Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/25/23


Area Forecast Discussion
National Weather Service Quad Cities IA IL
908 PM CDT Fri Mar 24 2023 .UPDATE... Issued at 906 PM CDT Fri Mar 24 2023 Quick secondary update on headlines. Chicago has added LaSalle county, and given the forecast and layout of headlines, I`ve added Putnam to fill a visual hole in the hazard map. Again, for us, it looks like our highest totals will be in Whiteside and adjacent sections of Carroll County. UPDATE Issued at 841 PM CDT Fri Mar 24 2023 The arc of rainfall lifting northward continues to slowly lift north. This is handled well by the short term guidance, showing light qpf falling through 06z tonight. However, models are showing a rapid transition to snow in that axis, especially near the Quad Cities and northeast by 06z. While that seems aggressive, there is notable dry low level air in north central Illinois, with a pocket of lower to mid 20s dewpoints in the vicinity of Rockford. The small reservoir of drier air, is already allowing for a ice pellet mix near Aurora via MPING reports. Thus, at least a mix should be in place from the Quad Cities northeast well before the time of maximum lift. Regarding the period of maximum lift, with the deformation zone in the 09z through 14z time frame, there is an indication that a short period of very deep dendritic growth of 3-5 kft is possible, along with the HRRR suggestion of thunder. I do think the Kuchera accumulations are too bullish in lacking the compression of such wet snow on warm ground, but the dendritic growth may allow for at least an hour of 2+ inch per hour snowfall rates in the advisory counties. The best signal for a longer duration of these rates is in Whiteside and southeast Carroll counties. So, it`s posssible should these trends develop, a overnight upgrade to a warning could occur with amounts potentially in the 5-10 range there. No changes on headlines this evening. ERVIN && .SYNOPSIS... Issued at 309 PM CDT Fri Mar 24 2023 18z surface data has low pressure in southeast Oklahoma with a frontal boundary into southern Missouri while high pressure was over the Great Lakes. Dew points were in the 20s across the Great Lakes and into the central and northern Plains with 30s and 40s from the Ohio Valley into the southern Plains. && .SHORT TERM...(This evening through Saturday) Issued at 309 PM CDT Fri Mar 24 2023 The current winter weather headlines have been expanded south and east. Dry air from the high over the Great Lakes will keep dry conditions until almost sunset across the area. Around sunset rain from the storm system will slowly move into the southern areas and expand northward through midnight. After midnight the rain will cool the atmosphere and force the rain over to all snow in roughly a two hour period; the most likely time frame being 2 to 4 AM. The snow will be a very wet type and initially will melt on contact with the warm ground and roads. However toward sunrise snowfall rates are expected to increase to 1-1.5 inches per hour. Once this snowfall rate occurs snow will begin to accumulate on grassy surfaces. A slushy accumulation on the roads is expected as roadway temperatures cool. Bridges and overpasses will have the best chances of becoming slick and snow covered. The snow will end from west to east Saturday morning with dry conditions Saturday afternoon. As for snowfall amounts there has been a slight shift to the east with the axis of the heaviest snow. Additionally there will be sharp gradients on the western and eastern edges of the snow axis. The axis of the heaviest snow currently looks to be from just east of the Quad Cities, through Sterling, IL and a little east of Rockford, IL. Amounts in the advisory area look to be 3-6 inches east of the Mississippi and generally north of I-80. South of I-80 and west of the Mississippi amounts of 1 to 3 inches are expected. .LONG TERM...(Saturday night through Friday) Issued at 309 PM CDT Fri Mar 24 2023 Cooler than normal through mid-week then above normal temperatures with a significant storm system. Saturday night Assessment...high confidence Quiet, dry and chilly conditions will be seen as high pressure moves through the Midwest. Sunday through Monday night Assessment...medium to high confidence An upper level disturbance followed by a weak storm system will move through the area. The disturbance will bring some light snow or a rain/snow mix to the area on Sunday. The weak storm system is forecast to bring a rain/snow mix to the area Sunday night followed by rain Monday into Monday night. Right now the model consensus has slight chance pops Sunday, chance pops Sunday night into Monday and then slight chance pops Monday night. Snow accumulations for either event look to be a dusting. At the very worst localized 1 inch amounts are possible. Tuesday/Tuesday night Assessment...high confidence Quiet, dry but cooler than normal conditions will be seen as high pressure quickly moves through the Midwest. Attention then turns to the significant storm system. Wednesday through Friday Assessment...high confidence on a storm system. Medium confidence on timing The global models bring a significant storm system through the area and suggest that it will arrive in two parts; the first Wednesday into Wednesday night and the second Thursday into Friday. From a big picture view the two separate systems will pull much warmer air into the area. The precipitation type looks to be all rain with the warm air over the area and a potential for thunderstorms. Temperatures will be slightly below normal on Wednesday but will climb to above normal by Friday. Right now the model consensus has slight chance to chance pops Wednesday, chance pops Wednesday night and Friday with likely pops Thursday and Thursday night. Overall rainfall looks to be light to moderate but could be locally heavy from thunderstorms. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 616 PM CDT Fri Mar 24 2023 MVFR conditions will rapidly advance over southeast Iowa and northwest Illinois this evening, as rain spreads northward. This rain will likely reach CID and DBQ by mid to late evening, as it changes to wet snow there on arrival. There will be a period of poor flying weather for southeast Iowa through Illinois tonight through mid morning Saturday, a wet snow and rain system brings IFR conditions, possibly LIFR in moderate rain, and for a time, potentially heavy wet snow in the 08z to 14z time period. Winds will be east this evening, then trend north overnight, but are not expected to be strong. A trend towards VFR is expected as the system moves away from the area Saturday between 14z west and 18z along the Mississippi River. Farther west, from CID to DBQ, this improvement will occur early, and there is some potential that those areas remain VFR and dry through the event. && .HYDROLOGY... Issued at 903 PM CDT Fri Mar 24 2023 Have issued a Flood Watch for Moline and Joslin on the lower Rock River basin. Still 48+ hrs away but given western shift to heavier qpf axis now projected over the basin owing to moderate confidence at this range to go ahead and issue. Still, uncertainty in how much of the qpf falls as rain versus snow with influence on runoff. The Flood Watch also remains in effect for La Moine River near Colmar. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...Winter Weather Advisory from 4 AM to 1 PM CDT Saturday for Clinton-Jackson-Scott. IL...Winter Weather Advisory from 4 AM to 1 PM CDT Saturday for Bureau-Carroll-Henry IL-Jo Daviess-Mercer-Putnam-Rock Island-Stephenson-Whiteside. MO...NONE. && $$ UPDATE...Ervin SYNOPSIS...08 SHORT TERM...08 LONG TERM...08 AVIATION...Ervin HYDROLOGY...McClure
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
