Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/19/20

Area Forecast Discussion
National Weather Service Amarillo TX
633 PM CDT Tue Aug 18 2020 .AVIATION... VFR conditions expected for the 00Z TAF period. Winds will range between southeasterly and southwesterly between 5-15 kts throughout the TAF period with sct mid level clouds. Meccariello && .PREV DISCUSSION... /Issued 201 PM CDT Tue Aug 18 2020/ SHORT TERM...Today through Tomorrow Night... High pressure remains anchored over portions of NV/UT/AZ/CA with northwest to northerly flow spreading across the Rocky Mountains and adjacent plains, becoming more northeasterly flow over the Panhandles. Several minor perturbations can be identified on the latest GOES water vapor imagery, with the most notable wave moving southeast into northeast NE. At the surface, weak southerly winds were evident across the Panhandles with few clouds as temperatures were rising into the low 90s. The eastern zones had dew points around 60, with upper 40s dew points in the west. Instability was very limited across the area with forecast RAP soundings indicating too much dry air and unfavorable mid level temperatures. Thus, dry conditions are expected today. For tonight, a subtle 600mb to 400mb wave moves down the northernly flow with 250mb speed max extending from eastern SD to south central KS. Progged soundings and 700mb theta-E output indicated an increase in moisture from northwest to southeast just ahead of the wave. 850mb Theta-E fields stay fairly dry through tonight, but there may be just enough elevated lift and moisture to kick off a few showers mainly rooted around 500mb in the northeastern zones after 06z. While there is some elevated instability, it is very limited; with values on the order of 200 J/kg. Moreover, while a few thunderstorms can`t be ruled out, most of the activity will remain showers, and these showers may linger into Wednesday morning in the eastern zones. Better 700mb to 400mb moisture will be in place Wednesday afternoon as northeast flow aloft becomes more northwesterly. This helps induce stronger lee troughing and better return flow near the surface, while mid level winds also increase in response to another subtle mid level wave. With more moisture being in place and better timing, this wave should support a few thunderstorms in the area by mid afternoon into the overnight period. Mixing is also expected to be sufficient so that convective temperatures may be reached, further aiding isolated storm development in the afternoon (esp. for southern zones). However, models do suggest the cap may be fairly strong tomorrow, and this should limit convective coverage. Any storms that do form will have about 800 to 1200 J/kg MLCAPE to work with, with LCL heights mixing to around 2000 to 3000m. Therefore, wind would seem like the primary threat given the high bases expected (DCAPE 1000-1500 J/kg). That being said, wind fields tomorrow are better than they have been in some time with plenty of directional shear progged. Effective bulk shear of around 50 knots will be possible across the central and eastern zones, with 40 knots across the west in the afternoon and evening. 0-3km helicity increases to around 300 m^2/s^2 in the evening supported by a modest low level jet. Thus, if storms can overcome the cap and become surface based, high based supercells will be possible. The high LCL values and relatively lacking 0-1km shear suggest tornadoes are unlikely, however landspouts can`t be ruled out near any outflow boundaries. Any rotating storm could produce both large hail and damaging winds. Storm activity should diminish a few hours after dark, but could see some lingering activity shift into the southeast zones depending on timing of upper wave and low level jet. Ward LONG TERM (Thursday through Monday)... The long term will be noted by convection developing off the higher terrain and potentially moving into the Panhandles by the evening hours of both Thursday and Friday. Otherwise, confidence for precipitation into the weekend and next week looks low, albeit not necessarily zero chances. Temperatures are also seasonable in the long term ranging from the lower to upper 90s, but a couple days we will be flirting with triple digits for a few areas. High pressure will slide south/southeast and become more centered over the Desert Southwest by Thursday. This may provide us with more of a northwesterly flow pattern aloft as noted at 700 mb, resulting in better convection off the mountains impacting the Panhandles. However, the flow at 500 mb is more northerly which may lend to less favorable chances across the Panhandles. Chances for diurnally initiated convection to form off the mountains Thursday and Friday are looking favorable, but the question is whether or not the steering flow aloft will allow those thunderstorms to travel into the Panhandles by the evening. Forecast soundings suggest a potential 40-50 knot low level jet (Clayton - 50kts | Dalhart - 40kts) which could further enhance our chances into the overnight hours (9pm to 2am). For now, it does look like the western half of the forecast area will have at least a small chance (20-30%) for thunderstorms in the evening hours. Severe weather chances do not look all that likely (weak sheer, low CAPE, limited forcing), but given the inverted-v soundings we could certainly have some strong wind gusts if we can tap into some monsoonal moisture aloft (potentially increased by hurricane Genevieve). The wind field also suggest the storm motion would be slow around 10-20 mph Fri/Thur evenings. Beyond Friday, the steering flow aloft does not look favorable for thunderstorms to impact the Panhandles. Upper level pattern suggests we could be under northerly/northeasterly flow which would hinder our thunderstorm chances. That said, we will have to watch the position of the upper level high out to our west as we progress into the weekend. Guerrero && .AMA Watches/Warnings/Advisories... TX...None. OK...None. && $$ 29/36
Area Forecast Discussion
National Weather Service Bismarck ND
924 PM CDT Tue Aug 18 2020 .UPDATE... Issued at 924 PM CDT Tue Aug 18 2020 Radar suggests isolated showers over southwest North Dakota. Despite high cloud ceilings, a couple showers in Hettinger County now appear strong enough that rain is likely reaching the ground. This activity appears to be in response to weak mid level forcing possibly interacting with a N-S oriented surface dryline along and east of Highway 22. There does not appear to be enough instability this far west for thunder. Have added a slight chance of showers to most areas south and west of the Missouri River through 1 AM CDT. The rest of the forecast remains unchanged. UPDATE Issued at 821 PM CDT Tue Aug 18 2020 As of this writing, no convection has initiated and it appears increasingly unlikely that it will with increasing CIN. One possible exception may be in an area to the south and west of Devils Lake, where satellite shows an area of altocumulus clouds expanding in coverage with subtle upstream mid level energy barely evident on water vapor. We have trimmed back PoPs to just include a slight chance of thunderstorms from the Devils Lake Basin southward through the James River Valley and adjacent areas through the night. Sky cover was also increased over southwest North Dakota based on current trends. UPDATE Issued at 622 PM CDT Tue Aug 18 2020 Convective initiation is starting to look more unlikely. Most CAMs have trended away from any thunderstorms developing, and recent RAP soundings suggest CIN will not sufficiently erode. The just- launched 00Z Bismarck RAOB also shows mixed layer capping. The 18Z NAMNest does still show some potential in the James River Valley around 8-9 PM, so will leave a slight chance mentioned. If a storm does develop, the environment remains favorable for a conditional severe threat. && .SHORT TERM...