Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/27/20

Area Forecast Discussion
National Weather Service State College PA
1112 PM EDT Wed Aug 26 2020 .SYNOPSIS... A slow moving frontal boundary in the vicinity of Pennsylvania will bring the potential for scattered showers and locally strong to severe thunderstorms each afternoon or evening into the weekend. The remnants of Hurricane Laura are forecast to track across Virginia on Saturday with limited rainfall impacts expected in central Pennsylvania at this time. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... A warm and mainly dry late evening across central PA with increasing humidity. Severe weather threat for late tonight appears to be waning but will still see scattered coverage of showers and thunderstorms moving across portions of NC and NE PA now through 2-3 AM or so. HRRR and WRF have backed off a bit on earlier solutions and still track a cluster of showers and likely isold tsra over NE PA after midnight. Elsewhere an isolated shower or storm is possible, but most areas will remain dry overnight. With dewpoints forecast to surge back into the 60s, min temps tonight will be much warmer/muggy than last night in the low 60s to around 70F. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... Little change at this time for Thursday, as D2 outlook conts to indicate significant severe thunderstorm enhanced risk for north central/northeast PA. SPC defines significant severe tstms as any storm that may produce one or more of the following elements: tornado with EF2 or greater damage, damaging winds 75 mph or greater, hail 2" in diameter or larger. The D3 outlook downshifted to MRGL (from D4 15% or SLGT equivalent) for the southern 3/4 of the CWA. The setup for Thursday will continue to feature a robust low level moisture recovery in the wake of northeastward-lifting warm front. The rich mid 60s to low 70s dewpoints combined with peak heating (max temps in the 80s to low 90s) should yield moderate instability. The ENH risk area will reside within a belt of stronger NW flow aloft with 30-40kts of effective bulk shear supporting fast- moving organized storms, including bowing segments and supercells. There is some uncertainty with storm initiation due to potential capping inversion with 700mb temps around 10C in the warm sector. HREF updraft helicity tracks are focused over southern NY which may suggest a greater svr potential there. While the primary threats are sig svr damaging winds and large hail, all severe hazards are possible from mid afternoon through early evening. Max HX values should get close to 100F across the lower Susq. Valley Thursday afternoon. Additional strong storms with gusty to locally damaging wind threat are possible on Friday afternoon - mainly to the south of q-stationary boundary extending from the Great Lakes into the northern Mid-Atlantic. There is a broad model signal for moderate to perhaps locally heavy QPF amounts across the northwest part of the area heading into Friday night/Saturday morning. This would be the point where moisture from Laura would be transported northward along cold front pushing east from the Great Lakes/Ohio Valley. Therefore, increased POPs in conjunction with the latest NBM and upped QPF as well. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... A cold front accompanying a progressive northern-stream trough will advance southeast through the OH Valley and Northeast States, reaching the Middle Atlantic during the evening on Saturday. Showers and thunderstorms will be ongoing along and ahead of the front. Additional storms will likely develop as the warm sector destabilizes during the afternoon, posing a threat for mainly damaging wind. SPC has maintained the 15% or SLGT risk equivalent area over central and eastern PA. The remnants of Laura are forecast to track to the south of PA Saturday and Saturday night. Some moisture entrainment is possible along/ahead of aforementioned cold front. At this time, rainfall impacts appear to be limited especially given the ongoing drought conditions across much of west-central PA and any soaking rain would most likely be welcome to help ease the drought conditions. We will continue to monitor for shifts in the track and an increase in heavy rainfall potential. Behind the front and Laura, much cooler air will move into the region late this weekend and into next week. Expect high temps to be more in the 70s and lower 80s with low humidity. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... At 03z, most of central PA is experiencing VFR conds, although BFD just saw its vsby drop below 2 miles. Have to think that this will only be a temporary drop in vsby there, as clouds are thickening quickly over nrn PA. Lowering cigs are expected overnight as a warm front edges into the region, with possible MVFR cigs across the nrn and wrn highlands based on model guidance. SHRA/TSRA are projected to drop southeastward from the eastern Great Lakes and slide across north-central and northeastern PA overnight, and have added VCSH to the BFD and IPT TAFs. Additionally, strong winds a couple thousand feet off the surface will result in LLWS over much of the area overnight. Conds should become VFR area-wide after sunrise Thursday morning. However, TSRA are expected to develop Thursday aftn and continue into the evening hours, some of which could produce locally gusty winds and hail. Outlook... Fri...AM low cigs possible wrn highlands. Sct PM tsra impacts possible. Sat...Widespread showers and reductions are expected. Sun-Mon...Generally VFR w/ no sig wx expected. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir/Gartner NEAR TERM...DeVoir/Gartner SHORT TERM...DeVoir/Gartner/Travis LONG TERM...DeVoir/Travis AVIATION...Evanego
Area Forecast Discussion
National Weather Service Duluth MN
957 PM CDT Wed Aug 26 2020 .SHORT TERM...(This evening through Thursday night) Issued at 353 PM CDT Wed Aug 26 2020 We will continue to see chances of showers and thunderstorms increase this afternoon and evening as a cold front passes through the region. A very humid air mass has settled across the Northland this afternoon, characterized by dew point temperatures in the upper 60s and lower 70s. Cloud cover has been rather tough to diminish this afternoon, with partly to mostly cloudy skies across the region. This has likely helped to keep instability slightly lower than what many of the global models are progging, with the RAP model indicating mixed-layer CAPE between 1000 to 2000 J/kg. Despite the lower-end instability, deep-layer shear is supportive of organized convective updrafts, with values in the 35 to 45 knot range. With this convective parameter space, the Storm Prediction Center continues to have a Slight Risk across the southern portions of the region, including along and south of a line from Poplar, MN to French River, MN to Sand Bay, WI. The CAMs do appear to be progging at least some strong to severe storms later this evening, although they appear to be more isolated in nature, at the moment. Once the cold front passes through the region tonight, drier conditions are expected for Thursday as an area of high pressure noses into the region from the Canadian Prairies. Expect sunny skies to start the day, with increasing cloud cover from the west in the afternoon as a precursor to increasing chances of showers and storms for Thursday night, as a mid-level shortwave trough shifts eastward into the region. No severe storms are expected at that time. High temperatures for Thursday will be in the mid 70s north to the lower 80s south. .LONG TERM...(Friday through Wednesday) Issued at 353 PM CDT Wed Aug 26 2020 The long-term forecast will have a few chances for showers and thunderstorms Friday and Monday, but overall will remain mostly dry. The first of these chances of precipitation will be Friday as the Northland is progged to be between a warm front to our south and an amplifying upper-level shortwave trough, with a decent positive vorticity maxima. The high-resolution models are generally indicating that the activity along the front will remain to the south, but activity along the shortwave trough will scrape across the Borderland region Friday afternoon. The global models show this scenario, as well. Severe potential appears very low as this time, with very marginal instability of mixed-layer CAPE up to 500 J/kg possible. Deep-layer shear is a bit better, with values in the 40 to 45 knot range. The Day 3 convective outlook from SPC only has the region under a General Thunderstorm risk. Once this shortwave passes through, much calmer conditions are expected for the weekend, with partly to mostly sunny skies across the region. As the shortwave trough departs to the east, northwesterly upper-level flow will help support cold air advection for Friday night. This cooler air will linger with us through much of next week, leading to high temperatures Saturday through Wednesday in the upper 60s and lower 70s, along with more comfortable dew point temperatures. There will be another opportunity for showers and thunderstorms for Sunday night through the day Monday as a high-amplitude upper-level trough will sweep along the International Border region. Despite some decent large-scale forcing, instability appears to be very minimal, with most-unstable CAPE values of a few hundred J/kg - not very supportive of strong thunderstorms. This trough will likely bring a rather wet and soggy Monday due to the prolonged period of rainfall. The global models begin to diverge for Tuesday and Wednesday, with with discrepancies in terms of precipitation chances. There appears to be some phasing differences regarding an upper-level trough. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 642 PM CDT Wed Aug 26 2020 A cold front moving through the region is currently causing showers and thunderstorms in the Northland. After this line moves east, VFR conditions are present behind it. Precipitation chances are already minimal for INL and BRD from this point onward, and HIB and DLH are quickly decreasing as well. Conditions at HIB and DLH should improve in the next couple hours to MVFR or VFR. HYR will be affected by the front into tonight as the line moves through. Fog is possible tonight at DLH and HIB and could lower conditions to MVFR or IFR. && .MARINE... Issued at 942 PM CDT Wed Aug 26 2020 Showers and thunderstorms have moved out of the area, and no further precipitation is expected out over the lake through the rest of tonight. But we are not done yet! More showers and thunderstorms are expected Thursday night into Friday over western Lake Superior. These storms are not expected to be severe. Other than storms, conditions are quiet with light winds and waves below 2 ft over the next 48 hours. && .PRELIMINARY POINT TEMPS/POPS... DLH 59 78 58 71 / 40 0 50 60 INL 53 75 55 72 / 10 0 50 60 BRD 59 80 58 76 / 50 10 50 50 HYR 62 82 59 75 / 50 0 70 70 ASX 62 78 58 73 / 40 0 60 70 && .DLH WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. LS...None. && $$ SHORT TERM...JTS LONG TERM...JTS AVIATION...Kossen MARINE...LE/Kossen
Area Forecast Discussion
National Weather Service Northern Indiana
607 PM EDT Wed Aug 26 2020 .SYNOPSIS... Issued at 328 PM EDT Wed Aug 26 2020 Another warm and muggy night is in store tonight, with partly cloudy skies and lows in the 70s. Highs Thursday will climb up into the upper 80s and low 90s again. There are chances for showers and thunderstorms Thursday into Saturday morning, with the greatest chances Friday into Friday night. Strong to severe storms are possible late Thursday afternoon and evening, then again on Friday, though confidence is low. && .SHORT TERM...(This Evening through Thursday) Issued at 328 PM EDT Wed Aug 26 2020 Another warm and muggy night is in store for the forecast area, with temps only falling into the low 70s under partly cloudy skies. We saw a record warm minimum temperature at KSBN last night, and suspect we`ll be close again tonight. Focus turns to Thursday into Thursday night. Expect we`ll see mostly dry conditions through the first part of the day, with capping inversion in place and generally weaker forcing. Some of the guidance outputs some shower activity in the morning/early afternoon for areas south of US 30 thanks to a push of WAA ahead of a weak shortwave moving through the flow aloft, but doesn`t look too impressive at this point. Have slight chance pops to account for this activity. The best chance for storms and severe weather would be in the late afternoon/evening generally along/north of the toll road (I 80-90) as the cold front sinks southward from Central Lower Michigan and upper level forcing increases. By the 18-21z timeframe DCAPE in the north and central CWA is around 1500-2000 J/kg and bulk 0-6 km shear is on the order of 20-30 knots in our N-NE (along/north of I 80-90). Front is expected to become stationary and linger overnight, so what we get as far as storms in general or even severe weather Thursday into Thursday night will depend on how far south it makes it and where exactly it sets up. If severe weather does develop, the main threat would be damaging winds-though hail and heavy rain can`t be ruled out. Some of the guidance, including the NAM suggests the fronts stays north of our CWA and we remain underneath the upper level ridge longer, which would mean we`re mostly dry Thursday with the exception of the morning chances south of US 30. Overall, confidence is low. && .LONG TERM...