Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/21/23


Area Forecast Discussion
National Weather Service La Crosse WI
928 PM CST Wed Dec 20 2023 .KEY MESSAGES... - Light precipitation threat returns to the area starting Thursday later afternoon. Most areas will just see drizzle or rain, but will have to watch for some very light icing Thu night into early Friday morning north of Interstate 94 in Wisconsin. - Well above normal temperatures are expected into next week with record temperatures forecast for the weekend and Christmas. - Additional periods of rain are expected starting Sunday. Confidence is starting to increase for more significant precipitation amounts with this system. && .UPDATE... Issued at 926 PM CST Wed Dec 20 2023 Made some minor changes to the forecast through Friday morning. Reviewing the upper air data to the south in the moist plume coming north, the RAP initializations and forecast are a bit too aggressive with the precipitable water values per 00Z KOUN/KFTW upper air soundings. Forecasts have also slowed the moist surge into the area a few hours. This gives a bit of pause with doing too aggressive a change to the rain chances. However, the synoptic warm front is really taking shape through northern MO and low-level saturation is increasing north of the front in srn IA as evidenced by the 3kft clouds developing. This area will work north Thursday, along with the low-level warm front. This focal point of lift and with about 1-1.6km of depth to the low- level saturated layer, some patchy drizzle will probably accompany the warm front as ceilings fall into the 800-1200 foot range by very late afternoon Thu in northeast IA / far swrn WI. The warm front then progresses northeast with low-clouds and saturation along it. As overnight temperatures cool, saturation will increase further in the boundary layer, thus drizzle areas working northeast look more favorable into Friday morning. This puts the I-94 and north area on a collision course with freezing drizzle potential with wet-bulb temperatures near freezing. Not only is there the warm front but a trough shifting in from the west out of MN to again cause some light lift for enhanced collision-coalescence in the saturated layer there. The latest NBM probabilities of freezing rain suggest a 15-30% chance of occurrence (over 100 members in that blend). Thus, continued the glaze of ice possible forecast in northcentral WI Thu night into Friday morning. This will be one forecast focus for the overnight shift. && .DISCUSSION... Issued at 306 PM CST Wed Dec 20 2023 MILDER WITH RAIN LIKELY FOR LATE WEEK: Sub tropical jet cutting across bottom of upper low off California coast will eject two minor short wave troughs that will bring some sensible weather to the area to close out the week. Big picture suggests highest probabilities for precipitation overall remains across our southern and eastern areas. Mild temperature regime should also limit bulk of precipitation to liquid, supported with latest precipitation type ensemble output. Limited to no impacts expected. First wave will be associated with low level moisture advection and broad lift leading to an increase in clouds overnight into Thursday morning, especially lower stratus. Probabilities of ceilings under 5kft increase dramatically starting late morning tomorrow according to 20.12z HREF, climbing well above 80% by afternoon. A browse of RAP soundings suggest possible drizzle as well with saturated lower level above a drier layer, but not sure there will be enough boundary layer lift to generate much. Many of the available CAMS suggest sort of a speckled solution with light amounts so something to watch. Second wave appears a bit stronger but 20.12z guidance suggests it might track a bit further south than the first. GFS/ECMWF spread associated precipitation on Friday farther into our forecast area while NAM would suggest less chances with a more southern track. Ensemble data still leans towards higher precipitation chances, ranging from 75-90% in eastern Iowa to southwest Wisconsin, to 20- 40% closer to Twin Cities. While bulk of area should be warm enough to support liquid, there could be a few hours with a mixed precipitation threat across parts of north central Wisconsin, especially Friday morning. Ensemble guidance in Medford, WI area suggests about a 50-50 split of rain versus freezing rain with light amounts /and accumulation/ overall. Again, something to watch given lower confidence of precipitation even spreading that far north to begin with. RECORD WARMTH THIS WEEKEND AND CHRISTMAS: In the wake