(This afternoon through Wednesday night) Issued at 211 PM CDT Tue Aug 18 2020 Temperatures have been coming up a bit quicker than initially thought this afternoon, and with Medora and Beach already seeing observed temperatures of 97 thus far, think it is likely that we will see a handful of sites in the low 100s before all is said and done. The heat, along with dewpoints in the mid 30s to mid 40s across the far west, has led to very dry and near critical fire weather conditions. The good news is that winds should remain fairly light here through the afternoon, generally 10 to 15 mph with gusts up to 20 mph. The other story for this afternoon and evening will be thunderstorm chances across the central and southern James River valley. There will be a nice overlap of 35 to 45 knot effective shear and moderate to strong instability, but the question of sufficient forcing to break the cap still remains. A stationary/pseudo warm front is currently just east of the Highway 83 corridor, drifting east slowly. While this boundary may serve as the focus for a few updraft attempts this afternoon, it remains unclear whether we will see enough convergence at the surface to actually get storms. If updrafts are able to sustain themselves and break through the cap, a conditional severe weather threat still remains. It is worth noting that CAMs continue to show little, if any, development this afternoon or evening. Later on tonight, a better chance for showers and thunderstorms looks to be possible across the southern James River valley as another subtle wave rides down the ridge on the nose of stronger warm air advection. It isn`t out of the question that one or two of these storms could become strong to severe. Wednesday will be another hot day with widespread highs in the mid to upper 90s. The western third of the state will once again be very dry with minimum afternoon relative humidity values in the 15 to 20 percent range. Thus, near critical fire weather conditions will be likely again Wednesday afternoon, but winds will be light. Another wave will bring slight chances of thunderstorms to the west and north central Wednesday evening and overnight. With meager instability and shear forecast, severe weather is not anticipated with this activity. .LONG TERM...(Thursday through Tuesday) Issued at 211 PM CDT Tue Aug 18 2020 Another wave moves through on Thursday with chances of thunderstorms starting across the southwest in the afternoon and moving into the central overnight. Instability and shear may be sufficient for a strong storm or two in the far southwest but widespread severe is unlikely. Another chance for some isolated to scattered strong storms looks possible on Friday across the central and James River valley as these subtle waves keep trying to flatten the ridge. A slight cool down and mainly dry weather comes into the picture over the weekend, but highs will still remain above average for most. The global models agree that broad troughing will begin to setup across the western CONUS by the end of the weekend and beginning of next week, which suggests a possible uptick in thunderstorm activity next week. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 622 PM CDT Tue Aug 18 2020 VFR conditions and light winds are expected through the forecast period. There is a very slight chance of a thunderstorm near KJMS this evening and tonight. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Hollan SHORT TERM...ZH LONG TERM...ZH AVIATION...Hollan
Area Forecast Discussion
National Weather Service Caribou ME
922 PM EDT Tue Aug 18 2020 .SYNOPSIS... A cold front crosses the waters this evening. High pressure slowly builds in Wednesday through Thursday. Low pressure approaches the region Friday and Saturday. && .NEAR TERM /THROUGH WEDNESDAY/... 915 PM Update: Stronger showers and isolated thunderstorms have continued a little longer than even what CAMs are showing, so I xtnded the mention of isold tstms another hr or two into late eve, thinking that this current activity may be the last of stronger cnvctn before dissipating ovr the next few hrs. Otherwise, latest avbl mid eve sfc obs were used to make adjustments to fcst hrly values of temp/dwpts into the late ngt with, again, no sig chgs to fcst ovrngt lows needed attm. Prev Disc: Showers w/isold tstms into early evening as upper trof interacts w/the slow moving frontal boundary. The strongest storms will be across the Maine Central Highlands into the Bangor and Interior Downeast region. Some of the storms could contain hail and strong wind gusts. Sounding data coming in from the RAP and NAMNEST showed 0-6km shear around 40 kts w/MU CAPE climbing to near 1000 joules. Lapse rates are steepening allowing for good updrafts to keep storms going. Heavy rainfall also a threat w/PWS around 1.25". Further n, threat is less as the atmosphere has been worked over earlier rain. However, radar and satl lightning imagery showing storms in Quebec pushing east. Not ruling out the potential for some tstms, but potential is not as high as it is further s. Looking for activity to wind down later in the evening as the forcing weakens w/the upper trof pushing e. Expecting some partial clearing later in the evening into the overnight hrs. SSW winds less than 10 mph to become W w/speeds about 5 mph or. Will go ahead and add some patchy fog in for overnight. Cooling down w/overnight temps dropping into the 50s. An upper trof in conjunction w/a sfc trof will be the focus for some showers across northern and western areas on Wednesday. Lapse rates are forecast to steepen during the day w/some sfc heating. So, cumulus will pop but question is the extent of the cloud tops. Given that moisture above limited to below 700mbs, decided not to mention tstms. Plus CAPE is forecast to be less than 100 joules. The NAM and GFS support this setup. W winds are expected to pick up by the afternoon at 10-15 mph. This will aid in drying things out. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... The exit of low pressure to the north appears to take place quicker, and thus the core of breezy winds will pass to the north of the CWA Wednesday night. With stable air overnight, little of these winds will actually mix down. Exception will be higher terrain in the Central Highlands where gusts to 35 mph may be possible. The quicker departure means lighter winds Thursday afternoon as well. Thus, while RH values will still be lower in the afternoon, decent widespread rain today and lighter winds means conditions for elevated fire danger are less likely than previously forecast. A sustained breeze around 10 mph will still keep a drying trend through Thursday afternoon. NW flow becomes W as low levels couple with a zonal jet through Friday. High pressure to the south will build return flow across the region as broad low pressure advances from the west. The system will lack much moisture as southern sources are cut off, so have kept shower PoPs lower through the day Friday. Cloud cover across the north will again keep temperatures cooler in the mid-70s && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... The extended continues to feature uncertainty in regards to location of moisture and forcing. What is of higher confidence is mentioning the slight chance for rain showers through the weekend. Moisture will be in vicinity of the region, and diurnal heating should be able to kick of some scattered showers during the morning and afternoons, especially across the north. Canadian has now taken an approach similar to the ECMWF, creating a weak boundary across central New England, back across the northern Great Lakes. This will slowly slide south through the weekend. Northern stream moisture, while limited, will continue to spread into northern New England into early week. Zonal flow remains aloft as surface low pressure intensifies near the Great Lakes and tracks towards New England towards Tuesday. This would likely bring warmer temperatures into the region ahead of it, with cooler air into mid-week. && .AVIATION /22Z TUESDAY THROUGH SUNDAY/... NEAR TERM: Some IFR/MVFR across the terminals into the evening. Some tstms are expected mainly KBGR and KBHB airfields. SSW winds 5-10 mph. Improvement later in the evening into the overnight w/VFR. The exception to this will be across KFVE for MVFR cigs. Some MVFR and perhaps IFR overnight into early morning w/fog. Wednesday...Basically VFR for all terminals after some MVFR/IFR for patchy fog. W winds increasing to 10-15 mph. SHORT TERM: Wed night: Variable conditions between MVFR and VFR at the northern terminals from KPQI north in clouds and showers with VFR expected after midnight. VFR expected from KHUL south to KBHB. Breezy W winds diminish during the evening. Thu & Thu night: VFR, gusty WNW winds picking up in the morning through afternoon. SW near/along the Downeast coast. Winds slacken in the evening and overnight. Some showers across the north. Fri and Fri night: MVFR possible at the northern terminals, but timing is highly uncertain. Some rain showers possible. VFR should continue Downeast. Showers increase in coverage overnight. Sat and Sun: Variable conditions between MVFR and VFR in possible showers at the northern terminals during the afternoons. VFR expected Downeast. && .MARINE... NEAR TERM: Below SCA criteria right into Wednesday. S wind becoming SW tonight at 10 kt. Some fog is possible over the waters. SW winds becoming W on Wednesday and increasing to 10-15 kts. Seas to remain at 2-3 ft. SHORT TERM: Waves 2 to 3 feet through Friday. Winds remain below SCA criteria, but approach 25 kt Thursday afternoon from the SW. Winds slacken through Thurs night. Waves build 3 to 4 ft over the weekend as low pressure passes north of the waters. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...None. MARINE...None. && $$ Near Term...VJN Short Term...Cornwell Long Term...Cornwell Aviation...VJN/Cornwell Marine...VJN/Cornwell
Area Forecast Discussion
National Weather Service Charleston SC
955 PM EDT Tue Aug 18 2020 .SYNOPSIS... A weak cold front will stall over or near the region tonight. This stationary front will remain over the region and gradually weaken into the weekend. High pressure is then expected to prevail early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... As of 950 PM: I will update the forecast to remove headlines for the Coastal Flood Advisory. Residual rain remains across extreme SE GA and offshore waters. The showers should gradually dissipate by midnight. I will update temperatures to align with recent observations. As of 830 PM: The forecast area has been generally worked over with convection this afternoon and evening. The remaining convection appears limited to the marine zones off of SC coast and just south of the Altamaha River. It appears that the ongoing convection will continue through the rest of this evening. Late tonight, HRRR indicates that a few showers and thunderstorms will linger off the coast, mainly dry over land. Convection is expected to increase offshore during the pre-dawn hours as a disturbance approaches from the south. Previous Discussion: This evening and tonight: The initial convective cluster developed across Candler, Jenkins, Bulloch, and Screven counties. That cluster has thrown out a nice outflow boundary that is progressing eastward and should continue to kick off new updrafts as it moves. Further east, the sea breeze is initiating along the Charleston County coast and is starting to move to the east within the broader steering flow. SPC mesoanalysis shows 1,000-1,200 J/kg of DCAPE across much of the area, so there will be the potential for strong wind gusts. The main convective cluster was producing 40-50 knot on base velocity data, indicative of the wind potential in this environment. We could need a few more Severe Thunderstorm Warnings before storms weaken later this evening. Also of note, we will have to monitor convective trends later this evening around the time of high tide (~8:20 pm) for possible fresh/salt water flooding issues in Downtown Charleston. Once the diurnal activity weakens later this evening we should see a lull before possibly seeing isolated to scattered showers and thunderstorms late tonight. Models seem to favor the South Carolina coast and the Charleston Tri-County for this possible late night activity. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Moderate confidence this period. The area will remain between troughing to the west and ridging to the east which will keep abundant moisture and periodic upper-level forcing in place. Combine these factors with mesoscale boundaries from the sea breeze and convective outflows and the result will be higher than normal rain chances, mainly each afternoon/evening. Deep layer shear could increase a bit the next several days but still be fairly marginal to support much severe weather, however isolated instances of damaging winds certainly cannot be ruled out. Temperatures should remain near to slightly above normal. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... The mid-level trough over the Lower Mississippi Valley Friday night will weaken through the weekend. Meanwhile, high pressure in the Atlantic will gradually shift towards the Southeast U.S. early next week. At the surface, the stationary front over or just west of our area will dissipate this weekend, with Atlantic high pressure approaching the coast. Sea breeze convection will be possible each afternoon/evening. Though, coverage should be at or just below normal. Temperatures will be near normal. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... The forecast area has been generally worked over with convection this afternoon and evening. Expecting VFR conditions overnight at KCHS and KSAV. Convection is expected to increase offshore during the pre-dawn hours as a disturbance approaches from the south. This activity is expected to spread over KCHS between 15-18Z, highlighted with a TEMPO. Extended Aviation Outlook: Occasional flight restrictions are possible in showers and thunderstorms, especially during the afternoon and evening hours. && .MARINE... Tonight: Winds along the land/sea interface will peak in the 10-15 knot range this evening and then should steadily drop off to 5-10 knots late tonight. Seas will average 2-3 feet. Mariners should monitor conditions through the evening for thunderstorms approaching and moving into the local waters, capable of producing strong wind gusts. Wednesday through Sunday: Moderate to high confidence this period. A stationary front will remain inland the next few days, gradually weakening into the weekend. High pressure is then expected to prevail early next week. Expect backing winds to the south/southeast each day near the coast along with some higher gusts due to the sea breeze. At night, winds should veer more southwesterly as the land breeze and nocturnal jet form. Conditions overall should remain below Small Craft Advisory levels but mariners can expect gusty winds in/near thunderstorms, and the potential for isolated waterspouts to form along the land breeze each morning. && .TIDES/COASTAL FLOODING... For the evening high tide, current tidal departures are running around 0.8 ft and we should be on track for the Charleston Harbor to peak around 7.3 ft MLLW. A Coastal Flood Advisory has been issued for high tide around 8:20 pm. Astronomical contributions from the new moon and perigee will result in elevated tides (the Perigean Spring Tides) through the week. At least minor coastal flooding and associated Coastal Flood Advisories will be possible around the times of the evening high tides through at least Thursday, and especially along the South Carolina coast. If heavy rain coincides with these elevated evening tides, significant flooding could develop in some areas, especially in downtown Charleston. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED SHORT TERM...RJB LONG TERM...MS AVIATION...NED MARINE...BSH/RJB TIDES/COASTAL FLOODING...