(Thursday Night through Wednesday) Issued at 328 PM EDT Wed Aug 26 2020 Our chances for severe weather Friday into Friday night will in part depend on how things set up Thursday into Thursday night with the frontal boundary. Additionally, how remnants of hurricane Laura are absorbed into the northern stream flow. The surface low projected to develop to our northwest over NW IA/MN Friday morning should shift eastward along the stationary boundary into southern Ontario by Saturday morning. This will bring a cold front through the CWA. Current model runs suggest the remnants of Laura will mainly focus to the south of our CWA, which is depressing given that we really need rain around here. This could also stunt some of the moisture and forcing needed to really kick things off severe-weather wise. Expect we`ll see rain and chances for storms Friday, with severe weather potential conditional on the aforementioned factors. Overall, agree with SPC`s slight risk outlook for Friday, though confidence is low at this point. Dry conditions are expected Saturday afternoon into early Monday as high pressure builds into the region. Highs will be cooler, only reaching into the 70s and low 80s. In the wake of the cold front, forecast to be out of the area by Saturday morning, expect gusty north-northwest winds which will whip up waves to around 5 to 6 feet on Lake Michigan. Direct onshore wave angles of approach in addition to wave periods of 5 to 6 seconds will be extremely supportive for the development of dangerous currents. Anticipate a beach hazards statement/high swim risk for Saturday, and at least a moderate risk on Sunday (could be high swim risk still despite slightly lower forecasted wave heights). The forecast for Monday afternoon into Tuesday is a little uncertain, with models disagreeing on the timing/strength of an upper level trough and subsequent surface low and frontal boundaries. The GFS has a steeper and more progressive solution (big surprise) and brings us a decent shot of rain (and t-storm potential) where the ECMWF is less amplified and keeps us mostly dry (with main precipitation areas north and south of our CWA). Kept the consensus pops for now, as a lot will depend on how remnants of hurricane Laura are absorbed earlier in the week. Wednesday appears mostly dry with a surface high over the CWA and either zonal or slightly ridged flow aloft, per both the GFS/ECMWF, but Thursday the ECMWF brings another trough into the central plains and lifts a surface low and associated precipitation into our CWA starting in the morning. Kept pops low given lower confidence at this point out. Highs should be in the mid-upper 70s to around 80F. && .AVIATION...(For the 00Z TAFS through 00Z Thursday Evening) Issued at 541 PM EDT Wed Aug 26 2020 An upper level ridge continued over the area and was helping to limit storm development. Low level moisture should increase overnight and may help to bring MVFR ceilings to the terminals (especially FWA). Given the latest NAM and HRRR runs, have kept just scattered lower clouds with VFR conditions prevailing. Can not rule out a brief 2000 ft ceiling between 10Z and 15Z, but for now will leave low ceilings out. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ SYNOPSIS...MCD SHORT TERM...MCD LONG TERM...MCD AVIATION...Skipper Visit us at Follow us on Facebook...Twitter...and YouTube at:
Area Forecast Discussion
National Weather Service North Platte NE
707 PM CDT Wed Aug 26 2020 .SYNOPSIS... Issued at 324 PM CDT Wed Aug 26 2020 H5 analysis from earlier this morning had high pressure anchored over the Four Corners and a secondary area of high pressure was located over western Georgia. A low amplitude ridge of high pressure extended north of these two features into the upper Mississippi valley. Further west, a trough of low pressure extended from the Oregon coastline, south southwest to a point approximately 700 miles off the central California coast. A strong low was located over eastern Quebec with a trough extending south toward Bermuda. Hurricane Laura was approximately 200 miles southeast of the mouth of the Sabine river. At the surface, a weak frontal boundary extended from the western Nebraska Panhandle into northeastern South Dakota. Winds behind this boundary were northerly, while south of the boundary, winds were either southwesterly or southerly. Skies remained mostly clear this afternoon, with a few higher clouds in western portions of the forecast area. Temperatures as of 2 PM CT ranged from 91 at Gordon to 98 at Thedford. && .SHORT TERM...