Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/08/21

Area Forecast Discussion
National Weather Service Bismarck ND
955 PM CDT Wed Apr 7 2021 .UPDATE... Issued at 939 PM CDT Wed Apr 7 2021 Light rain continues to slowly diminish over the southern James River Valley this evening. Cloudy skies over the southeast quarter of the state with clear skies west and mainly high thin cloudiness central and into northeast ND. For the late evening update we did drop temperatures a little lower over portions of the west and central as a very dry atmosphere remains over the area and a good radiational cooling setup with surface high pressure over the area, light winds and clear skies west or thin high clouds central. Updated text products will be sent shortly. UPDATE Issued at 553 PM CDT Wed Apr 7 2021 Low pressure system remains situated over the central plains with a band of deformation rain clipping our far southeast CWA. Latest guidance shows rain continuing in the same general area this evening and into the overnight, but gradually weakening as the vorticity weakens as it becomes more sheared within this area. Then Thursday as another vorticity lobe rotates east to west from Minnesota into the Dakotas on the north side of the upper low another round of light rain may push into the southern James River Valley after a brief break Thursday morning. Farther west, high pressure at the surface and aloft will remain over the western Dakotas into Manitoba. This will make for a mainly clear night tonight, with cool low temperatures. Previous forecast had a good handle on this. Will take a closer look at temperatures with the late evening update. Made some minor tweaks to sky and precip based on the latest radar and satellite trends, otherwise no changes to the going forecast. && .SHORT TERM...(This evening through Thursday night) Issued at 230 PM CDT Wed Apr 7 2021 Highlights of the short term include rain continuing into tonight in Dickey and LaMoure Counties, near critical fire weather further west, and a strong cold frontal passage Thursday night. As of early afternoon, a complex middle- and upper-level low was located over the Central Plains, with its northern-most vorticity maxima over eastern SD. The associated midlevel deformation and frontogenesis and related warm air advection aloft north of that low continues to yield rain in southeastern ND, and as far west as Dickey and LaMoure Counties. A sharp gradient in the rainfall footprint exists to its west where a wedge of dry low-level air is in place in the subsidence regime away from the ascent aloft, but the rainfall has tended to be a bit further west than most global models had expected at this point in the day. In contrast, rapid-refresh guidance including recent HRRR cycles are assimilating the rainfall shield well and so we relied on them to construct PoPs through tonight, but with rainfall remaining in the southern James River valley. In south central ND, the overlap of low humidities and gusty winds on the periphery of the stronger low-level wind fields associated with the low to the south has been minimized in space and time so far. High-level clouds may be impeding the full mixing potential to an extent, and while forecast soundings suggest near-critical fire weather conditions will continue through early evening in Emmons, Kidder, McIntosh, and Logan Counties in particular, observational trends to this point suggest that we do not need to upgrade them to a Red Flag Warning. Otherwise, transitory shortwave ridging aloft will across western and central ND tonight and Thursday in advance of a deepening and progressive shortwave trough that will dig into eastern MT and WY by 12 UTC Friday. Given light winds and clear skies a relatively cool night is expected tonight, especially in the Hettinger, Mott, Glen Ullin, and Beulah/Hazen areas where a surface ridge axis will be in close proximity. Thus, we relied on the cooler edge of NBM membership for forecast lows, particularly in that area, similar to what the prior forecast was advertising, and based in part on trends from last night in a similar scenario. On Thursday, the recently-well-verifying time-lagged RAP and HRRR cycles suggest widespread minimum humidities in the teens, but low-level flow within the well-mixed boundary layer is forecast to be relatively weak, precluding the need for any fire weather headlines at this time. A surface warm front is forecast to move into western ND during the afternoon, and low-level west-southwest flow and a thermal ridge characterized by temperatures at 850 mb in the 12 to 14 C range suggests highs will likely reach the low to mid 70s F in the west on Thursday, closer to the 75th+ percentile of NBM membership. The 00 through 12 UTC global deterministic and ensemble guidance is in strong agreement that a surface cold front will move across western ND Thursday night. Strong low-level cold air advection and increasing winds aloft with 40 kt speeds at 850 mb suggest post- frontal northwest winds will be gusty, with a reasonable worst- case scenario suggesting near-advisory winds are possible across southwestern ND for a time Thursday night. DCVA aloft behind the front could also generate light precipitation in the west Thursday night, as supported by ensemble-driven PoPs in the 40-60 percent range. .LONG TERM...(Friday through Wednesday) Issued at 230 PM CDT Wed Apr 7 2021 The main highlights for the long term period will be the potential for near critical fire weather conditions Friday and Saturday afternoons, along with a couple chances for light precipitation. At the beginning of the long term period, a shortwave trough will begin to eject from the Central Rockies in Wyoming and Colorado into the Central Great Plains. This system will push a cold front through North Dakota, entering the state from the west Thursday night. It is looking increasingly likely that a few light rain and/or snow showers will accompany the front in western, especially southwestern, portions of our CWA. Most guidance keeps the precipiation confined to this area, but we will continue to monitor how this system evolves. In general, most areas receiving precipitation will see a tenth or less of QPF according to the latest NBM runs and GEFS ensemble member means. Behind the front, relatively strong northwesterly winds around 15-25 knots will usher in even drier air with minimum afternoon relative humidities potentially dripping into the upper teens across the far west. The combination of winds and low relative humidities would result in near critical fire weather conditions Friday afternoon despite any morning precipitation, mainly to the west of Highway 83 as cloud cover will keep relative humidity from dropping as low to the east. Saturday afternoon will likely see near critical fire weather conditions as well with minimum relative humidities in the upper teens more widespread across the area, however winds appear to be slightly weaker at this time and thus will be a limiting factor. The next chance for precipiation will be more widespread, albeit light, and arrive Saturday night into Sunday. A deeper H500 trough is expected to follow behind the exiting shortwave trough as it transitions into a closed low across the Midwest. This deeper trough and its associated weak surface low will likely provide enough dynamic support for widespread light rain/snow showers across North Dakota, but just how much precipitation and where it falls remains highly questionable. WPC cluster analysis shows good agreement with the arrival time of this system, but is still showing obvious differences in QPF amounts. A few GEFS members showing over an inch, along with the Canadian and GFS deterministic forecasts which are also relatively high, remain outliers with regards to QPF Sunday- Monday. However, analysis of all available guidance including the NBM shows little confidence in accumulations above a tenth of an inch during this time period, with the highest totals being across the north-central. Temperature wise, expect mild temperatures to continue into the weekend with slightly below normal temperatures to begin next week. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 939 PM CDT Wed Apr 7 2021 MVFR ceilings possible at KJMS late tonight and Thursday. VFR conditions expected at all other TAF sites through the forecast period with only some mid and high level clouds. Northerly surface flow will continue at KJMS and KBIS through the forecast period with breezy conditions at KJMS Thursday afternoon. Generally light and variable winds at KDIK KXWA and KMOT tonight, becoming southeast on Thursday. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...TWH SHORT TERM...CJS LONG TERM...Gale AVIATION...TWH
Area Forecast Discussion
National Weather Service Denver/Boulder CO
834 PM MDT Wed Apr 7 2021 .UPDATE... Issued at 829 PM MDT Wed Apr 7 2021 Quiet night with only minor grid adjustments in the short term, the forecast is in good shape. && .SHORT TERM...(This evening through Thursday) Issued at 251 PM MDT Wed Apr 7 2021 Upper level ridging moved over Colorado today creating subsident flow and drier conditions. There was enough of a low level pressure gradient to create gusty winds especially over the eastern plains. Some of the stronger gusts have reached around 45 mph. Tonight, dry weather will continue with slightly above normal low temperatures. Winds will relax as the mixing in the boundary layer decreases after sunset. Upper level ridging will continue to be over Colorado tomorrow although it will flatten between a trough over the Midwest and another one over the northern Rockies. No precipitation is expected and there should be minimal cloud cover. Highs will be around 10 degrees above normal with gusty winds that could reach 35 mph across the plains. The mild, dry, and windy conditions will lead to critical fire danger across the northern I- 25 corridor and the eastern plains. This fire danger is discussed further in the fire weather section below. .LONG TERM...(Thursday night through Wednesday) Issued at 251 PM MDT Wed Apr 7 2021 Our up and down pattern is expected ton continue into next week, with a few passing systems wedged between warmer and dry days. Winds will decrease overnight Thursday night and moisture should increase slightly ahead of an approaching shortwave trough. The trough and its associated surface cold front should pass across the area on Friday, bringing much cooler temperatures (highs in the low to mid 50s) and a return of windy conditions to the plains. Strong QG descent should be located over the area with 40kt mid level flow. As the previous long term discussion mentioned, 30-40 mph winds with higher gusts still looks likely during the afternoon. Over the mountains, there is just enough moisture for a few rain and snow showers, but otherwise no precipitation is expected with this next system. Ridging quickly builds back in on Saturday with much warmer temperatures anticipated. Winds will also die down a bit as the flow aloft weakens a bit. Another system works its way into the area Sunday, with yet another cold front. Early signals indicate more moisture than the Friday "storm" and there could be some light rain or snow across the area by Sunday night. Forecast guidance also indicates an unsettled pattern as we start next week, with the potential for another storm system or two through mid-week. It`s too early to begin speculating when, where, or how much precipitation falls, but I`ll note that ensemble guidance is a bit more optimistic than this forecaster as we head into mid-April. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 829 PM MDT Wed Apr 7 2021 Northerly winds will weaken and switch to drainage by 06z with VFR conditions. During the late morning tomorrow, gusty northwest winds redevelop with gusts up to 25 knots. No precipitation or ceilings are expected. && .FIRE WEATHER... Issued at 251 PM MDT Wed Apr 7 2021 A few factors will lead to critical fire danger tomorrow which prompted the issuance of a Red Flag Warning. Above normal highs in the upper 60s to low 70s mean conditions will be warm enough for critical fire danger. Models differ on dew points with the HRRR having dew points in the low single digits across the plains while the NAM Nest has dew points in the upper teens to low 20s. The HRRR usually over-mixes and the NAM Nest is typically too moist in the boundary layer so I split the difference with dew points forecast to be in the low teens. This will result in relative humidities reaching the low teens across all of the plains. There will be enough low level flow and boundary layer mixing to generate gusty winds. Most areas will see gusts between 30-35 mph which meets Red Flag criteria. Despite the above normal precipitation for March and early April, the fuels have not "greened up" enough to subdue fire weather. The only exception is the Palmer Divide which saw the most snowfall yesterday and should stay moist enough to limit fire danger. A Red Flag Warning was issued for the northern I-25 corridor and eastern plains from noon to 7pm Thursday. && .BOU WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from noon to 7 PM MDT Thursday for COZ238- 242>251. && $$ UPDATE...Cooper SHORT TERM...Danielson LONG TERM...Hiris AVIATION...Cooper FIRE WEATHER...Danielson
Area Forecast Discussion
National Weather Service Grand Forks ND
