Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/18/20

Area Forecast Discussion
National Weather Service Boise ID
854 PM MDT Fri Apr 17 2020 .DISCUSSION...No forecast changes through midday Saturday, but the new HRRR threatens isolated showers and/or thunderstorms in all of eastern Oregon Saturday afternoon, i.e., earlier than our forecast. For now the HRRR is the only model that does it so we won`t update at this time. But if other 00Z models come in with earlier showers, the overnight forecast package will probably include them. Otherwise, the current forecast looks fine, with several degrees warming expected Saturday, and a milder night Saturday night. && .AVIATION...VFR. Mostly clear, then increasing high and mid level clouds Sat afternoon/evening. Isolated showers/thunderstorms with MVFR and mountain obscurations expected after Saturday/21Z. Thunderstorms could produce erratic gusts of 20-30 kt. Snow levels above 6kft MSL. Surface winds: outside of storms, variable 8 kt or less, becoming W to NW 5-15 kt after Saturday/18Z. Winds aloft at 10kft MSL: SW to W 5-15 kt. Sunday Outlook...Mostly VFR. Isolated showers bringing MVFR conditions through Sunday morning. Snow levels generally around 5500-6500 ft MSL. && .PREV DISCUSSION... SHORT TERM...Tonight through Sunday night...Another cool, clear night under a dry and stable air mass. An upper trough will approach the region from the northwest on Saturday, increasing clouds from north to south through the day. Southeast Oregon and northern portions of the w-central Idaho mountains will see isolated showers develop by early evening with the slight chance they develop into thunderstorms. Passage of a front Saturday night will bring gusty winds to 25 mph. Showers will continue across portions of southeast Oregon and southwest Idaho south of the Snake Plain Saturday night into Sunday as the trough crosses the area. Thunderstorms are again possible Sunday afternoon across higher terrain surrounding the central Snake Plain. Shower activity will diminish by Sunday evening as the trough exits eastward. Temperatures will be slightly above normal through the weekend. LONG TERM...Monday through Friday...High pressure over the Pacific Northwest will help drive an upper low to our south leaving a slight chance for shower activity through higher elevations close to the NV border Monday afternoon. As this ridge weakens, a stronger system will push through Wednesday creating scattered showers through early Thursday. Drier conditions expected Friday as we sit in between systems. Temperatures swill it above normal through mid week then drop to near normal behind the frontal system. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ DISCUSSION...LC AVIATION.....SH PREV SHORT TERM...DG PREV LONG TERM....JC
Area Forecast Discussion
National Weather Service Denver/Boulder CO
840 PM MDT Fri Apr 17 2020 .UPDATE... Issued at 830 PM MDT Fri Apr 17 2020 Have updated the grids this evening to account for patchy fog the appears be developing, primarily along the South Platte River Basin. Latest HRRR shows very shallow moisture lingering across this area most of the night. Otherwise, no other adjustments needed. && .SHORT TERM...(This evening through Saturday) Issued at 214 PM MDT Fri Apr 17 2020 Water vapor imagery showing very dry and subsident airmass across northeast Colorado this afternoon with warming temperatures and melting snow. Temperatures have risen into the upper 40s/lower 50s with bare ground, while snow covered areas temperatures struggling still in the 30s. For tonight, mainly clear skies but will see some increase in middle and high level moisture in advance of storm system over the desert southwest. For Saturday, a closed low now over Southern California will gradually weaken and move across Southern Colorado Saturday afternoon with some weak to moderate QG ascent with this system. However, the best ascent will be across Southern Colorado. Coupled with some moisture and steepening lapse rates will result in a good chance for mountain showers and possibly a few thunderstorms as well in the afternoon. Some of these showers will also bleed over the adjacent plains and Palmer Divide. Surface based CAPE values up around 800j/kg so don`t really expect any severe storms. Temperatures will continue to warm into the 50s except 40s over snow covered areas. Current forecasts has things in good shape so only minor changes. .LONG TERM...