(This evening through Thursday night) Issued at 324 PM CDT Wed Aug 26 2020 The main forecast challenges in the next 36 hours are precipitation chances tonight, then again on Thursday night. Over the next 24 hours, there will be a gradual weakening of the persistent ridging across the northern plains and northern Rockies. This will allow shortwaves to enter the Dakotas Thursday into Thursday night, increasing the threat for thunderstorms (more on this later). For tonight, there was some indication with this morning`s HRRR of thunderstorm development in the panhandle late this afternoon into the evening hours. Some of this activity was progged to move into the northwestern forecast area early this evening, then dissipate. The 12z NAM12 and NAMNest develop some limited convection off to the west of the forecast area and dissipate it before it reaches the western forecast area. As has been the case in this regime the past few days, the HRRR is the most "ambitious" with development of precipitation with its morning runs, then it backs off of it as you trend into the afternoon hours. The same thing is occurring right now as the latest 18z HRRR develops convection over the Cheyenne ridge which never makes it into the eastern panhandle. This model trend was echoed by the NAM12 and NAMNest from this morning which are dry for us tonight. That being said, decided to strip out pops in the NW Sandhills for tonight and keep them confined to the eastern panhandle. With respect to the weak frontal boundary which is currently draped across the northern forecast area. This feature is expected to lift slowly north as a warm front Thursday morning, becoming oriented across far Southern South Dakota by 21z Thursday. Late in the day Thursday, a northern stream disturbance will track from Montana into North Dakota. This will force the frontal boundary south into northern Nebraska Thursday evening increasing the threat for thunderstorms in the Dakotas and northern Nebraska. A decent low level jet will develop Thursday night from central Nebraska into northeast Nebraska. The nose of this feature will extend across northern Nebraska. Larger scale forcing will be even stronger across South Dakota Thursday night and am expecting the best chances for pcpn to be north of the forecast area with some chances in northern portions of the forecast area. Unfortunately, given weak forcing further south, pcpn chances are going to be minimal along and south of Interstate 80. As for highs Thursday, I went ahead and increased them some over guidance in northern Nebraska given the expected location of the surface front over southern South Dakota late in the afternoon. .LONG TERM...(Friday through Wednesday) Issued at 324 PM CDT Wed Aug 26 2020 The cool front will be pushed south into Kansas Friday resulting in cooler and drier conditions across western and north central Nebraska. The threat for precipitation will increase Saturday into Saturday night as mid level warm air advection and a surface warm front lifts across the area. Temperatures will warm back to more seasonal levels Sunday behind the warm front with highs in the mid 80s to lower 90s. This brief warmup will be followed by the threat for thunderstorms Sunday night as a strong cold front tracks through the forecast area. Behind the front, highs Monday and Tuesday will be in the 70s, with upper 70s to lower 80s for Wednesday. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 706 PM CDT Wed Aug 26 2020 Fairly quiet aviation conditions are expected across the region through Thursday afternoon. There is a low chance of some thunderstorms across northern Nebraska Thursday evening. Confidence remains low in development at this time and any thunderstorms that do develop will only impact KVTN mainly after 00Z Friday. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Buttler SHORT TERM...Buttler LONG TERM...Buttler AVIATION...Kulik
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
840 PM PDT Wed Aug 26 2020 Updated aviation discussion .SYNOPSIS...Typical summertime pattern to continue through the week. Potential for rain late in the weekend before returning to seasonal trends. && .SHORT TERM...Tonight through Friday...Current satellite is showing smoke from California and Oregon wildfires moving northeastward. Upper level winds will be in our favor for the most part but patchy smoke across the Lane and Linn county Cascades is likely through the tomorrow morning. The HRRR is showing a clearing of smoke on the west side of the Cascades by Thursday morning. Otherwise, typical summertime pattern is expected to continue through the end of the week. Weak influence from the Northeast Pacific high will keep skies clear and temperatures will trend upward by Friday. Weak east winds and building heights will produce inland high temperatures into the upper 80s on Friday. Expect late night to early morning marine stratus to form in coastal river valleys and lower Columbia River. Strengthening of the thermal low over the OR/CA border will bring gusty northerly winds in the afternoon across the Willamette Valley and along the coast. -BPhillips .LONG TERM...Friday night through Wednesday...Temperatures will trend down by Saturday as a weakening