Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/27/22

Area Forecast Discussion
National Weather Service La Crosse WI
959 PM CST Sat Nov 26 2022 .UPDATE... Issued at 958 PM CST Sat Nov 26 2022 We continue to monitor the storm system for Tuesday/Tuesday night. So far with the new models that are in this evening, we continue to see the band setting up to our northwest, so no changes to the current forecast for then. Before then, we do see light rain spreading northeast overnight and affecting the far southeast portion of the forecast area. && .DISCUSSION...(This evening through Saturday) Issued at 200 PM CST Sat Nov 26 2022 Key Messages: - Band of accumulating snow expected on Tuesday from south- central Minnesota to north-central Wisconsin, but uncertainty remains with regards to impacts and exact location. - Seasonal temperatures from Sunday into next weekend aside from a brief cold spell midweek. TONIGHT - MONDAY: COOLER, RAIN SKIRTS TO THE EAST It was a beautiful Saturday across the forecast area with highs topping out in the low to mid 50s--a solid 10+ degrees above average for this time of year. However, this warmth is fleeting as a cold front dropping southeastward from central Minnesota sweeps through the region tonight. To the south, water vapor imagery depicts a cutoff low over the Texas Panhandle starting its northeastward migration in response to an approaching northern stream wave (also the culprit for our cold front). This approaching system brings an increase in mid and high level clouds this afternoon/evening and keeps these clouds around for much of the day on Sunday. Short range guidance continue to trend eastward with the track of the lifting low/wave and its surface reflections. Given these trends, have all but removed the mention of precipitation from the forecast for southwest Wisconsin/northeast Iowa for Sunday. Highs on Sunday are trending a hair warmer (upper 30s to low 40s) with the bulk of the cold air staying to the north and the lessening threat of precipitation. Monday will be quiet weather-wise with mid to high clouds streaming overhead ahead of our midweek system. TUESDAY - WEDNESDAY: BAND OF ACCUMULATING SNOW LIKELY The latest EPS/GEFS ensemble guidance continues to hone in on south-central Minnesota up through north-central Wisconsin as the corridor that has the highest likelihood of seeing accumulating snow on Tuesday. The NBM snowfall probabilities have been steadily increasing and shifting southeast--encroaching into the northern/western forecast area. Along and northwest of a Rochester, MN to Medford, WI line in the last 24 hours, NBM probabilities for greater than 2 inches of snow have increased from 30 to 70 percent while the probabilities for greater than 4 inches of snow have climbed from 0 to 20-30 percent. This snow comes courtesy of a surface low ejecting from western Kansas and reaching the Great Lakes region by Tuesday night. There will be ample moisture return ahead of the low off the Gulf with specific humidity and water vapor transport values around the 90th percentile of normal. This moisture rides over a modest frontogenesis zone within a realm of stout isentropic ascent and modest kinematic lift. A few caveats ride with this forecast. The first is that the GFS deterministic profiles hint at is a possible misalignment between the strongest Fgen forcing/moisture and the narrow DGZ. Due to steep lapse rates through the DGZ, this mesoscale forcing will need to line up perfectly to maximize the snow production potential. We are still three days out from the event, plenty of time for things to change on such a small scale. The second potential fly in the ointment is the rain/snow line during the day on Tuesday, which will be flirting closely with the south flank of the strongest Fgen forcing. The thought at this point is that the precipitation loading under the main band will keep the p-type as snow, but with a quick transition to rain just south of the band. This makes the placement of the band even more crucial for snow amounts. If surface wet bulb values remain above freezing under the band, this may reduce snowfall accumulation amounts and impacts. However, as cold air rushes in Tuesday evening, this should transition whatever precipitation remains to snow. The duration of the snow is also a source of uncertainty as an increasing number of ensemble members linger light QPF values through Tuesday night and into Wednesday morning closer to the upper level trough passage and stronger kinematic lift. This is reflected well in the latest NBM, which keeps mentionable PoPs until midday Wednesday. Winds will be blustery on the backside of the system with gusts of 25-30 kts likely on Wednesday, possibly increasing the impacts of any light snow still falling. The going snowfall forecast through Tuesday afternoon follows slightly under the EPS/GEFS mean, with a 1-2 inch stripe of snow along and northwest of the aforementioned line from southeast MN to north-central WI. Amounts in the band may certainly be higher if the issues noted above correct themselves. Given the broader synoptic lift in place, most locales in the forecast area will see light snow with this event by the time it exits on Wednesday, with the highest totals