern 1/2 of our CWA. These may produce locally 1"-2" (or more) of rainfall into mid morning along with large hail. With either scenario, a rain-cooled outflow from these storms may impact much of our region even for areas that don`t receive rain (ie. look at the 00z HRRR sfc T from 12z-15z). The effect this would have is to both delay the arrival of the heat across our Heat Advisory area and shorten its duration today, with a focus on hazardous heat mainly after 2pm and especially toward late afternoon/evening. If storms trend even slower and further west than currently indicated, the heat may take even longer to get here, but once it does, the heat index readings are shown to abruptly reach into the low 100s by late afternoon across the Advisory area. A few storms could manage to fire Wednesday evening/night but more likely this will occur across SE Lower Michigan. Still, there is some upper divergence east of US 131 from 00z-06z Thursday and a LLJ of around 40 kts will be overhead, with best low level convergence across SE Lower Michigan. && .SHORT TERM...(This evening through Wednesday night) Issued at 325 PM EDT Tue Aug 22 2023 -- Possibly severe storms overnight with heavy rain -- Thunderstorms continue to be expected for areas mostly north of I-96 overnight with the severe threat decreasing as one moves from north to south. This notion is supported both by NBM guidance and by the 22/12Z HREF 24 hour ensemble maximum updraft product available on SPC`s web page. This maximum updraft area coincides with WPC`s excessive rainfall marginal risk area. As mentioned previously, severe thunderstorm hazards would lead with hail, especially early if the storm mode remains relatively discrete into our northern zones as suggested by the convection allowing models. A full blown MCS is expected to blossom upscale, but models are quite consistent with weakening this feature towards the morning hours as it dives southward. This makes sense given that we expect an eastward directed and persistent low level jet over northern Wisconsin overnight. As the MCS moves away from this low level forcing and becomes increasingly parallel to the lower tropospheric flow, this will reduce the severe threat considerably but locally heavy rain will continue to be a concern. -- Oppressive heat and diminished air quality Wednesday -- A heat advisory is still planned for much of the forecast area Wednesday. With the heat and significant incoming shortwave radiation comes elevated ozone production. Please refer to the Department of Environment, Great Lakes, and Energy website for further details. -- Low chances for severe storms Wednesday afternoon/evening -- HREF mean MUCAPE forecasts indicate a plume of 3500-4000 J/kg instability poking into our western forecast area Wednesday afternoon. However, near surface flow along with an ill-defined low level jet both look slightly divergent and this will be accompanied by continued capping from a hybrid subsidence/EML inversion. Given less than optimal conditions for storms, we have carried relatively low (20 percent) PoPs for this time - but as noted previously, the conditional threat for severe weather remains relatively high with all of the possible hazards being possible if any storms do manage to develop. .LONG TERM...(Thursday through Tuesday) Issued at 325 PM EDT Tue Aug 22 2023 Some changes are in the offing. The strong upper ridge over the Central U.S.-- responsible for numerous high temperature records to the west/south of Michigan -- will steadily break down and retreat to the west late this week. While the ridge will bring more heat/humidity to West Michigan Thursday, the repositioning of the upper ridge will allow northwest flow aloft to develop and this will result in cooler and much drier weather this weekend into early next week. -- Heat and humidity continue Thursday -- A fair amount of uncertainty surrounds Thursday`s forecast, particularly as it pertains to thunderstorm chances and heat. Models suggest we start the day with a west-east front draped across Lower Michigan. Weakish large-scale forcing may be provided by mid level impulses dropping into the region from the WNW /which will also serve to flatten persistent upper ridge just to our west/. The low level air mass will remain quite moist, and models support MLCAPEs in excess of 2k J/kg. However, with very warm mid level air mass centered in the vicinity of 800-700 mb, we may remain capped off entirely to deep/moist convection in spite of moisture and