front pushes into the region Friday night. Inland locations should expect low 80s and coastal locations will see upper 60s. Most ensemble members show zero QPF associated with this disturbance so the region will likely stay dry. A second disturbance is expected to dip south Sunday night into Monday which has a greater chance of bringing some precipitation to the area. Light rain is possible across the northern half of the CWA and will dissipate by Monday afternoon. By Monday night, high pressure will build back bringing temperatures up into the mid to upper 80s by the middle of next week. -BPhillips && .AVIATION...High pressure will maintain mainly VFR conditions in the interior the next 24 hours under mostly clear skies. The exception will be a few hours of MVFR cigs in the vicinity along the Lower Columbia River between 10-17Z. Will also see another round of breezy northwest to north winds with occasional gusts to 20 kt between 19- 04Z. Onshore flow along the coast will allow MVFR or lower conditions to redevelop over the next few hours and persist into Thursday morning. Expect conditions similar to last night with a period of vsbys below 2SM and cigs at or below 500 ft. Any reduced flight conditions look to improve by late Thursday morning with VFR conditions thereafter. Refer to for detailed regional aviation weather and hazard information. KPDX and APPROACHES...Mainly VFR the next 24 hours under mostly clear skies, but a few hours of MVFR cigs in the vicinity is possible between 12-15Z. Breezy northwest winds with occasional gusts to 20 kt likely between 19-04Z. /64 && .MARINE...High pressure remains anchored over the Pacific through the next several days. Winds are northerly as the inverted thermal trough, that stems from California to Oregon, persists through the weekend. Winds will likely be strongest in the afternoons as the thermal gradient increases. Expect gusts up to 25 mph through all of the waters, with the more consistent and stronger winds in the central outer waters. The Small Craft Advisory remains in effect through Thu morning. There is a chance for another round of small craft winds Thu afternoon but at this time, models are showing winds staying just below thresholds. Seas at 4 to 5 ft with a northwesterly swell at 7 to 9 seconds will continue through the middle of next week. -Muessle && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 2 AM PDT Thursday for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 NM. Small Craft Advisory from 5 PM this afternoon to 2 AM PDT Thursday for Coastal waters from Cascade Head to Florence OR out 10 NM. && $$ Interact with us via social media:
Area Forecast Discussion
National Weather Service Phoenix AZ
430 PM MST Wed Aug 26 2020 .SYNOPSIS... Temperatures will remain unseasonably hot for the majority of the week with readings exceeding excessive heat thresholds for many communities through Thursday. Thunderstorm chances will decrease today into Friday, mainly favoring high terrain areas to the east of Phoenix. Monsoon moisture looks to gradually return this weekend into early next week leading to an increase in thunderstorm chances along with their associated weather hazards such as strong wind, heavy rain and blowing dust. Given the increase in moisture, temperatures will cool over the weekend and into next week and fall to near seasonal normal levels. && .DISCUSSION... Latest water vapor imagery shows mid-upper level moisture embedded within the anticyclonic flow. Mesoanalysis places the mid- tropospheric Monsoon High over north-central Arizona, which is resulting in a very weak flow through the column. Meanwhile, sounding and model-based PWATs are near 1.4 inches, which is near or slightly below normal while surface dewpoints are generally in the 50s. Latest visible satellite imagery reveals some areas of mid clouds and even some light showers across the Imperial Valley. Morning run of the HREF generally pointed to only isolated activity along the periphery of the Monsoon High, across the Mogollon Rim and across Pima County in southern Arizona. However, earlier runs of the HRRR suggested a southward propagating outflow boundary would possibly collide with another boundary to initiate convection across the Valley this evening. The HRRR has since backed off, owing to a weaker or even non-existent boundary from Yavapai County. Nevertheless, it can`t be ruled out entirely and the NBM guidance indicates a 10-20% chance of rainfall. However, CAM-based reflectivities remain modest, suggesting only strong wind gusts at most. Another low probability but possible scenario per the latest U of A GFS-based WRF suggests convection