(Saturday night through Friday) Issued at 214 PM MDT Fri Apr 17 2020 A weak shortwave will move across Colorado Saturday evening into Sunday. The upper level jet will be further south bringing mostly orographic snow to the higher mountains with the increased moisture associated with the disturbance. As the jet pushes north over the region lapse rates across the higher elevations will be in the 8-9 C/km range increasing showers over the mountains with a slight chance over the plains by the evening hours on Sunday. Temperatures will be closer to seasonal normals with highs in the lower 60s across the plains. For Monday, west to northwest flow will be across the area with enough mid-level moisture for some isolated showers in the mountains by the afternoon. Temperatures will include their upward climb with highs reaching into the mid-60s. For the remainder of the week an upper level trough will move across the southern Rockies Tuesday with the best lift and moisture over the desert southwest. Models are showing enough CAPE for some isolated showers and storms for the plains by the afternoon/evening hours Tuesday. Conditions will dry our slightly on Wednesday with some mid-level ridging given the models desire to put in pops. Will keep on the dryer side with on a slight chance across the higher elevations to account for any diurnal showers. Temperatures will be around seasonal normals through the week with highs registering into the 60s to possibly lower 70s for some areas out east. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 830 PM MDT Fri Apr 17 2020 MVFR vsbys a short time ago with patchy fog developing at KDEN. Light northwest winds at this time, expected to go to drainage later this evening which should shift the fog north and east of KDEN. If this drainage wind does not kick in then patchy fog may linger at KDEN and well as KBJC overnight. Outside of this, VFR expected tonight with mainly clear skies. Some increase in mid/high level moisture during Saturday which may lead to a brief window for showers in the afternoon. I went ahead and added a prob30 group to account for the showers. Could see some brief outflow wind gusts 20-25 kts with any showers that develop near the terminals after 21z. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Cooper SHORT TERM...Entrekin LONG TERM...Bowen AVIATION...Cooper
Area Forecast Discussion
National Weather Service Caribou ME
915 PM EDT Fri Apr 17 2020 .SYNOPSIS... High pressure will build in tonight into Saturday while Low tracks south of the region. A cold front will cross the region later Sunday night through early Monday. Low pressure will approach from the west Tuesday and pass through the region on Wednesday. && .NEAR TERM /THROUGH SATURDAY/... 9:15 pm update: Just about all of the diurnal showers have dissipated. There could still be a flurry in spots near Stockholm and Loring, but likely just a bit of virga. It is now mainly clear across the FA, but still partly cloudy across northern Aroostook County. Attention turns to low pressure moving out of the OH Valley and into western PA as of 9 pm. The low will track to the NY bight by 12Z Saturday spreading clouds across the Downeast Region overnight. Made some minor adjustments to the forecast based on the current and expected conditions, but overall the changes were mostly minor. Previous discussion: The sfc trof swinging across the region this afternoon w/rain- snow showers. Steep llvl lapse rates with cold air aloft has allowed for instability. Some of the activity included gusty winds and brief heavy rain/snow as was evident in Frenchville(KFVE) this afternoon. The latest HRRR along the NMM guidance did well in coverage and showing the potential for heavier activity. The sfc trof will be passing off to the east w/winds dropping off and clearing skies. Temps will drop off sharply after sunset w/the winds dying off. Some areas back across the Allagash and St. John Valley could see mid to upper teens by 6 AM Saturday. High pres builds across the region on Saturday while low pres passing by to our s. The northern fringe of the precip shield could skirt the coastal region, especially along the outer islands on Saturday. The latest NAM/GFS show some light precip along the coast. The ECMWF matches close and has been consistent with this setup. Decided to stay w/the midnight crew`s thinking of 20-30% percent chances for some light rain along the coast. Further n, dry and less clouds w/miler temperatures. Daytime temps for Saturday should reach near normals. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... Ridge will build quickly behind exiting low pressure, with SW flow restricting much cool NW wind in its wake. This advects warm air into the region as well as some clearing remaining through the early afternoon. Temps warm into the upper 40s across the north with 50s across central and Downeast areas. Clouds increase during the afternoon as a weakening cold front approaches from the west. Expect rain showers to arrive during the evening across the north, and pass through Downeast after midnight. As temperatures drop with the passage, some of the rain showers will change to light snow showers across the north up to the early Monday morning hours. Expect QPF to remain low as guidance continues to suggest weakening with its translation eastward. Clouds will begin to clear Monday afternoon behind the front, tho temperatures will be cooler than Sunday as winds get a little breezy w/ mixing out of the NW. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... GFS and Canadian continue to keep a mid-Atlantic storm system tracking outside the Gulf of Maine Tuesday, with the ECMWF now agreeing. As a result, have trended PoPs down earlier along the Downeast coast. Tuesday will remain mostly dry as another system approaches. Low pressure tracking along the southern tier of Canadian Provinces will gain energy as a jet noses in from the NW. Intensification looks to take place over the eastern Great Lakes with the system becoming vertically stacked over central Quebec. There remains the differences of timing and location of this low, which will determine if Maine sees its precip from a frontal passage or the low tracking through the state. A more progressive frontal passage would be warm, resulting in mostly rain, while a low track across the state would yield cooling conditions across the north. This could provide some mention of snow, particularly on the back side as cool air filters around the low. Either case supports a push of cool air that could support a rain/snow mix as the system tracks to the east, so have kept a chance in the forecast, mainly from the Central Highlands north. PoPs decrease Wednesday night, with a few lingering snow showers possible across the north. Zonal flow takes over briefly with widespread westerly motion across New England as a high exits the mid-Atlantic coast. The next precip comes as a storm carries up the return flow towards the Northeast. Broad low pressure develops, with a few lows approaching, one towards the Gulf of Maine, and another across the Ohio Valley. While GFS and ECMWF both show these systems developing, timing and placement are not in high confidence at this time and will keep forecasts below likely categories. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... NEAR TERM: VFR through Saturday. The caveat is KBHB where MVFR cigs are possible w/low pres passing by to the south. MVFR ceilings were introduced with the 00z Tafs starting around 18Z. SHORT TERM: Sat Night - Sun...VFR all terminals with the exception of BHB on Saturday night where MVFR cigs are possible. Sun night...MVFR northern terminals in low cigs and -shrasn. SW winds around 5-10kt. Mon through Mon night...VFR under high pressure all terminals. NW winds 5-10kts gusting to 15-20kts in the afternoon. Tue - Tues Night...Becoming MVFR in the afternoon. S winds 5-10kts gusting to around 20kts near BGR and BHB in the afternoon. Rain showers arriving in the afternoon will change to a mix of rain and snow across northern terminals, occasional IFR will be possible. Wed...MVFR/IFR will improve towards VFR late Wednesday as precip tapers west to east. SW winds becoming W with gusts approaching 25 kt during the afternoon. && .MARINE... NEAR TERM: Extended the SCA until 10 pm EDT this evening. Still getting gusts to low end SCA. The wind will slowly diminish tonight as high pressure builds into the region. Conditions are expected to be below SCA levels later this evening and through the day Saturday. SHORT TERM: Below SCA criteria is expected Sunday with winds increasing towards SCA in the evening and early overnight hours. Waves will respond to a SW fetch, becoming highest along the Washington County coast. Winds and waves again fall below SCA Monday afternoon through Tuesday morning. Another SCA may be needed Tuesday into Wednesday as a storm system approaches from the west. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...None. MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ050- 051. && $$ Near Term...CB/Hewitt Short Term...Cornwell Long Term...Cornwell Aviation...CB/Hewitt/Cornwell Marine...CB/Hewitt/Cornwell
National Weather Service Jackson KY