Area Forecast Discussion
National Weather Service Cheyenne WY
545 PM MDT Tue Aug 18 2020 .SHORT TERM...(This evening through Thursday night) Issued at 128 PM MDT Tue Aug 18 2020 Tonight...The HRRR model suggests no more than isolated evening thunderstorms on tap, which looks reasonable considering CAPE and warm temperatures aloft. Could see a few strong thunderstorms across the Nebraska Panhandle where CAPE will be locally higher. Wednesday/Wednesday evening ...With slightly cooler temperatures aloft, and the addition of increased low and mid level moisture, we expect to see an areal increase of afternoon and evening thunderstorms, mainly along a low level convergence axis from Douglas to Cheyenne in the afternoon, then across the Nebraska Panhandle in the evening where storms will transition to. Thursday/Thursday night...Heights aloft continue to decrease, and with adequate low and mid level moisture, we expect isolated to scattered late day shower and thunderstorm coverage. Slightly cooler compared to Wednesday. .LONG TERM...(Friday through Tuesday) Issued at 128 PM MDT Tue Aug 18 2020 Ridging aloft prevails Friday through Sunday, and with limited low and mid level moisture, mostly dry conditions should prevail. Zonal flow aloft prevails for Monday and Tuesday, with enough moisture for at least isolated late day thunderstorms on Tuesday. Temperatures will continue above climatological normals. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 527 PM MDT Tue Aug 18 2020 VFR flight conditions expected at all terminals through 6Z. A very low chance of VCSH for the western Nebraska Panhandle terminals this evening, so they were omitted in the TAFs. Wind gusts should dissipate to 10 knots or less near 2Z. Model guidance from the HRRR shows that smoke from the CO wildfires should stay to the south of the state line overnight into tomorrow morning. High level CIGs may hover overnight due to the transition into northwest flow at the higher levels of the atmosphere by 6Z tonight. && .FIRE WEATHER... Issued at 128 PM MDT Tue Aug 18 2020 An unusually hot and dry weather pattern continues with widespread highs in the 90s and minimum RHs in the lower teens and upper single digits. This is creating a favorable situation for new fire starts given the fuels status. Despite this, fire weather concerns should remain fairly low with winds below critical thresholds. Increasing chances for thunderstorm activity through Thursday. Any thunderstorms may produce gusty and erratic surface winds, as well as frequent lightning. Dry thunderstorms do not appear particularly likely with sufficient low-level moisture, but storms will still be on the high-based side. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Red Flag Warning from noon to 8 PM MDT Wednesday for WYZ301>303- 305>310. NE...None. && $$ SHORT TERM...RUBIN LONG TERM...RUBIN AVIATION...BW FIRE WEATHER...RUBIN
Area Forecast Discussion
National Weather Service Grand Forks ND
1032 PM CDT Tue Aug 18 2020 .UPDATE... Issued at 1031 PM CDT Tue Aug 18 2020 Not much going on currently, with mostly clear skies. Can`t completely rule out some isolated/widely scattered storms developing later tonight as a weak shortwave comes down out of southeast Saskatchewan, but not overly impressed as given lack of current activity in that area. Will continue to keep some low POPs after midnight. UPDATE Issued at 719 PM CDT Tue Aug 18 2020 Showers that tried to get going dissipated under a pretty strong cap, and CAMs have backed off on convection this evening. Still could see some storms later tonight as the shortwave moves down, with some elevated CAPE around 1000-1500 J/kg later tonight can`t rule out some stronger cells pulsing up. Removed POPs for this evening but will keep isolated-scattered storms after midnight. && .SHORT TERM...(This afternoon through Wednesday night) Issued at 307 PM CDT Tue Aug 18 2020 Monitoring severe potential for this afternoon and evening, with a few marginal cells possible. Weak southerly surface gradient is in place with some return flow resulting in warmer temps and slightly increased Td values in the 60s. Objective RAP analysis showing ML CAPE has increase to around 1500 J/KG, however CIN remains high and this capping is keeping activity elevated in nature (and as a result much weaker) where a few showers (occasional lighting) in southeast ND at the time of this discussion. This afternoon-tonight: Next embedded impulse is just now moving into southern Manitoba and should progress down the RRV this evening/overnight. Additional afternoon mixing could help weaken capping, so I can`t rule out storm initiation before the main period of forcing arrives, but latest runs of the HRRR are very promising. Overall chances for showers/storms increase as the evening goes on (likley remaining scattered) with the strongest QPF consensus from CAMs after 03Z...of course this would be after instability decreases. There is enough variance between CAMs in track/coverage that I can`t rule out activity just about anywhere in our CWA, but confidence overall isn`t high. There is a window where ML CAPE 1500-2500 J/KG may coincide with 25-30kt effective shear to support marginal severe storms through early evening. In addition, DCAPE is shown to remain 1000-1500 J/KG this evening raising the possibility for microburst potential. Pulse type severe convection appears favored, with hail to 1 inch and 60 mph winds the main concern through sunset. Wednesday-Wednesday night: Combination of rising heights/increasing low level southerly flow will result in even warmer temps higher humidity Wed, with highs in the 80s to near 90 (warmest in ND). If they develop tonight, lingering elevated showers/storms should exit our region Wednesday morning to the south/southeast with models favoring a period of subsidence dry conditions during the day. WAA/low level moisture increases, so we actually see higher CAPE values reflected in guidance across our south by the afternoon. Capping and a lack of forcing will limit thunderstorm potential where the parameters would be more favorable to strong/severe storms. The next impulse that could support storm initiation doesn`t arrive until later Wednesday evening and NBM has limited PoPs (slight chance) along the international border. Parameters do not appear favorable for severe in our north. .LONG TERM...(Thursday through Tuesday) Issued at 300 PM CDT Tue Aug 18 2020 An upper level ridge will remain in place over the High Plains through the first part of the extended period...with minor perturbations tracking through the flow helping trigger shower/isold storm activity. The upper ridge will be to gradually weaken and become more zonal into the weekend. Expect a weak front to drop across the area for Sunday night and Monday with another chance for precipitation. Will see temps cool down for the end of the period...with highs around 80 and lows in the upper 50s which is near seasonal averages. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 719 PM CDT Tue Aug 18 2020 VFR conditions at all TAF sites and that will continue through the period. Some scattered to isolated convection, best chances around KFAR after midnight so only have a mention there. Winds from the south will shift to a more southwesterly direction tomorrow morning, but will be mostly under 12 kts. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. $$ UPDATE...JR SHORT TERM...DJR LONG TERM...Hopkins AVIATION...JR
Area Forecast Discussion
National Weather Service Green Bay WI