instability. Best chances for mainly late day storms will be over western and northern parts of forecast area. As for the heat -- with surface dew points still likely to be in the 70s, if we can realize enough sunshine to reach/exceed 90F, Heat Advisory criteria may once again be a factor for Thursday for areas south of a Grand Haven to Lansing line. Heat indices in these areas may near 100F Thursday afternoon. -- Cooler air arrives this weekend -- Thursday`s surface front will drop south of the area by Friday, as a stronger short wave aloft approaches the Great Lakes from the NW late Friday. This is expected to supply scattered showers late Friday into early Saturday. High pressure will then drop into the upper Great Lakes by late Saturday and Sunday. This will result in sunshine, daytime highs in the low-mid 70s, and nighttime lows in the mid 40s to lower 50s for Saturday, Sunday, and Monday. Enjoy. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 632 PM EDT Tue Aug 22 2023 Primarily VFR conditions are expected at all the terminals through 00Z Thur. However there are potential caveats in the forecast late tonight into Wednesday morning when there is potential for a line of strong thunderstorms to move in from the nnw. Considerable uncertainty in thunderstorm evolution still exists but if storms materialize and hold together into the early morning hours they could bring brief LIFR/IFR conditions in heavy rain and potential for some gusty winds and hail. Any convection should move out of our area by mid to late Wednesday morning and be followed by a return to VFR conditions for the late morning and afternoon hours. Any convective redevelopment later tomorrow would likely hold off until after 00Z Thur. && .MARINE... Issued at 325 PM EDT Tue Aug 22 2023 Will be issuing a small craft advisory and beach hazards statement starting tonight and lasting at least into Wednesday afternoon. Guidance suggests a corridor of strong southeasterly flow developing ahead of a thunderstorm complex overnight. Although that direction is not favorable for nearshore wave growth, speeds could be quite substantial. Then, the background flow veers around to more of a southwesterly direction by Wednesday afternoon, allowing for robust wave growth across all but our southernmost marine zones. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from 8 AM EDT Wednesday through Wednesday evening for MIZ037-043-050-056. Heat Advisory from noon Wednesday to 2 AM EDT Thursday for MIZ056-057-064-065-071>073. LM...Small Craft Advisory from 8 AM to 11 PM EDT Wednesday for LMZ846>849. && $$ UPDATE...Hoving SHORT TERM...TJT LONG TERM...Smith AVIATION...Laurens MARINE...TJT
Area Forecast Discussion
National Weather Service Spokane WA
228 PM PDT Tue Aug 22 2023 .SYNOPSIS... Rainfall from Hilary brought beneficial rains to the region this morning and afternoon. A few more hours of light precipition is in store for Eastern Washington and the Idaho Panhandle. Warmer than normal temperatures return late this week and shower chances on Friday. && .DISCUSSION... Beneficial rains have mostly come to an end in the Spokane area. Any heavy rain activity will be confined to the northern mountains and Southeast WA and the Southern Panhandle. There is still a 20% chance of measurable rain through this evening in Spokane County, but we will rapidly dry out overnight. The rain cooled air mass has kept it incredibly cool with Spokane airport measuring 59 degrees at 1 pm. Heavier showers and thunderstorms have blossomed in the Blue Mountains and moved northeast into the L-C Valley. Am monitoring the flash flood threat there as we have discovered how vulnerable they can be when PWAT anomalies are around 200%. A couple storms have moved over it but they are moving fast enough where training storms are the larger concern. Will quickly dry out tonight. Tomorrow will bring elevated fire weather conditions with breezy southwest winds with the passage of the trough offshore the WA coast. There will be no red flag conditions but ongoing fires (especially in the North Cascades and Canada with fires that did not receive rain) could become more active. /Butler Thursday through Tuesday: A low pressure system will move out of the Gulf of Alaska and sit off the Pac NW coast through the weekend. It will merge with a low off the CA coast and that wave gets pushed into the Pac NW on Friday. We will continue to see temperatures warm each day through next Monday. Temperatures will be 10 to 15 degrees above