808 PM EDT Fri Apr 17 2020 .UPDATE... Issued at 808 PM EDT FRI APR 17 2020 An outflow from the rain across northern Kentucky has shifted southward through the evening hours with a sharp temperature drop from the low 70s into the 50s being seen behind this boundary. Meanwhile, rain continues to impact areas along or north of I-64, and this rain should start to spread southward over the next few hours. Wind gusts have subsided so the lake wind advisory and SPS were allowed to expire. The only changes was to tighten up the temperature gradient through tonight as that outflow moves south and to speed up the exit of precipitation late tonight. && .SHORT TERM...(This evening through Saturday night) Issued at 455 PM EDT FRI APR 17 2020 20z sfc analysis shows a healthy area of low pressure moving into the Ohio Valley with a warm front lifting northeast through Kentucky. A cold front trails this low and is poised to enter western Kentucky shortly. This setup led to an impressive gradient in temperatures across the CWA with upper 50s found north of the boundary and low 70s seen to the south. The southern warmth was enhanced by gusty southwest winds (up to 35 mph) - particularly this afternoon. Additionally, the clouds thinned and were mostly absent this afternoon south of the front and ample sunshine certainly contributed to the temperature climb. Meanwhile, dewpoints varied from the mid 40s north (and closer to the pcpn associated with the sfc low) to the upper 20s and lower 30s in the warm sector. The higher temperatures and lower dewpoints also dried out much of the southeast (to around or just below 25 percent) this afternoon with the gusty winds making for a fire weather concern throughout the latter part of the day. The higher winds have prompted the need for a continuing of the NPW for Lake Winds and also an SPS for the higher wind gusts (and low RH) elsewhere - through 8 pm. The models are in good agreement aloft through the short term portion of the forecast. They all depict a fairly sharp, but open, trough pressing southeast deeper into the Ohio Valley with some significant height falls and energy. This feature quickly sweeps through eastern Kentucky tonight followed by fast northwest flow. The pattern will then become more zonal into Saturday night with additional, but much weaker, energy heading this way from the Southern Plains for Sunday. Given the limited model spread have favored the blend as reflected by the NBM with a strong lean on details for the fropa tonight from the HRRR and NAM12. Sensible weather will feature a rude end to the sunshine and warmth that much of eastern Kentucky enjoyed this afternoon as a cold front presses through the CWA tonight. This will mean soaking rain showers passing through most of the area overnight with the winds settling after dark - switching northwest as the front passes. Cannot rule out a rumble of thunder with the front, as well but the instability appears too limited at this time to include in the grids. Colder air follows with readings back down in the mid to upper 30s by daybreak. High pressure then moves overhead for the first part of the weekend, though, despite plenty of sunshine, highs will only be in the mid to upper 50s on Saturday. The high shifts off to the east later that night and should set up a decent ridge to valley split into Sunday morning - just ahead of return flow and a potential for showers from the southwest. With the temperature split that night some frost can be anticipated in the valleys, as well. Mainly adjusted temperatures on Saturday night for the ridge to valley differences. As for PoPs, tweaked them more toward the NAM12 late tonight into Saturday morning mainly raising and lingering them longer. .LONG TERM...(Sunday through Friday) Issued at 300 PM EDT FRI APR 17 2020 The extended period will likely feature two periods of wet and active weather and an extended period of dry weather in between. The first round of rain is on track for Sunday and Sunday night, as a large area of low pressure moves across the Tennessee valley region. The rain should first begin moving into our southwestern counties early Saturday morning, and should be exiting the area by early Monday morning. Some of the model data is trying to bring a bit of precip into eastern Kentucky Monday night through Tuesday, but due to model uncertainty, decided to go dry for that time frame for now. We should see dry weather from early Monday through early Monday afternoon. After that, it looks like we will see another round of rain from late Wednesday through the end of the week. This second round of rain would be in response to another large area of low pressure that is currently progged to move across the Ohio and Tennessee valley regions. Instability is questionable enough that thunder was left out of the forecast for now. Temperatures will max out mainly in the 60s each day, with nightly lows only falling into the 40s and 50s for the majority of the period. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) ISSUED AT 808 PM EDT FRI APR 17 2020 An outflow boundary continues to slowly push southward this evening with winds shifting from the southwest to the west or northwest. This boundary will continue to sag southward tonight with winds continuing to shift to the west or northwest across most TAF sites. Rain will also spread southward overnight with ceilings coming down to low end MVFR. Higher ridgetops are more likely to end up in IFR conditions after 06z. These low ceilings will continue through dawn before eroding by early Saturday afternoon. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...KAS SHORT TERM...GREIF LONG TERM...AR AVIATION...KAS