of the weak shortwaves departing the region Friday, temperatures will continue to increase this weekend as upper-level ridging will allow for warm advection to push our temperatures even further above normal. Little change has been noted in the guidance over the past 24 hours with the 20.12z EC EFI still showing a very robust signal for warm temperatures with values of 0.8 to 0.9 for high temperatures over Christmas. Consequently, keeping forecast current with the latest NBM suggesting highs in the upper 40s to middle 50s for much of the region this weekend and into early next week. Anomalous moisture suggested in guidance is the main instigating mechanism for some of these ridiculous low temperatures going into next week. The 20.12z GFS and EC continue to show precipitable waters of 350% to 400% of normal the night before Christmas. Consequently, temperatures are not expected to cool much from daily maximums. As a result, forecast low temperatures on the morning of Christmas Eve and Christmas reflected in the NBM are from the upper 30s to middle 40s, maybe even some upper 40s in our extreme south. This is further supported with the 20.12z EC EFI with values of 0.9 to 0.95 for minimum temperatures and a shift tails of 1, suggesting that these temperatures are well out of the normal. Therefore, many records likely will be broken, more information can be found in the climate section. PRECIPITATION TRENDS FOR CHRISTMAS EVE AND BEYOND: The upper-level pattern by Christmas depicts an upper-level trough, digging into the Great Plains region. Generally speaking, the 20.12z global models show a broad area of surface low pressure developing south of our region. Confidence is increasing that this could be a fairly wet pattern with the total QPF from now till mid-week showing high probabilities (60-100% chance) of seeing 0.5" in the 20.12z EC ensemble and GEFS from now till next Tuesday evening. Ensembles disagree a bit more on the exact location of the optimal moisture axis though. This is shown in the 1" probabilities in the 20.12z GEFS and EC ensemble where the EC keeps high probabilities (50-90%) for our region but the GEFS trends them lower (10-50%). Remember that since these are total probabilities they cover earlier precipitation as well so would be overdone to a degree. Another thing to consider is the cold advection behind this system and how that would play into what our conditions might look like after Christmas. While it is clear there will be some cold advection behind this system, it continues to not look that impressive across deterministic guidance with only somewhat seasonable air being advected into our region. This is further shown in the 20.12z EC ensemble showing virtually no probabilities (less than 10% chance) of 850mb temperatures going below 10C. As for any winter precipitation on the backside of this system after Christmas, confidence still remains low. This will be contingent on how the deformation zone sets up with the departing low which based on probabilities in both the 20.12z GEFS and EC ensemble for 1" of snow (10-20% chance), remains a low confidence forecast. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 548 PM CST Wed Dec 20 2023 VFR conditions are expected through the early morning Thursday. Then, the beginning of a fairly widespread LIFR-IFR-low MVFR ceiling period as abundant moisture streams north and across the area. Current observations across eastern KS depict MVFR ceilings moving northward representing that moisture layer. With the distance away and slow movement north versus previous forecasts, have slowed the arrival of MVFR conditions at the airfields. The MVFR ceilings should move in from the southwest Thursday overspreading the area. Confidence is lower on IFR at this time but the 20.18Z HREF guidance would suggest areas south and west of La Crosse would have the higher probabilities (60-80%). For now, have lowered ceilings to lower MVFR late Thursday /20Z/ at KRST. However, IFR probabilities are increasing every hour after 20Z at KRST, so future TAFs will include it (after 22.00Z). The moisture will continue to stream northward and overnight cooling and weak lift will promote DZ, IFR ceilings, and lowering visibilities too Thursday night into Friday morning across the region. This will have greater impacts on aviation and travel regionally. && .CLIMATE... Issued at 306 PM CST Wed Dec 20 2023 Based on current forecast trends over Christmas, record high and low temperatures at La Crosse and Rochester may be challenged with Rochester having a higher likelihood at achieving records. Below