641 PM CDT Fri Mar 24 2023 ...AVIATION UPDATE... .UPDATE... Issued at 632 PM CDT Fri Mar 24 2023 Issued update to expand fog coverage for tonight. && .DISCUSSION...(This evening through Friday) Issued at 355 PM CDT Fri Mar 24 2023 Key Messages: * Messy pattern with mostly near to below normal temperatures this weekend through early next week * Small, but potent, shortwave could bring band of organized showers and possibly a narrow swath of wet snow Saturday afternoon into the overnight. However, confidence on exact location remains low. * A similar system could affect the area once again late Sunday into Monday, but this is also low confidence. * Return flow sets up middle of next week ahead of next upper trough forecast to impact region Thu into Fri. Forecast Details: First day back on the forecast desk in quite some time and first thing that struck me was how messy of a pattern we`ll be in through Monday. Upper flow will be generally zonal/SWrly and progressive, but one that is riddled with small, but potent, shortwave troughs. Each of these will give us at least scattered chcs for mostly light precipitation, including ongoing wave of lgt rain over the S today, another round Sat aftn/night, and potentially yet another wave Sun into Mon. Ongoing wave has brought quite a bit of cloud cover for most areas, and even some light radar returns to mostly far W and S zones. Radar returns are likely a bit overdone relative to ground truth, with a fair amount of this activity falling as virga (at least on the leading edges), owing to cloud bases 6-9K ft, and sfc RH 40 to 50 percent. Anything more than sprinkles will probably limited to our KS zones, and even these areas probably only see a few hundredths. This activity will weaken substantially by midnight as the wave deamplifies and shifts E. Late overnight, the same areas that received light precip today (far W/SW) could develop some fog. Recent HRRR runs have backed off on the overall coverage and N extent compared to last night`s 00Z/06Z runs...but think clearing skies amidst light winds in areas that have seen little to no mixing today do argue for the potential. Have kept it patchy, for now, but evening shift may need to ramp up the wording for at least SW quarter of CWA if current model output persists. The next system is forecast by most models to arrive during the afternoon and evening hrs Sat. Think any measurable pcpn prior to 18Z is pretty unlikely. Some of the initial activity Sat aftn may even have a rumble or two of thunder given non-zero MUCAPE. There continues to be indications that *just enough* cold air could be present to switch rain over to wet snow, at times, most notably into Sat night. Strong late March sun angle and air temps well into 40s will make changeover to snow prior to sunset Sat eve very difficult. However, loss of daytime sun/heating and modest CAA could allow for at least W zones to change over to wet snow after sunset. Some hi-res guidance suggests a bit of convective element to the precip Sat aftn into Sat night that could enhance snow rates enough to get some slushy accums around 1" in relatively narrow swath, but 2" and 4" soil temps in the low to mid 40s, along with only 3-5 hr window for more than modest snw rates, will make widespread accums more than this pretty difficult. Furthermore, confidence on where this band of enhanced pcpn is not exactly high as models range anywhere from our N (NAM/GFS), to central (HREF/RAP/HRRR), to KS zones on Canadian/EC. Tend to prefer a more central or southern solution at this time. Even the most aggressive output suggests peak pcpn/snow amounts will only be about a county wide. Best pcpn chcs should shift E Sun AM, but with the messy pattern in place at least slgt chc PoPs will continue into the day Sun. Models vary widely with respect to timing of next wave, anywhere from Sun eve start time to not until later in the day on Mon. Regardless, the system will probably be similar to Saturday`s in that initial rain may mix with and change to wet snow, but amounts remaining on the light side. Cool conditions continue through early next week, but at least dry conditions should return for Tue and Wed. Return flow will set up Wed into Thu ahead of potentially more organized upper trough late next week. However, confidence on details is low attm given usual weak/quick bias of GEFS relative to EPS. Wed looks to be the warmest day with highs in the mid 50s to upper 60s. NBM guidance is wildly variable on Thu, with nearly 25-30 deg spread between just the 25th and 75th percentiles. The temp spread in guidance argues for strong system, but QPF output is not overly impressive as brunt of positive PWAT anomalies and shunted S/SE of the region...unfortunately. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday) Issued at 632 PM CDT Fri Mar 24 2023 Winds are expected to become southeasterly then switch to the southwest around 06z. A northerly wind shift is expected around 15z with winds becoming northeasterly by the afternoon. Low ceilings are expected beginning around 09z to 10z and continuing until 14z to 15z. Fog is also possible during this time but confidence is low. && .GID WATCHES/WARNINGS/ADVISORIES... NE...NONE. KS...NONE. && $$ UPDATE...Schuldt DISCUSSION...Thies AVIATION...Schuldt
Area Forecast Discussion
National Weather Service Grand Rapids MI
1019 PM EDT Fri Mar 24 2023 LATEST UPDATE... Update .UPDATE... Issued at 1019 PM EDT Fri Mar 24 2023 Recent runs of the HRRR and NAM-Nest lend enough confidence that Osceola county is likely to see the same amounts and impacts as the other counties already in the warning, so have expanded the warning in that regard. Have also extended the end time of the headlines to 8 PM Saturday to account for lingering light snow but mostly the strong winds on the back side of the low pressure system. Concern is that any locations (especially in the warning) which remain cold enough to keep the sticky snow on trees during the day may be at increased risk of power outages at the tail end of the event. Farther south, expectations are mostly the same for a wintry mix including a tenth of an inch of glaze possible (especially in southern Newaygo to Montcalm). This storm is reminiscent of Feb 27 in terms of track, strength, and precipitation (liquid water equivalent) amounts, though temperatures at the surface are perhaps less supportive of freezing rain this time. Northern Kent and Ionia counties are worth a mention of freezing rain possible early in the morning but not confident enough to include them in the advisory. Due to marginal temperatures both at the surface and a few thousand feet aloft creating challenges ascertaining precipitation types, and considerable spread in the models leading into this event, confidence in the forecast is lower than usual. Nonetheless, precip (water) amounts of an inch or more falling in about 12 hours has the potential to be impactful even this late in the season. && .DISCUSSION...(This evening through next Friday) Issued at 330 PM EDT Fri Mar 24 2023 -- Winter Weather Tonight through tomorrow -- Bottom line up front...Have upgraded the watch area to a warning for Mason, Oceana and Lake Counties. Have issued an advisory for Osceola, Lake, Mecosta, Isabella, Newaygo, Muskegon and Montcalm. As the forecast has evolved for this system, there have been major questions on timing and intensity. The biggest concern will be heavy snow along the US 10 corridor and in Oceana county as the low tracks northward. Upwards of 6 to 10 inches will be possible. Snowfall rates of an inch per hour will be possible between 12Z to 18Z tomorrow. While Osceola and Lake counties are on the fringes, they could have higher amounts through their northern halves. Based on latest guidance have left them out as the biggest snowfall rates and ratios will be further north and west. Freezing rain is expected along a corridor that includes Muskegon, Newaygo, Mecosta, Isabella and Montcalm counties. There will be a region where the low level jet will bring in warmer air aloft. Couple this with cold SFC temperatures and periods of freezing rain will be possible with the greatest ice accumulations of 0.10-0.20 with a glaze or more possible north of I-96. Areas near and north of Rockford in Kent county could see ice accumulations up to a tenth of an inch. Along and south of the I-96 there could be a brief period of Freezing rain but temperatures will be very marginal. Overnight lows through this area will be above freezing so while locally there could be spots overall it will be primarily rain. -- Periods of Heavy rain with Gusty winds through SE-- Periods of heavy rainfall are possible south of the I 96 corridor with ponding on roadways possible but no flooding expected. Out ahead of the cold front will be a Low Level jet that will bring gusty winds upwards of 30 to 40 mph. The highest wind gusts will be southeast of Jackson with gusts of 40 to 45 mph possible. Have left the region out of an advisory for now but expect the gustiest winds to be Saturday afternoon. The upper level low that will bring the above weather will exit to the northeast Saturday night into Sunday. Expect cold convergent flow to move into the region Sunday. -- Chance of Precipitation early next week -- A weaker system looks to clip the southern portion of Michigan early next week but there is great disparity in the mid to long range models. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 835 PM EDT Fri Mar 24 2023 Numerous challenges/hazards for aviation the next 24 hours as the center of a strengthening low-pressure system tracks through lower Michigan on Saturday. The forecast for winds, ceilings, vis, and types of precipitation lean on a blend of today`s higher resolution models (12Z HREF) with preference to the 18Z HRRR which has proven to work reasonably well at this lead time for the last several storm systems over the past month. Between 06 and 12 Z, ceilings will drop quickly to IFR from south to north as precipitation begins. For the first several hours, precipitation may be a mix of ice pellets or freezing rain at or just north of MKG and GRR. Mostly snow with LIFR to VLIFR vis is expected for a large part of the daytime at and north of LDM, RQB, and MOP. For AZO, BTL, LAN, and JXN, surface temperatures should be barely warm enough for rain during the early hours of precipitation though there may be an icing layer between 1000 and 2000 feet until 12Z. As the center of low pressure approaches and passes by the vicinity of many TAF sites between 11 and 15 Z, expect periods of 30 knot LLWS below 2000 feet, wind shifts, and for some locations temporarily light and variable winds at the surface (keep in mind the LLWS). West winds strengthen with gusts 30 to 40 knots over much of the area after 18z with a changeover to snow in the remaining holdouts before precip diminishes around/after 23Z. && .MARINE... Issued at 330 PM EDT Fri Mar 24 2023 While the gusty easterly flow will be offshore it will be strong enough to reach SCA criteria tonight into tomorrow. So have issued an SCA until tomorrow. The bigger concern will be the gusty winds upwards of 30 to 40 kts along and behind the frontal boundary that could bring Gales to the entire lakeshore tomorrow. Based on that have gone with a Gale watch from Saturday morning through Saturday night. The gradient will be strong enough and all the high res models are in fair agreement. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Storm Warning from 4 AM to 8 PM EDT Saturday for MIZ037>039-043. Winter Weather Advisory from 4 AM to 8 PM EDT Saturday for MIZ040. Winter Weather Advisory from 2 AM to 8 PM EDT Saturday for MIZ044>046-050-051. LM...Small Craft Advisory from 2 AM to 11 AM EDT Saturday for LMZ844>849. Gale Warning from 11 AM to 10 PM EDT Saturday for LMZ844>849. && $$ UPDATE...CAS DISCUSSION...Ceru AVIATION...CAS MARINE...Ceru
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1013 PM EDT Fri Mar 24 2023 .SYNOPSIS... A line of showers with embedded thunderstorms will cross the area overnight into mid-day Saturday. Dry and warm weather will return for Sunday. Rainfall chances return Monday and Tuesday as a warm front approaches from the south. && .NEAR TERM /THROUGH SATURDAY/... As of 1000 PM EDT Friday: The forecast continues to be in good shape. Convection can be seen organizing into more of a linear mode as it crosses western TN and MS. This is as expected. This activity is still progged to enter the Smokies in the 4 to 5 am time frame, likely on a weakening trend, but may be strong. This seems to be well-handled in the grids, so no significant changes were needed with this update. A shortwave trough will eject from the Southern Plains into the Mid-MS Valley tonight as it takes on a negative tilt during this transition. As the shortwave enters the OH Valley by daybreak Saturday, an attendant cold front will swing into the area from the west. CAMs continue to produce a robust line of storms as the main frontal zone enters the western fringe of the CFWA overnight, where the best upper forcing will be available with this event. There`s not much SBCAPE to work with despite great vertical wind shear with a LLJ on the order of 50-60 kts. CAMs continue to weaken this line as it moves across the mountains, but enough MLCAPE (100-500 J/kg) along this main line will be enough to support a straight-line damaging wind threat. The low-level flow will remain unidirectional and straight-line hodographs indicate that any tornado threat is almost nonexistent. Still, effective SRH values in the 0-500m layer could allow for a quick spin up tornado embedded within the line of storms if a bowing segment can develop. Otherwise, expect this line to gradually weaken as it pushes across the area from overnight tonight in the mountains through the Piedmont zones around daybreak Saturday into the mid-morning hours in the far eastern zones, near the I-77 corridor. Based the timing of PoPs along this line with the HRRR and HRW-FV3. The line will be quick-moving, so a hydro threat will be very low-end, but localized 1.00"+ QPF amounts can`t be ruled out in locations that get stuck under strong thunderstorms. Generally speaking, most locations should receive between a tenth to a half an inch, with even lesser amounts further east (I-77 corridor) as the line of storms will be its weakest in this area. Dry air entrainment will quickly filter in following the fropa as gusty winds develop late Saturday morning into Saturday afternoon, while the synoptic cold front enters the area a few hours following the main line of storms. With deep mixing and very gusty winds at the top of the boundary layer (~775-725 mb), went ahead and issued a Wind Advisory for all mountain zones that will be in effect from midnight tonight through 00Z Sunday. Gusty winds will also impact the Piedmont zones, but confidence wasn`t high enough to warrant a Wind Advisory. Otherwise, Saturday afternoon should be nice regarding the sensible weather as the clouds scatter out and good insolation hits the surface. Expect temperatures to run 10-15 degrees above normal, despite a cold fropa. Last thing, a Fire Danger Statement has been issued for the NC Piedmont zones along the I-40 corridor as dewpoints should mix out very quickly behind the main frontal zone and gusty winds will help dry up fuel moisture levels as well. With lower QPF amounts forecasted in this area, decided that under the consideration of the alluded parameters and approval from NCFS, a Fire Danger Statement was warranted for these locations. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... As of 145 PM Friday...A break in active weather is on tap for Sun as flat ridging aloft dominates the pattern. This will allow for a transient sfc high to track northwest of the FA and helping to maintain a relatively dry airmass. Surface td/s will mix out into the 30 percent and perhaps even a little lower, which could make for afternoon fire weather concerns mainly for NE GA. Things begin to change Sun night as embedded h5 s/w energy traverses the flow and instigates a sfc trof along and north of an existing stationary bndry while lifting it north as an active warm front into mid-day. The NAM looks a little too energized with this system and develops a rather stout sfc low and thus higher QPF amts. This idea was tempered down with a blend of the more conservative GFS/CMC solns. Still, expect a decent amt of rain across the srn zones of around an inch where convective enhancement will be possible. The precip gets shunted south during the afternoon as a well agreed upon sfc high and suppression works in from the northwest. High temps will be arnd 80 F Sun and a little tricky Mon depending on possible lingering cloud cover south. But for now, anticipate maxes reaching abt 10 degrees abv normal. Mins will remain well abv normal thru the period with lows held in u50s to arnd 60 F most locales. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 225 PM Friday...The pattern becomes a little uncertain Tue as srn stream energy is progged to push in from the west and interact with an existing sfc bndry to the south. The models disagree sigfnt/ly with the amt of llvl moisture and dyno lift and therefore the scope of areal precip coverage, esp the likelihood of measurable precip making it north into the FA. So, have maintained the low chance PoPs for now as models such as the 12z GFS are quite dry and suppressive during this time. Strong high pressure shud return to the area Wed and slowly crosses to the southeast thru Thu. Deeply dry air will accompany this feature and no good chance of rain will be had until late Thu into early Fri. The guidance is in decent agreement with the synoptic pattern late week, which features strong cyclogenesis across the MS Valley swinging a moist warm front over the FA then warm sector convec activity during the day on Fri. Will have time to work out the details of this possible system over the next few days. Temps will generally remain around normal levels thru the period with some drop off below normal possible on Wed with a cP airmass mixing in. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... At KCLT and elsewhere: VFR conditions to start out the 00z TAFs. A cold front will push a line of showers and thunderstorms from west to east across the area in the roughly 09z-15z time frame. Gusty winds, lower visibilities, and MVFR cigs will all be possible with this line of storms and is represented with a PROB30 at all terminals. The line will lose intensity as it crosses the mountains and pushes into the Piedmont, but high-res guidance shows enuf structure that TS seems warranted at all TAF sites. Gusty southwest winds will pick up right ahead of the line and continue through the end of the TAF period. Clouds will scatter out behind the front by early aftn. Outlook: Moisture returns Sunday into early next week. This may result in another period of associated restrictions at area terminals. Dry high pressure returns the middle of next week. && .FIRE WEATHER... A deeply dry airmass will work into the area Sat behind a cold front. Mixing heights rise quite deep and tap into strong wind energy which will translate fairly strong and gusty winds to the sfc across the area. Surface dewpoints will also mix out and allow for RH values into the lower 30 percent range. After coord with NC land managers, it was decided a Fire Danger Statement will be beneficial for the NC Piedmont zones Sat afternoon where small fuels and brush will likely remain the driest. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...Wind Advisory until 8 PM EDT Saturday for GAZ010-017. NC...Wind Advisory until 8 PM EDT Saturday for NCZ033-048>053-058- 059-062>065-501-503-505-507-509. Increased Fire Danger from Saturday afternoon through Saturday evening for NCZ035>037-056-057-501>506. SC...Wind Advisory until 8 PM EDT Saturday for SCZ101>103. && $$ SYNOPSIS...SBK NEAR TERM...ARK/CAC SHORT TERM...SBK LONG TERM...SBK AVIATION...ARK FIRE WEATHER...SBK