Area Forecast Discussion
National Weather Service Lake Charles LA
925 PM CDT Fri Apr 17 2020 .DISCUSSION... Updated POP/wx grids earlier to account for increasing convection over the region (especially the coastal waters), which seems to be being handled well by various high res guidance. However convection has appeared to stall somewhat over the nwrn zones, likely due to mid/low-level capping as noted in the 00z KLCH soundings. However the approach/passage of our next shortwave aloft and sfc cold front could help erode the cap and allow for further convection later this evening. Other thermodynamic parameters in the sounding do point to the potential for some severe weather, primarily hail/damaging wind gusts. Elsewhere, inherited grids/zones look in good shape as is per obs/trends. Update out shortly. 25 && .PREV DISCUSSION... /issued 628 PM CDT Fri Apr 17 2020/ AVIATION... A cold front is expected to push through the area late this evening and through the overnight hours. Ceilings will lower to MVFR then IFR during this timeframe. Thunderstorms currently developing ahead of the front will lift northeastward through the evening with VCTS possible at KAEX/KBPT/KLCH. Winds behind the front will shift to northeasterly behind the front early Saturday morning and will remain out of the northeast into the afternoon hours. IFR ceilings should gradually mix up to MVFR by mid to late morning and remain MVFR through most of the afternoon. PREV DISCUSSION... /issued 332 PM CDT Fri Apr 17 2020/ DISCUSSION... Wx map shows cool front across C and NE TX, with a warm and more humid airmass ahead of the front this afternoon. Across our region, temperatures are in the upper 70s to lower 80s with dewpoints ranging through the 60s. The upper air pattern expected to remain fairly zonal over the weekend into next week, which will keep our region under the influence of rapidly changing weather conditions. The first shortwave and cool front tonight. Latest blended & HRRR guidance shows showers and isolated thunderstorms to pick up late this afternoon and evening across Inland SE TX/C LA with the approach of the cool front. SPC has just outlined area in Marginal Risk of severe thunderstorms, with a few strong to briefly severe storms anticipated. Primary severe threat will be damaging wind gusts. Highest rain chances of 40-50% should remain north of the U.S. 190 corridor. The second shortwave and northward moving warm front expected Saturday and Saturday afternoon. This will enhance moisture and lift accompanied by the weak frontal boundary moving back northward. With this will be increased chances of showers and thunderstorms. SPC has our region in a Marginal Risk of severe weather during this time period, with a primary threat of hail if the storms reach severe limits. The third and most significant upper level shortwave will be moving eastward across the Gulf states Sunday and Sunday night. With this will be a well defined sfc low over the ArkLaTex region moving eastward as well. While specific severe weather parameters will have to fall into place, preliminary forecasts show a significant threat of severe weather Sunday afternoon into the early evening hours. For this, SPC has outlined the region along and north of I-10 in an Enhanced Risk of severe weather, Slight Risk south of I-10 into the coastal waters. Again, 48 hours out, specifics are a little uncertain, but appears to be trending for an MCS or individual supercell development. This would bring all modes of severe weather possible (tornadoes, damaging wind, and large hail). For Monday through early Wednesday, tranquil weather expected behind the departing storm system. However, another significant storm system is possible late Wednesday night into Thursday across the southern U.S. but too far out for specifics. DML MARINE... A weak cold front will bring a brief period of light offshore flow tonight into early Saturday morning. The front is expected to return north as a warm front Saturday afternoon and evening, allowing onshore flow to resume through Sunday. A Pacific cold front will move across on Sunday night, with a chance of strong to possibly severe thunderstorms ahead and along the front. Expect brief offshore flow for Monday, with onshore flow resuming for Tuesday. The next chance of showers and thunderstorms is expected Wednesday. DML && .PRELIMINARY POINT TEMPS/POPS... AEX 58 75 63 80 / 40 40 50 90 LCH 65 79 69 82 / 30 50 30 70 LFT 66 80 69 84 / 30 40 30 70 BPT 65 77 69 82 / 40 50 30 70 && .LCH WATCHES/WARNINGS/ADVISORIES... LA...None. TX...None. GM...None. && $$ PUBLIC...04
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
851 PM CDT Fri Apr 17 2020 .UPDATE... 851 PM CDT Relatively quiet weather across the area this evening, with weak surface high pressure ridge drifting southeast through the cwa. Lingering low clouds across the southeastern counties have just about moved out of the area, while remnants of high-based open celled stratocu deck continues to diminish in coverage to the northwest. Only concern tonight is with the potential for some fog or low stratus development, particularly across the southern portions of the forecast area withing the light/variable wind regime of the surface ridge. Combination of these light winds, clearing skies and surface dew point spreads already in the 2-4 degree range would suggest at least some fog potential there. Farther north of the ridge axis, winds have turned southwest and will increase above the surface overnight which would allow better mixing in the top of the boundary layer. Model guidance continues to favor areas south of the Illinois and Kankakee rivers for the best probability of fog/low clouds overnight, in line with our going forecast. Overall, going forecast appears to be on track at mid-evening, with no significant changes needed at this time. Ratzer && .SHORT TERM... 248 PM CDT Through Saturday... Points of note for the short term forecast are the possibility of spotty graupel showers through early this evening over northern Illinois, potential for fog tonight, and wind gusts to 40-45 mph for north of I-80 on Saturday afternoon. Snow cover is quickly melting across the area with some locations seeing 3-4 inches of depth at 10 a.m. already vanished despite cloud cover, showing the influence of warm ground underneath and solar radiation penetration through the clouds. Satellite water vapor imagery indicates a slightly positively titled northern stream upper wave across Wisconsin, and this brings with it a -31C 500mb cold pocket. This cold pocket combined with residual low-level moisture and convergence across southeast Wisconsin and northern Illinois could spark isolated late afternoon showers. The HRRR has been consistently indicating this, and despite it trying at times to convect too readily, the soundings do show a low-level CAPE up to 25-50 J/kg. There already has been some light graupel reported with a shower in Round Lake, IL earlier this afternoon. Don`t foresee any of this being a big deal, but sounding profiles do support graupel potential under any showers that can develop. Any activity should fade early evening. While much of the clouds upstream are close-celled, incoming subsidence behind the aforementioned upper wave should result in clearing spreading in from the northwest. This means some locations central and southeast CWA would clear pretty late in the day. These locations already have temperature-dew point spreads less than 7 degrees, and the far southeast CWA even has cloud bases under 700 ft indicating ample boundary layer moisture. This presents concerns for fog, possibly even dense in places, especially with any added moisture from melt/sublimation. Guidance hydrolapses generally lean a little more toward stratus but the current boundary layer conditions and with clearing expectations do warrant some fog mention in the forecast and messaging. Southwest winds will be on the increase late tonight, especially at the top of the boundary layer. This would indicate that any fog that does develop may ease some toward daybreak, limiting impacts. Saturday will see a deep surface low of 986 mb track across northern/central Ontario. This will steer its warm sector over the area and fairly sharp pressure falls during the day. This will drive sustained southwest winds approaching 20 kt for north of I-80 in the afternoon. Gust magnitude has potential to be maximized given an expected sunny sky and being in the warm sector, with surface temperatures to climb well through the 50s and possibly even 60. If sufficient mixing can happen, some gusts to 45 mph in the north would materialize given the forecast vertical profiles on all available guidance. Will message gusts of 40+ mph in the north and 30+ in the south. Would commonly be more of a fire weather concern this time of year, but fuels/ground moisture and even boundary layer relative humidity are expected to be high enough not to warrant an elevated threat. MTF && .LONG TERM... 348 PM CDT Saturday night through Friday... After a windy day on Saturday, winds should gradually diminish Saturday night as the atmosphere decouples. Winds could remain fairly breezy overnight ahead of an advancing weak cold front, which will also help keep low temperatures in the 40s across the area. Have maintained slight chances for precip