are some of the temperature records to watch over the holiday period: * - Record may be challenged La Crosse Date Record High Record Warm Low Forecast High Forecast Low ----- ----------- --------------- ------------- ------------ 12/23 59F(1877) 49F(1877) 49F 38F 12/24 61F(1889) 41F(1936)* 53F 44F 12/25 55F(1936) 46F(1936)* 50F 45F Rochester Date Record High Record Warm Low Forecast High Forecast Low ----- ----------- --------------- ------------- ------------ 12/23 47F(2020)* 33F(2005)* 49F 38F 12/24 41F(2021)* 36F(1936)* 51F 44F 12/25 50F(1936) 38F(1936)* 47F 42F Additionally, the 1-day precipitation record for Rochester on Christmas Eve is 0.94" and is 0.75" for Christmas Day. The 1-day precipitation records for La Crosse are 1.21" for Christmas Eve and 1.61" for Christmas Day. An interesting note about Rochester`s current record high on Christmas Eve is that it is the coldest record high at Rochester for the year tied with January 3rd, 2007. As a result, if the record is broken on Christmas Eve, January 3rd would have the definitive coldest record high at Rochester of 41 degrees. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ UPDATE...Baumgardt DISCUSSION...Naylor/TJS AVIATION...Baumgardt CLIMATE...Naylor
Area Forecast Discussion
National Weather Service Hastings NE
551 PM CST Wed Dec 20 2023 .KEY MESSAGES... - Fog issues (including at least some dense fog) these next few nights/mornings: Although there is still some uncertainty whether it will be mainly be of the lighter (1 mile or more visibility) or denser (1/4 mile or less visibility) variety, fairly widespread fog is looking increasingly-likely both tonight-Thurs AM and Thurs night-Fri AM. - Rain potential keeps increasing especially in our south Thurs-Thurs night: Although not a "major soaker", rain chances and forecast amounts keep creeping upward (and northward) within mainly our southern coverage area (CWA). - Friday the overall-nicest day of the next week: Not only is Friday the only upcoming day through at least Tuesday that features an entirely dry forecast, but it`s also likely to feature the most sunshine of any day through then as well. - Saturday-Tues storm system still our overall-biggest concern/issue: Unfortunately we are still a few days away from gaining any semblance of "higher confidence" in exactly how this system plays out, but if anything latest trends point toward increasing potential for at least spotty (and most likely weaker) thunderstorm activity mainly Sat evening into Sunday daytime, and PERHAPS a bit more snow accumulation potential mainly Sunday evening into Monday night (including Christmas). && .DISCUSSION... Issued at 448 PM CST Wed Dec 20 2023 -- PRIMARY CHANGES IN THIS FORECAST "PACKAGE" VERSUS THE PREVIOUS (EARLY-AM) one: 1) Although we don`t have any formal Advisories out at this time, we are "hitting" fog a bit bit harder for tonight-Thurs AM and also now Thurs night-Fri AM in our forecast products and Hazardous Weather Outlook (HWOGID). 2) The Thurs-Thurs night system (all RAIN) continues to trend a bit stronger and farther north, with at least a few hundredths of an inch rain possible as far north as roughly the Hastings/York areas, and parts of especially our KS zones favored to pick up a good 0.10-0.20". 3) The coverage of slight thunderstorm chances (embedded within much higher chances for rain showers) for Sat evening-Sunday daytime has expanded to now include nearly the entire CWA. In theory, these should be non-severe storms based on the most likely scenario. Otherwise, there has actually been minimal change with the overall timing and rain/snow chances (PoPs) with the holiday system, as the first slight chances (20%) move in Saturday afternoon, peak at widespread 70-90% Sat night into Sunday, remain up in the solid 50-70% range Sun night into Mon, and then taper off down into the 20-30% range Mon night-Tues. -- PRIMARY FORECAST CHALLENGES/UNCERTAINTIES (including all further discussion of longer-term periods Fri daytime-Wed): 1) Just how widespread/dense/impactful might fog be these next couple of nights/morning? Fog is almost always a notoriously fickle beast to pin down much before it "shows its hand", and there are at least some cons against truly widespread/dense fog development (probably more so for tonight than Thurs night?) See short-term-specific paragraphs below for more on this topic. 