957 PM CDT Wed Apr 7 2021 .UPDATE... Issued at 954 PM CDT Wed Apr 7 2021 Forecast working out as expected. Did usual tweeking to tighten up the western edge and to decrease chances rest of the night in our southeastern fcst area. 500 mb low drifting north into far SE ND with dry slot moving into Wadena/Park Rapids area. Lingering rain band continues over the same area as 00z with some slight movement north closer to Baudette while west edge holding tight from near TVF to Crookston to Hillsboro. HRRR has some very light precip eventually moving west as rain band diminishes overnight. So kept low pop just west of where rain is currently. UPDATE Issued at 711 PM CDT Wed Apr 7 2021 Compact 500 mb low in NE SD and it is not moving much and is progged to eventually be absorbed into the main 500 mb low currently in Kansas that is moving NNE. Rain area on the north and west side of the SD upper low will continue thru the evening from SE ND into north central MN in basically the same area it is now. Not much push west is anticipated, though west edge could still wobble west 20-30 miles or so. This position of the rain shield looks to keep the rain east of Grand Forks, but some chance a little bit could sneak west tonight. Rainfall intensity will diminish overnight into Thu AM, then next wave of rain will arrive into WC MN Thursday late morning/midday and spread north as main 500 mb low moves NNE. Once again how far west does this second wave of rain reaches is questionable, but most models do have at least some rain reaching the immediate northern RRV Thu night. T-storms are not expected in west central MN so rainfall amounts with this second wave will not be as heavy as which fell today..where 2-3 inches was common in parts of Otter Tail, Grant and Wadena counties. && .SHORT TERM...(This afternoon through Thursday night) Issued at 323 PM CDT Wed Apr 7 2021 Near critical fire weather is ongoing across northeast ND, with rain from the southern Red River Valley and across west central MN. Larger trough with a stronger closed mid/upper center location in the souther plains and a secondary center further north over SD/southern MN. This is responsible for a region of broad deformation/synoptic ascent. Additional organization of rain bands is coming from mid level frontogenesis and at least some instability (better upright instability is further southeast in MN). Eventually a second wave interacts and the initial deformation zone pivots along an inverted trough axis tonight and Thursday, with lingering (lighter) rain. Strongest signal for additional rain totals over an inch is still from far southeast ND into west central MN, while there will be a sharp cut off on amounts due to drier air in the north and west. Best chance for measurable rainfall in the northern RRV will be during/after this pivot later tonight/Friday, but that will be near the edge (some member as still dry fro those areas). Regarding fire weather: Dry BL flow on the northwest side of this system has supported RH values in the upper teens/lower 20s across the Devils Lake Basin, northeast ND, and far northwest MN this afternoon. Winds are generally holding in the 15-20 mph, with only sporadic higher gusts. This aligns with the idea of near critical fire weather conditions, as previously messaged. As the system evolves Td values eventually increase and while gusty winds continue into Thursday (maybe even higher than today), lowest RH values will tend to be above 40 percent in all but the far western part of the Devils Lake Basin. .LONG TERM...(Friday through Wednesday) Issued at 323 PM CDT Wed Apr 7 2021 As we look forward into the weekend, precipitation chances for the northern plains continue to be likely. As Friday moves forward, rain will end from west to east, and skies will clear out for Saturday. Due to this, high temperatures will reach the mid 50s to low 60s from the Red River Valley west to the Devils Lake Basin, and the low 50s east of the valley into Minnesota. Sunday into Monday, a low pressure system will cut itself off from the jet stream and descend into western North Dakota in the upper and mid levels. This low will produce rain showers all day Sunday across eastern North Dakota and northwestern Minnesota, and the chance for precipitation will last into Tuesday evening. The uncertainty with this system lies in the mode of precipitation, whether or not a change over will occur, and exact amounts. Thus, confidence is on the lower end of the spectrum. Heading into the future, there is uncertainty and significant model spread as to how this system will break down. Some members point to a blocking pattern setting up, however, confidence is low at this range. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 711 PM CDT Wed Apr 7 2021 Expect to see ceilings lowering into SE ND and thru most of MN (mainly BJI) tonight into Thursday with IFR cigs in BJI and MVFR cigs moving into FAR. Some chc of IFR Fargo area late tonight/Thu AM. Otherwise TVF/GFK likely to remain VFR though brief MVFR cigs are possible later Thursday as rain moves in. DVL to be VFR thru the pd. Gusty NE winds tonight will diminish for Thursday. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. $$ UPDATE...Riddle SHORT TERM...DJR LONG TERM...AK AVIATION...Riddle
Area Forecast Discussion
National Weather Service North Platte NE
631 PM CDT Wed Apr 7 2021 .SHORT TERM...(This evening through Thursday night) Issued at 318 PM CDT Wed Apr 7 2021 The ongoing rain-snow deormation zone operating across wrn and ncntl Nebraska this afternoon will gradually decay as a strong upper low deepens across northeast Missouri this evening. The Missouri low then tilts negative as it moves into the Midwest Thursday and Thursday night. The models suggest a pronounced area of wrap-around rain will reach into ncntl Nebraska tonight through Thursday and end early Thursday evening. The basic forecast of temperatures, humidity, wind, sky and rain chances tonight through Thursday night leans on the short term model blend plus bias correction where appropriate. The gradual clearing from west to east tonight will stop across Holt county where wrap around will be underway. This will hold up lows across ern Holt county. The guidance blend was very close to the short term blend and lows in the upper 20s to mid 30s are in place overnight. It would seem much colder lows are likely but temperatures at the 850mb level rise about 6C overnight from 0C to 6C. Additional warming continues Thursday with temperatures at the h850mb level rising to 12C supporting highs in the 60s to around 70, except across Holt county where the wrap around clouds and perhaps light rain will occur. The models are in very good agreement sweeping a powerful Pacific cold front into western Nebraska late Thursday night or very early Friday. The rain or snow chances in place across nwrn Nebraska are post-frontal associated with a cold pool aloft- -25C at h500mb and -10C at h700mb. .LONG TERM...(Friday through Wednesday) Issued at 318 PM CDT Wed Apr 7 2021 A portion of the upper low operating along the coast of British Columbia this afternoon will drop quickly through wrn and ncntl Nebraska Friday. We should see an increase in winds to 20-25 mph with gusts 40 to 45 mph behind the cold front during the day. Winds aloft increase to 40-50kts at the 850-800mb levels supporting this forecast. The 700-500mb cold pool aloft and moisture below should at least support scattered rain and snow showers. POPs for this forecast are limited to 40 percent and later forecasts will likely increase chances as warranted. A brief warm up similar to Thursday is in place for Saturday with highs in the 60s to around 70 supported by h850mb temperatures around 12C. A second upper low will drop through the nrn Plains Sunday. No POP is in place Sunday as the low may track to far east to affect wrn and ncntl Nebraska. Isolated to scattered rain or snow showers are in place Tuesday and Wednesday for what appears to be cold air aloft. Temperatures at h700mb are steady around -8C Monday through Wednesday and this would support highs in the 50s. The precipitation would appear to be diurnally driven with no organized forcing shown in the models, just a broad trof across the cntl and wrn U.S.. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 631 PM CDT Wed Apr 7 2021 VFR conditions are expected to prevail through the forecast period. Winds will decrease during the evening, first in northern Nebraska including KVTN then closer to midnight for southwest Nebraska including KLBF. However, wind gusts will increase again tomorrow morning across the area, lasting through the afternoon. Ceilings will begin to lift this evening and begin to clear in the early morning hours. && .FIRE WEATHER... Issued at 318 PM CDT Wed Apr 7 2021 Wetting rain this afternoon and high humidity tonight would seem to preclude any sort of critical fire weather condition Thursday afternoon. The area of concern is western Nebraska south of highway 2 where wind gusts of 25 to 30 mph should develop and the best guess on humidity is around 15 percent using the RAP model to 12 percent in the HRRR. Elevated fire weather conditions driven by low afternoon RH are expected in the same region Saturday through Monday. Strong northwest winds may develop Sunday. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...CDC LONG TERM...CDC AVIATION...Meltzer FIRE WEATHER...CDC
Area Forecast Discussion
National Weather Service New Orleans LA
1100 PM CDT Wed Apr 7 2021 .AVIATION... .06Z TAF FORECAST... For tonight, the main focus will be an approaching cold front and strong/severe storms expected to press east across the area through the early morning hours. Have timed approximate arrival times of impacts to area TAF sites per latest short-range guidance and observed trends which brings this line across the region generally from after midnight for far western areas, racing east to the MS coastline by 10-11Z. Expect a broken line of thunderstorms to temporarily reduce flight categories with gusty, erratic downdraft winds the main threat, as well as periods of reduced VIS from heavy rain. This activity will exit to the east after 12Z with only a few isolated SHRA remaining across coastal SE LA and coastal MS, with improving conditions/VFR flight categories expected thereafter into the day on Thursday. KLG && .EVENING UPDATE... /issued 812 PM CDT Wed Apr 7 2021/ Main focus with the forecast update this evening is with the risk of strong to severe storms later tonight. Going through a large suite of short-range CAM guidance confidently illustrates this activity to persist east across our area later tonight. Analyzing the pre-storm environment ahead of this line reveals a few interesting points to monitor for this evening... 1) Observing recent radar trends from KPOE reveals a tail-end convective plume identifiable also from GOES-16 w/ some nearing -70C cloud tops over Ft. Polk, LA. This area of convection resides right at the tail end of a 30-35kt jet which is forecast to press east tonight. A few WoFS members identify this quite well and evolves it into a messy line or bow segment entering Pointe Coupee Parish/Wilkinson Co, MS between 10PM and 11PM. This may be a localized area to monitor for the potential of a few strong wind gusts, which could even continue to progress east across our SW MS counties or along/north of I-10/12 tonight. As far as severity goes by analyzing vertical wind profile trends, we do see some uptick of 925mb winds collocated within this messy, broken line which may locally enhance this line segment, especially if any mesoscale cold pooling can develop behind this cluster to help accelerate this line east. Can`t rule out a few severe wind gusts tonight, especially in the latest D1 00Z SLGT risk area (along/north of I-10/12), with primarily sub-severe wind gusts (30-40mph) potential to the south towards the SE LA coastline. 2) The 00Z KLIX observed sounding this evening indicates a few noticeable differences in the pre-storm environment when visually comparing a few CAM soundings, mostly in the moisture profile below 500mb. The magnitude of deep moist return flow in the mid/lower troposphere is being slightly underplayed by CAM`s, with perhaps more compressional warming/sinking in the model guidance owing to a stronger 700mb subsidence/cap inversion. Observed soundings are much more moist, with this cap steadily eroding due deep moist ascent in progress. This leads me to believe that the line to the west may likely fill in towards the LA coastline with such deep moisture along and ahead of the line (similar to what HRRR simulated reflectivity trends have shown) by what could be a blow up of some weak coastal cells, eventually merging into a broken line as it races east beyond I-55 after midnight. But again, the severe wind risk will be more limited for far southern/coastal SE LA areas, with the better risk along/north of I-10/12. 3) Even though damaging wind gusts will be the main risk tonight, a few isolated weak tornadoes cannot be ruled out. Model soundings indicate largely curved low-level hodographs owing to rather modest SRH (ranging upwards of ~300m2/s2 0-1km SRH to ~400m2/s2 0-3km SRH). If surface winds can remain backed (S to SSE) enough nearest to the deepest convection, a quick weak spin up can not be ruled out generally along/north of I-10/12. Will have to watch observations south of the interstate to determine if a tornado risk will extend to the coast. If winds shift more SSW to SW ahead of the line, this will likely cause the line to become more cold- pool dominant reducing a tornado risk. However, supportive deep- layer shear exists well to the coast so a spin up or two even south across SE LA could still be possible. We will be closely watching it. Overall, we are not anticipating a signifficant severe weather event, rather more of a sub-severe line with a few severe wind gusts or a few quick spin ups possible. This activity will exit to the east by around 11-12Z with improving conditions/clearing skies Thursday morning with no significant adjustments necessary for afternoon highs (just leaning slightly on a warmer bias). Look for more details about the extended with the AM package early Thursday morning. KLG PREV DISCUSSION... /issued 321 PM CDT Wed Apr 7 2021/ SHORT TERM (Tonight through Friday)... Tonight into Thursday morning, an upper level trough is expected to move through the area, enhancing rain chances. Southerly surface winds ahead of the system will help to enhance the warm air advection and moisture advection into the area. Upper level divergence ahead of the system will help to enhance lifting in the environment as well. As the system moves through, the dynamic forcing will be enough when combined with other parameters to provide a favorable environment for strong to severe storms. A Slight Risk of Severe Weather is in effect for our northern most area for tonight and overnight. And a Marginal Risk of Severe Weather is out for the rest of our area. The main threats from this system will be gusty winds (up to 60mph or greater) and frequent lightning. A few tornadoes and hail cannot be ruled out either. Localized heavy rainfall will be possible as well inside of thunderstorm development. The main timing of these threats will be from 10pm through 6am for most of our area. Thursday and Friday, after the system moves through the area Thursday morning, zonal flow will dominate the upper level pattern. Southerly surface winds will help to enhance warm air advection and moisture advection for the area. Upper level divergence will help to enhance lifting for the atmosphere as well these days. As a result, showers and storms will be possible throughout the area, primarily during peak daytime heating hours both of these days. Frequent lightning will be possible with these showers along with locally heavy rainfall. MSW LONG TERM (Saturday through Wednesday)... Saturday into Sunday, another upper level low pressure system will make its way through the area. Southerly surface winds ahead of the system will continue to enhance warm air advection and moisture advection into the area. Upper level divergence will act to enhance the lifting in the environment as the system moves through the area. Looking at the shear, the speed shear looks like it will be favorable for severe weather development, but the directional shear may be limited, looking at the models. The best directional shear / helicity will be in the Southwest Mississippi counties and northern Southeast LA Parishes. Another interesting note and potential limiting factor for severe weather development is the timing of the parameters, however. Looking at some of the model consensus, the timing of the best helicity and directional shear may not line up with the best lifting and upper level divergence. This will be something important to monitor as we get closer to the event. Overall, the main threats from this system based on the parameters will be gusty winds, frequent lightning, and the potential for a few tornadoes. Locally heavy rainfall inside thunderstorm development will be possible as well. Monday through Wednesday, zonal flow will dominate the upper level pattern. Easterly surface winds will allow for some enhancement (or maintaining status quo) of moisture advection and warm air advection into the area. Upper level divergence will act to enhance the lifting in the environment primarily Tuesday and Wednesday. As a result of these conditions, showers and storms will be possible across the area Monday through Wednesday, mainly during daytime heating hours during these days. The main impacts from these storms would be frequent lightning and locally heavy rainfall inside thunderstorm development. Overall, these storms will be scattered in coverage and overall rainfall totals are expected to be low in general. In addition to the scattered showers, maximum temperatures are expected be higher than normal for this time of year with most locations forecast to be in the upper 70s to low 80s for this time period. MSW MARINE... Winds will be moderate (<15 knots) and southerly tonight through Saturday morning. Saturday morning through Sunday morning, winds will be southerly and strong (15-20 knots). Sunday, winds will be shifting from southerly to northerly to easterly and will be moderate (<15 knots). Winds will be easterly and moderate (<15 knots) Monday through Thursday morning. Wave heights will correspond to the wind speeds. MSW && .PRELIMINARY POINT TEMPS/POPS... MCB 61 83 64 82 / 90 10 10 40 BTR 62 85 66 85 / 90 10 10 30 ASD 65 83 65 82 / 90 30 10 50 MSY 67 83 69 83 / 90 40 10 40 GPT 66 81 66 79 / 80 50 30 50 PQL 65 80 64 79 / 70 60 30 60 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...None. GM...None. MS...None. GM...None. && $$
Area Forecast Discussion
National Weather Service Louisville KY
906 PM EDT Wed Apr 7 2021 .Forecast Update... Issued at 905 PM EDT Wed Apr 7 2021 Current radar image shows returns associated with this evening convection dissipating and exiting out of our CWA as of 01z. We will get a break for a couple of hours before our next wave of rain/storms arrive associated with a line of showers/thunderstorms across western IL and entering far western KY. These showers/storms will reach our far western CWA around midnight and continue to push eastward overnight and into tomorrow morning. Due to the overnight/early morning timing, some of this activity will weaken so not anticipating strong storms like we saw this afternoon. The rest of the forecast looks to be on track through the overnight and into tomorrow. && .Short Term...(This evening through Thursday) Issued at 315 PM EDT Wed Apr 7 2021 KLVX radar is showing showers and storms pop up within the last hour over west-central KY and southwest IN as expected. Some thunderstorms could produce small hail this afternoon, but overall severe threat appears low given the limited amount of wind shear. By 00z this evening, some lingering showers and storms will be possible across our southern IN counties in a region where the environment could be possibly holding onto some sfc based instability and higher moisture content. RAP/HRRR model soundings show SBCAPE values could be over 1000 J/kg and PWATs well above 1.2". RAP does show some sfc based CIN develop after 02z due to a developing low level inversion, so expect us to see a break from any activity between then and 05-06z. Precip shield will move in from the west late tonight/early Thu AM ahead of the cold front boundary attached to the deep low. Guidance continues to suggest the precip shield will be weakening, potentially limiting QPF amounts for our region. By 12z, the western edge of the weakening north-south oriented line of showers should be near the I-65 corridor and continuing eastward. With a LLJ working overhead, expect to see sfc winds increase for Thursday morning and afternoon hours, with gusts of 20-30 mph not out of the question. The LLJ will continue to help advect deep Gulf moisture into the region, which correlates to the highest QPF amounts east of the I-65 corridor in the range of 0.75-1.0" storm total. To the west, a dry slot could be working into western KY, helping to clear out skies and increase heating by the late morning to early afternoon hours over our CWA. SPC has expanded the Day 2 Convective Outlook Marginal risk to include our eastern CWA. HREF ensemble shows more cellular structure possible to develop on the back edge of the precip shield where best destabilization looks to occur ahead of the cold front and within a region of clearing sky cover. Model soundings show cool temps aloft that support an uncapped environment, and with sfc temps warming to the low 70s and dewpoints near 60. HREF/HRRR both indicate some marginal instability will be nosing into our eastern CWA by the afternoon, with highest instability over our Lake Cumberland region. Even with the deep cyclone set to occlude by tomorrow, 850mb jet will continue to hold steady over the region with winds of 30-40kts expected from our region the Great Lakes. Per SPC, this low level jet should provide sufficient flow for an isolated damaging wind threat despite marginal instability. .Long Term...