confined to the Fgen band. END OF THE WEEK: DRIER, BRIEFLY COOLER In the wake of our midweek storm system, Canadian air rushes southward and keeps highs solidly in the 20s/low 30s for Wednesday into Thursday per the tightly-clustered NBM guidance. The vast majority of the ensembles shunt the surface ridge axis east of the forecast area by Thursday afternoon in a continued progressive/ amplified regime. A moderating southerly flow on the backside of the ridge should bring temperatures back to around average for the end of the week. Confidence in the overall temperature and precipitation forecast decreases quickly into the weekend as the next shortwave ejects eastward along the International border, but given the active pattern, some place in the north-central CONUS will probably see snow over the weekend. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 550 PM CST Sat Nov 26 2022 VFR conditions through the evening, however MVFR conditions should expand from MN southward Sunday morning. High clouds have been on the increase well to the north of the storm system over northern Texas/Oklahoma. This storm system will continue to spread mid clouds northward tonight, however, an advancing trough from the north will drag a cold front through this evening. North to northeast flow will deepen with stratus developing behind the cold front. The latest RAP has the stratus arriving around 09Z-12Z at KRST and around 12Z-15Z at KLSE, however observations of stratus are limited over Ontario, thus will need to monitor the timing on this. The stratus continues Sunday morning, but tries to break up some in the afternoon. Wind shift to the northwest 5 to 15kts with stronger gusts 20 to 25kts Sunday. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...NONE. MN...NONE. IA...NONE. && $$ UPDATE...Zapotocny DISCUSSION...Skow AVIATION...Zapotocny
Area Forecast Discussion
National Weather Service Lincoln IL
719 PM CST Sat Nov 26 2022 .SYNOPSIS... Issued at 313 PM CST Sat Nov 26 2022 Ahead of a low pressure system approaching from the south, rain will overspread central Illinois this evening to bring widespread precipitation totals of 0.75" to 1.5" by noon Sunday. On the back side of the low, the area will be much cooler Sunday and Monday with afternoon highs in the 40s across the board. Another system will bring warmer weather but also another chance for rain by Tuesday. && .UPDATE... Issued at 716 PM CST Sat Nov 26 2022 As of 7 pm this evening, low pressure is centered over the far NW corner of Arkansas while aloft, a negatively tilted shortwave trough is noted over northern Arkansas and is producing showers across portions of Missouri and southern Illinois. Rain associated with these features is on track to spread north across the forecast area through the evening, but have slowed down the timing a few hours. 00Z KILX sounding continues to show a deep layer of dry area up to around 500 mb that will take some time to saturate. Latest runs of the HRRR/RAP show the axis of heaviest precip from roughly Jacksonville through Bloomington where rainfall amounts in excess of 1.0 to possibly 1.5 inches is expected through midday Sunday. This is a slight jog north from earlier expectations. Otherwise, forecast largely remains on track. && .SHORT TERM...(This evening through Sunday) ISSUED AT 313 PM CST Sat Nov 26 2022 Mostly clear skies have allowed temperatures to warm into the mid 50s - around 5 to 8 degrees above normal for this time of year - amidst strong southerly flow ahead of an approaching low pressure system. Warm air advection will continue through this evening, but with sunset at 4:34 PM CST the loss of surface heating will prevent temperatures from rising much (if any) more at this point. Simulated reflectivities from the CAMs suggest rain will overspread the CWA at some point between roughly 7 and 10 PM, with the heaviest burst of rain during the 11 PM to 4 AM timeframe. The NAMNest and HRRR are each suggesting pockets of 50+dBZ will be embedded within the main precipitation band, mainly east of I-55. 40% percent of members in the GE have 1" or more of 24 hour QPF at KBMI for the period ending at 6 PM tomorrow. Our forecast is closer to the NBM 90th percentile, which looks similar to the ensemble mean from HREF, and has a large swath of 1" or greater amounts falling mainly between 06z and 12z Sunday (i.e., midnight and 6 AM). The maximum QPF from HREF has pockets of upwards of 1.75" of 6-hour QPF across our area, which suggests that locally even heftier amounts than forecast are possible with embedded convection within the warm-frontal rain band tonight. With 3 hour Flash Flood Guidance (FFG) around 1.8-2.0" across our CWA, we will need to keep a close eye on the rainfall rates tonight and monitor for flash flooding, which could be an issue if most of that 6-hour QPF falls within a shorter time period. It will be a mild night for temperatures, as abundant cloud cover mitigates radiational cooling. Lows in the 40s are forecast across the board, with the warmest locations being in our southeast CWA. Sunday will be much cooler, as cold air advection develops amidst gusty northwest winds in the wake of the low which is projected to reach Lake Erie by noon. North and west of I-57, highs are expected to be in the 40s; when combined with wind gusts of 25 to 30 mph, this will yield wind chills in the 30s throughout the day. The bulk of the rain should exit the CWA by 11 AM, though an isolated shower or two cannot be ruled out throughout the remainder of the day given the weak surface based instability driven by steep low level lapse rates behind the cold front. .LONG TERM...(Sunday night through Saturday) ISSUED AT 313 PM CST Sat Nov 26 2022 Near normal temperatures will continue Monday as surface high pressure dominates our weather in the wake of the aforementioned low pressure system. However, by Tuesday, another system is forecast to develop across the midsection of the country, and ahead of this system strong warm advection will bring above normal temperatures to central IL yet again. South of I-70, there will be around an 80-90% probability for high temperatures in the 60s, with those probabilities tapering to around 30% for KPIA where highs in the mid to upper 50s are more likely. Depending on the track of the surface low, convective activity might be possible with its approach Tuesday night. 83% of the Grand Ensemble (GE) has nonzero CAPE at KLWV from 9 PM Tuesday to 3 AM Wednesday, and several members have over 500 J/kg, which is the cause for the chance of thunder in the forecast. NBM has 25+% percent probabilities for thunder there during that time, which seems reasonable. SPC has the 15% risk for severe weather well to our south. We`ll continue to monitor whether there`s a severe threat for our area, but at this time the risk appears low. It will ultimately be a function of the track and strength of the low, as a stronger surface cyclone could yield sufficiently high kinematic fields to overcome the lack of instability for convection, though that is appearing increasingly unlikely with each iteration of model output. Considerable uncertainty surrounds Wednesday`s temperature forecast at this point. Ultimately, it will depend on the timing of the low, and could be one of those situations in which Wednesday`s high occurs before sunrise. Given the differences in the way deterministic and ensemble models are handling the low, NBM is struggling. Its interquartile range (IQR) for high temperatures at KLWV spans 38 to 56 Wednesday. By definition, this means there is a 50% probability that high temperatures will fall within that range, and a 50% chance that high temperatures will fall outside of it. In other words, the likelihood of high temperatures either (1) greater than 56 or (2) less than 38 is equal to the probability that high temperatures will be between 38 and 56, which signifies incredible uncertainty. The IQR is narrower farther north on Wednesday, which implies the cold front is more likely to cross those areas early and hold temperatures down for a chilly day. NBM gives a ~60% chance that high temperatures will be below freezing at KGBG on Wednesday, which is not surprising given 61% of the GE has 850 temps plunging to less than -10C there during the 3 PM to 9 PM timeframe Wednesday afternoon. As skies clear and high pressure rebuilds over the region Thursday morning, efficient radiational cooling will likely bring temperatures into the teens in parts of the area. The NBM gives a 75% probability for lows less than 20 at KPIA. Otherwise, it will be a breezy midweek time period. The EPS` mean 6 hour max wind gust forecast is between 32mph and 38mph from noon Tuesday through 6 PM Thursday at KAAA. Quite a few members are suggesting we`ll gust over 40mph at some point though. On the bright side, the number of members suggesting we`d gust over 50mph has trended down over the past couple runs. Uncertainty in the synoptic scale pattern becomes evident in cluster analysis by day 7 (6 PM Thursday to 6 PM Friday). By that time, the primary solution is for ridging to be building back into the area while the CONUS coasts are overtaken by weak troughing. However, one cluster (dominated by the CMCE) has a trough developing in the country`s midsection, and another (predominantly the EPS) is significantly more amplified. The latter solution has 500hPa heights increasing to upwards of 560 dam. Only three of its members have 24 hour maxT less than 45F at KAAA for Friday, while 36% of the other two clusters combined have highs less than 45F. NBM suggests there`s around a 30% chance we`ll return to the 50s by Friday, with probabilities for 50+ increasing further for Saturday. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 521 PM CST Sat Nov 26 2022 Low pressure will track from roughly St Louis to Danville overnight into Sunday morning. As this occurs, ceilings will lower to MVFR and IFR and rain will overspread the terminals. Conditions at DEC and CMI will be the lowest closest to the low track. Uncertainty is greatest at PIA which is expected to be very near the back edge of the IFR clouds and for now is favored to bottom out MVFR. S/SE winds in place now will gradually back through the period, becoming NE early Sunday morning, then northwest by late morning and picking up with gusts around 20 kt. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Deubelbeiss SYNOPSIS...Bumgardner SHORT TERM...Bumgardner LONG TERM...Bumgardner AVIATION...Deubelbeiss