along the front Sunday, mainly across our far southeast, although there is the potential for a dry frontal passage, as indicated by the ECMWF. Quiet weather remains on track through the beginning of the work week with dry conditions and near seasonable temps are expected with highs in the 50s to low 60s across the area. This will be a welcome sight as we exit this fairly long stretch of below normal temps. Highs near the lakeshore will be slightly cooler any days with onshore flow, including Sunday and Tuesday where temps will be closer to the upper 40s and low 50s. Midweek and beyond turns more unsettled bringing multiple chances for precipitation as several waves eject off the Rockies and track across the area. Out ahead of the first wave, temperatures on Wednesday could soar into the upper 60s to near 70, as noted in the previous discussion. The current forecast remains on the lower end of guidance, however, so this may need to be increased in later forecasts if the trend continues. It is too soon to narrow down specifics for any of these days given the variability of the timing and placement of each individual shortwave, but there is some support for thunder potential with the Wednesday and Thursday systems. In collaboration with neighboring offices have held off on a formal thunder mention with this forecast package given a weaker thunder signal in forecast soundings. Petr && .AVIATION... For the 00Z TAFs... Aviation forecast concerns: * Potential for fog/low stratus development tonight, primarily south of the Chicago terminals. * Strong southwest winds Saturday with gusts 35-40 kts. Weak surface high pressure ridge was transiting the area early this evening, with extensive area of MVFR ceilings now exiting the Chicago terminals. Winds backing west-southwest as the surface ridge moves through and will remain from that direction overnight. Lingering scattered/broken VFR layers will persist this evening, gradually thinning and dissipating late. Earlier precipitation and melting of wet snow cover, combined with cloud cover and modest winds through the day, have left the boundary layer somewhat moist. Shallow mixing near/in the surface ridge axis tonight may support the development of fog and/or low stratus as clouds scatter and temps fall off after sunset. Winds just above the boundary layer increase to 20-25 kt beyond this evening, which especially across northern parts of the forecast area may preclude extensive fog development but could potentially result in some stratus development. High-res numerical model guidance generally focuses the greatest potential for such fog or stratus development from the southwest Chicago suburbs into east central IL and northern IN overnight, with GYY the most likely of our terminals (or nearby) to potentially see stratus or fog. Have not included a vis restriction or ceiling at GYY as confidence is fairly low, and other terminals have lower probability of such restrictions. Will continue to monitor satellite and surface obs trends for development this evening. On Saturday the surface high pressure moves south of the area across the lower Missouri and Ohio valleys, while fairly deep surface low pressure passes north of the Great Lakes. This sets up a strengthening surface pressure gradient across the western Great Lakes region, producing strong southwest winds across the forecast area. As diurnal mixing deepens into the midday and afternoon hours, forecast soundings indicate the potential for 35-40 kt wind gusts to mix to the surface. The boundary layer will likely remain fairly well mixed into the evening hours as well, so gusts will likely persist through/beyond sunset though with a decrease in magnitude as the mixed layer becomes more shallow. Above the boundary layer however, winds are expected to increase into the 40-45 kt range above 1500-2000 ft agl. This could be a potential LLWS situation if the surface winds/gusts decouple more strongly. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Gale Warning...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...noon Saturday to 10 PM Saturday. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Las Vegas NV
822 PM PDT Fri Apr 17 2020 .SYNOPSIS...A low pressure system continues to slide across the area, with the area most favorable for afternoon showers and storms shifting to southern Nevada and northwest Arizona for Saturday. Additional weak storm systems will approach the region next week, keeping some shower chances in place across parts of the region and keeping any warm ups in check. && .UPDATE...Updated POPs for the overnight hours based on latest NBM and camPOPs. Compact closed low positioned over eastern San Bernardino County this evening. Satellite shows cloudtops cooling east of the low across Mohave County, and as far north as eastern Clark County within area of ascent. This corresponds to the areas of expanding returns on radar. Over the next 3-6 hours, this area will continue to shift east over northwest Arizona before the low moves further east into north central Arizona by daybreak Saturday. Area of subsidence just behind the low has brought an end to the earlier thunderstorms over Inyo and San Bernardino Counties. Again, as the low moves further east that area of subsidence will overspread the rest of eastern California and southern Nevada bringing an end to the showers and ushering in clearing skies. The only exception will be further west across the southern Sierra and Owens Valley where showers associated with the next shortwave will continue overnight. No impacts expected overnight as the threat for gusty outflow winds up to 35 mph has passed and rainfall overnight will mainly be less than 0.10". That second shortwave will cross the region on Saturday bringing another round of showers and isolated thunderstorms mainly north of Interstate 40. && .SHORT TERM...Through Saturday. The focus for the short term is an upper-level low coming onshore to the California coast and associated shower and thunderstorm chances. Activity is ongoing in Inyo county, with a few lightning strikes this morning. Not expecting activity to get too crazy there today with crowded cumulus field and early start prohibiting much in the way of instability. Overall, scattered showers with a few lightning strikes here and there expected across Inyo and even arching into Esmeralda and portions of Nye county through the day. Latest RAP indications indicate two primary pockets of ingredients outside of Inyo county. The first is in southern San Bernardino county late this afternoon. Modest CAPE of 750-1000 J/kg, along with 20kt of 0-6km shear could support a few showers and storms. Downdraft CAPE of 750-1000 J/kg and dry low levels will also support wind potential, even with weaker showers. Outflow gusts may reach 40 MPH if anything manages to develop there. A secondary area is indicated by the RAP in northern Mohave county. Here, CAPE values of 1000-1500 J/kg will overlap with 25-35 kt of shear will be capable of supporting decent thunderstorms. However, these parameters rely on moistening low levels in the evening, and are far away from forcing, which results in a low probability of occurrence. Nonetheless, it bears watching as this area is receiving good insolation today. For Saturday, its a general shift eastward in the area for afternoon shower and storms, generally across parts of Clark and Lincoln counties, with perhaps some lingering popups further wester in Nye, Esmeralda, and Inyo counties. .LONG TERM...Sunday through Wednesday. After a brief lull Sunday, expecting another active period as a trough digs into the West Coast and swings through Monday and Tuesday. Some consistency in the timing of the main trough pushing through, however there are numerous pieces of energy that come together as it moves west so still some uncertainty in the details of the evolution of the trough. In general, expect showers at times and breezy winds the beginning of next week. Latest models look weaker than previous runs, so the threat of widespread significant impacts is decreasing. Temperatures should remain near normal through the beginning of next week, then a warm up is possible midweek. && .AVIATION...For McCarran...Northerly winds will begin relaxing this evening with typical drainage winds expected tonight. There is an outside chance of some outflow making it into the valley from distant showers in California, but direction should generally be between 180 and 230 and gusts 20-25 kts if that happens. Saturday will start with light and variable winds, but by the afternoon showers and storms look to develop on the mountains and move across the valley. These will be capable of producing some gusty and erratic winds if they do form. Any threat of storms should clear the area by the evening with southwest winds after sunset. Freezing level tomorrow afternoon should be around 9500ft MSL. Ceilings should remain above 8 Kft through the period. For the rest of southern Nevada, northwest Arizona and southeast California...Decreasing shower activity expected tonight, with showers and storms developing once again tomorrow, generally from a KIFP-KTPH line and eastward. Showers and storms may produce some temporary wind gusts up to 35 kts. No prevailing IFR conditions are forecast with ceilings likely remaining above 8Kft. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && $$ UPDATE...Pierce SHORT TERM/AVIATION...Steele LONG TERM.............Nickerson For more forecast information...see us on our webpage: or follow us on Facebook and Twitter