2) Do RAIN chances need to trend higher (and perhaps a bit farther north yet) for the Thurs-Thurs night system? While confidence is pretty high that the vast majority of truly measurable rain potential will focus south of Interstate 80, there are definite questions as to whether most of the rain remains in our far southern (KS) zones or perhaps gets up closer to Hwy 6/I-80 corridors. See short-term-specific paragraphs below for more on this. 3) The "Big Holiday Weekend/Christmas System (various thoughts/latest trends): - To be up front, we are still a full two days away (Friday) from at least the vast majority of the wintry side of this storm making it into our official "winter forecast window" when we start issuing more official potential totals, graphics (including probabilistic) etc. Hopefully by then things look little clearer than they do know, but compared to some bigger storm systems that consistent more of one/coherent low pressure system as it approaches the Central Plains, the fact that this one will clearly feature a complex interaction/merger of two initially-distinct waves likely means (more than usual) that it might be at least Saturday before the picture really starts becoming clearer. - In the basic big picture: If anything, the overall timing of this system has come into decent agreement in the ECMWF/GFS model world, with the first isolated/scattered rain showers perhaps breaking out mainly Saturday afternoon, the vast majority of showers/embedded thunderstorms occurring Sat night into Sun AM, the vast majority of snow (MAYBE some mixed precip in the transition zone?) occurring Sunday afternoon through Monday AM (west to east transition), with a turnover to all-snow likely CWA-wide by later Mon afternoon-night. At least for now, the vast majority of snow appears to be departed by sunrise Tuesday, but especially the ECMWF suggests the parent low could stall over the Midwest, and perhaps drag another "lobe" of light snow potential southward over us before departing for good (at least for now though, our official forecast is precip-free by Wednesday). - Thunderstorm potential: While at this Day 3-4 range it still looks like most/all storms would be of the weakish variety, there does appear to be a bit more potential than 24 hours ago of realizing at least weak/modest elevated instability on the order of 200-500 J/kg. In theory, a few cores with small hail probably cannot be ruled out Sat evening-night. Of course, a "worse case scenario" would be something surface-based and possibly severe trying to form Sunday daytime, but as long as the main surface low track and associated dry slot remain at least slightly to our south, then this concern should be minimal. That being said, this bears close watching as (for example) the severe storm event of 12-15-21 was not exactly on our "radar" at this point in time either. - Overall precipitation/snowfall trends: Taking 12Z deterministic runs at face value, it`s clear that the ECMWF is giving us more of a wintry impact than the GFS which gives us almost no snow (its latest run fails to truly phase the upper system together into one more powerful vort max). But turning to the ECMWF ensemble world (almost always the best approach this far out in time), it is worth noting: 1) Overall precipitation amounts (including melted snow) have increased a bit, with now a 60-90% chance that nearly our entire CWA sees at least 0.50" out of this. 2) Potential for at least a few inches of snow has increased as well, with probs for at least 1" of snow now up to 50-70% especially in our west half, and 30-50% probs for at least 3" in this same area. If this system were closer in time and we were forced to put more definitive snow totals toward it, this would suggest a fairly wide coverage of 2-4", not a "major snow storm", but certainly enough to cause nuisance travel issues. 3) Non-zero chance for mixed precip types in the rain/snow transition zone: Although FAR from a certainty, latest ECMWF hints at at least a little freezing rain/icing potential mainly Sun night-Mon AM before a full transition to snow occurs. Something to watch, but far too soon to put much stock in. - Winds: Although perhaps trending a touch stronger than 24 hours ago, this system does still not look particularly windy (unless the surface low intensifies further), with gusts more along the lines of 30 MPH than say 50 MPH. That`s more than enough for now on this system, especially with any wintry-impacts still 4-5 days away and plentiful (at least minor) changes in model data likely. -- SHORTER TERM FORECAST DETAILS FOCUSED SOLELY ON THE NEXT 36 HOURS: (through late Thurs night/Fri AM): - Current/recent weather scene as of 4 PM: As was suspected as a possibility, the morning began with a narrow ribbon of dense fog in our eastern zones. While