Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/22/20

Area Forecast Discussion
National Weather Service Cleveland OH
920 PM EDT Tue Jul 21 2020 .SYNOPSIS... High pressure will move east of the area tonight as a warm front lifts northeast across the area. Low pressure will move into the western Great Lakes late tonight. As the low pressure system moves east toward Maine, a pre-frontal trough will move east during the afternoon tomorrow. A cold front trailing the trough will move east across the area tomorrow night. Another weak low pressure system will move southeast across the area Thursday night followed by a high pressure ridge that will build southeast over the area through the weekend. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... Previously mentioned convective activity that skirted the southern part of the forecast area has now moved southeast towards the Ohio River. Focus turns to upstream convective activity across central IN, with a well developed MCS moving into the Indianapolis metro within the next hour. While models generally are not capturing the scope of this activity, the HRRR seems to be initializing it somewhat, although at a diminished and delayed capacity. Generally expect the bulk of the activity to weaken as it moves into Ohio, with the stronger convection generally staying south of the forecast area. Still expecting some weaker convection/precip to move into the Findlay area sometime in the 05-06Z time frame as the low level jet noses northeastward towards the area, with 500-1000 j/kg MUCAPE residing along the I-75 corridor. Original discussion... A fast moving upper level shortwave trough will move east across the Great Lakes region during this period. This upper level feature will trigger a weak wave of low pressure at the surface over Minnesota that will deepen tonight through Wednesday as it moves into the Great Lakes region. A line of convection moving east across Indiana at this time is expected to weaken before it arrives in our area tonight. However, as the strong positive vorticity maximum and shortwave trough arrive over the area late tonight, expecting another round of showers and thunderstorms to move east over the area tonight into tomorrow morning. This activity was currently over Missouri. The surface low pressure system will force a warm front northeast across the area tonight followed by a pre-frontal trough tomorrow afternoon and a cold front tomorrow night. As the surface features move through the area, moisture associated with the system will be present and support threat for rain across the area. Latest satellite data shows precipitable water values around 1.9" advecting north with the warm front. This will support the potential for a very moist environment tomorrow when periods of moderate to heavy rain will occur in the convection. During the overnight period, forecast area is outlooked for a marginal risk for severe thunderstorms over the western quarter of the forecast area. General thunder is expected elsewhere. The day 2 outlook suggests a marginal risk for severe thunderstorms over the entire forecast area for tomorrow. Warm air advection will begin to return tonight in the wake of the warm front. This will allow temperatures to stay in the lower to middle 60s extreme east to upper 60s and lower 70s elsewhere. Highs tomorrow will be in the middle to upper 80s over much of the area with the exception of northwest Pennsylvania where highs will be in the lower 80s. Tomorrow night`s lows will drop slightly into the middle to upper 60s due to passage of the cold front. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... A cold front is expected to move southeast across the area early Thursday morning with some scattered showers/thunderstorms possible in the afternoon/evening hours. Temperatures will be right around average behind the cold front. High pressure begins building in from the northwest on Friday, though an isolated showers/thunderstorm could still be possible Friday afternoon with weak instability developing with diurnal heating. Temperatures on Friday will be very similar to Thursday. && .LONG TERM /SATURDAY THROUGH TUESDAY/... High pressure expected to have a stronger influence on the local weather on Saturday with mostly sunny skies and no precipitation chances. Hot weather returns on Sunday and Monday as high pressure departs to our east, with high temperatures in the low 90s expected. With high dew points in the low 70s possible, heat indices in the mid to upper 90s may be possible on Sunday/Monday. Slightly cooler temperatures expected on Tuesday as models key in on an approaching upper-level trough. Isolated to scattered thunderstorms expected Sunday through Tuesday, mainly during the afternoon hours with diurnal heating. && .AVIATION /00Z Wednesday THROUGH Sunday/... Generally lower confidence TAF forecast over the next 12-15 hours. Ongoing decaying SHRA/TSRA will briefly impact KMFD, and may impact KCAK over the next hour or two. Otherwise, focus of the forecast is SHRA/TSRA potential generally after 06Z from west to east across the area. Highest confidence for SHRA/TSRA and ceiling/vis reductions is at KFDY, with lowering confidence farther east through the 12Z-15Z window. A break in precip and generally VFR conditions expected mid morning through the afternoon, with more TSRA potential late in the period as a cold front moves southeast across the region. Light/variable winds through much of the overnight will increase a bit our of the west/southwest by midday Wednesday. Outlook...Occasional non-VFR possible through Wednesday night and again possible Sunday afternoon. && .MARINE... A warm front is expected to lift north across Lake Erie late this evening into early tonight, allowing southerly winds of 10 knots or less to develop during the overnight hours tonight. Southwest winds of 15 knots are then expected during the daytime hours Wednesday. A cold front will then move southeast across Lake Erie late Wednesday night into early Thursday morning allowing west to northwest winds of 10 knots to develop on Thursday. High pressure builds east across the Great Lakes region on Friday and Saturday with relatively weak winds on both of those days. By Saturday night, a warm front lifts north across Lake Erie with southwest winds of 10 to 15 knots developing on Lake Erie Sunday and Monday. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...None. PA...None. MARINE...None. && $$ SYNOPSIS...Lombardy NEAR TERM...Greenawalt/Lombardy SHORT TERM...Saunders LONG TERM...Saunders AVIATION...Greenawalt MARINE...Saunders
Area Forecast Discussion
National Weather Service Cheyenne WY
527 PM MDT Tue Jul 21 2020 .SHORT TERM...(Late this afternoon through Thursday) Issued at 315 PM MDT Tue Jul 21 2020 Latest VIS satellite imagery showed towering CU along the Laramie Range, with isolated thunderstorms indicated by KCYS radar. Convection is forming along the MUCAPE axis of 2000-2500 j/kg per SPC mesoanalysis and stalled surface boundary. Anticipate convection increasing in coverage and intensity through late afternoon, with storm motion to the ESE. Could be a few right-moving supercells per model hodographs. 19Z HRRR continues convective trends with scattered strong to severe convection affecting the I-25 corridor and high plains of southeast WY and much of the western NE Panhandle through mid-evening. 0-6km shear is 25-35 kt, with primary hazards large hail up to 2 inches and damaging wind gusts of 60 to 70 mph. Convection will diminish late this evening across western NE. Upper ridge will be centered over the south-central Plains Wednesday and Thursday. Surface boundary will begin a slow motion to the east, with drier air aloft spreading to the east into the high plains. Anticyclonic circulation around the upper high will advect subtropical/monsoonal moisture into the CWA. Scattered convection will develop during the afternoon and linger into the evening. Best instability and shear will be located east of the CWA, with a limited severe threat for the southeast NE Panhandle. A similar convective pattern is expected Thursday with a limited severe threat for the northeast NE Panhandle. Above normal temperatures will prevail with daytime highs in the 80s and 90s and nighttime lows in the 50s and 60s. .LONG TERM...(Thursday Night through Monday) Issued at 406 AM MDT Tue Jul 21 2020 Upper level ridge axis begins to shift slightly to the east over the central CONUS by Thursday evening. On the heels of the departing ridge axis from the CWA is a shortwave trough that will slowly propagate south and east through Friday. The associated cold front looks to stay north of the area however, thus daytime highs should still be very warm for this time of year for Friday. As the shortwave trough stays further to the north of our forecast region as it propagates eastward for Friday into the weekend, the monsoon moisture will begin to slowly make its way northward over the intermountain west. Medium range guidance for Friday through the weekend show a subtropical high advecting the moisture northward thanks to the clockwise airflow over Mexico. Model disagreements are still present however on the timing of the moisture advecting into the area. The Euro and Canadian model guidance show several impulses of moisture by Sunday and Sunday night making its way over the CWA, but the GFS has a slower solution that is also noted to be slightly eastward of the CWA leaving the region with less moisture overall. Weak upper level ridging to potential zonal flow for Tuesday shows the area warming back up slightly. If the long term models agree on a solution with the upper level ridging, we could be looking at near record highs to close out the end of the month of July. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 521 PM MDT Tue Jul 21 2020 Wyoming TAFS...VFR, with occasional thunderstorms producing MVFR and wind gusts to 45 knots at Laramie and Cheyenne until 02Z. Wind gusts to 23 knots at all terminals after 15Z Wednesday. Nebraska TAFS...VFR at Chadron and Alliance, with occasional thunderstorms producing MVFR and wind gusts to 35 knots from 01Z to 03Z. Wind gusts to 27 knots after 15Z Wednesday. VFR at Scottsbluff until 06Z, with occasional thunderstorms producing MVFR and wind gusts to 45 knots from 01Z to 03Z, then MVFR from 06Z to 15Z, then VFR. Wind gusts to 24 knots after 15Z Wednesday. VFR at Sidney, with occasional thunderstorms producing MVFR and wind gusts to 45 knots from 01Z to 03Z. Wind gusts to 25 knots after 15Z Wednesday. && .FIRE WEATHER... Issued at 225 PM MDT Tue Jul 21 2020 Scattered thunderstorms will develop along the Front Range this afternoon and move east onto the plains through this evening. A stalled frontal boundary will shift slowly east of the Front Range Wednesday, and into the plains Thursday. Drier air west of the Laramie Range will spread into southeast Wyoming and western Nebraska later this week. Isolated to scattered afternoon and evening thunderstorms will continue this weekend and early next week. Winds will be light, except near thunderstorms. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MAJ LONG TERM...BMW AVIATION...RUBIN FIRE WEATHER...MAJ