Area Forecast Discussion
National Weather Service Indianapolis IN
949 PM EDT Fri Mar 24 2023 .Forecast Update... Issued at 948 PM EDT Fri Mar 24 2023 - FLOOD WATCH remains in effect for much of southern Central Indiana - WIND ADVISORY remains in effect late tonight through mid Saturday Afternoon - Rain overnight; Heaviest Rains south of I-70. Surface analysis this evening shows low pressure in place over SE MO and NE TN. A warm front extended east across TN from the low, while a cold front was found along the Mississippi River Valley. Central Indiana remained within the cool sector with moist easterly flow in place. Aloft, water vapor showed a trough in place over the Rockies with ridging in place over the middle Atlantic states stretching north into Ontario. This was resulting in SW flow aloft flowing into the Ohio Valley. Deep moisture was seen ahead of the broad trough streaming north through the Mississippi and Ohio Valleys, ahead of the surface low. Regional radar shows a large shield of precipitation over southern IL, entering southern Indiana, with stronger storms across western TN and Mississippi. 3 hour precip observations across Central Indiana have generally been less than one-third of an inch. Overnight the surface low is expected to push northeast along the Ohio River. This will keep Central Indiana within the cool sector, but in a favorable location for some heavier rains on the north side of the low path. HRRR pushes the heavier rains over southern IL across Central Indiana through 06Z-08Z. Forecast soundings concur with a saturation column overnight with pwats reaching over 1 inch. Thus the ongoing flood watch appears on track as more heavy rains will be possible overnight, resulting in areal flooding Will use 100 pops for most pops overnight, but pops will rapidly fall toward daybreak as the low passes east and dry air begins to intrude into the system. At that time a strong pressure gradient will begin to develop across Central Indiana in the wake of the low. This will allow for the beginning of impacts covered by the Wind Advisory. && .Short Term...(This evening through Saturday) Issued at 302 PM EDT Fri Mar 24 2023 Primary short term weather concerns are (1) flooding with the second round of rain this evening/tonight (2) strong wind Saturday. A deepening mid-latitude system with in dominant southern stream will interact with a significant subtropical moisture connection to bring another period of moderate to heavy rainfall to the region. At midday, a stationary synoptic front was located near the Ohio River with relatively cool/moist conditions north of the boundary, including fog and drizzle. Once the system moves closer later today, deep isentropic ascent will increase (maximized near the 305-K surface), and rain will fill in north of the synoptic boundary. See the hydrology section below for more details, but we are accepting an HREF mean for QPF which generally confines heavier amounts across southern Indiana. This will be where the primary flood risk is and for this reason we will cancel the northern portion of the Flood Watch and continue the southern sections (generally south of I-70). Although ensemble members have a few outliers for heavier amounts over the I-70 corridor, this seems low probability, and often dynamic PV readjustment from intense convection to our south will favor the southernmost QPF footprint in our region. Most of the warm advection-driven rain should move east of the area during the night with models showing dry conveyor belt moving over central Indiana thereafter. This scenario usually still yields drizzle due to low-level saturation and convergence/ascent, but rainfall intensity and amounts will decrease by then. There may be just enough instability for some thunder, but most of the deeper/intense convection will be confined to the frontal band just south of our area. However, we`ll need to watch two aspects of the convection potential. 1. The potential for a slight northward shift of the more pronounced warm sector into our southern counties such that deeper more intense convection and an attendant wind threat reach our southernmost counties early tonight. This is a low probability, as the most likely scenario should be for this convection to outpace northward surging moisture/instability, and thus weaken over our area. 2. Scattered convective cells early in the morning behind the aforementioned band, due to steepening midlevel lapse rates atop a still moist PBL. This scenario could lead to a peak in conditional instability, and would at least drive scattered convective showers. Given strong winds aloft, these may enhance already windy conditions driven by the tightening MSLP gradient. In fact, we issued a Wind Advisory earlier for the pre-dawn hours into Saturday afternoon given a consistent signal for post-cold front MSLP gradient-driven winds, augmented by modest amount of mixing. 45 mph gusts seem probable, and briefly higher possible. && .Long Term...(Saturday night through Friday) Issued at 302 PM EDT Fri Mar 24 2023 * Seasonable With Light Rain Chances At Times Through Wednesday * Potential For More Significant Rainfall Again Late Next Week Mostly quiet conditions are expected early in the period as weak surface high pressure builds in behind the departing surface low that is expected to bring another round of heavy rain tonight. The weak surface high should move east on Sunday with return flow helping to advect some moisture into the area. A weakening shortwave moving through may produce isolated showers during the day, but confidence is low due to marginal moisture and overall forcing. There is a better chance for showers late Sunday into Monday morning as a second shortwave trough with an associated weak surface low moves through. However, the gulf will remain cutoff which will limit moisture return ahead of this system and precipitation totals. Most areas will only see QPF amounts around a few tenths of an inch at most. Mundane weather returns through midweek with upper ridging and surface high pressure building in. A deepening trough across the western CONUS is expected to bring more active weather to the region late next week. Increasing moisture/warm air advection could bring precipitation into the area by Wednesday night. The better chance for rain likely arrives later in the week as a developing surface low over the plains approaches the region. Guidance suggests increasing southerly flow will help advect anomalous moisture into the area. This along with increasing dynamics may bring another 1 to 2" rainfall event to the area. Although a lot of uncertainty still remains in regards to exact timing, strength, and track of the surface low which could significantly impact rainfall amounts. Expect confidence to remain low until models are in better agreement. && .Aviation...