this fog dissipated by mid-late morning, extensive mid-high level clouds have streamed overhead all day, resulting in cloudy/mostly cloudy skies and holding temps down at least slightly below expectations most areas (highs ranging from low-mid 40s central/northeast to more upper 40s south and especially far west). Winds have been light (mainly at/below 7 MPH), and generally out of the east. In the mid-upper levels, water vapor satellite and short term model data depict us under broad southwesterly flow aloft, with our first disturbance of interest gradually heading our way from the AZ/NM border area. - This evening-overnight: The paramount concern is how extensive and dense/impactful fog will be. Taking models such as HRRR at face value, there would be a good chance of widespread/dense fog across much of the CWA tonight. While that cannot be ruled out especially in the very light, mainly easterly/northerly wind regime. That being said, the night will start with quite a bit of high cloud cover (which will hamper cooling and perhaps fog development somewhat), although there will likely be some breaks/thinning of high clouds as well. SREF visibility probs are not as aggressive as HRRR, showing more muted fog potential, and is one of the main reasons it was decided to "punt" any possible formal Advisory to later shifts. Nonetheless, potential for a fog-ridden Thurs AM commute is there, and is covered in our HWO. Precip-wise, the vast majority of the CWA will remain dry tonight. However, as low clouds gradually thicken/saturate in southern zones, felt a slight chance of drizzle was warranted before sunrise in our extreme south-southeast (Osborne/Mitchell counties mainly). Low temps tonight could easily vary by 10+ degrees given differences in cloud cover/dewpoint levels, and are aimed from mid-upper 20s northwest to mid-upper 30s far southeast. - Thursday daytime-overnight: The disturbance currently over the Desert SW will arrive into our CWA by late in the day, and then depart eastward generally along the NE/KS border overnight. This system has trended a bit stronger/further north than 24 hours ago. Considering our forecast was dry just 48 hours ago, this has been a change. In short, PoPs have been increased (probably not enough?) with rain chances spreading as far north as Highway 6 in the afternoon, but with the highest chances 30-50% in KS zones during the afternoon, then increasing more in the evening especially far southeast. There is some uncertainty as to how far north the north edge of rain will be, with higher-res models (such as HRRR) keeping most rain in our KS zones, while latest ECMWF/GFS bring at least a few hundredths of an inch up to at least the I-80 corridor. Based on current trends, rain potential will probably increase further in the next forecast package, but we are not talking big amounts, with even our far south unlikely to exceed 0.25" Turning to fog potential, this could honestly be a a pretty big forecast headache. Not only could Thursday start out with areas of fog (some dense), but following a likely lull in fog coverage/intensity during the afternoon, places especially just behind the departing area of rain could easily "fog in" again Thurs evening-overnight in a continued moist low- level/light wind regime. However, the light winds will be turning more westerly/downslope with time, which would tend to slowly scour fog out from west-to-east heading toward the first part of Fri daytime. Plenty of uncertainty here. Temperature- wise, nudged highs down a good 2-5 degrees for Thurs in anticipating of widespread clouds/rain/fog being a factor, with most areas aimed mid-upper 40s and any low 50s favored extreme west/northwest. Like tonight, lows Thurs night will likely exhibit a good 10+ degree gradient across our CWA, and have them ranging from mainly upper 20s far west, to upper 30s/near 40 far southeast. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 545 PM CST Wed Dec 20 2023 Significant Weather: IFR to LIFR VSBYs and CIGs becoming increasingly likely for late tonight through at least Thu AM. Tonight: Will start off VFR with SCT to BKN high clds...but after about 03-04Z, several pieces of guidance have been fairly consistent in developing and expanding fog across both terminals, perhaps slightly earlier and more dense at EAR than GRI. However, seems increasingly likely that BOTH terminals will see VSBYs fall to around or less than half mile by 08-11Z, with CIGs/VVs likely not any better at only 200-300ft. Winds will be lgt and vrbl during this time. May very well need a Dense Fog Advisory overnight. Confidence: CIGs/VSBYs - Med, Wind - high. Thursday: IFR to LIFR VSBYs and CIGs seem probable to persist through most, if not entire, AM...with latest RAP/HRRR blends not showing any significant improvement (to MVFR or VFR VSBYs) until 18-20Z. And even so, this will probably be a situation where ground VSBYs improve, but CIGs still remain very low at only 300-800ft. Winds will remain lgt at around 5kt, or less. Assuming we never fully mix out of the stratus Thu aftn, then overall patter would support another round of at least IFR CIGs/VSBYs Thu eve into overnight. Confidence: CIGs/VSBYs - Medium, Wind - high. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ DISCUSSION...Pfannkuch AVIATION...Thies
Area Forecast Discussion
National Weather Service Marquette MI
626 PM EST Wed Dec 20 2023 .SHORT TERM...(This evening through tonight) Issued at 204 PM EST WED DEC 20 2023 Key Message: -Lake effect cloudiness, but otherwise quiet through Thursday morning. RAP analysis shows a 1039 mb high pressure over far northwestern Ontario but otherwise not many synoptic scale features in the Great Lakes with mostly zonal flow aloft. 850mb temperatures are around -5 C, which is just cool enough for some low level overcast lake effect cloudiness, but anticyclonic surface flow is keeping anything notable from precipitating out of those clouds. As the high shifts east, winds will veer more southeasterly than the current easterly and northeasterly flow. Temperatures should fall to the dew point Thursday morning in the low to mid 20s, and with not particularly strong gradient winds, windshields might get a bit frosty prior to the morning commute, which will be the biggest weather impact through Thursday morning. .LONG TERM...(Thursday through Wednesday) Issued at 158 PM EST WED DEC 20 2023 Upper air pattern consists of a closed 500 mb low off the CA coast with a ridge across the ern U.S. 12z Thu. A shortwave trough moves into the upper Great Lakes on Fri. Troughing moves onto the west coast and into the Rockies by 00z Sun. Did not make too many changes to the going forecast. In the extended, the GFS and ECMWF show a 500 mb trough in the Rockies moving into the western high plains 12z Sun. This trough moves into the plains 12z Mon and then slows down as it moves into the central U.S. 12z Tue. The trough then moves into the Great Lakes region 12z Wed. Model differences continue with this system as the ECMWF is slower and the GFS is more progressive and further east while the Canadian model is more towards the ECMWF for the evolution of the system but even slower. This system still bears watching as it could be strong, but right now the pcpn looks to start off as rain before the colder air arrives later in the period and will have to watch its track. Manual progs have this system further north than previous forecasts. Confidence is still low as models have different solutions. Temperatures will stay above normal for this forecast period. The possibility of a white Christmas is still hard to predict in a lot of places. The places that have seen 3 to 6 inches of snow the past several days might have enough to keep it until Christmas Day when it melts in the north to northwest lake effect snow belts. However, the places that have less than 3 inches of lake effect snow will probably be able to melt this off as temperatures go above normal through then and will see a brown Christmas. This would be in most areas away from the lake effect snow belts and especially in the southern U.P. Next chance of pcpn will be late on the 24th and into the 26th and this would mostly be rain. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 626 PM EST WED DEC 20 2023 Lake-effect clouds and MVFR cigs prevail at all 3 TAF sites, though SAW may lower to high-IFR Thursday morning and IWD may improve to VFR at times tonight. No visibility restrictions or precipitation are expected. Winds will slowly veer from ENE to SE through the TAF period at 5-10 kt, except for some higher winds and gustiness at CMX. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 158 PM EST WED DEC 20 2023 Winds gradually diminish back down to around 20 kt late tonight as winds veer southeast. With high pressure over Quebec moving northeast on Thursday, winds gradually veer south with strongest winds expected over the east half of the lake up to 25 kt. Winds diminish below 20 kt Thursday night and generally remain near or below 20 kt through Sunday before increasing to 20 to 25 knots Sun night into Mon. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...GS LONG TERM...07 AVIATION...EK MARINE...07