Area Forecast Discussion
National Weather Service Goodland KS
908 PM MDT Tue Jul 21 2020 .UPDATE... Issued at 907 PM MDT Tue Jul 21 2020 Confidence in storm activity lasting into Nebraska is on the low side based on current data. Therefore have lowered rainfall chances for the night. && .SHORT TERM...(This evening through Wednesday night) Issued at 137 PM MDT Tue Jul 21 2020 Sunny skies prevailed across the region early this afternoon, with a weak frontal boundary stalled along the Nebraska border. Satellite and 500mb RAP analysis showed northwest flow aloft as a shortwave trough moved into eastern Kansas and high pressure built over the desert southwest. At 1:30 PM MT, temperatures ranged in the 80s with east/southeast winds at 10 to 15 mph. Tonight...Chances for showers and thunderstorms return to the forecast late this afternoon through the overnight hours. A few storms are anticipated to form along the Front Range and push east into eastern Colorado late this afternoon where diurnal heating will aid the development of roughly 1000-1500 J/kg of MLCAPE. Coverage should be isolated and at this time, it is very hard to say how far east storms will make it due to weak capping that will be in place. Nevertheless, a few strong to severe storms will be possible, mainly west of Highway 25, from the late afternoon into the evening. Large hail and damaging winds will be the main threats. Additionally, locally heavy rainfall could cause flash flooding. Guidance does suggest that an area of convection meanders along the Nebraska border through the overnight hours/early Wednesday. With these storms moving into an unstable environment, cannot rule out isolated instances of large hail and strong winds. Otherwise, expect lows in the 60s. Wednesday and Wednesday night...Storms may linger across the northeastern portion of the region early Wednesday morning before exiting around sunrise. Sunny skies are expected midday with high temperatures in the 90s. Southerly winds will be breezy, gusting up to 30 mph in the afternoon and evening. Another round of thunderstorms is forecast to form along a lee trough in the afternoon and evening. Although uncertainty remains on exactly where storms will develop, the best chance for severe weather will be along and north of Interstate 70, with large hail, damaging winds, and heavy rainfall possible. Low temperatures fall into the 60s/low 70s overnight. .LONG TERM...(Thursday through Tuesday) Issued at 118 PM MDT Tue Jul 21 2020 At the start of the extended period the models are showing the local area under the influence of a strong upper-level high and ridge over the Plains that is producing weal southwesterly flow aloft over the Central High Plains region. This pattern looks to be the dominating feature for the period. Above normal temperatures (middle 90s) are anticipated through the weekend before we see a slight cooling (upper 80 to lower 90s) on Monday. Daily chances for showers and thunderstorms are possible during the extended forecast, mainly in the afternoon and evening hours. However, confidence in widespread moisture is low at this time. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 546 PM MDT Tue Jul 21 2020 VFR conditions forecast for the TAFs. Main focus is whether any thunderstorms will move near KMCK around 6z tonight. At this time confidence is low enough to leave out a mention in the TAF. Current data suggests the storm coverage will either remain north of the site or dwindle in coverage as it approaches the site. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ UPDATE...JTL SHORT TERM...JBH LONG TERM...BW AVIATION...JTL
Area Forecast Discussion
National Weather Service Hanford CA
131 PM PDT Tue Jul 21 2020 .SYNOPSIS... A couple afternoon thunderstorms are again possible over the higher elevations of the Sierra Nevada this afternoon. Slightly cooler tomorrow and Thursday as low pressure moves through, with a rebound back to normal temperatures this weekend. && .DISCUSSION... The low pressure system that is nearing the California coastline is bringing some high level cloud cover today along with slightly lower afternoon highs. Some cumulus clouds are forming over the Sierra Nevada as of this writing and may evolve into isolated thunderstorms as the upper trough aids in lift. Latest run of the HRRR is targeting the Sierra Nevada in Fresno County for the best chance of thunderstorm development this afternoon. The trough is expected to move overhead tomorrow, bringing down afternoon highs generally 3-6 degrees below average for mid to late July as upper heights fall. Hi resolution guidance is looking more bearish for convective coverage tomorrow, so storms will likely be confined north of Fresno County if they do form. Breezy conditions along the west side hills may develop by afternoon as the trough moves inland as well. Slightly cooler again Thursday as the closed low weakens and opens into an open wave and moves northeast out of the area. Thereafter, upper heights are projected to rise slowly into the weekend, which should result in a modest warming trend. Blended model guidance is suggesting the return of triple digit heat for most of the forecast area by next Monday. && .AVIATION... Isolated thunderstorms along the Sierra Crest through 03z Wednesday. Otherwise, VFR conditions will prevail elsewhere across the central California interior during the next 24 hours. && .AIR QUALITY ISSUES... None. && .CERTAINTY... The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is medium. Certainty levels include low...medium...and high. Please visit for additional information an/or to provide feedback. && .HNX WATCHES/WARNINGS/ADVISORIES... None. && $$ public...Bollenbacher aviation....Bollenbacher