will develop across the Valley, but late this evening associated with the weak moisture convergence. Models continue to indicate excessive heat will continue through at least tomorrow across much of the Desert Southwest. Subtle cooling is then anticipated Friday, as the aforementioned Monsoon High weakens, while drifting to the south and east. Today is the average day for the last 110 degree temperature in Phoenix, but it appears 110 degrees will be reached again Thursday, which would equal 49 days so far this summer! && .PREVIOUS DISCUSSION... As we move from Thursday into Friday, guidance is very consistent in calling for a continued downward trend in convection across the area as an upper low moves into position along the central California coast; this serves to shunt the high to the east and set up a weak southerly steering flow. Moisture also appears to gradually diminish along with instability and temperatures. For the most part storms will be quite isolated and should only affect high terrain areas well to the east and southeast of Phoenix with POPs in the single digits each day across most of the lower elevations. As we move through the weekend and into the early part of next week, there are clear model signals that moisture will gradually make a return, and the monsoon will begin to heat up again. As the upper low near the California coast has more of an impact, steering flow gradually turns from weak southerly to stronger southwest or west/southwest. Despite the more "unfavorable" nature of the steering flow, significant tropical moisture pooling off Baja associated with a passing system begins to be pulled north and spreads into much of southern Arizona with time. Both the ECMWF and GFS/GEFS reflect this trend and we have correspondingly raised POPs with time; by Sunday and Monday isolated to scattered showers and storms are expected favoring high terrain but still likely affecting lower deserts as far west as the lower Colorado River Valley. Model guidance as well various ensemble member output begin to sort of go off the rails and diverge early next week with some solutions arguing for a drying northwest flow aloft while others keep a very moist southwest flow in place. There is way to much inconsistency that far out in time so we will keep a rather broad brush moderate grade monsoon forecast in place thru the end of the forecast period - Tuesday afternoon. && .AVIATION...Updated at 2330Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Very similar weather scenario through Thursday evening as has been experienced the past couple days. Competing outflows from the northeast and southwest may create frequent wind shifts this evening though the weaker storms to the north as compared to yesterday may limit (or negate) the potential for the northerly wind shift to actually develop. Stronger storms to the southwest have a better chance of sending outflow into terminals later this evening. Nevertheless, speeds do not look that impressive and any gusts (if there are any) certainly look below 20kt. Chances for actual SHRA at any aerodrome is 10% or less. Confidence is good that the typical easterly wind should settle in after midnight and persist into mid afternoon Thursday. Southeast California/Southwest Arizona including KIPL and KBLH: No major weather impacts will exist through Thursday evening under mostly clear skies. Trends in wind directions and speeds should be similar to the past several days with the typical diurnal switches, and with speeds below 12kt. && .FIRE WEATHER... Saturday through Wednesday: A cooling trend is likely this weekend through early next week. Storm coverage looks to stay diminished on Saturday, but will start to increase again Sunday into next week. Occasional wetting rains are possible starting Sunday evening continuing into next Wednesday. Afternoon humidity levels will generally fall into a 15-25% range while morning humidity levels will generally be 30-45% at lower elevations and 45-70% higher terrain. Outside of thunderstorm areas, winds should be weak and follow typical diurnal patterns. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ534-537- 540>553-555-556-560>562. Excessive Heat Warning until 8 PM MST Thursday for AZZ530>533- 535-536-538-539-554-559. CA...Excessive Heat Warning until 8 PM PDT Thursday for CAZ561>563- 565>570. && $$ DISCUSSION...Hirsch PREVIOUS DISCUSSION...CB AVIATION...Smith/Percha FIRE WEATHER...Hirsch/Feldkircher
Area Forecast Discussion
National Weather Service Reno NV