(00Z TAF Issuance) Issued at 652 PM EDT Fri Mar 24 2023 Impacts: * IFR to LIFR visibility and ceilings expected overnight and into Saturday morning. * Steady rain arriving and persisting through the evening and early overnight hours, particularly at HUF, BMG and IND. * Moderate winds begin early Saturday. Discussion: Cool and moist NE flow will continue across the TAF sites this evening as low pressure moves along the Ohio River. Radar shows a rain shield associated with this feature over MO/Arkansas and southern IL poised to push northeast within the flow across Central Indiana. Based upon progression of the system, highest precip amounts and heaviest rain should remain across southern parts of Central Indiana. Nonetheless...IFR Cigs are expected to remain across the TAF sites as the surface low passes to the south. Forecast soundings and time heights are on board with this as saturation remains within the lower levels. As the low departs on Saturday, cigs are expected to improve to MVFR, but a stronger pressure gradient is expected to develop, leading to gusty winds persisting much of the day. && .Hydrology... Latest HREF probability match-mean QPF has widespread >0.75" amounts across central Indiana with >1.5" amounts confined generally to southern Indiana. There are a few outlier members (i.e., NAM nest) that bring ~1.5" amounts further north toward the I-70 corridor, but since this is a low probability scenario we will re-align the Flood Watch to fit this latest data. Intensity may be enough for tributary and some overland flooding later tonight into early Saturday especially near and south of I-70, roughly. This is where previous rainfall has saturated soil to the point 3-hour flash flood guidance is near or below one inch. MMEFS ensembles for main stem river levels show that widespread minor to moderate river flooding is likely, particularly across the White River and lower Wabash basins. OHRFC operational forecasts confine the moderate flooding to the lower White, Mount Carmel on the Wabash and Seymour on the East Fork White, with minor flooding for the rest of the these basins and the upper White remaining below flood stage. This is based on the southward trend of the heaviest precipitation and is the most likely scenario. Should one of the outlier members mentioned above play out, the flooding threat will increase and moderate flooding further north would be more likely. River flooding is expected to continue into next week, cresting early-mid week on most main stems and perhaps not until late week on the lower Wabash. && .IND WATCHES/WARNINGS/ADVISORIES... Wind Advisory from 4 AM to 5 PM EDT Saturday for INZ030-031- 036>042-044>049-051>057-060>065-067>072. Flood Watch until 8 AM EDT Saturday for INZ051>057-060>065- 067>072. && $$ Update...Puma Short Term...BRB Long Term...Melo Aviation...Puma Hydrology...CP/BRB
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1110 PM EDT Fri Mar 24 2023 .UPDATE... Issued at 1110 PM EDT FRI MAR 24 2023 Eastern Kentucky is essentially shower-free as of 3z, as the focus turns to upstream convection ahead of a pressing cold front. The wavering boundary across Eastern Kentucky today has slowly drifted back north, currently residing across the northern 2/3rds of the CWA per the latest surface obs/analysis. CAMs suggest the upstream line of showers and storms to weaken east as instability dwindles with time. That said, RAP soundings along with other high res guidance suggests limited 100-300 J/kg of MUCAPE across mainly the southwestern third of the CWA into the overnight. This, tied with an increasing (45-60 kt) LLJ and sufficient shear, could pose an isolated risk for strong storms/bowing features- particularly if the current Middle TN storms can sustain themselves enough as they meander northeast. Have updated PoPs based on the latest CAM and radar trends, along with minor tweaks in sky grids. Lastly, have refined T/Td/Wind grids by loading and blending in the latest obs. Updated grids have been sent to NDFD and Webfarms. UPDATE Issued at 850 PM EDT FRI MAR 24 2023 Showers have generally diminished across Eastern Kentucky as of this hour, as the wavering frontal boundary builds back north as a warm front. Have refined PoP grids, along with sky grids, to better reflect the latest rad/sat trends. Have also blended in the latest high resolution guidance for PoPs through the overnight along and ahead of the approaching cold front. Additionally, have refined hourly T grids to account for the north to south gradient. Where denser clouds and more persistent rain occurred this afternoon, temperatures were running cooler than forecast and much cooler than locations nearer to the Tennessee border. Outside of these tweaks, Td and wind obs were also loaded and blended. Updated grids along with a fresh set of zones with the changes have been sent. && .SHORT TERM...(This evening through Saturday night) Issued at 455 PM EDT FRI MAR 24 2023 JKL has endured round 1 of this ongoing system today, now for round 2 overnight. An upper level low and trough is located across the Central Plains this afternoon, and should continue to push towards the Mid-Mississippi Valley overnight. Given a strong upper level ridge in place just off the Florida Coast, which isn`t budging, the pressure gradients between the two systems will substantially increase throughout the night and into the day tomorrow, once the low makes it to the Lower Great Lakes. At the surface, a cold front has now stalled from west to east across the state through much of the day, mainly affecting the northern half. A surface low pressure system is currently located across the Southern Plains, becoming phased with the upper level low, and continuing to push farther northeast towards the Mid- Mississippi Valley and then the Lower Great Lakes by tomorrow morning. This system will gain considerable strength as it makes this transition, deepening from a 1004 mb low this afternoon, to a 986 mb low by Saturday afternoon/evening (according to the latest ECMWF). This strong of a pressure change is also indicative of increased winds along this system. During the day today, the stalled front brought rain to much of eastern Kentucky. The original thought was that the far southeast of the state would remain relatively dry, with most of the moisture focused from west to east along the stalled boundary. However, mother nature played a little game, and brought a decent line of showers and embedded thunderstorms oriented from SW to NE across the eastern half of the state, resulting in updates to pops throughout the morning and early afternoon. Now, as we head into the late afternoon hours, the moisture is becoming more confined to the frontal boundary in the northern portion of the CWA, while the SE is drying back out. Shower and thunderstorm coverage is also ramping back up across western KY, as the surface low begins to near them from the west. Heading into the overnight, as the surface low continues to track northeast, this stalled front will quickly lift back north as a warm front. This may bring a period of drying conditions across eastern KY once the front moves north out of the CWA, at least for a few hours. It won`t last long though, as the next cold front then sweeps through the state on the tail of the quick-moving low. Showers and embedded thunderstorms are expected along and just ahead of the frontal boundary, passing through eastern KY generally between 5 and 12Z overnight. SPC has kept the better severe risk more to our southwest, though a portion of the slight risk and 2% tornado risk make their way into our far SW counties, west of I-75. Ultimately, instability doesn`t look that great across this portion of the state, especially as we head into overnight and lose even more heating. Very little CAPE exists. The concern, however, is the amount of wind being generated through the atmosphere with this system, and the ability for it to gust down to the ground with any shower or thunderstorm that develops. The 2% tornado risk is caused likely to do more with the amount of low level wind sheer and potential twisting in the 0-3km, vs. the actual instability present to allow for lift and long-lived/organized storms. Just behind the front, models are still showing strong evidence of a llvl jet setting up across the central and eastern portion of the state, along with a jet streak in the upper levels shortly thereafter. There is just so much wind with this system. By the time the front moves though, within an hour or two, we will lose the overnight inversion in the lowest levels, and will begin mixing stronger winds down to the ground. It`s unusual to see an inversion break between 9 and 12Z, but all signs lead to it happening. Much drier air entraining in behind the departing system won`t help things either, as this allows for better mixing. Winds will start gusting across eastern KY as soon as the front moves through - as early as 8Z in the western CWA. They will continue to gain strength throughout the early afternoon, with peak gusts still between 40 and 45 knots in the northern portion of the CWA, and between 35 and 40 kts elsewhere (especially on the ridgetops). It was no surprise that Wind Advisories began getting hoisted for multiple NWS offices today ahead of this wind threat. After collaboration, LMK (along with IND) was in agreement in our earlier onset for the NWP, with ILN and RLX delaying their start time a bit given their location farther north and east. The wind advisory will begin at 8Z and continue through 0Z Saturday. It is possible that we could lose the best pressure gradients a few hours before 0Z, and highest gusts may begin to subside - but would rather have it out just in case and cancel if need be, verses having to extend it for just a couple hours. Otherwise, for Saturday, conditions should be quite nice - albeit windy. High pressure will develop and settle over the state by that evening and overnight. This high pressure will also be concurrent with a llvl inversion, preventing any stronger winds aloft from being able to make it down to the surface from that point forward. Skies will clear out throughout the day Saturday, and rain chances will come to an end. A couple of the CAMs do try to bring in a few small showers, likely from wrap around moisture, into the state during the day. However, there is little confidence in this. Did include some slight chances in the far SE high-terrain given lingering moisture and strong upslope flow, along with stronger agreement amongst the CAMs. With clear skies and high pressure in place, did include a bit of a ridge/valley split for Saturday night, though not much. Winds aloft will still be honking - the jet streak will actually be strengthening across the Ohio Valley, advecting WSW flow into the region. So without the CAA, and subsidence through the column, it will be interesting to see just how much some of the deeper valleys can drop. Temperatures should range from the upper 30s to the low 40s. .LONG TERM...