National Weather Service Wilmington OH
944 PM EDT Tue Jul 21 2020 .SYNOPSIS... Upper level energy will cross the region this afternoon and help lift a warm front northeast of the I-70 corridor this evening. A more vigorous shortwave will approach from the west overnight, spreading showers and thunderstorms across the region from northwest to southeast. This upper level wave and eventual surface cold front will lay out west to east through northern Kentucky Wednesday night and early Thursday, with a lull in activity expected from Thursday through the weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... The convection that was primarily diurnally-driven/initiating off of a weakening outflow boundary which pivoted southeast through the ILN FA has since waned locally, setting up an environment with a fairly stable boundary layer -- especially near the I-70 corridor and points northward. This is well- reflected not only on SPC mesoanalysis page with ample CIN positioned from near Dayton to Columbus and points north but also by the nearly-saturated surface obs with dewpoint depressions of only 5 degrees or so for most locales from east- central IN through central Ohio. With this being said, the aforementioned convectively-generated outflow petered out from approximately Butler Co to Ross Co OH, leaving an instability gradient oriented west-to-east across the southern third of the local area. The evolution of this somewhat untapped environment will need to be watched as a fairly organized MCS approaches from the west through midnight. Short- term hi-res data continues to handle the situation very poorly and even the HRRR continues to play catchup with regards to the evolving situation by several hours. Do think that the hi-res models are also overestimating the BL CIN across the southern third of the local area and are therefore killing the convection too quickly as it progresses east closer to the ILN FA through 11 PM. Although some of the cloud tops have warmed over the past hour or two -- there are still potent updrafts firing along the leading edge (as seen on GOES-16 IR and through traditional radar interrogation techniques). With the upstream environment still relatively ripe for convection -- with about 1500j/kg MLCAPE in south-central/central IN -- feel that the MCS may continue to have episodic strengthening of updrafts on the leading edge of an increasingly-cold pool dominated complex through the next 2-4 hours or so. While the cloud-bearing /deeper-layer flow would suggest more of an ENE propagation, the complex may attempt to develop more to the southeast in the direction of the more robust low level instby pooling across south-central IN/southeast Indiana. This should result in better maintenance of convection of the southern flank -- perhaps eventually trailing to the southwest of the main MCS later in the overnight with the strengthening of a LLJ -- as it moves into SE IN and SW OH/northern KY by midnight. Not a clear-cut situation by any means -- but will likely see most robust convection focus further south with time as the northern segment of the MCS will be running into a thermodynamically-unfavorable environment near the I-70 corridor. Many factors at play here but decided to introduce likely PoPs in the west/central parts of the area between about 11 PM and 3 AM as the core of the convective complex -- or what remains of it -- quickly pushes east. With decent LL/effective shear and a moderately unstable environment immediately ahead of the strongest cores, will likely see at least /some/ severe threat evolve into the western parts of the local area through about 1 AM or so. Beyond this, the evolution of the mesoscale environment remains a bit more uncertain, so will at least say that spots from near Dayton to Wilmington to Maysville and locales further to the southwest may see a low end severe threat evolve for several hours later this evening. Will likely see at least a few SPSs for gusty winds by midnight in our west/southwest. Feel that the expansion of the MRGL risk east into the SW part of the ILN FA is well-warranted to cover the evolving weather situation late this evening. The MCS /eventually/ will begin suffer on account of diurnally- induced stabilization of the environment and an outrunning of the main convective line from the source of focus/lift. This being said, even after the MCS moves through -- with the remnants exiting our east by about 08z or so, additional LLJ- induced shower activity will continue to sprout across IN/western OH through daybreak as the main elongated S/W energy approaches from the WNW. Will see temps bottom out in the lower 70s area-wide. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Storms will spread NW to SE and linger for the bulk of the day, keeping highs in the low to mid 80s in the north and near 90 in the southeast which may stay dry for a better portion of the day. Storms will line up on a more w-e boundary that lays out south of the Ohio River later overnight, possibly lingering in the evening for the eastern sections of the CWA and Scioto Valley. Lows will be around 70 and could go lower if the cold front is more pronounced with a northwest flow, versus the westerly shift noted attm. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Mid level short wave energy will move across the lower Great Lakes through the day on Thursday. This will help push a cold front southeast into the upper Ohio Valley Thursday into Thursday night, leading to an increasing chance of showers and thunderstorms as we head through the afternoon. The front will then stall out along the Ohio River as it weakens Thursday night into Friday. As a result, will linger some lower chance pops through Friday, especially across southern portions of our fa. Highs Thursday and Friday will be in the mid to upper 80s. Mid level ridging over the mid Mississippi Valley will try to build a little more to the northwest through Saturday, but some very weak mid level energy dropping down the front side of the ridge may be enough to allow for an isolated shower or thunderstorm Saturday afternoon. The ridge will then begin to break down with northwest flow aloft setting up across the region through early next week. Occasional weak short waves dropping down from the northwest will lead to some lower end chances for thunderstorms at times for Sunday and Monday. Highs both days will be in the upper 80s to lower 90s. A cold front may eventually push southeast into the region heading into Tuesday, resulting in some better chances for showers and thunderstorms by the end of the long term period. Highs on Tuesday will be in the mid to upper 80s. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... For the most part, VFR conditions will prevail through the entire period for all sites. Isolated showers/storms will wane through the first hour or so of the valid TAF period before a decaying cluster of storms again moves through by/past 05z or so. There is a great deal of uncertainty regarding the overnight activity and its maintenance as it progresses eastward into the local area between 05z-11z or so. It appears that western sites of KCVG, KDAY, and KLUK may see the best chance of showers/storms during this time period, but confidence is admittedly fairly low in each site being impacted by a SHRA or remnant TSRA. Surface winds will generally be light and variable for the overnight period but will be convectively-determined with various mesoscale boundaries/features persisting through the overnight period. Winds, in general, will increase to about 8-10kts past 15z from the southwest. Main item of interest for the daytime period will be fairly widespread but disorganized convection developing as early as 15z. Activity will be somewhat chaotic in nature, so timing out a particular impact at one particular terminal is difficult at best. Decided to broad-brush a VCTS for all sites with TEMPO TSRAs from late morning through the afternoon -- with an earlier initiation expected for western sites of KCVG, KLUK, and KDAY. May also see isolated activity linger past sunset/00z Thursday. Any storm from late morning through the afternoon will be capable of brief gusty winds and reductions to both CIGs and VSBYs to MVFR or lower. OUTLOOK...Thunderstorms will be possible at times through Wednesday night. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Franks NEAR TERM...KC SHORT TERM...Franks LONG TERM...JGL AVIATION...KC
previous forecast discussion noted the potential for heat headlines
by the weekend and given the strong signal across guidance for
aclimatological heat and humidity (this forecast again has afternoon heat indices of 95-100 both Saturday and Sunday) it`s hard to disagree with that assessment. Further contributing to the misery will be the lack of relief at night with lows only dropping into the mid 60s interior and staying in the 70s along the Lake Superior shoreline where there will be continued downslope warming through the night on the south wind. As for precip chances, well that`s a bit harder to say. On the large scale, it seems the height gradient will actually be too far north for much precip during the day Saturday or Sunday. Any ridge rollers would follow the height gradient across western and northern Lake Superior. Thus, Isle Royale and the Keweenaw have the best chances for storms Saturday and Sunday. However, with so much moisture and instability around, it`s possible the lake breezes convect each day, so more or less held on to the NBM`s chance POPs each day. The better chance area-wide right now looks to be Sunday night into Monday when a cold front drops southward across the UP. Experimental CIPS Analog Guidance shows somewhat of a severe weather signal as well, which makes sense with the continued high CAPE and at least modest deep layer shear. But of course those details are difficult to discern so far out, so stay tuned for updates. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 622 PM EDT TUE JUL 21 2020 Rain showers will continue to move through tonight with increasing low level moisture. Will maintain MVFR conditions into tonight with the potential for periods of IFR at KIWD. Expect all sites to lower to IFR by early Wed morning. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 415 PM EDT TUE JUL 21 2020 Low pressure will pass south of Lake Superior tonight into Wednesday with east to northeast winds to near 20kts. A few northeast gusts to 25 knots are possible over far western Lake Superior. These winds will weaken and shift northerly late Wednesday in response to high pressure building in from the west. Generally light winds will continue into Friday as high pressure continues to dominate. South to southwest winds could increase as high as 15 to 25 knots by Saturday as another trough/frontal system approaches from the Northern Plains. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...JLB LONG TERM...RJC AVIATION...07 MARINE...JLB
Short Term forecast discussion from this afternoon is still
relevant as we move into tomorrow.