142 PM PDT Wed Aug 26 2020 .SYNOPSIS... Thunderstorms are expected through the evening for northeast California and portions of western Nevada. Typical westerly winds will also increase this afternoon across the region. Chances for isolated to scattered thunderstorms continue over high terrain and northeast California through the end of the week, least likely on Thursday. The air quality will continue to be a concern due to smoke from regional wildfires. && .DISCUSSION... Satellite data (and a quick peek out the window) is showing cumulus beginning to develop mainly along the Sierra/Sierra Front into northeast CA and far northern NV. With plenty of lingering moisture and added forcing from the jet stream draped across this region, we`ll see thunderstorms once again this afternoon and evening. Storms will mainly be isolated in coverage, but we could see a bit more coverage in far northeast CA, generally between Susanville, Burney, and Alturas north and east toward Rome, Oregon. One change to the forecast was to add a slight chance for thunderstorms overnight across portions of northern Nevada, mainly from near Pyramid Lake north and east. The lingering jet streak along with a subtle upper level wave could bring the necessary forcing for storms. The HRRR and the HREF are both hinting at nocturnal storms as well. While storms will be putting down rain, the concern is the increased storm motions with the potential for dry lightning strikes outside of thunderstorm cores. The trough remains centered over northern California, but begins to weaken, with drier air moving into the area Thursday. This should keep thunderstorm chances at bay, but with general troughiness and PWATs creeping back up, a few storms will once again be possible Friday, mainly along the Sierra. Still seeing quite a range of possibilities in ensemble guidance for next week. The big message is that it will remain dry, but the question is whether or not we`ll be seeing a developing low and cold frontal passage the early part of next week, or if this feature remains well to the east. There is better agreement it will remain east, however, there is enough evidence to give the trough feature a second look. Next Monday could be rather windy if we see this feature, or we could be seeing typical afternoon breezes. The current NBM high temperature guidance for lower valleys next Tuesday range from mid 70s to low 90s, not instilling a lot of confidence in the overall forecast. Otherwise, smoke and haze will remain a concern as long as the wildfires are ongoing. The latest HRRRx smoke runs are indicating the worst conditions in northeast California and northern Nevada north of I-80. -Dawn && .AVIATION... Typical westerly afternoon winds today with gusts 18-25 kts at terminal sites. Thunderstorms are possible this afternoon and evening, but coverage will be less than what we have seen recently. Very isolated storms are possible along the Sierra and Sierra Front, with a 10% chance of seeing a storm in the vicinity of KRNO/KCXP/KTVL/KMEV/KTRK. Storms are more likely to form in northeast California into far northern Washoe County. We could also see isolated nocturnal storms tonight north and east of Pyramid Lake. The greatest concern for storms today will be gusty and erratic outflow winds along with brief heavy rainfall obscuring terrain. Otherwise, smoke and haze remains a problem due to a large number of ongoing wildfires. Pockets of MVFR conditions are possible, especially just before to a few hours after sunrise, with improvement during the day as mixing improves. The worst conditions remain in northeast California and far western Nevada north of I-80. Slantwise visibility will be degraded across the entire region. -Dawn && .FIRE WEATHER... Storms this afternoon are still expected across northeast California, the Sierra, and far western Nevada. For the most part storms will be isolated, with the greatest coverage likely to be in between Susanville, Burney, and Alturas north and east toward Rome, Oregon. Storm motions through this region are slowing as we get into the evening, from around 20-25 mph to around 15 mph, which will lessen, but not negate, the risk of new fire starts. One change to the forecast was to add a slight chance for thunderstorms overnight across portions of northern Nevada, mainly from near Pyramid Lake north and east. While storms will be putting down rain, the concern is the increased storm motions with the potential for dry lightning strikes outside of thunderstorm cores. Storms should remain isolated in coverage, so between this and the fact is will be raining, we are not planning a Red Flag Warning at this time. -Dawn && .REV Watches/Warnings/Advisories... NV...None. CA...None. && $$ For more information from the National Weather Service visit...