(Sunday through Friday) Issued at 340 PM EDT FRI MAR 24 2023 A ridge of high pressure will bring dry weather to eastern to begin the extended period on Sunday. After that, we can expect periods of scattered rain showers to affect the area, as a series of upper level disturbances move across the eastern third of the CONUS. In general, temperatures will be above average, with highs on the warmest days topping out in the upper 60s to lower 70s. THe coolest days will be Tuesday and Wednesday, when we should see max values in the upper 50s and lower 60s. These cooler temperatures will be attributed to widespread cloud cover, scattered rain showers, and cooler air that will all be associated with a passing upper low. After a brief period of dry weather Tuesday night through early Thursday morning, another bout of soaking rain may occur to end the week, as another area of low pressure and its surface cold front push through the region. Winds will pick up and be quite gusty during the passage of the end of week weather system. We may see some frost, especially in valleys, late Tuesday night into early Wednesday morning, as temperatures fall into the low to mid 30s. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) ISSUED AT 850 PM EDT FRI MAR 24 2023 Showers have started diminishing across most of Eastern Kentucky as of TAF issuance, allowing most sites to begin in the VFR category. That said, where there is more consistent activity nearer to the boundary, MVFR CIGs are in place and even brief visibility reductions for SYM. As the boundary builds north as a warm front into the night, all sites will return to VFR. As this occurs, winds aloft will increase as a strong low level jet takes shape across the area. LLWS of 35 to 45 kts will be possible for a few hours (generally 4z-9z), before an approaching and passing cold front allows for showers and storms into Saturday morning and the better mix down of these winds. Guidance was optimistic through the night, where low end VFR is possible, but dips to MVFR or lower can`t be ruled out within heavier showers or storms. Post front, VFR will prevail with CIGs increasing and cloud coverage thinning overall through the day Saturday. As surface winds increase along and behind the front late tonight, sustained values of 15 to 25 kts and gusts between 30 and 40 kts should be expected into Saturday morning through the afternoon. These will slacken toward the end of the period and into Saturday night. && .JKL WATCHES/WARNINGS/ADVISORIES... Flood Watch through Saturday morning for KYZ044. Wind Advisory from 4 AM to 8 PM EDT Saturday for KYZ044-050>052- 058>060-068-069-079-080-083>088-104-106>120. && $$ UPDATE...BB SHORT TERM...JMW LONG TERM...AR AVIATION...BB
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
923 PM CDT Fri Mar 24 2023 .UPDATE... Issued at 923 PM CDT Fri Mar 24 2023 Couple tweaks to going forecast, mainly to expand the winter storm warning a tier of counties south and adding a few counties into an advisory. Very little to add to the very well written and informative afternoon short term AFD below. Satellite imagery this evening is a text book example of cyclogenesis. Pronounced mid level dry intrusion and attendant plume of steep mid and upper level lapse rates adjacent to the blossoming TROWAL over northern Missouri really is a classic set-up for convective snow and possible thundersnow Saturday morning. Have introduced slight chance of thunderstorms into the grids over northern IL 09-15z. Trend in hires guidance has been upward this afternoon and early evening with QPF and given PWATs (nearing 3/4") getting about as high as they can get with snowfall, hard to dispute the higher QPF. The HRRR modeled snow depth (which accounts for compaction and melting) has been trending upward as well (this is different than the 10:1 and Kuchera method snowfall forecasts) with max accums over 10" within the band of heavy snow. This HRRR product did pretty well with snowfall amounts last wet snow event earlier in the month, so given its track record opted to err on side of caution and expand headlines a bit farther south. The HRRR snow depth is bringing 6" totals into northern/western Lee, most of DeKalb, and northwestern Kane County. Snowfall rates could reach 2"/hour, which would likely result in snow eventually accumulating even on untreated main roads. Updated WSW has been issued and derived products will be out momentarily. - Izzi && .SHORT TERM... Issued at 257 PM CDT Fri Mar 24 2023 Through Saturday... Main forecast messages through Saturday: * Widespread rain arriving this evening, quickly transitioning to a wet snow in far northern Illinois overnight (transition to all snow occurring later towards daybreak towards the I-88 and I-80 corridors and the heart of the Chicago metro) * Intense snowfall rates (likely 1+"/hour at times) are likely to produce a narrow corridor of 6+" of heavy, wet snow accumulation in portions of interior northern Illinois and in locations near/along the Illinois-Wisconsin state line * Travel impacts in the form of sharply reduced visibilities and slushy snow accumulations on roadways are likely within the corridor of heavier snowfall. Uncertainty exists whether snow will accumulate on main thoroughfares due to mild antecedent conditions and near-surface air temperatures remaining near 32F, though accumulations are more likely on secondary/untreated roadways, as well as bridges and overpasses. * The Winter Weather Advisory for Ogle, Winnebago, Boone, McHenry, and Lake counties in far northern Illinois has been upgraded to a Winter Storm Warning. This is where 6+" of snow accumulation is presently most likely to occur. The timing of this headline was left unchanged (from 1 AM CDT through 1 PM CDT). * A Winter Weather Advisory remains in effect for Lee, DeKalb, and Kane counties from 1 AM CDT through 1 PM CDT. Northern Cook County has been added to this advisory, though only from 7 AM CDT through 1 PM CDT given the expected later start time of snow there. At least 3" of snow may fall in at least portions of these counties, and the heavy snow rates may lead to hazardous travel here as well. * There is still room for the location of the narrow heavy snow corridor to wobble north or south by roughly a tier of so of counties. Thus, headline changes may still need to be made tonight once observational trends become clearer. [Updated at 3:40 PM CDT to provide additional details] Surface cyclogenesis is well underway over the Ozarks and Ouachitas of western Arkansas and eastern Oklahoma with a recent surface analysis revealing the center of a 1002 mb surface low near Fort Smith, AR at 19Z. Strong upper-level divergence downwind of the base of an upper-level trough currently centered over the southern Rockies/southern High Plains and in the right entrance region of a 155+ kt upper-level jet core will foster the continued deepening of this low as it lifts northeastward, with a mean sea level pressure of about 985-990 mb likely to be attained by the time the low center reaches our latitude around daybreak tomorrow. Excellent synoptic forcing for ascent will cause a broad shield of precipitation to spread into our forecast area from south to north throughout this evening, while winds will gradually become blustrier with time as the center of the deepening low approaches. With surface temperatures in the mid 30 to low 40s (coldest north; warmest south) at the onset of precipitation, most, if not all of our forecast area will see rain initially. However, thermal profiles in interior far northern