(Thursday night through Wednesday) Issued at 222 PM EDT Wed Apr 7 2021 Most shower and storm activity associated with a large, occluded upper level low (ULL) will be winding down by Thursday evening and push east of the region by midnight. Most guidance forecasts the ULL to lift north overnight Thursday into Friday with weak ridging building in from the south into the lower Ohio Valley. This may promote enough subsidence aloft that we stay dry for most of the day Friday, though a few models hint at convection developing during the day. Not seeing much in the way of lifting mechanisms to support convection, and with weak capping in place, any activity should be largely isolated. A weak wave coming out of the southern Plains will likely phase with a stronger shortwave trough diving into the Midwest on Saturday. This will result in a deepening low pressure system as it moves toward the lower Ohio Valley region. Models vary on the overall phasing and evolution of the systems, but in general it looks like we will see widespread precipitation on Saturday. Instability will be very limited, but given the dynamic forcing with this system, we`ll likely have some embedded thunderstorms within the main precipitation shield. Precipitation could linger Sunday morning across northern parts of the region due to wrap-around moisture associated with an occluded low pressure. Otherwise, upper level ridging building in from the west along with high pressure nosing in from the southwest will transition us to drier conditions. Weather beyond Monday remains quite uncertain due to large model spread in the handling and evolution of various shortwave troughs that swing through the north- central U.S. At this time, won`t deviate much from current blended forecasts and hold on to small PoPs. && .Aviation...(00Z TAF Issuance) Issued at 725 PM EDT Wed Apr 7 2021 Impacts: Mostly VFR conditions through the evening and overnight with MVFR ceilings possible for SDF/HNB/BWG by tomorrow morning. Returning to VFR later in the afternoon. Rain showers after midnight into the first half of the day with the possibility of thunder around SDF mid morning to around midday. Winds will also be gusty out of the south with gusts 20 to 25 kts through most of the forecast period. Discussion: As of writing this discussion there were rain and thunder around SDF but moving out. Some rain could linger to the start of the TAF cycle for SDF, while the rest of the TAF sites remain dry with VFR. Conditions remain VFR for most of the evening and overnight until about 12-14Z for HNB/SDF/BWG where we could see MVFR CIG for a couple of hours as a cold front works into the region. Expect CIG to lift back to VFR levels and rain diminish just past midday and into the afternoon. Winds will also be gusty out of the south for most of the period with gusts of 20-25kts. Confidence: Moderate for timing and location of storm chances as well as ceiling timing. High for gusty winds. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...BTN Short Term...CJP Long Term...DM Aviation...BTN
National Weather Service Morristown TN
958 PM EDT Wed Apr 7 2021 .UPDATE... EVENING UPDATE. && .DISCUSSION... The forecast timing of the onset of showers will be adjusted slightly later with this update. There is good agreement among the high-res rapid refresh models that showers will begin to reach our SW counties around 09Z, so will drop PoPs before that time. All other parameters appear on track this evening. The potential for severe storms on Thursday is looking a little more concerning with the latest model runs, particularly in the afternoon when models show redevelopment occurring. MLCAPE values in the NAM rise to 1500 J/kg while wet bulb 0 heights drop below 10 kft. Deep layer shear is supportive of discrete supercells. Recent HRRR runs are pointing in that direction as well. The main threats in this environment appear to be primarily large hail with damaging wind gusts as a secondary threat given the dry air aloft that builds in during the afternoon. DGS && .AVIATION... 00Z TAF DISCUSSION. VFR conditions will persist through the night. Toward morning, showers are expected to spread into the area from the SW, bringing MVFR cigs to CHA in the morning, with a chance of MVFR vis with thunderstorms. These should spread into TYS late in the morning, although cigs are expected to stay higher due to a southerly downslope flow off the mountains. The downslope flow will help weaken showers and keep cigs VFR at TRI in the afternoon. DGS && .PREV DISCUSSION... /ISSUED 330 PM EDT Wed Apr 7 2021/ SHORT TERM...(Tonight and Thursday)... This afternoon mid to upper level ridging is beginning to shift east of the forecast area as a low pressure at the surface approaches the Mississippi Valley and a mid to upper level low lies over the central Plains states. A cold front was moving into the western part of Arkansas with a line of showers and thunderstorms developing along and ahead of the cold front at mid afternoon. A few showers were occurring across middle TN and the Cumberland Plateau at this hour. At mid afternoon temperatures were about 10 degrees above normal in the mid 70s to lower 80s. Skies were most sunny east and partly cloudy west. Expect a mostly clear evening after clouds gradually decrease west. isolated showers and a possible thunderstorm possible plateau counties next few hours before dissipating before sunset. Overnight moisture will continue to increase ahead of the cold front moving into the Lower Mississippi Valley. Temperatures will be mild with lows dropping into the 50s to near 60. The line of storms are expected to weaken as they move away from the upper level support over Missouri late tonight moving into middle Tennessee. The steady precipitation with this system may become more scattered as it moves onto the plateau late tonight. Rain showers and a few thunderstorms are possible before sunrise Thursday or about 12Z. The stacked low will then move slowly north to northeast toward the Great Lakes Thursday. Showers and thunderstorms will increase during the day as heating increases. The convection should weaken in the morning and then strengthen during the afternoon. Some strong storms possible later in the day with gusty winds and marginally severe hail, especially if significant heating occurs. Temperatures will stay mild in the 70s, possibly closer to 80 across the eastern valley near the mountains with enough early clearing. TD LONG TERM...(Thursday night through Wednesday)... We start the period with a large stacked low pressure system drifting north across the upper Mississippi Valley/western Great Lakes region. This system will drag a weak front though our area Thursday night. Will carry a few showers/possibly some thunder for the first part of the night, but forcing looks to be minimal and PoPs will be no higher than low chance. We will be in southwest flow aloft behind the front, with no significant cooling. We should be between systems on Friday, and the model soundings indicate northern sections may be capped with little or no convection. Soundings look a bit more favorable for convection south. Models have been inconsistent and given the uncertainty will keep low chance PoPs for showers/thunderstorms all areas on Friday with highest PoPs south. Much higher confidence for a round of precipitation Saturday, as models in decent agreement that a strong short wave will move southeast out of the northern Plains into the Mississippi Valley before lifting northeast into the eastern Great Lakes region. Surface low pressure will develop to our west and track northeast, dragging a cold front through our area Saturday night. The low level jet will increase out of the south Friday night into Saturday, bringing significant moisture. Downslope flow may inhibit precipitation early on Friday night/early Saturday in the northern/central valley areas, and while direction is still uncertain it looks marginal for some mountain wave enhancement of the winds for late Friday night and/or Saturday. This will bear watching as it gets closer. Right now it looks like the rain begins moving in late Friday night and continues into Saturday, and convective energy looks to be quite low so will go no more than chance thunder despite likely/categorical PoPs. There will be considerable shear present with this system, so we will need to monitor for any signs of an increase in available convective energy which would lead to the possibility of strong/severe storms. Drier air will move in behind the front late Saturday night into Sunday with surface high pressure building in from the southwest and heights rising as a ridge aloft begins to build in. Monday will be dry and warm, but there remains significant uncertainty for the Tuesday/Wednesday time frame as models show considerable spread. Right now another short wave and moisture starved front looks to move through sometime in that time frame, and will carry low PoPs both days for showers. LW && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$
Area Forecast Discussion
National Weather Service Nashville TN
810 PM CDT Wed Apr 7 2021 .UPDATE... FOR EVENING DISCUSSION. && .DISCUSSION... A broad area of showers and thunderstorms is progressing eastward across West Tennessee and eastern Arkansas, along and ahead of a surface boundary that will eventually come through Middle Tennessee later tonight and tomorrow morning. Expect this activity to weaken the farther east it goes, but some strong to severe storms are still possible in our area, mainly west of I-65. The HRRR brings the leading edge of this activity across the Tennessee River between 03-04Z, and into Nashville Metro between 06-07Z, with considerable weakening thereafter. The 00Z sounding from OHX does show some instability, but is also somewhat dry and lacking in significant low-level wind shear. The surface-based CAPE is 700 J/kg and the LI is -2. PWAT is 0.98" and the 0-3 km storm- relative helicity is 78. Hourly grids are holding up well thus far and see no need for a forecast update at this time. && .AVIATION... 00Z TAF DISCUSSION. VFR conditions will continue for a few more hours, but showers and a few thunderstorms will approach from the west by 03-04Z and bring MVFR cigs/vis to BNA/MQY/CKV. CSV will see reduced flying categories, too, but not until after 07Z. VFR should return for all terminals by 18Z Thursday. South to southwest winds will continue to be gusty through the period. && .OHX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION......08 AVIATION........Unger
Area Forecast Discussion
National Weather Service Paducah KY
600 PM CDT Wed Apr 7 2021 .UPDATE... Issued at 558 PM CDT Wed Apr 7 2021 Aviation update. && .SHORT TERM...(Tonight through Friday night) Issued at 239 PM CDT Wed Apr 7 2021 Convective activity will quickly wane after 00-02z tonight has instability decreases to basically nothing. This will leave a solid shield of light to moderate rain that will pass through much of southern IL, west Kentucky, and southwest IN late tonight through early Thursday morning. Some light showers may linger into the post-daybreak morning hours in our extreme east/northeast counties, and isolated light wraparound rain showers are possible during the afternoon hours Thursday, with the best chances along I-64. There will also be considerable cloud cover with high temperatures in the middle to upper 60s. We`ll rapidly warm up and dry out for a brief period Friday as H5 ridging builds over the region. High temperatures will rebound into the middle to upper 70s. However, precipitation looks to return Friday night into Saturday morning as a disturbance passes somewhere near the lower Ohio Valley. There is still considerable model uncertainty regarding the forecast evolution of this system, so confidence is low regarding the placement and amounts of rainfall. .LONG TERM...(Saturday through Tuesday) Issued at 239 PM CDT Wed Apr 7 2021 Forecast confidence is fairly high through the weekend and then plummets as we head into and through next week. A compact storm system over eastern Kansas at 12Z Saturday will push east across Missouri through the day and then lift northeast Saturday night. In response a surface low will develop and lift northeast across our region during the day. Widespread showers and some thunderstorms are expected through the day with the heaviest rain, 1/2" to 3/4", generally over the eastern half of the region. The greatest coverage is expected in the morning with more scattered coverage in the afternoon. At this time severe weather seems extremely unlikely. As the storm system lifts northeast away from our region we should be dry Saturday night through Sunday. Looking at next week, the flow aloft becomes rather chaotic with numerous upper lows/troughs flying around and interacting with one another. This creates a low confidence forecast for the week. The 12Z ECMWF continues to be the wet model and is similar to its 00Z run. It brings a cold front through the area under west northwest flow aloft late Monday, and generates some light QPF over far southern portions of the region behind it into Monday evening. Meanwhile, the GFS has upper ridging over the area. The forecast is dry for now. The 12Z ECMWF continues its wet trend Tuesday night through Wednesday, with a prolonged period of rain as a large positively- tilted trough pushes east into the region. The surface system is well to our south, and this looks like a frontogenetical/isentropic lift situation for our region. Unfortunately, the GFS and CMC are dry with upper ridging over the region. The upper pattern becomes rather amplified and blocky next week, and the details seem to hinge on how progressive or not the flow is in the northeast. The ECMWF is more progressive which allows it bring the system in here by mid-week, while the GFS/CMC are not progressive which holds the ridge over us and the next storm system well to our west. This is a very low confidence situation, but we will have slight chance PoPs for showers Tuesday night through Wednesday. As for temperatures, we will be a bit above normal Saturday through Monday, and then after a cold front moves through late Monday, readings will drop down near normal Tuesday and Wednesday. Of course, if we end up wet Wednesday, temperatures may be cooler. && .AVIATION... Issued at 558 PM CDT Wed Apr 7 2021 Timing of showers and thunderstorms into and through the WFO PAH TAF sites modeled fairly well with the HREF and HRRR numerical guidance. MVFR ceiling and visibility conditions will occur within one to six hours prior to cold front/wind shift line tonight, with a gradual return to VFR conditions within another six to twelve hours. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...None. MO...None. IN...None. KY...None. && $$ UPDATE...Smith SHORT TERM...DWS LONG TERM...DRS AVIATION...Smith
Area Forecast Discussion
National Weather Service Blacksburg VA
827 PM EDT Wed Apr 7 2021 .SYNOPSIS... Weak stationary front will backdoor into the area tonight into Thursday, bringing an uptick in moisture. A complex low pressure systems will bring periods of showers and scattered thunderstorms to the area Thursday afternoon through Saturday and will push a cold front across the eastern United States Sunday. && .NEAR TERM /THROUGH THURSDAY/... As of 800 PM EDT Wednesday... Main change this hour was to increase temperatures as on average current readings are about 5-degrees warmer than advertised. Dewpoints also a bit lower. Adjustments were made through 06Z, but still plan to reach minimum temperatures advertised by morning due to dryness of air mass. Also, made winds a bit more northeast to east overnight/early Thursday and increased speeds a bit as shown by NAMNest and HRRR. Fairly good wedge progged to spread in from the east by morning and then be reinforced "in situ" as rain showers move in from the southwest tomorrow afternoon. As of 1235 PM EDT Wednesday... Warm but increasing threat of showers and a few storms Thursday afternoon. Increasing cumulus field this afternoon across the mountains although still more sun than clouds keeps impact of solar insolation near full strength to bring temperatures into the 70s and lower 80s. Tonight, front across the Virginia tidewater heads west and may see some increase in the cloud cover toward Lynchburg as winds turn east, but rain threat is nil. Thursday, the front starts to head back across the Virginia piedmont as a warm front, while a cold front enters the Ohio/Tennessee Valley. Model consensus shows an initial wave of showers/few thunderstorms moving across the area Thursday but overall coverage looks scattered but could be a better zone of development from the Greenbrier Valley/Alleghanys southeast to the foothills of VA and New River Valley. For now keeping pops under 60 percent, with highest chance in this corridor from Lewisburg to Roanoke/Blacksburg/Rocky Mount, with lower threats in the upper TN Valley/NC mountains and east of Buckingham VA south into NC. Mild lows tonight in the upper 40s to lower 50s, except some lower 40s in the deeper valleys like Burkes Garden. Cloud cover will keep temperatures a few degrees lower than today but still about 6 to 10 degrees above normal. Confidence in this forecast is moderate to high. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 200 PM EDT Wednesday... Scattered showers and a slight chance of thunder with warm temperatures as the weekend begins... Increased moisture advection on Thursday will increase shower chances across the area for Thursday night overnight into Friday. A cutoff low situated to our west tracks northwards Thursday night, bringing a cold front across the Gulf states. Southerly flow ahead of this front will cause that moisture advection. Limited instability will prevent widespread thunderstorms late Thursday, but enough forcing from a stationary boundary and some elevated CAPE warrants a slight chance remain in the grids until just after midnight. Friday sees more interaction with the stationary boundary in the area sliding a bit further south. Not expecting strong interaction as a high off the New England coast and the high cloud cover from Thursday onward will suppress surface temperatures and instability Friday. For Saturday there is good agreement in the guidance for a cold front to pass over the Mid-Atlantic late on Saturday. The front will bring much better dynamic setup than Thursday or Friday`s events, so have isolated thunder in the forecast for a few hours given the limited instability. Overall have kept temperatures a few degrees under guidance with the continuous cloud cover throughout the period. That said, highs will still be in the 60s and 70s, a few degrees above normal for early April. Lows will categorically be in the 50s through Saturday. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 200 PM EDT Wednesday... Conditions dry out to start next week... After the front and associated precipitation moves out east Sunday morning, upper ridging and broad surface high pressure will keep our pattern pretty inactive. The next chance at showers will be overnight Wednesday at earliest, as the leading edge of a deep positively tilted trough approaches the Mid-Atlantic. This break in rain will probably encourage some good prescribed burn conditions in the middle of the week. Increased post frontal winds on Sunday and Monday help dry out fuels, before calmer winds and modest RH`s in the midweek. Temperatures will rebound a bit from the weekend, highs staying healthily above normal for this early in the spring. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... As of 800 PM EDT Wednesday... Generally VFR conditions expected through the TAF valid period. Extensive high cloud cover expected through the forecast period as a result of widespread strong convection currently aligned along the MS river and moving east overnight. Some mid-level moisture also noted resulting in areas of SCT-BKN080-100. Overnight, VFR conditions will remain in place with surface air mass dry and dewpoints in the 30s/40s and temperatures in the 50s and 60s. Overnight, a backdoor front will move into the area from the east. Winds will veer overnight to the northeast and then more toward the east/southeast during the day Thursday. NAMNest and HRRR show fairly healthy winds Thursday and the potential for gusts of 20-25kts around BLF and 15-20kts in the LYH/DAN/ROA area. Overnight, wind speeds should remain mostly less than 8kts. By Thursday afternoon, a closed upper low in the Midwest will begin to shift east into the OH Valley. This will allow a warm front to lift north through our area by afternoon with elevated convection likely along this warm front in the 18Z-22Z time frame. This has been indicated in the western TAF sites (BLF/LWB/BCB) with PROB30 for TSRA. Elsewhere, convection appears to marginal to include in the TAF at this time. Potential for MVFR conditions will be limited to the PROB30 groups at this time. /Confidence Levels in Forecast Parameters/ Ceilings - Moderate to High, Visibilities - High, Winds - Moderate to High, Thunder Chances - Low. Extended Aviation Discussion... MVFR or worse ceilings/visibility are expected to evolve across the region Thursday night into Friday as the wedge of cool easterly flow dominates the area. Meanwhile, aloft weak disturbances will track across the area from a broad area of low pressure aloft in the OH Valley. This will keep cloudy, damp, wet, drizzly and perhaps at times foggy conditions in place into the early part of the weekend. Additional shower and thunderstorm chances are expected over the weekend as a stronger upper-level low pressure area moves toward the region from the southwest Sunday. Conditions should improve somewhat early next week as the upper low weakens and moves north of the area. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS/WP NEAR TERM...RAB/WP SHORT TERM...VFJ LONG TERM...VFJ AVIATION...RAB