1038 PM CDT Tue Aug 18 2020 Updated aviation portion for 06Z TAF issuance .SHORT TERM...Tonight and Wednesday Issued at 356 PM CDT Tue Aug 18 2020 The latest RAP analysis and satellite/radar imagery show high pressure stretching from northwest Ontario to the central Great Plains early this afternoon. Daytime convective clouds popped by late in the morning across the region, but the vertical extent is not nearly as high as the past few days. Looking to the northwest, mid-level warm advection is occurring over northwest Ontario, with a few showers reported northwest of Lake Superior. As this warm advection zone spreads southeast, forecast concerns mainly revolve around shower chances over northern WI. Tonight...High pressure will remain centered across the region. The warm advection and associated cloud cover will slide southeast across the Upper Peninsula and northern WI through the night. But models portray mid-level lapse rates and elevated instability as relatively weak, and keep most precip chances north of the U.P. border. Will carry a very small chance of a shower right near the border after midnight. Temps should be warmer than last night due to more cloud cover. Lows ranging from the upper 40s in the cold spots to the middle 50s. Wednesday...The warm advection zone will proceed southeast across northeast Wisconsin. Mid-level instability and moisture convergence appears to remain north of the U.P. border once again, so will leave a slight chance across the far north. Should see more in the way of cloud cover, but warming low level temps will offset. Highs ranging from the upper 70s to lower 80s. .LONG TERM...Wednesday Night Through Tuesday Issued at 356 PM CDT Tue Aug 18 2020 The main highlights for this forecast period are the various chances for showers and storms across far northern Wisconsin through Friday and the potential for a more significant system to move over the region late Friday night through late Saturday night. Wednesday night through Friday...The upper-level northwest flow will remain dominant over the western Great Lakes region through this period. At the surface, a nearby high pressure system will keep conditions mostly sunny and dry across much of central and east- central Wisconsin. Weak WAA across the northern Wisconsin/Upper Michigan border throughout this time period will allow clouds to develop. Isolated showers and non-severe storms may also develop over this area at times as well. The upper-level northwest flow will begin to flatten into Friday afternoon ahead of an approaching shortwave. Friday night through Saturday night...Although this time period looks to be the best chance to see widespread showers and storms, there are many uncertainties. Model guidance is in good agreement with the broad synoptic characteristics with a shortwave moving across the region during this time period. However, the ECMWF and Canadian continue to show this as a relatively weak system while the GFS has a much stronger system moving across the region. As mentioned in previous forecasts, the GFS continues to not have much support from its ensemble members, so will avoid this solution. Since the models have slowed the overall system`s progression to move over the region sometime between early Saturday morning and Saturday evening, the system may be able to tap into enough instability during peak heating to produce some strong to severe storms. Deep layer shear appears to be limited during the system`s passage which would hinder storm organization, however, PWATs are approaching 1.75 inches. Any showers or storms that develop during this time period could bring heavy rain. Will continue to closely monitor as changes are expected to occur within the next 3 to 4 days with this system. Rest of the extended...Once the shortwave system exits the region Saturday night, the forecast area will see the return of an upper- level northwest flow and a surface high pressure system for Sunday into early next week. This will bring slightly cooler air back to the region causing either slightly above normal or near normal temperatures. && .AVIATION...for 06Z TAF Issuance Issued at 1037 PM CDT Tue Aug 18 2020 Aviation weather issues during the next 24-36 hours are expected to be relatively limited in duration and coverage. Middle clouds will drift into the area from the north at times, and diurnal clouds with VFR bases are expected during the mid-day and afternoon hours. It still looks like patchy fog will probably develop again tonight (like the past several nights) in north- central Wisconsin. Will carry a tempo group with IFR vsbys in the KRHI TAF to account for it. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....MPC LONG TERM......Hykin AVIATION.......Skowronski
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1058 PM CDT Tue Aug 18 2020 .UPDATE... Issued at 1048 PM CDT Tue Aug 18 2020 Updated to include 06z aviation discussion below. && .SHORT TERM...(This evening through Wednesday night) Issued at 239 PM CDT Tue Aug 18 2020 High pressure will keep the weather mainly dry for the next couple of days. The lone exception is a weak disturbance that could bring some showers and possibly a thunderstorms across the region north of I-94 late tonight into Wednesday morning. Highs on Wednesday will be a few degrees warmer than today. Early afternoon satellite imagery and RAP surface analysis showed high pressure over the Upper Mississippi River Valley. A few cumulus developed on the eastern side of this surface high, while areas to the west were mostly clear aside from a few high clouds. The only precipitation to speak of was some weakening showers in eastern North Dakota. A strong upper level ridge was set up across the western CONUS, and weak shortwave troughs will ride this ridge across the Upper Midwest. One of these features was currently located across southern Manitoba, and HiRes models are in good agreement with developing scattered precipitation as the PV anomaly slides southeast later tonight into Wednesday. Mid level lapse rate on the order of 7 to 7.5 C/km will allow around 1000 J/kg of MUCAPE to develop over northern Minnesota but just a fraction of that will develop across the northern part of the Twin Cities forecast area in central Minnesota and west central Wisconsin. Forecast soundings show cloud bases around 10kft, so expect scattered high- based rain showers, and possibly some thunderstorms to the north late tonight into Wednesday morning. .LONG TERM...(Thursday through Tuesday) Issued at 239 PM CDT Tue Aug 18 2020 This period continues to be dominated by the almost stationary upper ridge over the western CONUS. Early next week this upper ridge will begin to dissipate and allow for a pattern change across the CONUS. Expecting warmer weather Thursday and Friday ahead of a cold front moving through the Upper Midwest. Ahead of this cold front temperatures will be in the 80s with some temperatures near 90 possible in western Minnesota. Behind this cold front temperatures should fall back to near normal this weekend into next week. This cold front will also provide our best precipitation chances, mainly on Friday and Saturday. Ahead of the front daytime heating could lead to an unstable environment with surface based CAPE values around 3000 J/kg. This would support thunderstorms Friday and Saturday. The shear in this environment is less certain so there remains uncertainty in how strong storms could be. There is another possible chance for precipitation early next week as another front passes through the Upper Midwest. && .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) Issued at 1048 PM CDT Tue Aug 18 2020 VFR with high pressure moving east of the region over the next 24 hours. Mainly clear skies but there is a small chance of a few SHRA/TSRA north of I-94 from the pre-dawn hours into late morning. Potentially only the WI sites may experience any issues. Chances are too low for inclusion at this point but it does bear some watching as the 12z TAF set approaches. Otherwise, light southerly winds overnight become more SW during the day Wednesday with speeds near 10kt. KMSP...No additional concerns. /OUTLOOK FOR KMSP/ Thu...VFR. Wind SSW at 10-15 kts. Fri...VFR with -TSRA possible late. Wind SW at 10 kts Sat...VFR with TSRA possible. Wind S at 10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ UPDATE...JPC SHORT TERM...JRB LONG TERM...NDC AVIATION...JPC
National Weather Service Morristown TN
923 PM EDT Tue Aug 18 2020 .UPDATE... EVENING UPDATE. && .DISCUSSION... PoPs will need to be rasied in northern sections with the evening update as showers and thunderstorms moving out of KY and Middle TN have held together. Radar shows a weakening trend to the showers, and this should continue as heating is lost and the upper jet streak pulls farther away. Some temp/dewpoint adjustment will also be made to better align with current obs, but lows in the 60s are on track. DGS && .AVIATION... 00Z TAF DISCUSSION. Showers and thunderstorms across KY and Middle TN will gradually move into East TN, but they will be weakening after sunset as heating is lost and they encounter drier air. So for the TAFs, only TRI is expected to have a threat of TS and MVFR conditions. Tomorrow afternoon, showers and thunderstorms are expected to develop and be more numerous around the area as an upper level trough approaches, so a PROB30 will be mentioned at all sites, along with VCTS. DGS && .PREV DISCUSSION... /ISSUED 331 PM EDT Tue Aug 18 2020/ SHORT TERM...(Tonight and Wednesday) Key Messages: 1. Widely scattered showers/storms, mainly north of I-40, developing late this afternoon through tonight, but no heavy rain expected. 2. Showers/storms increasing through the day Wednesday with cooler temps, but most areas will see light to moderate rain totals. Discussion: Late afternoon/evening... Latest satellite and RAP analysis at 1830Z shows a vigorous H5 shortwave rotating through the MS Valley downstream of a 600 DM heat ridge over the western CONUS. The axis of the H5 shortwave was oriented from roughly S IL through W TN with a weak surface low over central KY. One cold front extended S from the low through W TN and MS while a second cold front was draped across S GA and the Carolinas. As the H5 shortwave and associated surface low and cold front continue slowly eastward this evening, scattered convection will materialize from the N Plateau through NE TN and SW VA in response to diffluence under the right entrance region of a 40-60 kt H30 jet, convergence ahead of the approaching low-level boundary, and some weak instability from daytime heating. However, coverage of convection will be widely scattered due to the continued presence of significant dry air through the column and only about 200 J/Kg of MLCAPE and less than 1000 J/Kg of surface CAPE. This drier air is keeping PWAT values slightly below the climatological average at 1.15 to 1.25 inches, so any convection will only contain moderate rainfall rates. Tonight and Wednesday... The aforementioned H5 shortwave will continue to press through the TN valley overnight with the surface cold front slowly moving into the region. This front is progged to be oriented up the Valley by 12Z. In the wake of this initial shortwave, a deep, positively tilted mid/upper longwave trough will be reinforced over the MS Valley placing a belt of strong SW flow aloft over the S Appalachians and Carolinas aligned parallel to the low-level front. This will cause the front to stall in the vicinity of the S Appalachians and western Carolinas Wed. In terms of precip, pulled back PoPs tonight to chance/slight chance, with greatest potential over far northern areas. The reason being that the shortwave is timed with the diurnal minimum, mid level moisture will still be slow to increase, and the best jet dynamics look to progress farther away overnight leaving only weak upper diffluence over our region. Better chances for showers/storms will arrive Wed afternoon through the evening as a secondary shortwave dives through the mid MS Valley and approaches the region. As this second shortwave further deepens the longwave trough, another 40-60 kt southwesterly H30 jet streak will develop over the central Appalachians placing the region in the favored right entrance, and this upper jet will also strengthen the low-level southerly flow leading to increasing moisture, isentropic ascent, and convergence along the stalled frontal boundary. This will allow for widespread showers/storms increasing from late morning through the afternoon as daytime instability builds. MLCAPE of 1500-2000 J/Kg and the deeper lifting will allow for locally heavy downpours, but PWATs will only increase to 1.3 to 1.6 inches which will keep the heaviest rain spotty. Have widespread likely PoPs Wed afternoon with some categorical PoPs in SE TN and along the mountains closer to the boundary. Went slightly below the NBM for highs due to mostly cloudy skies and greater precip coverage. Garuckas LONG TERM...(Wednesday Night through Tuesday) A wet extended period will take place for several days but will start to change Sunday. Mid and upper level trough over the eastern states Wednesday night through Saturday at least. A weak front across the forecast area Wednesday night will help to focus scattered to numerous showers and storms well into the evening. A weak closed upper low is also forecast to form across the lower Ohio and western Tennessee Valleys from about Wednesday night and continue through Saturday morning. Weak shortwaves moving in from the west and northwest will be enhanced by the upper low and any surface boundary still lingering over the region. Periods of showers and some thunderstorms are expected each day and into at least the evenings during this time. Some heavier rainfall amounts will be possible Friday and Friday night especially along the eastern mountains and across southwest North Carolina which could produce some localized flooding. Starting Sunday the trough begins to shift to the northeast and ridging strengthens over the southeast states. Showers and thunderstorms will be less widespread and be more numerous in the higher elevations. Temperatures will be below normal from Thursday through Saturday in the lower to mid 80s and then warm into the mid 80s to lower 90s the last 3 days. TD && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 69 89 67 85 68 / 20 70 20 70 60 Knoxville McGhee Tyson Airport, TN 67 86 66 84 67 / 20 60 20 60 40 Oak Ridge, TN 66 86 65 84 68 / 30 60 20 60 30 Tri Cities Airport, TN 63 83 62 81 64 / 40 60 20 60 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$
Area Forecast Discussion
National Weather Service Phoenix AZ
900 PM MST Tue Aug 18 2020 .SYNOPSIS... Strong high pressure will continue to dominate the weather pattern and maintain very hot conditions. High temperatures across the lower deserts will be near or above 110 through the next 7 days. Isolated thunderstorms with strong gusty winds and areas of blowing dust will be possible this afternoon and evening across south-central, west and southwest Arizona. The more favorable monsoon pattern will continue as moisture increases over the weekend. && .DISCUSSION... At 8 pm this evening, an exceedingly strong upper level ridge remained parked across the western states; latest 500mb plot depicted 599dm heights over northern Arizona with values around 596- 597dm over the central deserts. The high temperature in Phoenix reached to 115 again today and that makes 5 of the last 6 days with a high of 115 or greater! Moderately strong northeast steering flow of 15-20kt supported convection moving into the central deserts from the eastern Rim, however surface dewpoints in the 40s over the deserts does not provide the best support for storms holding together after they move off the high terrain and into the low elevations. For most of the afternoon and early evening, storms have been minimal over the central deserts with little in terms of outflow winds. However, it appears that at least one last wave will be moving in from the east/northeast during the mid to late evening, leading to some shower activity with possibly an embedded storm. CAPE not overly high from the evening sounding, although latest SPC mesoanalysis graphic showed a pocket of MLCAPE around 1000j/kg to the northeast of Phoenix. We can expect some gusty easterly outflow winds starting to move through the greater Phoenix area after 930 pm along with some convective activity. After midnight convection should dissipate leaving behind partly cloudy skies. Forecasts have been tweaked and look to be in decent shape. .PREVIOUS DISCUSSION... Strong high pressure remains situated just to the northwest, putting our region under east-northeast flow. With little change in the environment since yesterday, we will once again see a chance for storms over the AZ high terrain to move toward the lower deserts. The best MLCAPE early this afternoon is over western AZ and southern CA, where moisture is higher. Already seeing strong storms in southern CA, including in Joshua Tree National Park. 12Z HREF does suggest slightly better chances for storms to progress into portions of southwest AZ and southeast CA later this evening on strong outflows from west-central AZ. MLCAPE is nonexistent in southeast AZ, including the Phoenix area early this afternoon, which means convective initiation is heavily dependent on surface heating through the rest of the afternoon. SBCAPE is still minimal at the moment over the same areas. HREF keeps SBCAPE on the low end, so it will likely be tough to get storms too far south off the eastern Rim (i.e. south of Gila county). HRRR is still the most aggressive CAM, but has done fairly well the past couple of days, and does have isolated strong storms push into the Globe area east of Phoenix. It is tough to say whether storms will be able to maintain strength into the Phoenix area late this afternoon and evening, but should at least see outflow winds push in from the east to northeast and we shall see if the outflows will be strong enough to develop new storms. DCAPE is still high around 1500 J/kg across the lower deserts, which does support strong outflows that may once again kick up a lot of dust. One additional note, nearly all GEFS members have been consistent the past couple of days showing measurable precip (0.1") in downtown Phoenix this evening. So there`s some hope if you want to believe the GEFS. The EPS remains dry, but has been consistently too dry. Any storm this that develops this afternoon and evening will have the primary threat for strong to severe downburst winds, which again may kick up a lot of dust, but localized flash flooding and lightning are also concerns. With the strong high pressure still dominating the weather pattern, extreme temperatures will continue. An Excessive Heat Warning remains in effect through this Thursday for south-central AZ to southeast CA. Temperatures should trend slightly cooler the next few days and into the weekend as the high pressure weakens and drifts southeast back toward central AZ. Despite the location of the high being closer, high temperatures are favored to finally stay below 110 for a few days. Unfortunately, this may not last as GEFS and EPS mean show the high restrengthening and shifting back northwest by early next week. Hurricane Genevieve is currently off the central Mexican west coast and is expected to track northwest, staying west of Baja California. NAEFS and EPS mean do show a slight increase in moisture pushing into the southwest by this weekend, with PWATs climbing up to 1.5- 1.8 across the area. This should continue to support daily thunderstorms. Storm chances in for the lower deserts do drop off for the end of the week and early weekend with the high placement and weaker/less favorable steering flow. However, with the high eventually shifting back northwest and the moisture in place, we should see better storm chance return by early next week. && .AVIATION...Updated at 0000Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Conditions remain somewhat favorable for another evening of isolated convection into the Phoenix area, given decent easterly steering flow and a weak disturbance rotating around the high and into the central deserts. Dewpoints however remain rather low and in the 40s, not what we would like to see for sustaining high terrain storms into the low desert. Better chance for gusty outflow winds; first shot of outflow from the north/northeast after 01z and after about 03z, maybe another burst from the east to southeast. Have played out this narrative in the TAFs but backed off a bit on the blowing dust, going with a TEMPO group for vis around 4-5SM at the terminals. Kept gusts generally 25kt or less. Given that most of the hi-res models that we looked at are not overly bullish on strong outflows into the Phoenix metro this evening, confidence is not especially high. This will be a tricky evening. Do not expect overly low cloud bases with FEW-SCT around 9-10k and BKN-OVC decks aoa 15k feet this evening; clouds to thin after midnight becoming mostly FEW-SCT mid/high debris decks. Winds should favor the east at the TAF sites after midnight and thru late morning before turning to light southwest after 19z Wednesday. Southeast California/Southwest Arizona including KIPL and KBLH: Chances for evening convection a bit better than normal today but mainly across portions of La Paz and eastern Riverside county. Have no mention of convection at KIPL, just winds favoring the southeast. Do feel that an isolated shower or storm could affect KBLH after 03z so kept the VCTS going at the TAF site until 06z. Winds could gust up to about 30kt from east or northeast should storms develop and threaten the terminal. Clouds should not be overly low tonight, just FEW-SCT 9-10k feet and SCT-BKN aoa 15k feet this evening with clouds thinning after midnight becoming mostly FEW-SCT mid/high level debris cloud decks. Winds should generally favor the south to southwest next 24 hours at KBLH when outflow winds are not present. && .FIRE WEATHER... Friday through Tuesday: High pressure will persist across the Desert Southwest this week but will weaken slightly, resulting in a slight decrease in temperatures from excessive heat thresholds seen earlier in the week. Moisture will also begin to increase Friday into the weekend associated with remnants of Hurricane Genevieve in the eastern Pacific. The increased moisture may become a bit more favorable for thunderstorm activity, even across the lower deserts, although primary storm chances will stay across high terrain areas to the east of Phoenix each day. Min RH will drop into the teens each day with overnight recoveries generally in the 35-50% range, but higher from SW AZ to SE CA. Winds will generally remain light aside from some typical afternoon breezes. However, any storms that develop have the potential to produce gusty, erratic winds. && .CLIMATE... Record high temperatures: Date Phoenix Yuma El Centro ---- ------- ---- --------- 8/18 112 in 2011 116 in 1960 115 in 2015 && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Thursday for AZZ530>556- 559>562. Heat Advisory until 8 PM MST Thursday for AZZ557-558-563. CA...Excessive Heat Warning until 8 PM PDT Thursday for CAZ560>570. && $$ DISCUSSION...CB PREVIOUS DISCUSSION...Benedict AVIATION...CB FIRE WEATHER...Rogers CLIMATE...MO
Area Forecast Discussion
National Weather Service Blacksburg VA
837 PM EDT Tue Aug 18 2020 .SYNOPSIS... Low pressure will slowly approach the area from the lower Ohio River Valley today. The system looks to stall across the area for the remainder of the week as waves of energy roll on through. This will bring back the need for the umbrella with increasing shower and storm chances areawide. Storm chances start to lower a bit heading into the weekend ahead. && .NEAR TERM /THROUGH WEDNESDAY/... As of 820 PM EDT Tuesday... The most significant changes made at this time were to the pops and temps. Ramped up pops further east and south as scattered activity continues along the entire length of the Blue Ridge with the main area of showers/thunderstorms creeping into the western zones from KY and WV. HIRES simulated radar from HRRR and NAMNest show a new area of showers/thunderstorms developing overnight just to our west and then moving across CWA during the late night/early morning hours. Thus, pops were adjusted to show this. Temperatures running a bit cooler than expected due to cloud cover this afternoon and spotty showers. However, dewpoints were running a bit higher than expected, so cooling overnight may not be quite as pronounced as earlier thought. As of 155 PM EDT Tuesday... A noticeable difference this afternoon as the humidity slowly starts to build thanks to southwesterly flow. Temperatures are also a nudge warmer with upper 70s and low 80s west of the I-81 corridor and mid to to upper 80s off to the east. Radar remains clear as 1730z with some development off to the west of Charleston, West Virginia and down to the south of WIlkesboro, North Carolina. This development is associated with a digging upper level trough and approaching area of low pressure from the Ohio River Valley. SBCAPE values currently sit between 1000-1500 j/kg across our region with higher instability values of 2000-2500 j/kg off to the west across southern Ohio and Indiana. Currently no mention of severe weather from the Storm Prediction Center but isolated to scattered convection looks to be expected in areas north and west of the US-460 and I-64 stretch heading into the early evening hours. PWATS still remain low at 1.0 to 1.2 inches across the region but some recovery is expected overnight when the overall weather pattern for the rest of the week is expected to change. PWATS by Wednesday morning should recover back to 1.4 to 1.6 inches as humidity values rise a bit more. This leaves a chance of showers especially in areas over the mountains west of the Blue ridge along with some areas of patchy fog in the river valleys. Fog will burn off quickly after 14z and with some holes in the clouds, convection should start to form after 18z Wednesday afternoon. With the low pressure system pushing through and the trough in place coverage looks to be widespread. Locally heavy rainfall can be expected with the potential for localized flooding. Storm coverage starts to drop off by Wednesday evening with some leftover chance pops and patchy fog heading into Thursday morning. Temperatures during the period will remain at or slightly below average. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... As of 135 PM EDT Tuesday... An upper trough west of the Appalachians Thursday will deepen and slowly move east into Friday night. This will increase diurnal convection chances in Friday as the increased southerly flow increases moisture into the region. A surface boundary will remain across the Southeast generally from the coast of the Carolinas into the Gulf Coast states. An area of high pressure over the Mid-Atlantic region Thursday morning will slide east into the Atlantic ocean by Friday. With recent heavy rains, there is the potential for flooding depending on the locations and intensities of the thunderstorms. Temperatures during the short term period will be cooler than normal, with high readings generally from the mid 60s in the mountains to the lower 80s in the piedmont. Overnight low temperatures will vary from the mid 50s in the mountains to the upper 60s in the piedmont. Forecast confidence is high during the short term period. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 135 PM EDT Tuesday... The pattern through Sunday will be dominated by a strong ridge over the Four Corners region of the US, while continued troughing remains over the eastern half of the US with a Bermuda high settled over the Atlantic. Embedded pieces of energy will round the base of the longwave trough. The aforementioned, coupled with ample moisture settled in place, this will bring daily chances of showers and thunderstorms through Sunday. By the first of next week, models begin to break down the strong ridge over the western states and trough over the east, giving way to broad ridging over much of the CONUS. Without much forcing, showers and storms will become more isolated and diurnal/orographically driven. Temperatures will remain near normal through the weekend, to slightly above normal through the beginning of next week. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/... As of 830 PM EDT Tuesday... Mostly VFR conditions still in place, but wetter, more humid, more unsettled weather expected for the remainder of the week. A weak cold front will sag into the region from the northwest tonight and stall across the area Wednesday, similar to the past several events. Isolated showers have popped up along the entire length of the Blue Ridge from time-to-time this afternoon/evening, and that continues as of now with about 10% coverage at the moment. Meanwhile, a larger area of diminishing showers/thunderstorms was approaching the area from the west. This activity is expected to reach the western counties within the next couple of hours and gradually decrease as it spreads further east. Showers and thunderstorms are expected to redevelop just to our west across far southwest VA/eastern TN/eastern KY later tonight and then spread further into the CWA by daybreak. Thus, have included or introduced VCSH and -SHRA accordingly as this precipitation is expected to enter the western areas around 06Z-08Z then diminish as it moves east. More robust and widespread showers/thunderstorms are expected to develop during the afternoon along and east-south of the Blue Ridge. Periods of MVFR conditions will accompany the showers/thunderstorms. Thickening clouds and precipitation overnight will limit the development of dense fog. Have limited time and duration of such and confined mainly to BCB and LWB. Ceilings will be mostly VFR this evening, then drop into the MVFR range early Wednesday, remaining mostly MVFR to VFR during the day Wednesday. Winds are expected to be chaotic and light, mostly southwest this evening becoming northeast early Wednesday, then veer back to a southerly direction by Wednesday evening. /Confidence in Forecast Parameters/ Ceilings - Moderate to High, Visibility - Moderate to High, Winds - Low, Thunderstorm Potential - Moderate. Extended Aviation Discussion... A slow moving and deepening area of low pressure aloft will evolve to our west resulting in abundant tropical moisture being drawn northward into the region and a return of MVFR conditions due to widespread showers and thunderstorms for the remainder of the week. Some improvement to aviation is expected as we head into the weekend. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...ET NEAR TERM...ET/KK/RAB SHORT TERM...KK LONG TERM...BMG AVIATION...ET/KK/RAB
Area Forecast Discussion
National Weather Service Las Vegas NV
200 PM PDT Tue Aug 18 2020 .SYNOPSIS...Excessive heat will last through much of the week with continued record temperatures. Isolated thunderstorms will continue into the evening across northwest Arizona and parts of the Mojave Desert and drift gradually westward while accompanied by strong wind gusts. A very slight lowering of temperatures is expected late in the weekend into early next week as high pressure shifts slightly eastward. && .DISCUSSION...tonight through Tuesday. Tonight...Convection has started firing over the higher terrain of the southern Great Basin and Mojave Desert. Look for storms to move off the higher terrain and into the nearby valleys, i.e Owens Valley and Morongo Basin/Barstow. HRRR has been consistent in showing convection propagating west-southwest across southern Mohave County and into the lower Colorado River late this afternoon, between 5 and 7 pm. Primary concern will be gusty winds as forecast soundings depict Invert-V profiles with plenty of DCAPE. Localized heavy rain/hail possible under stronger cores as well but storm motion should inhibit the threat of flooding. HRRR, as well as other HREF members indicate convection will dissipate by late evening. Outside of smoke/haze from nearby fires skies will be mostly clear to partly cloudy overnight. Wednesday-Tuesday...The anomalously massive ridge is forecast to slip southeast and weaken by just a tad by the weekend. Instead of of H5 heights hovering between 597-600 dm they will dip to between 591-594 dm. Bottom line, this will keep temperatures running well above normal going into the weekend and the start of next week. The Las Vegas high temperature is not forecast to be below 110 degrees until Sunday. Numerous daily record highs/high minimum temperatures will continue to be broken/tied along with record consecutive days of highs above a specific temperature. Will keep our heat product going through Thursday with option to extend in the the coming shifts. Isolated thunderstorms remain possible for the region Wednesday and Thursday, specifically favoring the higher terrain. As the high slowly shifts off to our southeast models indicate drier and more stable air wrapping into the western periphery of the high leading to the removal of thunderstorm potential over the southern Sierra Nevada and central Nevada Friday and Saturday. More uncertainty creeps into the convective potential Sunday into early next week with just how much moisture may creep into the region as Hurricane Genevieve brushes the southern tip of the Baja Peninsula. && .FIRE WEATHER...Hot temperatures with light terrain-driven winds are expected through the week. Near daily chances for isolated thunderstorms can be anticipated, particularly across the Mojave Desert and Sierra regions through Thursday. Storms will be capable of producing strong outflow winds which may aggravate ongoing fire activity and increase the rate of spread of new fire starts. && .CLIMATE... DAILY RECORD HIGH MAXIMUM TEMPERATURES TUE 8/18 WED 8/19 THU 8/20 Las Vegas, NV 111 (1992)* 111 (1992)* 110 (1950)* Bishop, CA 105 (2001)* 106 (1950) 105 (2015) Barstow, CA 111 (1992)* 111 (2018)* 109 (2018)* Needles, CA 115 (2015)* 117 (2018)* 120 (1919) Kingman, AZ 109 (1915)* 111 (1915) 107 (1915)* Death Valley 125 (2001)* 124 (1992)* 126 (1931) DAILY RECORD HIGH MINIMUM TEMPERATURES TUE 8/18 WED 8/19 THU 8/20 Las Vegas, NV 86 (2018)* 90 (2018)* 89 (2018)* Bishop, CA 67 (1970) 67 (1961) 65 (1997) Barstow, CA 80 (2001)* 80 (1973)* 82 (1973)* Needles, CA 91 (2018)* 93 (2018)* 95 (2018) Kingman, AZ 80 (2001) 76 (1999)* 80 (2001) Death Valley 98 (2013)* 99 (2003)* 99 (2018)* *-Current forecast may be close to current record values. && .AVIATION...For McCarran...Storms south of the valley will likely create outflow, arriving as southerly winds across valley this this evening. Winds will then favor typical drainage trends later tonight with light and variable to easterly winds to start tomorrow. By Wednesday afternoon, more storms are expected in the surrounding mountains will be capable of producing gusty, outflow winds in the valley, even if the storms themselves do not enter the valley. For the rest of southern Nevada, northwest Arizona and southeast California...Winds should remain light and follow typical diurnal trends for the next day or two outside of any thunderstorm outflow. The Sierra Nevada will continue to support afternoon thunderstorms with coverage elsewhere, especially in southeast California and northwest Arizona increasing both this evening and again Wednesday evening. Gusty and erratic outflow winds around 40 MPH look like for the Colorado River Valley. && .SPOTTER INFORMATION STATEMENT...Strong wind gusts are likely today from thunderstorm activity across Northwest Arizona and along the Colorado River Valley. Spotters are encouraged to report any significant weather, such as heavy rainfall, strong wind impacts, or blowing dust according to standard operating procedures. && $$ DISCUSSION...Pierce AVIATION...Steele For more forecast information...see us on our webpage: or follow us on Facebook and Twitter