Illinois look cold enough to where precipitation may either be snow or a rain/snow mix initially at onset, or will quickly change over to all snow within 2-3 hours of onset after robust dynamic/evaporative cooling all but eliminates any lingering hydrometeor melting energy within the atmospheric column. This transition to all snow should be more gradual farther south towards the I-88 and I-80 corridors and into the heart of the Chicago metro, but the expectation is that thermal profiles should become supportive of mostly or all snow at these locations by around daybreak Saturday. Locations south of I-80, and even more so south of the Kankakee and Illinois river valleys, may not witness this full changeover and only see rain throughout the duration of this event. Can`t rule out some embedded thunderstorms occurring in the southern half or so of our CWA as well given the dynamics in play. As has been discussed the past couple of days, intense snowfall rates likely exceeding 1"/hour at times are likely to be seen wherever the main snowfall deformation axis sets up, owing to the strong synoptic forcing for ascent that will be augmented by robust mesoscale forcing induced by a pronounced frontogenetic circulation, as well as the presence of steep upper-level lapse rates/convective upright instability and deep column moisture. As is usually the case in these late-season events, heavy snow rates will be a must in order for any meaningful snow accumulations to occur given the mild antecedent conditions that we`ve experienced in the lead-up to this event, as well as the fact that near-surface air temperatures likely won`t fall much below freezing throughout the duration of the event, and should even remain above freezing across a large chunk of our CWA that is expected to see snow. This scenario is actually somewhat similar to the one we saw two weeks on March 9-10, when strong frontogenetic forcing coincident with steep lapse rates laid down a swath of 6+" of snow across far northern Illinois into southern Wisconsin despite mild antecedent conditions and marginal air temperatures. Road impacts with that event were primarily limited to secondary, untreated, and elevated roadways with mild pavement temperatures and road treatments keeping most main thoroughfares in relatively good shape, and have a hunch that something similar may be seen with this event. Regardless of whether the snow ends up accumulating on roadways, sharply reduced visibilities are likely within the more intense snowfall, and that on its own could still lead to hazardous travel for any motorists who will be traveling early Saturday morning in northern Illinois. The frontogenesis signal with that March 9-10 event was perhaps not as pronounced and more ephemeral than what most forecast guidance is suggesting will be the case for this event, which leads to the thinking that the snow rates with this event will be more intense and longer lasting than what we saw two weeks ago. However, one key consideration with this setup that wasn`t present for the March 9-10 event is that there is a large wad of convection to our south. Since models often struggle with handling convection, there are often errors in how they handle the intensity and placement of snowfall on the northern sides of systems like these. As a result, there are still some lingering uncertainties regarding exact snowfall totals and the placement of the narrow heavy snow corridor, which based on recent guidance, could still shift north/west or south/east by a tier or so of counties compared to what we`re currently forecasting. For seemingly the umpteenth this cold season, a sharp snowfall gradient is also likely to be seen somewhere between the Illinois-Wisconsin state line and the I-88/I-80 corridors and heart of the Chicago metro, where a longer duration of rain and slightly milder surface temperatures will limit how much snow will be able to accumulate. Putting everything together, confidence was high enough in a narrow corridor of 6+" of snow accumulation occurring across our far northern counties to warrant an upgrade to a Winter Storm Warning there, even though overall travel impacts may not necessarily end up being truly Winter Storm Warning-worthy. The Winter Weather Advisory was kept for Lee, DeKalb, and Kane counties, where heavy snowfall may produce lesser accumulations, but still some travel impacts. Northern Cook County was also added to this advisory with confidence now being slightly higher in 3+" snow accumulations and associated travel impacts occurring in at least far western portions of this headline zone. Precipitation should end from west to east late Saturday morning and into the afternoon. Warming daytime temperatures and perhaps some glimpses on sunshine may melt a large chunk of the newly minted snowpack prior to sunset. Ogorek && .LONG TERM... Issued at 122 PM CDT Fri Mar 24 2023 Saturday night through Friday... Broad troughing and attendant cyclonic flow looks to persist across the CONUS through next week. Numerous mid-level perturbations are slated to ride along the associated fast jet streak, and while widespread precipitation isn`t forecast each day during the extended, several chances for precipitation (some of the wintry variety) exist. The follow-up disturbance to Saturday`s storm system is slated to arrive during the day on Sunday. This looks to be a fairly compact and lower amplitude one, and guidance remains all over the place regarding placement, timing, and moisture depth/saturation. A fairly steep reservoir of lapse rates are forecast to precede the main forcing with this feature, but the compact nature, fast forward motion, and lacking moisture suggest just carrying some lower-end PoPs for the time being. Thermal profiles will be right on the cusp of supporting rain/snow across our area, but based on the currently-advertised surface temperatures, any wintry precipitation doesn`t look to be of the overly impactful variety. Arriving fast on the heels of this feature will be a third perturbation late Sunday night into Monday. This again looks to be a very short wavelength shortwave, but potentially of higher amplitude than the previous and riding along the sharp, cyclonic shear side of a robust 160+ kt jet streak. Still seeing plenty of spread in the guidance at this range, but there is a general, developing signal of a deepening surface reflection translating across central Illinois into Indiana during this period. Ensemble guidance continues to depict a narrow west-east oriented swath of some snow accumulations as this feature acts to sharpen up a well-established baroclinic zone. While not off the charts, moisture (PWATs a bit north of a half inch) and instability may be in somewhat better supply with this disturbance, so we`ll continue to keep an eye on guidance trends over the next few days. The latest multi-model consensus suggests the best chances for any slushy snow accumulations focusing across far northern Illinois and towards the Wisconsin state line. We may get into a brief break in the action during the middle of the week as an expansive 1025-1030 mb high builds across the Upper Midwest. This will be short-lived, however, as model guidance is in good agreement regarding the next round of lee cyclogenesis taking place Wednesday night and Thursday across the plains. Still way too far out for much stock in any single model run/solution, but the overall consensus seems to favor a deepening surface low tracking somewhere off to our north and west to close out the week. Carlaw && .AVIATION... For the 00Z TAFs... 638 PM...Forecast concerns include... Snow overnight/Saturday morning with lifr/vlifr cigs/vis. Strong/gusty northeast winds shifting northwest Saturday morning. Light rain currently over central IL will slowly spread north and increase in coverage this evening. The rain will change to snow first across northwest IL after midnight and this transition to snow will spread southeast across the rest of the terminals in the predawn hours. While timing tweaks may be needed as trends emerge, current tafs look in good shape. As the precipitation transitions to snow, there could be a brief period of sleet at ORD/DPA. Visibilities also may drop into the 1/2sm range at ORD/DPA. There is some potential for 1/4sm, especially at RFD but confidence too low to include with this forecast. While the heaviest snow is expected to fall just northwest of ORD/DPA, if it were to shift further to the southeast, then lower conditions may become prevailing and persist longer. The snow is expected to slowly weaken in intensity by midday and end from west to east during the early afternoon, possibly mixing with some light rain or drizzle. Northeast winds will slowly increase this evening with gusts into the lower/mid 20kt range. Directions will become more northerly by daybreak when gusts into the 30kt range will be possible, though gusts may diminish during the heaviest snow periods. Directions will shift to the northwest during the mid/late morning and then become more westerly during the afternoon with speeds/gusts slowly diminishing. Speeds are expected to diminish under 10kts Saturday evening. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Winter Storm Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008...4 AM Saturday to 1 PM Saturday. Winter Weather Advisory...ILZ103...7 AM Saturday to 1 PM Saturday. Winter Weather Advisory...ILZ010-ILZ011-ILZ012...4 AM Saturday to 1 PM Saturday. IN...None. LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744- LMZ745...1 AM Saturday to 4 AM Sunday. && $$ Visit us at weather.gov/chicago Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSChicago www.twitter.com/NWSChicago www.youtube.com/NWSChicago