average for the end of August. Valley readings in the mid 80s to near 100 are expected for the weekend. Winds will generally be under 15 mph through the period. There will be a northerly push down the Okanogan Valley and onto the Waterville Plateau Thursday morning, and then more widespread north to northeasterly winds on Friday morning and early afternoon. Friday as the wave from California moves into the region we will see an increase in clouds with a 20-40% chance of precipitation region wide. Convection still looks to be confined from the Blue Mountains to about Lookout Pass. Uncertainty comes into the forecast come next Monday and Tuesday with what to do with the low off the coast. 30% of ensemble models suggest by Tuesday the low moving onto the west coast. Chance of precipitation begins to enter the forecast beginning Monday and continues through Tuesday. Even though there is high uncertainty on the timing of the trough moving in, the impacts have the potential to be high, with dry and windy conditions and a chance of thunderstorms if it moves through during the afternoon. /Nisbet && .AVIATION... 18Z TAFs: Rain intensity for KGEG-KSFF-KCOE-KPUW will wind down over the next 6 hours. Heavy rain will bring down visibility and ceilings for a few hours this afternoon at KLWS. A return of smoke from the HRRR smoke model will filter in from the southwest Wednesday with breezy winds. /Butler && .PRELIMINARY POINT TEMPS/POPS... Spokane 52 77 48 82 53 87 / 10 0 0 0 0 20 Coeur d`Alene 53 75 48 82 54 87 / 30 10 0 0 0 10 Pullman 48 75 43 80 49 81 / 50 0 0 0 0 40 Lewiston 63 81 56 89 61 88 / 70 10 0 0 0 40 Colville 41 76 38 81 42 88 / 10 10 0 0 0 10 Sandpoint 49 74 44 79 50 84 / 20 10 0 0 0 10 Kellogg 58 73 51 80 57 86 / 50 10 0 0 0 20 Moses Lake 51 79 48 84 59 86 / 0 0 0 0 0 30 Wenatchee 58 80 55 83 63 84 / 0 0 0 0 10 30 Omak 55 80 52 85 58 89 / 10 10 0 0 0 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Flood Watch until 11 PM PDT this evening for Central Panhandle Mountains-Idaho Palouse-Lewis and Southern Nez Perce Counties-Lewiston Area. WA...Flood Watch until 11 PM PDT this evening for Lower Garfield and Asotin Counties-Northeast Blue Mountains. && $$
Area Forecast Discussion
National Weather Service Raleigh NC
1033 PM EDT Tue Aug 22 2023 .SYNOPSIS... A backdoor cold front will settle south and across the Carolinas tonight. Canadian high pressure will briefly follow and extend across the middle Atlantic and Carolinas Wednesday into Thursday. && .NEAR TERM /THROUGH TONIGHT/... As of 1030 PM Tuesday... The anomalously strong mid/upper ridge will continue to be centered to our west over MO tonight. At the surface, 1023 mb high pressure is currently centered over the eastern Great Lakes region, while a backdoor cold front extends from the NW Piedmont into the Sandhills. The front will continue to move SW, clearing all of central NC in the next couple of hours. Ahead of the front, winds are mainly calm, but behind it, they are northeasterly and there are isolated gusts to 15-20 kts. Brought down forecast gusts a bit given their very sporadic nature, and they will diminish from NE to SW overnight. Otherwise, isolated light to moderate showers continue to move south across the central and southern Coastal Plain, with another area around the Triad, coincident with a band of low-level moisture convergence along and just behind the front. Thus extended POPs farther west in the Piedmont to account for this. It has been difficult finding any stations reporting measurable rain, and latest radar trends show diminishing returns. The last several runs of the HRRR also backed off on the higher totals. So any rainfall amounts are expected to be light, less than a tenth of an inch, and POPs are still only in the slight to low chance range. Lower dew points behind the frontal passage are a bit delayed, but NE flow will eventually advect cooler and drier air into the region overnight, as is evident by the lower-to-mid-50s dew points currently observed at KHNZ and south-central VA. Low temperatures will range from lower-60s NE to lower-70s SW. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 355 PM Tuesday... Nly to nwly mid/upper-level flow, and accompanying periods of mostly thin mid/high-level cloudiness, will be directed across cntl NC and around a weakening mid-latitude anticyclone that will drift across MO and into the Ozarks. It should otherwise be mostly sunny/clear after a band of lingering stratus/stratocumulus drifts swwd and out of the srn NC Piedmont around sunrise Wed. At the surface, Canadian high pressure will build across and offshore the Northeast and middle Atlantic, while extending swwd across the Carolinas. The presence of this ridge will result in markedly cooler and drier air (than recent days), with forecast high temperatures of 83 to 89 F and with afternoon surface dewpoints mostly in the low-mid 50s. Some upr 40s will not be out of the question based on upstream conditions over n-cntl VA, where surface dewpoints in the mid-upr 40s have been observed this afternoon. Calm or nearly so will then favor strong radiational cooling of the fresh continental/Canadian airmass, with low temperatures mostly in the lwr-mid 60s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 255 PM Tuesday... The high pressure aloft centered over the Midwest Thu will slowly retreat westward to over the Four Corners through early next week. Several shortwaves will ride the periphery of the upper level ridge. The initial wave should clip or skirt just NE of the area on Thu. However, as the high retreats westward, the subsequent waves will have a greater impact on central NC. Expect a return to diurnally driven convection coincident with passing shortwaves aloft Fri to Sun. For now, it appears central NC will be sandwiched between the ridge to the west and the trough to the NE Fri and Sat, with the trough becoming dominant and extending into the region Sun/Mon. Forecast confidence decreases beyond Mon owing to increasing differences in the medium-range model solutions. At the surface, the ridge extending SW through the area from a high off New England should shift offshore Thu/Thu night. Meanwhile, a low will trek eastward through the OH Valley/southern Great Lakes and into the Northeast. A trough will set up over the area on Fri, with a return to more southerly flow across central NC. The trough should remain in place Fri night, and Sat before a cold front slides into the area Sat night/Sun. As mentioned earlier, medium-range guidance really begins to diverge Sun/Mon, with low confidence in the forecast beyond that point. Temperatures: Temperatures should generally be 3-6 degrees above normal Thu/Thu night, highs in the upper 80s/low 90s and lows upper 60s/low 70s. Still expect Friday to be the hottest day, with highs ranging from mid 90s to low 100s. Heat index values could approach Heat Advisory criteria (105) in several places Fri afternoon. Not a whole lot of relief Fri night, with lows only dipping into the low to mid 70s. Continued hot on Sat, highs in the 90s, around 90 along the VA border to near 100 along the SC border. Heat Index values topping out in the 100-104 degree range again Sat. Temperatures should then fall closer to normal Sun and near to below normal on Mon. Precipitation: While an isolated shower or two cannot be ruled out along the VA border on Thu, will keep the forecast dry for now. Chances for and coverage of aft/eve showers and storms increase from Fri to Sun, with the chances persisting into early next week. && .AVIATION /2330Z TUESDAY THROUGH SUNDAY/... As of 730 PM Tuesday... A cold frontal boundary is slowly sagging south through central NC and currently stretches from west of TDF (Person County), just west of KRDU to Newton Grove/Mount Olive area and is identifiable as a radar fine-line. Immediately behind the fropa, fleeting scattered light showers and isolated moderate showers have been observed and are expected to continue through the late evening, which is supported by Hi-Res guidance. Some guidance shows showers increasing in intensity in the vicinity of FAY after the fropa leading to a chance (30%) for light/moderate rain near FAY. This threat is captured with a VCSH from 3-8z, but if confidence increases, a prevailing SHRA and lower cigs/vsby to low-MVFR to near IFR may be introduced. Otherwise, behind the fropa, a brief period of ENE winds, gusting up to 17-18kts, will be possible at all TAF sites before subsiding with boundary-layer stabilization. Drying behind the front will bring VFR conditions and light NE winds, 5-10kts, heading into Wednesday. -Swiggett Looking beyond 00z Thursday, the influence of high pressure and dry/continental air over NC will favor prevailing VFR conditions through at least early Fri, followed by a chance of showers/storms as a front settles across the region late Fri into the upcoming weekend. -MWS && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...Danco SHORT TERM...MWS LONG TERM...KC AVIATION...Swiggett/MWS