ABM && .AVIATION... 00Z TAF DISCUSSION. Showers and thunderstorm activity should continue to wind down, with the exception being at KCHA where a line of storms from northern GA may move over the airport in the first couple of hours of the TAF. Fog may once again form overnight, but certainty on location of fog wont increase until we see where rain has occurred this evening. Another round of storms is expected tomorrow, but coverage should be higher than what we saw today. ABM && .PREV DISCUSSION... /ISSUED 330 PM EDT Tue Jul 21 2020/ SHORT TERM (This Afternoon through Wednesday)... Current water vapor imagery and RAP upper air analysis depict a trough stretching from the Upper Mississippi River Valley southwestward into the southern Plains with a ridge across the western Atlantic into the southeastern U.S. This ridge has been the main feature for the last several days. At the surface, there is a front to the north stretching from IL to the east into the Mid- Atlantic. This front is forecast to wash out as a more dynamic system moves in from the northwest associated with the aforementioned upper trough. Current radar imagery indicates scattered convection across the area with best coverage, so far, over the higher elevations. The cu field is expanding on visible satellite imagery and should see the coverage of showers and storms increase throughout the afternoon. Temperatures are in the upper 80s to mid 90s early this afternoon with surface dewpoints in the upper 60s and lows 70s. The atmosphere remains relatively unchanged over the last several days with modest CAPE values and little to no shear. In this typical summertime atmosphere, cannot rule out a strong to marginally severe storm or two with an isolated damaging wind gust being the main threat. Most storms will remain well below severe criteria. Additionally, PW values are in the 1.7-1.9 inch range. Therefore, any storm that does form could produce heavy rainfall. With the lack of any upper flow to really move the storms, localized flash flooding could become an issue with some of these storms. Convection should begin to diminish in coverage and intensity around sunset but with the instability and outflow initiated storms, precipitation could linger into the early overnight period. Lows tonight will once again range from the upper 60s to mid 70s. Some patchy fog could be possible around sunrise, especially for areas that experience rain later this afternoon and evening. The upper level trough will move across the Great Lakes and Ohio River Valley on Wednesday. Upper level heights will fall slightly across the area but the ridge looks to remain resilient and 500 dm heights will still be 590 dm+. The front should remain to the north of the forecast area throughout the short-term forecast period but will drop southward across IL/IN/OH on Wednesday. Heating throughout the day will yield similar instability as the past several days. The forecast area will also be in the right entrance region of a 60-80 kt 300 mb jet that will be located across the eastern Great Lakes into the Northeastern U.S. This will provide some weak synoptic lift as well. This lift will be coupled with elevated PW values in the 1.8-2.0 inch range. Therefore, have a bit higher confidence in coverage of showers/storms tomorrow afternoon. A few of these could be strong to marginally severe with an isolated damaging wind gusts being the main threat but most storms will remain well below severe criteria. Additionally, these showers/storms will produce heavy rainfall and could lead to some area of localized flash flooding. Best chances for a strong to severe storm will be across southwest Virgina closer to the lift and front. Highs will be slightly cooler tomorrow but will still be in the upper 80s to low 90s for most locations. MA LONG TERM (Wednesday Night through Tuesday)... Key Messages: 1. Higher chances for showers/storms continues Thursday; some could produce localized flooding and isolated damaging winds and hail. 2. Turning hotter and drier this weekend through early next week with only scattered afternoon/evening thunderstorms. Discussion: Wednesday Night Through Thursday Night... As the mid/upper shortwave over the Great Lakes translates E Wed night, the associated surface low will move along the borders of upstate NY and SE Ontario and drag a cold front into the lower OH valley and central Appalachians before the boundary briefly stalls. This front and upper level support from the shortwave passing to the N will keep chance PoPs for showers/storms Wed night, but coverage will not be very widespread due to nocturnal cooling. Coverage of convection will rapidly increase from mid morning through the afternoon Thursday as a secondary shortwave digs into the NE U.S. and begins to push the front slowly southward through the S Appalachians region. The strongest forcing is tied to the aforementioned shortwave over the NE, but some confluence aloft and mid level vorticity, likely associated with old convection, will work with daytime instability, lack of capping, and convergence along the boundary to generate widespread convection. Seasonably high values of instability are expected with MLCAPE of 1500 to just over 2000 J/Kg and LI`s of -6 to -8, but deep layer shear is weak at only 10-20 kts in the 0-6 Km layer. The highest shear is over NE TN and SW VA. SPC Day 3 outlook just outlines general thunder, but this environment supports localized severe weather with damaging winds the main hazard, but slightly lowering WBZ heights could also support localized hail. DCAPE is a little low mostly in the 500-700 J/Kg range, so any wind damage should be spotty. The bigger impact will be locally heavy rain from convection since the weak flow will lead to slow storm motions and backbuilding, and PWATs of 1.8 to just over 2 inches supports efficient rainfall rates. Any areas that see heavy rain on Wed will be the most primed for localized flooding. Convection will wane after dark Thurs night, but with the front crossing the region, kept chance/slight chance PoPs through the night. Temps will be seasonable this period (upper 80`s/low 90`s for highs and upper 60`s/low 70`s for lows). Friday and Friday Night... The cold front should push S of the region through the morning on Fri as NW flow develops over the eastern CONUS in the wake of the stronger NE U.S. shortwave, and surface high pressure moves into the Great Lakes. This will bring drier air into the region, but very limited cooling. There will be afternoon instability again, but took PoPs down significantly from the NBM with chance across the region Fri since the front will be moving S. Went dry Fri night with nocturnal cooling and drier air finally winning out. Highs will still reach the upper 80`s/low 90`s with lows in the upper 60`s/low 70`s. Saturday through Tuesday... This period still looks to have building heat, but deterministic and ensemble guidance have all trended slightly farther W with the center of the ~594 DM H5 high this weekend, which will then begin to retrograde toward the Rockies by Tues as shortwave energy dives into the Great Lakes and brings back a NW flow pattern by midweek. This means that highs in the low 90`s with perhaps a few mid 90`s are most reasonable during this period with chance PoPs each afternoon as diurnal instability interacts with weak perturbations rotating around the eastern periphery of the high. Garuckas && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 74 93 73 93 73 / 30 40 20 60 20 Knoxville McGhee Tyson Airport, TN 73 91 73 92 72 / 30 40 30 70 30 Oak Ridge, TN 73 91 72 92 72 / 30 40 30 70 30 Tri Cities Airport, TN 69 89 69 87 68 / 20 40 40 70 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$
Area Forecast Discussion
National Weather Service Nashville TN
708 PM CDT Tue Jul 21 2020 .UPDATE... FOR EVENING DISCUSSION. && .DISCUSSION... Will opt to delay the decreasing pops as isol to sct coverage persists. Hrrr wants to hold on to the activity into the evening and given the current cape values this looks believable. This evenings upper divergence appears to shift over eastern areas by 03Z and so the best shot of convection holding on is across that area. Otw, overnight lows still look acceptable. No other changes. && .AVIATION... 00Z TAF DISCUSSION. Isolated to scattered convection again in place across middle TN this afternoon. A weakening shortwave axis will be on approach tomorrow and thus, afternoon coverage will be greater as compared with today`s activity. Otw, tover values are running positive this afternoon and so for the overnight, just light fog will again be possible, particularly for areas where rainfall occurred earlier. && .OHX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION......11 AVIATION........21
Area Forecast Discussion
National Weather Service Blacksburg VA
906 PM EDT Tue Jul 21 2020 .SYNOPSIS... An upper ridge across the southern U.S. will maintain itself into Thursday before a front arrives late in the week. && .NEAR TERM /THROUGH WEDNESDAY/... As of 905 PM EDT Tuesday... Widely scattered storms continue under an axis of DCAPE values in excess of 1000 J/KG, so locally damaging winds are still possible for the reminder of the evening. 23Z HRRR has a good handle on the current location of convection and keeps storms across the VA southside until around midnight-1 AM EDT. Adjusted POPs up in this area. There will be a weakness in the upper ridge as a shortwave passes into the Ohio Valley late tonight. This may help a complex of storms move into WV by daybreak, but the model consensus is to keep this west of our area through 12Z (8 AM EDT) Wednesday. With a stagnant airmass in place, followed persistence for lows and bumped up lows at ROA closer to values experienced Tuesday morning. Wednesday appears somewhat similar to this afternoon as storms fire up noon or just before. Difference is a slight cooling aloft with trough moving across the upper Ohio Valley. SPC has a slight risk for severe north of U.S. 60, as better upper support/shear push across northern WV/VA, and density from storms may sink the convective system south toward Lynchburg to Roanoke/Lexington by mid afternoon. Overall storm coverage looks more numerous in the Shenandoah Valley and mountains, with less southside VA/NC piedmont. Highs Wednesday will be in the mid 80s to around 90 west, to mid 90s east. The exception will be the highest terrain of SW VA/NW NC with upper 70s to lower 80s above 3500 feet. See climate section below for records. Forecast confidence is average for storm location/coverage this evening and again Wednesday, but high on temperatures. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... As of 200 PM EDT Tuesday... An area of low pressure will cross over Maine in association with a passing upper level trough during Wednesday night into Thursday. It will drag a cold front toward Ohio and Pennsylvania by Thursday afternoon, which should spark another round of showers and thunderstorms across the Mid Atlantic. There remains plenty of instability ahead of this front based on the ample heat and humidity. Thus, the Storm Prediction Center has highlighted a marginal risk of severe weather mainly along and east of the Blue Ridge. The record consecutive streak of 22 days for hitting at least 90 degrees (June 23 through July 14 in 1966) at Roanoke will be toast by midday Thursday as we reach day 23 of this current streak. The cold front should slowly sag southward through central Virginia by Thursday night into Friday, which will push the focus for convection toward the Virginia and North Carolina border during Friday afternoon. Meanwhile, the impressive upper level ridge responsible for all the heat will start to shift westward toward the Plains as the upper level trough digs further across the Northeast. Slightly drier air could infiltrate from the northwest by Friday night as high pressure takes control over New York. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 200 PM EDT Tuesday... The cold front should push further southward across North Carolina on Saturday and eventually head offshore toward the latter half of this weekend. Confidence is increasing for shower and thunderstorm chances to diminish by Sunday based on better agreement between the ECMWF and GFS models. Still, a chance will be left across the northwest North Carolina mountains as orographical lift may spark isolated convection. Temperatures could be a little cooler for Saturday compared to earlier in the week, but this slight reprieve will be brief as the influence of the upper level trough should fade away by Sunday. If the record streak of 90-degree days at Roanoke is not halted by Saturday, it will continue well into next week as heights aloft rise during Sunday and Monday. Consequently, the heat and humidity should begin to creep up again. The potential for showers and thunderstorms could tick up by Monday afternoon west of the Blue Ridge as the next cold front and its associated upper level trough enters the Ohio River Valley. Convection chances increase further on Tuesday as the trough digs southward and pushes the cold front toward the Appalachian Mountains. The slower ECWMF solution was favored for the latter part of this forecast as the GFS seems too fast given this summertime pattern. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/... As of 645 PM EDT Tuesday... Scattered showers and thunderstorms across portions of southwest Virginia will gradually diminish this evening. Kept VCTS for all TAF sites except KLYH until 02-03Z (10-11 PM EDT). Once the storms diminish VFR conditions will prevail for most TAF sites overnight, but MVFR fog, or worse, is possible at KLWB before dawn Wednesday. Expect better coverage of thunderstorms on Wednesday, especially after 18Z (2 PM EDT), and included VCTS at all TAF sites, as it is too early to pinpoint which locations will be directly impacted. These storms will have the potential to produce gusty winds and heavy rain and should they move over a TAF site, a short period of IFR conditions are possible. Extended Aviation Discussion... Overall mainly VFR weather to continue through most of the week. We will continue to have afternoon and early evening scattered storms through the extended period. Thus periods of sub-VFR are possible in storms, and potential for late night/early morning fog at LWB/BCB and perhaps other locations depending on where there is daily significant rainfall. && .CLIMATE... Record temps for today at climate locations: Tuesday 07/21/2020 Site High/Year Warm Low/Year BLUEFIELD 94 1934 78 1934 DANVILLE 102 1977 75 2015 LYNCHBURG 103 1926 80 1930 ROANOKE 104 1926 75 2008 BLACKSBURG 99 1926 74 1934 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS/WP NEAR TERM...WP SHORT TERM...PH/PW LONG TERM...PW AVIATION...PH CLIMATE...WP
Area Forecast Discussion
National Weather Service Sacramento CA
331 PM PDT Tue Jul 21 2020 .SYNOPSIS... Gradual cooling trend this week. A few late day thunderstorms are expected over the mountains. Keep an eye to the sky if in the mountains. Southwest breezes continue near the Delta with locally breezy conditions elsewhere. && .DISCUSSION... Visible satellite imagery shows some convective cumulus clouds beginning to bubble up along the Sierra crest this early afternoon. Additionally, plenty of mid/high clouds continue to stream onshore the central California coast, providing some filtered sunshine to the San Joaquin and southern Sacramento Valleys. Main story for today will be the potential for afternoon/evening convection in the higher elevations across portions of central and northern California. The latest HRRR and 3-km NAM are generally keeping the convection along/east of the Sierra crest as well as near the peaks of the coastal ranges, but will closely monitor radar as the afternoon progresses. Upper level low centered off the northern California coast will push inland over the next 24-48 hours. This upper low along with moisture in the mid/upper levels will provided a renewed opportunity for showers and isolated thunderstorms for the mountains on Wednesday. Additionally, a welcomed relief from the triple digits will be finally realized in the northern Sacramento Valley by tomorrow as onshore flow continues to ramp up and temperatures moderate closer to seasonal normals. Trough will sag over the West Coast into the second half of the week with highs near or even slightly below normal. // Rowe && .EXTENDED DISCUSSION (Saturday THROUGH Tuesday)... Short wave energy moving through Wrn Canada on Sat should result in a more stable atmosphere over Norcal, and little if any thunderstorm activity in our CWA (south of Hwy 50), even though a broad weak trof will remain over our region. Re-establishment/re-orientation of this weak trof over Norcal could trigger isolated convection over the Nrn Mtns/ Srn Cascades Sun/Mon. This will be followed by drier, more stable flow over Norcal on Tue as a longer wave trof is forecast to develop over the Ern Pac/along the Wrn Coast of NOAM by the middle of next week. Temperatures should remain close to average on Sat, then trending slightly warmer into early next week. This will mean a return to triple digit temps up north and mid to upper 90s in the Srn Sac/Nrn San Joaquin Valley and lower foothills. Onshore flow will have an ameliorating influence on temps in the marine/Delta influenced areas. JHM && .AVIATION... VFR at Norcal TAF sites with some local/enroute wx concerns. First, scattered afternoon/evening thunderstorms over Sierra between 21z Tue-03z Wed with isolated storms over Trinity Alps/Shasta Co mtns. Second, local areas of smoke (FU HZ) from Wildfires mainly Shasta and Plumas Counties. Third, SWly surface wind 25g35kt through the Carquinez Strait/Delta with marine stratus spreading into coastal range valleys and Wrn Solano after 06z Tue with TOPS 020-025. Stratus retreating to the coast after 18z Wed. Upper low off the SFO Bay area coast spreading high cloud cover (BKN AOA 200) over SAC area/SCK/MOD TAF sites through 07z Wed with conditions becoming SKC thereafter. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$