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1036 PM CDT Fri Mar 24 2023 .SHORT TERM... (Through Late Saturday Night) Issued at 239 PM CDT Fri Mar 24 2023 Latest analysis shows surface low pressure near northwest AR, approaching the southwest sections of MO. A broad area of rainfall extends east along a quasi-stationary boundary that runs through northern Arkansas into Tennessee. Another line extends southward through western Arkansas along a cold front extending south of the surface low. Low pressure will lift northeast ahead of a negatively tilted upper level trough this evening through Saturday morning. The surface boundary makes a slight jaunt northward ahead of the surface low, lining up near the MO Bootheel. All CAMs support some form of widespread rainfall along the west-east oriented boundary ahead of the surface low with better convective potential in closer proximity of the boundary extending east of the surface low. Much of the SBCAPE remains south of the MO/AR border eastward into the Tennessee Valley with little concern for stronger storms further north. However, heavy rainfall overrunning the boundary is likely to impact far southern sections of the CWA (especially Reynolds, Iron, and Madison Counties), where 2-3 inches have already fallen. Hi-res meteograms indicate heavy rainfall may affect the same areas with a majority of HRRR and SREF members adding 1-2 inches with roughly half of the members at 2-3 inches as far north as KFAM by Saturday morning. The Flood Watch will remain in place as-is. Meanwhile, as the surface low deepens, the mid-level low closes off as it traverses mid-MO tonight. A broad deformation zone is expected to take shape on the back side of the system late tonight into Saturday morning. In between the leaf of mid to upper lift and the surface low, dry air wraps into the system, creating a void for some locations in a southwest to northeast orientation, generally between Jefferson City and St. Louis. So, while widespread rainfall initially overspreads all areas this evening, those under the dry air intrusion will likely see more of a scattered coverage later tonight into Saturday morning. The bulk of the precipitation associated with the deformation zone track from central MO through northeast MO and west-central Illinois, resulting in a broad area of 0.50-1.00 inch amounts north of the heavier rainfall to the south. Little has changed since the last update regarding the system`s departure. As it begins to exit to the northeast Saturday morning, cooler air wraps in behind the system, which could cause some snow to mix in over far northeast Missouri. While sounding show sub- freezing temperatures aloft, the lowest 2k feet trend above freezing with mid-30s near the surface. This all occurs in a brief 2-3 hour window between 10z and 13z before moisture evacuates the mid to upper levels. Therefore, the chances for accumulating snowfall are quite low. Dry conditions will settle in behind the system Saturday with breaks in the overcast skies Saturday afternoon. There is a weak shortwave the tracks from the central Plains along the MO/IA border Saturday night, providing low chances for an isolated shower. Moisture is limited further southeast of the shortwave. While showers may initially extend southeast through portions of central Missouri, better support and moisture remains over northern sections of the CWA. Anything that pans out is expected to result in just a couple hundredths of an inch over northern sections of the CWA. Maples .LONG TERM... (Sunday through Next Friday) Issued at 239 PM CDT Fri Mar 24 2023 The period begins with an expansive closed low being the dominant feature over the Hudson Bay on Sunday. Broad cyclonic flow over Canada gradually bleeds into predominantly zonal flow over the central U.S., acting to channel multiple upper level shortwaves from the Pacific Northwest through the central Plains. Saturday night`s shortwave and weak associated surface low will continue to move east along the MO/IA border early Sunday morning. Its compact nature should keep most precipitation north of the CWA, though an isolated shower is not out of the question in northeast MO and west-central IL, focusing along a wing of weak mid-level f-gen and narrow corridor of deeper saturation (near IA/MO/IL borders). Much of the day Sunday remains dry elsewhere with a north-south spread in temperatures (low 50s north/mid-60s south). A second shortwave located just east of the Four Corners Region has better potential to bring light rain to the area Sunday night. Though upper level flow is being characterized as zonal, there is a slight lean out of the southwest, which will carry the shortwave east-northeast into the mid-Mississippi Valley. The 850mb fields show a varying degrees of mid-level low development between individual guidance underneath the upper ascent of the shortwave running near the MO/IA border. Soundings depict deeper saturation than the previous shortwave, coinciding with an area of mid-level forcing along a west-east oriented baroclinic zone. Isentropic lift will result in an area of light rainfall somewhere within 18z Sunday through 12z Monday window. GEFS/EPS ensembles show approximately 50 percent of the members with measurable rainfall between 03z through 15z moving west to east. CMC ensembles are a bit more bullish with 70 percent of members favoring measurable rainfall in the same period. When increasing the QPF threshold to 0.25 of an inch, each of the ensembles show lower potential with 20 percent or less of the members favoring such. All-in-all, a quick light rain event is looking more likely. Rain moves east Monday morning with the start of the work week leaning in favor of dry weather and near normal temperatures. Zonal flow brings yet another weak upper shortwave along the MO/IA border ahead of a mid-level thermal ridge situated to our west. It initially looked like it would remain dry as this wave lacks moisture. However, a few members do support a brief bout of isolated showers late Monday night into early Tuesday. Current NBM PoPs of 20- 30 percent (00z-06z Tue) may have a bit more bark than bite with little indication that any steady rainfall will result. Confidence begins to wane in the midweek period as spatial and temporal details diverge and create greater spread amongst the ensemble guidance. Despite this, general themes can be parsed out that show surface ridging building in from the northern Plains as mid to upper ridging amplifies over the central U.S. While the placement of the surface high and amplitude of the mid/upper ridging pattern varies between guidance, the patter provides some confidence that temperatures will moderate from mid to late week. By Thursday, an amplified upper trough extends southward over the Intermountain West, further amplifying the ridge over the Midwest. While a majority of GEFS/EPS/CMC ensemble members remain dry through late Wednesday, Thursday (important day in St. Louis...wink wink) looks less certain. The pattern will support an increasing potential for precipitation as the trough moves east. Strengthening southerly flow and upper ridging ahead of the trough draw moisture northward with a milder, progressively more active pattern to end the period. Maples && .AVIATION... (For the 06z TAFs through 06z Saturday Night) Issued at 1033 PM CDT Fri Mar 24 2023 Although the bulk of the steadier rain has moved east, another round of rain will move into northern parts of the region overnight. This is most likely to affect Quincy, where some snow may mix in by morning. Rain could also approach Columbia or Jefferson City. IFR conditions prevail at all sites, but some periods of MVFR improvement have been observed. Occasional deterioration to LIFR is also possible. Winds turn to the north and then west by morning with conditions improving during the morning to early afternoon. By afternoon, VFR is likely area wide. Kimble && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX